JP3027947B2 - Method of forming fine wire structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a fine line structure made of a semiconductor material on a silicon substrate. More specifically, the present invention relates to a method for forming a thin wire structure for forming a thin wire structure of germanium or a silicon germanium mixed crystal on a silicon substrate.

[0002]

2. Description of the Related Art In recent years, electronic devices and optical functional devices using semiconductors have been increasingly enhanced in performance, functionality and miniaturization. Conventionally, in the process of forming a fine structure, particularly on a silicon substrate, a lithography method using light, an electron beam, an ion beam, X-rays, or the like has been used as a fine structure processing technique. However, with further technological progress, it is expected that it will be necessary to process a fine structure to a size of 0.1 μm or less with high precision in the future, but the above-mentioned lithography technique will not realize this. Have difficulty.

[0003] Therefore, recently, particularly in a thin film forming process, a method of forming a desired fine structure using a phenomenon in which a semiconductor substance is deposited on a substrate in a self-organizing manner has begun to be used.

For example, in Japanese Patent Application Laid-Open No. Sho 62-231202, a Si-Ge mixed crystal (silicon-germanium mixed crystal) is grown on a silicon (111) off substrate. S in the valley of a serrated structure
By growing i (silicon) and Ge (germanium), a thin line structure is formed. In addition, Japanese Unexamined Patent Publication No.
In Japanese Patent No. 154114, a fine structure on the order of nanometers is formed by using two types of step structures existing on the surface of a silicon substrate and adjusting the amount of selective growth of Si or Ge and the growth interruption time. I have. More recently, Maruno and colleagues have reported that Surfactant-me
diated epitaxy of Ge on pa
rtally Ga-terminated Si
(111) surfaces "(App
led Physics Letter vol.6
8 (1996), pp. 2213), by selectively adsorbing Ga (gallium) on the silicon substrate in advance, and by epitaxially growing Ge on a portion of the surface of the silicon substrate where Ga is not adsorbed. It is disclosed that a Ge island structure can be formed along a step on a surface of a silicon substrate.

[0005]

However, according to the method disclosed in Japanese Patent Application Laid-Open No. Sho 62-231202, a Si-Ge mixed crystal is used to grow the surface of a silicon substrate before growing Si or Ge. A saw-tooth structure must be formed, which complicates the process of forming a fine wire structure. Further, in the method disclosed in Japanese Patent Application Laid-Open No. 4-154114, when forming a fine structure, it is necessary to precisely control the selective growth amount and the growth interruption time of Si and Ge in order to adjust the substrate temperature and the material supply amount. , The degree of vacuum, etc., must be strictly controlled, and it has been difficult to form a fine structure to desired dimensions with high precision. Furthermore, the method by Maruno et al. Requires a step of removing the Ga attached to the fine structure after forming the fine structure of Ge, so that the formation process of the fine structure is also complicated.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of forming a fine wire structure which can simplify the process of forming the fine wire structure and can form the fine wire structure to a desired size with high accuracy.

[0007]

The present invention utilizes the phenomenon that a Ge island structure is formed when Ge is epitaxially grown on a silicon substrate.

First, the principle of formation and growth of a Ge island structure will be described with reference to an example in which a Ge island structure is formed and grown on a silicon substrate. FIG. 5 shows that a plurality of germanium islands (hereinafter, referred to as surface)
It is described as "Ge island". 6) is a perspective view showing the silicon substrate in a state where the Ge islands are formed, and FIG. 6 is a perspective view showing the silicon substrate in a state where Ge islands are uniformly distributed on the surface.

In general, Ge grown on a silicon substrate 1
Has a lattice mismatch of about 4%, and the Transki-
It is known to have a Krastanov-type growth mode. That is, at the beginning of epitaxial growth, G
e grows in layers, and the surface of the Ge film becomes flat. When the growth is further continued and the Ge film thickness exceeds about 3 atomic layers, the Ge surface is flattened on the surface of the silicon substrate 1 as shown in FIG.
An island 5 is formed. Normally, such an island structure is formed randomly on the silicon substrate 1, and when the growth is further continued, the Ge islands are finally uniformly formed on the surface of the silicon substrate 1 as shown in FIG. Distribute.

As described above, when the silicon substrate is flat, the island structure is formed at random on the silicon substrate. However, the present inventors have found that the Ge islanding phenomenon strongly depends on the structure of the steps formed on the surface of the silicon substrate.

The method for forming a thin wire structure according to the present invention comprises the steps of [11-
2] A silicon substrate having a (111) plane inclined on the surface is heated in a vacuum, and the silicon substrate is subjected to [-1--
12) flowing a direct current in the direction to form a portion in which a plurality of steps consisting of steps of a monoatomic layer are gathered and an atomically flat portion on the surface of the silicon substrate; 0.1 molecular beam composed of semiconductor material
Irradiating at a deposition rate of １1 atomic layer / min.

