Browse Prior Art Database

Improved Lithographic Processing Methods for Non-Planar Stepped Surfaces

IP.com Disclosure Number: IPCOM000047498D
Original Publication Date: 1983-Nov-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 3 page(s) / 51K

Publishing Venue

IBM

Related People

Bassous, E: AUTHOR [+2]

Abstract

This article relates to the generation of resist patterns with high resolution and good linewidth control over extreme topography. Resist patterns exhibiting high resolution, good linewidth control, and large aspect ratio, over topographically structured surfaces, are highly desirable for the fabrication of VLSI circuits. Methods are described herein for improving the definition of such lithographic patterns by promoting better planarization of substrate topography in single and multilayer resist processes. It is widely assumed that planarization of substrate topography is solely determined by the resist coating thickness and the maximum step height. It is also assumed that adequate planarization is achieved in practice by applying a resist layer approximately twice as thick as the maximum step height.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 52% of the total text.

Page 1 of 3

Improved Lithographic Processing Methods for Non-Planar Stepped Surfaces

This article relates to the generation of resist patterns with high resolution and good linewidth control over extreme topography. Resist patterns exhibiting high resolution, good linewidth control, and large aspect ratio, over topographically structured surfaces, are highly desirable for the fabrication of VLSI circuits. Methods are described herein for improving the definition of such lithographic patterns by promoting better planarization of substrate topography in single and multilayer resist processes. It is widely assumed that planarization of substrate topography is solely determined by the resist coating thickness and the maximum step height. It is also assumed that adequate planarization is achieved in practice by applying a resist layer approximately twice as thick as the maximum step height. Experiments indicate, however, that these assumptions are not always valid. Planarization is significantly affected by the horizontal dimensions of surface steps, their periodicity or proximity to neighboring steps, and the characteristics of the resist and its mode of application. Figs. 1a, 1b and 1c illustrate the effect of these factors on a surface patterned with sets of parallel steps 0.8 mm high and 2.5 to stepped 25 mm wide. The surface was coated with single and multiple layers of PMMA (polymethyl methacrylate) resist of different molecular weight. The peak-to-valley amplitude of the undulations of the resist coating is plotted against the pitch of the stepped surface. The amplitude represents the degree of planarization or levelling accomplished by the resist layer covering the stepped surface. For the same topography, the amplitude decreases, that is to say, planarization improves, as: 1. The average molecular weight decreases. See Fig. 1a. 2. The number of resist layers increases. See Fig. 1b. 3. The step width and spacing decrease. See Fig. 1c. These observations suggest the following two methods to improve planarization over stepped surfaces. Proximity Step Method to Control Line. The width of a resist line is known to vary as it traverses a large surface step due to the...