JP2710114B2 - Surface modification method by ion irradiation - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for modifying a surface by ion irradiation, particularly to a method for forming an amorphous layer on a surface. (Conventional technology) The material surface modification technology using ion irradiation is a high-performance material surface for improving the durability of steel materials, improving the adhesiveness of polymers, and making it conductive, including the manufacture of semiconductor devices in the electronics industry. Its importance is increasing with the development of technology. In particular, in the production of semiconductor devices, when an amorphous layer is formed on the surface of a crystalline substrate and then fine processing is performed by selectively etching away only the amorphous layer, the formation of the amorphous layer on the surface of the substrate requires high density of the semiconductor device. Higher precision is required in accordance with higher integration and higher integration, and higher precision control of the amorphous layer thickness is expected. Conventionally, when forming an amorphous layer on the surface of the substrate, generally use high acceleration voltage ions of tens to hundreds of kV, the ion irradiation is usually performed at a temperature of the substrate subjected to ion irradiation at a temperature higher than room temperature I have. However, such high-energy ion irradiation means at a relatively high temperature does not
As disclosed in the specification of JP-A-56-56626, the thickness of the amorphous layer cannot be controlled, for example, a crystal is formed again on the surface of the substrate. In addition, there is a problem of radiation damage that the crystal structure is considerably disturbed below the formed amorphous layer. On the other hand, semiconductor devices, particularly VLSI, ultra-thin layers of about 100 mm,
In the production of SI, three-dimensional IC, etc., it is desired that the control accuracy of the amorphous layer thickness be as high as possible. Also, usually 400 after ion irradiation for recovery from irradiation damage.
Thermal annealing of up to 800 ° C is performed, but high-temperature heating in this thermal annealing not only causes problems such as deterioration of the base material and heterointerface and diffusion of impurity atoms, but also requires lowering the temperature of the process. It can be a fatal defect in VLSI devices. (Problems to be Solved by the Invention) The present invention relates to the formation of an amorphous layer, which is one of the typical modes of surface modification by ion irradiation, from the surface to 1000
An amorphous layer having a desired thickness is easily formed with high precision within the range of Å, and the surface damage is reduced, and a surface modification method by forming an amorphous layer that does not require thermal annealing after ion irradiation is provided. I do. (Means for Solving the Problems) The present inventor has studied the formation of an amorphous layer and the damage caused by ion irradiation with the intention described above. The present inventors have found new knowledge on the relationship between the present invention and the present invention and have proposed the present invention. That is, the present invention uses an ion accelerated at a low accelerating voltage of 2000 V or less in a low temperature region of 20 ° C. or less, and irradiates the inorganic semiconductor material with ions to form an amorphous semiconductor within a depth of 1000 mm from the surface. This is a surface modification method by ion irradiation characterized by forming a layer. The present inventor has found that when ion irradiation is performed on the crystal surface of the base material, the surface layer becomes amorphous, but at the same time, recrystallization 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 acceleration voltage. This recrystallization is the dominant factor of the amorphous layer thickness. We found a new phenomenon of dependence. The condition of 20 ° C. or lower in the present invention is based on the above findings, and is important for controlling the thickness of the formed amorphous layer with high accuracy. That is, when the substrate temperature at the time of irradiation (hereinafter also referred to as irradiation temperature) exceeds 20 ° C., a recrystallization phenomenon is observed during or after ion irradiation, and even if the accelerating voltage is manipulated, the desired temperature can be obtained with high accuracy. It is difficult to obtain a thick amorphous layer. Dependence of the thickness of the amorphous layer on the acceleration voltage is observed, and it can be suitably used in an irradiation temperature of 20 ° C. or lower, preferably in a temperature range of −100 to 20 ° C. Cooling the substrate temperature to a temperature lower than −100 ° C. is not practically useful because the substrate is contaminated, the cooling device is complicated, and the processing capacity is reduced. Therefore, in the present invention, an appropriate irradiation temperature may be selected from the range of 20 ° C. or less, preferably −100 to 20 ° C., and more preferably −80 to 0 ° C. in consideration of the type of ion, acceleration voltage, dose amount, and the like. . During the irradiation, the temperature of the substrate (sample) should be kept as constant as possible. For this purpose, it is also a preferable method to attach a temperature controller to the sample stage and perform heating and cooling. In addition, the condition of accelerating voltage of 2000 V or less for irradiation ions in the present invention is considerably smaller than the conventional general accelerating voltage of several tens to several hundreds kV. It is important together with the condition below ℃. When the acceleration voltage exceeds 2000 V, the reduction of irradiation damage is insufficient, and it becomes difficult to omit the thermal annealing step after ion irradiation. Further, from the viewpoint of good control of the thickness of the amorphous layer, it is desirable that the irradiated ions have a low energy to some extent.
