JPH053437B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to fabrication of superlattices, crystal growth, fabrication of optical devices such as semiconductor lasers and light emitting elements, and electronic devices such as FETs, and cleaning of solid surfaces. This invention relates to a solid state evaporation control method that controls evaporation by counting each monoatomic layer layer by layer when it is necessary to evaporate a thin film on the surface of a solid material on the atomic order.

[Prior Art] When evaporating the surface of a solid material, there has never been an example in which only an extremely thin film layer on the surface is removed by controlling it on an atomic order. However, recently, in the semiconductor field, it has become necessary to create devices with atomic dimensions, such as quantum well lasers and superlattice devices.
As seen in No. 59-169125 (Crystal Growth Film Thickness Control Method and Mixed Crystal Composition Ratio Determination Method) and Japanese Patent Application No. 1987-169126 (Crystal Film Thickness Measurement Method), crystals are grown while counting monoatomic layers one by one. The technology has also been perfected. However, when it comes to actually manufacturing laser devices, ROHM's Tanaka, Mushigami, Ishida, Fukada et al. published a paper (Japanese Journal of Applied Physics).
Vol.24, No.2, February, 1985 pp.L89−L90)
As shown in Figure 2, it has become necessary to partially remove once grown crystals and re-grow them, and it is necessary to precisely control evaporation to determine the film thickness that should remain.

In addition, as shown in Japanese Patent Application No. 176613/1984 (molecular beam epitaxy growth method), when manufacturing FETs and permeable base transistors, once exposed to the atmosphere, the surface becomes dirty.
In order to keep the surface clean, there is also a technology that coats it with arsenic (As). However, if a dirty surface could be cleaned by evaporating only a few atomic layers of the extremely thin film on the surface,
There is no need to coat As, and the device fabrication process can be simplified. However, this evaporation control of several atomic layers has not been done conventionally.

Furthermore, the case where the modulated superlattice has a three-terminal structure as shown in Japanese Patent Application No. 58-136171 (semiconductor devices) and the paper by Yokoyama, Imamura, Oshima, Nishi, Muto, Kondo, and Reimizu et al. (Japanese Journal of Applied
Ph´ysics Vol.No.5, May, 1984 pp.L311−L312)
As seen in Figure 2, when fabricating a fine superlattice element such as a hot electron transistor, it becomes necessary to attach metal electrodes to a predetermined number of atomic layers. It is necessary to know that the number of layers has been reached. Therefore, it is strongly expected to control the evaporation of each monoatomic layer.

[Objective of the Invention] Therefore, in view of the above-mentioned points, an object of the present invention is to precisely control the partial evaporation process necessary for manufacturing processes such as light emitting diodes and semiconductor lasers, and to By controlling evaporation to clean the surface of a material or controlling the evaporation of an ultra-thin film layer on the surface necessary to create a superlattice element, we can precisely remove the ultra-thin film layer from the surface of a solid material. Another object of the present invention is to provide a solid evaporation control method that allows accurate evaporation.

[Structure of the Invention] In order to achieve the above object, the present invention provides an electron beam generated by an electron gun that is scattered and reflected on the surface of a solid material when the electron beam is incident on the surface of a solid material to evaporate the solid material. Alternatively, it is characterized in that the evaporation of a substance constituting the surface of the solid material is controlled in synchronization with the temporal change in the intensity of the diffracted electron beam or the temporal change in the absorption current flowing through the solid material.

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

FIG. 1 shows an example of the configuration of an evaporator used to carry out the present invention. Here, 1 is the target solid material (hereinafter referred to as the substrate), 2 is the electron gun,
3 is an incident electron beam emitted from the electron gun 2 and incident on the substrate 1; 4, 5 and 6 are respectively
They are a reflected electron beam 4, a diffracted electron beam 5, and a scattered electron beam 6 that have been reflected, diffracted and scattered by the electron beam.
Reference numeral 7 denotes a fluorescent screen that emits light due to the collision of these electron beams, thereby making the electron beams visible.
A camera or lens 8 guides the image on the fluorescent screen 7 once to the end face of an optical fiber 10 attached to an XY stage 9. 11 is a photodetector that detects light from the optical fiber 10;
A-D converts the analog signal from the photodetector 11 into a digital signal and supplies it to the computer 13.
It is a converter. The computer 13 sends control signals for each device to the controller 14. Here, A-D
The converter 12 and controller 14 can be integrated with the computer 13 by selecting a suitable computer 13.

