JPS63238271A - Method for modifying surface by radiation of ion - Google Patents

Abstract

PURPOSE:To easily form an amorphous layer on the surface of a compd. base material such as GaAs by radiating ions of a specified gas accelerated at a specified low temp. and a specified low acceleration voltage on the surface of the base material. CONSTITUTION:Ions of a rare gas such as Ar, He, Ne or Xe or other gas such as N as an ion source are accelerated at a low temp. of <=20 deg.C, especially -100-20 deg.C and a low acceleration voltage of <=2,000V, especially 50-2,000V and the accelerated ions are radiated on the surface of a base material such as GaAs. An amorphous layer of a prescribed thickness can easily be formed without requiring a heat annealing stage after the radiation.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for modifying a surface by ion irradiation, and particularly to a method for forming an amorphous layer on the surface.

(Conventional technology) Material surface modification technology using ion irradiation is used to improve the functionality of material surfaces, including the production of semiconductor devices in the electronics industry, improving the durability of steel materials, and improving the adhesiveness and conductivity of polymers. Its importance is increasing as the world ages. Particularly in the production of semiconductor devices, when microfabrication is performed by forming an amorphous layer on the surface of a crystalline substrate and then selectively etching and removing only this amorphous layer, the formation of the amorphous layer on the surface of the substrate is difficult due to the high density of the semiconductor device. As technology and integration become more sophisticated, higher precision is required.
High precision control of the amorphous layer thickness is expected.

Conventionally, when forming an amorphous layer on the surface of a substrate, ions with a high acceleration voltage of several tens to hundreds of kV are generally used, and the ion irradiation is usually performed at a temperature of the substrate receiving ion irradiation higher than room temperature. There is. However, with such high-energy ion irradiation means at relatively high temperatures, the control accuracy of the amorphous layer thickness is at most ~1000 ultra-fine,
Further, there arises the problem of irradiation damage in which the crystal structure is disturbed to a considerable extent even below the formed amorphous layer.

On the other hand, semiconductor devices, especially VLSI, which require ~100 ultra-thin layers and ~1000 ultra-fine processing.
, ultra-super LSI, three-dimensional RC, etc., it is desired that the control accuracy of the amorphous layer thickness be as high as possible.

In addition, in order to recover from irradiation damage, 400
Thermal annealing is performed at ~800°C, but the high-temperature heating in this thermal annealing not only causes problems such as alteration of the base material and heterointerface, and diffusion of impurity atoms, but also requires lowering the process temperature. This can be a fatal defect in VLSI devices.

(Problems to be Solved by the Invention) The present invention provides a method for easily forming an amorphous layer with a desired thickness with high precision in forming an amorphous layer, which is one typical aspect of surface modification by ion irradiation. In addition, the present invention provides a surface modification method by forming an amorphous layer that causes less radiation damage and does not require thermal annealing after ion irradiation.

(Means for Solving the Problems) As a result of research on amorphous layer formation and irradiation damage caused by ion irradiation with the intention of creating a ridge, the present inventor found that:
We have discovered new knowledge regarding the relationship between these, the temperature of the substrate subjected to ion irradiation, and the acceleration voltage, and have come to propose the present invention. That is, the present invention is a surface modification method by ion irradiation, characterized in that ion irradiation is performed in a low temperature region of 20° C. or lower using ions accelerated at a low acceleration voltage of 2000 V or lower.

The present inventors have found that when the crystalline surface of a base material is irradiated with ions, the surface layer becomes amorphous, but at the same time, recrystallization also occurs during or after irradiation depending on the base material temperature. Furthermore, above a certain temperature, the recrystallization rate is large and there is almost no dependence on the accelerating voltage, and this recrystallization is the dominant factor in the amorphous layer thickness, but below a certain temperature, the recrystallization rate is small and the accelerating voltage We discovered a novel phenomenon of dependence.

