JPS621219A - Forming method for soi structure - Google Patents

Abstract

PURPOSE:To make the temperature of the end section of a region, which must be single-crystallized, sufficiently higher than the inside by projecting laser beams having beam width irradiating at least two insular semiconductor films and turning a first semiconductor film existing between the two insular semiconductor films into the single crystal. CONSTITUTION:An silicon oxide film 2 is formed onto an silicon substrate 1, and a polysilicon film 3, an silicon oxide film 4 as a cap film, an silicon nitride film 5 and a polysilicon film 7 are each shaped onto the oxide film 2. The polysilicon film 7 is formed to a striped shape while leaving both sides on a region 9, in which a SOI single crystal must be formed, at that time to expose the silicon nitride film 5, and an silicon nitride film 6 is shaped onto the film 7. Multiplayer films consisting of the silicon oxide film 4, the silicon nitride film 5, the polysilicon film 7 and the silicon nitride film 6 function as an antireflection film to Ar laser beams, and multilayer films on the region 9, in which the single crystal composed of the silicon oxide film 4 and the silicon nitride films 5, 6 must be shaped, serve as a reflecting film to laser beams.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention provides a method for forming an insulating film on an insulating film by laser beam annealing.
5OI (semiconductor on insulator) with semiconductor single crystal region
1n-sulator) substrate.

(Prior art and its problems) Conventionally, when forming an SOI structure, a silicon substrate is used as the base semiconductor substrate, a silicon oxide film is used as the insulating film, a polysilicon film is used as the semiconductor film, and a polysilicon film on the silicon oxide film is used. The polysilicon film was melted and recrystallized by laser annealing. Furthermore, in order to prevent contamination of the polysilicon film that occurs when laser annealing is performed in the atmosphere, a method has been adopted in which a cap film of an insulating film is formed on the polysilicon film. However, since the spatial power distribution of the laser beam emitted from the laser oscillation tube is usually a Gaussian distribution, the temperature at the end of the melted region of the polysilicon film is lower than that inside the region. Recrystallization therefore starts from the edge of the melted region and proceeds inward. At this time, since the outside of the melted region is a polysilicon film, the recrystallized region becomes polycrystalline, and the melted region cannot be made into a single crystal. (IEICE technical research report CPM83-13) To solve this problem, the following method is used.

First, as shown in FIG. 2, a silicon oxide film 2 is formed on a silicon substrate 1, a polysilicon film 3 is formed thereon by the CVD method, and the surface is oxidized to form a silicon oxide film 4 and a silicon nitride film 5. form. Thereafter, a polysilicon film 7 is formed on the region 9 where a single crystal silicon film is to be formed, and a silicon nitride film 6 is further formed on the entire surface of the substrate. At this time, the polysilicon film 7 is adjusted so that the reflectance R1 for the laser beam in the region where the polysilicon film 7 is present is greater than the reflectance R2 in the region where the polysilicon film 7 is not present (R1>R2). Determine the film thickness. Next, a laser beam with a beam diameter 8 equal to the width of the polysilicon film 7 is used as shown in FIG.
As shown in a), it is possible to shape the distribution 10 so that the end portion of the region 9 where the SOI single crystal is desired to be formed is larger than the inside portion.

Furthermore, during laser annealing, the laser power is also absorbed by the polysilicon film 7, and the heat stored in this polysilicon film 7 is used during recrystallization to direct the region 9 where an SOI single crystal is to be formed.
can be conveyed to. At this time, the temperature distribution within the polysilicon film 3 is higher at the end of the region 9 where the SOI single crystal is desired to be formed than at the inside, as shown by 11 in FIG. 2(b).

As a result, in the region 9 where it is desired to form an SOI single crystal, recrystallization progresses from the inside to the outside of this region, and the region 9 becomes a single crystal region. (Third Novel Functional Device Technology Symposium Proceedings, p. 243-256) However, the polysilicon film 7 has good heat retention because it is surrounded by an insulating film. Therefore, the heat generated by the beam annealing is stored and transferred to the polysilicon film 3 by heat conduction during recrystallization. On the other hand, since the polysilicon film 3 has a larger area than the polysilicon film 7, heat easily escapes to the surroundings.

