KR100539465B1 - Formation Method of Surface Blister for Si Layer Splitting - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a surface bubble for separating a silicon thin film. In particular, when an SOI wafer is manufactured by a smart-cut method, microcrack induced by hydrogen, which is an essential condition for thin film layer separation, It relates to a method in which surface bubbles appearing as a result of formation are formed.

According to the present invention, there is provided a method for forming a surface bubble for separating a thin film from an SOI substrate, comprising: a first step of thermally oxidizing a predetermined thickness of a first substrate; A second step of implanting ions into a predetermined depth deeper than the thickness of the thermal oxide film of the first substrate; A third step of bonding the ion implanted first substrate to a second substrate; A fourth step of separating the ion implanted thin film having the surface bubbles formed by microcracks by heat-treating the bonded first and second substrates in a range of 300 to 600 ° C. for 10 to 30 minutes; And it proposes a surface bubble forming method comprising a fifth step of polishing the separated thin film surface.

Therefore, when the SOI wafer is manufactured by smart-cut technology, the present invention reduces the heat treatment time and reduces the separation process error of the ion-injected silicon wafer by determining whether the thin film is separated by the formation of surface bubbles. Can be.

Description

Formation Method of Surface Blister for Si Layer Splitting

The present invention relates to a method for forming a surface bubble for separating a silicon thin film. More specifically, when the SOI wafer is manufactured by the smart-cut method, a surface bubble is formed that appears as a result of the formation of microcracks induced by hydrogen, which is a prerequisite for thin film layer separation. will be.

In general, single crystal materials are required to manufacture high performance microelectronic or optoelectronic devices in various fields, particularly in the semiconductor field. In many cases, only a thin surface layer on the order of 10 nm to several μm is made of a single crystal material, and the rest of the body may be made of any suitable material. The epitaxial layer can be grown by a well-established epitaxial method when the substrate on which the epitaxial layer is formed is a single crystal and has a lattice constant close to the lattice constant of the surface formed thereon.

On the other hand, when the thin film formed on the substrate has a very different lattice constant from the substrate or is polycrystalline or amorphous, it cannot be grown by the epitaxial method.

Therefore, in the prior art, a single crystal material layer has been prepared on a substrate by a layer transfer method when the coefficients of thermal expansion of the two substrates are similar. That is, a thin single crystalline thin film from the first substrate to the second substrate is bonded by bonding a single crystalline first substrate and a second substrate having a different lattice constant from the first substrate, and then removing the remaining first substrate except the thin single crystalline thin film. As a result, the single crystal layer was formed on the second substrate.

This layer transfer method is described in Bruel's U.S. Patent 5,374,215 and in Bruel's published article "Silicon on insulator material technology" (Electronic Letters.vol. 31, 1995, pp. 1201-1202). The realization of a thin monocrystalline silicon layer on a silicon oxide substrate was accomplished by wafer bonding the hydrogen implanted single crystal silicon substrate followed by heat treatment. This heat treatment results in the final macrocracking at a location close to the maximum concentration of hydrogen injected by formation, growth and coalescence of hydrogen filled microcracks essentially parallel to the junction interface, resulting in a single crystal thin film becoming the second substrate. The thin film is separated from the first substrate by being transferred to the substrate.

However, this method is possible only if the difference in thermal expansion coefficient between the first substrate and the second substrate is very small or the same. This method is one of the technologies for manufacturing SOI wafers and is called a smart-cut method.

Smart-cut technology has been successfully applied to fabricate silicon on insulator (SOI) wafers. SOI is a structure in which a silicon (Si) thin film layer is placed on an insulator such as SiO _2, and electronic devices or optical devices are made on the silicon thin film layer. The basic idea behind SOI is to make the device switch faster by reducing parasitic capacitance.

In order to fabricate SOI wafers using smart-cut technology, a thermal oxidation process is used to oxidize a silicon substrate to a certain thickness by heat, and hydrogen is used to separate a thin film of a certain thickness. Ion implantation process for deep implantation, wafer bonding process for attaching ion implanted wafers to other silicon substrates, heat treatment process for separating hydrogen-implanted layers by heat-treating the bonded wafers at high temperature, and separating thin film surfaces It must undergo a chemical-mechanical polishing (CMP) process.

Thermal oxide film formation, hydrogen ion implantation, wafer direct bonding, and thin film transfer process in the manufacturing process requires a lot of manufacturing time and advanced technology. In particular, when the thin film is not separated after the thin film transfer process, the fabrication of the SOI wafer ends in failure. Therefore, it is obvious that physical conditions in which the thin film can be separated after ion implantation and conditions for expressing the phenomenon in a short time are required.