The condition of 20° C. or lower in the present invention is based on the above knowledge, and is important for controlling the thickness of the amorphous layer to be formed with high precision. That is, the irradiation temperature is 20℃
If it exceeds 20%, a recrystallization phenomenon will occur during or after ion irradiation, and it will be difficult to obtain an amorphous layer with a desired thickness with high precision even if the accelerating voltage is manipulated. The amorphous layer thickness shows acceleration voltage dependence, and can be suitably used at an irradiation temperature of 20°C or lower, preferably -100 to 20°C.
temperature range. Note that cooling the substrate temperature to a temperature lower than -100°C may contaminate the substrate, complicate the cooling system,
This is not practically useful due to a decrease in processing capacity. Therefore,
In the present invention, an appropriate temperature may be selected from a range of 20°C or lower, preferably -100 to 20°C, more preferably -80 to 0°C, taking into account the type of ion, accelerating voltage, dose amount, etc.

Further, the acceleration voltage of irradiated ions in the present invention is 2000V.
The following conditions are considerably smaller than conventional acceleration voltages of several tens to hundreds of kV, but are important along with the condition of an irradiation temperature of 20° C. or less from the viewpoint of reducing residual damage from irradiation. When the accelerating voltage exceeds 2000 V, irradiation damage is insufficiently reduced and it becomes difficult to omit the thermal annealing step after ion irradiation. Furthermore, from the point of view of good control of the amorphous layer thickness, it is desirable that the irradiated ions have a certain degree of low energy, and if the energy is too low, it will be difficult to form an amorphous layer. In order to form the amorphous layer thickness with high precision, 5
It is desirable to use a low acceleration voltage of 0 to 2000V. That is, considering the specific value of the desired amorphous layer thickness and the allowable degree of residual damage from irradiation, the voltage is 2000 V or less, preferably 50 to 2000 V, and more preferably 100 to 1500 V.
Low-temperature irradiation may be performed by employing an appropriate acceleration voltage within the range of .

Within the preferable ranges of the irradiation temperature and low accelerating voltage described above, in general, the lower the irradiation temperature, the higher the dependence of the amorphous layer thickness on the accelerating voltage, and the lower the accelerating voltage, the smaller the amorphous layer thickness.

Based on these findings, specific irradiation temperatures and accelerating voltages may be determined and adopted as appropriate, taking into consideration the type of base material on which the amorphous layer is to be formed.

When performing ion irradiation, gases that serve as ion sources include:
Any conventionally commonly used one can be used. For example, rare gases such as argon, helium, neon, and xenon, nitrogen, and the like are preferred, but various other gases such as oxygen, chlorine, fluorine, and fluorocarbons can be used without particular limitation. Furthermore, it is also possible to use a mixture of two or more types of gas.

Furthermore, the base material to be surface-modified in the present invention is not particularly limited, and may include GaAs+GaP+ InP+ InAs, which is commonly used in the production of semiconductor devices in the electronic industry.
.

InSb, A j! GaAs, GaAsP +
3) In addition to semiconductor materials such as Sing and 5iJ1-based materials, garnet for magnetic bubble elements and Li for optical integrated circuits
It is also applied to Nb0+ etc.

The ion irradiation device for carrying out the present invention is one that can apply the accelerating voltage specified in the present invention and can satisfactorily control the temperature of the substrate to be surface modified to the specified temperature. Any existing ion irradiation device may be used, and a conventional ion irradiation device can be appropriately modified and used.

(Function) At the temperature at which ion irradiation was conventionally performed, that is, higher than room temperature, recrystallization progresses during or after ion irradiation, and the dependence of the amorphous layer thickness on accelerating voltage is extremely small. In the low temperature region defined by the present invention, a good dependence of the amorphous layer thickness on the accelerating voltage is observed.

The reason for this is presumed to be that by keeping the substrate temperature low during ion irradiation, the thermal movement of atoms is suppressed and the recrystallization rate is kept sufficiently low. In addition, the reason why the amorphous layer thickness is affected by the energy of the irradiated ions is that the degree of interaction between the irradiated ions and the base material depends on the energy, and at higher energies, they penetrate deeper and become amorphous. . Furthermore, if the energy of the irradiated ions is excessively high, the unevenness at the interface between the amorphous and crystal inside the base material becomes large, and the damage tends to reach deep below the amorphous layer, whereas at low energy, Since it is assumed that a flat interface is formed, it is thought that the residual damage caused by irradiation is small in the case of low-energy irradiation ions.

(Examples) Several examples will be given below to concretely demonstrate the effects of the present invention, but the present invention is not limited to these examples and can be modified as appropriate without departing from the gist of the present invention. .

