JP2764595B2 - Method for manufacturing semiconductor device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a method for forming a monoatomic-layer thin layer of S (sulfur) on the surface of a semiconductor substrate having a compound semiconductor region containing Ga (gallium) as a main component. And a method of manufacturing a semiconductor device having a coating layer formed thereon.

2. Description of the Related Art Problems to be solved by the prior art and the invention The surface of GaAs (gallium sulfide) has a peculiar instability, which is one reason that the commercialization of GaAs semiconductor devices has not progressed as expected. Regarding a Schottky barrier (metal-semiconductor rectification barrier) formed on a compound semiconductor region made of GaAs, it is difficult to form a Schottky barrier having a desired via height or to form a Schottky barrier with a small reverse current with good reproducibility. Was.

On the other hand, the present inventors have proposed an MIS comprising an n-type GaAs-SiO ₂ film (silicon oxide film) -Al (aluminum) electrode system.
In the (metal-insulator-semiconductor) structure, it has been found that a good MIS characteristic can be obtained by forming an S thin layer at the monoatomic layer level on the GaAs surface by treating the GaAs surface with an ammonium sulfide solution. Also, for a Schottky barrier structure composed of an n-type GaAs-Al electrode, etc., the GaAs surface is treated with an ammonium sulfide solution to form S (sulfur) on the GaAs surface.
It has been found that when a thin layer is formed, good Schottky barrier characteristics can be obtained. In addition, the results of these studies were presented at the 20th Solid State Device and Materials Conference (August 24 to 26, 1988) sponsored by the Japan Society of Applied Physics.

However, since the S thin layer is extremely thin, such as a monoatomic layer or a diatomic layer, the S of the S thin layer is removed from the GaAs surface during the process of forming the metal layer and the insulating layer on the upper surface of the S thin layer. It may be dissociated and the surface stabilizing effect of the S thin layer may be impaired.

Therefore, an object of the present invention is to solve the above problem and to provide a method of manufacturing a semiconductor device capable of forming a metal layer or an insulating layer on the upper surface of a thin S layer satisfactorily.

Means for Solving the Problems In a method of manufacturing a semiconductor device according to the present invention, a thin layer made of S (sulfur) is formed on a surface of a compound semiconductor region of a semiconductor substrate having a compound semiconductor region containing Ga (gallium) as a main component. After formation, a coating layer is formed on the upper surface of the thin layer while the semiconductor substrate is cooled.

Further, in the method for manufacturing a semiconductor device according to the present invention, after the coating layer made of metal is oxidized to form the first insulating layer,
A second insulating layer is further formed on the upper surface of the first insulating layer.

The coating layer is formed by vacuum deposition while cooling to a temperature of -50 ° C or less until the layer thickness reaches 10 °. Further, the thickness of the coating layer made of a metal to be converted into the first insulating layer is formed to 300 ° or less.

Since the coating layer is formed while the semiconductor substrate is cooled, the number of S atoms dissociated from the surface of the compound semiconductor region is reduced. In the case where the coating layer is a metal layer, a structure in which the compound semiconductor region is coated with an insulator can be formed by forming the coating layer very thin and then oxidizing it to convert it to a metal oxide layer. Of course, the coating layer can be left as a metal layer and used for a part of a semiconductor structure that forms a Schottky barrier and ohmic contact. When the coating layer is an insulating layer,
It can be used as it is for the surface stabilization structure and the MIS structure by the coating layer.

Embodiment 1 A method of forming a Schottky barrier will be described as an embodiment of a method of manufacturing a semiconductor device according to the present invention with reference to FIGS.

First, as shown in FIG. 1A, a semiconductor substrate (1) including an n-type compound semiconductor region (2) made of GaAs, H ₂ SO
₄ to prepare an aqueous solution of the etchant and ammonium sulfide retention concentrations 1N to room temperature consisting of (sulphate) -H ₂ O ₂ (hydrogen peroxide) -H ₂ O (water).

The impurity concentration of the compound semiconductor region (2) is about 5 × 10 ¹⁵ cm
It is ^-3 . Ammonium sulfide contains about 8% S in excess of the standard compound represented by the chemical formula (NH ₄ ) ₂ S, and is specifically represented by the chemical formula: (NH ₄ ) ₂ Sx (x = 1.08). Ammonium sulfide. It is desirable that x ≧ 1.02.