Here, an A-D converter 12, a computer 13
When the controller 14 adopts a simple control algorithm, the controller 14 includes an analog circuit that detects the maximum value, minimum value, or maximum value and minimum value of the output change of the output of the photodetector 11, and a counter that coefficients the number of times of detection. and a sequencer that sends control signals to each device in a predetermined order. It is also possible to directly monitor the output of the photodetector 11 using the recorder 15 and manually operate it if necessary.

16 is a shutter drive device; 17 is a shutter that opens and closes a molecular beam, ion beam, electron beam, etc.; 18 is a thermocouple that measures the temperature of the substrate 1; 11 is an electric thermometer; 20 is a heater that heats the substrate 1; 21 is a power source for the heater 20; 22 is a substrate holder that holds the substrate 1; 23 is an ammeter that measures the current flowing through the substrate 1; 24 is an electron multiplier that captures electrons scattered by the substrate 1; is an ammeter that measures the current flowing through the electron multiplier tube 24. Reference numeral 26 is a window through which light passes, and the light from the light source 27 is passed through a light amount adjuster 28 that adjusts the intensity of this light, and further passed through a scanner 29 that scans the output light on the surface of the substrate 1. 1. 30 is an ion gun that injects an ion beam into the substrate 1; 31 is its power source; 32
33 is a power source for the electron gun 32; 33 is a powerful electron gun having an output sufficient to provide sufficient energy to the substrate 1; 34 is a cell that generates a molecular beam, 35 is cell 3
4 power source. 36 is a vacuum chamber that houses the substrate 1 and is sealed in a vacuum. 37 is a power source for the light source 27.

Now, the incident electron beam 3 emitted from the electron gun 2
is reflected or diffracted after being incident on the surface of the substrate 1, and the reflected electron beam 4 and the diffracted electron beam 5 with an appropriate diffraction direction reach the fluorescent screen 7 and project a fluorescent image. do. This is called a diffraction image. This diffraction image is captured by the camera or lens 8.
- An image is formed on the Y stage 9, and the light at a suitable point is guided to a photodetector 11 through an optical fiber 10, and its output signal is supplied to a computer 13 through an A/D converter 12. The computer 13 analyzes the supplied output signal and outputs the signals to each shutter 17 and light source 2.
7. Light amount adjuster 28, scanner 29, ion gun 3
0. Necessary ones of the powerful electron gun 32 and the cell 34 are controlled via the controller 14. 1st
In the evaporator shown in the figure, by filling the molecular beam cell 34 with a material for crystal growth, for example, Ga, Al, or As for crystal growth of GaAs, AlGaAs, or AlAs, not only evaporation from the substrate 1 but also Crystal growth on the substrate 1 can also be made possible at the same time.

Reflected electron beam 4, which is particularly strong among diffraction images
FIG. 2 shows an example of an actual measurement in which the time change in the intensity of the superimposed image of the zero-order Laue point (hereinafter referred to as the specular spot) was recorded on a recorder. This diagram is
The substrate 1 is made of GaAs, an As molecular beam is always applied to the substrate, and the substrate temperature is 750°C.
The shutter was opened and GaAs was grown layer by layer using the technology disclosed in Japanese Patent Application No. 59-169125 (Crystal Growth Film Thickness Control Method and Mixed Crystal Composition Ratio Determination Method).
Crystal growth was stopped by closing the Ga shutter after growing 11 layers. While the Ga shutter is open, the intensity of the specular spot shows periodic oscillations corresponding to the growth of 11 layers of GaAs. Furthermore, temporal oscillations in the intensity of specular spots are observed even after the Ga shutter is closed and GaAs growth is no longer possible. This is caused by the evaporation of the GaAs crystal, and one vibration is a layer of GaAs (Ga and As are counted as a pair), which is 2.83 Å thick in the [100] crystal orientation. corresponds to the layer).

Curve A in FIG. 3 shows the relationship between the frequency of oscillation caused by this evaporation and substrate temperature, and curve B in FIG. 3 plots the relationship between evaporation rate and substrate temperature from one cycle of oscillation. The activation energy ΔE associated with evaporation is approximately 4.7 eV. This activation energy also depends on the amount of As molecular beam that is constantly irradiated.
At all plot points in Figure 3, except for the one marked C, the amount of As is equivalently measured as pressure by a vacuum pressure gauge placed across the molecular line, and is 4.8 x 10 ^{- 4} Pa. Point C in Figure 3 shows the evaporation rate when the molecular dose of As is 8×10 ^-5 Pa in terms of equivalent pressure. This shows that the evaporation rate also depends on the molecular dose of As.