When a plurality of steps consisting of steps of a monoatomic layer are formed on the surface of a silicon substrate and an atomically flat portion is formed, and a semiconductor material is deposited on the silicon substrate, an island structure of the semiconductor material is formed. Is easily formed in a portion where steps are gathered, and is hardly formed in an atomically flat portion. Furthermore, the island structure grows preferentially in the direction along the step, and finally, the adjacently formed island structures are united to form a fine line structure.

As described above, since the island structure made of the semiconductor material is formed in a self-organized manner in the portion where the steps are gathered, the substrate temperature of the silicon substrate, the supply amount of the semiconductor material, and the vacuum There is no need to precisely control the growth conditions of the island structure such as the above, and it is not necessary to remove the deposits after forming the fine line structure.

[0014]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view showing a silicon substrate having a fine line structure formed on its surface.

As shown in FIG. 1, a thin wire structure 6 according to the method for forming a thin wire structure according to the present embodiment includes a bunching step 3 where a plurality of steps 2 each formed of a step of a single atomic layer are gathered, The surface is formed on the surface of the bunching step 3 on the surface of the silicon substrate 1 on which the terrace 4 which is a flat portion is formed.

Here, the forming process of the bunching step 3 will be described. FIG. 2 is a perspective view showing a silicon substrate from which a (111) off plane is cut out, and FIG. 3 is a perspective view showing a silicon substrate on which a bunching step and a terrace are formed.

As shown in FIG. 2, the (111) off plane is cut out, and the step 2 of the monoatomic layer is uniformly formed. When a direct current is applied in the X-axis direction, a part of Si on the surface of the silicon substrate 1 is diffused, and as shown in FIG. 3, a bunching step 3 in which a plurality of steps 2 composed of steps of a monoatomic layer are gathered; An atomically flat terrace 4 is formed. This phenomenon is caused by the formation of the bunching step 3 in which the steps 2 are aggregated and the terrace 4 in which the correct (111) plane appears on the surface, rather than the steps 2 being evenly distributed on the (111) off surface. It is thought to be caused by a more stable state.

Next, a method of forming a thin wire structure according to this embodiment will be described.

FIG. 4 is a perspective view showing the silicon substrate in a state where an initial Ge island is formed on the surface.

As shown in FIG. 4, in step 2, there is a portion called “kink 2a” in which the linearity of step 2 is disturbed, so that Ge atoms diffused on silicon substrate 1 have such a kink. 2a. Therefore,
In bunching step 3 where kink 2a is dense,
There is a high probability that the Ge islands 5 are formed with the captured Ge atoms as nuclei.

After the Ge islands 5 are formed, when Ge is further epitaxially grown, the Ge islands 5 grow in the direction along Step 2. This is because the diffusion speed of Ge atoms in the direction crossing step 2 (X-axis direction in FIG. 4) is significantly lower than the diffusion speed in the direction along step 2 (Y-axis direction in FIG. 4). It is. Therefore,
Ge island 5 formed on bunching step 3
Grows preferentially in the direction along the step 2, and eventually, as shown in FIG. 1, the Ge islands 5 formed adjacently on the same step 2 and adjacent to the upper and lower step 2 The Ge islands 5 thus formed are united with each other to form a thin line structure 6 on the bunching step 3.

As described above, the islanding phenomenon of Ge strongly depends on the structure of step 2, and the portion where step 2 of the monoatomic layer is formed on the surface of the silicon substrate 1, that is, FIG. In the portion where the bunching step 3 shown in FIG. 4 is formed, the Ge island 5 is easily formed, and the step 2 is not formed collectively, and the atomically flat portion, that is, the terrace 4 shown in FIG. The Ge islands 5 are hardly formed in the portions where there is.

As described above, in the method of forming the fine wire structure 6 according to the present embodiment, after the bunching step 3 and the terrace 4 are formed on the surface of the silicon substrate 1, a number of Ge islands 5 are formed on the bunching step 3. , Ge islands 5 are grown in the direction along the step 2 and are united with each other to form the fine wire structure 6.

Therefore, in the step of forming the fine wire structure 6, it is not necessary to precisely control the growth conditions of the Ge island 5 such as the substrate temperature of the silicon substrate 1, the supply amount of Ge, the degree of vacuum, and the like. There is no need to remove deposits after formation. Therefore, the process of forming the fine wire structure 6 can be simplified, and the fine wire structure 6 can be formed to a desired size with high accuracy.

Further, in this embodiment, the case where the Ge thin line structure 6 is formed on the silicon substrate 1 has been described, but a compound semiconductor such as Si-Ge is used for the material of the thin line structure 6 other than Ge. be able to.

The width of the thin wire structure 6 can be arbitrarily set by changing the width of the bunching step 3 or the supply amount of Ge to be vapor-deposited. It can be set arbitrarily by changing the off inclination angle.

[0028]

Next, a description will be given of an embodiment of the method for forming the Ge thin line structure 6 on the silicon substrate 1 shown in FIGS.

