JPH10242096A - Method of stabilizing gaas layer surface, manufacturing gaas semiconductor device and method for forming semiconductor layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove an oxide from a GaAs layer surface and passivate the surface with P, etc., such that P atoms partly enter As sites to form GaP layer difficult to oxidize on the GaAs surface, by exposing this surface to an H-contg. plasma and then phosphine-contg. plasma. SOLUTION: A plasma irradiation 11 is applied to a GaAs substrate 1, by exposing it to an H-contg. plasma and then plasma of phosphine. The H-contg. plasma removes oxides from the GaAs layer surface and phosphine plasma passivates the surface with a P or GaP protective layer or film. These plasmas are pref. successively irradiated on the substrate 1. The irradiation times of the H-plasma and phosphine plasma are pref. approximately 10min and 20min, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment method for removing an oxide on the surface of a GaAs layer and thereafter preventing the surface from being oxidized.
The present invention relates to a method for stabilizing the surface of an aAs layer, a method for manufacturing a GaAs semiconductor device, and a method for forming a semiconductor layer.

[0002]

2. Description of the Related Art GaAs semiconductors are used for manufacturing semiconductor devices such as optical devices and high-speed devices. In the manufacturing process, the semiconductor substrate is subjected to various treatments on the manufacturing line until the semiconductor device is completed, and is also exposed to the air in the line. A natural oxide film is formed on the surface of the semiconductor exposed to the atmosphere, but a surface oxide film induced by a thermal process and a plasma process is also formed. For removal of these oxide films, in the case of a GaAs semiconductor, for example, a GaAs substrate is immersed in a hydrofluoric acid solution to form Ga ₂ O ₃ formed on the surface.
And so on.

[0003] Also, the literature (JAPANESE JOURNAL OF APPLIE)
D PHYSICS VOL.29, No.6, JUNE, 1990, pp.L864-866, Sugino
et. al.) discloses a method of exposing a GaAs substrate to phosphine plasma to remove Ga oxide.

[0004]

However, the method of removing an oxide film in which a GaAs substrate is treated with a hydrofluoric acid solution has the following problems. First, since only the Ga oxide is removed and the oxide of As cannot be removed, the surface becomes excessive (As rich). In addition, there is no function of protecting the surface after removing the oxide, and for example, if the surface is exposed to the air after the removal, the oxide is formed again on the surface.

[0005] In addition, these cause undesirable characteristics in the characteristics of the semiconductor device. For example, A
When a gate electrode having a Schottky junction is formed on the s-rich surface, the leakage current of the gate increases.
Further, As atoms entering the site of Ga atoms are called anti-site As, and anti-site As forms a long-lived level. When carriers are trapped in this level, the drain is affected by the carriers. The change in the current cannot follow the change in the gate voltage, which causes a so-called drain lag.

In the method described in the above document, G
Although the oxide a can be removed, it is difficult to remove As ₂ O ₃ , which is an oxide of arsenic (As), and there remains a problem in device characteristics.

Accordingly, an object of the present invention is to use a surface treatment method for removing oxides on a GaAs surface and preventing an oxide film from being formed on the surface after the removal.
An object of the present invention is to provide a method for stabilizing the surface of an As layer, a method for manufacturing a GaAs semiconductor device, and a method for forming a semiconductor layer on a GaAs layer.

[0008]

Therefore, the present invention has the following configuration.

According to a method for stabilizing the surface of a GaAs layer according to the present invention, the method for stabilizing the surface of a GaAs layer used in the manufacture of a semiconductor device comprises exposing the surface of the GaAs layer to a plasma of a hydrogen-containing gas, Is performed by exposing to the plasma.

As described above, when the surface of the GaAs layer is exposed to the plasma of the hydrogen-containing gas, GaAs is generated by radicals of hydrogen.
The oxide of s is removed. Then, when the GaAs surface is exposed to a phosphine-containing gas plasma, the GaAs surface is protected by phosphorus (P). Some of the phosphorus atoms enter the As site and
At least a part of the As surface becomes GaP. For this reason,
Even if the surface is protected and exposed to the atmosphere, the surface from which the oxide has been removed is not oxidized again, so that the surface is stabilized.

In the method of manufacturing a GaAs semiconductor device according to the present invention, an introduction step of introducing an impurity into a GaAs layer by an ion implantation method, a cap film step of forming a cap film on the GaAs layer after the introduction step, and a cap film step A GaAs semiconductor device manufacturing method comprising: an active layer step of activating impurities to form an active layer by activating heat and a gate step of forming a Schottky gate electrode on the active layer. And at least one step between the active layer step and the gate step
A plasma treatment is performed in which the surface of the s layer is exposed to a plasma of a hydrogen-containing gas and then to a plasma of a phosphine-containing gas.