In this example, an ion gun, a sample stage, and a vacuum gauge are installed in the ion irradiation chamber. The ion gun is connected to a power source, and the sample stage is connected to a manipulator, and their positions and angles with respect to the ion gun are connected. can be changed freely. The chamber also communicates with a gas source through a gas pipe and with a vacuum pump through an exhaust pipe. Furthermore, the sample stage is connected to a cooling source (temperature controller).

This cooling source is used to control the amorphization caused by ion irradiation with high precision by keeping the temperature of the sample placed on the sample stage low and constant.

When a voltage is applied from a power source to an ion gun attached to a chamber, ions are generated. Ions based on the gas used (for example, Ar'' when using argon gas,
When neon gas is used, Ne') is irradiated onto the substrate on the sample stage to form an amorphous layer on the surface of the substrate. In this example, at a gas pressure of I x 10-'Torr, Ion irradiation was performed until the amorphous layer thickness was saturated at a power density of 0.01 to 1 μA/(!II to form an amorphous layer. The amorphous layer thickness was determined using an X-ray photoelectron diffraction device and a scanning electron microscope device. After the amorphous layer was removed by chemical etching, the residual damage caused by irradiation was evaluated using the photoluminescence method in the following four stages.

◎... No damage observed ○... Slight damage △... Some damage observed ×... Significant damage observed Example 1 and Comparative Example 1 GaAs, gas as base material Using Ar as a seed, the substrate temperature was set to 100.40.20. O, -30 and -100°C, and the acceleration voltages were s, oo at each substrate temperature.

The voltage was changed stepwise from (2) to 100V.

The results are shown in Table 1. At a substrate temperature of 100.40°C, no dependence of the amorphous layer thickness on the accelerating voltage was observed;
Good acceleration voltage dependence is observed below 0°C, especially below 0°C. In other words, the amorphous layer thickness is controlled with high precision by manipulating the accelerating voltage.

(Left below) Example 2 and Comparative Example 2 GaAs was used as the base material, gas was used as the gas type, and the base material temperature was set to 7 at each acceleration voltage at an acceleration voltage of 200.800V.
The temperature was changed stepwise from 5°C to -100°C. The results are shown in Table 2.

(The following is a blank space) Example 3 Using GaAs as the base material and N2 as the gas species, the temperature of the base material was changed stepwise from 0°C to -80°C at each acceleration voltage at an acceleration voltage of 200,800V. The results are shown in Table 3.

(Left below) Example 4 The same procedure as in Example 3 was carried out using GaAs as the base material and Ne as the s gas species. The results are shown in Table 4.

(Left below) Example 5 and Comparative Example 3 A meter was used as the S1% gas species as the base material, and an accelerating voltage of 20
At 0,800V, the substrate temperature was 75℃ at each acceleration voltage.
The temperature was changed stepwise from -80°C. The results are shown in Table 5.

(The following is a blank space) (Effects of the Invention) As specifically shown in the above examples, the present invention enables surface modification by easily forming an amorphous layer of a desired thickness with high precision, and The residual damage caused by irradiation, which was a major drawback in conventional surface modification by ion irradiation, is also very small, and the thermal annealing step after ion irradiation can be omitted.

The ability to easily form an amorphous layer of a desired thickness with high precision is extremely significant when microfabrication is performed by selectively etching away an amorphous layer formed in semiconductor device manufacturing. Furthermore, omitting the thermal annealing step not only simplifies the process, but also is extremely beneficial in the VLSI manufacturing process, which requires lowering the process temperature.

Claims (6)

[Claims] (1) Ion irradiation was performed at a low temperature of 20°C or less for 20°C.
A surface modification method characterized in that it is carried out using ions accelerated at a low acceleration voltage of 00V or less. (2) The surface modification method according to claim 1, wherein the surface modification is to form an amorphous layer on the surface. (3) -100 to 20℃ as a low temperature range of 20℃ or less
The surface modification method according to claim 1, which is carried out at a temperature range of . (4) The surface modification method according to claim 1, which is carried out at a low acceleration voltage in the range of 50 to 2000V. (5) The surface modification method according to claim 1, which is carried out using rare gas ions or nitrogen ions as irradiation ions. (6) The surface modification method according to claim 1, which is carried out using a gallium arsenide-based substance as the base material subjected to ion irradiation.