The synthesis, properties and lithographic performance of poly(3-butenyltrimethylsilane sulfone) (PRTMSS) as an imaging and pattern transfer layer for two-layer resist systems is reported. 3-Rutenyltrimethylsilane (BTMS) was copolymerized with sulfur dioxide over a wide range of temperatures in the presence of a variety of free radical initiators to give a high-molecular-weight product (Mn = (4-9).105; M_w/M_n = 2-2.8), soluble in many common organic solvents. PRTMSS is thermally stahle in air up to 170-180°C and has a Tg of 120°C. It is chemically stable and resistant to hydrolysis. PRTMSS films spun from solution in cyclopentanone or chlorobenzene on top of hard-baked Novolac-type photoresist used as a planarizing layer were exposed to a 20 keV electron beam and developed in 2- butanol at 14 to 16°C. Sensitivity of the resist was 1.0-1.5 μC/cm² and contrast was 1.3-2.5. Half-micron gratings were transferred into the thick, planarizing layer by oxygen reactive ion etching (0₂ RIE). The processing latitude of PRTMSS is considerably wider than that of poly(NTMS butene sulfone), although careful control of the processing parameters is required. The degradation and passivation mechanisms of PRTMSS in 02 RIE have been studied by several surface-sensitive analytical techniques and their results are briefly discussed.

The bottleneck of quantitative characterization of resist materials is being relieved by the introduction of a commercial system with multiple channel capabilities working directly on silicon wafers. This convenience for the process engineer comes at considerable inconvenience in data analysis, primarily due to exposure standing wave effects from substrate reflection. On silicon, for example, an exposure variation of a factor of 8 occurs over a vertical distance of 65 nm within the resist. Data from this very thin layer can span almost the entire range of exposure state M of the resist and two orders of magnitude change in development rates. Experimental and software techniques developed in a benchmark study of the well characterized Kodak 820 resist are reported. Several software techniques were established for data analysis. A depth-dependent filtering technique was used to improve the signal-to-noise ratio of the rate vs depth data from the slowly developing channels. This noise is due to the high sampling rates, which are necessary to simultaneously monitor the most rapidly developing areas. A post processor for SAMPLE was developed to process the normal output of exposure state M versus depth and generate M values for the exposures specified in the data from the measurement system. A three column vector of development rate R, exposure state M and depth z is then generated for plotting R(M,z) and numerically fitting algebraic models. Measurements and data reduction were made on silicon wafers with various thin film coatings. A hard-baked resist coating was sufficiently absorbing that very little oscillation in the development rate with depth was observed. For aluminum coatings, it was not possible to get good thickness vs time or rate data. The rate versus depth on bare silicon wafers could be made well behaved after filtering. The resulting R(M,z) curve for bare silicon was somewhat noisy. Thus the use of a hard-baked coating is indicated in practice for resist characterization studies.

The random copolymer comprised of trimethylsilylmethyl methacrylate (SI) and chloromethyl styrene (CMS) is shown to function as a negative acting e-beam and deep UV resist. The resist is prepared using free radical solution polymerization techniques. Reactivity ratios were calculated using the least squares treatment of Fineman-Ross, and were determined to be 0.49 and 0.54 for SI and CMS, respectively. This material exhibits etching resistance in an 0₂ reactive ion etching discharge, and is applicable to bileveli pthographic processes. The resist system exhibits an e-beam and deep UV sensitivity (pg. ) equal to 1.95 11C/cm² and 18mJ/cm², respectively. The ratio of etching rates of the planarizing layer HPR-206 to this material is 12 to 1 in 0₂. Preliminary results indicate this system to have submicron resolution capability.

The interaction of ion beams with polystyrene has been studied by using product analysis and ion beam pulse radiolysis, which can directly observe reactive intermediates produced by high energy ion irraciation. The resisit sensitivity per unit absorption dose increases with increasing stopping power or LET (linear energy transfer). The interaction between excited states (and ionic species) produced by high density electronic excitation of ion beams increases with increasing stopping power or LET and high density electronic excitation was confirmed directly for the first time on the basis of ion beam pulse radiolysis data.

This paper describes the design and preparation of a negative tone, oxygen etch resistant DUV photoresist. This two-component resist system is composed of an oxygen plasma etch resistant matrix resin, poly(trimethylsilylmethylstyrene), and a monomeric radical generator such as trichlorobenzene or 3,3'-diazidodiphenylsulfone.

We introduce the DESIRE system, a noval approach to dry developed resist systems. DESIRE is a single layer system based on selective silylation. The optical spatial information is translated into silicon being built into the resin during the silylation treatment. A negative working version will be discussed. The process flow is given and a set of results showing submicron dimensions with high aspect ratio and good linewidth control are presented. The excellent features of the system make it a possible candidate for use in submicron applications with UV exposure tools.