In other words, it has the effect of raising the temperature at the center of the region 9 where the SOI single crystal is to be formed and lowering the temperature at the end. Therefore, with this conventional method, it is not possible to create a temperature difference as large as intended. Therefore, there may be cases where 2 single crystals cannot be formed.

In addition, due to the uneven thickness of each thin film, the difference between R1 and R2 is different from the initial design, and becomes 10 in FIGS. 2(c) and 2(d). In this case, the temperature distribution within the polysilicon film 3 is as shown in FIG. 2(C).

As shown in 11 of (d), the temperature distribution is opposite to the initial intention that the temperature at the end of the region 9 where the SOI single crystal is formed is lower than the inside, and as a result, the crystal growth during recrystallization proceeds inward from the end of the region 9, so a single crystal region cannot be obtained.

(Purpose of the invention) An object of the present invention is to provide a method for forming an SOI structure that allows for the formation of an SOI structure.

(Structure of the Invention) According to the present invention, a polycrystalline or amorphous first semiconductor film is formed on a substrate having an insulating layer formed on at least the surface, and then a first insulating film is formed thereon. forming a second semiconductor film divided into a plurality of ventral island shapes thereon; forming a second insulating film on the first insulating film and the second semiconductor film; A method for forming an SOI structure is obtained, characterized in that a first semiconductor film existing between a laser semiconductor film of a multilayer film consisting of a second insulating film and a second semiconductor film is made into a single crystal.

(Examples) Hereinafter, the present invention will be explained using examples. In this embodiment, a polysilicon film is used as the semiconductor film, a silicon oxide film is used as the insulating film, and an argon gas laser is used as the laser beam.

FIG. 1(a) is a cross-sectional view of a sample subjected to laser annealing. First, as shown in FIG. 1(a), a silicon substrate 1
A silicon oxide film 2 is formed thereon to a thickness of lpm, and then a polysilicon film 3 is formed thereon to a thickness of 0.5pm. On top of this, a silicon oxide film 4 is applied as a cap film. Silicon nitride film 5. Each polysilicon film 7 has a thickness of 900 mm, 1
Form 400 and 1700 people. Here, a polysilicon film 7 is formed in a stripe shape, leaving a region of about 10 to 12 meters wide on both sides of the region 9 in which the SOI single crystal is to be formed, exposing the silicon nitride film 5. 900 people thick. At this time, silicon oxide film 4, silicon nitride film 5. Polysilicon film7. Silicon nitride film 6
A multilayer film consisting of a silicon oxide film 4. serves as an anti-reflection film against the light. The multilayer film made of silicon nitride film 5°6, that is, the multilayer film on the region 9 where a single crystal is to be formed, is as follows.
It becomes a reflective film for laser light.

Next, a small polysilicon film is applied to this sample in a region 9 where a single crystal is to be formed in a Gaussian distribution with a beam diameter 8 that can simultaneously irradiate the striped portions of the polysilicon 7 on both sides of the sample 14 and the inner portions thereof. It becomes larger in the area below 7. The laser power is also absorbed by the polysilicon film 7, and when the silicon film 3 recrystallizes, the heat accumulated in the polysilicon film 7 is absorbed into the region of the silicon film 3 located below the polysilicon film 7. can be conveyed to. Therefore, the temperature distribution in the polysilicon film 3 is as shown in Figure 1.
As shown in FIG. 1, the distribution is higher at the edge of the region 9 where it is desired to form an SOI single crystal than at the inside. In other words, in the conventional method, heat conduction from the polysilicon film 7 works to reduce the temperature difference and hinders the formation of a single crystallized region, but in the present invention, the heat conduction works to increase the temperature difference. This is a factor that promotes crystallization.

From the above results, when the polysilicon film 3 is recrystallized, in the region 9 where a single crystal is desired to be formed, the temperature is higher at the edges than inside, and therefore crystal growth progresses from the inside to the edges. do. As a result, a single crystal silicon region can be formed at a desired position.

Furthermore, even if the heat conduction from the polysilicon film 7 changes in the SOI mono-distribution, the temperature distribution within the polysilicon film 3 will change as shown in FIGS. 1(c) and 1(d), respectively. With the aid of heat conduction from the silicon film 7, a temperature distribution suitable for SOI single crystallization is achieved. Therefore, an SOI single crystal can be formed more easily than the conventional method.

