JPS6269508A - Manufacture of compound semiconductor device - Google Patents

Abstract

PURPOSE:To form a flat layer interface with no recession nor projection at an atomic layer level by separating only excessive atoms such as isolated atoms and clusters on the topmost surface of a growth layer from the surface after coating the surface of a substrate with a raw material. CONSTITUTION:A Ga molecular beam is evaporated from a raw material Ga 17 by opening a Ga cell shutter 20, As is evaporated from a raw material As 18 by opening an As cell shutter 21 and GaAs is grown on the surface of an InP substrate 12. The temperature of the substrate 12 is set at 400-500 deg.C. After a main shutter 22 is closed, an In cell shutter 19 is opened and the shutter 20 is closed. Such a state is held for approx. 1min or longer. Then, only excessive Ga atoms on the topmost surface of a GaAs thin film layer formed on the substrate 12 is separated from the surface and a perfectly flat growth layer atom surface underneath is exposed. This forms a flat layer interface with no recession nor projection at an atom layer level.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a molecular beam epitaxial growth method. More specifically, the present invention relates to a molecular beam epitaxial growth method for forming a single crystal thin film used as a microwave device or a light emitting/light receiving device.

[Prior art]

As a manufacturing method for compound semiconductor devices, especially optical devices,
Epitaxial growth methods are commonly used because of the ease of growing thin, uniform layers and controlling the composition ratio of component elements.

Among them, a technique that has recently received particular attention is the molecular beam epitaxial growth method (hereinafter referred to as "MBE" for simplicity).
For example, W, T
, Tsang by Nikkei Electronics Yang, 308
, 163 (1983), the MBE growth method and devices utilizing periodic thin film structures are described in detail.

For example, in a multi-quantum well type laser as shown in FIG. 2, it is necessary to alternately and periodically form different types of layers with thicknesses of several tens of λ to several 1000 λ in the light emitting part. It is necessary to form a mixed crystal single crystal thin film with a multicomponent composition without periodicity in the lower layer, and in such cases, MBE
The growth method is extremely advantageous.

Furthermore, by alternately and periodically stacking different types of growth layers each having a thickness of one atomic plane (i.e., atomic layer superlattice, hereinafter abbreviated as MSL), the electrical properties can be significantly improved. has also been theoretically predicted (T., Yao, J.J.A., P22 (1983)
)L680).

FIG. 3 shows an MBE growth method of a conventional compound semiconductor device manufacturing method. In Fig. 3(a), a cell shutter ■ is placed on the semiconductor substrate ■ bonded on the substrate holder ■.
By opening, for example, group III raw material A (e.g. Ga
)■ is attached. At this time, since the cell shutter (2) is closed, the group (2) raw material B (for example, Al) (2), which is different from the group (1) raw material A (2), does not adhere to the semiconductor substrate (2). However, here, group V raw materials (for example, As)
Cells are omitted. That is, in FIG. 3(a), a growth layer of a compound semiconductor (for example, GaAs) made of group II raw material A is formed on a semiconductor substrate.

In order to constitute a compound semiconductor device, further, a growth layer of a compound semiconductor (for example, kl A,s ) made of a group III raw material B, which is different from A, is formed in the Y layer,
It forms a hetero interface (Fig. 3 Q))).

In the conventional method, Fig. 3(a) to Fig. 3(1)
) is within a few seconds. That is, in FIG. 3(a), after closing the cell shutter ■ to complete the formation of the compound semiconductor growth layer made of the group ■ raw material A■, the formation of the compound semiconductor growth layer made of the group ■ raw material B■ is started. The time required to open the cell shutter ■ to start the process was within a few seconds.

[Problem that the invention seeks to solve]

However, it is generally known that unevenness of ±1 atomic plane or more exists in a heterointerface formed using such a compound semiconductor device manufacturing method.

Such unevenness at the hetero interface causes, for example, a shift in the emission wavelength of a quantum well type light emitting device.
Decreases controllability of device performance.

In addition, microwave elements that flow electrons parallel to the hetero interface (for example, high electron mobility transistor HEMT
), scattering of electrons occurs due to the unevenness of the hetero interface, reducing electron mobility and reducing the operating speed of the microwave element. Furthermore, since unevenness of ±1 atomic plane exists at the hetero interface, it is currently not possible to form an MSL over a wide area, such as the entire surface of a 2-inch-ψ wafer. Also, recently,
While performing MBE growth, reflection electron diffraction (
A method has been proposed to control the flatness of the surface of the grown layer so that there is no fluctuation of ±1 atomic layer by observing it with RHEED (for example, T, Sakam
oto et al., J, J, A, P, 23 (1984,) L-6
57), even using this method, it was not possible to obtain a flat interface with no fluctuations in the ±1 atomic plane (No. 32).
Proceedings of the Regenerative Physics Association Lecture 81P-ZA-
12, (1985) P744. ).

