Derek B. Dove

Ti/Ti‐N Hf/Hf‐N and W/W‐N multilayer films with high mechanical hardness

Ti/Ti‐N, Hf/Hf‐N, and W/W‐N multilayer films with very thin individual metal and metal‐nitride layers were developed, with hardness of the structure much higher than that of single‐layer nitride films. Hardnesses with value between 3500 and 5000 kg/mm2 or higher were observed in the multilayer films. This is an improvement over that of single‐layer metal‐nitride films where hardnesses between 2200 and 2800 kg/mm2 are typically achieved. The improvement is thought to be due to the fact that the grains are restricted to a very small size in the thin individual layers of the sandwich structure. The multilayer films, in general, have better adhesion and less defects than the single‐layer films. These films were prepared on room‐temperature substrates by a simple sputtering process and have potential applications, as in hard coatings.

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.

Contrast properties of reflective liquid crystal light valves in projection displays

Projectors that use reflective light valves must employ beam splitters or analogous components to separate bright-state light from dark-state light, since both states must propagate in the space above the light valve. Polarization ray tracing shows that such beam splitters will not usually achieve high rejection of dark-state light when the beam has the typical angular divergence of about ±10°. At such propagation angles, different rays in the beam will have appreciably different planes of incidence at tilted optical coatings in the system (because of the compound angles involved). If the light valve is mirrorlike in dark state, we show that to correct the depolarization resulting from compound incidence angles, it is necessary that the optics introduce no rotation in the illuminating polarization. To a reasonable approximation, such a rotation in polarization will double in the return pass through the optics. To the same approximation, induced ellipticity in the illuminating polarization will cancel in double pass, and pure rotation can be converted to pure ellipticity with a quarterwave retarder. An important qualification, however, is that a light valve can only be exactly mirrorlike in restricted cases [i.e., if linearly polarized input light remains exactly linearly polarized (though possibly rotated) at all wavelengths when it reaches the mirror backplane of the light valve, independent of small manufacturing errors]. We calculate contrast loss in the more realistic case of a reflective twisted nematic liquid crystal (TNLC) light valve interacting with tilted coatings in the projection optics over finite numerical aperture (NA), and discuss the impact on LC thickness tolerances and spectral bandwidth Δλ. We extend our results to apply to more general light valves and more general projection optics configurations. Dark-state background is found to scale as NA2 (or in some cases as ∼NA2Δλ2). Because of this interaction, the complete system almost always shows a lower contrast than the light valve alone.

Design and fabrication of a prototype projection data monitor with high information content

A prototype 28-in.-diagonal desktop data monitor capable of displaying 2048 × 2048- pixel images has been designed, built, and evaluated. The monitor uses optical projection technology. A reflective, crystalline silicon active-matrix light valve using liquid crystal electro-optics and a digital electronic interface architecture is described. This rear-projection monitor has four million resolvable pixels, uses three light valves to achieve color, has a low-gain surface diffuser screen, and functions as a fully interactive, color personal computer monitor with motion video capability. The monitor is 20 in. deep.

Structure and orientation of films prepared by reactive sputtering of Ni, Fe, and NiFe in Ar/N2 mixtures

Using controlled N2/Ar sputtering gas mixtures, rf‐sputtered films were prepared from Fe, Ni, and Ni81Fe19 targets, and their structure and orientation were studied by x‐ray diffraction. When no N2 was introduced during sputtering, all the films were oriented in the highest density planes; i.e., in (110), (111), and (111) for α‐Fe, Ni, and γ‐Ni81Fe19, respectively. With increasing N2 introduction, however, the orientation shifted to lower density planes, and eventually nitrides were formed. Multilayer films of metal and nitride were prepared with the Ni81Fe19 target by repetitive supply of N2 for short periods during sputtering. Strong orientation effects were observed depending on the number of layers grown. In addition, the x‐ray diffraction of these films presented evidence of epitaxial growth of the nitrides (Ni,Fe)4N on the alloy layers.

Thermally stimulated current studies of hole transport in a layered organic photoconductor

Thermally stimulated current (TSC) measurements have been peformed on a layered organic photoconductor based on p‐diethylaminobenzaldehyde diphenylhydrazone (DEH) dispersed in bisphenol A polycarbonate. Well‐defined transient current peaks were observed, indicative of a hole transport process having an activation energy of ∼0.5 eV at an applied electric field of 10 V/μm. This TSC feature is attributed to carriers which are thermally activated from electron donor states associated with the DEH molecules responsible for transport in this medium. This transport peak is clearly distinguished from the higher temperature secondary structure which is attributed to trap states. Measurements of the steady‐state photoconductivity over a range of temperatures also yield approximately the same activation energy for the transport process.

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.

Hafnium dioxide etch‐stop layer for phase‐shifting masks

Phase‐shift masks were prepared using sputter deposited films for the phase‐shift layer and etch stop layer on fused quartz silica substrates. It has been found that the combination of SiO2 for the phase‐shift layer and HfO2 for the etch‐stop layer offers a unique combination of properties advantageous for the preparation of phase‐shift masks. The optical transmission properties of HfO2 layers with or without a SiO2 phase‐shifting layer on quartz substrates are presented.

Fe/Fe‐N multilayer films with low coercivity zero magnetostriction and high saturation magnetization

A method of fabricating of Fe/Fe‐N multilayer films in the form of alternating thin films of Fe separated by very thin interlayers of Fe‐N sputtered in the presence of nitrogen is described. It was found that the properties of these films depended on the thickness of Fe and Fe‐N layers and the bias voltage. There is a region where the composite films have coercivity less than 1 Oe, with zero or near‐zero magnetostriction. The normally high saturation magnetization of Fe with value of 20 kG was preserved.