As described above, when the surface of the GaAs layer is exposed to the plasma of the hydrogen-containing gas between the introduction step and the cap film step, oxides on the GaAs layer surface are removed by hydrogen radicals. Next, when the substrate is exposed to a phosphine-containing gas plasma, the surface of the GaAs layer is stabilized as described above. Therefore, the activation and annealing of the impurities in the active layer are performed stably. In addition, between the active layer process and the gate process, when a plasma treatment is performed by exposing to a plasma of a hydrogen-containing gas and then to a plasma of a phosphine-containing gas, the oxide on the surface is removed and protected as described above. Is stabilized. Therefore, the interface between the active layer and the gate electrode (gate interface) can be formed with good reproducibility.

In the method of forming a semiconductor layer according to the present invention,
In the method for forming a semiconductor layer on a GaAs layer, before forming the semiconductor layer, a plasma treatment is performed in which the surface of the GaAs layer is exposed to a plasma of a hydrogen-containing gas and then exposed to a plasma of a phosphine-containing gas.

As described above, when the surface of the GaAs layer is exposed to the plasma of the hydrogen-containing gas before forming the semiconductor layer on the GaAs layer, and then subjected to the plasma treatment of the plasma of the phosphine-containing gas, the oxide on the GaAs surface becomes oxide. Is removed, a protective layer or a protective film is formed on the surface as described above. Therefore, even if the surface is exposed to air, the surface is not oxidized again, so that the semiconductor layer is formed stably and defects of the formed semiconductor layer are reduced.

In the method for forming a semiconductor layer according to the present invention,
In a method for manufacturing a semiconductor layer in which a GaAs film is grown on a GaAs layer, a plasma treatment is performed in which a GaAs film surface is exposed to a hydrogen-containing gas plasma and then exposed to a phosphine-containing gas plasma.

As described above, when the GaAs film is formed on the GaAs layer, and the surface is exposed to the plasma of the hydrogen-containing gas and then to the plasma of the phosphine-containing gas, the oxide on the surface of the GaAs film is removed. After that, a protective layer or a protective film is formed on the surface as described above. For this reason, the surface is not oxidized again even when exposed to air, so that a GaAs film whose surface is stabilized is formed.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the accompanying drawings. In addition, the same portions are denoted by the same reference numerals, and overlapping description will be omitted.

FIGS. 1 and 2 show GaAs according to the present invention.
FIG. 2 is a schematic process cross-sectional view showing one embodiment of a method for manufacturing a GaAs semiconductor device, for describing a surface treatment method and the like of s. Based on these, a method for manufacturing a GaAs semiconductor device will be described. Although the case where the semi-insulating GaAs substrate 1 is used will be described, a substrate in which a GaAs semiconductor layer is formed on an insulating substrate or the like may be used. Hereinafter, a field effect transistor having a Schottky contact (hereinafter referred to as an FET) will be described as an example of a semiconductor device. However, the surface treatment method according to the present invention is not limited to this. Electron Mobili
ty Transistor: HEMT, MIS (Metal Insulator Sem)
The present invention can also be used for a method of manufacturing a structure FET or the like.

An N-type first impurity layer 5 is formed by introducing an impurity on the GaAs substrate 1 (FIG. 1A). The N-type first impurity layer 5 becomes the active layer 15 when the impurity is activated by the heat treatment, and thus is formed between the source and the drain of a FET to be formed later. The impurity layer 5 is formed, for example, by performing ion implantation using the photoresist 3 patterned by photolithography as a mask. As an example of conditions for ion implantation, Si is used as an impurity, an acceleration voltage is 30 [keV], and a dose is 2 × 10 ¹² [cm ⁻² ]. This condition is determined based on the performance of the manufactured FET, such as the threshold voltage and the transconductance.

Next, an impurity is introduced into the GaAs substrate 1 to form a high-concentration N-type second impurity layer 9 (FIG. 1).
(B)). When the impurities are activated by the heat treatment, the N-type second impurity layer 9 becomes the N + layer 19 which becomes the source and drain diffusion layers of the FET. The source and drain diffusion layers are formed in an isolated region on the substrate 1 in the N-type first impurity layer 5.
Are formed. The impurity layer 9 is formed by performing ion implantation using the photoresist 7 patterned as described above as a mask. As an example of conditions for ion implantation, Si is used as an impurity, and an acceleration voltage of 120 [ke] is used.
V], and the dose amount is 2 × 10 ¹³ [cm ⁻² ]. This condition is determined based on the characteristics of the FET to be manufactured.

