JPH03159118A - Method for thermally treating single-crystal gallium arsenide wafer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method of heat treating a gallium arsenide single crystal wafer implanted with impurity ions, and particularly to a method for improving the economy and uniformity of properties required for heat treatment. Concerning.

[Prior Art] Gallium arsenide semiconductor wafers have excellent features such as high electron speed, magnetoelectric conversion properties, and stability of these properties against changes in environmental temperature. For this reason,
It is used as a material for industrially extremely important devices such as FETs (field effect transistors), high frequency and high speed devices such as ICs and LSIs, and Hall devices. In these devices, electrons are often used as carriers when creating a channel for current to flow in the circuit, and ion implantation is used as a method for creating the channel layer.

Here, as an example, a case will be described in which a channel layer is formed by implanting impurity ions, such as Si ions, into the surface of a semi-insulating gallium arsenide wafer.

Si accelerated to an energy of several tens to strokes + KeV.”
When ions are implanted into the surface of a semi-insulating gallium arsenide wafer and the wafer is heated at 700 to 900° C. for several minutes, an n-type conductive layer is formed on the surface of the semi-insulating gallium arsenide wafer. Using this as a channel, a device can be manufactured by drawing a fine circuit using photolithography. The implanted S I+t8 ions exhibit n-type characteristics by occupying Ga positions, but do not occupy substitution positions as they are implanted. Furthermore, the crystal surface is damaged by the implanted ions and becomes amorphous. The reason for heat treatment after implantation is that by heating, Si”,
, to allow ions to occupy substitution positions and to alleviate crystal disorder. At this time, if there are impurities that act as acceptors in the crystal wafer, the electrons emitted from the implanted ions are captured, and the crystal wafer does not appear to be a supernatant. The ratio of activated ions to implanted ions is called activation rate, and activation rate is an important parameter that influences device characteristics.

When integrating elements, the activation rate of each element must be the same. Furthermore, even in the case of individual elements, in order to produce elements with uniform characteristics with good reproducibility, it is necessary that the activation rates of the individual elements manufactured in the same web be the same.

However, in a crystal wafer, there are acceptor levels that are considered to be based on crystal defects and donor levels that are involved in their generation/disappearance and electrical compensation, and these usually exist non-uniformly. Therefore, it is difficult to obtain a uniform activation rate within the wafer plane, and to improve this, the crystal itself is heat-treated to improve uniformity, or the wafer is heat-treated before ion implantation.

[Problems to be Solved by the Invention] As mentioned above, the uniformity can be considerably improved by the conventional heat treatment of the crystal itself or the heat treatment of the wafer before ion implantation (for example, as disclosed in Japanese Patent Laid-Open No. 62-226900). ).

However, this method has the following two drawbacks.

The first is that when crystals or wafers are used without any treatment, there is an economic disadvantage due to the increase in burr compared to the other, and the second is that even if the uniformity is improved before ion implantation, it is difficult to activate the ions after implantation. The problem is that non-uniformity may occur again during heat treatment.

Regarding the first point, the characteristics are improved compared to untreated crystal wafers, and the economic effect is large. Second
Regarding the point, 700, which is actually used for activation heat treatment,
At temperatures of ~900°C, the above-mentioned acceptor is likely to occur,
It is also known that it tends to be unevenly distributed.

This non-uniform distribution appears as variations in threshold voltage when FETs are fabricated on the wafer.

It is an object of the present invention to eliminate the drawbacks of the prior art described above, to improve the uniformity of the activation rate of gallium arsenide semiconductor devices manufactured using the ion implantation method, and to improve this uniformity economically. An object of the present invention is to provide a method for heat treating a gallium arsenide single crystal wafer.

[Means for Solving the Problems] The heat treatment method for gallium arsenide single crystal wafers of the present invention consists in performing a special heat treatment that is extremely different from conventional heat treatment in the heat treatment of gallium arsenide single crystal wafers after ion implantation. This allows activation of implanted ions and homogenization of wafer characteristics at the same time.

As shown in FIG. 1, the heat treatment conditions require a three-step process after desired impurity ions are implanted into the surface of a gallium arsenide single crystal wafer.

First, in the first process, 100% of gallium arsenide single crystal wafers were processed for ion activation and uniform crystal defect distribution.
Heat to a high temperature of 0°C or higher. Homogenization does not occur at temperatures below 1000°C.

The next process is reheating to a temperature below 600° C. to uniformize the donor level, which is called EL2.

The temperature is desirably within the range of 400 to 600°C. The temperature reduction from too'c to 600° C. is carried out rapidly within as short a time as possible in order to eliminate non-uniformity factors.

Finally, to generate sufficient donor level concentration, 80
Heat at a high temperature of 0°C or higher. No donor levels are generated at temperatures below 800°C.

During these heat treatments, arsenic (AS) dissociates from the wafer surface and deteriorates the characteristics, so to prevent this, As
Create an atmosphere. Possible methods for creating an As atmosphere include placing the wafer in an ampoule and using sublimated As gas thrown into the ampoule, using arsine gas, or using As ions implanted into the surface of the wafer.

Further, the gallium arsenide single crystal is preferably doped-free semi-insulating gallium arsenide or Cr-added semi-insulating gallium arsenide.

[Operation] After implanting desired impurity ions into the surface of a gallium arsenide single crystal wafer, the gallium arsenide single crystal wafer is
When heated to a high temperature of .degree. C. or higher, the implanted ions are activated, and at the same time, the distribution of crystal defects existing in the crystal wafer is made uniform. If it is cooled to room temperature in this state, the donor level called EL2, which is necessary for semi-insulating properties, will disappear or become unevenly distributed depending on the cooling conditions.

