JPS6260218A - Thin film growth method - Google Patents

Abstract

PURPOSE:To prevent the electric characteristics from deteriorating by a method wherein a compound semiconductor substrate or compound semiconductor basic film is irradiated with Sb molecular beam before they are epitaxially grown and after removing any impurity atoms on the surface, a specified compound semiconductor thin film is grown. CONSTITUTION:An InP substrate 28 is heated while keeping the degree of vacuum near the substrate 28 at 1X10<-6>Torr-1X10<-5>Torr using As4 molecular beam (a) and then further irradiated with Sb molecular beam (b) at the intensity of 1X10<-8>Torr. Later the cell shutter 31 of an In cell 33 and the other cell shutter 34 of Ga cell 36 are opened and then an InGaAs thin film is continuously grown on the InP substrate 28. In other words, the compound semiconductor thin film is irradiated with electrically neutral Sb molecular beam immediately before said thin film is molecular beam-epitaxially grown. Through these procedures, the impurity carrier concentration can be reduced by one figure to increase the electron mobility improving the electric characteristics of InGaAs thin film.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a crystal growth method for forming a compound semiconductor thin film used as a microwave device or a light emitting/light receiving device. For example, in a high electron mobility transistor (hereinafter abbreviated as "HEMT") as shown in FIG. 2, it is necessary to form a thin film with a thickness of several 100 Å to several 100 OA as a channel layer. This invention relates to a thin film growth method for forming structures.

(Prior art and its problems) If impurity atoms remain on the surface of the substrate or the underlying thin film layer before thin film growth, the electrical properties of the thin film layer formed thereon may deteriorate, or Or there is a surface condition. For this reason, thin film growth methods such as those described below have been conventionally used.

8, 4, and 5 are diagrams for explaining the conventional molecular beam epitaxial growth method (hereinafter abbreviated as MBE method) for forming a conventional ■-V group compound semiconductor thin film.
FIG. 2 is a schematic diagram of the growth chamber of the E apparatus viewed from above.

In Figure 3, ■ is a substrate holder, ■ is a substrate, ■ is a cell shutter, ■ is a ■ group raw material (for example, Ga or In), ■ is a cell, ■ is a V group raw material (for example, As or P), and ■ is a It is a cell.

In the conventional method for growing ■-V group compound semiconductor thin films by MBE growth, in Figure 3, group V elements are made into molecules or atoms from cell ■ and irradiated onto substrate ■ in a growth chamber with a high degree of vacuum. By doing so, the substrate temperature is increased while suppressing the desorption of Group V elements from the substrate (1), and only the impurity atoms on the substrate surface are desorbed. However, it is necessary to heat the substrate to a high temperature higher than this temperature.

However, by heating the substrate to a high temperature higher than the above-mentioned critical temperature, the substrate holder (2) is also heated to a high temperature due to thermal conduction, and more impurity gas is desorbed from the substrate holder (2). This results in a total reduction of the Huck-Clland vacuum in the growth chamber, which increases the impurity concentration of the subsequently grown thin film layer and deteriorates the electrical properties. Separately, for example, after the entire thin film layer is grown on the substrate, electrodes are formed or microfabrication is performed in the atmosphere outside the growth chamber, and then the upper thin film layer is regrown on top of it. In this case, it becomes necessary to remove impurities on the underlying thin film layer. At this time, if the material is heated to a high temperature higher than the critical temperature, an alloying reaction will occur between the underlying thin film layer and the electrode metal more than necessary, and the properties of the thin film layer will deteriorate. Alternatively, if the underlying thin film layer has a multilayer thin film structure, doping atoms or matrix atoms may diffuse between adjacent thin film layers, deteriorating the electrical properties of the thin film layer interface or the thin film layer itself. Put it away.

