John P. Stirniman

Optimizing proximity correction for wafer fabrication processes

A key requirement for any proximity correction method is the ability to accurately predict proximity effects for any given circuit configuration. In this paper we present a methodology for characterizing proximity effects from measurements taken on a processed wafer. The characterization will determine what types of effects are present, which effects can be corrected, and it will quantify behavior parameters for a generalized proximity error model.

Optical proximity effects correction at 0.25 um incorporating process variations in lithography

We study the optical proximity effect and its correction using empirically derived models for DUV lithography taking into account random process variations. The sensitivity of corrected configurations to different sources of process variation (exposure dose, defocus) is evaluated. For correction at a centered condition (optimum dose, zero defocus), problems may arise in ill-conditioned areas (inside corners of T-shape features, butting line-ends, etc.), when going away from the best focus and/or exposure dose, within the exposure/defocus window. Correction for sharp corners (aggressive correction) shows a stronger sensitivity to defocus than less corner sharpening (conservative correction). Furthermore, we study what types of design configurations tend to print poorly with process variations and investigate alternative correction optimization schemes that stabilize the printing performance in such areas. Various optimization alternatives to improve performance within the process window are evaluated.

Alternating PSM optimization using model based OPC

We describe proximity correction methods for alternating phase shift mask (APSM) designs, including graduated phase transition PSM, phase-conjugate, also known as dual trench PSM, and double exposure clear and dark field PSM. We determine the magnitude and characteristics of proximity errors inherent to APSM, and compare them with the corresponding characteristics of binary masks. We present our investigations on integrating APSM and proximity correction, including CD control improvements at nominal conditions and through focus. We examine the limitations of each APSM/proximity correction alternative. All correction methods and proximity error characterizations were done using TAURUS - OPC. This includes phase shift mask model generation, boolean operations for generating intermediate correction layers, proximity correction, and boolean post- processing to generate the final output layers. We show that large imaging distortions near phase transitions regions require proximity correction and the size of the proximity correction serifs is large due to a Mask Error Factor less than 1.0.

Dual-mask model-based proximity correction for high-performance 0.10-μm CMOS process

Selective strong phase shift mask techniques, whereby a phase-shift mask exposure is followed by a binary mask exposure to define a single pattern, present unique capabilities and problems. First, there is the proper exposure balance and alignment of the two masks. Second, there is the challenge of performing optical proximity correction that will account for two overlaying exposure models and masks. This is further complicated by the need to perform multiple biasing and adjustments that are often required for development processes. In this paper, we present results for applying a new OPC correction technique to a dual exposure binary and phase-shift mask that have been used for development of 100 nm CMOS processes. The correction recipe encompasses two models that were anchored to optimized processes (exposure, NA, and ?). The correction to the masks also utilized boolean techniques to perform selective biasing without destroying the original hierarchical structure. CMOS technology utilizes isolation with pitches of active device regions below 0.4 ?m. The effective gate length on silicon is in the range of 0.08 to 0.18 ?m. Patterning of trench openings and gate regions are accomplished using deep-UV lithography.

Understanding the parameters for strong phase-shift mask lithography

In this paper we analyze selective alternating PSM synthesis and OPC modeling parameters, taking into account lithographic constraints to PSM conformance. The results shown include phase and trim regions size and shape impact on the images printed on wafers at optimum conditions and through focus, at ideal as well as in the presence of errors in phase and transmission due to mask manufacturing.