KR950007482B1 - Method for vapor deposition - Google Patents

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Description

Meteorological Growth Method

1 is a configuration diagram of a MOCVD apparatus having a growth monitor system used in the first embodiment of the present invention.

2 is a cross-sectional view for explaining the basic principle of the present invention.

3 is a graph showing an example of the change in reflection intensity due to the thickness d of the thin film.

FIG. 4 is a graph showing the change in reflection intensity with growth in the growth of Al _x Ga _1-x As thin films by varying the flow rate of growth gas at a substrate temperature of 700 ° C. FIG.

FIG. 5 is a graph showing the relationship between the Al composition _x of Al _x Ga _1-x and the ratio b / a to the intensity a of the Ga _1-x As substrate of the bone intensity b in the reflection intensity curve shown in FIG. .

6 is a graph showing the relationship between the Al composition x and the refractive index n in AlxCa _1-x As.

7 is a graph showing a change in reflection intensity with growth of a multilayer film in a second embodiment of the present invention.

* Explanation of symbols for main parts of the drawings

(1): substrate (2): thin film

(4): light (5): quartz reaction tube

(6): Susceptor (9): Laser light source

(16): photomultiplier tube

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vapor phase growth method, which is most suitable for epitaxial growth of compound semiconductor thin films by MOCVD (Metalorganic Chemical Vapor Deposition).

In the vapor phase growth method, in the vapor phase growth of a film on a substrate in a vapor phase growth apparatus, light is incident on the film from a direction substantially perpendicular to the surface thereof, and the light is changed in accordance with the time change of the intensity of the reflected light. By controlling the growth conditions of the film, it is possible to easily and surely control the growth rate and composition of the film.

In recent years, in order to manufacture high-performance semiconductor devices, the epitaxial growth technology has become an important technology. In particular, AlGaAs-based devices, such as laser diodes, devices using heterojunctions such as high electron mobility field effect transistors (HEMT) and heterojunction bipolar transistors (HBT), cannot be manufactured without epitaxial growth technology. .

When epitaxial growth is performed, it is inherently preferable to monitor growth parameters such as the composition of the growth layer and the growth rate at the time of growth in situ, but including an epitaxial growth device of silicon, In the conventional epitaxial growth apparatus, it is difficult to monitor the growth parameters on the spot. Therefore, it is a reality that the practical apparatus does not monitor the growth parameter on the spot.

In recent years, a method of observing epitaxial growth of AlGaAs by MBE (Molecular Beam Epitaxy) method by semi-fast electron diffraction (RHEED) method has been proposed as a surface observation of a growth layer or a feedback method to a growth device. However, this method is not considered practical. Because the MBE method has a high anisotropy inherent in MBE, the spatial fraction of molecular flux molecular beams does not achieve in-plane uniformity of growth without rotation of the substrate, and thus requires rotation of the substrate. However, since the substrate vibrates or oscillates by this rotation, observation by the RHEED method of injecting an electron beam at a low angle becomes very difficult.

Meanwhile, J. Appl. Phys. 51 (3), pages 1599 to 1602, March 1980), in the ellipsime tric (polarization analysis) method during epitaxial growth of GaA1As-GaAs superlattices by MOCVD The method of performing the spot observation of growth is proposed. This ellipsometric method injects polarized light from a fixed low angle onto the surface of the growth layer, and obtains information on the thickness and refractive index of the growth layer from the phase information of the reflected light. This method is quite effective, but (1) the window of the incident light and the window of the outgoing light is imposed, which imposes a big limitation on the structure of the growth apparatus. (2) The angle of incidence of the incident light needs to be set precisely. The adjustment of the moment and angle is cumbersome. ③ Because of the low angle of incidence, the incident light passes through the growth gas over a long distance, so the invasion of noise caused by the disturbance caused by the gas is large. It has a fatal effect on the measurement. (5) Since the measurement data is obtained as phase information, it is necessary to link it with a calculator in order to extract it as a growth parameter.

An object of the present invention is to provide an extremely novel and effective gas phase growth method which corrects various defects as described above with the prior art.

First, the basic principle of the present invention will be described.

As shown in FIG. 2, the thin film 2 of thickness d is laminated on the substrate 1, which is said to lie in the gas phase 3. As shown in FIG. Now, when the light 4 of wavelength lambda is vertically incident on the thin film 2, Fresnel at the interface between the thin film 2 and the substrate 1 and at the interface between the gas phase 3 and the thin film 2 The reflection coefficient of (Fresnel) is expressed by the following ① and ② expressions, respectively.