It can be seen as follows that one cycle of the intensity oscillation of the specular spot caused by evaporation completely corresponds to further evaporation of GaAs. First, AlAs, which hardly evaporates even at the temperature at which GaAs evaporates, is grown sufficiently thickly on a GaAs substrate. Next, a Nd layer of GaAs is grown thereon. When observing the oscillations caused by evaporation after growth has stopped, the oscillation phenomenon stops occurring 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.
If Ns matches Nd at this time, one vibration due to evaporation completely corresponds to the evaporation of one layer of GaAs. The number of growth layers Nd is 10 on curve a in Figure 4.
The vibrations during crystal growth and evaporation are shown in the case of . As is clear from the figure, in this case Nd and Ns
is a perfect match. FIG. 5 shows the relationship between Nd and Ns obtained through a number of similar experiments. From the figure Ns
It can be seen that it is at most 1 even if it matches or differs from Nd. Among the points shown in this figure,
In the case where Nd and Ns match, the intensity change of the speckle spot shown in curve a in Fig. 4 shows a significant decrease in the intensity that occurs when the shutter of Ga is started. This is due to the fact that the shape of one cycle has significantly collapsed. Is the diagram for this case the curve b in Figure 4? Indicated with a mark. If this correction is made and the number of growing atomic layers is determined correctly, the value will match Ns. From the above,
It is known that Ns corresponds to the number of evaporated atomic layers.

Based on Figure 3, the substrate temperature Td at which the evaporation rate of the substrate increases, the temperature Ts at which almost no evaporation occurs, and the temperature Tg suitable for crystal growth are selected, and the intensity of the specular spot as shown in Figure 6a is determined. By changing the substrate temperature in synchronization with the time changes as shown in FIG. 6b, it is possible to accurately and precisely control the evaporation of the constituent elements on the substrate surface layer by layer. Td, Ts and Tg
The temperature can be reached and maintained by feedback controlling the substrate temperature measured by the thermocouple 18. This temperature control may be in the form of a computer instructing a target temperature to a general temperature controller, or alternatively, the computer may be in the form of controlling the heater power supply 21 via the controller 14 based on the readings of the thermometer 19.

The crystal growth and evaporation processes shown in FIG. 6a are as follows. First, let the substrate temperature be Tg,
Growth starts at time t ₀ , and after growth of 6 monoatomic layers,
Growth is stopped at time _t1 , and at the same time the substrate temperature is raised to Td to start evaporation. At time _t2 when the intensity of the specular spot oscillates twice, the substrate temperature is set to Ts.
evaporation is interrupted. Then the time
If the substrate temperature is raised to Td again at _t3 , evaporation will resume. The illustrated example shows a case where the specular spot can be observed to vibrate three times up to time _t4 . If we take this process as a whole, we can see that a total of 5 vibrations, and therefore 5 atomic layers, have been evaporated. If six layers are grown when only one layer is required, five layers can be easily removed by the above process. This technique can easily be used to re-grow crystals or evaporate defined atomic layers of crystals to clean surfaces. Furthermore, since the evaporation process can be precisely divided at arbitrary positions, it is easy to perform some processing on the crystal surface or to observe the surface during the evaporation process.

Furthermore, as is clear from FIG. 3, when the As molecular dose is 4.8×10 ⁴ Pa in equivalent pressure, the activation energy for GaAs evaporation is 4.7 eV, so energy exceeding this energy is emitted from the light source 27. light and electron gun 3
By applying an electron beam from 2 or an ion beam from an ion gun 30, the evaporation of GaAs can be performed using a special spectroscopic spot, similar to the process shown in FIG. can be controlled in synchronization with changes in intensity. Furthermore, when using light, electron beams, and ion beams as energy sources, selective evaporation from only specific areas of the substrate can be precisely controlled by irradiating only specific areas of the substrate surface. I can do it.

FIG. 6c shows the case using light. If light is extracted from the light source 27 during the time periods between t ₁ and _{t 2} and between t ₃ and _{t 4} and irradiated onto the substrate surface, a total of 5 layers of GaAs will be formed.
can be evaporated. In FIG. 6e, a strong electron beam is emitted from the electron gun 32 from _t1 to _t2 and from _t3 to _t4.
Figure 6f shows the case where ion gun 3 is irradiated only between
The case where the ion beam was irradiated from 0 to t ₁ to _{t 2} and from t ₃ to _{t 4} was shown. In either case, the same evaporation results as in FIG. 6a can be expected.

