Line Edge Profiles Research Articles

Simulation of dry etched line edge profiles

Computer simulation of dry etching is used to explore line edge profiles obtained in IC processing. The model divides the process into isotropic or chemically reactive etching and directional or ion illuminated etching. The algorithm simulates the time evolution of the two dimensional profile by advancing nodes on a string according to the local anisotropic and isotropic rates. The accuracy of the model and its applicability to IC processing are illustrated through comparison with known mathematical cases and experimental results. Experiment and simulation are used to explore the residue left at a step with anisotropic etching and the amount of under cut necessary in producing stepped arsenic implanted polysilicon layers.

Modeling ion milling

A string segment motion algorithm is presented and used in conjunction with SEM observation of line edge profiles to study phenomena in ion milling which result from the angular dependence of etch rates. The algorithm allows samples to be rotated and includes shadowing, automatic faceting,and special boundary conditions at interior and exterior corners. The accuracy of the algorithm is demonstrated by comparison with known mathematical results. Simulation is used to study how the shape of the angular etch rate curve and the modification of the local etch rate at corners affect the line edge profiles. Comparisons with experimental results are made to check the algorithm assumptions and applicability. The comparisons include preferentially etched Si, a soft Au mask on a hard NiFe substrate and a hard Ti mask on a soft Au substrate.

A general simulator for VLSI lithography and etching processes: Part I—Application to projection lithography

A simulator is described which produces line-edge profiles at various key stages in integrated circuit processing. Optical models are included for contact and projection lithography. The effects of multiple wavelengths, defocus, and partially coherent sources may be simulated in projection lithography. The positive resist model of Dill is used with the string development model of Jewett to obtain resist line-edge profiles. The string model is generalized to surface reaction rate limited etching of any layer. The application of the simulator to projection lithography is illustrated with a number of examples including monochromatic and multiwavelength exposure, the effect of a post-exposure anneal, plasma descum, and defocus.

<title>In Situ Characterization of Positive Resist Development</title>

The exposure of certain positive photoresists has been shown by Dill and co-workers to be modelable in terms of a local inhibitor concentration which results in a local development rate. The development process is assumed to be a surface etching reaction in which the surface velocity is the local development rate. The characterization of resists for the purpose of line-edge profile simulation therefore involves the measurement of development rate for controlled exposure dose profiles. In this paper a technique is described in which the resist thickness is continuously plotted during development. The low frequency capacitance is measured using a conducting substrate as one plate, and the highly conductive developer as the other plate of the capacitor. The inverse capacitance, proportional to the composite resist-oxide thickness, is obtained using an analog divider. Examples of standing wave effects in Shipley AZ 1350 resists, and resist development rate modification using chlorobenzene are presented.

Simulation of x-ray resist line edge profiles

X-ray resist line edge profiles are explored as a function of exposure, mask, and resist properties. The study is based on an exposure-scission and development-etching model of positive resists. Development rate curves for two actual and three hypothetical resists are used. The simulation is implemented by using a string of points to follow the contour of the developer–resist interface as a function of development time. Control of the resist profile suitable for liftoff of 0.4-μm lines is explored in the context of low flux levels for a high throughput production environment. High aspect ratio lines (3:1) and profiles degradation due to mask edge effects for Alkα and CuL exposures are considered.