After each ion implantation, the resists 3 and 5 are removed.

After that, the GaAs substrate 1 is irradiated with plasma 1
1 (FIG. 1 (c)). The plasma irradiation 11 is performed by exposing to plasma of hydrogen gas (hereinafter, referred to as hydrogen plasma), and then exposing to plasma of phosphine (PH ₃ ) gas (hereinafter, referred to as phosphine plasma). The oxide on the surface of the GaAs layer is removed by irradiation with hydrogen plasma, and the surface is passivated with a protective layer or a protective film of phosphorus (P), GaP, or the like by irradiation with phosphine plasma. It is preferable that the GaAs substrate 1 be continuously irradiated with these plasmas. An example of conditions for forming these plasmas will be described.

Hydrogen plasma conditions: Gas pressure: 0.2 [Torr] High frequency (RF) power density: 0.18 [W / cm ² ] Phosphine plasma conditions: Gas pressure: 0.2 [Torr] High frequency (RF) Power density: 0.18 [W / cm ² ] As the plasma irradiation time, hydrogen plasma is 10
[Min], the phosphine plasma is desirably about 20 [min]. Detailed conditions for the plasma processing are determined by the FET manufacturing process.

The hydrogen plasma may be a plasma of a hydrogen-containing gas, and the phosphine plasma may be a plasma of a phosphine-containing gas. In particular, the plasma of the phosphine-containing gas is preferably a plasma of a gas containing phosphine and hydrogen. High-purity phosphine is highly toxic and is used after dilution. Further, as the diluent gas, hydrogen which is a constituent element of phosphine is preferable from the viewpoint of converting the semiconductor surface to phosphorous (P). These conditions are
It is appropriately determined by an ET manufacturing process, a device for forming plasma, and the like.

The type of plasma is 13.56 [MHz].
Although it is preferable to generate normal high-frequency plasma using the method described above, plasma generated at other frequencies may be used. Further, a plasma irradiation apparatus in which the plasma generation chamber and the semiconductor substrate installation chamber are the same is preferable because it is simple. On the other hand, a separation-type plasma irradiation apparatus in which a plasma generation chamber and a semiconductor substrate installation chamber are separated from each other, such as an ECR plasma apparatus, is preferable because the substrate is not directly exposed to plasma, so that damage to the substrate by plasma is reduced. . Further, hydrogen, phosphine, or the like may be formed in a plasma state by excitation with laser light. In order to control the state of the surface after plasma irradiation,
Preferably, the substrate 1 is appropriately heated.

After the plasma irradiation, a cap film 13 is formed on the surface of the substrate 1 (FIG. 2A). The cap film 13 plays a role of an annealing protection film, and is formed using an insulating film made of SiN, SiON, or the like. These films can be formed by an annealing protective film forming apparatus employing a chemical vapor deposition (CVD) method or the like. The oxide on the surface of the GaAs layer is removed by plasma irradiation, and the surface is passivated with phosphorus (P) or the like. In addition, some of the phosphorus atoms enter the As site and the GaAs surface becomes GaP, which is less susceptible to oxidation than GaAs. Therefore, a stable surface can be formed, so that no oxide is formed on the surface even when the substrate 1 is exposed to the air again. Therefore, it is possible to separate the plasma irradiation apparatus for performing the plasma processing 11 from the annealing protective film forming apparatus. That is, the substrate surface treatment before the cap film growth and the cap film 13
It is not necessary to perform the film formation continuously without exposing the film to the atmosphere, that is, it is not necessary to perform the film formation in an in-process, so that the process margin can be increased.

After the cap film 13 is formed, heat treatment is performed on the substrate 1.
In this case, the N-type first semiconductor layer 5 and the N-type second semiconductor layer 9 are annealed and the impurities are activated to form the active layer 15 and the N + layer 19, respectively. By performing plasma irradiation before the formation of the cap film 13, the oxide on the surface is removed and excess As is compensated, so that activation and annealing are stably performed. Therefore, not only can an FET having reduced leakage current and drain lag be manufactured, but also a process with higher reproducibility can be realized.

