JPH0483331A - Silicon crystal surface treatment method - Google Patents

Abstract

PURPOSE:To enable an atom step structure of a surface of a crystal thin film to be controlled arbitrarily by allowing direct current to be flown to an electrode, by allowing temperature of a silicon crystal substrate to be controlled within a temperature where phase transition between a super structure of a surface and a basic structure occurs or within a specified range from the temperature and a certain amount of time to be retained. CONSTITUTION:By allowing direct current to be flown to an electrode terminal, temperature of a silicon crystal substrate 1 is retained to a temperature Ts where phase transition from a basic structure of a crystal to a super structure occurs regarding a structure of a crystal surface or within + or -50 deg.C, namely Ts+20 deg.C. At this time, by selecting current direction and current-conduction time properly, a step interval on a silicon surface can be set to a desired value. After a specified current-conduction time passed, temperature of the silicon crystal substrate is set to a room temperature or a temperature which is lower than Ts-50 deg.C depending on the succeeding process. The step structure 2 which is formed on a surface of the silicon crystal substrate 1 does not change much at a temperature which is lower than Ts-50 deg.C, thus enabling a crystal growth process utilizing the desired step structure 2 to be performed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to technology for crystal growth of thin films of semiconductors, metals, etc., and silicon crystal surface treatment for forming fine elements such as integrated circuits using these thin films. It is about the method.

[Prior Art] In recent years, attempts have been made to create ultra-high-speed devices by confining electrons in a narrow region of several to tens of atomic layers to generate quantum effects and increase the movement of electrons.

For this purpose, a thin linear region (with a width of several to several dozen atomic layers)
It is necessary to form quantum wires) or box-shaped regions (quantum boxes) with dimensions of several to ten atomic layers in the vertical and horizontal directions on the surface of the crystal material. The technology for forming these quantum wires and quantum boxes is as follows:
A substrate whose crystal surface is tilted several degrees with respect to the crystal lattice plane (
A method using a tilted substrate is being considered. On the surface of a tilted substrate, atomic layer steps appear at regular intervals, so by appropriately selecting the tilt angle of the surface, flat areas (terraces) between atomic layer steps can be created.
can be set to any desired width. By selectively growing crystals on these terraces, it is possible to create thin line arrays consisting of periodic arrays of two types of crystals (Reference (Fukui: [
"Fabrication of quantum wires using epitaxial growth" Applied Physics 58 (1989> 1381)). In addition, by selectively etching a part of this fine line array or destroying it by ion irradiation, the length direction of the fine line can be restricted.
A quantum box can be formed.

[Problems to be Solved by the Invention] However, conventionally, the intervals between atomic layer steps are determined by the inclination angle of the crystal surface, and the intervals on one crystal surface are the same. Furthermore, in order to change the interval between two atomic layer steps, it is necessary to prepare samples with other tilt angles. Therefore, it has not been possible to control and form atomic layer steps with different intervals on one type of crystal substrate. Therefore, the crystal substrate had to be changed depending on the structure of the device to be formed.

On the other hand, in addition to the devices using quantum wires and quantum boxes described above, quantum wells that utilize one-dimensional quantum effects utilize extremely thin films with a thickness of several to ten-odd atomic layers. In this case, if a large atomic layer step exists at the interface of the thin film, the mobility of electrons will decrease due to surface scattering. Therefore, the interface of the thin film is required to be flat at the atomic level. It is desirable that a device using such an ultra-thin film quantum well be formed on a substrate whose crystal surface coincides with a lattice plane, contrary to the above-described inclined substrate. However, it is extremely difficult to match the actual substrate surface and the lattice plane with an accuracy of within 0.1 degree using current cutting and polishing techniques. Currently, the guaranteed accuracy of crystal substrates used as commercially available products is generally 0.2 degrees, and those with higher precision are extremely expensive.