[Means for solving problems]

Therefore, for the above purpose, the present inventors experimentally observed the behavior of attached atoms on the substrate surface and conducted various studies. As a result, we found new evaluation results as shown in Figure 4. Figure 4 shows the 400° angle on the Tnp (100) substrate.
At C to 500°C, the As pressure is approximately 1X1O-6 Tor
After evaporating the Ga raw material and depositing it on the InP substrate surface under the conditions of r ~ l ”Torr
This figure shows the results of Auger electron spectroscopy performed in an adjacent analysis chamber while maintaining the temperature of 1000 Ω (~IXI O” Torr, ). The relative intensity of the subsequent In Auger electron peak is expressed, assuming that the In Auger electron spectroscopy peak intensity is 1.0.The horizontal axis is the time when the Ga cell shutter was opened and the Ga raw material was evaporated.

However, the time in this case is not the accumulated time (, G
The time from opening to closing of the a-cell shutter corresponds to one time of -0-. That is, in the fourth figure, approximately 4. Although plotted at intervals of ~5 Sec, for example, a plot corresponding to 20 sec is 4. This does not mean that Ga raw material evaporation of 20 sec was repeated 5 times, but that Ga raw material evaporation of 20 sec was repeated once.
It means that it has gone around. Looking at the results in Figure 41,
Overall, the longer the Ga shutter release time is, that is, the longer the Ga raw material is deposited, the lower the In peak intensity from the InP substrate is. This means that as Ga atoms adhere to the surface of the InP substrate, the detection rate of In Auger electrons from the underlying InP substrate decreases. However, in detail, about 15-16 se
It decreases rapidly in a stepwise manner every c. This means the following phenomenon.

That is, for example, from Q sec to 16 sec, the In peak intensity does not change within the error range.

In other words, if the Ga cell shutter is opened for less than 16 seconds, the Ga atoms once attached to the InP substrate surface will be removed within the time (approximately 80 m1n) from when the Ga cell shutter is closed until the substrate temperature is lowered to room temperature. , I
It is detached from the nP substrate surface, and the 1nP substrate surface reappears on the outermost surface. Since the Ga As layer thickness is approximately 0.19 μm when continuous growth is performed for 3 hours under the same conditions such as Ga molecular beam intensity, As pressure, and substrate temperature,
The GaAs layer thickness in the case of continuous growth for 16 seconds is about 2.
8A, which corresponds to the thickness of one atomic layer of GaAs crystal within the measurement error range.

This phenomenon can be explained as follows.

FIG. 5 is a sectional view showing the generally well-known state of the outermost surface of the grown layer.

That is, for example, isolated atoms A, two-dimensional clusters B, and three-dimensional clusters C are formed on the outermost surface of the growth layer (FIG. 5(a)). On the other hand, the cross section near the most human plane of a completely flat grown layer at the atomic level is as shown in FIG. 5 (1). The atoms on the outermost surface of the growth layer in Figure 5 (1)) are:
It is constrained by interatomic bonding forces from its 4 nearest neighbors. However, the isolated atom A in Figure 5(a) is 2
It receives only the binding force from the closest neighboring atoms, and
Atoms at the ends of two-dimensional cluster B receive binding forces only from the three nearest neighbors. However, for simplicity, the number of nearest atoms on the paper in Figure 5 is shown here,
To be precise, the three-dimensional direction (direction perpendicular to the paper) must also be taught. Therefore, the total binding force is the weakest for the isolated atom A, and the second weakest is for the atoms at the ends of the two-dimensional cluster B.

Therefore, in order for an atom to detach from the outermost surface in Figure 5(b) against the total binding force from the 4 nearest atoms, the isolated atom A or the two-dimensional cluster B in Figure 5(a) must be More energy is required than for the atoms at the ends to detach. Fifth
In the three-dimensional cluster C in Figure (a), the atom at the top is equivalent to an isolated atom, and the two atomic planes below it are each equivalent to a two-dimensional cluster. Therefore, the fifth
Only the isolated atom A two-dimensional cluster 813-dimensional cluster C in Figure (a) is desorbed, and atoms are not desorbed from a flat surface at the atomic level with no unevenness as shown in Figure 5(b). By artificially applying energy (for example, thermal energy from heater heating or laser heating), the conventional top surface as shown in Figure 5(a) can be changed to the surface as shown in Figure 5(b). can be improved. For this purpose, there are two methods described below.

