JPH0722133B2 - Vapor phase growth equipment - Google Patents

Description

The present invention relates to a vapor phase growth apparatus, and MOCVD (M
It is the most suitable to be applied to the etalorganic chemical vapor deposition equipment.

[Outline of Invention]

The present invention provides a light source, a reaction tube having a window through which light from the light source passes and a substrate on which a film having a different absorption coefficient is grown, and at least an amplitude of light emitted from the light source. A data collecting section for detecting the quantity and detecting at least the quantity of the amplitude of the reflected light intensity due to the multiple reflections on the surface and interface of the film grown on the substrate; and The growth rate and the composition of the film are controlled by controlling the growth condition to a desired value based on the information of at least one of the growth rate and the composition of the film and returning to the growth of the film on the substrate. And / or the composition can be controlled easily and surely.

[Prior Art] In recent years, an epitaxial growth technique has become an important technique for producing a high-performance semiconductor element. Especially AlGa
As-based devices, that is, devices using heterojunctions such as laser diodes, high electron mobility field effect transistors (HEMTs), and heterojunction bipolar transistors (HBTs) cannot be manufactured without epitaxial growth technology.

In the case of performing this epitaxial growth, it is essentially preferable to monitor the growth parameters such as the composition of the growth layer and the growth rate at the time of growth (in-situ monitoring). In-situ monitoring of growth parameters is difficult with the device. For this reason, the actual situation is that the practical equipment does not monitor the growth parameter on the spot.

Recently, AlGaAs by MBE (Molecular Beam Epitaxy) method
High-speed electron beam diffraction (RHEED)
A method for in-situ observation by the method has been proposed as a method for observing the surface of a growth layer or a feedback method to a growth apparatus. However, this method is considered to have poor practicality. This is because in the MBE method, the spatial distribution of molecular beam flux is MBE.
Due to its inherently high anisotropy, in-plane uniformity of growth cannot be obtained without rotation of the substrate, and therefore rotation of the substrate is necessary, but this rotation causes the substrate to vibrate or swing. Therefore, RHEED that makes the electron beam incident at a low angle (frequency)
This is because the observation by the method becomes extremely difficult.

On the other hand, J.Appl.Phys.51 (3), pp.1599-1602 (1980 3
(Moon) proposed a method for in-situ observation of growth by ellipsometry (polarization analysis) during epitaxial growth of GaAlAs-GaAs superlattice by MOCVD method. In this ellipsometry method, polarized light is incident on the surface of the growth layer from a fixed low angle, and information on the film thickness and the refractive index of the growth layer is obtained from the phase information of the reflected light. This method is quite effective, but it requires a window for the incident light and a window for the emitted light, which greatly limits the structure of the growth apparatus. It is necessary to set the incident angle of the incident light strictly. Since the sample is set on the heating table, it is troublesome to adjust the overall alignment and angle.Since the incident light passes through the growth gas for a long distance due to the low-angle incidence, the noise caused by the gas disturbance is It is said that penetration is large, a slight position change or vibration of the sample has a fatal effect on the measurement, and the measurement data is obtained as phase information, so it is necessary to link it with a computer to extract it as a growth parameter. There are various drawbacks.

[Problems to be solved by the invention]

It is an object of the present invention to provide a very new and effective vapor phase growth apparatus in which the above-mentioned various drawbacks of the prior art are corrected.

[Means for solving problems]

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

As shown in FIG. 2, it is assumed that a thin film 2 having a thickness d is laminated on a substrate 1 and placed in a gas phase 3. Now when light 4 of wavelength λ is vertically incident on this thin film 2, this thin film 2
The Fresnel reflection coefficient at the interface between the substrate 1 and the substrate 1 and at the interface between the gas phase 3 and the thin film 2 are represented by the following equations and equations, respectively.

here, Is the complex index of the material j, It is represented by. However, nj is Is the real part of kj = (4π / λ) αj (αj: absorption coefficient of substance j).