Next, an ohmic electrode 17 is formed on the N + layer (FIG. 2B). The ohmic electrode 17 becomes these electrodes when formed on the source and drain diffusion layers. An ohmic electrode 17 made of AuGe / Ni is formed on the N + layer. These electrodes are formed by physical vapor deposition such as sputtering and vapor deposition.
ition: PVD) method.

Subsequently, a Schottky gate electrode 21 is formed (FIG. 2C). The gate electrode 21 is formed on the active layer 15 sandwiched between the source and the drain so as to divide the active layer 15 into a source side and a drain side. This electrode is preferably formed by a physical vapor deposition method such as a sputtering method or an evaporation method, a lift-off method, or the like.

Prior to forming the Schottky gate electrode 21, the GaAs substrate 1 is again exposed to hydrogen plasma.
Next, it is preferable to perform a plasma treatment of exposing to phosphine plasma. With this configuration, the surface of the GaAs layer is stabilized before the formation of the gate electrode by this plasma irradiation, so that not only the leakage current of the gate is reduced, but also the barrier φ _Bn viewed from the gate electrode side is reduced. A Schottky barrier having an appropriate size and an n value (ideality factor) closer to 1 can be formed stably. That is, a higher performance FET can be manufactured with good reproducibility. Further, the hydrogen plasma may be a plasma of a hydrogen-containing gas, and the phosphine plasma may be a plasma of a phosphine-containing gas. The conditions for forming these plasmas are simple if they are the same as the plasma irradiation conditions before the formation of the cap film 13 described above, but are determined in detail by the FET manufacturing process, the apparatus for forming plasma, and the like.

As described above with reference to the drawings, G
Exposing the aAs layer to hydrogen plasma to remove oxides on the surface of the GaAs layer and then exposing the surface to phosphine plasma to passivate the surface with GaP or the like also compensates for excess As, so that activation and annealing are performed. Is performed stably. Therefore, not only can an FET having reduced leakage current and drain lag be manufactured, but also a process with good reproducibility can be realized.

The present invention is not limited to the manufacture of GaAs-FETs, but can be applied to the manufacture of high-speed devices and optical devices. That is, Organic Metal Vapor Phase Deposition (OMV) is formed on a GaAs substrate.
PE) method, molecular beam epitaxy (Molecular Beam Epita
The present invention can also be used for growing a semiconductor crystal or the like by a chemical or physical vapor deposition method such as an xy (MBE) method or an evaporation method. The semiconductor material to be grown is not limited to GaAs, but may be GaP, InGaAs, InP, GaS
b or the like. In particular, a semiconductor material that is effective for epitaxial growth and has good lattice constant matching is preferable. For example, for GaAs, AlGaAs,
GaInP, InGaAs and the like are preferable, and InGaAs is preferably InGaAs, InGaAsP and AlInAs. As shown in FIG. 3, before growing a semiconductor layer, a plasma treatment 31 of a hydrogen-containing gas and then a phosphine-containing gas is performed (FIG. 3A).
Since the natural oxide film on the surface of the substrate is removed and the surface is passivated, the semiconductor layer and the epitaxial layer are not only stably grown (FIG. 3B), but also the grown semiconductor layer 33 and the like. Also have good quality with few defects.
By doing so, it is not necessary to perform a series of steps continuously without exposing it to the atmosphere, that is, it is not necessary to perform the steps in-process, and it is possible to increase the process margin.

The surface treatment method by plasma irradiation is as follows.
The present invention is not limited to the GaAs substrate, and it is effective to grow the GaAs film 35 on the substrate 1, for example, after epitaxial growth, as shown in FIG. When the plasma treatment 37 is performed in this manner, when another semiconductor layer is subsequently epitaxially grown or another step is performed, a new natural oxide film or the like is not generated even if the surface is exposed to the air. Therefore, a stable surface can be obtained. Therefore, since it is not necessary to perform a series of steps in-process, the process margin can be increased.

Although the N-type GaAs layer has been described above, the same effect can be obtained by performing the same plasma treatment on the P-type GaAs layer. Also,
The plasma processing includes in-situ plasma processing in which the plasma generation chamber and the wafer processing chamber are the same, or remote plasma processing in which the plasma generation chamber and the wafer processing chamber are different, and the remote plasma processing has less ion damage to the semiconductor layer. There are features.

[0035]

As described above in detail, in the method for stabilizing the surface of a GaAs layer according to the present invention, when the surface of the GaAs layer is exposed to a plasma of a hydrogen-containing gas and then to a plasma of a phosphine-containing gas, plasma irradiation is performed. The oxide on the surface of the GaAs layer is removed, and the surface is passivated with phosphorus (P) or the like. In addition, some of the phosphorus atoms enter the As site and the GaAs surface becomes GaP, which is less susceptible to oxidation than GaAs. Therefore, even if the substrate is exposed to the air again, no oxide is formed on the surface, so that the surface can be stabilized.

