Grayscale PhotoLithography (GPL) enables the patterning of various 3D microstructures in a single lithography step with high throughput. For various 3D optical filtering devices to be functional, high vertical resolution and accuracy are key factors. This precision can, in part, be improved by an adapted mask design construction when using GPL as the 3D patterning method. Here we study different mask design approaches to achieve high resolution staircase like structures patterning using GPL. We found that by using different design flavors, we enlarge the range of available densities for grayscale applications. A relevant design choice also allows us to increase the theoretical vertical resolution enough so that the remaining limitations come not from the mask itself but from the process. The Mask Error Enhancement Factor (MEEF) is also shown to be improvable by tuning the dose sensibility of the design.
KEYWORDS: 3D mask effects, Grayscale lithography, 3D modeling, Data modeling, 3D microstructuring, 3D acquisition, Semiconductors, Profilometers, Process control, Photoresist processing
Optical grayscale lithography offers the possibility to pattern 3D microstructures at large scale and high throughput for HVM semiconductor industry [1-4]. 3D structures uniformity is of importance to ensure homogeneous and at-best performances of several tens of millions of functional elements. This uniformity can be impacted in part by the optical mask variability. Impact of mask variability can be quantified in terms of Mask Error Enhancement Factor (MEEF) [5] for optical grayscale lithography which can be calculated by using resist contrast curve. It has been shown that MEEF is highly dependent on mask densities [5]. Once the mask is fabricated, the impact of mask variabilities on lithography can be controlled by process optimization. In this paper we evaluate the impact of process parameters on optical grayscale MEEF by theoretical and experimental means.
Impact of mask CD errors on microlens and pillar structures fabricated using grayscale lithography technique is studied. CD errors were evaluated from the mask SEM images using contour based metrology. Mask error enhancement factor for grayscale lithography is proposed based on mask (or design) chromium density for given 3D structure to be patterned. Impact of mean-to-target CD mask error and local CD variations on target critical parameters were studied separately. For grayscale lithography, the global mask error enhancement factor calculated to study impact of mask CD errors were found to be non linear and highly dependent on the mask (or layout) chromium density. Surface topography of given grayscale target was found to be highly dependent on the local CD variations. We also found that intentional local CD variation can be used to effectively tune certain target parameters.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.