Arnold W. Yanof

A new operating regime for electroplating the gold absorber on x-ray masks

Abstract A new technique for more repeatably and more controllably electroplating gold films for use as the absorber on x-ray masks is presented. Films electroplated from a gold-sulfite based bath containing high concentrations of thallium-based brightener possess low stresses (

Toward a unified advanced CD-SEM specification for sub-0.18-μm technology

The stringent critical dimension control requirements in cutting edge device facilities have placed significant demands on metrologists and upon the tools they use. We are developing a unified, advanced critical dimension scanning electron microscope specification in the interests of providing a unified criterion of performance and testing. The specification is grounded on standard definitions and strong principles of metrology. The current revision is to be published as a SEMATECH document. A new revision, now in progress, will embody the consensus of a vendor/user conference.

Accelerated radiation damage testing of x-ray mask membrane materials

An accelerated test method and resulting metrology data are presented to show the effects of x- ray radiation on various x-ray mask membrane materials. A focused x-ray beam effectively reduces the radiation time to 1/5 of that required by normal exposure beam flux. Absolute image displacement results determined by this method indicate imperceptible movement for boron-doped silicon and silicon carbide membranes at a total incident dose of 500 KJ/cm2, while image displacement for diamond is 50 nm at 150 KJ/cm2 and silicon nitride is 70 nm at 36 KJ/cm2. Studies of temperature rise during the radiation test and effects of the high flux radiation, i.e., reciprocity tests, demonstrate the validity of this test method.

Improving metrology signal-to-noise on grainy overlay features

High temperature metal deposition produces large grain size and a highly visible surface morphology due to grain boundaries. When an interconnect layer photoresist pattern is aligned, grainy metal results in noisy signals from optical metrology equipment. The overlay metrology tool hardware and software configuration and target design must be optimized to obtain the best possible signal-to-noise. A powerful metric is developed herein to single out the noise component due to the overlay target image distortions. This methodology is suitable to a production environment. A variety of techniques based upon the target noise metric, including designed experiments, are employed to optimize the overlay measurements configuration.

Overlay measurement and analysis of x-ray/optical lithography for mix-and-match device applications

A joint Motorola/IBM experiment was performed in mix-and-match lithography across widely separated locations. A simple pattern placement metrology data set was created, and x-ray masks were manufactured according to this data. The same data was converted into a 5x reticle and optically stepped on wafers. The x-ray mask was designed to print upon two optical fields with one x-ray exposure. The x-ray mask was aligned to the wafers to produce box-in- box images for overlay metrology. The main overlay problems encountered were systematic offsets between x-ray and optical images, and average magnification error of approximately 8 ppm. The magnification error is substantial because of the 3 degree(s)C temperature difference between the optical stepper stage and the x-ray mask-writer. In an actual device run, the magnification differences will be removed by compensation in the e-beam writing of the x-ray mask. Offsets will be removed by use of a send-ahead wafer to determine the correct offset alignment in the x-ray stepper.

Production metrology and control of color filter array photolithography for CMOS imagers

The color filter array (CFA) for an image-producing semiconductor device is composed of patterned red-, and green- and blue-colored photoresist structures. CFA photolithography is rather different from that of most semiconductor process levels.

Contrast sensitivity methods for acceptable limits of visual defects in CMOS sensors

This work characterizes three different types of sensor defects, and investigates the applicability of the Contrast Threshold Function (CTF) of the human visual system to the manufacturing test criteria for CMOS image sensors. The sensor defect types characterized are resist streaking, dye color spots, and orange-peel photodiode sensitivity noise. Algorithms are presented to objectively identify and rate the severity of each. Visual evaluations determined the subjective level of detectability and objectionability of each. The spatial frequency and modulation of the defects were measured, and compared with an appropriate CTF. The result is the minimum defect levels noticeable in test images can be almost order-of-magnitude higher than the known CTFs determined for the limits of human visual system sensitivity.

Techniques and Tools for Photo Metrology

Publisher Summary This chapter discusses the critical dimension (CD) scanning electron microscope (CD-SEM) and the optical overlay tools which provide the most important final measurements for lithographic control. Electrical CD measurement is also discussed, because of its growing importance as a CD control method in cutting edge microprocessor fabrication. This chapter also covers optical metrology tools for film thickness control. A guide to the statistical interpretation of metrology data is also given. The purpose of the CD-SEM is still to gain from a top-down scan or image sufficient information about a complex cross-sectional shape to predict electrical device performance. This has become a difficult task with multiple requirements. The scan or image have high resolution to represent details of the top surface, the side wall, the foot, and any residual material in between features. The CD-SEM consists basically of an ultrahigh vacuum electron column which produces a tiny electron probe on the wafer surface; an accurate stage for locating the features to be measured on the wafer a detector which collects the electrons that arise from the impact of the probe upon the wafer surface (called “secondary” electrons or “SE”); and a sophisticated computer for interpreting the images and controlling the entire system.

Electrical and SEM testing of absorber defectivity in the plated-gold process for x-ray masks

It is widely recognized that the 1:1 x-ray mask is the most technically challenging aspect of proximity x-ray lithography, since high resolution and precise pattern placement must be achieved completely free of defects. SEM investigation is an excellent tool for x-ray mask inspection. However, it is sometimes assumed that only the SEM has sufficient resolution to perform meaningful defect detection on x-ray masks. An electrically probed test chip pattern for x-ray mask defectivity measurement and improvement has been designed and implemented. This pattern is printed with an optical stepper on silicon wafers with plating base. These are then processed like an x-ray mask through x-ray absorber definition. Since the absorber is a high-conductivity metal and the substrate is insulating, electrical shorts and opens correspond to extra and missing absorber. This paper describes a series of defect types revealed by these two rather different methodologies: SEM inspection of completed masks using the KLA SEMSpec, as well as the electrically probed test chip pattern. The two methods are compared and contrasted. The main nuisance and genuine defects in our x-ray mask process are catalogued.