The synthetic reflection coefficient R considering multiple reflection is It is represented by. here, Is. The measured reflection intensity is | R | ² . From the equations and equations, it can be seen that the reflection intensity changes periodically with an increase in d. And from the formula and the formula, m = 0,1,2, ...
... It turns out that As an example, the substrate 1 is GaAs and the thin film 2
FIG. 3 shows the result of calculation of the formula in the case where is AlxGa _1- xAs (x = 0.57). However, n = 4.11, α _{1 for} calculation
= 81800 cm ^-1 , n = 3.66, α = 24200 cm ^-1 , n ₃ = 1 and α ₃ = 0 were used. As shown in FIG. 3, if an increase in d at normal incidence, that is, an oscillation of the intensity of reflected light accompanying growth, is observed, then n _{2 of} the thin film 2, and thus the composition of the thin film 2, can be determined. .

The present invention has been devised based on the principle as described above. That is, the vapor phase growth apparatus according to the present invention, a light source,
A substrate on which a film having a different absorption coefficient (for example, compound semiconductor thin film 2) is grown is held inside, and a reaction tube having a window portion for passing light from the light source (for example, He-Ne laser light 4), and the light source. A data collecting unit for detecting at least the amount of amplitude of light emitted from the device and for detecting at least the amount of amplitude of reflected light intensity due to multiple reflection at the surface and interface of the film grown on the substrate; The growth condition (for example, the flow rate of the growth gas) is controlled to a desired value on the basis of the information on at least one of the growth rate and the composition of the film obtained by the attenuation of the amplitude at And a growth control unit for returning.

[Work]

With this configuration, it becomes possible to easily monitor the growth parameters on the spot during growth,
The data obtained thereby can be fed back to the growth apparatus to control the growth conditions.

〔Example〕

An embodiment in which the present invention is applied to a MOCVD apparatus will be described below with reference to the drawings.

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

As shown in FIG. 1, in the MOCVD apparatus according to the first embodiment, the substrate 1 is placed on the inclined upper surface of a susceptor 6 made of carbon, for example, provided in a quartz reaction tube 5 capable of source pressure. . Further, in the quartz reaction tube 5, a susceptor 6
A table 7 having the same height as the susceptor 6 is provided on the upstream side of the so that the growth gas (or reaction gas) can smoothly flow in the quartz reaction tube 5. Then, while the substrate 1 is heated to a predetermined temperature by the RF coil 8 provided on the outer periphery of the quartz reaction tube 5, a growth gas is flown through the quartz reaction tube 5 as indicated by an arrow A, so that a thin film ( (Not shown).

In the MOCVD apparatus according to the present embodiment, in addition to the above-mentioned configuration similar to the conventional MOCVD apparatus, the following monitor system is provided to monitor the growth of the thin film based on the principle described above. . That is, first, the He-Ne laser light source 9 is provided at a position apart from the quartz reaction tube 5 by a predetermined distance,
Laser light 4 (λ =
6328Å) chopper 10, lens 11 (for example, focal length 500m
m) and the quartz reaction tube 5 so that they can be incident on the substrate 1. Substrate 1 of this laser light 4
The reflected light by the reflection mirror 12 is reflected by the reflecting mirror 12, and then the diffuser plates 13 stacked on each other and ND (Ne (Ne) for attenuating the incident light).
The light is incident on a photomultiplier tube 16 through a color filter 15 for transmitting only light having a wavelength of 600 nm or more, and is detected. The 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 chopper 10 to the recorder 18, and records the time change of the reflected light intensity by the thin film 2 on the chart. You can do it.

On the other hand, a part of the laser light 4 emitted from the He-Ne laser light source 9 is reflected by the flat surface of the lens 11 and then reflected by the reflecting mirror 19.
It is reflected by and is incident on the power meter 20, and its output signal is amplified by the amplifier 21 and sent to the recorder 22 to record the time change of the reflected light intensity by the lens 11 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 fluctuates, the time change of the intensity of the reflected light by the thin film 2 can be accurately performed. It can be measured.