Further, in the method of manufacturing a GaAs semiconductor device according to the present invention, between the introduction step and the cap film step, or between the active layer step and the gate step, the wafer is exposed to the plasma of the hydrogen-containing gas and then the plasma of the phosphine-containing gas. Plasma treatment is performed. Therefore, the surface of the GaAs layer is stabilized as described above, so that the process margin can be increased. Since the activation and annealing of the impurities in the active layer are performed stably, not only the leak current and the drain lag can be reduced, but also a process with good reproducibility is realized. In addition, since the gate interface is stabilized, not only the leakage current of the gate is reduced, but also the barrier φ _Bn viewed from the gate electrode side is a suitable size, and the n value (ideality factor) is further increased. A gate electrode having a Schottky barrier close to 1 can be formed stably.
Therefore, a highly reliable and high performance FET can be manufactured.

Further, in the method of forming a semiconductor layer according to the present invention, since the GaAs layer is subjected to the plasma treatment of exposing to the plasma of the hydrogen-containing gas and then to the plasma of the phosphine-containing gas, the surface of the GaAs layer is stabilized as described above. You.
For this reason, the surface is not oxidized again even when exposed to air, so that the process margin can be increased. Further, the semiconductor layer can be stably grown, and defects in the grown semiconductor layer can be reduced. In addition, when the surface of the GaAs film formed on the GaAs layer is subjected to the plasma treatment, the surface of the GaAs film can be stabilized.

[Brief description of the drawings]

1 (a) to 1 (c) show GaAs according to the present invention.
FIG. 4 is a schematic process cross-sectional view showing one embodiment of a method for manufacturing a GaAs semiconductor device, for describing a surface treatment method of s and the like.

FIGS. 2A to 2C show GaAs according to the present invention.
FIG. 4 is a schematic process cross-sectional view showing one embodiment of a method for manufacturing a GaAs semiconductor device, for describing a surface treatment method of s and the like.

FIGS. 3 (a) and 3 (b) show GaAs according to the present invention.
It is a schematic process sectional view showing one embodiment of a method of forming a semiconductor layer on an s layer.

FIG. 4 is a schematic process sectional view showing one embodiment of a method for forming a semiconductor on a GaAs layer according to the present invention.

[Explanation of symbols]

1: GaAs semiconductor substrate, 3: resist, 5: N-type first
Impurity layer, 7 resist, 9 N-type second impurity layer, 1
1, 31, 37: plasma treatment of hydrogen gas and then phosphine gas, 13: cap film, 15: active layer, 17
... ohmic electrode, 19 ... N + layer, 21 ... gate electrode,
33: grown semiconductor layer, 35: grown GaAs semiconductor layer

Claims (4)

[Claims] 1. GaAs used for manufacturing a semiconductor device
A method for stabilizing a surface of a GaAs layer, comprising: exposing a surface of the GaAs layer to a plasma of a hydrogen-containing gas, and then exposing the surface of the GaAs layer to a plasma of a phosphine-containing gas. 2. An introduction step of introducing impurities into the GaAs layer by an ion implantation method, a cap film step of forming a cap film on the GaAs layer after the introduction step, and a heat treatment after the cap film step to remove the impurities. GaAs comprising an active layer step of activating to form an active layer, and a gate step of forming a Schottky gate electrode on the active layer
In the method for manufacturing a semiconductor device, between the introduction step and the cap film step and between at least one of the active layer step and the gate step,
A method for manufacturing a GaAs semiconductor device, comprising: exposing a surface of the GaAs layer to a plasma of a hydrogen-containing gas and then exposing the surface of the GaAs layer to a plasma of a phosphine-containing gas. 3. A method for forming a semiconductor layer on a GaAs layer, comprising: exposing the GaAs layer to a plasma of a hydrogen-containing gas before forming the semiconductor layer, and then exposing the GaAs layer to a plasma of a phosphine-containing gas. A method for forming a semiconductor layer, comprising performing a treatment. 4. A method of manufacturing a semiconductor layer for growing a GaAs film on a GaAs layer, comprising: exposing the GaAs film to a plasma of a hydrogen-containing gas, and then exposing the GaAs film to a plasma of a phosphine-containing gas. A method for forming a semiconductor layer.