When irradiating light, ultraviolet rays with energy higher than the activation energy for decomposition of the elements constituting the solid material may be irradiated using a light source such as an excimer laser or a mercury lamp, or at a temperature at which evaporation proceeds. A light source such as a CO ₂ laser or a YAG laser may irradiate strong visible light or infrared rays that are sufficient to heat the substrate surface. In either case, a light source strong enough to uniformly irradiate the entire board may be used, or a relatively weak light source may be used and the scanner 29 may be used to direct the light beam to any desired turn on the board. A light source and scanner may be used to advance the evaporation by focusing and increasing the illumination locally, and by sequentially scanning the focal point to advance the evaporation over the entire substrate surface.

When using strong electron beams or ion beams,
Electrons or ions with energy higher than the activation energy for decomposition may be used, or even if the energy of each electron or ion is low, an electron beam or ion strong enough to heat the substrate surface to a temperature at which evaporation proceeds may be used. Ion beams may also be used.

Furthermore, as in the case of light, the entire surface of the substrate may be irradiated, or a focused electron beam or ion beam may be scanned. In addition, the electron gun 2 and the powerful electron gun 32 or the ion gun 3
0 at the same time, mutual interference may occur and the reflected electron beam 4, diffracted electron beam 5, and scattered electron beam 6 may change significantly, which may impede observation. , there is no problem if each control power source is used alternately at a cycle sufficiently shorter than the time for one layer evaporation.

As shown by the difference between point C and other points in Figure 3, considering that the evaporation of GaAs from the substrate depends on the amount of As molecular beam, By changing the pressure of the component material with the higher vapor pressure defined in relation to the solid material, such as by changing the pressure of the component material of group V which is the component with higher vapor pressure in some cases, It is also possible to control the evaporation of GaAs, etc. from the surface. In FIG. 6d, Pg is the amount of known radiation suitable for crystal growth, Pd is the amount of molecular beam that increases the evaporation rate, and Ps is the amount of molecular beam that decreases the evaporation rate. Here, as shown in the figure, Pd is used between t ₁ and _{t 2} and t ₃ and _{t 4} , Ps is between t ₂ and _{t 3} , and so on.
By controlling the As pressure in synchronization with the time change in specular spot intensity, the amount of pressure from the substrate surface increases.
The evaporation of GaAs can be controlled in the same manner as in the case of controlling by the substrate temperature described above.

In the case of GaAs, the As pressure, that is, the amount of As molecular beam, may be controlled, but in the case of InP, InGaP, AlSb, etc.
In the case of AlGaSb, etc., it can be controlled by the pressure of P or Sb, and it can be controlled by changing the pressure of a component having a high vapor pressure determined in relation to the solid material.

As shown above, evaporation of GaAs from a substrate can be precisely controlled by controlling the substrate temperature, the amount of light, electron beam, ion beam, or AS molecular beam. It is also easy to control two or more of the control factors simultaneously for comprehensive control. Note that although FIG. 1 shows a light source 27, a light amount adjuster 28, a scanner 29, an ion gun 30 and its power source 27, and a powerful electron gun 32 and its power source 33, the above devices are not used. Needless to say, there is no need to provide one.

In the embodiment shown above, in order to control the evaporation state, it is necessary to measure and analyze the temporal change in the intensity of the specular spot. This is achieved by supplying the signal through the DA converter 12 to the computer 13, where it is analyzed. As a method for analyzing intensity oscillations due to GaAs evaporation, Japanese Patent Application No. 59-169125 (Crystal Growth Film Pressure Control Method and Mixed Crystal Composition Ratio Determination Method) was used to analyze intensity oscillations during GaAs crystal growth. methods can be applied. As aforementioned,
If the analysis criteria are simple, the computer 13
It is also possible to replace it with an analog circuit, a counter, a sequencer, etc.

Further, in the above embodiment, only the method of measuring and utilizing the intensity change of the specular spot has been described, but it is also possible to perform control in synchronization with the intensity change of another diffracted electron beam 5 or the scattered electron beam 6. can be done in exactly the same way. In particular, in the case of the scattered electron beam 6, in order to prevent a point image from forming on the fluorescent screen 7, the optical fiber 10
The signal can be increased by placing a lens adjacent the end face of the optical fiber to focus a wide range of fluorescent light into the optical fiber.