A novel terpolymer of a methylated phenol, p-trimethylsilylmethyl phenol and formaldehyde was synthesized. With a 9.7wt% Si content, the polymer displayed an RIE resistance 10 times greater than hard-baked HPR 204. The organosilicon novolac was employed as a base resin component of bilevel resist systems for both photo and electron-beam lithography. The low molecular weight polymer behaves as a positive resist when mixed with a dissolution inhibitor. In photo-lithography, the dissolution inhibitor was a diazoquinone based chemical which was converted to an acidic species during irradiation. In electron-beam lithography, poly (2-methyl-l-pentene sulfone) (PMPS), which depolymerizes upon electron-irradiation, functioned as the dissolution inhibitor. When the silylated novolac was used as a photoresist, coded 0.8μm line/space patterns were obtained with a sensitivity of -120 mJ/cm². When employed as,an electron-beam resist coded 0.75μm line/space patterns were resolved with a dose of 8μC/cm⁴.

Thick coatings (5-15μm) of a new dual image, aqueous developable photoresist can be exposed using a light attenuating photomask consisting of clear, opaque and grey areas and then processed to yield thermally stable 3-dimensional structures which are potentially useful as mechanical and optical components of devices. In the positive mode, relief and intaglio images are produced by processing similar to positive novolak based resists with 1- 2μm resolution and with the added feature that the images can be made thermally stable to temperatures >300° C. Negative mode processing of coated wafers imaged with the special mask produces thermally stable structures with tunnels or hollow chambers as well as cantilever beams. Because these structures are crosslinked at the time of development, processing in the negative mode shows much wider latitude than is the case in the positive mode. Images by negative mode processing are capable of submicron resolution, higher aspect ratio (>3 vs <1.6), and inward sloping wall profiles adjustable by exposure. The acid hardening resin compositions cover a broad range of compositions so that resins can be tailored to meet specific property requirements.

The paper describes a new approach to thermally stabilize the already imaged profile of high resolution positive photoresists such as ULTRAMAC" PR-914. ***XD-4000, an aqueous emulsion of a blend of fluorine-bearing compounds is spun on top of the developed, positive photoresist-imaged wafer, and baked. This allows the photoresist to withstand temperatures up to at least 175 deg. C. while essentially maintaining vertical edge profiles. Also, adverse effects of "outgassing" in harsh environments, ie., plasma and ion implant are greatly minimized by allowing the high resolution imaged photoresist to be post-baked at "elevated" temperatures. Another type of product that accomplishes the same effect is ***XD-4005, an aqueous emulsion of a high temperature-resistant polymer. While the exact mechanism is yet to be identified, it is postulated that absorption of the "polymeric" species into the "skin" of the imaged resist forms a temperature resistant "envelope", thereby allowing high resolution photoresists to also serve in a "high temperature" mode, without reticulation, or other adverse effects due to thermal degradation. SEM's are presented showing imaged ULTRAMAC" PR-914 and ULTRAMAC" **EPA-914 geometries coated with XD-4000 or XD-4005 and followed by plasma etched oxide,polysilicon and aluminum. Selectivity ratios are compared with and without the novel treatment and are shown to be significantly better with the treatment. The surface-treated photoresist for thermal resistance remains easily strippable in solvent-based or plasma media, unlike photoresists that have undergone "PRIST" or other gaseous thermal stabilization methods.

As Bowden has pointed out in his recent discussion on high resolution lithography, conventional photoresists are not particularly suitable for use in the deep ultraviolet (DUV) regime.' The reasons for this are: (1) the novolac resin is a strong absorber at wavelengths shorter than 300 nm;2 and (2) the products produced upon irradiation of the photoactive compound (PAC) absorb in this region (which prevents the phenomenon known as "photobleaching" from occurring). Of these two difficulties the first appeared, to us, to be the more restrictive. Therefore we chose to investigate alternate resins, more transparent in the DUV region, to substitute for novolac. We initially sought to remain within the realm of the dissolution inhibition mechanism and to utilize conventional PAC's. Although it was possible to prepare resins having improved UV absorbtion characteristics (a maleimidestyrene copolymer will be discussed here) and to formulate positive acting resists from them, we found that the resists were not able to adequately form high resolution images with vertical wall profiles. Examples of this behavior are presented. Because of the apparent inability to obtain satisfactory wall profiles, we abandoned the methods based on the dissolution inhibition mechanism. We then elected to explore the so-called "chemical amplification" approach pioneered by Wilson, Ito, Frechet, and their coworkers. To this end, maleimide styrene copolymer was substituted on the nitrogen atom with the tertbutyloxy carbonyl group. This resin, upon application of heat, reverts to maleimide styrene via a process which is apparently catalyzed in the presence of acid. These observations led us to develop a photoresist based on a mixture of a photoacid and the N-blocked maleimide/styrene resin. Details of the performance of this resist are presented.

An attempt was made to improve the resolution capability of positive photoresists applicable to VLSI semiconductor processing. It was found out that in general, when the contrast (y(gamma)-value) of resists is made higher, the exposure latitude and the mask size reproducibility tend to be lowered. Study was made how to raise Y-value without decrease in the exposure latitude and the mask size reproducibility. It was necessary to design a new type of novolac resin that has a molecular weight and a molecular structure different from the existing materials. Many kinds of cresol-formaldehyde type novolak resins were synthesized and evaluated. Such items as the isomeric structure of cresol, the position of the methylene bond and the influence of molecular weight were investigated. As a result of the optimization of these items, a number of different resist materials that exhibit improved resolution capabilities were obtained. It is also remarkable that the introduction of the new polymer design not only enabled to improve resolution capabilities, but also made the process latitude much wider at various points of resist work including, prebaking temperature, developing time and developing temperature, compared to the so far commercially available products. This new material makes it possible to obtain fine pattern resolution required in VLSI processing. Moreover, wider latitude of processing conditions assures higher yields of the circuits.

