JP2554735B2 - Substrate surface temperature measurement method and semiconductor thin film crystal growth method and growth apparatus using the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method and an apparatus capable of accurately measuring a substrate temperature during semiconductor crystal growth.

[Prior Art] It is indispensable to determine a substrate temperature in a semiconductor epitaxial growth technique and give other suitable crystal growth conditions to obtain a good-quality semiconductor epitaxial layer with good reproducibility. However, the molecular beam epitaxial growth method (MBE method) and metal-organic vapor phase epitaxy method (MOCVD method), which have recently become more important as a growth technique for ultra-thin film semiconductors, lack an accurate means for measuring the substrate temperature. It was a cause of low reproducibility and low yield. There have been two types of methods that have been generally used as substrate temperature measuring methods: (i) thermocouple method and (ii) infrared method. Each will be described below.

(I) Thermocouple method Fig. 5 shows a schematic diagram of a conventional substrate temperature measuring method in the MBE method. The substrate 18 whose temperature is to be measured is supported by a substrate holder 19 which is usually made of molybdenum and which is bonded to the substrate holder 19 by an indium thin film 20. The substrate 18 is heated by the heater 21. The temperature of the substrate is measured by a thermometer (not shown) in contact with the lead wire 23 with the thermocouple 22 in contact with the substrate holder.

FIG. 6 is a schematic diagram showing another conventional example of the substrate temperature measuring method in the MBE method. The same parts as those in FIG. 5 are designated by the same reference numerals and the description thereof will be omitted. In FIG. 6, the substrate holder 19 is hollow, and the indium thin film 20 that contacts the substrate 18 and the substrate holder 19 is not used in this example. FIG. 7 is a schematic diagram showing a conventional example of a substrate temperature measuring method in the MOCVD method. In the figure, a substrate crystal 24 is supported on a substrate holder 25, a thermocouple small hole 26 is opened in the substrate holder 25, and a thermocouple 27 is embedded in the thermocouple small hole 26.

The problem with the thermocouple method is that if the thermocouple is brought into contact with the substrate crystal itself to be measured, the substrate crystal will be damaged, making accurate temperature measurement impossible.
It is generally said that there is an error of ± 100 ° C. in the configuration of FIG. 5, an error of ± 200 ° C. in the configuration of FIG. 6, and an error of ± 50 ° C. in the configuration of FIG.

In the growth of III-V group compound semiconductors in the MBE method and the MOCVD method, when the substrate temperature changes by 10 degrees, the adsorption process of material atoms on the crystal growth surface changes, which deviates from the optimum crystal growth condition.

(Ii) Infrared method This method is also a very commonly used method, and Fig. 8 shows a schematic diagram thereof. Substrate crystal 18 is a hollow substrate holder
Supported by 19, the substrate 18 is heated by a heater 21. The infrared rays 28 emitted from the substrate 18 pass through the observation window 29. The wavelength of the passing light is selected by the filter, the intensity is detected by the infrared detector 30, and the intensity is converted into the temperature corresponding to the intensity. In this case, the infrared radiation from the substrate is assumed to be black body radiation, but the problem is that its emission power must be assumed to be an appropriate value, and the light quantity is an absolute measurement, so the observation window This is the point where the measured value is affected by dirt. Due to these problems, the measurement accuracy of the substrate temperature is said to be ± 50 ° C even under ideal conditions, and even with this method, sufficient reproducibility has not been obtained.

As a method to solve these problems, 2
Attempts have been made to accurately determine the temperature of only one point by vapor-depositing the seed metal and observing the eutectic point, but the eutectic point of thin-film metals is difficult to measure and is not a good method. . As another method, a two-color thermometer was devised in the infrared method. In this method, the temperature is measured by the relative value of the light quantity at the two wavelengths, so it is less affected by the contamination of the observation window. However, one of the two wavelengths is infrared light with a long wavelength, so that it is generally applied to a semiconductor substrate. On the other hand, it becomes transparent light. Therefore, it was impossible to improve the accuracy of ± 50 ° C even by this method.

[Problems to be Solved by the Invention] Therefore, an object of the present invention is to solve the above-described problems,
It is an object of the present invention to provide a method and an apparatus capable of accurately measuring a substrate temperature and thereby growing a good-quality epitaxial layer.

[Means for Solving the Problems] In order to achieve such an object, the first embodiment of the present invention irradiates the surface of a substrate with light and measures the intensity of reflected light from the surface of the substrate to obtain a reflection spectrum. It is characterized in that the temperature of the substrate surface is measured by obtaining data and comparing the reflection spectrum data with the known data of the temperature dependence of the band gap of the substrate material.

A second aspect of the present invention is to irradiate a substrate surface with light and at the same time irradiate a substrate surface with modulated light, obtain a reflectance spectrum from reflected light from the substrate surface synchronized with the modulation, and calculate the reflection spectrum and the band of the substrate material. The temperature of the substrate surface is measured by collating with known data of the temperature dependence of the gap.