In addition, instead of making the electron beam visible on a fluorescent screen and then measuring it with the photodetector 11, the target electron beam can be guided to the electron multiplier 24, or conversely, the electron multiplier 25 can be placed at an appropriate position. By doing so, it is also possible to directly observe the intensity of the target electron beam. In that case, the output of the multiplier tube 24 may be taken out as a signal by the ammeter 25, and the following control will be exactly the same as in the case of using the above-mentioned fluorescent screen.
The absorbed current flowing into the substrate 1 may be taken out as a signal by the ammeter 23 and taken out as control information, and in this case as well, control can be performed in exactly the same way as in the case of the diffraction image described above. Furthermore, although it is possible to measure the period of one vibration by observing only one point using one of the various types of measurements mentioned above, it is possible to reduce errors caused by deformation of the waveform for each vibration period. For this purpose, it is also possible to use multiple types of measurement methods in combination, or to simultaneously measure the intensities of multiple diffracted electron beams, and to cross-reference the results. In particular, to observe a plurality of point images on a phosphor screen, it is sufficient to provide a complex circuit from the optical fiber 10 to the photodetector 11, but instead, a circuit from the camera or lens 8 to the photodetector 11 can be provided. Instead of using a highly sensitive television monitor system, it is also possible to observe the intensity of multiple point images using image processing technology.

Above, we have mainly talked about the evaporation of GaAs, but - group compound semiconductors other than GaAs,
Furthermore, for solid materials in general, including Si, Ge, etc., periodic development corresponding to the evaporation of a single atomic layer can be observed in either reflection, diffraction, scattered electron beam intensity, or current flowing into the substrate. If so, it goes without saying that the present invention can be effectively applied.

[Effects] As is clear from the above, according to the present invention, constituent substances in a solid material are changed in synchronization with time changes in the intensity of reflected, diffracted or scattered electron beams and in the current flowing into the substrate. By controlling the evaporation of , it is possible to accurately and precisely remove the surface of a solid material one atomic layer at a time. Therefore, the present invention provides a technique for reducing surface roughness to an atomic scale amount, cleaning while strictly maintaining flatness, regrowth from a precisely calculated depth position, and furthermore, It is extremely useful for applications such as burying metal layers in soil. The present invention makes a significant contribution to the fabrication of semiconductor lasers, the realization of superlattice devices, superstructure devices, and the like.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an example of the structure of an evaporator used to carry out the present invention, Fig. 2 is a diagram showing an actual measurement example of temporal change in specular spot intensity, and Fig. 3 is a diagram showing the frequency and substrate. Characteristic diagrams showing the relationship with temperature and the relationship between evaporation rate and substrate temperature. Figure 4 is a diagram showing the temporal change in specular spot intensity during crystal growth and evaporation. Figure 5 is a graph showing the number of grown layers.
Characteristic diagrams showing the relationship between Nd and the number of vibrations Ns caused by evaporation, Figures 6a to 6f illustrate temporal changes in the intensity of specular spots and how various factors are changed in synchronization with this change. FIG. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Electron gun, 3... Incident electron beam, 4... Reflected electron beam, 5... Diffracted electron beam, 6...
...Scattered electron beam, 7...Fluorescent screen, 8...Camera or lens, 9...X-Y stage, 10
...Optical fiber, 11...Photodetector, 12...A
-D converter, 13, 14...computer, 15
... Recorder, 16 ... Shutter drive device, 17
... Shutter, 18 ... Thermocouple, 19 ... Electric thermometer, 20 ... Heater, 21 ... Power supply, 22 ...
... Substrate holder, 23 ... Ammeter, 24 ... Electron multiplier, 25 ... Ammeter, 26 ... Window, 27 ... Light source, 28 ... Light amount controller, 29 ... Scanner, 3
0...Ion gun, 31...Power source, 32...Powerful electron gun, 33...Power source, 34...Cell, 35...Power source, 36...Vacuum chamber, 37...Power source.

Claims (1)

[Claims] 1. When an electron beam generated by an electron gun is incident on the surface of a solid material to evaporate the solid material, the period of the intensity of the electron beam reflected, diffracted, or scattered on the surface of the solid material. A method for controlling evaporation of a solid, characterized in that the evaporation of a substance constituting the surface of the solid material is controlled in synchronization with a periodic time change or a periodic time change of an absorption current flowing through the solid material. 2. A solid evaporation control method according to claim 1, characterized in that the evaporation of the substance is controlled by changing the temperature of the solid material. 3. The solid evaporation control method according to claim 1, characterized in that the evaporation of the substance is controlled by changing the pressure of the element substance having a higher vapor pressure determined in relation to the solid material. solid state evaporation control method. 4. A solid evaporation control method according to claim 1, characterized in that evaporation of the substance is controlled by irradiating the solid material with light. 5. A solid evaporation control method according to claim 1, characterized in that evaporation of the substance is controlled by irradiating the solid material with another electron beam. 6. A solid evaporation control method according to claim 1, characterized in that evaporation of the substance is controlled by irradiating the solid material with an ion beam.