The future use of deep UV sources such as excimer lasers in optical projection lithography will push resolution limits down to 0.5 micron and possibly even beyond. Looking ahead to deep UV lithography, questions arise as to whether any current resists can be used with deep UV exposure and whether there is any difference in resist processing between the conventional blue/near UV and deep UV lithography. Using an excimer laser source and contact printing we have undertaken an evaluation of several novolak resists and their processing for future use in 248 nm lithography. The 0.8 micron pitch features on the lx masks can be replicated using 0.5 micron thick resists. Studies of the development process using real time interferometric resist thickness measurements indicate differences in the behavior of the resists to the deep UV exposure compared to near UV exposures. For the novolak based resists the principal difference is reduced contrast due to poor light transmission and due to the presence of crosslinking reactions which lead to decreased development rates. The slower development rates become significant in terms of processing only when the novolak resists are post-exposure baked to minimize standing waves.

Polymethacrylamide (PMAAm) and copolymers of MAAm with methyl methacrylate were synthesized and evaluated for their applicability to electron beam lithography. The sensitivity of PMAAm has previously been reported as less than 1 μC/cm², with thermal stability at temperatures up to 330°C.' Despite these claims, further lithographic evaluation of this resist system is apparently absent from the literature. This research was conducted to further investigate the lithographic performance of these resists and to determine their sensitivity using current definitions. Using PMAAm homopolymer (Mw = 8.1 x 10⁵), with a 15 minute prebake at 200°C, the lithographic results were much poorer than expected. Patterns exposed to doses of 10 μC/cm² or lower could not be developed using water as the developing solvent. Forced developing with Na2SiO3 solution (pH=10) developed lower doses than water, but much greater thinning was observed. An unexposed thinning of 10% occurred when developing exposures of 15 μC/cm² with water, and 40 μC/cm² with Na₂SiO₃ solution (20 KV). Swelling of the unexposed polymer and some adhesion problems were observed. The high sensitivity previously reported for PMAAm' can not be attributed solely to chain scission efficiency (Gs), which has been reported to be only 1.5 times that of PMMA (Gs determined by Y-irradiation). An induction period in the dissolution of unexposed polymer has also been sugggested as contributing to the sensitivity of this resist. In the present work, dissolution induction periods were observed with laser interferometry for the unexposed films, but the magnitude of these induction periods could not account for a large enhancement of sensitivity. Imide crosslink formation may have been responsible for the previously reported sensitivity of PMAAm.' In the present work, imid formation was not observed, either after prebaking coated wafers at 180 to 240°C or heating of polymer solutions for 7 hours at 80°C. Apparently, the conditions for useful formation of imide are difficult to reproduce. Because of the problems encountered with the PMAAm homopolymer during lithography, a series of MMA MAAm copolymers were synthesized and evaluated as potential resists. These copolymers eliminated the problems of swelling and poor solubility of the homopolymer, but sensitivity enhancement over that of PMMA was minimal.

Fundamental processes and molecular design principles for high sensitivity dry developable X-ray resist are discussed experimentally and theoretically. Three factors, i.e., high G (number of chemical effect per 100 eV photon), high N (number of monomer unit in which a single chemical effect causes developable modification of polymer property) and high μm (mass absorption coefficient of monomer) are considered for design of a high sensitivity resist. Small modification of polymer resulting in high contrast was tried by doping tin into polymer film in a capacitively coupled gas flow type plasma polymerization reactor. The oxygen reactive ion etching rate of the film was successfully varied from 1700 to 100 A/min by changing the atomic ratio of tin to carbon from 0 to 26 %. A general way to connect a chemical effect to a dry developable polymer modification is discussed.

The performance of the image reversal process is evaluated. As image reversal includes process parameters to control the slope of the resist profile it offers the possibility to compensate for the bulk effect. Additionally dye can be added to the resist to some extent, to reduce reflections at the substrate, without degrading the slope. Data was collected to quantify the potential of image reversal with respect to the latitude for development and exposure dose variations for both the imidazole, the ammonia and the AZ5214 process. Trends indicating how to find the best operating point for each process will be discussed. To demonstrate the submicron capabilities of image reversal resist patterns with lines and spaces down to 0.5 μm over 0.5 μm topography will be shown.

Computer simulation is a well established tool in the design and processing of integrated circuits. The best known such simulation program in microlithography is SAMPLE (1), which is based on the Dill model (2). A new computer simulation program, PROSIM, has been developed (3). It uses the aerial image calculated by SAMPLE and the string development algorithm of SAMPLE, but replaces calculated photoresist development rates with rates measured using in-situ interferometry. Three different positive photoresist systems were investigated under varying process conditions typically examined during the characterization process. PROSIM simulated profiles and exposure latitudes are in good agreement with experimental measurements, showing that PROSIM can be used as an effective tool to aid in the characterization and optimization of positive resist processes.