Where n _j (j = 1, 2, 3) is the complex refractive index of material j,

It is expressed as Where n _j is the real part of n _j , k _j = (4π / λ) α _j (α _j : absorption coefficient of substance j).

Synthetic reflection coefficient R considering multiple reflection

It is expressed as here,

to be. The measured reflection intensity is | R│ ² . From equations ④ and ⑤, the reflection intensity changes periodically with increasing d. And from the expressions ④ and ⑤, m = 0, 1, 2, _...

It can be seen that. As an example, Fig. 3 shows the result of calculating the equation (4) when the substrate 1 is GaAs and the thin film 2 is AlxGa _1-x As (x = 0.57). However, n ₁ = 4.11, α ₁ = 81800cm ^-1 , n ₂ = 3.66, α ₂ = 24200cm ^-1 , n ₃ = 1, α ₃ = 0 for calculation. As shown in FIG. 3, when the increase of d in the normal incidence, i.e., the vibration of the intensity of the reflected light accompanying the growth, is observed, the composition of n ₂ of the thin film ₂ , and thus the thin film ₂ , can be obtained. It can be seen that.

The present invention has been devised in accordance with the principle as described above. In other words, the vapor phase growth method according to the present invention is for vapor phase growth of a film (e.g., compound semiconductor thin film 2 such as ALGaAs, GaAs, A1As, etc.) on a substrate in a vapor phase growth apparatus (e.g., a MOCVD apparatus). The light (e.g., He-Ne laser light 4) is incident on the film from a direction substantially perpendicular to the surface thereof, and the growth conditions of the film (e.g., Flow rate).

The vapor phase growth method of the present invention irradiates a surface of a thin film formed on a substrate mounted on a susceptor having a slightly inclined mounting surface with light having an angle of incidence substantially perpendicular to the surface thereof. The acceptor rotates at a constant speed around its central axis, periodically irradiates the substrate on the susceptor with light, receives the light reflected from the thin film, monitors the growth parameters, and establishes it according to the reflected light compared with the reference light. And generating a parameter display signal and controlling the growth conditions of the thin film according to the growth parameter unfolding signal.

In this way, the growth parameters can be easily monitored on the spot during growth, and the data obtained thereby can be returned to the growth apparatus to control the growth conditions.

Next, the present invention will be described with reference to the drawings in accordance with an embodiment applied to the vapor phase growth of a compound semiconductor by the MOCVD method.

First, a first embodiment of the present invention will be described.

1 is a MOCVD apparatus used in this embodiment. In this MOCVD apparatus, the substrate 1 is placed on an inclined upper surface of, for example, the susceptor 6 made of carbose, disposed in the pressure sensitive quartz reaction tube 5. In the quartz reaction tube 5, a base 7 having the same height as the susceptor is disposed upstream of the susceptor 6, and the growth gas (or reaction gas) is a quartz reaction tube 5 The inside flows smoothly. Then, the growth gas flows through the quartz reaction tube 5 as indicated by arrow A while the substrate 1 is heated to a predetermined temperature by the RF coil 8 wound around the outer surface of the quartz reaction tube 5. A thin film (not shown) is grown on the substrate 1.

In the MOCVD apparatus according to the present embodiment, in order to monitor the growth of the thin film in accordance with the above-described principle in addition to the above-described configuration as in the conventional MOVCD apparatus, the following monitor system is provided. That is, first, a He-Ne laser light source 9 is disposed at a predetermined distance from the quartz reaction tube 5, and the chopper 10 emits the laser light 4 (λ = 6328 kV) emitted from the laser light source 9. ), The lens 11 (for example, a focal length of 500 mm) and the quartz reaction tube 5 can be made to enter the substrate 1. The reflected light by the substrate 1 of the laser light 4 is reflected by the reflector 12, and then stacked on each other, the diffusion plate 13, the ND (Neutral Densnity) filter 14 for attenuating the incident light, and the wavelength. The light is incident on the photomultiplier tube 16 through the color filter 15 for passing only light of 600 mm or more. This photomultiplier tube 16 is connected to a lock-in amplifier 17. The lock-in amplifier 17 is also connected to the chopper 10, and sends only the output signal of the laser light 4 selected by the laser light 4 selected by the chopper 10 to the recorder 18, thereby providing a chart. It is possible to record the time change of the reflected light intensity by the thin film 2 on the image.