A third aspect of the present invention is an irradiation means for irradiating the surface of the substrate with light, a light receiving means for receiving the reflected light reflected from the surface of the substrate, spectral data of the reflected light received by the light receiving means, and a band gap of the substrate. It is provided with a collation calculation means for collating the temperature dependency data of 1. and the temperature of the substrate surface.

[Operation] According to the present invention, the substrate crystal is irradiated with white light or monochromatic light having a variable wavelength, the reflected light is measured to obtain a reflection spectrum, and the band gap is estimated based on the reflection spectrum. However, the substrate temperature can be obtained from the temperature dependence of the band gap of the known substrate material. With this method, the bandgap changes sensitively with respect to temperature, so that highly accurate measurement can be performed. For GaAs, for example, the bandgap is given by

Here, Eg is the band gap, and T is the absolute temperature of the substrate. An example of the reflection spectrum near the absorption edge of n-GaAs is shown in FIG. In FIG. 1 (A), the horizontal axis represents wavelength λ.
And the vertical axis represents the reflectance R. FIG. 1 (A) shows the change in reflectance when the wavelength is changed when the temperature is kept constant, and the peak position of the reflection spectrum is used as a guide for the band gap. The measured temperature is obtained by comparing the measured spectrum with the data of the temperature dependence of the band gap that is stored in advance. When the temperature of the substrate measured by actually pressing the thermocouple against the substrate and the temperature corresponding to the peak position were compared, they were coincident within an error range of ± 5%.

FIG. 1B shows an example of the photoreflectance spectrum near the absorption edge of n-GaAs. The horizontal axis represents the wavelength λ, and the vertical axis represents the reflectance change ΔR / R. Here, R is the reflectance when irradiating unmodulated light, and ΔR is the difference between R and the reflectance when irradiating modulated light. In this case, in FIG. 1 (B), the position of the valley of the spectrum is used as a guide for the band gap, and similarly to FIG. 1 (A), the measured temperature is obtained by comparing with the data of the temperature dependence of the band gap. When the temperature of the substrate measured by actually pressing the thermocouple against the substrate and the temperature corresponding to the position of the valley are compared, they match within an error range of 5%.

The reflection spectrum and photoreflectance spectrum of FIGS. 1 (A) and 1 (B) have some differences depending on the conduction type even with the same GaAs, and n-GaAs, p-GaAs, semi-insulating G
For each of the aAs, the measurement accuracy can be further improved by making a kind of calibration curve based on the correspondence between the spectrum corresponding to Fig. 1 and the thermocouple and determining the temperature of the substrate based on this. .

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

Embodiment 1 FIG. 2 is a schematic view showing an embodiment of the present invention. White light emitted from the external white light lamp 1 is condensed by the condenser lens 2, reflected by the half mirror 3 and condensed by the condenser lens 4. The condensed light passes through the observation window 5,
The substrate 7 supported by the substrate holder 6 is irradiated.
The reflected light from the substrate 7 is guided to a spectroscope 9 through an optical system including a condenser lens 4, a half mirror 3 and a condenser lens 8. The reflectance of each wavelength, that is, the reflection spectrum, of the light dispersed by the spectroscope 9 is instantaneously measured by a photodetector 10 such as a CCD array, and the obtained reflection spectrum is shown in FIG. 1 (A). It becomes like Comparing the band gap obtained from this with the data of the computer 11 which stores the temperature dependence data of the band gap,
Obtain the substrate temperature. The temperature of the substrate thus obtained is displayed on the display 12.

Embodiment 2 FIG. 3 is a schematic view showing another embodiment of the present invention. The light emitted from the external white light lamp 1 is dispersed by the spectroscope 9 and only monochromatic light is extracted. Here, the spectroscope is configured to continuously output monochromatic light having different wavelengths. Monochromatic light whose wavelength changes with time is condensed by the condenser lens 2 and pulsed by the chopper 13,
It is reflected by the half mirror 3 and is condensed by the condenser lens 4. The condensed light passes through the observation window 5 and illuminates the substrate 7 supported by the substrate holder 6. The reflected light from the substrate 7 is guided to the photodetector 10 through the optical system including the condenser lens 4, the half mirror 3 and the condenser lens 8, and the reflected light is detected. The detected signal is amplified by a lock-in amplifier 14 driven by a chopper 13 and the reflected spectrum signal is guided to a computer 11. The obtained band gap is compared with the temperature dependence data of the band gap stored in the computer 11. And the results obtained,
That is, the substrate temperature is displayed on the display 12.

Example 1 and Example 2 are simple and practical methods, but since the reflectance itself is measured, the accuracy at a high substrate temperature (> 500 ° C.) is slightly deteriorated.

Embodiment 3 FIG. 4 is a schematic view showing still another embodiment of the present invention.