As described above, the step structure of the crystal surface obtained by conventional cutting and polishing does not have sufficient controllability to meet the requirements of various device structures. In recent years, Latyshev et al. have shown that when a sample is heated to 1000°C to 1350°C using a direct current on a silicon surface, atomic layer steps can be uniformly distributed on the surface, or there may be atomic layer steps ranging from a few to 10, depending on the direction in which the current is applied. We found that the surface where atomic layer steps on the number side are periodically assembled (step punching) changes reversibly (References (A, V, L)
atyshev, A.L., Aseev, A.B.
Krasilnikov and 5. l5teni
n: 'TRANSFOR)4ATION ON CL
EAN 5i (111) 5TEPPED 5URFA
CE DURING SUBLIMATION” 5u
rface 5science 2) 3 (1989)
157. ). FIG. 4 schematically shows changes in the atomic layer step structure depending on the current direction. As shown in the same figure (a), the temperature of the silicon crystal substrate 1 is 1050°C to 1250°C.
Now, if we take the direction in which the current I flows upwards through the monoatomic layer step 2, this monoatomic layer step 2 will be uniformly distributed, and if we take the direction in which the current I flows in the opposite direction, that is, in the downward direction through the monoatomic layer step 2, we will get the same figure. As shown in (b), step punching occurs in which a step band 3 in which monoatomic layer steps 2 are densely gathered is generated. Further, the temperature of the silicon crystal substrate 1 is 125
Conversely, from 0"C to 1350"C, the monoatomic layer step 2
Step punching occurs in the downward direction. When this step punching occurs, the interval between step bands 3 in which the monoatomic layer steps 2 are densely gathered is much wider than the step interval in the case of uniform distribution as shown in the figure (a>), and the interval between step bands 3 is The interval of atomic layer step 2 is also shown in the same figure ('
It becomes wider than in the case of a>. When using this step punching, the step interval can be controlled to some extent, but at what position the step punching occurs, and the step interval at a particular position is completely contingent. . Therefore, the range in which this phenomenon can be utilized for device fabrication has been limited.

Therefore, the present invention has been made in order to improve the problems in the conventional silicon crystal surface treatment method, and its purpose is to improve the surface of a silicon crystal substrate whose surface is inclined with respect to the crystal plane, or to treat the surface of a silicon crystal that is grown on the substrate. An object of the present invention is to provide a silicon crystal surface treatment method that allows arbitrary control of the atomic step structure on the surface of a crystalline thin film.

[Means for Solving the Problems] In order to solve these problems, the silicon crystal surface treatment method according to the present invention provides a silicon crystal surface treatment method in which a crystal substrate is oriented at the edge of a silicon crystal substrate whose surface is inclined with respect to a crystal plane. A DC current is applied to the electrode, and the temperature of the silicon crystal substrate is controlled to a temperature at which a phase transition between the surface superstructure and the basic structure occurs, or within a range of ±50°C from that temperature. It has a step of holding the temperature for a certain period of time.

[Function] In the silicon crystal surface treatment method of the present invention,
The atomic step structure on the surface of a silicon crystal substrate or the surface of a crystal thin film grown on the substrate can be arbitrarily controlled.

[Example] Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows the first method of silicon crystal surface treatment according to the present invention.
It is a figure which shows the flowchart for explaining the process by the Example. In the same figure, first, after cleaning a silicon crystal substrate whose surface is inclined with respect to the crystal plane (
Step 11): Install an electrode terminal on the edge of the silicon crystal substrate for passing a current through the silicon crystal substrate (Step 1)
2).

Next, the silicon crystal substrate is heated in an ultra-high vacuum, preferably at 1X.
It is introduced into a vacuum at a pressure of 10-9 Torr or less (step 13). Next, in order to obtain a clean surface, the temperature of the silicon crystal substrate is maintained at a high temperature, preferably 1000 DEG C. or higher, for several to several tens of seconds (step 14). This is done by resistively heating the silicon crystal substrate by passing a current such as direct current or alternating current through the electrode terminals, or by heat radiation from a separately installed heater. Thereafter, by flowing a direct current to the electrode terminal, the temperature of the silicon crystal substrate is maintained at a temperature Ts at which the crystal surface structure undergoes a phase transition from the basic structure of the crystal to a superstructure, or within ±50°C, for example, Ts + 20°C. (Step 15). At this time, by appropriately selecting the current direction and the current application time, the step interval on the silicon surface can be set to a desired value. After a predetermined energization time has elapsed, the temperature □ of the silicon crystal substrate is set to room temperature or to a temperature lower than Ts-50°C depending on the next process (step 16). Since the step structure formed on the surface of the silicon crystal substrate hardly changes at a temperature lower than T s -50° C., it is possible to perform a crystal growth process using a desired step structure. In the case of growing a silicon crystal thin film, it is also possible to change the step structure of the grown silicon crystal thin film by returning to the current heating process after forming the silicon crystal thin film.