Next, the result of measurement of reflected light intensity when AlGaAs is grown on a GaAs substrate heated to 700 ° C. by using the MOCVD apparatus according to this embodiment configured as described above will be described. For the growth, TMG (trimethylgallium) and TMA (trimethylaluminum) were used as the raw materials for Ga and Al, respectively, and the flow rate of TMG was fixed at 10 ml / min.
The flow rate of A was changed to 4 types of 5 ml / min, 10 ml / min, 20 ml / min, and 40 ml / min. In order to prevent the reactant from accumulating on the inner wall of the quartz reaction tube 5 and hindering the transmission of light, the growth gas was made to flow at a high flow rate (1 m / sec or more).

FIG. 4 shows the measurement result of the reflection intensity. After growth, the Al composition x of the obtained Al x Ga _1- x As thin film was determined from the photoluminescence measurement, and was 0.26, 0.40, 0.57, 0.7, respectively.
Was 2. After the growth, the film thickness d of the AlxGa _1- xAs thin film is measured by a scanning electron microscope (SEM), the real part n ₂ of the refractive index is obtained from the formula, and I = I ₀ exp from the attenuation rate of the reflection intensity.
The absorption coefficient α ₂ was obtained based on the formula (−α ₂ d) (reflection intensity when I ₀ : d = 0, I: reflection intensity when film thickness d).
The results are shown in the table below. The GaAs data in this table is
First, AlAs was laminated on a GaAs substrate, and it was obtained from vibration analysis of the reflection intensity curve of GaAs when GaAs was grown on this AlAs.

Next, a method for obtaining the growth parameter during the growth of the thin film will be described based on the above results. FIG. 5 is a plot of the ratio b / a of the reflection intensity b of the first trough of the vibration in each reflection intensity curve of FIG. 4 to the reflection intensity a of the GaAs substrate against Al composition x. Using the graph shown in FIG. 5, the Al composition x of AlxGa _1- xAs that is now grown can be determined from the reflection intensity of the first valley after the start of epitaxial growth. The thickness of the thin film corresponding to the first valley of the reflection intensity is approximately 40 nm. Also the 6th
The figure is a graph of the above table. The discontinuity of n near x = 0.8 in FIG. 6 is due to the band gap of AlxGa _1- xAs. If the Al composition x is known from FIG. 5, the refractive index n can be obtained from this FIG. Therefore, by using this refractive index n, the film thickness up to the first trough of the reflection intensity can be obtained from the formula, and by dividing this film thickness by the growth time, the growth rate of the thin film can be determined. it can. In addition, once the calibration curve is created based on the graphs and equations shown in FIGS. 5 and 6, the above procedure can be directly performed based on this calibration curve without any calculation thereafter. .

As described above, the growth rate of the Al x Ga _1- x As thin film and the Al composition x can be monitored in-situ during the growth, so if these are different from the desired values or if it is desired to change the values, these By returning the above data to the MFC (mass flow controller) of the MOCVD apparatus to readjust the growth gas concentration, the desired growth rate and Al composition x can be controlled easily and reliably.

Next, the measurement error due to the deviation of the incident angle of the laser beam 4 on the thin film 2 will be examined. When the incident light deviates from the normal incidence, the optical path length in the film becomes long, and the period of interference becomes short. When the optical path length becomes 1% longer, that is, when the interference period becomes 1% shorter, the incident angle is as follows when the thin film 2 is AlGaAs (n ₂ =
In case of 3.5), it becomes as follows. That is, n ₃ sin θ = n ₂ sin θ ′ (θ: incident angle, θ ′: refraction angle, n ₃ : gas phase refractive index (= 1)) is established according to Snell's law. Therefore, cos θ ′ = 0.99 Then θ ′ = 8 °, so θ
= Sin ^-1 (3.5sin8 °) = 30 °. Therefore, even if the incident angle deviates from the vertical by 30 °, the measurement error is as small as 1%.
In this respect, it is extremely advantageous as compared with the measurement by the ellipsometry method.

