JPH01147827A - Manufacture of multilayer semiconductor substrate - Google Patents

Abstract

PURPOSE:To form a single crystal layer having few irregularities onto an insulator by bringing the thickness of a semiconductor layer melted and recrystallized by laser beams to 1500Angstrom or less. CONSTITUTION:An SiO2 film 2 in thickness of 1mum is shaped onto a single crystal Si substrate 1, and poly Si 3 in thickness of 1500Angstrom is deposited onto the film 2 through a CVD method. Poly Si 3 is irradiated with argon laser beams 4 diaphragmed to a diameter of 100mum and the laser beams 4 are scanned in 25cm/s. Since the greater parts of laser beams 4 reach up to the Si substrate 1 and the substrate 1 is heated, temperature distribution in molten Si 5 is made gentler than conventional examples (poly Si in thickness of 6000Angstrom ), and the irregularities of the surface of a single crystal Si film 6 after recrystallization are inhibited to 150Angstrom or less.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a multilayer semiconductor substrate, and particularly to a method for forming a semiconductor single crystal film on an insulator and using this as a substrate to form circuit elements such as transistors. It is related to.

[Prior art] Conventionally, in order to increase the speed and density of semiconductor devices, attempts have been made to manufacture semiconductor integrated circuits with low stray capacitance in which circuit elements are separated by dielectrics, and so-called 3-dimensional integrated circuits in which circuit elements are stacked three-dimensionally.
Attempts have been made to manufacture dimensional circuit elements, and one method is to form a semiconductor layer on an insulator and construct the circuit element in the semiconductor crystal. As a method for forming this semiconductor crystal layer, a polycrystalline or amorphous semiconductor layer is deposited on an insulator, and only the surface layer is heated by irradiating the surface with energy beams such as laser light or electron beams.
There is a method of forming a single crystal semiconductor layer.

3A to 3E are schematic process cross-sectional views of this conventional manufacturing method.

This manufacturing method will be described below with reference to the drawings.

First, an oxide film 2 made of a silicon dioxide film with a thickness of 1 μm is formed on the main surface of a single-crystal silicon substrate 1, and then a thick polycrystalline silicon 10 is further deposited on the oxide film 2 by chemical vapor deposition (CVD). Deposit at 6000A (see Figure 3A)
. Next, while scanning the argon laser beam 4 focused to a diameter of 100 μm at a scanning speed of 25 cm/s, the polycrystalline silicon 10
irradiate. Then, the polycrystalline silicon 10 in the area irradiated with the laser beam 4 is melted and becomes molten silicon 11.
By solidifying and recrystallizing it, Ill crystallized silicon 12 is formed (see FIG. 3B).

Regarding the mechanism of this single crystallization, please refer to JP-A No. 61-04846.
8 provides details. When one scan of the laser beam 4 is completed, the laser beam 4 is moved 30 μm perpendicularly to the scanning direction to perform the next scan. When the scanning of the laser beam 4 over the entire surface of the wafer is completed in this manner, the entire surface of the polycrystalline silicon 10 becomes monocrystalline silicon 12 (see FIG. 3C).

A MOS (MOS) transistor, etc. is fabricated on this single crystal silicon 12 according to a normal process, and in order to reduce the junction capacitance junction area and improve the performance of the device, a film of the single crystal silicon 12 is used to fabricate a transistor. The impurity junction depth is determined by the diffusion of the implanted impurity (approximately 1
It is necessary to make it thinner than 500A-0°15 μm). Therefore, by exposing the wafer in the state shown in FIG. 3C to an oxidizing atmosphere at about 1000°C for a long time,
Oxidize the surface of 2. Then, the surface portion of the single crystal silicon 12 is oxidized to become a single crystal silicon 6 with a thickness of 1500 Å, and an oxide film 13 with a thickness of 9000 Å is formed thereon (see FIG. 3D).

Finally, the top layer oxide film 13 is removed by etching to expose the single crystal silicon 6 with a thickness of 1500 Å (see Figure 3E), and elements are formed on this single crystal silicon 6 using a normal transistor manufacturing process. Form.

[Problems to be Solved by the Invention] In the conventional method of manufacturing a semiconductor device, a thickness of 6000 mm
Since the polycrystalline silicon of A was melted and recrystallized, there was a problem in that the surface unevenness of the recrystallized silicon caused by the movement of the molten silicon occurred at a level difference of 60 OA. The mechanism of this surface unevenness generation will be explained with reference to FIGS. 4 to 6.