According to this method, by using a silicon crystal substrate whose surface is inclined with respect to the crystal plane, the basic step interval or the interval of a step band where steps are gathered can be set by the inclination angle. By using electrical heating near Ts, which is the lowest temperature at which movement of the steps occurs, the step interval can be changed while maintaining the parallelism of the steps. Ts -50℃
At lower temperatures, the mobility of the steps decreases and the step structure changes little. In addition, in the temperature range higher than T s + 50°C, the mobility of the step increases, so
The directions of the steps are not aligned in one direction, making it impossible to obtain a linear step structure.

Although this embodiment describes the case of heating in vacuum, step structure control by electrical heating can also be applied to surface treatment of silicon crystals in the air, under reduced pressure, or under increased pressure.

Furthermore, effects similar to those of silicon crystal can be expected with crystal materials other than silicon.

Figure 2 shows [112] for the (111) plane of silicon crystal.
] shows the relationship between the interval of a step band where steps are gathered and the heating time when the present method is applied to a surface that has one skin in the direction. On the silicon (111) surface, the transition temperature Ts between the basic structure 1×1 and the super 11B* 7×7 is 830°C. In the example shown in the figure, the temperature of the silicon crystal substrate was set to Ts+20°C, that is, 850'C.

If the direction of current flow is set to the direction in which step punching occurs, heating for less than 1 minute results in the same 60 nm as when the current flows in the opposite direction, 200 nm for 16 minutes, and 60 nm for 60 minutes.
It became 00 nm. In the case of the direction opposite to the direction of the step punch, there is almost no change in the step interval even after 60 minutes of heating.

FIG. 3 shows the second method of silicon crystal surface treatment according to the present invention.
It is a figure which shows the flowchart for explaining the process by the Example. In the figure, the temperature of the silicon crystal substrate in step 15 is controlled not only by direct current but also by an indirect heater and infrared light.

Step 17: Controlled by auxiliary heating means provided outside the silicon crystal substrate, such as a laser beam or an electron beam.
), the temperature of the silicon crystal substrate surface is set within Ts±50°C. In this case as well, the same effects as in the first embodiment can be obtained.

[Effects of the Invention] As explained above, according to the present invention, an electrode for flowing a directional current to the crystal substrate is installed at the edge of the silicon crystal substrate whose surface is inclined with respect to the crystal plane, and directly to this electrode? By having a process of flowing an X current, controlling the temperature of the silicon crystal substrate at a temperature at which a phase transition between the surface superstructure and the basic structure occurs, or within a range of ±50°C from that temperature, and maintaining it for a certain period of time. This has made it possible to arbitrarily control the atomic step structure on the surface of a silicon crystal substrate or the surface of a crystal thin film grown on a substrate, which was previously difficult, and has had a great effect on the development of quantum effect devices and optical devices. It has an extremely excellent effect of bringing about

[Brief explanation of the drawing]

FIG. 1 shows the first method of silicon crystal surface treatment according to the present invention.
FIG. 2 is a diagram illustrating the relationship between step band spacing and heating time in the first embodiment of the present invention, and FIG. FIG. 4 is a diagram illustrating a flowchart of steps for explaining the second embodiment of the processing method, and is an explanatory diagram of step punching caused by electrical heating. ■・−・Silicon crystal substrate, 2・・Atomic layer step, 3・・・Step band. Figure 1

Claims (2)

[Claims] (1) In the silicon crystal surface treatment method of the silicon crystal substrate surface before or during the growth of a silicon crystal thin film or a silicon crystal thin film on the silicon crystal substrate surface whose surface is inclined with respect to the crystal plane, An electrode is installed at the edge of the silicon crystal substrate to allow a directional current to flow through the crystal substrate, and a direct current is passed through the electrode to adjust the temperature of the silicon crystal substrate to the temperature at which a phase transition between the surface superstructure and the basic structure occurs, or A silicon crystal surface treatment method comprising the step of controlling the temperature within a range of ±50°C and maintaining it for a certain period of time. (2) In claim 1, an electrode for passing a directional current through the crystal substrate is installed at the edge of the silicon crystal substrate, and a direct current is passed through the electrode to adjust the temperature of the silicon crystal substrate to a temperature at which a superstructure appears or a temperature at which a superstructure appears. A silicon crystal surface treatment characterized by including the step of heating the surface of the silicon crystal substrate from the outside using an auxiliary heating means, in the step of controlling the temperature within ±50°C and holding it for a certain period of time. Method.