John L. Staples

Metal-semiconductor contacts for GaAs bulk effect devices

Abstract An alloy of Au, Ge and Ni has been shown to produce uniform linear electrical contacts to GaAs over a resistivity range useful for bulk effect devices. Batch fabrication of devices with contacts of controlled size and shape is readily accomplished by evaporating the contact material through masks onto the semiconductor surface. An eutectic alloy of Au and Ge also produces a linear contact but tends to produce nonuniform films. The preparation of the contact materials, surface treatment of the GaAs, and device fabrication procedures are described.

Application of the aerial image measurement system (AIMS)TM to the analysis of binary mask imaging and resolution enhancement techniques

The newly developed Aerial Image Measurement System (AIMSTM*) was used to quantify the lithographic benefits of several resolution enhancement techniques as compared to standard binary mask imaging. This system, a microscope based stepper emulator, permits rapid characterization of mask images from both binary and phase shifted mask (PSM) patterns at multiple focal planes. The resultant images are captured digitally with a CCD camera and analyzed using an exposure-defocus tree technique to quantify the depth-of-focus as a function of exposure latitude. The AIMS is used to extract both phase and transmission errors from captured aerial images of all the masks evaluated. AIMS results are compared to wafer electrical linewidth data. A 0.5 numerical aperture (NA) DUV stepper was used with a partial coherence of 0.6 combined with IBM APEX-E resist process. Collected data were analyzed using techniques identical to the AIMS analysis, allowing for a high level of consistency. Comparative data focused on binary mask imaging for the verification of the AIMS results. Trends associated with feature sizes and types are discussed.

New tool for phase-shift mask evaluation: the stepper equipment aerial image measurement system--AIMS

The aerial image measurement system is an optical system for measurements on phase shift masks under chosen stepper characteristics of NA, sigma, wavelength and depth of focus. The present tool operates at I-line or DUV (248 nm) and commonly 5 or 6 inch reticles can be handled. The image obtained is optically equivalent to that incident on resist, but is highly magnified so that it can be recorded using an UV CCD camera. Typically, features of interest are recorded as a through focus series; image intensity is digitized and may be analyzed in a variety of ways so as to produce intensity contours or profiles. Combined with simple models for predicting resist behavior a great deal of information may be obtained on the expected printing performance of a given reticle as a function of intensity and depth of focus prior to actual resist tests.

A 10.5-in.-diagonal SXGA active-matrix display

A 157-dot-per-inch, 262K-color, 10.5-in.- diagonal, 1280 × 1024 (SXGA) display has been fabricated using a six-mask process with Cu or Al-alloy thin-film gates. The combination of high resolution and gray-scale accuracy has been shown to render color images and text with paperlike legibility. The low-resistivity gate metallization and trilayer-type TFTs with a channel length of 6-8 µm were fabricated with a six-mask process which is extendible to larger, higher-resolution displays. A combination of double-sided driving and active line repair was used so that open gate lines or data lines did not result in visible line defects. A flexible drive-electronics system was developed to address the display and characterize its performance under different drive conditions.

Application of an Aerial Image Measurement System to Mask Fabrication and Analysis

Application of an Aerial Image Measurement System (AIMSTM) to binary and phase- shift mask fabrication and evaluation is described. The AIMS tool, an optical system which measures the aerial image directly from a mask, provides rapid feedback on lithographic performance for a variety of stepper configurations through modifications of the wavelength, numerical aperture, and illuminator design. The AIMS tool has been applied during the implementation of an alternating phase-shift mask (PSM) fabrication process in order to understand the impact of the etched-quartz sidewall on lithographic performance. AIMS measurements were used to extract the effective phase and transmission as a function of phase- etch depth as well as post-etch treatment condition. A set of basic test structures are proposed which can be used in conjunction with the AIMS tool to automate the extraction of transmission, phase, and second-level overlay for phase-shifting processes such as alternating and attenuating PSM.