1 [Other MB for growing 1-V compound semiconductor thin film
As the E method, the method shown in FIG. 4 has also been conventionally used. In Figure 4, ■ is a substrate holder, ■ is a substrate, [phase] is an ion gun, ■, ■ is a cell shutter, O is a group ■ raw material, ■ is a cell, ■ is a group V raw material, [phase] is a cell, O is Ar
This is the gas inlet. In the method shown in FIG. 4, Ar gas is introduced into a vacuum apparatus, and the surface of the substrate (1) is irradiated with an Ar ion beam using an ion gun (phase) (k). As a result, the surface of the substrate (1) can be cleaned without increasing the substrate temperature. However, due to the irradiation with the Ar ion beam, the surface of the substrate (1) is severely damaged by radiation, and the crystal lattice on the surface of the substrate (2) is significantly disturbed, resulting in the generation of many defects. As a result of this, the crystallinity of the thin film layer grown on the substrate surface is also significantly reduced, and the electrical properties are also deteriorated.

Furthermore, as shown in FIG. 5, chemical vapor phase etching of the substrate surface using a reactive gas (such as HCA' gas) immediately before growth, which is commonly performed in vapor phase epitaxial growth, can be applied to MBE. It is also possible. In Figure 5, [phase] is the substrate holder, [phase]
is the substrate, ■, [phase] is the cell shutter, ■ is the ■ group raw material,
@ indicates a cell, [Yes] indicates a group V raw material, [phase] indicates a cell, and [phase] indicates a reactive gas inlet. In the method shown in FIG. 5, as in the method shown in FIG. It is not necessary to heat the substrate to a high temperature, and furthermore, as in the method shown in FIG. 4, the substrate surface can be cleaned without causing irradiation damage by an unaccelerated ion beam. However, introducing such reactive gas t1 into the ultra-high vacuum equipment will also etch the materials that make up the ultra-high vacuum equipment and the exhaust system materials. It also reacts with fine lines.

This is a significant problem in stable operation of ultra-high vacuum equipment. Furthermore, etching of device constituent materials other than the substrate surface means that new impurity gas is generated due to etching, which deteriorates the electrical characteristics of the subsequently grown I-V compound semiconductor thin film. It can also be a cause.

(Means for problem decomposition method) Therefore, in order to solve the above problems, the present inventors
Various studies were carried out including Auger electron spectroscopic analysis of the surface of compound semiconductor substrates or compound semiconductor underlayers. As a result, we discovered the following phenomena. That is, for example, as shown in Figure 6, impurity atoms such as carbon C and oxygen O are present on the InP substrate surface after heating cleaning at 400°C for 1 hour while irradiating all As molecules, which are group V elements. remains. However, by performing heating cleaning at 400°C for 1 hour while irradiating As molecules, and irradiating the sb molecular beam for about 2 seconds just before the end of the heating cleaning, carbon C Auger electron peaks caused by impurity atoms such as oxygen and O have completely disappeared. A similar phenomenon was observed when heating cleaning was performed at 400° C. for 10 minutes and then Sb molecular beam was irradiated just before the end of heating cleaning. Furthermore, when irradiating with an Sb molecular beam, it is necessary that the number of Sb atoms to be irradiated is smaller than the number required to form an entire one atomic layer on the compound semiconductor substrate or the compound semiconductor base film. This is because when irradiation with more group III atoms than is required to form one atomic layer results in the removal of impurity atoms such as oxygen O and carbon C, a significant surplus of Sb atoms remains. This changes the composition and atomic spacing of the surface of the ground film, which adversely affects the subsequent growth of the compound semiconductor thin film.

Figure 7 shows the spectrum of Auger electron spectroscopy when approximately a/l O, the number of atoms required to form one atomic layer of Sb molecular beam kx, is supplied. Although the C peak has disappeared, the sb peak has not appeared, indicating that cleaning is being performed without leaving excess sb atoms on the InP substrate surface. means. The surface cleaning effect of irradiation with Sb molecular beams was observed even when the substrate temperature was 300 to 500°C.

In this way, all of the sb molecular beams can be removed from the impurity atoms on the surface of the compound semiconductor substrate or compound semiconductor base film constituting the atomic layer, and unlike accelerated ion beams, neutral atoms can be removed. Therefore, there is no irradiation damage 2 to the surface. Furthermore, unlike reactive gases, it does not etch the vacuum device itself.

