JPH0545128B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for accurately measuring the temperature of a solid material when crystal growth or evaporation of the solid material is performed in a vacuum.

[Prior art] Conventionally, solid materials in vacuum (hereinafter referred to as substrates)
During crystal growth and evaporation, thermocouples and pyrometers were used to measure the surface temperature of the substrate. This will be explained below with reference to the drawings. Figure 2 is a schematic diagram of the crystal growth and evaporation equipment.
1 is a substrate, 2 is a substrate holder that holds the substrate 1, 3
is a heater that heats the substrate 1, 4 is a thermocouple, 5 is a pyrometer, 6 is a pyrometer viewing window, 7
is the cell of crystal growth material, 8 is each cell 7
9 is a vacuum chamber.

When growing crystals on the substrate 1, the substrate 1
It is necessary to accurately know the temperature before and during growth, but it has been difficult to obtain accurate values using conventional methods using thermocouples or pyrometers. First of all, in the case of the former type of thermocouple, due to its operating principle, in order to obtain an accurate value, the temperature of the two-metal fusion part at the tip of the thermocouple must match the substrate temperature. It must be brought into contact with the substrate 1 or the substrate holder 2 with sufficiently good thermal contact. Good thermal contact in a vacuum state can be achieved by screwing, etc., but in that case, it takes a lot of effort to attach and detach the substrate holder 2, and it is not necessary to rotate the substrate holder 2 in a vacuum. It becomes possible. In crystal growth, rotation of the substrate 1 is an extremely effective means to obtain a uniform growth layer, but if you try to make good thermal contact with the thermocouple,
Incompatible with substrate rotation technology. On the other hand, if the temperature is measured without bringing the thermocouple into contact with the substrate holder 2, there is no heat conduction through the gas because it is in a vacuum, and the heat transfer between the substrate holder 2 and the substrate holder 2 is caused only by conduction by radiant heat. Since contact is made, the temperature of the thermocouple is significantly different from the temperature of the substrate holder 2, and may cause an error of ±50° C. or more.

Furthermore, the method of remotely measuring the surface temperature of the substrate 1 using the pyrometer 5 through a window provided in the vacuum chamber 9 is greatly affected by dirt on the viewing window 6 due to crystal growth. Depending on how dirty it is, temperature measurement is often impossible. Furthermore, although accurate temperature measurement cannot be expected unless the infrared emissivity from the crystal surface is known, the detailed value of the infrared emissivity of the grown thin film itself is often unknown.

For the above reasons, it has been impossible to accurately and stably determine the substrate temperature using the conventional techniques.

[Object of the Invention] Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks and provide a method for stably measuring the substrate temperature more accurately and with good reproducibility.

[Structure of the Invention] In order to achieve the above object, the present invention makes an electron beam incident on the surface of a solid material, and changes over time the intensity of the electron beam reflected, diffracted, or scattered on the surface of the solid material, or It is characterized by detecting the period of time change of the absorbed current flowing through the sensor and determining the surface temperature of the solid material from the period.

[Example] The present invention will be described in detail below with reference to the drawings.

FIG. 1 shows an example of the configuration of a measuring device implementing the present invention. In this apparatus, an electron gun 10 and a fluorescent screen 12 are additionally provided in the vacuum chamber 9 shown in FIG. Alternatively, the electron multiplier 18 can be provided alongside or in place of the fluorescent screen 12. Further, an ammeter 22 for measuring the current flowing through the substrate 1 due to the incident electron beam 11 emitted from the electron gun 10 and incident on the surface of the substrate 1 is installed alongside the fluorescent screen 12 and the electron multiplier 18 or instead of them. It is also possible to provide one. When the fluorescent screen 12 is provided, a camera or lens 13 is provided in front thereof, and an XY stage 14 to which one end of an optical fiber 15 is fixed is provided behind the camera or lens 13. optical fiber 15
A photodetector 16 is arranged at the other end. When installing the electron multiplier tube 18, its output current is measured by the ammeter 1.
Measure according to 9. Photodetector 16 and ammeter 1
One or more of the outputs 9 and 22 can be recorded by the recorder 17. A series of A/D converters 20 and computers 21 can also be provided instead of or in conjunction with the recorder 17.

