Edward D. Babich

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.

Mechanism of microwave plasma etching of polyimides in O 2 and GF 4 gas mixtures

Abstract A mechanistic study of microwave plasma etching of polyimides in oxygen plus CF 4 gas mixtures was carried out with several mutually complementary surface-sensitive characterization techniques. In-situ X-ray photoelectron spectroscopy was used to characterize the polyimide surfaces before and after etching while multiple internal reflectance and Fourier transform IR spectroscopy was employed to obtain additional information on molecular structure and chemical bonds on these surfaces. In addition, steady-state and temperature-programmed mass-spectrometric measurements were made to identify the etching products, their precursor states and desorbing species. When the experimental evidence obtained by these techniques is pieced together a coherent picture of the etching process emerges. Attachment of atomic oxygen produced in the plasma to selected carbon sites on the PI surface causes aromatic ring opening, forming precursors to volatile etching products. Addition of CF 4 to oxygen plasma in small amounts increases the efficiency of oxygen production and concomitant flourination of aromatic carbon provides excess energy for ring opening and promotes imide and ether bond cleavage. At higher CF 4 concentrations flourination exhausts the reaction sites for oxygen, thus inhibiting the etch rate. Thermal desorption studies indicate that the fluorine coverage desorbs in the first stage as fluorine molecules.

A simplified silylation process

This paper discusses a simplified ‘‘silylation’’ process, which converts typical diazo‐type photoresists into oxygen plasma etch barriers that are insoluble and thermally stable. Previous workers have reported on a silylation process that incorporates silicon in the resist in the gas phase. This paper reports on the use of a bifunctional silylation agent, which when diffused into the patterned resist using a solvent carrier, crosslinks the novolac resin, incorporating silicon in the matrix. The mechanism and the properties of the resist film after silylation such as thermal stability, reactive ion etch (RIE) resistance, silicon content, and solubility will be discussed.

A comparison of the electron beam sensitivities and relative oxygen plasma etch rates of various organosilicon polymers

Abstract A study of the electron beam sensitivities and oxygen plasma etch rates of a variety of organosilicon polymers is discussed. The particular structures investigated include polysiloxanes, polysilmethylenes, polysilazanes. polysilanes, polysilphenylenes, and organic polymers with side silyl groups. The influence of pendant organic groups and heteroatoms in the main polymer chain on the plasma etch rates and electron beam sensitivities is also addressed.

A simple bilayer lift-off process

Abstract This paper discusses a simplified “lift-off” process, which consists of two layers. This consists of an underlayer of soluble, thermally stable polyimide, and a new process, “silylation”, which converts typical positive photoresists into oxygen RIE barriers. The uses of this new material and process for chip and packaging applications are described in this paper.

The use of organosilicon polymers in multilayer plasma resist processing

Abstract The unique resistance of organosilicon polymers to oxygen plasmas has led to their widespread use in multilayer resist processing. A study of their etching properties shows a correlation between their structure and etching characteristics. Often, these characteristics are obtained by means of laser interferometric techniques. Using a model of this laser signal we have identified various processes which combine to form an oxygen plasma resistant layer atop these organosilicon polymers. In particular, we have discovered that the etching characteristics of these polymers is relatively independent of the specific structure. Rather, the silicon content of these polymers plays the dominant role in providing resistance to these plasmas. For polymers having a high silicon content, the laser signal is regular and sinusoidal; for lower concentrations (

Diazopolysiloxanes: unique imageable barrier layers

Abstract This paper describes new types of organosilicon photoresists, sensitive throughout the ultraviolet region from 2000 to 45A. The synthesis is based upon a simple condensation reaction of 3-aminopropyl-substituted polysiloxanes with photosensitive naphthoquinone diazosulfonyl chlorides. These polymers when used in bilayer systems are very sensitive, high contrast negative photoresists with sensitivities of about 10 mJ/cm 2 at 4047A and (γ) of 1.4. Because of the inorganic polysiloxane backbone, they are resistant to oxygen plasmas, with an etch rate ratio of 50:1 (photoresist/diazosiloxane), and they are thermally stable up to 400°C. The synthetic procedure, mechanisms of crosslinking and processing characteristics of these materials are discussed along with data concerning their resolution capabilities and lithographic applications.

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%.

Organometallic materials in lithography: A review

Organosilicon polymers have found many uses in the electronics industry in the last 25 years due to their low‐dielectric constant and water‐repelling properties. These uses include insulators and encapsulating materials (RTV) for electronic parts. More recently, siloxanes have been incorporated into polyimides for the purpose of increasing the water resistance, improving mechanical properties, and preventing atomic oxygen attack of polyimides [R. H. Bott, J. D. Summers, C. A. Arnold, L. T. Taylor, T. C. Ward, and J. E. McGrath, J. Adhes. 23, 67 (1987)]. In only the last few years, some uses of organosilicon polymers in lithography have been reported. In this paper, a review of these uses will be presented and the requirements for organosilicon materials in lithographic applications will be outlined.

Polysiloxanes for deep UV lithography

Abstract The sensitivity of linear siloxane polymers has been increased in the deep uv by the addition of photoinitiators. The resist system discussed in this paper has a sensitivity of 20mJ/cm 2 at 2537A., with a contrast (γ) of 2.6. When used as a thin imaging layer in a double layer system, 0.75um resolution has been achieved on the PE500 exposure tool. Data is presented on exposure linewidth variation, resist stability, and etch rate in an oxygen plasma.