JPH1019693A - Method of measuring stress of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the stress of a specified minute area with high resolution by comparing the energy measured value corresponding to the forbidden band width of the part to be measured of a semiconductor with that natural to the semiconductor to measure the shift tendency and shift quantity. SOLUTION: A laser beam having a photon energy larger than the forbidden band width natural to semiconductor which is emitted from a laser beam source 3 is reflected and converged by a converging mirror 6 to irradiate a sample 1. The electron excited within a semiconductor base by the emitted light emits a light when it is returned to the base state. The emitted light is incident on a spectroscope 9, and the spectrum is detected by a light detector 10 and displayed 12. In the spectrum, the line revealed on the shortest wavelength side is equal to the energy of the semiconductor forbidden band width, and the forbidden band width obtained in the state having no stress becomes the value corresponding to the forbidden band width natural to semiconductor. This stored value is compared with the sample measured value, whereby compression or extension can be judged from which side of long and short wavelength sides it is shifted on, and the stress can be measured from the shift quantity with high resolution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for non-destructively measuring a stress inherent in a semiconductor device formed on a silicon semiconductor substrate or a compound semiconductor substrate such as gallium arsenide, and more particularly to a method using a photoluminescence method. Related to a stress measurement method.

[0002]

2. Description of the Related Art When a semiconductor device is formed on a silicon semiconductor substrate or a compound semiconductor substrate such as gallium arsenide, a diffusion layer of a predetermined conductivity type is formed in the semiconductor substrate, and then a diffusion layer is formed on the surface of the semiconductor substrate. Electrode wiring to derive,
An insulating film or a surface protective film for insulating the electrode metal is formed. In most cases, the film formed on the surface of the semiconductor substrate has a different coefficient of thermal expansion from that of the semiconductor substrate, and depending on the conditions for forming the film, this may result in stress in the semiconductor substrate.

For example, when a nitride film is formed as a protective film on a gallium arsenide substrate by a plasma CVD method, the gallium arsenide substrate is heated to about 350 ° C. to deposit the nitride film. Thereafter, when the gallium arsenide substrate is returned to room temperature, stress is applied to the gallium arsenide substrate because the thermal expansion coefficients of the gallium arsenide and the nitride film are different. If the stress is large, the gallium arsenide substrate and the nitride film are peeled off, the nitride film no longer functions as a protective film, and there is a problem that reliability is reduced. Further, when stress is applied to the gallium arsenide substrate, the electrical characteristics of the semiconductor device formed on the surface change. Therefore, it is very important to know the stress inherent in the semiconductor substrate.

[0004] Conventionally, as a method of measuring the stress inherent in a semiconductor substrate, a generally performed method will be described with reference to FIG. A method of forming a nitride film 22 on a gallium arsenide substrate 21 and measuring stress applied to the entire substrate,
The stress is measured by measuring the amount of deformation (warpage) A of the substrate. Here, assuming that the Young's modulus of the gallium arsenide substrate is E, the thickness of the gallium arsenide substrate is d, the deformation amount A, the Poisson's ratio is v, the thickness of the nitride film is t, and the size of the substrate is l, stress (stress) The quantity X can be represented by X = E · d2 · A / (3 (1-v) t · l2).

However, this method is a method of measuring the stress amount of a substrate having an area large enough to measure the change amount A, and can only measure the stress amount existing in the entire gallium arsenide substrate. That is, the amount of stress at a predetermined position (specified minute region) on the gallium arsenide substrate cannot be measured. Furthermore, the measurable stress amount is 10 9 dyn / cm 2 or more, and there is a disadvantage that the measurement resolution is low.

[0006]

However, the conventional stress measurement method has a problem that a minute area cannot be measured and the resolution is low. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a stress measurement method having a high resolution capable of measuring a stress amount in a specific minute region of a semiconductor device formed on a semiconductor substrate. .

[0007]

According to the present invention, in order to achieve the above object, an energy value or a wavelength corresponding to a forbidden band width of a measured portion of a semiconductor is measured by using a photoluminescence method. By comparing the energy value or wavelength corresponding to the intrinsic band gap inherent in the semiconductor, the tendency of the shift to determine whether the stress applied to the semiconductor is expansion or contraction, and the shift amount to determine the stress amount It is to be measured. The measurement was performed within the range of the spot diameter of the light source used for the photoluminescence method, and the measurement of the stress amount of 10 9 dyn / cm 2 or less became possible.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below by taking a gallium arsenide substrate as an example. First, FIG. 1 shows an explanatory diagram of the photoluminescence method. As shown in the figure,
The laser light excited by the laser power supply 2 is emitted from the laser light source 3, and the interference filter 4 and the optical chopper 5
The light is reflected by the focusing mirror 6 and focused, and is irradiated to a desired position on the sample 1.

As the irradiation light, a laser beam having a photon energy larger than the band gap of gallium arsenide is selected. Note that the light is not limited to laser light as long as it is coherent light. The irradiation of the laser light excites electrons in the gallium arsenide substrate, and when the excited electrons return to the ground state, light emission occurs. This emitted light enters the spectroscope 9 via the focusing lens 7 and the light source cut filter 8.