One is to detach only the isolated atoms A, 2-dimensional cluster B, and 3-dimensional cluster C shown in FIG. 5(a), and the isolated atoms shown in FIG. 5(b)
In this method, the substrate is heated at a constant temperature to prevent desorption from a flat surface such as a flat surface, and growth is performed by increasing the molecular beam intensity by 1. In this case, if the attached atoms remain in the isolated atom or cluster state for a long time until they form a complete one-atomic surface, they will detach, so if there are more atoms than are detaching, It needs to be supplied from raw materials, and in this sense the molecular beam intensity needs to be relatively high. That is, as isolated atoms diffused on the surface are incorporated into a cluster and the cluster grows, a molecular beam intensity greater than that required to finally form one atomic plane is required.

In this method, after the molecular beam irradiation is stopped, the substrate temperature is maintained at the same temperature, thereby making it possible to desorb only the isolated atoms on the outermost surface and Clascou. The other method is to perform irradiation at a desired molecular beam intensity in a state where the substrate temperature is relatively low so that even isolated atoms and clusters are not desorbed, and after stopping molecular beam irradiation, the topmost surface This method involves heating the material to a temperature that only releases isolated atoms and clusters, and then holding the temperature at that temperature for a certain period of time. In this method, the substrate temperature during growth (during molecular beam irradiation) is low and isolated atoms and clusters are not desorbed.
Since raw material utilization efficiency is high and the molecular beam intensity can be reduced, the cell temperature can be lowered and impure outgassing can be reduced.

However, it becomes necessary to modulate the substrate temperature as the cell shutter opens and closes, which complicates the method.

〔Example〕

FIG. 1 shows the compound semiconductor device manufacturing method of the present invention. In FIG. 1(a), a Ga cell shutter @ is opened to evaporate a Ga molecular beam from a Ga raw material @, and
InP substrate 0 pasted on the substrate boulder by evaporating the cell shutter
G a As was grown on the surface for 20 sec. The substrate temperature was set at 4.00 to 500"c. After that, the main shutter C1 was closed to cut off the molecular beam irradiation from each cell. The molecular beam from Ga cell 0 and In cell 1 ( Because the directivity is good and the spread is small, by closing the main shutter ■, the InP
Irradiation to the substrate is completely cut off. On the other hand, the As atoms evaporated from As cell 1 have poor directivity and large dispersion, and after closing the main shutter 〇, they also go behind the main shutter ■ and irradiate the TnP substrate surface. . This means that even if the InP substrate is heated to 400'C to 500°C with the main shutter ■ closed, the P missing that tends to occur in InP substrates will be absorbed by As.
This is advantageous because it has the effect of being suppressed by the As pressure. Main shutter @ after closing, I
Open the n cell shutter and close the Ga micelle shutter (Fig. 1(b)). This state was maintained for about 1 minute or more. During this period, as mentioned earlier, rnP
Only the excess Ga atoms on the outermost surface of the GaAs thin film layer formed on the substrate (i.e., the isolated atoms and clusters shown in FIG. 5(a)) are removed from the surface,
We were able to reveal a completely flat atomic plane of the growth layer directly below. Also, during this time, by closing the Ga cell shutter [Co., Ltd.] and opening the In cell shutter 0, Ga-t!
It is possible to prevent impurity gas generated from the cell shutter due to reheating of the Lucha soter from directly irradiating the 1nP group and plate, and also to prevent the In molecular beam immediately after opening the In cell shutter [phase]. It is possible to stabilize fluctuations in strength.

Then, by opening the main shutter @, InA
The growth of s can be repeated. For InAs, follow the same procedure as shown in Figure 1.
By periodically stacking GaAs and I n
We were able to fabricate a monoatomic layer superlattice (MSL) of As. FIG. 6 compares the electrical properties of the MSL obtained by the present invention and that obtained for the purpose of manufacturing MSL using the conventional method. The MSL produced using the present invention has significantly improved electron mobility.