On the other hand, a part of the laser light 4 emitted from the He-Ne laser light source 9 is reflected on the flat surface of the lens 11, and then is reflected by the reflector 19 to be incident on the power meter 20, The output signal is amplified by the amplifier 21 and sent to the recorder 22 so that the time variation of the reflected light intensity by the lens 11 is recorded on the chart. Therefore, by dividing the intensity recorded by the recorder 18 by the intensity recorded by the recorder 22, even if the output of the laser light source 9 varies, the time change of the intensity of the reflected light by the thin film 2 is accurately measured. I can do it.

Next, the result of measuring the reflected light intensity when AlGaAs is grown on a GaAs substrate heated to 700 ° C using the MOCVD apparatus according to the present embodiment configured as described above will be described. In the growth, TMG (trimethylgallium) and TMA (trimethylaluminum) were used as raw materials of Ga and Al, respectively, and the flow rate of TMG was fixed at 10 m1 / min, and the flow rates of TMA were 5 m1 / min, 10 m1 / min, and 20 m1. It changed into four types of / min and 40m1 / min. In order to prevent the reactants from depositing on the inner wall of the quartz reaction tube 5 and preventing the transmission of light, the growth gas was allowed to flow at a high velocity (1 m / sec or more).

4 shows the result of measuring the reflection intensity. After the growth, the Al composition x of the obtained Al _x Ga _1-x As thin film was found from the measurement of photoluminescence, and was 0.26, 0.40, 0.57, and 0.72, respectively. After the growth, the film thickness d of the Al _x Ga _1-x As thin film was measured by a scanning electron microscope (SEM), and the real part n ₂ of the refractive index was obtained from the equation (6), and from the attenuation factor of the reflection intensity, I = I ₀ exp The absorption coefficient α ₂ was obtained according to the formula (−α ₂ d) (I ₀ : reflection intensity when d = 0 and I: reflection intensity when film thickness d). The results are shown in the following table. The GaAs data in this table is obtained from the vibration analysis of the GaAs reflection intensity curve when AlAs is first deposited on a GaAs substrate, the AlAs are loaded, and GaAs is grown on the AlAs.

TABLE 1

Next, on the basis of the above results, a method of obtaining the growth parameters during the growth of the thin film will be described. FIG. 5 shows the ratio b / a to the reflection intensity a of the GaAs substrate of the reflection intensity b of the first valley of the vibration in each reflection intensity curve of FIG. 4 with respect to the Al composition x. Using the graph shown in FIG. 5, after the start of epitaxial growth, the Al composition x of AlxGa _1-x As growing now can be obtained from the first reflection intensity. The thickness of the thin film corresponding to the valley of the first reflection intensity is approximately 40 mm. Moreover, refractive index n can be calculated | required from FIG. Therefore, the refractive index n can be used to determine the film thickness from the equation ⑥ to the valley of the first reflection intensity, and the film growth rate can be determined by dividing the film thickness by its growth time. The above procedure can be directly performed in accordance with the calibration curve after the calibration curve has been prepared in accordance with the graphs shown in FIGS. 5 and 6 and the equation (6).

As described above, the growth rate of the Al _x Ga _1-x As thin film and the Al composition x can be monitored at the site during the growth. Therefore, if they are different from the desired values or if the values are desired to be changed, these data are transferred to the MOCVD apparatus. By reconditioning the growth gas concentration by returning to the MFC (mass flow controller), the desired growth rate and the Al composition x can be easily and reliably controlled.

Next, the measurement error by the deviation of the incident angle of the laser beam 4 to the thin film 2 is examined. When the incident light shifts from normal incidence, the length of the optical path in the film becomes long, and thus the period of interference is shortened. The incident angle when the length of the optical path becomes 1% long, that is, when the period of interference is shortened by 1%, becomes as follows when the thin film 2 is AlGaAs (n ₂ = 3.5). In other words, from Snell's law, n ₃ sin θ = n ₂ sin θ '(θ: incident angle, θ': refractive angle, n ₃ : refractive index of gas phase (= 1)), so cosθ '= 0.99 in this equation. Since θ 'is 8 °, θ = s in ^-1 (3.5 sin 8 °) = 30 °. Therefore, even if the angle of incidence is shifted by 30 degrees from the vertical direction, the measurement error is very small (1%). This is very advantageous compared to the measurement by the ellipsometric method.