Below, GaAs is used as the material for the solid material substrate 1.
Let us explain the case where crystals are selected. Also, the first
The device shown in the figure uses a fluorescent screen 12 as an example.

In order to grow crystals on a GaAs substrate, it is necessary to heat the substrate to approximately 400°C or higher. To make devices such as semiconductor lasers, it is said that it is best to grow crystals at a temperature of about 700°C. In order to measure such temperature, the following method is used in the present invention. First, the incident electron beam 11 from the electron beam 10 is reflected, diffracted, or scattered on the substrate surface, and the reflected electron beam and the diffracted electron beam with appropriate diffraction directions project point images on the fluorescent screen 12. . These point images are formed on an X-Y stage 14 by a camera or lens 13, and one of the points is supplied from the X-Y stage 14 to a photodetector 16 via an optical fiber 15. The recorder 1 records the time change in the output of the photodetector 16.
7 can be observed and recorded.

Temporal change in intensity at a point called the specular spot, where the specular reflection with the highest intensity and the 0th-order Laue point overlap in the diffraction image, with the temperature of the substrate 1 set at 750°C and the As molecular beam always applied. is shown in Figure 3.

It is known from Japanese Patent Application No. 59-169125 (Crystal Growth Film Thickness Control Method and Mixed Crystal Composition Ratio Determination Method) that the intensity of specular spots oscillates during growth.
It can be seen that it oscillates over time even after growth has stopped.
Curve A in FIG. 4 shows the relationship between the period of oscillation and the substrate temperature after the growth is stopped. This result shows that the amount of As molecular beam is equivalently measured as pressure by a vacuum gauge installed across the molecular beam, which is 4.8×
This is when the temperature was 10 ^-4 Pa. As is clear from this figure, temperature can be determined inversely from the period of vibration. When the results of the characteristic curve A in Figure 4 are stored in a computer and the period of vibration is measured by the computer, the computer automatically compares the stored results with the measured period and automatically adjusts the temperature. Of course, it is possible to measure One period of this oscillation consists of one layer of substrate (Ga and
(a layer in which a pair of As atomic layers is counted as one layer) corresponds to evaporation.

This can be known as follows. First, AlAs, which hardly evaporates even at the temperature at which GaAs evaporates, is grown sufficiently thickly on a GaAs substrate. Next, a GaAs Nd layer is grown thereon. If we observe the oscillations caused by evaporation after the growth has stopped, the oscillation phenomenon will no longer occur after Ns oscillations. This is thought to be because all the GaAs in the Nd layer has evaporated and the AlAs layer has been exposed, but if Ns matches Nd at this time, one vibration due to evaporation will completely correspond to the evaporation of one GaAs layer. There will be. Curve a in Figure 5 shows the number of growth layers Nd
The vibrations during crystal growth and evaporation are shown when is 10. As is clear from the figure, in this case Nd
and Ns match perfectly. FIG. 6 shows the relationship between Nd and Ns obtained through a number of similar experiments. From the figure, it can be seen that Ns is the same as Nd, or even if they are different, it is at most 1. Among the points shown in this figure, those where Nd and Ns do not match are the specular points shown in curve a in Figure 5.
This is because the intensity change of the spot was markedly reduced when the Ga shutter was opened, and as a result, the shape of the normally occurring first period of vibration was greatly disrupted. In such a case, curve b in Figure 5
Against? Indicated with a mark. If the correct number of growth atomic layers is determined by correcting this, the value is NS
matches. From the above, it is known that Ns corresponds to the number of evaporated atomic layers.

Therefore, by utilizing this fact, the substrate temperature can be determined from the evaporation rate. Curve B in FIG. 4 shows the relationship between substrate temperature and evaporation rate obtained from curve A in FIG. This evaporation rate was measured when the amount of As molecular beam was at an equivalent pressure of 4.8×10 ^-4 Pa, and changing the As pressure also changes the evaporation rate. An actual measurement example when the amount of As molecular beam is 8×10 ^-5 Pa in equivalent pressure is shown at point C in Figure 4.
It was shown in However, since this relationship between evaporation rate and temperature does not depend on the structure of the device, the relationship between the evaporation rate and the substrate temperature, which is accurately measured by some method, must be determined under various As molecular doses. By doing so, it is possible to accurately measure the temperature of substrates in different states in different devices. Furthermore, the evaporation rate increases by about 70% for a 10 degree rise in substrate temperature, making it possible to calculate extremely accurate temperature measurements.