Further, a heterostructure as shown in FIG. 7 was fabricated by applying the method according to the present invention at each interface. That is, semi-insulating In
On the P substrate, a single layer of 0.48 InO, 52 As buffer, In 6.5 s Ga o, 47
A S operating layer [phase], Aj? 04B In O,52
As X ”-Sa layer @s Alo, 4.B Ino5
In the process of sequentially growing the 2AS doped layers @, at the interface of each layer, approximately 1
Holding was continued for more than a minute (substrate temperature was 400 to 50°C). FIG. 8 shows a comparison of the electrical characteristics of the heterostructure shown in FIG. 7 formed at each interface using the present invention and that formed using the conventional method. The material in which the heterointerface is formed using the present invention has higher electron mobility. Furthermore, InA produced using such the present invention
MSL consisting of s and GaAs, I n 6.5 B
Ga O, 47As and Aj'o, +s nO, 52A
When we prototyped a field effect transistor using a heterostructure consisting of an s layer, we were able to obtain a field effect transistor with faster operation speed than conventional transistors.

=l← In this example, the InP substrate temperature was maintained at a constant temperature throughout, but under the situation shown in Figure 1 (l), it was decided to raise the InP substrate temperature. Therefore, it was possible to shorten the time required to flatten the outermost surface of the growth layer.

〔Effect of the invention〕

As described in 2 below, the present invention employs a method for each layer in which, after attaching the raw materials listed in 11x to the substrate surface, only surplus atoms such as isolated atoms and Claskue atoms on the outermost surface of the growth layer are removed from the surface. Therefore, it is possible to form a flat layer interface with no unevenness at the atomic layer level, and it is also possible to form an atomic layer superlattice without strictly controlling the molecular beam intensity. It has a unique effect.

[Brief explanation of drawings]

FIGS. 1(a), (b), and (c) are diagrams for explaining the compound semiconductor device manufacturing method of the present invention, and FIG. 2 is a multi-quantum well laser manufactured by the MBE growth method. 3(a) and (b) are diagrams for explaining a conventional compound semiconductor device manufacturing method. Results of Auger electron spectroscopy Figures 5(a) and (b) are cross-sectional views near the surface of the grown layer to explain the state of the outermost surface of the grown layer. Measurement results comparing the electrical properties of a monoatomic layer superlattice with those produced by conventional methods,
Figure 7 shows Ino5aG ao, 4.7 A S and "
FIG. 8 is a cross-sectional view of a heterostructure made of 0.52 AIo, + 8 As. FIG. 8 is a diagram showing the measurement results comparing the electrical characteristics when the structure shown in FIG. 7 was fabricated using the present invention and the conventional method. It is. [Main reference numbers] 1. IOMBE equipment growth chamber 2, semiconductor substrate 8.11 Substrate holder 41. ■Group raw material B cell 5,〃A cell 6,〃B 7,〃A 8,〃B cell shutter 9,■Group raw material A7 shutter 12, 1nP substrate 1.3. In cell 1, 4. Ga cell 15, As cell 16, In raw material 1.7. Ga raw material 18, As raw material 10, In cell shutter 20, Ga tt 21, As'/22, main shutter 23, semi-insulating InP substrate 24, A%4B InO,52As buffer single layer 2
5, I no, 53 GaO, +7 A, s operating layer 26- A 1o, 4 a I no, s 2
AS spacer single layer 27, A16.4B In6.
52 As doping layer A, P-type GaAs B, P-type Gax'Al! , -x: AsC, non-doped GaAs well D, non-doped Gax A, g, -xAs barrier E, n-type GakAl-, xAs F, n-type GaAs se-7, ψ flat t-t-+＞円Φ淋su- H, 1-1- to Shinjiaji/Misaki

Claims (2)

[Claims] (1) Inside a growth chamber maintained under high vacuum, a raw material stored in a cell is made to fly in a predetermined direction, and the raw material is attached to the surface of a substrate supported within the growth chamber to grow as a single crystal. In the line epitaxial growth method, after the above raw material is deposited on the substrate surface, the substrate temperature is kept as it is, or the substrate temperature is kept after being heated to a high temperature, and the excess that does not form a complete one-atomic plane on the outermost surface is It is characterized by the fact that only atoms are removed from the surface to reveal a completely flat growth layer atomic plane directly below, and then different types of raw materials are attached to form a flat interface with no irregularities. A method for manufacturing a compound semiconductor device. (2) A method for manufacturing a compound semiconductor device according to claim 1, characterized in that growth layers of different types each having a thickness of one atomic plane are alternately and periodically stacked.