Measuring and testing – Gas content of a liquid or a solid
Patent
1994-09-20
1996-10-29
Williams, Hezron E.
Measuring and testing
Gas content of a liquid or a solid
422 78, 422 80, 436155, 7386312, 7386311, G01N 100
Patent
active
055698379
DESCRIPTION:
BRIEF SUMMARY
1. Field of the Invention
This invention pertains to an apparatus for analyzing semiconductor chips. More particularly, this invention is applicable in a process of heating a sample (a semiconductor chip) of about 10 mm square in a vacuum, measuring the desorption gas degassed from the sample by a mass spectrometer, and modifying the semiconductor manufacturing process for increasing the yield thereof.
2. Description of the Related Art
There is known a technology for assessment and modification of a semiconductor manufacture process by placing a semiconductor chip sample in a vacuum chamber, irradiating infrared beams thereon to heat the chip, directing the gas desorbed from the chip to a mass spectrometer for measurement, and assessing and modifying the manufacturing process of semiconductors based on the result of the measurement. This technology is extremely effective for increasing the yield of the semiconductor manufacture process.
The prior art apparatus for applying this technology is structured so that an appropriate table for mounting a sample is provided within a vacuum chamber and a silica glass window is opened on the shell of the vacuum chamber to introduce infrared beams into the chamber through the window to heat the sample therein. It is necessary to break the vacuum of the chamber every time a sample is introduced or discharged.
The amount of gas desorped from the sample by heating is extremely small because the sample size is very small, i.e. about 10 mm square and about 1 mm thickness or less, and the manufacture process is controlled to be extremely clean. However, when the vacuum in the chamber is broken as stated above, water vapor is absorpbed on the inner wall of the vacuum chamber, the sample stage in the chamber or the like. As those are heated while the sample is being measured, the gas degassed therefrom acts as a background noise to deteriorate the measurement precision.
This invention aims to solve the problem encountered in the prior art by providing an apparatus for minimizing the background noise which hampers the measurement of gas desorped from the heated sample.
SUMMARY OF THE INVENTION
The inventor of this application has repeated assessment of the process for improving the measurement precision.
The first important point gained for this assessment is not to introduce the environmental air into the vacuum chamber as it causes a background noise. The inventor therefore decided to maintain the vacuum within the chamber for quite a long time, which not only includes the time when a sample is being introduced to or discharged from the chamber but also the time when the measurement is not being conducted. For this purpose, a loading lock mechanism is provided in a space of which volume is sufficiently smaller than that of the vacuum chamber and which is separated from the vacuum chamber by means of a gate valve. When a sample is introduced into or discharged from the chamber, the vacuum of the loading lock mechanism alone is broken. As a sample is being conveyed into the vacuum chamber, the space containing the loading lock mechanism (which will be described as a loading lock chamber hereinafter) is evacuated by means of an evacuating line which is different from the line for maintaining the vacuum in the chamber, and the gate valve is opened. The evacuating line for the space containing the loading lock chamber is preferably an entirely different line from the line used for maintaining the vacuum of the gate chamber, but the evacuating pump may be commonly used in part or as a whole for the two lines, so long as the vacuum in the chamber is not affected when the vacuum within the loading lock chamber is broken.
The second critical point is to heat the sample alone. It was discovered that in the prior art, as infrared beams were introduced through a large glass window opened on the shell of the chamber, it unavoidably heated other places than the sample per se, such as the shell surface or a manipulator in the chamber to create the background gas. Therefore, the inventor
REFERENCES:
patent: 3946228 (1976-03-01), Biermann
patent: 5162233 (1992-11-01), Komori et al.
Esco Ltd
Larkin Daniel S.
Williams Hezron E.
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