In the above, the temperature is determined by extracting the specular spots from the diffraction image, but all the points on the fluorescent screen 12 show a time change in intensity during the evaporation of the substrate, and the oscillation period is the same as that of one layer of evaporation. In order to correspond to time, the vibration period at any point may be measured. Furthermore, since it is known that similar vibrations exist in the absorbed current flowing through the substrate, the vibrations may be observed using the ammeter 22. No matter which vibration phenomenon is used, the only object to be measured is the period.
The calibration curve from Specular Spot can be used without any modification whatsoever. Furthermore, instead of using the system from the fluorescent screen 12 to the photodetector 16, an electron multiplier 18 and an ammeter 19 may be used to measure the time change in reflected, diffracted, or scattered electron intensity. Needless to say, it is possible to observe the vibrations of

Further, the measurement method of the present invention is not limited to the case where GaAs is used as a substrate, but can be applied to any solid material as long as the vibration phenomenon of the electron beam diffraction image due to evaporation can be observed.

[Effects] According to the temperature measurement method according to the present invention, temperature can be measured with very high accuracy, so detailed control of crystal growth conditions is greatly facilitated. Since the phenomenon used in the present invention is directly dependent on the temperature of the substrate surface, it is not affected by various temperature non-uniformities in the vicinity of the substrate holder, so it is possible to obtain measurement values with excellent reliability and stability. I can do it. Furthermore, the measured values obtained are independent of the equipment and are also dependent on whether reflection, diffraction, or scattered electron beams or absorption currents are used as the object of vibration observation, or which diffracted electron beams are used. Therefore, the measured values are excellent in uniformity and objectivity.

The highly accurate and highly stable temperature measurement obtained by the present invention is extremely useful for producing many devices including semiconductor lasers without variation. Moreover, even if there is a type of device that does not allow any re-evaporation of the crystal during crystal growth, the measurement method of the present invention can be applied in the surface cleaning process by heating the substrate, which is always performed at the initial stage of growth. As a result, temperature measurement can be calibrated for thermocouples, pyrometers, etc., which have poor reproducibility and long-term stability, so the effects of applying the present invention are great.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an example of the structure of a measuring device used to carry out the present invention, Fig. 2 is a block diagram showing an example of a conventional measuring device, and Fig. 3 is a block diagram showing an example of a conventional measuring device.
Figure 4 shows an actual measurement example of the change in spot intensity over time. Figure 4 is a characteristic diagram showing the relationship between vibration frequency and substrate temperature and the relationship between evaporation rate and substrate temperature. Figure 5 is a graph showing the relationship between crystal growth and evaporation. FIG. 6 is a diagram showing the temporal change in the intensity of specular spots, and is a characteristic diagram showing the relationship between the number of grown layers Nd and the number of vibrations Ns caused by evaporation. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Substrate holder, 3... Heater for heating the substrate, 4... Thermocouple, 5... Pyrometer, 6... Peephole, 7... Cell for crystal growth material, 8... Cell Shutter, 9... Vacuum chamber, 10
... Electron gun, 11 ... Incident electron beam, 12 ... Fluorescent screen, 13 ... Lens, 14 ... X-Y stage, 15 ... Optical fiber, 16 ... Photodetector, 17 ... Recorder, 18 ...electron multiplier tube, 1
9... Ammeter, 20... A-D converter, 21...
Computer, 22...Ammeter.

Claims (1)

[Claims] 1. An electron beam is made incident on the surface of a solid material, and the period of the time change in the intensity of the electron beam reflected, diffracted, or scattered on the surface of the solid material or the time change of the absorbed current flowing through the solid material is detected, and the period is determined. A surface temperature measurement method characterized in that the surface temperature of the solid material is determined from.