Bruce W. Dudley

Microstructures for particle beam control

Submicron lithography presents significant challenges to the fabrication of high‐density complex devices. Resolution, speed, critical dimension precision, variable design sets, and registration generally are conflicting goals for a lithography system. In this paper, we will present a new concept in electron or ion beam lithography with the potential to write far submicrometer patterns at speeds well beyond those of single beam systems currently available. This structure serves as a combined multiple aperture and beam deflection structure in a high‐speed multibeam raster scan writing system. The principle device structure to be discussed consists of an array of apertures micromachined into a portion of a silicon substrate with electrostatic deflection lines connected to each aperture. This structure is a key part of a lithography system with targeted 0.1‐μm‐pixel resolution. Apertures of 0.08 μm2 diameter with 10% dimensional control have been fabricated along with multiple multipole lenses using various m...

Silylated acid hardened resist process: A deep ultraviolet surface imaging technique

A deep ultraviolet surface imaging technique using a silylated acid hardened resist (SAHR) is described. The resist, Shipley XP‐8928, contains a meta, para‐cresol novolak resin which has a high optical absorbance in the deep ultraviolet (DUV). This reduces complications from substrate reflections and restricts the image to the near‐surface regions. The exposed regions, which become crosslinked, are less susceptible to vapor silylation by agents such as trimethylsilyldiethylamine (TMSDEA). The unexposed regions may be easily silylated. An anisotropic oxygen reactive ion etching is used to transfer the surface image through the bulk of the resist. This paper discusses the kinetics of silylation with TMSDEA, the resulting silicon distributions in the film before and after etch, and the lithographic performance of the process. Silicon distribution throughout the film is determined by Rutherford backscattering spectrometry and illustrated by stained cross sections. It is found that the film surface saturates a...

Microstructures for control of multiple ion or electron beams

Structures have been fabricated with the potential to provide multiple particle beam control for high-speed direct-write lithography with the potential of gigahertz date rates and 0.1- mu m pixel sizes. The principal device structure consists of an array of apertures capable of supporting individual deflectors that is built into monolithic single-crystal silicon substrate. The construction of versions of these structures with very small 0.08- mu m apertures and with aperture/Einsel lens combinations has been demonstrated. Far-submicrometer ( >

Comparison of metrology methods for measurement of micron and submicron resist and polysilicon features

As the feature size requirements of TJLSI devices continue to decrease below the practical limits of standard optical metrology, alternate measurement methodologies will be utilized on a more routine basis during device fabrication. A series of linewidth measurements of photoresist on polysilicon and etched polysilicon equal line/space gratings having nominal linewidths ranging from 0.45 jim to 2.0 p.m has been performed using a variety of metrology techniques. Features fabricated using a 248 nm deep UV laser stepper and 405 nm near UV stepper were used in the experiments. Top-down low-voltage SEM measurements, electrical resistance measurements, confocal ultraviolet laser scanning microscope profiles, and SEM measurements on cleaved cross sections are compared. By measuring a large number of points on each line and die, the variability of the linewidths themselves, the measurement precision of the techniques, and the measurement bias between the methods are isolated. Experimental procedures and measurement techniques are described along with the resultant data.

Enhancement of deep-UV patterning integrity and process control using antireflective coating

In this paper, we describe the results of experiments performed using wafers having either phosphorous (POCl3) doped polysilicon, LPCVD silicon nitride, LPCVD silicon dioxide, LPCVD silicon dioxide over POCl3 doped polysilicon, evaporated aluminum, or CVD tungsten thin films, patterned with and without the use of deep UV anti-reflective coatings. The parameters of reflectance control, critical dimension control, focus/exposure latitude, and resist profiles were studied for line/space gratings and contacts. Incorporation of anti-reflective coatings was shown to be very beneficial for reducing the impact of highly reflective substrates, grainy surfaces, and topographical features encountered during deep UV imaging. The ARC process is independent of the substrates reflectivity, allowing the same exposure dose for all substrates studied. Without ARC the optimum exposure dose for the same substrates varied over a 35% range. ARC also provides slightly increased exposure and focus windows for some substrates, and was shown to significantly improve linewidth control on rough substrates such as POCl3 doped polysilicon and tungsten. The grainy surface of the tungsten wafers was nearly impossible to pattern without the use of an anti-reflective coating; without ARC, there was virtually no process window (approximately 2 mJ/cm2) for retention of 0.50 micrometers features.