The mechanism of development for positive photoresists can be described using a membrane model for the thin polymer film dissolution process instead of a simple surface-dissolution model. The model is consistent with previous findings on the factors controlling the dissolution, i.e., solubility changes due to quinone-diazide photochemistry, creation of free volume due to nitrogen gas evolution, dissolution rate effects due to cation size, and surface modification by adsorption of chemicals. One of the key reactions of the membrane model, the conversion of the phenol to a phenolate on the novolac polymer, seems to have been overlooked in previous studies. This reaction must go to completion for any dissolu-tion process to occur, and it requires a pH greater than 12.5. The membrane model will be presented and specific, supporting experiments will be discussed.

The system performance of the THE i-line 10X wafer stepper with the Zeiss prototype 0.315 NA lens has been reported in previous papers.^1,2 This paper describes the enhanced optical properties achieved using advanced processing materials and process optimization. Theoretical verses actual resolution and depth of focus results will be presented using the following materials: Ciba Geigy i-line sensitive photoimagable polyimide, AZ52140 positive resist, Shipley S2400 and S1400 microposit resists and General Electric's contrast enhancement material 388. Submicron resolution was achieved using all of the aforementioned materials; 0.75 micron lines and spaces using Ciba Geigy photoimagable polyimide, 0.5 micron lines and spaces using AZ5214, S2400, and S1400 microposit resists, and 0.375 micron lines and spaces when GE contrast enhancement material 388 is used with positive photoresist. Modulation Transfer Curves (MTF) for the Zeiss 10 78 34 lens and the various resist films used will be constructed to explain these results. The theoretical depth of focus range was adhered to when using both positive resists and polyimide. Enhanced depth of focus was achieved using GE's contrast enhancement material 388 with the positive resists tested. The theoretical and actual image distortion effect at focus values outside the theoretical depth of focus range is examined and the impact of future lenses coupled with current process technologies will also be discussed.

This paper describes experiments on the effect of using contrast enhancement material, CEM-420, on photoresist imaging over an aluminum substrate on thermal oxide steps. Wafers with oxide step heights ranging from 0.4μm up to 1.04μm were used to explore the potential advantage in using CEM-420. Various thicknesses of CEM and photoresist were prepared to determine the combination that provides the best process parameters. A full factorial ex-periment with three levels of each of the three variables, PR, CEM, step, was performed. A minimum of three levels is required in order to reveal the curvilinear effects. Each combination received a different range of ten level exposure energies. The CD's at the top and bottom of the step were measured with a SEM. The data from experiments were analyzed by RSM, a software program from CompuServe. Regression analysis was used for model fitting. The effect of resist thickness, CEM thickness, step height, and exposure energy on CD is discussed. The required minimum print bias under different conditions for lμm line/space feature sizes on mask is discussed.

The effect of several key process variables on the litho-graphic performance of Altilith CEM-420 was investigated. Linewidth control in the resist image was measured by etching the substrate and electrically probing the resulting polysilicon lines with a Prometrix LithoMap LM20 system. Scanning electron microscopy was also used for some of the linewidth measurements over topography. The CEM-420 process was most effective when used in conjunction with an optimized photoresist process. We investigated lowering the resist softbake temperature and/or increasing the developer concentration. In each case the CEM-420 process performed better with the original processing conditions. Increasing the thickness of the CEM-420 layer improved linewidth control whether expressed as the change in critical dimension with change in exposure dose or as the ability to image different feature sizes at a given exposure dose. CEM-420 dramatically improved linewidth control over topography. Exposure times increased by a factor of between two and three with CEM-420. The effect of increasing exposure time on wafer throughput was miffimal. CEM-420 provided improved resolution with sodium, potassium, and metal-ion-free developers. Proximity effects were reduced with CEM-420. Modeling studies agreed with the exper-imental results showing increased exposure latitude for small feature sizes, improved resist profiles, and a reduction in the effect of standing waves.

We describe an approach to submicron optical lithography that offers the potential, in conjunction with i-line lenses, to reach 0.5 microns using organic, spin-on materials. In this method, a resist layer is coated with a thin layer (0.5 μm or less) of photobleachable polymeric dye, which is sensitive to the imaging radiation while the resist is not. Image exposure creates a latent image in the dye, which is transferred into the resist by deep UV blanket exposure under conditions such that the dye is unreactive. The top layer (polymeric dye) is then removed and the resist developed. Computer simulations based on a 365nm, 0.42 N.A. imaging system predict a resolution of 0.50 pm with linewidth control of ±10% for ±10% exposure variations at 1 depth of field defocus, for all features types and sizes. There is no exposure penalty in this mechanism; the dose required to bleach the dyes is comparable to that for conventional positive resists.

The controllable patterning of micrometer and submicrometer resist features on metal layers is critical for many VLSI processes, but the exposure of photoresist to near normal incidence illumination will result in spatial, energy variations coupled into the photoresist i.e., standing waves. The dominant factor that determines the amplitude of the standing wave is the substrate reflectivity. The deleterious effects of light reflected from the photoresist/substrate interface are well documented. Thin, sputtered Si films have been found an effective antireflection coating for reducing standing wave effects over metal layers and thus improving resist linewidth control, resolution and sidewall angle. The optical constants of Ar sputtered Si have been measured and this data is used to simulate the resultant reflectivity as a function of Si thickness. In our particular application the optimum Si thickness is determined not just by the minimum in reflected signal but also by the minimum required signal to noise ratio required to accurately align the die.