The light emitted from the external white light lamp 1 is dispersed by the spectroscope 9 and monochromatic light whose wavelength changes with time is continuously extracted. The monochromatic light is condensed by the condenser lens 2,
It is reflected by the half mirror 3 and is condensed by the condenser lens 4. The condensed light passes through the observation window 5 and illuminates the substrate 7 supported by the substrate holder 6. At the same time as irradiating the substrate 7 with monochromatic light, the laser beam 17 pulsed by the chopper 13 that emitted the He—Ne laser light source 15 is condensed by the condenser lens 16 and irradiates the substrate 7. The monochromatic light is modulated by the laser beam, and the modulated light is condensed by the condenser lens 4,
It is guided to the photodetector 10 through the optical system of the half mirror 3 and the condenser lens 8 and extracts the component of the monochromatic light reflected from the substrate in synchronization with the modulation signal. As a result, the obtained reflectance spectrum is obtained, and the spectrum is as shown in FIG. 1 (B). The reflectance spectrum is amplified by the lock-in amplifier 14 and guided to the computer 11 as a reflectance spectrum signal. The reflectance spectrum is collated with the temperature dependence data of the band gap stored in the computer 11, and the obtained result, that is, the substrate temperature is displayed on the display 12. The reflectance spectrum is a photoreflectance because it is modulated by the laser beam. For this reason, it becomes extremely easy to find and discriminate the singular point of the reflection spectrum, and the band gap can be determined with high accuracy, and thus the substrate temperature can be accurately determined. Create a calibration curve by matching the temperature determined by the obtained reflection spectrum and the temperature measured by pressing a thermocouple against the substrate crystal at 500 ° C, and from room temperature to 800 ° C.
When the two were compared at any temperature up to, the maximum difference between the two was 3 ° C.

Although the laser beam is used in the present embodiment, in order to cause modulation and not affect the reflection spectrum during measurement, the laser beam has energy larger than the band gap of the substrate crystal and is equal to or less than the band gap. It is necessary to irradiate the substrate crystal with light which is 1/10 or less of the light intensity of white light or monochromatic light in the energy region of 1.

In each example, although it has an observation window in the normal direction perpendicular to the substrate crystal surface, it is located in the same plane as this normal line,
At least one observation window may be provided in each of the two directions that have the same angle from the normal and are located on the reflection side with respect to the normal.

[Effect of the Invention] As described above, according to the present invention, the temperature of the substrate crystal can be measured accurately and quickly without any other influence. This allows the temperature of the substrate crystal to be accurately controlled, which improves the reproducibility of a good-quality semiconductor epitaxial layer and improves the yield.

[Brief description of drawings]

FIG. 1 shows the relationship between reflected light and wavelength, FIG. 1A is a characteristic diagram showing an example of a reflection spectrum, FIG. 1B is a characteristic diagram showing an example of a photoreflectance spectrum, and FIG. ~ Fig. 4 is a schematic diagram showing an example of the substrate temperature measuring method of the present invention, and Fig. 5 to Fig. 8 are schematic diagrams showing an example of the conventional substrate temperature measuring method. 1 ... External white light lamp, 2 ... Condensing lens, 3 ... Half mirror, 4 ... Condensing lens, 5 ... Observation window, 6 ... Substrate holder, 7 ... Substrate, 8 ... Condensing Lens, 9 ... Spectrometer, 10 ... Photodetector, 11 ... Computer, 12 ... Display, 13 ... Chopper, 14 ... Loquin amplifier, 15 ... He-Ne laser light source, 16 ... Focusing Lens, 17 ... Laser beam, 18 ... Substrate, 19 ... Substrate holder, 20 ... Indium thin film, 21 ... Heater, 22 ... Thermocouple, 23 ... Lead wire, 24 ... Substrate crystal, 25 ... … Substrate holder, 26… Small hole for thermocouple, 27… Thermocouple, 28… Infrared, 29… Observation window, 30… Infrared detector.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01L 21/66 H01L 21/66 T

Claims (4)

(57) [Claims] 1. A substrate surface is irradiated with light, the intensity of light reflected from the substrate surface is measured to obtain reflection spectrum data, and the temperature dependence of the reflection spectrum data and the band gap of the substrate material is known. The temperature of the substrate surface is measured by collating with the data of 1. 2. A substrate surface is irradiated with light at the same time as the substrate surface is irradiated with modulated light, and a one-sided emissivity spectrum is obtained from reflected light from the substrate surface synchronized with the modulation. A method for measuring a substrate surface temperature, which comprises measuring the temperature of the substrate surface by collating it with known data of the temperature dependence of the bandgap. 3. A crystal growth method for a semiconductor thin film, which comprises growing a crystal of a semiconductor thin film while measuring the temperature of the substrate surface using the method for measuring a substrate surface temperature according to claim 1. 4. An irradiation means for irradiating the surface of the substrate with light, a light receiving means for receiving the reflected light reflected from the surface of the substrate, spectral data of the reflected light received by the light receiving means, and a known band of the substrate material. And a collation calculation means for collating the temperature dependency data of the gap to calculate the temperature of the substrate surface.