Process techniques for improving performance of positive tone silylation

Two approaches that control the overflow of silylated material that can occur subsequent to surface imaging of acid-hardened resists are introduced. Treatment of the resist surface with a cross-linking agent [bis(dimethylamino)dimethylsilane] prior to silylation can produce a surface layer with the physical integrity to constrain silylated material. Alternatively, the unexposed areas of the resist may be partially removed by development with a basic solution. The surface depressions thus produced allow volume expansion to occur during silylation without causing overflow.

Monte Carlo modeling of secondary electron signals from heterogeneous specimens with nonplanar surfaces

A Monte-Carlo simulation program has been modified to allow specifying the specimen surface as a series of regions with arbitrary shape and composition. It also models the production of the secondary electron signal. This has been applied to a systematic series of experiments with 0.5 and 1.0 micrometers lines of photoresist, and compared to experimental measurements using an SEM. The qualitative agreement indicates that the model can be used to study the effects of variations in operating conditions such as accelerating voltage, as well as the effect of changes in specimen geometry or composition.

Submicron Metallization Utilizing a Versatile Trilayer Resist/Liftoff Process

Lift-off technology provides an alternate metal patterning technology to that of subtractive etching. In this paper, we characterize a trilayer resist process which provides a practical means for producing the stencils which are required for successful lift-off in a 1.6 μm metal pitch CMOS process, with biasing for nominal mask design rule or wider metal interconnections. The trilayer structure we describe consists of a planarization layer of polydimethylglutarimide (PMGI), a spin-on organosilicon polymer intermediate layer, and a positive novolac photo-imaging layer. All three layers can be coated and cured sequentially in automated equipment, and the intermediate and planarization layers can be etched in-situ, minimizing wafer handling and contamination. The rationale for use of lifted off metal interconnections and requirements for liftoff stencils are described. In this paper, we characterize dimension biasing and proximity effects for the photoresist layer, organosilicon layer, and PMGI layer, as well as the final lifted off metal interconnections. Minimal proximity effects and differential biasing due to feature size variations are shown for feature sizes ranging from 0.7 - 2.0 μm, with biasing in favor of wider metal interconnections.

Wavelength tuning for optimization of deep-UV excimer laser performance

Experiments were performed to quantify the central laser wavelength setting which provided optimum imaging performance for two generations of deep UV steppers: GCA ALS Laserstep and GCA XLS Laserstep. Significant performance enhancements resulted by adjusting the central wavelength setting of the ALS system by -0.23 nm from the original baseline wavelength (point of minimum distortion). The baseline wavelength of the more advanced lens of the XLS system was closer to optimum, with acceptable imaging performance parameters over a >0.04 nm band. Lens characterization methodologies are described.

Strategies for deep-UV patterning of half-micron contacts using negative photoresists

Contact structures represent some of the most challenging features to image using deep UV excimer laser lithography. A single resist process, exposure dose, and focal setting must compensate not only for variations in the reflectivities of gate (Le, polysilicon) and diffusion (i.e., oxide) substrates, but must deal with variations in underlying topographical features which create a non-uniform resist film over a non-planar imaging surface. Commercially available deep UV photoresists are negative toned, requiring the use of clear field photomasks for imaging of submicron contact structures. In this paper, we describe three strategies for enhancing the ability to image contact structures using currently available negative toned chemically amplified deep UV photoresists: (1) optimization of central exposing laser wavelength, (2) incorporation of anti-reflective coatings, and (3) optimization of resist film thickness for sidewall profile enhancement. These approaches should also enhance imaging of contacts using positive tone photoresists, once they are commercially available