Although a polycrystalline film was used as the semiconductor film in the above embodiment, it is clear that an amorphous film may also be used.

Further, in the embodiment described above, the polysilicon film 7 used for heat storage is formed in a striped shape, but the shape is not limited to this, and may be separated into islands in the range to be irradiated with the beam. However, if the island is so wide that it cannot be irradiated with the laser beam, heat will escape to the semiconductor parts that are not irradiated with the laser beam, and it will not play the role of heat storage, so it is better to set the size of the island according to the beam diameter. .

Further, the anti-reflection film and the insulating film constituting the reflective film are not limited to those in the above embodiments, and may be arranged so that the reflective film and other parts serve as an anti-reflection film on the region where a single crystal is desired to be formed.

(Effects of the Invention) In the present invention, the heat stored in the polysilicon film 7, which was used to prevent damage, is a factor that promotes single crystal growth. (can obtain a good single crystal film.

Furthermore, even if the difference between the opposite wheel and the opposite wheel becomes smaller due to unevenness in the thickness of each thin film during sample formation, or the power distribution changes due to an error in the alignment position of the beam, 1. The temperature difference between the end and the inside of the region to be single crystallized can be made sufficiently large.

[Brief explanation of the drawing]

FIG. 1(a) is a cross-sectional view of the sample in the present invention, FIG.
b) is a diagram showing the laser power distribution and temperature distribution incident on the polysilicon film 3 when the present invention is used, and FIG.
) is the case when there is unevenness in the thickness of each thin film in the present invention.
A diagram showing the laser power distribution and temperature distribution incident on the polysilicon film 3, FIG. 1(d) shows the laser power within the polysilicon film 3 when misalignment of the laser position occurs in the present invention. Diagram showing distribution and temperature distribution, Figure 2 (
Figure 2 (a) shows the laser power distribution and temperature distribution when using the conventional method, and Figure 2 (d) shows the distribution within the polysilicon film 3 when the laser position misalignment occurs in the conventional method. FIG. 3 is a diagram showing laser power distribution and temperature distribution. In FIGS. 1 and 2, 1 is a silicon substrate, 2 and 4 are silicon oxide films 3.
7 is a polysilicon film 5, 6 is a silicon nitride film 8 is a laser beam diameter 9 is a region where an SOI single crystal is to be formed 10 is a laser power distribution 11 incident on the polysilicon film 3 is a temperature distribution within the polysilicon film 3 It is. Director of the Institute of Industrial Science and Technology 1 Figure 8 Laser beam diameter 9S01 Single crystal formed region 10 Laser power distribution incident on the polysilicon film 3 11 1 degree distribution within the polysilicon film 3 71-1 Figure 8 Laser beam diameter 9S01 single crystal Distribution of laser power incident on the region 10 where crystals are desired to be formed 10 and the polysilicon film 3
1 Temperature distribution in polysilicon film 3 1-2 Figure position 1 Silicon substrate 2,4 silicon film 4 silicon substrate
3,1 Polysilicon film 5.6 Silicon nitride film 8 Laser beam diameter 9S01 Region where single crystal is desired to be formed 10 Laser power distribution incident on polysilicon film 3 11 Temperature distribution within polysilicon film 3 O 2 Figure position ( d) 8 laser beam diameter

Claims (1)

[Claims] A polycrystalline or amorphous first semiconductor film is formed on a substrate having an insulating layer formed on at least the surface, then a first insulating film is formed thereon, and a plurality of island-shaped semiconductor films are formed on the first insulating film. A second insulating film is formed on the first insulating film and the second semiconductor film to separate the first and second insulating films and the second semiconductor film. The laser beam reflectance of the multilayer film made of the first and second insulating films is made smaller than the laser light reflectance of the multilayer film made of the first and second insulating films, and then the beam width is set such that it can irradiate at least two island-shaped semiconductor films. A method for forming an SOI structure, characterized in that a first semiconductor film existing between the two island-shaped semiconductor films is made into a single crystal by irradiating the same with a laser beam.