Since it is difficult to form an amorphous layer, it is desirable to perform the formation at a low acceleration voltage of 50 to 2000 V in order to form a desired amorphous layer thickness with high accuracy. That is, taking into account the specific numerical value of the desired amorphous layer thickness and the allowable degree of irradiation residual damage, a suitable acceleration voltage in the range of 2000 V or less, preferably 50 to 2000 V, more preferably 100 to 1500 V is adopted and low-temperature irradiation is performed. Should be performed. In the preferable ranges of the irradiation temperature and the low acceleration voltage, generally, the lower the irradiation temperature, the higher the dependence of the amorphous layer thickness on the acceleration voltage, and the lower the acceleration voltage, the smaller the amorphous layer thickness. Based on these findings,
The specific irradiation temperature and the acceleration voltage may be appropriately determined and adopted in consideration of the ion type and the type of the base material on which the amorphous layer is formed. As a gas serving as an ion source, a gas generally used in the past when performing ion irradiation is arbitrarily used. For example, argon, helium, neon, rare gases such as xenon and nitrogen are preferable, but other oxygen, chlorine,
Various gases such as fluorine and fluorocarbon can be used without particular limitation. Furthermore, it is also possible to use a mixture of two or more gases. In addition, the substrate to be surface-modified in the present invention is not particularly limited as long as it is an inorganic semiconductor material, and GaAs and Ga which are usually used for manufacturing semiconductor devices in the electronics industry are not limited.
Semiconductor materials such as P, InP, InAs, InSb, AlGaAs, GaAsP, Si, SiO ₂ , and Si ₃ N ₄ are used. As an ion irradiation apparatus for carrying out the present invention, an acceleration voltage defined in the present invention can be applied,
Any material can be used as long as it can control the temperature of the substrate to be surface-modified to a specified temperature satisfactorily, and a conventional ion irradiation apparatus can be appropriately modified and used. (Operation) At temperatures higher than the temperature at which ion irradiation was conventionally performed, that is, higher than room temperature, recrystallization proceeds during or after ion irradiation, and the acceleration voltage dependence of the amorphous layer thickness is extremely small. In the low-temperature region defined by the present invention, good acceleration voltage dependence of the amorphous layer thickness is observed. It is presumed that the reason for this is that by keeping the substrate temperature low during ion irradiation, the thermal motion of atoms is suppressed, and the recrystallization rate is kept sufficiently low. In addition, the reason why the thickness of the amorphous layer depends on the energy of the irradiation ions is that the degree of interaction between the irradiation ions and the base material depends on the energy, and the higher the energy, the deeper the ions penetrate and become amorphous. . Furthermore, if the energy of the irradiation ions is excessively large, the unevenness at the interface between the amorphous and the crystal inside the base material becomes large, and the damage easily reaches deep under the amorphous layer. It is presumed that a simple interface is formed, and it is considered that irradiation residual damage is small in the case of low energy irradiation ions. (Examples) Hereinafter, the effects of the present invention will be specifically described with reference to some examples. However, the present invention is not limited to these examples, and can be appropriately changed without departing from the gist of the present invention. . In the present embodiment, an ion gun, a sample stage, and a vacuum gauge are installed in the ion irradiation chamber, and the ion gun is connected to a power source.
The sample stage is connected to a manipulator, and its position and angle with respect to the ion gun can be freely changed. The chamber communicates with a gas source through a gas pipe and a vacuum pump through an exhaust pipe. further,
For temperature control, attach a thermocouple to the sample holder to which the base material (sample) is attached. The temperature measured by this thermocouple is used as the "base material temperature (irradiation temperature)", and the signal (temperature) from the thermocouple is input to the temperature controller. The temperature was controlled so that there was no change in temperature due to ion irradiation due to the combination of cooling and heating, in other words, the substrate temperature during ion irradiation was kept constant. By doing so, the amorphousization by ion irradiation is controlled with high accuracy. When a voltage is applied from a power supply to an ion gun attached to the 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 on the substrate on the sample table, and an amorphous layer is formed on the surface of the substrate.
