dTEC Systems (United States)

The paper presents the use of the Linewidth Bias Monitor (LBM), the critical dimension (CD) uniformity mapping option of the ARIS 2li die-to-database mask inspection system, for incoming quality control (IQC) in the wafer fab. LBM is qualified for this purposes by comparing it's quantitative results with CD measurements. Masks, provided by different commercial vendors, are evaluated based on the LBM maps obtained during mask inspection. Mean-to-target and 3-sigma values are evaluated and compared.

This paper describes studies of various resists from multiple photoresist manufacturers. The main criteria used to select an appropriate resist candidate were iso/dense bias and critical dimension (CD) uniformity. Data has shown that processes commonly used in the industry are sensitive to loading. Etec Systems, Inc. continues to look for photoresist(s) that can mitigate the CD variation caused by this effect. The data presented in this paper shows that resist selection is key to iso/dense bias reduction. Data is presented from both an ALTA 3700 exposure tool and an i-line stepper system, and a correlation is drawn between these exposure systems. Various developer processes are discussed, ranging from puddle to immersion development.

As the requirements for photomask linewidth control continue to tighten, the necessity for performing proximity correction for electron beam mask exposure will increase. GHOST proximity effect correction is one method that can be used to ensure that critical dimension linearity over a large range of feature sizes meets mask user requirements. The GHOST strategy uses an additional exposure to correct for the backscatter component of the primary exposure. Because of the way the image using a GHOST correction is constructed, image contrast will be lower than exposures done without GHOST. This paper uses simulation to examine the process window that is available when GHOST is used and this process window is compared to that without GHOST. The effect of resist contrast on the process window is examined by simulating ZEP 7000 resist and comparing it to resists with other contrasts. The effects of dose, develop time, data bias and spot size on the process window are also examined.

Low energy electron microscopy (LEEM) has developed into one of the premier techniques for in situ studies of surface dynamical processes, such as epitaxial growth, phase transitions, chemisorption and strain relaxation phenomena. Over the last three years we have designed and constructed a new LEEM instrument, aimed at improved resolution, improved diffraction capabilities and greater ease of operation compared to present instruments.

Finite element (FE) models have been created to investigate mechanical distortions associated with mask blank fabrication and mounting in a horizontal orientation. A modal analysis was completed to quantify the natural frequencies for the mask blank as a predictive tool for possible vibration prevention or control. By modeling the substrate with layers associated with the mask fabrication process and then by prestressing these layers, the resulting out-of-plane distortions (OPD) and in-plane distortions (IPD) can be determined. Utilizing these models, the magnitude of the maximum IPD and OPD due to gravity have been determined as a function of the mounting location to optimize the mounting position.

An improvement in gamma-ray energy resolution is demonstrated for a room-temperature operated CdZnTe semiconductor detector that incorporates a parallel strip pseudo-Frisch-grid detector design. The device construction allows primarily for the measurement of electron charge carriers and not hole charge carriers. The detector is a three-terminal device that requires signal output to only one preamplifier, and its simplistic design offers an alternative method to single charge carrier type sensing to that of coplanar semiconductor gamma-ray detector designs.

Critical dimension (CD) uniformity performance has improved significantly over the years by optimizing postbaking and development steps. As we continue to improve CD uniformity with PBS, our focus has shifted to other steps in the process. The crossover step, the point in the process where both develop and rinse are introduced simultaneously, has often been thought to have little or no effect on the develop time or to influence the uniformity results. However, careful examination of this step has determined that the crossover time, spin speed, and concentration of the develop/rinse mixture can have a significant effect on CD uniformity. Reduction of the typical radial effect was noted. Several design of experiment projects were run to examine these variables. A screening experiment was first run to determine the significant variables and their influence on uniformity. An optimization run was then made on crossover conditions, which included examination of plates from several vendors. Repeatability and sensitivity of the process to other variables were also determined. Results and recommendations are presented in this paper.

A search was made to find a high-performance resist to manifest the high-resolution advantage of 50 kV electron-beam exposure. Four resists were evaluated: Shipley SAL-601, AT&T/OCG CAMP-6, IBM KRS, and IBM TNS. All resists were found to have high contrast ≳3 and were capable of resolving <0.25 μm line/space pairs at 3000 Å thickness. With the exception of TNS, the resists demonstrate a high bulk sensitivity of <15 μC/cm2 at 50 kV. The IBM KRS resist was found to have the highest figure of merit. It was capable of resolving less than 0.10 μm line/space at 4000 Å thickness. Furthermore, at 8000–10 000 Å, a resolution of ≤0.25 μm was obtained with a steep profile. The dry etch resistance of the resist relative to chrome was 2.4:1. This resist is not environmentally sensitive and needs no postexposure bake treatment. If KRS is made commercially available, it will be an outstanding resist for modern electron-beam/x-ray mask making and direct write for device fabrication.