Optics: measuring and testing – Of light reflection
Reexamination Certificate
1999-07-06
2001-01-30
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
Of light reflection
C356S328000
Reexamination Certificate
active
06181427
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to reflectometers, and in particular to a highly compact optical reflectometer system for obtaining reflectance data and images from a sample.
BACKGROUND OF THE INVENTION
There is much demand in industry for compact measurement systems and techniques for measuring the reflectance of devices, such as computer chips, flat panel displays, magnetic media used in data storage, and the like, during their manufacturing.
In many optical applications, there is often a need for designs having a high degree of compactness. For example, U.S. Pat. No. 5,024,493 to Fantuzzi et al. discloses a highly compact folded infra-red optical system having an effective focal length of about 240 mm and which employs three fold mirrors to fit the system into a package having a diameter of approximately 150 mm. Such compactness of design is technically challenging, but can result in significant advantages. In the present case, it enables accurate, spectroscopic, reflectance measurements of a sample where such sophisticated equipment could not previously be implemented due to space limitations. Such compactness can also result in cost-savings where space is at a premium.
Present day metrology instruments, including those using reflectometer systems, tend to be large and physically separated from the processing tools used to fabricate the devices. These processing tools are often in clean rooms, where air quality, temperature and humidity are tightly controlled. Conventional metrology instruments require 1.4-2.0 square meters of this costly clean room floor space. In addition, these metrology instruments are physically separated from the processing tools, so samples have to be removed from the processing tools and transferred to the metrology instruments. Often the environment inside the processing tool is designed to be even cleaner than the surrounding area. In such a case, the wafer must be placed in a sealed, airtight container while it is transferred. This takes time, causing costly delays in the production line.
Therefore, it is advantageous to integrate these metrology instruments into the processing tool. However, these processing tools are already designed to be as compact as possible because of the above mentioned cost of the clean room facilities in which they are housed. Thus, the size of an integrated metrology instrument is the determining factor in its ability to be integrated into a processing tool. At the same time, an integrated metrology instrument must provide highly accurate measurements of the samples in order to provide useful information on the performance of the processing tool. In addition, an integrated metrology instrument must provide these measurements quickly so as not to slow the production line.
SUMMARY OF THE INVENTION
The present invention is a compact, high performance optical reflectometer. It has been designed with the above-mentioned size, accuracy, and speed requirements in mind. The reflectometer may be mounted anywhere space is at a premium, and may be easily integrated into various types of manufacturing apparatus, such as semiconductor processing tools.
A first aspect of the invention is a compact reflectometer system capable of measuring reflectance from a sample. The reflectometer comprises illumination, signal and viewing subsystems. The illumination subsystem is for illuminating the sample and includes a light source, and at least one illumination subsystem fold mirror. The illumination subsystem forms a light beam, which illuminates a field of view (FOV) on the sample. The signal subsystem is for measuring at least one wavelength of light from the light source reflected from the sample and includes at least one signal subsystem fold mirror. The signal subsystem detects light reflected from a small, well-defined measurement spot in the center of the FOV. The viewing subsystem is for viewing the sample and includes at least one viewing subsystem fold mirror and captures a video image of the FOV. This image is used to locate areas of interest on the sample, so that the measurement spot may be precisely positioned within it. The reflectometer is designed such that the illuminating, signal and viewing subsystems occupy a volume of less than or equal to approximately 0.006 cubic meters.
The reflectometer of the present invention is designed to be highly compact. Many of the optical elements serve more than one purpose, thereby minimizing the total number of optical elements. The design also accounts for multiple fold mirror mounting planes for mounting multiple fold mirrors, with certain subsystems sharing certain fold mirrors. This allows the entire reflectometer to occupy a very small (i.e., 0.006 cubic meters) volume, even though the optical path for all the subsystems combined is about 0.9 meters.
By placing the reflectometer on an (x,y) or (r, theta) stage, it can be moved relative to a sample in order to measure different points on the sample. Conversely, the sample may be moved while the reflectometer is held fixed. The reflectometer may be used as the core of a tabletop system. It may be mounted onto a vacuum chamber, where it may measure a sample contained in the vacuum chamber through a viewport on the chamber. Because the system has no moving optical elements it is stable, reliable and mechanically simple
REFERENCES:
patent: Re. 34783 (1994-11-01), Coates
patent: 3572951 (1971-03-01), Rothwarf
patent: 4368983 (1983-01-01), Bennett
patent: 4552458 (1985-11-01), Lowne
patent: 5024493 (1991-06-01), Fantozzi et al.
patent: 5517312 (1996-05-01), Finarov
patent: 5747813 (1998-05-01), Norton et al.
patent: 6061129 (2000-05-01), Ershov et al.
Spady Blaine R.
Yarussi Richard A.
Downs Rachlin & Martin PLLC
Nanometrics Incorporated
Pham Hoa Q.
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