In this embodiment, in order to observe a change in the state of the surface of the silicon substrate 1 during the growth of Ge on the spot, an MBE apparatus having a vacuum reaching of 1 × 10 ⁻¹⁰ Torr and a scanning electron microscope are used. UHV-SEM combining (SEM)
The device was used. Since the vacuum chamber of the present apparatus also serves as a sample observation chamber and an MBE chamber of the SEM, the silicon substrate 1 is removed when heating, forming the bunching step 3 and the terrace 4, and depositing Ge in a vacuum. It has the advantage that it can be observed on the spot by SEM without taking it out of vacuum.

In the present embodiment, in the [11-2] direction, 0.3
A silicon substrate 1 cut out from a 4 inch p-type silicon (111) substrate inclined at an angle into a strip having a size of 4 mm long × 15 mm wide × 0.5 mm high was used. When the silicon substrate 1 was cut out, the longitudinal direction of the silicon substrate 1 was set to the [11-2] direction.

The silicon substrate 1 cut into strips was washed, placed in a sample holder of the apparatus, and inserted into a vacuum chamber. Then, the vacuum chamber was operated to make the inside of the vacuum chamber into an ultra-high vacuum state. Then, the silicon substrate 1
Is heated at a substrate temperature of 600 ° C. for 15 hours to form a silicon substrate 1
After degassing, [-1-12] was added to the silicon substrate 1.
While a DC current of about 1 A flows in the
Heated for 1 minute at ° C. As a result, it was confirmed by in-situ SEM observation that the Si oxide film formed on the surface of the silicon substrate 1 was removed and the bunching step 3 and the terrace 4 were formed.

Thereafter, the silicon substrate 1 is heated to a substrate temperature of 300.
The substrate was heated to a temperature between 600C and 600C, and the surface of the silicon substrate 1 was irradiated with a Ge molecular beam at a deposition rate of 0.1 to 1 atomic layer / minute. At this time, the Ge islands 5 were preferentially formed on the bunching step 3, and the Ge islands 5 preferentially grew in the direction along the step 2 with the elapse of the vapor deposition time, and the fine wire structure 6 was formed. Similarly, it was confirmed by in-situ SEM observation.

As described above, G on the silicon substrate 1
The thin wire structure 6 of e was able to be formed.

[0034]

As described above, according to the method of forming a thin wire structure of the present invention, (111) inclined in the [11-2] direction.
By heating a silicon substrate having a surface on a surface in a vacuum and applying a direct current to the silicon substrate in the [-1-12] direction, a plurality of steps consisting of steps of a monoatomic layer are assembled on the surface of the silicon substrate. Forming a portion that has been formed and an atomically flat portion, and irradiating a molecular beam of a semiconductor material onto the silicon substrate at a deposition rate of 0.1 to 1 atomic layer / minute. It is not necessary to precisely control the growth conditions of the island structure, such as the substrate temperature of the substrate, the supply amount of the semiconductor substance, the degree of vacuum, etc., and it is not necessary to remove the deposits after the formation of the fine wire structure. The process can be simplified, and the fine wire structure can be formed to a desired size with high precision.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a silicon substrate in a state where a fine line structure is formed on a surface.

FIG. 2 is a perspective view showing a silicon substrate from which a (111) off surface is cut out.

FIG. 3 is a perspective view showing a silicon substrate on which a bunching step and a terrace are formed.

FIG. 4 is a perspective view showing the silicon substrate in a state where an initial germanium island is formed on the surface.

FIG. 5 is a perspective view showing the silicon substrate in a state where a plurality of germanium islands are formed on the surface.

FIG. 6 is a perspective view showing the silicon substrate in a state where germanium islands are uniformly distributed on the surface.

[Explanation of symbols]

 Reference Signs List 1 silicon substrate 2 step 2a kink 3 bunching step 4 terrace 5 germanium island 6 thin wire structure

Claims (5)

(57) [Claims] 1. The (111) inclined in the [11-2] direction
By heating a silicon substrate having a surface on a surface in a vacuum and passing a direct current through the silicon substrate in the [-1-12] direction, a plurality of steps consisting of steps of a monoatomic layer are formed on the surface of the silicon substrate. Forming an aggregated portion and an atomically flat portion;
Irradiating at a deposition rate of 1 to 1 atomic layer / min. 2. The method according to claim 1, wherein the temperature of the silicon substrate is 1200 ° C. in the step of forming a portion where a plurality of steps each having a step of a monoatomic layer are gathered and an atomically flat portion on the surface of the silicon substrate. 2. The method for forming a thin wire structure according to 1. 3. A step of degassing the silicon substrate before forming a portion where a plurality of steps each composed of a step of a monoatomic layer are gathered and an atomically flat portion on the surface of the silicon substrate. The method for forming a fine wire structure according to claim 1, comprising: 4. The method according to claim 3, wherein the temperature of the silicon substrate in the step of degassing the silicon substrate is set to 600 ° C. 5. A method of irradiating a molecular beam of a semiconductor material onto the silicon substrate at a deposition rate of 0.1 to 1 atomic layer / minute, wherein the temperature of the silicon substrate is 300 to 600.
The method for forming a fine wire structure according to any one of claims 1 to 4, wherein the temperature is set to ° C.