Andrew T. S. Pomerene

Optical properties of hydrogenated amorphous‐carbon film for attenuated phase‐shift mask applications

The optical properties of a plasma‐deposited amorphous‐carbon film have been investigated in the ultraviolet (365 nm) and deep ultraviolet range (248 nm). By varying process conditions, the optical transmission through the films was tuned from 4% to 20% at 365 nm and from 3% to 9% at 248 nm. This tuneability was related to the hydrogen content of the film as affected by the process parameters. The index of refraction n measured by spectroscopic ellipsometry is ∼2 at the wavelengths used. These optical properties make this film attractive for use in single layer attenuated phase‐shift masks for potential application in 0.25 μm lithography at 365 and 248 nm.

Positive mode silylation process characterization

Abstract In this paper we wish to report on our progress in developing a positive TSI system with emphasis on what we believe is a novel approach for characterizing the silylation process.

Fabrication of high performance 512K static‐random access memories in 0.25 μm complementary metal–oxide semiconductor technology using x‐ray lithography

Functional 512K static random access memory (SRAM) devices containing more than 3.6 million transistors have been successfully fabricated in a 0.25 μm complementary metal–oxide semiconductor technology using compact storage ring x‐ray lithography. In this demonstration a comparison of critical dimension control was made between x‐ray and optical (i‐line and excimer laser) lithography by fabricating SRAM devices using both lithographic techniques. For the x‐ray fabricated devices the channel length, a key device performance parameter, was controlled to within 0.036 μm (3σ), demonstrating the excellent process robustness, and dimensional control available from x‐ray lithography. These SRAMs had excellent electrical characteristics, including cycle times of 1.8 ns and access times of 3.7 ns. The ability of the existing x‐ray lithography infrastructure to produce a fully functional (‘‘perfect’’) chip has been demonstrated in a companion device fabrication program. A 512K SRAM chip of a slightly different desi...

Practical Characterization Of 0.5 μm Optical Lithography

This paper establishes the characterization techniques that are needed to repeatedly fabricate submicron structures which are below the resolution specifications of an optical system. A two-parameter system is defined, consisting of a material or photosensitive component and an optical component, which represents the major contributors to process variability. Statistical inference and correlation analysis are used to estimate the effects and extent of the individual components on the total lithographic system. The photosensitive component, consisting of the photoresist, films and related chemistry, is shown to substantially represent the variability in the final linewidth of 0.5 μm structures. Positive and negative photoresist systems are compared and analyzed for run-to-run and within-run variability utilizing photoresist speed-point analysis. The optical component is explained by using a two-dimensional aerial image model which takes as input the numerical aperture, wavelength, coherence, aberrations and experimentally measured effects. A method for quantitatively measuring flare or background exposure is introduced.

Effect of photo acid generator concentration on the process latitude of a chemically amplified resist

A positive tone chemically amplified photoresist was evaluated for use on a 0.44 NA 248 nm excimer laser stepper. The effects of various formulation changes were examined with respect to exposure latitude, depth of focus, resolution, and bias between isolated and grouped features. Of particular interest was the relationship between the percent of photo acid generator (PAG) in the resist and the process latitude. It was found that several aspects of the process window increased as the PAG content of the resist decreased. An increase in dose was expected and observed with the decrease in PAG concentration. This would reduce excimer stepper throughput by approximately 25%.

Fabrication of high performance 512Kb SRAMs in 0.25 μm CMOS technology using x-ray lithography

Abstract Fully functional 512Kb static-random access memory (SRAM) devices containing more than 3.6 million transistors have been successfully fabricated in a 0.25 μm complementary metal oxide semiconductor (CMOS) technology using compact storage ring X-ray lithography thus demonstrating the functionality of the X-ray lithography infrastructure. A lithographic performance comparison was made between x-ray lithography and optical (excimer laser) lithography by fabricating SRAM devices using both lithographic techniques. The excellent process latitude and dimension control available for x-ray lithography is reflected in this comparison. A comprehensive discussion of the advantages of x-ray lithography is discussed in this paper.

A Single Expose Double Develop (SEDD) process for self-aligned lithographic applications

Abstract A Single Expose Double Develop process has been developed which incorporates the use of a tridensity mask to expose two self-aligned patterns in conventional photoresist with one masking step. This minimizes masking cycles and overlay errors which translates into increased yield. The resultant pattern can be customized for various applications, e.g. obtaining two dopant profiles with a single implant using a dual thickness photoresist pattern, transferring two patterns into underlying films with no alignment error using RIE or wet etching, etc... Experiments are shown which optimize the processing parameters of the photoresist to the density levels in the mask, utilizing characteristic curves for analysis. Process control is correlated to these curves through modelling and experiment. Examples of the applications of the SEDD process in VLSI devices and packaging are shown with SEM photographs.

Supporting early development of advanced high-performance logic with synchrotron orbital radiation lithography: a feasibility evaluation

The synchrotron x ray lithography (XRL) project described was conducted as a learning and feasibility vehicle for gate level lithography in support of IBMs most advanced CMOS logic programs. An electrically probable multilevel lithography test site was developed and characterized to exercise critical design, mask manufacture, alignment, exposure, and metrology issues in the 150 - 350 nm linewidth range. A fully capped silicided polysilicon gate stack was chosen for the electrical measurements in order to develop and demonstrate the XRL and related reactive ion etch process on a realistic, product-like substrate. This paper addresses test site design issues, elaborates on the mask manufacturing process, and presents SEM and electrical data from wafers processed at IBMs Advanced Semiconductor Technology Center. The data presented demonstrate the feasibility of supporting early device development and process integration with XRL and highlight the need for high resolution, defect free, proximity corrected masks to fully exploit the capabilities of x ray lithography.

Fast Dosimeter Film For Evaluation Of X-Ray Lithography Sources

This paper presents data on the soft x-ray behavior of the photochromic dosimeter film UVSC manufactured by Sensor Physics. In particular, the x-ray sensitivity measured with synchrotron storage ring x-ray sources will be presented and compared with a presently used dosimeter film which is many times less sensitive. Relevant properties of the film for x-ray source evaluation also will be presented together with data obtained with other x-ray lithography sources.

Optimization of ESCAP photoresist for x-ray lithography

Acid catalyzed photoresists have been examined for exposure using the Helios compact synchrotron x-ray source at the IBM Advanced Lithography Facility. A fundamental challenge with these photoresists is the sensitivity to contamination from the environment. This study attempts to optimize a new type of Environmentally Stable Chemically Amplified Photoresist (ESCAP) developed by IBM Almaden Research Center. A key feature of this new resist is that it does not require an extra polymer topcoat to seal out airborne contaminants. The establishment of a base process and then the enhancement of exposure latitude was the main objective of the optimization. A 5 factor Taguchi optimization was designed to test the effects of post exposure bake (PEB) temperature, PEB time, post apply bake (PAB) temperature, PAB time and develop time. Sixteen wafers were utilized to explore 3 levels for each factor. Twenty-four additional wafers were run using the optimized process with slight variations. These were split into 3 runs for an estimate of noise. The second optimization used 4 factors with 3 interactions. The 200, 300, and 500 nm isolated line structures were examined. A test for maximum photospeed pointed to the same optimum region for latitude as well as sensitivity. Across all conditions a 5X change in dose for linewidth was shown while the exposure latitude for the 500 nm varied from 21 to 54%. The slopes fit to the subsequent plots ranged from 2 - 6 nm/mJ. The PEB latitude was seen to be 10 - 14 nm/ degree(s)C.