FIG. 4 is a plan view showing the wafer during laser beam irradiation;
Figure 5 is a sectional view taken along line v-■ in Figure 4, and Figure 6 is a cross-sectional view of Vl in Figure 4.
-Vl sectional view.

As shown in FIGS. 4 and 5, the polycrystalline silicon 10 in the area irradiated with the laser beam 4 becomes molten silicon 11.
(2) The density of the molten silicon 11 is higher than that of solid silicon; (2) The intensity distribution of the laser beam 4 is high at the beam center and low at the periphery of the beam, a so-called Gaussian distribution; therefore, the temperature at the center of the molten silicon 11 is higher than the surrounding area. In other words, the volume of molten silicon 11 becomes smaller due to the reason (■), and ()
Silicon in the center of the molten silicon 11 moves to the periphery due to surface tension due to this reason. Therefore, since the molten silicon 11 is solidified from the periphery, the recrystallized single crystal silicon 12 has irregularities as shown in FIG. The size of the step (indicated by a in the figure) of this unevenness is approximately 600 in proportion to the thickness of the polycrystalline silicon 10. In this way, one scan of the laser beam generates irregularities of 600 A in an area with a beam diameter (melting width) of 100 μm. In reality, the laser beam is moved and scanned in steps of 30 μm, so that 600 concavities and convexities are formed on the single crystal silicon 12 with a period of 30 μm. This unevenness remains in the same shape even after oxidation in the subsequent process, so the 3rd E
Single crystal silicon 6 in the figure is 1200A to 1800A
The film thickness varies up to the impurity junction depth (15
00A) A thicker region is generated and the characteristics of the device formed in the single crystal silicon 6 are deteriorated.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a method for manufacturing a multilayer semiconductor substrate that obtains a single crystal semiconductor layer with less unevenness on an insulator.

[Means for Solving the Problems] In the method for manufacturing a semiconductor device according to the present invention, the thickness of the non-single crystal semiconductor layer melted and recrystallized by irradiation with energy beams or the like is set to 1500 Å or less.

[Function] The non-Ill crystal semiconductor layer of 1500A or less in this invention reduces the occurrence of surface irregularities when melted and recrystallized by irradiation with energy beams.

[Example] Figures 1A to 1C are schematic process cross-sectional views showing an example of the present invention.

Hereinafter, the manufacturing method of the present invention will be explained with reference to the drawings.

First, an oxide film 2 made of a silicon dioxide film with a thickness of 1 μm is formed on the main surface of a single-crystal silicon substrate 1, and then polycrystalline silicon 3 is deposited on the oxide film 2 to a thickness of 150 μm using the CVD method.
Deposit with OA (see Figure 1A).

Next, polycrystalline silicon 3 is irradiated with argon laser light 4 focused to a diameter of 100 μm while scanning at a scanning speed of 25 cm/s. Then, the irradiated polycrystalline silicon 3 is melted and becomes molten silicon 5, which is assimilated and recrystallized to form single crystal silicon 6 (see FIG. 1B).

The mechanism of this laser beam irradiation and recrystallization (single crystallization) is the same as the conventional method, but the power of the laser beam needs to be adjusted to an amount suitable for the structure shown in FIG. 1A. When the irradiation of the laser beam to the entire surface of the wafer is completed, the polycrystalline silicon 3 becomes the entire surface of single crystal silicon 6 (see FIG. 1C).

In this case, the movement of the shape of the molten silicon and the shape of the single crystal silicon basically become the same shape as explained in FIGS. 4 to 6 by a mechanism similar to that of the conventional method. However, since the film thickness of the melted polycrystalline silicon 3 is thin, the laser beam 4 is not completely absorbed by the polycrystalline silicon 3 (the amount of argon laser beam that penetrates into the silicon is 0.7μ).
m) Most of the heat passes through the polycrystalline silicon 3 and heats the silicon substrate 1. Since the heat of the silicon substrate 1 quickly diffuses downward, the temperature distribution within the molten silicon 5 becomes gentler than in the conventional example. As a result, the amount of movement of the periphery of the molten silicon 5 is approximately proportional to the film thickness of the polycrystalline silicon 3 (within a film thickness range of 1000 to 10000 A), so the step difference in the surface unevenness after recrystallization is within 150 A. is suppressed to a level that will not cause problems when creating later devices.

In the above embodiment, a laser beam is used as the energy beam, but the same effect can be obtained even if an electron beam is used.

In the above example, the device was formed as it was after single crystallizing polycrystalline silicon of 1500A, but before forming the device, the surface of the single crystal silicon was oxidized to further reduce the thickness of the single crystal silicon. Good too.