The present invention is to solve the above problems, the first object of the present invention is because the surface bubbles directly related to the separation of the thin film layer is formed and grown according to the heat treatment time as well as the heat treatment temperature range of the heat treatment temperature 300 ~ 600 ℃ By experimentally determining the time at which the surface bubbles are formed when is at, it is possible to reduce the overall processing time by reducing the heat treatment time at a specific temperature when manufacturing an SOI wafer.

A second object of the present invention is to allow the formation and growth of surface bubbles according to the heat treatment temperature can be investigated using an optical microscope when the heat treatment time is fixed.

A third object of the present invention is to allow the formation and growth process of the surface bubbles according to the heat treatment time when the heat treatment temperature is fixed.

The fourth object of the present invention is to observe the surface bubble formation and growth process using AFM (Atomic Force Microscope), which can measure a more microscopic world in a sample that is not observed on an optical microscope, the size and surface of the surface bubble Microscopic properties, such as roughness, can be investigated.

As the technical idea for achieving the above object of the present invention

In the surface bubble formation method for thin film separation of SOI substrate,

A first step of thermally oxidizing a predetermined thickness of the first substrate;

A second step of implanting ions into a predetermined depth deeper than the thickness of the thermal oxide film of the first substrate;

A third step of bonding the ion implanted first substrate to a second substrate;

A fourth step of separating the ion implanted thin film having the surface bubbles formed by microcracks by heat-treating the bonded first and second substrates in a range of 300 to 600 ° C. for 10 to 30 minutes; And

It provides a surface bubble forming method comprising a fifth step of polishing the separated thin film surface.

Hereinafter, with reference to the accompanying drawings, the configuration and operation of the embodiment of the present invention will be described in detail.

In the present invention, the heat treatment time at which the surface bubbles start to form in a specific heat treatment temperature range will be described in detail, and the formation and growth process of the surface bubbles according to the heat treatment time and the heat treatment temperature, and the geometric size of the surface bubbles are determined by the optical microscope and the AFM. The phase will be described in detail.

The present invention comprises the steps of thermally oxidizing a predetermined thickness of the first substrate; Ion implanting a predetermined depth deeper than the thermal oxide thickness of the first substrate; Bonding the ion implanted first substrate to a second substrate; Separating the ion-implanted thin films having surface bubbles formed by microcracks by heat-treating the bonded first and second substrates in a range of 300 to 600 ° C. for 10 to 30 minutes; And polishing the separated thin film surface.

In particular, the present invention provides a method of forming surface blisters through which a single crystal layer can be transferred from an essentially planar, mirror-polished first substrate to an essentially planar, mirror-polished second substrate. have.

The surface bubble is formed by heat treatment after hydrogen injection. Disorders caused by hydrogen injection during the heat treatment result in crystal rearrangement. Bubbles on the surface indicate that microcracks exist at the ion implantation depth Rp.

Thus, the formation of surface bubbles directly indicates the formation of microcracks induced by hydrogen, a prerequisite for layer splitting. In the smart-cut process of silicon, the heat treatment temperature required for thin film separation is usually about 500 ° C [M. Bruel, “Process for the production of thin semiconductor material films,” US Pat. No. 5,374,215 (1994), M. Bruel, Electron. Lett., 31, 1201 (1995). However, in the above-described prior art, the correlation between the heat treatment temperature and the heat treatment time required for thin film layer separation is not described in detail.

However, according to the present invention, the surface bubbles directly related to the thin film layer separation are formed and grown depending on the heat treatment time as well as the heat treatment temperature.

In the present invention, the silicon substrate used to investigate the conditions for forming the surface bubbles is a commercially available 5 inch boron doped p-type silicon wafer. The crystal direction and specific resistance of the single crystal silicon wafer are [100] and 12-18 ohm · cm, respectively. Before the hydrogen was injected into the silicon sample, the ion implantation depth for the implantation energy was calculated using the TRIM simulator. The dose of hydrogen When ions / cm ² and the injection energy is 90 to 100 keV (Example: 95 keV), a hydrogen injection depth of 8000 to 9000 Hz (Example: 8500 Hz) was obtained.

The ion accelerator used for hydrogen ion implantation is NEC's 2.0 MV tandem installed at KIST in 1995. In order to investigate surface blister formation in silicon samples implanted with hydrogen ions by using rapid thermal annealing (RTA) equipment, the silicon wafer is first ultrasonically cleaned in the order of trichloroethylene (TCE), acetone and methanol, followed by deionized water. (18MPa) and moisture was removed from the sample surface using nitrogen gas.

And hydrogen ions at an energy of 95 keV It was implanted into the silicon wafer at a dose of ions / cm ² . In the RTA chamber used for heat treatment of the silicon wafer, Ar gas was introduced into the chamber at a flow rate of 50 sccm when the basic pressure was 200 mTorr by a vacuum pump. And heat treatment was started when the pressure of the chamber was maintained at 1000 mTorr by the argon (Ar) gas introduced.