Besides, according to the above-mentioned first embodiment, there are various advantages as follows. That is, since the incident light to the thin film and the reflected light from the thin film pass through the same window, the limitation on the device is relaxed. Since the intensity and the optical path length of the light reflected by the thin film hardly depend on the change in the incident angle, it is not necessary to strictly adjust the optical axis of the light incident on the thin film. Since the optical path lengths of the incident light and the reflected light can be made shorter in the growth gas as compared with the low-angle incidence as in the ellipsometry method, noise caused by the gas disturbance is not generated.

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

In the second embodiment, a MOCVD apparatus similar to that of the first embodiment is used to grow a multilayer film, and the growth is monitored by the reflection intensity. Figure 7 shows TMG flow rate of 20ml / on a GaAs substrate.
After thinly growing GaAs, the TMA flow rate of 40 m on this GaAs.
The measurement result of the reflection intensity when AlAs is grown at l / min and then GaAs is grown on this AlAs is shown. As is clear from the reflection intensity curve shown in FIG. 7, the vibration due to GaAs appears clearly after the vibration due to AlAs. In the case of such a multilayer film, some calculation is required to determine its growth, but it is clear that it is obtained in the same manner as in the first embodiment. Therefore, by feeding back the growth parameters thus obtained to the MFC of the MOCVD apparatus, the composition and the growth rate can be controlled in the same manner as in the first embodiment.

Next, a third embodiment of the present invention will be described. In FIG. 8 below, parts having the same functions as those in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted as necessary.

As shown in FIG. 8, in the MOCVD apparatus according to the third embodiment, the light from the white light source 23 is incident on the high-speed scanning spectroscope 25 through the lens 24 and is dispersed, and the dispersed light is chopper 10 and lens 11. Also, the light is incident on the substrate 1 in the quartz reaction tube 5 through the beam splitter 26 almost perpendicularly to the surface thereof. The light reflected by the substrate 1 is reflected by the reflecting mirror 12, enters the photomultiplier tube 16, and is detected. The output signal of the photomultiplier tube 16 is amplified by the lock-in amplifier 17 and then input to the data collection unit 27. On the other hand, the light reflected by the beam splitter 26 enters the photomultiplier tube 28 and is detected, and its output signal is amplified by the lock-in amplifier 29 and then input to the data collecting section 27. There is.

The data collection unit 27 is connected to the growth control unit 30 having a built-in computer so that information can be exchanged between them. This growth control unit 30 is further MF
It is connected to the C control unit 31, and the MF is controlled by this MFC control unit 31.
By controlling C32, the amount of growth gas flowing in the reaction tube 5 can be adjusted. Further, the pressure information in the quartz reaction tube 5 is also input from the pressure measuring device 33 to the data collection unit 27, and this pressure information is input to the MFC control unit 31 via the growth control unit 30. By controlling the MFC 34 for gas, the pressure in the quartz reaction tube 5 can be adjusted.

Next, a method of monitoring growth parameters when a thin film is grown by the MOCVD apparatus according to the third embodiment configured as described above will be described.

First, a predetermined amount of growth gas is flown by the MFC 32 to start thin film growth. At the same time, the high-speed scanning spectroscope 25 scans the wavelength at such a speed that the change in film thickness due to growth can be ignored. At present, a high-speed scanning spectroscope 25 that can perform one wavelength scan in a time of 1 second or less is commercially available, and thus such a high-speed wavelength scan can be easily performed. The light reflected by the growing thin film is detected by the photomultiplier tube 16, and the value B / A obtained by dividing the reflected intensity output B of the lock-in amplifier 17 by the output A of the lock-in amplifier 29 is a function of the wavelength λ ( It is recorded as shown in FIG. 9 on the chart (not shown). On the other hand, the data of the reflection intensity B / A obtained as a function of this wavelength λ is input to the growth control unit 30 from the data collection unit 27 and analyzed, and then a signal according to the analysis result is sent to the MFC control unit 31. The MFC32 is controlled to control the composition and growth rate of the thin film to target values. If necessary, the pressure in the reaction tube 5 is adjusted by controlling the carrier gas flow rate by the MFC 34.