Next, cleaned and lightly etched with a solution consisting of H ₂ SO ₄ (sulfuric acid) -H ₂ O ₂ (hydrogen peroxide) -H ₂ O (water) surface of the compound semiconductor region (2).

The cleaned semiconductor substrate (1) is immersed in the solution of ammonium sulfide. The immersion time can be selected widely from several seconds to several hours. The semiconductor substrate (1) is taken out of the solution of ammonium sulfide, and the compound semiconductor region (2)
N ₂ (nitrogen) gas is blown to the surface of the, and the attached solution is removed. As a result, the surface of the compound semiconductor region (2) has a thickness of about 10 nm (100 °) and is covered with a film on an amorphous phase containing S as a main component. Subsequently, when the semiconductor substrate (1) is left in a vacuum (in a reduced-pressure atmosphere) for about 30 minutes, the coating on the amorphous material is almost completely lost.
On the surface of the obtained compound semiconductor region (2), as shown in FIG. 1 (B), an S thin layer (3) in a bonding state with Ga and As is formed. According to the observation by Auger electron spectroscopy, the S thin layer (3) has an extremely small thickness of about a monoatomic layer or a diatomic layer because S constituting ammonium sulfide is adsorbed on the GaAs surface. In addition, in order to obtain the S thin layer (3), another appropriate method may be adopted, such as rapidly diluting the solution with pure water after immersion in the ammonium sulfide solution.

Further, as shown in FIG. 1 (C), a metal layer made of Al (coating) was formed on the upper surface of the S thin layer (3) using an ultrahigh vacuum type vacuum evaporation apparatus schematically shown in FIG. The layer (4) is provided to form a barrier. The vacuum evaporation apparatus used in this embodiment is a bell-shaped vacuum vessel (bell jar).
(5) A support base (6) having a heater (not shown) for temperature adjustment built therein, a refrigerant container (7) adjacent to the support table (6), and a refrigerant container (7). It has an introduction passage (8) and a discharge passage (9), a boat-shaped evaporating dish (10), and an electron gun (11). The support (6) and the container (7) constitute a cooler (13).

When forming the metal layer (4), one main surface of the semiconductor substrate (1) having the S thin layer (3) shown in FIG. 1 (B) [the main surface on which the S thin layer (3) is formed) ] To the evaporating dish (10), the semiconductor substrate (1) is mounted on the support (6). The pressure inside the bell jar (5) is reduced to 1 × 10 ⁻⁷ Torr or more, and an Al plate material (12) as an evaporation source for forming the metal layer (4) is placed in the boat-type evaporation dish (10). ing. In the present embodiment, the support base (6) is attached to the container (7) for the refrigerant in order to form the metal layer (4) while the semiconductor substrate (1) is cooled. When liquid nitrogen is introduced into the container (7) through the introduction path (8), the semiconductor substrate (1) in contact with the container (7) via the support (6) is -100 ° C or lower, for example, about -150 ° C. Cooled to low temperature. In this state, when the surface of the Al plate (12) is heated by the electron beam irradiated from the electron gun (11), Al evaporated from the Al plate (12) adheres to the upper surface of the S thin layer (3). The nitrogen gas vaporized in the container (7) is discharged to the outside of the vacuum evaporation apparatus through the discharge path (9). The temperature of the semiconductor substrate (1) is adjusted mainly by a heater (not shown) built in the support (6).

As described above, a metal layer (4) having a thickness of about 2 μm is formed on the upper surface of the S thin layer (3), and a Schottky barrier is formed between the metal layer (4) and the compound semiconductor region (2). In FIG. 1 (C), the S thin layer (3) is drawn for convenience so as to exist as it is in FIG. 1 (B), but the S thin layer (3) is an extremely thin film. Therefore, it is not clear how the S thin layer (3) actually exists in the state of FIG. 1 (C).

In the present embodiment, the dissociation of S atoms deposited on the surface of the compound semiconductor region (2) is reduced by cooling the semiconductor substrate (1) during vacuum deposition, and the compound semiconductor region (2) formed by the S thin layer (3) is reduced. ) The surface stabilizing effect of (1) is exhibited favorably and reliably. Therefore, the barrier height φbn is a value (φbn ≒ 0.4 eV) that reflects the work function of Al relatively faithfully.
A Schottky barrier with a small reverse current can be formed.

