Optics: measuring and testing – Inspection of flaws or impurities – Transparent or translucent material
Reexamination Certificate
2002-06-27
2004-02-10
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
Transparent or translucent material
C356S239200, C250S559400
Reexamination Certificate
active
06690460
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to detecting abnormalities in a quartz window, and more particularly to using a laser beam to perform precise real-time monitoring of the quartz window for use with equipment employed in processing wafers.
2. Description of the Related Art.
The semiconductor industry provides chips that run everything from the leading edge computers to the microwaves. The industry has made great technological leaps in the past decade to make chips smaller and faster.
The manufacturing of microchips is performed by a process called lithography. The process revolves around a mask. The shape of a desired chip pattern is written to the mask by electron beams. The mask then becomes the basis for creating thousands of chips. The mask is put in front of a source of light, the light is flashed, and the shadow of the mask is projected onto a silicon wafer. The light that passes through the mask and hits the wafer changes its physical properties. Certain chemicals are used to etch away the parts of the wafer hit by light, not affecting those parts hidden from the light by the mask shadow. In this way, the desired shape of a circuit is transferred from the mask to the wafer. To make a complete chip, a mask with a pattern is flashed, the wafer is etched, another layer of silicon is deposited thereon, a different mask with a different pattern is flashed, and the whole process is repeated many times.
All IC semiconductor products originate from silicon wafers. After being refined, silicon is supplied as amorphous silicon, which means that the atoms are randomly arranged in the material. Under the proper conditions, silicon can be manufactured into epitaxial chunks, which basically means a single crystal. Most gems are examples of single crystals. Diamonds, for example, are merely carbon atoms arranged in a particular 3-D or lattice structure. To manufacture semiconductors, silicon is made use of in a similar lattice form.
Wafers are sliced from a single silicon crystal, which has to be “grown.” The growth is performed by melting silicon in a crucible. Pure silicon occurs in two forms—either as a single crystal, or as a collection of atoms with no particular arrangement, called polysilicon. A “seed” or a small silicon crystal is inserted into the crucible holding the molten polysilicon. As the seed is slowly drawn out, the molten silicon aligns with the crystal lattice in the seed. As it cools, the molten silicon expands on this crystal lattice forming an ingot. The entire ingot is drawn out as a single crystal made up of many silicon atoms. This ingot is then sliced into thin wafers, and each wafer is polished to a mirror-like finish. The mirror-like finish of the silicon wafer needs to have a pattern etched into it to make a useful circuit, or circuit element (discrete).
One example of wafer fabrication equipment is the Lam 9600 metal etcher. The Lam Rainbow model 9600 etch system is designed for metal etching of aluminum, aluminum silicon and a limited number of other metals and metal alloys. This is a six-inch tool, but, with some modification to the recipe and wafer transfer, a four-inch wafer can be processed in the system. This system is a single wafer processor and is intended to operate in the automatic mode with cassette-to-cassette wafer transfer. When the system starts operating, all robotic movements are initialized. Then, the transfer arm picks the wafer from the load cassette and transports it to the optical sensor for flat orientation. After the wafer is oriented, it is transported to the entrance load lock and pumped to a suitable transfer pressure. When the proper transfer pressure is reached, the wafer is transported into the chamber for processing. The processing gasses are turned on and stabilized, the RF power is turned on, and the process starts. After the process is complete, the wafer is transported to the exit load lock. This load lock is designed to perform a resist strip and dry surface passivation. The wafer is transported out of the exit (plasma) load lock to a rinse station for wet passivation, spin-dried, and then placed into the exit storage cassette.
One of the above processing steps requires a semiconductor wafer-heating chamber. Between a light source and a wafer, this chamber has an optical element for redistributing the light from the light source. The optical element is constructed in such a manner as to produce the desired illumination (and thus heating) pattern on a semiconductor wafer from the light source. Preferably, the light source is a long-arc lamp mounted above a base plate of a heating chamber. A primary reflector is mounted above the long-arc lamp and is shaped to produce a substantially uniform light distribution on the base plate. A quartz window is mounted between the arc lamp and the base plate. The quartz window acts as a lens to redistribute the light from the lamp and the reflector on the wafer. The window can be constructed as a diffraction grating with a series of lines formed by etching into the window or depositing material on the window to produce a diffraction pattern resulting in the desired illumination pattern on the wafer. Interchangeable quartz windows are used to produce different illumination patterns, which are appropriate for different wafer sizes and different types of heating processes.
A potentially expensive problem arises when the quartz window suffers a crack and all of the wafers that are being processed at the time are ruined and have to be scraped. It is essential to be able to predict in real time when the quartz window is no longer functioning properly so that appropriate actions could be taken to fix the problem.
Prior art methods disclosed the idea of real-time detection utilizing a laser beam. U.S. Pat. No. 5,125,741 issued to Okada et al. discusses a method and apparatus for inspecting surface conditions. This invention concerns inspection of surface conditions to detect locations, sizes and nature of flaws, defects or stains not only on a flat surface but also on an undulating or stepped surface, and includes the steps of scanning an inspected surface of a specimen with a spot-like laser beam projected obliquely from a light source; detecting the height of the inspected surface from a reflected image of the scanning light picked up by a TV camera located above the inspected surface, to maintain the surface at a constant height; converging reflected and diffracted light from the inspected surface toward a photo-detector having measuring points at the point of convergence and at a number of positions along a concentric circle around the point of convergence; measuring the energy of the reflected and diffracted light by photoelectric transducers connected to the respective measuring points; and displaying locations, sizes and nature of surface flaws, defects and stains of the specimen on a monitor, with combined use of the information provided by the picture image of the TV camera as to variations in surface level and cracks on the inspected surface.
Another general approach is shown in U.S. Pat. No. 5,570,431 granted to Gillard et al. for process and apparatus for automatically characterizing, optimizing and checking a crack detection analysis method. It describes a quantitative characterization of a crack detection analysis method achieved by determining the detection sensitivity and background noise produced by the analysis method by suitably processing images obtained from one or more control specimens prepared by the method and subjected to appropriate and optimized conditions of illumination. In addition, the crack detection analysis method is optimized by looking for the parameters, which influence the method, and determining the value thereof, which maximizes detection sensitivity and minimizes background noise.
U.S. Pat. No. 3,782,827 issued to Nisenson et al. describes an optical device for characterizing the surface or other properties of a sample. An optical device is disclosed, which is useful for characterizing the s
Chen Richard
Chen Tsai-Yi
Chiu Te-Chin
Font Frank G.
Nguyen Sang H.
Taiwan Semiconductor Manufacturing Co. Ltd.
Tung & Associates
LandOfFree
Real time detection of cracked quartz window does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Real time detection of cracked quartz window, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Real time detection of cracked quartz window will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3318069