(Example) FIG. 1 is a diagram for explaining an example of the thin film growing method according to the present invention. In Figure 1, [phase] is the substrate holder, [phase] is the InP substrate, [phase] is the sb raw material [phase]
indicates the cell, ■ indicates the cell shutter, and ■ indicates the In% of the ■ group raw material.
@ is cell, 0 is cell shutter, [phase] Ga, [phase]
indicates a cell, O indicates an As raw material, and ■ indicates a cell. In the embodiment shown in FIG. 1, an InP substrate [ temperature of about 400'
After heating for 10 minutes at Q, the Sb molecular beam was further heated on the InP substrate [phase] by opening the cell shutter [with] about #CI n O, 53Ga O, 47As.
The thin film was grown to approximately Q, 211 m. When an Ino, 5a GaO, 47As thin film on a semi-insulating InP substrate is formed to a thickness of 0.2 μm using this example, its electron mobility at room temperature is 11oooa! /V-3ec
, and the carrier concentration was lXl015an-8, but when heating cleaning was performed at 400°C for 10 minutes while irradiating with the As 4 molecular beam at 1xlO'Torr, no particles of 0.2 μm were formed. The electron mobility at room temperature is 8000 crl/V-sec, and the carrier concentration is 2×IO”QT+-8, which is 0.
That is, according to this example, the impurity carrier concentration is
can be significantly lowered, electron mobility also increases, and I n
The electrical properties of the O,53Ga O,47As thin film can be improved.

Furthermore, similar effects are observed even when the substrate temperature is in the range of 300 to 500°C, and Inoss GaO,
The electrical properties of the 47AS thin film were improved.

(Effects of the Invention) As described above, the present invention allows electrically neutral Sb molecular beams to be grown immediately before molecular beam epitaxial growth of a compound semiconductor thin film on a compound semiconductor substrate or a compound semiconductor base film. By irradiating a smaller number of particles than the number needed to form an atomic plane, residual impurities on the surface of the substrate or underlying film can be removed without causing damage due to irradiation while maintaining the temperature of the substrate or underlying film at a low temperature. It has a unique effect.

This effect is not observed even when the temperature of the substrate or underlying film is 300°C or higher.

[Brief explanation of the drawing]

Figure 1 is a diagram for explaining the entire thin film growth method according to the present invention, Figure 2 is a schematic cross-sectional diagram of a transistor with high electron mobility, and Figure 8 is a diagram for explaining the conventional heating cleaning method. Figure 4 is a diagram for explaining a conventional ion sputter cleaning method, Figure 5 is a diagram for explaining a cleaning method using a reactive gas, and Figure 6 is a diagram for explaining a cleaning method using a reactive gas. Figure 7 shows the results of Auger electron spectroscopy on the surface of an InP substrate after thermal cleaning at a low temperature and further irradiation with an sb molecular beam. It is a figure showing an analysis result. ■, ■, ■, [Phase] Substrate holder ■, ■, [Phase], [Phase] Compound semiconductor substrate or compound semiconductor base film ■, ■, ^, ■, [With] Cell shutter ■
, [Phase], ■ ■ Group raw material ■, [Phase], [Phase] ■ Group cell ■, [Phase], [Yes] Group V raw material ■, [Phase], [Phase] Group V seven group ■ Ion gun ■ Ar Gas inlet [phase] Reactive gas inlet [phase] Semi-insulating GaAs substrate [phase] GaAs buffer layer ■ GaAs channel layer @ Electron supply layer @ Semiconductor containing a high concentration of P-type impurities and having a large electron affinity ■ Gate electrode [with] Alloyed region [phase] Source electrode and drain electrode ■ Secondary electron storage layer [phase] In Raw material [phase] In Cell [phase] Ga Raw material [phase] Ga Cell [phase] As Raw material [phase] As Cell [phase] sb raw material No. 1 Diagram collection 2N Hayabusa 3 times 4 times

Claims (1)

[Claims] (1) In the molecular beam epitaxial growth method for growing a compound semiconductor thin film made of group III elements and group V elements on a compound semiconductor substrate or a compound semiconductor base film, an antimony (Sb) molecular beam is After removing impurity atoms on the surface of the compound semiconductor substrate or compound semiconductor base film by irradiating the semiconductor substrate or the compound semiconductor base film, a compound semiconductor thin film consisting of group III elements and group V elements is grown. Characteristic thin film growth method.