Embodiment 2 Next, a method of forming an MIS structure according to a second embodiment of the present invention will be described with reference to FIG.

First, the compound semiconductor region (2) was formed in the same manner as in Example 1.
After preparing a semiconductor substrate (1) having an extremely thin S layer (3) formed on the surface thereof, as shown in FIG. 3 (A), a metal made of Al is formed on the upper surface of the S thin layer (3). A layer (coating layer) (21) is formed. As in the first embodiment, the metal layer (21) is formed by depositing Al under vacuum while cooling the semiconductor substrate (1) to a temperature of -100 ° C or lower, for example, about -150 ° C. However, in the second embodiment, the thickness of the metal layer (21) is significantly smaller than that of the first embodiment, and is about 100 °.

Next, as shown in FIG. 3 (B), the semiconductor substrate (1) shown in FIG. 3 (A) on which the metal layer (21) is formed is heated in air to a temperature of about 350 ° C. The metal layer (21) is thermally oxidized. Thereby, the metal layer (21) is changed to a metal oxide layer (22) made of Al ₂ O ₃ (aluminum oxide) as an insulator as a first insulating layer. In the thermal oxidation step, since the metal layer (21) is formed in close contact with the upper surface of the S thin layer (3), the S atoms are not substantially dissociated from the surface of the compound semiconductor region (2) by heating. Therefore, the surface stabilizing effect of the S thin layer (3) is not impaired.

Next, as shown in FIG. 3 (C), the metal oxide layer (2
2) The well-known plasma CVD (Chemical Vapor Depos)
An SiO ₂ film (silicon oxide film) (23) is formed to a thickness of about 0.1 μm by a photo-chemical method. SiO ₂ film (2
An insulating film composed of only the metal oxide layer (22) without forming 3) may be used. However, the metal oxide layer (22) as the first insulating layer and the SiO ₂ film ( A better insulating film can be formed by using the insulating film composed of two layers in the above 23). In the plasma CVD, the semiconductor substrate (1) is heated to a temperature of about 350 ° C., but the metal oxide layer (22) is formed on the upper surface of the S thin layer (3). No problem occurs.

Subsequently, as shown in FIG. 3 (D), a metal layer (24) of Al having a thickness of about 2 μm is formed on the upper surface of the SiO ₂ film (23) by a well-known vacuum deposition method. Vacuum deposition of the metal layer (24) is a general method without cooling the semiconductor substrate (1), but the metal oxide layer (22) and the metal oxide layer (22) are formed on the upper surface of the S thin layer (3).
Since the insulating film made of the SiO ₂ film (23) is formed, no problem occurs as in the above oxidation step.

In the MIS structure formed as described above, the insulating film and the metal layer can be formed on the upper surface of the S thin layer (3) while minimizing the dissociation of S atoms from the S thin layer (3). Thus, the surface stabilizing effect of the S thin layer (3) is well maintained, and good MIS characteristics are obtained.

Modifications Various modifications can be made to the above embodiment of the present invention. For example, in order to form the S thin layer (3), a method using a solution treatment of ammonium sulfide as in Examples 1 and 2 is preferable. However, the S thin layer (3) may be formed by a method using another solution treatment such as sodium sulfide.

The surface stabilizing effect of the S thin layer (3) is based on a group III-V compound semiconductor mainly composed of Ga such as GaAs [GaAs, GaP (gallium phosphide), GaAsP (gallium arsenide phosphide). , GaAlAs (gallium aluminide arsenide)], the compound semiconductor region (2) may be a compound semiconductor.

Furthermore, the cooling of the semiconductor substrate (1) is particularly important in the initial stage of forming the coating layer. The initial stage is a period until the coating layer is empirically formed to a thickness of about 10 mm. Therefore, until the coating layer is formed to a thickness of 10 °, preferably 50 °, the semiconductor substrate (1) is cooled so that the overall temperature becomes about 50 ° C. or less, preferably -100 ° C. or less. It is preferable to form a coating layer. Thereby, the effect of preventing the dissociation of S atoms from the S thin layer becomes remarkable. After the initial stage, the coating layer can be continuously formed at the same temperature or a higher temperature.