The heat treatment temperature was changed to 350 ~ 600 ℃ in order to investigate the appearance of the surface bubbles according to the above heat treatment temperature. And the change of surface bubble with heat treatment time at specific temperature was investigated. In order to observe the surface bubbles formed on the surface of the sample after the heat treatment, the heat-treated sample was irradiated using an optical microscope (× 200).

Figure 1 shows the change of bubbles formed on the surface of the silicon sample as the heat treatment temperature is increased when the heat treatment time is 20 minutes. In FIG. 1 where the heat treatment temperature is 400 ° C., points in circle a are surface bubbles, and points in circle b are craters caused by surface bubbles bursting from the surface.

In FIG. 1, when the heat treatment temperature is 350 ° C., optically detectable surface bubbles are not observed. However, since bubbles start to appear at 400 ° C, they burst on the surface as the temperature increases, so the number of surface bubbles decreases and the number of craters rapidly increases. Therefore, as the heat treatment temperature increases to 350 ° C., 400 ° C., 500 ° C., and 600 ° C., surface bubbles are formed and then grow and eventually burst, leaving many craters on the sample surface.

Figure 2 is a micrograph showing the change of the surface bubbles with the heat treatment time when the heat treatment temperature is 400 ℃. Surface bubbles are mainly observed when the heat treatment time is 10 minutes at 400 ° C. However, when the heat treatment time is 20 minutes, the number of craters whose surface bubbles burst is increased. Therefore, the number of craters increases as the heat treatment time increases when the heat treatment temperature is fixed.

In conclusion, when the heat treatment time is fixed, the surface bubbles are formed more and more as the heat treatment temperature increases, and the number of craters popping out from the surface increases. In addition, when the heat treatment temperature is fixed, as the heat treatment time increases, more surface bubbles burst. 1 and 2, the number of bursting craters is more sensitive to the heat treatment temperature than the heat treatment time.

On the other hand, based on the above-described results alone, the heat treatment time at which the surface bubbles start to form at each heat treatment temperature cannot be determined. Therefore, the heat treatment time was changed at each temperature when the temperature range was 330 ~ 600 ℃ to find the time when the surface bubble is formed as a function of the heat treatment temperature in the sample injected with hydrogen ions.

3 is the time at which surface bubbles begin to form, measured as a function of heat treatment temperature. Formation of surface bubbles after heat treatment was investigated 200 times using an optical microscope. When the heat treatment temperature is 330 ° C for 100 minutes, surface bubbles start to form. On the other hand, at 500 ° C or higher, many bubbles start to form even after only one minute of heat treatment.

This means that the surface bubble formation time in the sample decreases rapidly with increasing temperature. After the surface bubbles were formed and grown on the sample surface according to the heat treatment temperature, it was already confirmed in FIG. 1 that the surface bubbles burst to generate craters. Therefore, the higher the heat treatment temperature to form the surface bubbles, the shorter the heat treatment time can be reduced in the SOI manufacturing process time.

In FIG. 3, when the heat treatment temperature was 350 ° C., the heat treatment time at which the surface bubbles began to be formed was 30 minutes. Using atomic force microscopy (AFM) with higher precision than optical microscopes, the formation and growth of surface bubbles can be described in greater detail. In addition, information is obtained on the surface roughness of the surface of the silicon sample having the surface bubbles and the diameter and height of the surface bubbles. Therefore, three samples having a heat treatment temperature of 350 ° C. and a heat treatment time of 10 minutes, 20 minutes, and 30 minutes were irradiated with AFM.

4 is an AFM (20 × 20 μm) photograph of a hydrogen-injected silicon sample heat treated at 350 ° C. FIG. Surface bubble formation was not observed when the heat treatment time was 10 minutes. And root mean square (RMS) roughness is 0.412 nm. However, when the heat treatment time is increased to 20 minutes, surface bubbles are observed. This surface bubble was not observed by the optical microscope of FIG. When the heat treatment time is increased to 30 minutes, it is confirmed that the surface bubbles grow by comparing with when the heat treatment time is 20 minutes.

In addition, when the heat treatment time was 20 minutes and 30 minutes, the diameter, height and surface roughness of the surface bubbles were measured using AFM, respectively. FIG. 5 is an AFM (20 × 20 μm) profile of a hydrogen implanted silicon sample heat treated at 350 ° C. FIG.

5 (a) and 5 (b) were obtained by scanning along a straight line displayed on the AFMs of Figs. 4 (b) and (c), respectively. The diameter and height of the largest bubbles on the scan line of Fig. 5 (a) are 1.7 μm and 7.6 nm, respectively, while in Fig. 5 (b) they are 4.25 μm and 16.8 nm. However, the RMS roughness in Fig. 5 (a) was 0.948 nm and the diameter and height of the surface bubbles were 2 to 3.5 μm and 1.1 to 7.6 nm, respectively.