In this embodiment, at a gas pressure of 1 × 10 ⁻⁴ Torr,
Ion irradiation was performed at a power density of 0.01 to 1 μA / cm ² until the thickness of the amorphous layer was saturated to form an amorphous layer. The thickness of the amorphous layer was determined using an X-ray photoelectron diffractometer and a scanning electron microscope, and the residual irradiation damage was measured by removing the amorphous layer by chemical etching and then changing the photoluminescence spectrum to a level where no damage was observed. The photoluminescence spectrum obtained when the ions were irradiated at an acceleration voltage of 5,000 V at a substrate temperature of −80 ° C. was a spectrum in which considerable damage was observed. Furthermore, the spectrum in the intermediate state was divided into two stages in which slight damage was observed when the damage was slight, and the overall evaluation was performed in the following four stages. …: No damaged layer is observed ○: slight damage is observed △: slight damage is observed ×: considerable damage is observed Example 1 and Comparative Example 1 GaAs was used as the base material, and Ar was used as the gas type. Material temperature
The temperature was set to 100, 40, 20, 0, −30 and −100 ° C., and the acceleration voltage was changed stepwise from 5,000 V to 100 V at each substrate temperature. The results are shown in Table 1. At a substrate temperature of 100 and 40 ° C, no dependence of the amorphous layer thickness on the accelerating voltage was observed.
Below, particularly at 0 ° C. or less, good acceleration voltage dependence is observed. That is, the thickness of the amorphous layer is controlled with high precision by manipulating the acceleration voltage. Example 2 and Comparative Example 2 GaAs was used as a base material, and Ar was used as a gas type.
At 0,800 V, the substrate temperature was reduced from 75 ° C to
The test was carried out by gradually changing the temperature to 0 ° C. The results are shown in Table 2. Example 3 GaAs was used as the base material, and N ₂ was used as the gas type.
At 0,800 V, the substrate temperature was increased from 0 ° C to -80 at each accelerating voltage.
C. in steps. The results are shown in Table 3. Example 4 The same operation as in Example 3 was performed using GaAs as a base material and N ₂ as a gas species. The results are shown in Table 4. Example 5 and Comparative Example 3 Si was used as a substrate, and Ar was used as a gas type.
At 800V, substrate temperature from 75 ° C to -80 ° C at each accelerating voltage
Until it was changed step by step. The results are shown in Table 5. (Effects of the Invention) As specifically shown in the above embodiment, the present invention can easily form an amorphous layer having a desired thickness with high accuracy to perform surface modification, and can perform conventional ion irradiation. Irradiation residual damage, which is a major drawback in the case of surface modification by lithography, is extremely small, and a thermal annealing step after ion irradiation can be omitted. The fact that an amorphous layer having a desired thickness can be easily formed with high precision is extremely significant when performing fine processing by selectively removing an amorphous layer formed in semiconductor device fabrication by etching. Furthermore, omitting the thermal annealing step is not only a simplification of the process, but also a VLSI manufacturing process that requires a low temperature process.
Extremely useful.

Claims (1)

(57) [Claims] 1. In a low temperature range of 20 ° C. or less, an inorganic semiconductor material is irradiated with ions using ions accelerated at a low accelerating voltage of 2000 V or less to a depth of 1000 mm from the surface. A surface modification method by ion irradiation, characterized in that an amorphous layer is formed within the range of (1). 2. The surface modification method according to claim 1, wherein the method is performed in a temperature range of -100 to 20 ° C as a low-temperature region of 20 ° C or less. 3. 2. The surface modification method according to claim 1, wherein the low acceleration region is performed in an acceleration voltage range of 100 to 1500 V. 4. 2. The method according to claim 1, wherein the irradiation is performed using a rare gas ion or a nitrogen ion. 5. The surface modification method according to claim 1, wherein the gallium arsenide-based material is used as a material to be subjected to ion irradiation.