Several kinds of dyeable negative photoresist materials for CCD micro color filters, developed in our Laboratories, are reported. Quaternary ammonium salt-terminating acrylate-glycidyl methacrylate copolymers with bisazides have been developed as negative working resists. Descriptions on their synthesis, lithographic data and the micro color filter process for these resists are mentioned.

Surface tension plays a role in many areas of lithography. One of them has been found to be formation of Benard cells in photoresist coatings at the center of a wafer. A relationship between these cells and ,'riations is proposed. Observations of the effects of evaporation, gravity, radius, dispense flow, spiv, lme, spin speed, type of solvent, type of solute and concentration of surfactant suggest that the formation of cells and striations follows the same principles that are active in conventional thick coatings. Surface tension measurements are reported that support this conclusion.

Polyimide has been identified as a useful material for microelectronic packaging because of its low dielectric constant and high temperature stability. Difficulties involved with reactive ion etching (RIE), a conventional technique for patterning thick polyimide films (thickness greater than 5 microns) with vertical walls, can be overcome by using photimageable polyimide precursors. The processing steps are similar to those used with negative photoresists. EM Chemical's HTR-3 photosensitive polyimide has been spun on up to a thickness of 12 microns. Exposure with a dose of 780 mJcm^-2 of ultraviolet light, followed by spin development produces clean patterns as small as 5 microns corresponding to an aspect ratio of 2.4. When the patterned precursor is heated, an imidization reaction occurs converting the patterned film to polyimide. Baking to ca. 400 degrees C results in substantial loss in the thickness and in line width. However, shrinkage occurs reproducibly so useful rules for mask design can be formulated. Near vertical wall structures can be fabricated by taking advantage of the optical and shrinkage properties of the polyimide precursor. After development, an undercut wall profile can be produced since the bottom of the film receives less exposure and is hence more soluble in the developer. During heating, lateral shrinkage pulls the top of the film inward producing a vertical wall since the bottom is fixed to the substrate by adhesion. As a result, fully cured polyimide structures with straight walls and aspect ratios greater than one can be obtained. Dielectric properties of the fully imidized films were investigated with capacitor test structures. A relative dielectric constant of 3.3 and a loss tangent of .002 were measured at 20 kHz. It was also found that the dielectric constant increases as a linear function of relative humidity.

A new positive working photoresist which is applicable to the two-layer resist techniq using a current g-line stepper has been developed. This resist consists of a naphth, quinone diazide photoactive compound and a silicon containing novolak resin, which synthesized from m-trimethylsilylphenol, m-cresol, and formaldehyde by condensation r action according to the standard method. The 0₂ RIE durability of this resist gets great with increase of molar fraction of the silylphenol in the binder. The resist comprising resin prepared from the silylphenol alone by condensation with formaldehyde shows the highest 0₂ RIE durability,although resolution, sensitivity, and coating property are n sufficient. These properties are improved by incorporation of m-cresol moiety into t binder resin. Novo 1 ak prepared from a mixture of 30 mole % of m- creso 1 and 70 mole % of t silylphenol gives sufficient resolution, reasonable sensitivity and good coating proper leaving RIE durability at fairly high level. The molecular weight and the content of t sensitizer were optimized. The resist is completely compatible with current resist processings. The sensitivity good enough for the usual application and essentially no unexposed-film thickness loss w observed when it is developed with 2.38% tetramethylammonium hydroxide solution. Gam] value is fairly large and line and space as small as 0.6um can be resolved with go, profiles when it is exposed using a g-line stepper equipped with a lens of N.A.=0.35. This resist can be applied to the two-level resist process. MP-1400 was used as planarization layer and after curing at 200 C the present resist was applied on that as thin imaging resist. After exposure and development of the top layer, the pattern of 0. line and space was transferred to the bottom resist by 0₂ RIE with nearly vertical sil walls. The etch rates of top and bottom resist are shown to be 450 and 1360A/min, respectively.

The fabrication of high density VLSI circuits has placed increased demands upon the pattern integrity of photoresist materials. The thermal and chemical effects of high current ion implantation and plasma etching, for example, have led resist manufacturers to formulate durable materials which will withstand harsh processing environments. However, this stability is frequently the cause of difficulties in resist mask removal following such process steps. This work reviews some of the chemical effects which new fabrication technologies have upon polymeric materials and the result of these effects on removal techniques. An afterglow system is presented which utilizes a high fluence of atomic oxygen to oxidize, and hence remove by volatile product formation, these durable and often denatured carbonaceous masking materials. Removal rates up to 6 pm per minute have been achieved. Denatured materials as produced by high current P+ ion implantation, resulting in a dose of 2.5E16 atoms/cm², have been typically removed at a rate of 1pm per minute. Further, the high flux of atomic oxygen necessary to achieve such rates is produced away from the device structures being processed. Flatband voltage shifts, of MOS struc-tures, induced by processing in this manner are typically less than 0.1 volt, whereas shifts of 1 to 4 volts were obtained by processing in an rf parallel plate plasma system in which the wafer is directly exposed to the oxygen generating region.