In addition, according to the first embodiment described above, in addition to the foregoing, there are various advantages as follows. That is, since the incident light and the reflected light to the thin film pass through the same window, the limitation on the device is relaxed. Since the intensity of the reflected light by the thin film and the length of the optical path hardly depend on the change in the incident angle as described above, it is not necessary to strictly adjust the optical axis of the incident light on the thin film. Since the lengths of the optical paths of the incident light and the reflected light in the growth gas can be shorter than in the case of low angle incidence as in the ellipsometric method, there is no occurrence of noise due to disturbance caused by the gas.

Next, a second embodiment of the present invention will be described.

In the second embodiment, the multilayer film is grown using the same MOCVD apparatus as in the first embodiment, and the growth is monitored by the reflection intensity. FIG. 7 shows that the GaAs was thinly grown at a TMG flow rate of 20 mL / min on a GaAs substrate, followed by the growth of AlAs at a TMA flow rate of 40 mL / min on this GaAs, followed by the growth of GaAs on this AlAs. As is apparent from the reflection intensity curve shown in FIG. 7, the vibration caused by GaAs clearly appears after the vibration caused by AlAs. In the case of such a multilayer film, some calculation is required to determine its composition, but it is apparent that the multilayer film is obtained in the same manner as in the first embodiment. Therefore, the composition and growth rate can be controlled similarly to the first embodiment by returning the growth parameters thus obtained to the MFC of the MOCVD apparatus.

As mentioned above, although embodiment of this invention was described, this invention is not limited to the above-mentioned two embodiment, Various deformation | transformation according to the technical idea of this invention is possible. For example, in the above-described first embodiment, the refractive index n, and therefore the Al composition x and the growth rate, were obtained from the valley of the first oscillation of the reflection intensity curve, but these data (n, growth rate) were obtained as initial parameters. Then, the measurement accuracy can be made higher by setting a parameter using, for example, a calculator with respect to the measured value of the reflection intensity obtained at any time. In addition, it is possible to increase the measurement accuracy by inputting the calculation of the peaks and valleys of the vibration of the reflection intensity into the calculator.

In addition, a MOCVD apparatus having a configuration different from that of the MOCVD apparatus shown in FIG. 1 used in the above two embodiments may be used. In the above two embodiments, although He-Ne laser light is used as the light for the monitor, other types of laser light or other light may be used as long as it is light of a single wavelength. In the above two embodiments, the present invention can be applied to the vapor phase growth of AlGaAs, AlAs, and GaAs.

According to the present invention, it is possible to monitor the growth parameters on the spot during the growth, and to return the data obtained to the growth apparatus, so that the growth rate and / or composition of the film can be easily and surely controlled. .

Claims (7)

A surface of a thin film formed on a wave mounted on a susceptor having a slightly inclined mounting surface is irradiated with light having an angle of incidence substantially perpendicular to the surface, and the susceptor is fixed around its central axis. Rotates at a speed, periodically irradiates the substrate of the susceptor with light, receives light reflected from the thin film, monitors the growth parameters, generates a growth parameter display signal in accordance with the reflected light compared with the reference light, and A vapor phase growth method of a thin film grown by vacuum deposition, comprising: a step of controlling feedback of the growth conditions of the thin film according to the growth parameter display signal. The vapor phase growth method according to claim 1, wherein the growth parameter display signal is obtained according to the intensity of light reflected by the thin film. 3. The vapor phase growth method according to claim 2, wherein one of the growth parameters is a refractive index, and the refractive index is determined from the intensity of the reflected light. The vapor phase growth method according to claim 2, wherein one of the growth parameters is a composition of the thin film. 3. The vapor phase growth method according to claim 2, wherein one of the growth parameters is a relative intensity of the reflected light with respect to the intensity of light irradiated on the thin film. 6. The vapor phase growth method according to claim 5, wherein the relative intensity of the reflected light with respect to the intensity of the irradiated light varies according to the wavelength of the irradiated light. The gas phase growth method according to claim 1, wherein the growth condition is adjusted by adjusting a flow rate of the reaction gas.

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