For this reason, it is reheated at a temperature of 600° C. or lower.

In this case, if the temperature is gradually cooled to below 600°C, a phenomenon that induces non-uniformity will occur during the cooling process, but if the temperature is rapidly cooled, a phenomenon that will induce non-uniformity during the cooling process will occur. No phenomenon occurs. When heated at a temperature of 600° C. or lower, nuclei for uniformizing EL2 are uniformly generated.

It is not produced uniformly at temperatures higher than 600°C.

Finally, when heated at a high temperature of 800°C or higher, the E
A donor level called L2 is generated in sufficient concentration. The concentration distribution of the donor level is extremely uniform because it is dominated by the distribution of uniformly distributed nuclei produced in the previous process.

As described above, according to the method of the present invention, by applying a special three-step heat treatment to the activation heat treatment after ion implantation, ion activation and uniformity can be achieved at the same time. , does not require a wafer heat treatment process before ion implantation.

[Example] Examples of the present invention will be described below along with comparative examples.

(Comparative Example 1) Additive-free semi-insulating G made by a pulling method with a diameter of 3 inches
The aAs crystal was processed into wafers without thermal treatment.

Si”y on a mirror-finished wafer with 75KeV energy
S ions were implanted at a dose of 3×10"Ctrl".

This wafer was placed in hydrogen gas containing 3% arsine gas for 8 hours.
Heat treatment was performed at 50°C for 15 minutes. F on the entire surface of this wafer
ETs were fabricated at 250 micron intervals, and the threshold voltage vt
When h was measured, the average value was 10.5■, and the threshold voltage variation σvth of all FETs was 150 mV.
It was big.

(Example 1) A wafer cut from the same 3-inch additive-free crystal as in Comparative Example 1 was implanted with ions under the same conditions and heat-treated in hydrogen gas containing 3% arsine gas. The conditions were 1100°C for 2 minutes, then lowered to 600°C for about 3 minutes, held for 15 minutes, and then heat-treated at 850°C for 5 minutes. When the same FET was fabricated and the threshold value vth was measured, it was found to be -0.9V, indicating that the activation rate was significantly improved compared to the comparative example.Also, the threshold variation σvth was 3 mV, which was a single digit At this time, for comparison, we made a sample in which the heat treatment was performed in an Ar gas atmosphere and evaluated it, and found that vth, which indicates the activation rate, was as low as 10.2 V, and σvth was also 100.
mV, which was large, and it was recognized that it was necessary to use As gas as the heat treatment atmosphere.

(Comparative Example 2) Example 1. Before cutting the same crystal as Comparative Example 1 into a wafer, it was heated at 1150° C. for 24 hours in an As atmosphere.

Heat treatment was performed at 600° C. for 30 hours and at 950° C. for 24 hours, and ions were implanted using the same process thereafter to produce an FET. Activation treatment after implantation was performed at 850° C. for 115 minutes. At this time, the wafer was placed in a quartz ampoule, and 20 t of As gas was added.
Solid AS was encapsulated together so that orr. vth
= -o, 6V, σVth = 7mV. Although the uniformity was improved compared to Comparative Example 1 due to the prior heat treatment, the activation rate was somewhat poor. This is thought to be due to the generation of inherent defects with acceptor levels during the activation heat treatment.

(Example 2) An FET was manufactured under the same conditions as Comparative Example 2. However, only the activation heat treatment conditions after implantation were changed. The wafer was placed in a quartz ampoule, the As pressure was the same as in Comparative Example 2, and the temperature conditions were 1100°C for 3 minutes, then 550°C for about 5 minutes.
The temperature was lowered to 850°C, held for 30 minutes, and further heat-treated at 850°C for 115 minutes. Vth=-0.9V, σVth=2mV
Both the activation rate and uniformity were good. This means that
Preliminary heat treatment, that is, heat treatment of the crystal itself and wafer heat treatment before ion implantation, does not matter whether or not they are performed (this means that they can be omitted).

(Example 3) 4-inch Cr-doped semi-insulating G manufactured by pulling method
An aAs crystal was produced. The Cr concentration in the crystal is 0. Ol =
0. O5ppm, carbon concentration is 3~3 x l Q l
4 cm −3. Below, when an FET was made under the same conditions as in Example 2, Vth=-Q, 85■, σ
V th = 2 mV, both the activation rate and uniformity were good.

[Effects of the Invention] According to the present invention, since the activation heat treatment after ion implantation is a three-step heat treatment, it is possible to simultaneously obtain an unprecedentedly good activation rate and uniformity.

In addition, since the implanted ions are activated and the wafer properties are made uniform at the same time, the conventional heat treatment for crystal uniformity and the heat treatment of the crystal wafer after ion implantation can be done in one go. It is highly economical.

[Brief explanation of the drawing]

FIG. 1 is a process diagram showing an embodiment of the heat treatment method for a gallium arsenide single crystal wafer according to the present invention.

Claims (1)

[Claims] After implanting desired impurity ions into the surface of a gallium arsenide single crystal wafer, the implanted impurity ions are placed in replacement positions in the semiconductor crystal lattice during heat treatment to make them electrically active. Heat treatment of gallium arsenide single crystal wafers, characterized by heating the crystal wafer to a temperature of 1000°C or higher, then rapidly cooling it, reheating it to a temperature of 600°C or lower, and then performing a final heat treatment at a temperature of 800°C or higher. Method.