The spectrum split by the spectroscope 9 is
The light is detected by a photodetector 10, amplified by a phase detection amplifier 11, and displayed on a display 12 such as an oscilloscope.

[0011] Of the spectra thus obtained,
It is known that the line appearing on the shortest wavelength side is equal to the energy of the band gap of the semiconductor. When no stress is applied to the semiconductor substrate to be measured, the forbidden band width obtained in this manner has a value corresponding to the forbidden band width inherent to the semiconductor. The value displayed on the display 12 may be either the energy amount or the wavelength.

FIG. 2 schematically shows the results of measurement of the wavelength of a sample in which a gallium arsenide substrate is subjected to a compressive or tensile stress by such a measuring method. As shown in the figure,
It was found that when a compressive stress was applied, the wavelength shifted to a longer wavelength, and when an extension stress was applied, the wavelength shifted to a shorter wavelength.

It has also been found that such a change correlates with the conventional measurement method described above. When the wavelength change (shift) amount of the emission peak is shown on the vertical axis and the stress amount measured by the conventional measurement method is shown on the horizontal axis, the relationship shown in FIG. 3 was obtained. It was also found that this relationship has a similar relationship for both compression and extension stress.

Therefore, if a value corresponding to the forbidden band width of the semiconductor substrate in a stress-free state is stored in advance and compared with a value obtained from measurement of the sample, it is determined whether the value moves to the longer wavelength side. , It is possible to know whether it is compression or expansion by moving to the shorter wavelength side. Further, the amount of stress applied to the sample can be known from the shift amount.

Since there is a difference in the amount of stress with respect to the shift amount depending on the type of semiconductor, it is necessary to prepare a graph shown in FIG. 3 in advance according to the type of semiconductor.
Further, even in the same semiconductor, the amount of stress with respect to the shift amount differs depending on the crystal orientation, and therefore, it is necessary to prepare a graph corresponding to the crystal orientation.

In the stress measuring method according to the present invention, the spot diameter of the laser beam is the measuring range. Since the apparatus used for the photoluminescence method uses a beam diameter of about 1 μm 2, it is possible to measure the stress amount in a range of about 1 μm 2. Further, since the wavelength measuring ability of the photodetector is 1 angstrom or less, it can be seen that the measurable stress amount is 10 9 dyn / cm 2 or less.

As a device for performing such a measurement, a mounting table for fixing a sample or a laser beam irradiating portion is used to adjust a laser beam to be irradiated and a predetermined portion to be measured of the sample. Or a structure provided with a microscope to confirm that a desired position is irradiated with the laser beam. Further, it is also possible to map the change in the amount of stress by measuring while moving the irradiation position of the laser light. Further, if necessary, a cryostat can be used to make the measurement temperature variable.

Although gallium arsenide has been described above, it goes without saying that the method of the present invention is effective not only for gallium arsenide but also for other compound semiconductors and silicon semiconductors as a method for measuring stress in a minute region. Nor.

[0019]

As described above, according to the present invention, 1
The amount of stress in a micro area of about um2 is 10 9 dyn / c
It has become possible to measure with high accuracy of m2 or less. The sample that can be measured only needs to be larger than the spot diameter of the laser beam, and the measurement of the stress amount can be performed even in a semiconductor device in which a semiconductor substrate, which could not be measured conventionally, is cut into chips.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram for explaining a photoluminescence method.

FIG. 2 is an explanatory diagram illustrating an embodiment of the present invention.

FIG. 3 is an explanatory diagram illustrating an embodiment of the present invention.

FIG. 4 is an explanatory diagram of a conventional stress measurement method.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 sample 2 laser power supply 3 laser light source 4 interference filter 5 optical chopper 6 focusing mirror 7 focusing lens 8 light source cut filter 9 spectroscope 10 photodetector 11 phase detection amplifier 12 display 21 gallium arsenide substrate 22 nitride film

Claims (2)

[Claims] An object to be measured of a semiconductor device formed on a semiconductor substrate is irradiated with light having a photon energy larger than the band gap specific to the semiconductor, and an original state of electrons excited by the light is restored. When returning to the ground state, a value corresponding to the band gap of the semiconductor of the emission spectrum emitted from the semiconductor is measured, and the measured value and a value of the emission spectrum corresponding to the band gap specific to the semiconductor are measured. A method for measuring stress of a semiconductor device, comprising measuring an amount of compression or expansion stress inherent in the measured portion by comparing. 2. The method for measuring stress in a semiconductor device according to claim 1, wherein the amount of compression or expansion stress existing in the measured part is obtained by measuring a wavelength corresponding to a band gap of the semiconductor in the emission spectrum. Comparing the measured wavelength with a wavelength corresponding to the semiconductor-specific bandgap, when the measured wavelength shifts to a longer wavelength side, calculates a compression stress amount according to the shift amount, and calculates a shorter wavelength side. And calculating a stress amount of expansion according to the shift amount when shifting.