As described above, according to the second embodiment described above, the reflection intensity data (function of wavelength λ) obtained in-situ during growth by wavelength scanning by the high speed scanning spectroscope is fed back to the MFC controller 31, and the MFC 32, By controlling 34, the growth parameters of the thin film, that is, the composition and the growth rate can be controlled easily and reliably as in the first embodiment.

Since the growth rate of the thin film can be easily changed during the growth, when the multilayer film is grown as in the second embodiment, for example, by slowing the growth rate, a multilayer film having a sharp interface can be obtained. Is possible.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described three embodiments, and various modifications can be made based on the technical idea of the present invention. For example, the control system for controlling the growth parameter by returning the intensity information of the light reflected by the thin film may have a configuration different from those of the above-mentioned three embodiments, if necessary.

Further, in the above-described first embodiment, the first reflection intensity curve
The refractive index n, that is, the Al composition and the growth rate were obtained from the second vibration trough, and these data (n, growth rate) were used as initial parameters for the measurement value of the reflection intensity obtained momentarily thereafter. By performing parameter fitting, it is possible to improve the measurement accuracy. Furthermore, it is possible to improve the measurement accuracy by inputting the intensity of the peaks and troughs of the vibration of the reflection intensity into the calculator and performing the calculation. Furthermore, in the three embodiments described above,
The case where the present invention is applied to the horizontal MOCVD apparatus has been described, but the present invention can be applied not only to the vertical MOCVD apparatus but also to other various vapor phase growth apparatuses.

〔The invention's effect〕

According to the present invention, the growth parameters can be easily monitored in-situ during the growth, so that the growth conditions can be controlled according to the data obtained thereby, and thus the growth rate of the film and It is possible to easily and surely control the composition.

[Brief description of drawings]

FIG. 1 is a block diagram of a MOCVD apparatus according to the first embodiment of the present invention, FIG. 2 is a sectional view for explaining the basic principle of the present invention, and FIG. 3 is an example of a change in reflection intensity depending on the thickness d of a thin film. Fig. 4 is a graph showing the change in reflection intensity with growth of an AlxGa _1- xAs thin film grown at various substrate gas temperatures of 700 ° C with various growth gas flow rates. Fig. 5 shows AlxGa
A graph showing the relationship between the Al composition x in _1- xAs and the ratio b / a of the valley intensity b to the intensity a of the GaAs substrate in the reflection intensity curve shown in FIG. 4, FIG. 6 is the Al composition in AlxGa _1- xAs. FIG. 7 is a graph showing the relationship between x and the refractive index, FIG. 7 is a graph showing the change in reflection intensity with the growth of a multilayer film in the second embodiment of the present invention, and FIG. 8 is a MOCV according to the third embodiment of the present invention.
FIG. 9 is a configuration diagram of the D device, and FIG. 9 is a graph showing an example of changes in the reflection intensity ratio B / A with wavelength, which is obtained in the third embodiment of the present invention. In the reference numerals used in the drawings, 1 ... Substrate 2 ... Thin film 4 ... Light 5 ... Quartz reaction tube 6 ... Susceptor 9 ... Laser light source 16, 28 ... Photomultiplier tube 25 ... High-speed scanning spectroscopy Container 27 …… Data collection unit 30 …… Growth control unit 31 …… MFC control unit.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Kunio Kaneko 6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation (72) Inventor Shozo Watanabe 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo No. Sony Corporation

Claims (1)

[Claims] 1. A light source, a reaction tube having therein a substrate on which a film having a different absorption coefficient is grown and having a window portion through which light from the light source passes, and at least an amplitude of light emitted from the light source. And a data collecting unit for detecting at least the amount of amplitude of the reflected light intensity due to multiple reflections on the surface and interface of the film grown on the substrate, and by the attenuation of the amplitude in the data collecting unit. A vapor phase growth apparatus having a growth control unit for controlling the growth condition to a desired value based on information on at least one of the growth rate and the composition of the film thus obtained and for returning the growth condition to the growth of the film on the substrate.