An alternative to bilevel and trilevel photolithography for 1.5 μm double metal VLSI processes is presented. It is accomplished by a single level resist process that uses AZ4210D dyed resist and high temperature post exposure bake. Scanning electron micrographs show that proximity reflective notching and linewidth variation across topography steps on a double metal production process can be virtually eliminated. We have been able to confirm, via SEM analysis, an enhanced diffusion mechanism of the photosensitizer in the temperature range of 130° to 140°C. Quantitative data comparing relective notching versus linewidth as a function of process parameters is presented. Though not presented, we have shown that the HTPEB single level resist process does not reduce throughput in our fabrication area. It is achievable using either track or batch develop techniques.

Data is presented on a positive photoresist designated as PR-1024 Megabit (MB), whose chemistry includes a cresol novolak, coupled with 2-1-4 diazonapthoquinone chloride. The type and M.W. of the coupled novolak were found to be of prime importance. UV absorption of the photoactive compound in the resist is in the range of 230 to 380 nm, with prominent peaks at 230, 270 and 370nm. Extensive SEM data is presented showing geometries obtained on the Micralign 600-552HT in the UV-3 mode. Micron capabilities are demonstrated with edge wall profiles of approximately 85°. A salient feature of the resist is its availability both in the ECA solvent mode (PR-1024MB) as well as "safe solvent" variety (EPA-1024MB). Exposure energies in the UV-3 mode were studied, ranging from 170 to 270 mJ/cm². Linewidth control of both isolated/group lines is reported at various exposure energies, indicating wide process latitude. Used as an I-Line photoresist, sub-micron capabilities (0.5 micron) were demonstrated with edge acuities in the 80°-85° range. Wide process latitude is demonstrated with both types of exposure tools. Using I-Line steppeis and projection aligners, exposure energies were varied up to and including the 270 mJ/cm² region. Dry processing (plasma etching) data will also be displayed.

The general functional performance of the ULTRAMiC; PR-900 series has been described in the last two SPIE conferences (March 1984/1985). The present new systems, EPA-914/EPA-964 are further evolution(s) of the earlier PR-900 series with the following significant advances: 1. A "safe solvent" system (using no CA). 2. In the case of EPA-964, a novolak system has been synthesized to have: a) elevated softening point (approx. 190°C) yielding resist images with no reticulation problem(s), when etched in typical plasma etchers without deep UV/PRIST treatments. b) EPA-964 yields suitable image quality, which however is not equivalent to the high resolution/high speed EPA-914 system. 3. Dyed versions for superior alignment, inspection and linewidth measurements. In the case of 2a, both EPA-914/EPA-964 resist/image replication via plasma processing into a variety of substrates was studied experimentally, using typical plasma etching equipment under a variety of plasma conditions. The relative requirements for postbake/deep UV/PRIST treatments for both resists, and their mechanisms, as well as the effect of the plasma chemistry on the different novolak systems, are discussed in detail. To study both 2a and 2b, the Perkin-Elmer DRM along with the Micralign 600 Model 552HT were used to contrast the photolithographic response of both resists. Some of the lithographic properties monitored in both metal-ion containing and metalion free developers are:

In order to extend the use of the EPA 914 into the submicron range, using conventional lithographic production tools, a modified version, EPA 914 IR has been formulated which is expected to have a shelf-life stability approaching conventional positive resists and allowing it to operate in a "negative" mode, without requiring the IMTEC/YES approach. The lithographic evaluation of EPA 914 IR described herein considers the following lithographic properties using both the Micralign 600-552HT and the GCA DSW 6000: *1. Linewidth control for both isolated/group lines. *2. Depth of focus vs. CD. 3. Linewidth control for nominal,--1.00 micron lines/spaces. 4. The effect of the following process parameters on lithographic properties (1-3) will be considered as well: a) Initial exposure b) Post-exposure bake c) Flood exposure d) Develop condition(s)

Photoproducts introduced for wet etching must now resolve one micron images, withstand reactive ion etching, ion milling, RF plasma and high dose ion implantation. Such resists should have necessary consistency to attain the required linewidth control for yield - productivity improvement. The performance characteristics of twelve major brands of Novolac - diazo positive photoresists were evaluated utilizing the following analytical techniques: Glass transition temperature of solids by differential scanning calorimetry yielded values in the range of 40-70°C. Thermo gravimetric analysis indi-cated solvent evaporation in these resists lie in the range of 120 - 145°C and onset of decomposition temperature of resists begin -250°C. Molecular weight distribution (or fingerprint) of these resists by Gel Permeation Chromatography in the G, H and I-line wavelength is investigated and polydispersity index which is a ratio of weight average molecular weight to number average molecular weight lie in the range of 3-4. These evaluated changes will be related to changes in processing parameters such as image stability at higher temperatures and outgassing in low pressure as a function of ther-mal history.