Meanwhile, in FIG. 5 (b), the RMS roughness was 3.66 nm and the surface bubble diameter and height were 2 to 6.7 μm and 5.8 to 22 nm, respectively. Therefore, as the heat treatment time is increased at the same heat treatment temperature from the AFM measurement results of FIGS. 4 and 5, the surface bubbles are formed and grown microscopically.

As described above, in the method for forming a surface bubble for thin film separation according to the present invention, the heat treatment time is determined at the same time as the formation and growth characteristics of the surface bubble according to the heat treatment time and the heat treatment temperature using RTA in a silicon wafer implanted with hydrogen ions. When the heat treatment temperature is selected to minimize the SOI wafer manufacturing process time is shortened, there is an advantage that can improve the productivity of the SOI wafer.

In addition, in the present invention, since the formation and growth of the surface bubbles with the heat treatment temperature and time are described in detail on the optical microscope and AFM, the size of the surface bubbles is controlled during the heat treatment process (SOI wafer which is the core material of the ultrafast electronic device). Technology related to the manufacturing process), the roughness of the thin film separated surface may be controlled during the heat treatment process.

In addition, the present invention is to develop a smart-cut when a single crystal thin film or epi thin film based on InP or GaAs other than silicon is formed on a substrate having a different lattice constant to develop a semiconductor hybrid integration technology. Surface bubble formation experiments can be used to find new process conditions for thin films to be separated and transferred without going through the process.

1 is a photograph showing the surface bubble and the crater shape formed according to the temperature change when the heat treatment time is 20 minutes according to an embodiment of the present invention.

Figure 2 is a photograph showing a surface bubble change formed according to the heat treatment time at 400 ℃ by an embodiment of the present invention.

3 is a graph showing the time when the surface bubbles start to form according to the heat treatment temperature according to an embodiment of the present invention.

4 is a photograph showing the surface bubble AFM image after heat treatment at 350 ℃ according to an embodiment of the present invention.

Figure 5 is a graph showing the AFM image of the surface bubble size after heat treatment at 350 ℃ according to an embodiment of the present invention.

Claims (8)

In the surface bubble formation method for thin film separation of SOI substrate, A first step of thermally oxidizing a predetermined thickness of the first substrate; A second step of implanting hydrogen ions to a predetermined depth deeper than the thermal oxide thickness of the first substrate; A third step of bonding the ion implanted first substrate to a second substrate; A fourth step of separating the ion implanted thin film having surface bubbles formed by microcracks by rearranging crystals during heat treatment by heat-treating the bonded first and second substrates in a range of 300 to 600 ° C. for 10 to 30 minutes; And And a fifth step of polishing the separated thin film surface. The method of claim 1, wherein the ion implantation conditions of the second step is a dose of hydrogen (dose) ions / cm ² and the surface bubble forming method characterized in that the injection depth of hydrogen is 8000 ~ 9000Å when the injection energy is 90 ~ 100 keV. The method of claim 1, wherein the first substrate ion-implanted in the second step is ultrasonically cleaned in the order of TCE, acetone, methanol, and washed with deionized water (18MΩ), to remove moisture on the surface of the substrate using nitrogen gas Surface bubble formation method characterized in that. The method of claim 1, wherein the RTA chamber used for the heat treatment in the fourth step, when the basic pressure is 200 mTorr by a vacuum pump, argon (Ar) gas is introduced 50 sccm, the argon (Ar) gas And the heat treatment is performed when the pressure in the chamber is maintained at 1000 mTorr. The method according to claim 1, wherein when the heat treatment time is fixed to 20 minutes in the fourth step, as the heat treatment temperature is increased to 400 ℃, 500 ℃, 600 ℃ to form a plurality of craters that are grown after the surface bubbles are formed to remain on the substrate surface Surface bubble formation method characterized in that. The method according to claim 1 or 5, wherein when the heat treatment temperature is 400 ℃ in the fourth step as the heat treatment time is increased to 10 minutes, 20 minutes, 30 minutes to increase the number of surface bubbles and the number of craters formed by the surface bubbles burst Surface bubble formation method characterized in that. The method of claim 6, wherein the formation time of the surface bubbles is rapidly decreased as the heat treatment temperature increases from 330 to 600 ° C. in the fourth step. The surface bubble of claim 1, wherein the diameter and height of the surface bubble and the surface roughness are measured by an atomic force microscope (AFM) when the heat treatment temperature is 350 ° C. and the heat treatment time is 20 to 30 minutes in the fourth step. Formation method.