Further, although the above embodiments do not specifically mention the atmosphere for laser beam irradiation, a vacuum atmosphere is preferable in order to avoid the effects of oxidation on the surface of single crystal silicon due to high heat during irradiation.

Furthermore, in Example 2, the polycrystalline silicon was directly irradiated with a laser beam to melt it, but the melting does not necessarily have to be done directly.

FIG. 2 is a cross-sectional view of the structure before laser beam irradiation according to another embodiment of the present invention.

In the figure, an insulating film 7 is further formed on the polycrystalline silicon layer 3'' with a thickness of 1500 Å shown in FIG.
The second polycrystalline silicon 8 in the upper layer is irradiated with an energy beam such as a laser beam.

Since the second polycrystalline silicon 8 is melted, the same effect can be obtained even if the polycrystalline silicon 3 having a thickness of 1:1500 Å is indirectly melted using the heat. In this case, the second polycrystalline silicon 8 and the insulating film 7 are removed by etching after irradiation with a laser beam of equal energy.
An element will be formed on the polycrystalline silicon 3 of A.

According to this embodiment, since single crystallization is performed with an insulating film formed on polycrystalline silicon, it also has the advantage of being less influenced by the atmosphere.

Any method for melting a non-single crystal semiconductor layer as described above may be used as long as it scans using thermal energy.

[Effects of the Invention] As described in 1- above, according to the present invention, since the thickness of the non-lit crystal semiconductor layer to be melted into a single crystal is set to 1500A or less, it is possible to form an lli crystal semiconductor layer with less unevenness on the insulator. This has the effect of greatly contributing to improving the performance of circuit elements formed in this semiconductor layer.

[Brief explanation of the drawing]

1A to 1C are schematic diagrams showing an embodiment of the present invention.
1', a cross-sectional view of the main body, FIG. 2 is a structural cross-sectional view of another embodiment of the present invention before laser beam irradiation, FIGS. 3A to 3E are schematic process cross-sectional views showing a conventional manufacturing method, and FIG. 5 is a plan view showing a wafer during conventional laser beam irradiation, FIG. 5 is a cross-sectional view taken along the line v--■ in FIG. 4, and FIG. 6 is a cross-sectional view taken along the line Vl--Vl in FIG. 4. In the figure, 1 is a silicon substrate, 2 is an oxide film, 3 is polycrystalline silicon, 4 is a laser beam, 5 is molten silicon, 6 is single crystal silicon, 7 is an insulating film, and 8 is polycrystalline silicon. Note that the same reference numerals in each figure indicate the same or corresponding parts. Patent applicant: Director of the Agency of Industrial Science and Technology Kozo Iizuka 1A Figure 1B Figure 10 IC Figure 82 Figure 3A Figure 30 Figure 3D Figure 3E Figure 4 Figure 85 Figure 6 Procedural amendment (self-motivated) month + 6th

Claims (5)

[Claims] (1) A step of preparing a semiconductor substrate having a main surface, a step of forming a first insulating film on the main surface of the semiconductor substrate, and a film thickness of 1500 Å or less on the first insulating film. a step of forming a non-single crystal first semiconductor layer;
A method for manufacturing a multilayer semiconductor substrate, comprising the step of melting and recrystallizing the first semiconductor layer to form a single crystal by applying thermal energy to the semiconductor layer while scanning. (2) The method for manufacturing a multilayer semiconductor substrate according to claim 1, wherein the thermal energy is generated by irradiation with energy beams. (3) The method for manufacturing a multilayer semiconductor substrate according to claim 2, wherein the energy beam is continuous wave argon laser light. (4) The step of monocrystalizing the first semiconductor layer includes a step of forming a second insulating film on the non-single crystal first semiconductor layer, and a step of forming a second insulating film on the non-single crystal first semiconductor layer. forming a non-single-crystal second semiconductor layer, melting the second semiconductor layer by scanningly applying thermal energy to the second semiconductor layer, and using the melting heat to melt the second semiconductor layer; A patent claim comprising the steps of: melting and recrystallizing the first semiconductor layer to form a single crystal through an insulating film; and removing the melted second semiconductor layer and the second insulating film. A method for manufacturing a multilayer semiconductor substrate according to item 1, item 2, or item 3. (5) The step of single-crystallizing the first semiconductor layer is carried out in a vacuum atmosphere,
The method for manufacturing a multilayer semiconductor substrate according to item 2 or 3.