As integrated circuit feature sizes shrink to sub-micron geometries, the need for a precisely defined and controlled photolithographic process becomes crucial. This paper outlines a method to improve an optical positive photoresist process using an innovative Response Surface Analysis (RSA) procedure. RSA has previously been employed to graphically model simple resist processes. In this procedure, exposure dose, develop time and concentration have been considered. The critical parameter (response), linewidth, is fitted to a set of linear hyperbola expressions. These expressions are then manipulated to directly calculate the conditions which replicate a desired linewidth. The associated process latitudes, response variations per process variable changes, are similarly derived. Optimal processing conditions are obtained mathematically using weighting factors derived from absolute and relative variations in the process. The accuracy and success of this procedure is demonstrated in improved linewidth control when operating at the optimal process condition. This improved control was observed in a stepper based applications laboratory. The results show the utility of this procedure as an effective tool to predict optimal processing conditions in an environment of complex variable interactions confounded by random and systematic errors.

The analysis proposed earlier by us for the evaluation of the contrast of diazo-type positive photoresists is extended to include the influence of standing waves and post-exposure bake. The dependence of the contrast on a large number of processing variables including exposure dose, development time, developer concentration, pre-and post-exposure thermal treatment, etc. is evaluated. For a substrate that is optically matched with the photoresist, however, the evaluation of contrast is exact and more direct using the recently derived closed form solution of Dill's equations. Further, assuming that the resist development occurs in two stages, first down to the substrate and then away from the center line, the variation of linewidth with the development time has been calculated for AZ1370 resist for a given aerial image intensity distribution across the resist surface. If the resist development occurs predominantly in the downward direction, then it is shown that the slope of the line channel sidewall is proportional to the contrast.

The model PROLITH is used to simulate advanced topics in lithography such as multi-level resists, contrast enhancement lithography, linewidth variations over topography, antireflective coatings, post-exposure bakes, and dyed photoresists. The applicability and usefulness of this model for these topics is discussed. Other areas in which the model PROLITH may be applied are suggested.

Reliable coverage of contact holes in the 0.8 to 1.25 micron range with sputtered metals requires sloping of the contact sidewalls. Conventional single layer resist and fluorocarbon based oxide etch techniques produce sidewalls close to 90 degrees. With mild alteration to the C2F6/CHF3 oxide etch chemistry to produce a highly selective oxide etch and separation of the printed resist openings from the substrate by a spacer layer of 1.5 to 3.5 microns in thickness a sloped contact can be etched into the dielectric. To generate the separation a cantilevered resist structure has been produced by modifying the sestertius multilayer resist process. The sestertius resist process is a "two and one-half" layer process, using PMMA as the bottom planarizing layer, a thin anti-reflective coating layer to block intermixing and to eliminate the effect of reflected light on patterning, and novolak resist as the top imaging layer. The undercut cantilever structure is produced by over exposing and over developing the PMMA. Controlled contact slopes between 60 and 90 degrees can be generated reliably. The degree of variation in contact angles over different topography is dependent on the percent variation of total spacer thickness. For typical MOS topography a variation in angle of less than 10 degrees is observed. The process has excellent repeatability and process control. Sputtered aluminum sidewall coverage is improved from the 10 to 25 percent range to the 45 to 65 percent range.

We have developed an undercoating material, SWK 436( Standing Wave Killer 436 ), that is composed of a polymer synthesized from the compounds that mainly consist of triazine derivatives and physically mixed dyes. It has an antireflective effect and no photoreactive property. Its maximum absorption is at about 450nm but it is designed to have a high degree of efficiency to absorb light at 436nm wave length. When SWK was applied to a bilayer resist system on an aluminum substrate, stsnding wave generation was quenched as it absorbed reflected or scattered light. The variation of resist pattern dimension was got to be lower. The resolution of resist pattern with SWK was resulted higher than the resolution without SWK on an aluminum substrate.

Requirements for the bottom layer of the trilevel resist system are examined with the aid of the SAMPLE simulator. Some conventional positive photoresists and our new bottom layer material RG-3900B are evaluated as a bottom layer. RG-3900B is a phenolic resin mixed with a novel azide compound. It is found that RG-3900B has the following excellent optical properties with relatively short baking time at about 200°C; it strongly absorbs the exposing light and is transparent at visible regions for alignment. Therefore, when applied as a bottom layer, it minimizes linewidth variations on highly reflective substrate topography without degradation of alignment accuracy. RG-3900B has been successfully applied to our various devices with multilevel metalization to obtain fine patterns.

A capped photoresist mask of Kodak 809 on PN with minimal undercut is developed. The advantage of leaving Kodak 809 cap is that it offers better erosion resistance in the chlorine-containing plasma. The undercut of PMMA is dependent on the incidence angle of ultraviolet light to the resist. A wide incident angle creates substantial undercut while a normal incidence produces very slight undercut.

