Thermal measuring and testing – Temperature measurement – Nonelectrical – nonmagnetic – or nonmechanical temperature...
Utility Patent
1998-03-17
2001-01-02
Fulton, Christopher W. (Department: 2859)
Thermal measuring and testing
Temperature measurement
Nonelectrical, nonmagnetic, or nonmechanical temperature...
C356S340000
Utility Patent
active
06168310
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method and a device for measuring a physical quantity of an object to be measured by applying laser beams to the object, more specifically to a method and a device for measuring a temperature of a semiconductor substrate without making physical contact with it, by the use of laser beams. Further, the present invention relates to a method and a device for measuring light wavelengths, more specifically to a method and a device for measuring light wavelength shifts occurring in a short period of time.
Currently, semiconductor device fabrication processes and design characteristics of semiconductor devices rely heavily on temperature control. Yet, delicate fabrication processes do not allow semiconductor substrates to be contacted by any sort of temperature measuring probe, etc. Hence, it is required to accurately measure the temperature of semiconductor substrates without contact.
As a temperature measuring device for such noncontact temperature measurement of semiconductor substrates, a device is known which uses the fact that the light transmittance of a semiconductor substrate decreases with increases of its temperature (see Japanese Patent Laid-Open Publication No. 271127/1988, Japanese Patent Laid-Open Publication No. 79339/1988, and Japanese Patent Laid-Open Publication No. 216526/1991, etc.).
Japanese Patent Laid-Open Publication No. 96247/1991 discloses a method for such noncontact temperature measurement of a semiconductor substrate to be measured which uses the fact that the intensity of a interfered light beam reflected from either the top or bottom surfaces of a semiconductor substrate varies depending on the temperature of the substrate. With changes in the temperature of the semiconductor substrate, the dielectric constant of the substrate changes as the substrate expands, altering its thickness, whereby variations in the intensity of the interfered light reflected therefrom can be used to measure the change in temperature of the substrate.
But, the temperature measuring method disclosed in Japanese Patent Laid-Open Publication No. 96247/1991 cannot determine whether or not the temperature is rising or falling.
A temperature measuring device which is based on the same principle as the temperature measuring method disclosed in Japanese Patent Laid-Open Publication No. 96247/1991 but which can measure the direction of temperature change has been proposed. See K. L. Saenger, et al., “Wavelength-Modulated Interformetric Thermometry for Improved Substrate Temperature Measurement”, Rev. Sci. Instrum., Vol. 63, No. 8, pp. 3862-3868, Aug. 1992.
The temperature measuring device described in the above reference uses an approximately 1.5 &mgr;m-oscillation wavelength semiconductor laser. This laser emits coherent laser beams which have been wavelength-modulated by an alternating current injected into the semiconductor laser, and the laser beams are applied to a semiconductor substrate to be measured. Interfered light of the reflected light from the substrate is detected by a photo-detecting element and converted to detected signals, and the detected signals are wavelength-differentiated by a lock-in amplifier. Based on processing of the differentiated and non-differentiated detected signals, it is determined whether the substrate temperature is rising or falling.
Currently, in the optical measurement field it is required to accurately measure light wavelength shifts taking place in a short period of time. Such accurate optical measurement is necessary especially to accurately measure stability of oscillation wavelengths of laser beams and amounts of wavelength shift amounts, and to measure accurately wavelength shifts of laser beams as they undergo rising and falling.
In the conventional wavelength measuring methods it has been generally known that light to be measured is spectrally diffracted by spectroscopes or optical spectrum analyzers for the measurement of wavelengths of the light to be measured. That is, in these methods, light to be measured is spectrally diffracted to measure spectral wavelengths, whereby wavelengths of the light to be measured are measured.
Thus, the conventional temperature measuring devices must include a large number of instruments and devices, such as the laser modulating means, the lock-in amplifier, etc., which makes the structure of such devices complicated and their costs high. This is a disadvantage. For accurate measurement of abrupt temperature changes, e.g. more than 100° C. per minute, instruments and devices which are operative at higher speeds are required, which adds further to the cost. This is also a disadvantage. Finally, conventional temperature measuring devices can measure the direction of temperature changes only when a waveform of interfered light crosses an average value, which makes precise temperature measurement impossible.
The temperature measuring device described in the reference above includes as a light source a semiconductor laser of a III-V compound semiconductor. Its oscillation wavelength is approximately 1.6 &mgr;m at most. In the case where light of such relatively short wavelength (&lgr;) is used, the measurable temperature ranges for various semiconductor substrates, such as silicon, GaAs, or others with relatively narrow energy band gaps, are small. This is because the energy band gaps of such semiconductors narrows as their temperatures rise. As a result, their absorption of laser beam light becomes larger. For example, a silicon wafer has a 1.12 eV energy band gap and absorbs laser light of approximately 1.6 &mgr;m wavelength when the measurement temperature reaches 750° C.
Furthermore, the temperature measuring device described in the reference above performs temperature measurement based on periodic variations in the intensities of interfered light reflected from the semiconductor substrate. Accordingly, the temperature cannot be substantially measured until the intensities of the interfered light varies through at least one period; maximum and minimum intensity values being given. Thus it is another disadvantage that temperature measurement cannot be conducted without changing temperatures until maximum and minimum intensity values of the interfered light employed are given.
It is also a disadvantage of the temperature measuring device described in the reference above that in the case where an object to be measured is a semiconductor substrate, such as silicon, GaAs or others, laser beams are adversely absorbed by the semiconductor substrate as its temperature rises, and the resulting temperature measurement is not accurate.
But according to the conventional wavelength measuring method using spectral diffraction, it is necessary to scan a required wavelength band for one wavelength measuring operation. Such method has found it difficult to measure wavelength shifts occurring in a period of some msec-scanning time.
In addition, according to the conventional wavelength measuring method using spectral diffraction, to improve accuracy of measuring wavelengths, it is necessary to elongate an optical path of light to be measured along which the light to be measured follow. Disadvantageously the wavelength measuring device for such method is accordingly large-sized.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a device for measuring physical quantities has a simple structure, and a method for measuring physical quantities which can precisely measure the direction of change thereof.
Another object of the present invention is to provide a device for measuring a temperature which has a simple structure, and a method for measuring a temperature which can precisely measure the direction of change thereof.
Still another object of the present invention is to provide a method and a device for measuring a temperature which can measure a wide range of temperatures.
Still another object of the present invention is to provide a method and a device for measuring a temperature which can measure a temperature immediately after the st
Fujimura Shuzo
Kikuchi Jun
Kurosaki Ryo
Serizawa Haruhiko
Arent Fox Kintner & Plotkin & Kahn, PLLC
Fujitsu Limited
Fulton Christopher W.
Pruchnic Jr. Stanley J.
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