The implementation of double patterning processes in 193 immersion lithography is moving forward. The industry is
examining several methods of producing robust double pattern images. These methods include thermal cure resists and
the use of a spin on chemical to cure the layer 1 resist image. Thermal cure resist systems require fewer processing steps
than a chemical curing process. An effective thermal cure process improves process throughput, reduces chemical costs
and reduces process complexity In either case, producing wafers with adequate CD Uniformity (CDU) relies on the
ability of the layer 1 resist to remain inert during subsequent processing steps.
The goal of this paper is to isolate and optimize the critical processing steps using thermal cured resists in order to
improve CDU. The system includes a layer 1 thermal cured resist and a traditional layer 2 resist. Processing was done
using a TEL Lithius I+ and an ASML XT Twinscan 1900i. The feature of interest is a 42 nm x-Hatch contact hole
produced by horizontal lines exposed with layer 1 and vertical lines exposed with layer 2.
By combining chemical and thermal curing techniques, we developed a simple "hybrid" curing system which offers
precise CD control of the first patterns after double patterning. This hybrid curing system involves thermal curing
followed by a liquid rinse process using a double patterning primer (DPP). DPP is an aqueous solution formulated with
surface curing agent (SCA) components and enhances "positive" interaction between L1 and L2 patterns. Taking
advantage of the CD growth with DPP treatment, we further developed three advanced patterning schemes: 1. "Shrink
Process Assisted by Double Exposure" (SPADE I), 2. "Space Patterning Assisted by Double Exposure" (SPADE II), and
3. "Sidewall Patterning Assisted by Double Exposure" (SPADE III). Using SPADE I, contact hole CD was reduced by
10~30nm and excellent through pitch performance was achieved. Using SPADE II, the first example of self-aligned
double patterning of contact holes has been demonstrated. After SPADE II, the contact hole pitch was reduced by 30%.
A novel method was developed to form sidewalls on the existing patterns using SPADE III. The 2D sidewall patterning
with contact holes was demonstrated and ~40nm sidewalls were formed using SPADE III. This can also be applied to
form sidewall patterns on line and space patterns to self-aligned double patterning of lines. In this paper, our recent
progress with SPADE technology is described and its potential use in the advanced patterning schemes is discussed.
The CD control of the first lithography (L1) patterns is a important issue in the single-etch double patterning (SEDP)
process. In this process, L1 patterns are cured either chemically or thermally and then subjected to the second
lithography (L2). A chemical curing process using a surface curing agent (SCA) often results in the CD growth due to
the "positive" interaction between the first and second resists. A thermal curing process using a thermal cure resist
(TCR) often results in the CD loss due to the volumetric shrinkage of the L1 patterns during the L2 process. By
combining SCA and TCR concepts, we developed a simple "hybrid" curing system which offers precise control of the
L1 CD after double patterning. This hybrid curing system involves thermal curing followed by a liquid rinse process
using a double patterning primer (DPP). DPP is an aqueous solution formulated with SCA components and enhances
"positive" interaction between L1 and L2 patterns. While CD loss of 5~6nm is observed without DPP treatment, ~11nm
CD growth was observed with TCR after DPP treatment. The L1 CD after double patterning was precisely controllable
by post-priming bake process with the rate of -0.3nm/°C in the temperature ranging from 120 ~ 150°C. Taking
advantage of the CD growth with DPP treatment, we further developed three different advanced patterning schemes: 1.
"Shrink Process Assisted by Double Exposure" (SPADE I), 2. "Space Patterning Assisted by Double Exposure"
(SPADE II), and 3. "Sidewall Patterning Assisted by Double Exposure" (SPADE III). Using SPADE I, contact hole CD
was reduced by 10~30nm and excellent through pitch performance was observed. SPADE I can also improve
LER/LWR when used in the formation of smaller trenches. SPADE II was developed for self-aligned pitch splitting of
contact holes and SPADE III was developed for self-aligned pitch splitting of lines. In this paper, the use of DPP in
various SPADE technologies is described and its potential in the advanced patterning schemes is discussed.
Two different pattern curing techniques were developed to stabilize first lithographic images for the single-etch double
patterning process. The first method uses a surface curing agent (SCA) that is coated on top of the patterned surface to
form a protective coating layer during the curing bake process. It was found that the surface curing process with SCA
offers minimum CD changes before and after the double patterning process. Virtually no CD change was observed with
the first lithographic images at various curing bake temperatures ranging from 120 ~160°C indicating the curing reaction
is limited on the patterned surface. The second method uses a thermal cure resist (TCR) that is a special 193nm
photoresist with a crosslinkable functional group to form an insoluble network upon heating at higher temperature. A
single-step curing process of the first lithographic images was achieved using TCR by baking the patterned images at
180°C for 60sec. A cross-line contact hole double patterning method was used to evaluate these two different curing
techniques and both SCA and TCR successfully demonstrated their capability to print 45nm contact holes with excellent
CD uniformity in immersion lithography (1.35NA) with a 45nm half pitch mask. It was also confirmed that both SCA
and TCR can be extended to the top-coat free immersion double patterning process using an embedded barrier layer
technique.
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