We have published methods for bringing highly reactive metal atoms and/or ions and volatile organic monomers together in the vapor phase, thus achieving deposition of uniform metal-containing polymer films on a desired substrate. In the present study of blending of gold and other metals with polyimides, an evaporated gold vapor was mixed with vapors of aromatic dicarboxylic dianhydride and of oxydianiline to deposit uniform films on the substrate. Deposited polymer films were heated at 300°C on a hot plate to remove an excess of either monomer, and to convert the polyamic acid to the polyimide films. An optical absorption band due to gold clusters in the films appeared around 600 nm. The resulting polyimide film was image-wise delineated, using a silicon-containing photo-resist and oxygen RIE, to give relief images with vertical wall profiles. The oxygen RIE rate was measured as a function of the gold content in the films. As long as gold particles are isolated, the RIE rate is not reduced significantly. This kind of imaging technology with a heavy gold content which produces polyimide films may be useful in x-ray mask fabrication and other processes. Polymer films other than polyimides with gold clusters have been reported.2'3

PMGI is a recently developed polymer which has features that make it of interest to the semiconductor industry. Some recent work and applications of this polymer are presented. Emphasis is placed on incremental results and on the achievement of consistency in the behavior of the polymer. The material is currently under evaluation at a number of different sites.

A new water-soluble contract enhanced material, WSP (Water-soluble Photopolymer), has been developed. The WSP is composed of a mainpolymer and a photobleachable reagents. The mainpolymer is a water-soluble polymer mixed with pullulan (refined through biotechnological process) and polyvinyl-pyrolidone (PVP). The photo-bleachable reagent is of a diazonium compound gorup. The introduction of the mainpolymer and photobleach-able reagent mixture has improved filmity, gas transparency, photobleaching characteristics and solubility in alkaline which are essential to the device fabrication. Submicron photoresist patterns are successfully fabricated by a simple sequence of photolithography process. The WSP layer has been applied to the bilayer resist system--deep-UV portable conformable masking (PCM)--that is not affected by VLSI's topography, and is able to fabricate highly accurate pattern. The aqueous developable layer, PMGI, with high organic solvent resistance is used in the bottom layer. Therefore, no interfacial mixing with conventional positive resist top layer is observed. Furthermore, deep-UV exposure method has been used for the KrF excimer laser optical system in order to increase high throughput. From the experiments, it has been confirmed that good resist transfer profile can be realized by the use of WSP, and that the submicron resist patterns with high aspect-ratio can be developed on the nonplaner wafer with steps of up to 41m by the combination of the WSP with the PCM system. By this technology, has been improved the weak point: variation in the line width due to the thickness of contrast-enhanced layer when the CEL technology is applied, and dependency of both the finished resist profile and the line-width accuracy on the thickness of the top layer resist when the PCM system is adopted.

A high resolution, easy to implement bilayer PMGI [poly[dimethylglutarimiden process has been developed for producing polysilicon gates for high density CMOS. One micron wide, proximity effect free, and very uniform poly lines were obtained. Unbiased mask dimensions were reproduced easily with optimum process latitude. A focus latitude of 5 microns for 1 micron dense (repeating line/space) pattern is reported. This was achieved using a conventional stepper with a nominal resolution of 1.1 microns and a depth of focus of +/-1.3 microns. The delta between the mask and the final wafer dimensions was virtually the same for lines ranging from 5 all the way to 1 micron, as well as for all single and dense lines showing no proximity effects. The after-etch linewidths were uniform to within a sigma of 0.04 microns across a 4 inch wafer. The process consisted of the following: The polysilicon was coated with a planarizing and antireflecting PMGI layer of about 1 micron. A 0.7 micron layer of conventional novolak resist was put on top. The image was formed in the top resist and transferred to the bottom by a deep UV flood exposure. The PMGI was developed in a aqueous-based solution completely removing the top resist in the process. The etching was done in a single wafer RIE machine. All the linewidth measurements were made on final poly structures using electrical techniques. The advantages of using PMGI over conventional materials such as PMMA are no interlayer mixing, aqueous-based developer chemicals, and better etch resistance. The process is very flexible and different schemes can be implemented as needed. A novolak cap can be retained for increased etch resistance by changing to a different aqueous developer solution; however, the simple uncapped approach was found to be already far superior to any single layer resist technique and it was easily implemented on conventional production equipment.

A new Portable Conformable Mask (PCM) bilayer process has been developed that uses Reactive Ion Etching (RIE) for development of the bottom PMMA layer to produce steep resist profiles. This new process uses a gas mixture of ( C2F6+CHF3 ) that effectively removes the PMMA resist, interfacial layer and that has a high rate of anisotropic development for the bottom PMMA layer --- combining the advantage of performance on a trilayer process with the relative simplicity of PCM. The development rate of the top resist layer is very small and result in very little thickness loss of the top imaged positive resist. The top layer of positive photoresist remains intact to protect the PMMA during etching process. This eliminates the requirement of an intermediate barrier layer or special resist materials. For the additional protection during etching process, the resist can be hardened by a deep ultraviolet ( DUV ) exposure after RIE development of PMMA and it is observed that small amount of DUV exposure effectively improves the plasma resistance on this resist structure. This new PCM process has been used for the dry etching process of aluminum film using a gas mixture of BC13+CF4+02. An optional layer of sputtered amorphous silicon can be used between the aluminum and the PMMA to act as an antireflection layer. Using this process and an EATON-OPTIMETRIX MODEL 8605H wafer stepper, 0.6μm line and space of equal width have been exposed and etched into 9000A of aluminum film. Critical process steps are given, the effects of variation in process parameters are described, and SEM photographs of the final results are shown.