Various materials can be selected for the coating layer as needed. For example, vacuum-deposited Si using quartz and alumina as deposition sources
It may be an insulating layer such as an O ₂ film or an Al ₂ O ₃ film. However, since the metal layer is more likely to cause migration (movement of constituent atoms) than the insulating layer, it is easier to form a layer of relatively good film quality on a low-temperature surface. Conditions can be easily set. Note that the metal layer to be converted to an insulating layer needs to be easily oxidized and converted to an insulator, and Al and Ta (tantalum) are preferable.

When the metal layer (21) is oxidized to form the metal oxide layer (22) as in the second embodiment, the thickness of the metal layer (21) should be about 300 mm or less to facilitate oxidation. Is practical. In order to cover the S thin layer (3) securely, 10Å
The above is practical. As a method of oxidizing the metal layer (21), thermal oxidation, plasma oxidation, anodic oxidation, or the like may be appropriately selected. If the metal layer (21) is as thin as about 10 °, natural oxidation or light thermal oxidation close to this may be used.

Effects of the Invention As described above, according to the present invention, a coating layer can be formed on an S thin layer formed on the surface of a compound semiconductor region without substantially impairing the surface stabilizing effect of the S thin layer. Therefore, the Schottky barrier and the ohmic contact, and furthermore, the surface protection structure and the MIS structure by the insulator coating can be formed so as to have good characteristics, respectively, which contributes to the improvement of the characteristics and the production yield of the semiconductor device using the compound semiconductor. .

[Brief description of the drawings]

FIG. 1 is a process diagram showing a method of manufacturing a semiconductor device according to one embodiment of the present invention, FIG. 2 is a cross-sectional view of an ultra-high vacuum type vacuum evaporation apparatus schematically shown, and FIG. FIG. 4 is a process chart illustrating a method for manufacturing a semiconductor device according to an embodiment. (1) ... semiconductor substrate, (2) ... compound semiconductor region,
(3) ... S thin layer, (4), (21) ... metal layer (coating layer), (13) ... cooler, (22) ... metal oxide layer (first insulating layer), (23) Silicon oxide film (second insulating layer)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI // H01L 21/203 (56) References JP-A-58-141576 (JP, A) JP-A-64-8613 (JP, A JP-A-2-137370 (JP, A) JP-A-2-185066 (JP, A) Japan Journal of Applied Physics Vol. 27, No. 7, July, 1988, PP. L1331-1333 (58) Fields investigated (Int.Cl. ⁶ , DB name) H01L 21/203 H01L 21/28-21/288 H01L 21/336-21/338 H01L 21/363 H01L 21/44-21 / 445 H01L 27/095-27/098 H01L 29/40-29 / 43,29 / 47 H01L 29/76 H01L 29/772-29/78 H01L 29/80-29/812 H01L 29/872

Claims (5)

(57) [Claims] 1. A semiconductor substrate having a compound semiconductor region containing Ga (gallium) as a main component. After forming a thin layer made of S (sulfur) on the surface of the compound semiconductor region, the semiconductor substrate is put into a cooler. A method of manufacturing a semiconductor device, comprising: forming a coating layer on an upper surface of the thin layer in a state where the semiconductor substrate is cooled by being attached. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the coating layer is formed by vacuum deposition while the semiconductor substrate is cooled to -50 ° C. or less until the thickness of the coating layer reaches 10 °. Method. 3. A state in which a thin layer made of S (sulfur) is formed on the surface of the compound semiconductor region of a semiconductor substrate having a compound semiconductor region containing Ga (gallium) as a main component, and the semiconductor substrate is cooled. Forming a coating layer made of metal on the upper surface of the thin layer, oxidizing the coating layer to form a first insulating layer, and further forming a second insulating layer on the upper surface of the first insulating layer. A method of manufacturing a semiconductor device. 4. The method of manufacturing a semiconductor device according to claim 3, wherein the coating layer is formed by vacuum deposition while the semiconductor substrate is cooled to -50 ° C. or less until the thickness of the coating layer reaches 10 °. Method. 5. The method of manufacturing a semiconductor device according to claim 3, wherein said coating layer has a thickness of 300 ° or less.