JP2526380B2 - Method for manufacturing multilayer semiconductor substrate - Google Patents

Description

Description: TECHNICAL 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 a circuit element such as a transistor. It is about.

[Prior Art] An attempt to manufacture a semiconductor integrated circuit having a small stray capacitance in which circuit elements are separated by a dielectric in order to increase the speed and density of a conventional semiconductor device, and a so-called three-dimensional circuit in which circuit elements are three-dimensionally stacked. Attempts have been made to manufacture devices, and one of the methods is to form a semiconductor layer on an insulator and form a circuit device 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 thereof with a laser beam or an energy beam of an electron beam, There is a method of forming a single crystal semiconductor layer.

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

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

First, the thickness of 1 μm on the main surface of the single crystal silicon substrate 1.
An oxide film 2 made of a silicon dioxide film is formed, and polycrystalline silicon 10 is deposited on the tatami oxide film 2 by chemical vapor deposition (CVD) to a thickness of 6000Å (see FIG. 3A). Next, the argon laser beam 4 with a diameter of 100 μm is scanned at a scanning speed of 25 cm / s.
Irradiate the polycrystalline silicon 10 while scanning with. Then, the polycrystalline silicon 10 in the area irradiated with the laser beam 4 is melted to become the molten silicon 11, which is solidified and recrystallized to form the single crystallized silicon 12 (see FIG. 3B).

The mechanism of this single crystallization is described in detail in Japanese Patent Application No. 61-048468. When one scan of the laser beam 4 is completed, the laser beam 4 is moved vertically by 30 μm in the scanning direction to perform the next scanning. When the scanning of the laser beam 4 on the entire surface of the wafer is completed in this way, the polycrystalline silicon 10 becomes the single crystallized silicon 12 over the entire surface (see FIG. 3C).

MOS transistors etc. are created on this single-crystal silicon 12 according to a normal process, but the film thickness of the single-crystal silicon 12 is used to create the transistor in order to reduce the junction capacitance junction area and improve the performance of the device. Impurity junction depth (about 1500Å
= 0.15 μm). Therefore 3C
The wafer shown in the figure is exposed to an oxidizing atmosphere at about 1000 ° C. for a long time to oxidize the surface of the single crystallized silicon 12. Then, the surface portion of the single crystal silicon 12 is oxidized, so that the thickness 15
Becomes 00Å monocrystalline silicon 6 and has a thickness of 9000Å on it
Oxide film 13 is formed (see FIG. 3D).

Finally, the uppermost oxide film 13 is removed by etching to expose the 1500 Å-thick single crystallized silicon 6 (see FIG. 3E), and the element is formed on the single crystallized silicon 6 by a normal transistor manufacturing process. Form.

[Problems to be Solved by the Invention] In the conventional method for manufacturing a semiconductor device, a thickness of 6000Å
Since the polycrystalline silicon of 1 is melt-recrystallized, there is a problem that the unevenness of the surface of the recrystallized silicon due to the movement of the molten silicon is generated at the level difference of 600 Å. The mechanism for generating the surface irregularities will be described with reference to FIGS.

FIG. 4 is a plan view showing the wafer at the time of laser light irradiation, FIG. 5 is a sectional view taken along line VV of FIG. 4, and FIG.
It is a VI-VI sectional view.

As shown in FIGS. 4 and 5, the polycrystalline silicon 10 in the region irradiated with the laser beam 4 becomes the molten silicon 11,
The density of the molten silicon 11 is higher than that of solid silicon, and the intensity distribution of the laser beam 4 is high at the center of the beam and low at the periphery of the beam.
The temperature at the center of 11 is higher than that at the periphery. That is, the volume of the molten silicon 11 becomes small for the above reason, and the silicon in the central portion of the molten silicon 11 moves to the peripheral portion due to the surface tension based on the reason. Therefore, since the molten silicon 11 is solidified from the periphery, this recrystallized single crystal silicon
No. 12 has irregularities as shown in FIG. The size of the step of this unevenness (indicated by a in the figure) is polycrystalline silicon 10.
It will be about 600Å in proportion to the thickness of. As described above, a single scan of the laser beam causes unevenness of 600 Å to occur in a region having a beam diameter (melting width) of 100 μm. Actually the laser light is 30μ
Since scanning is performed by moving by m, 600 .mu.m unevenness is formed on the single crystallized silicon 12 at intervals of 30 .mu.m. Since these irregularities remain in the same shape even after oxidation in the subsequent process, the single crystal silicon 6 in FIG.
The film thickness is varied from Å to 1800Å, and a region thicker than the impurity junction depth (1500Å) is partially generated to deteriorate the characteristics of the element formed in the single crystal silicon 6.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for manufacturing a multi-layer semiconductor substrate, in which a single crystal semiconductor layer having few irregularities is obtained on an insulator.

[Means for Solving Problems] A method of manufacturing a multilayer semiconductor substrate according to the present invention includes a step of preparing a semiconductor substrate having a main surface and a step of forming a first insulating film on the main surface of the semiconductor substrate. And a step of forming a non-single-crystal first semiconductor layer having a film thickness of 1500 Å or less on the first insulating film, and a penetration depth into the first semiconductor layer represented by the reciprocal of the absorption coefficient is the first. The step of irradiating while scanning the first semiconductor layer with a light energy ray having a characteristic of 4.67 times or more the film thickness of the semiconductor layer, thereby melting and recrystallizing the first semiconductor layer to form a single crystal. It is equipped with.

[Operation] The non-single-crystal semiconductor layer of 1500 Å or less in this invention is
The penetration length into the first semiconductor layer is the thickness of the first semiconductor layer 4.
When melting and recrystallizing by irradiating while scanning a light energy ray having a characteristic of 67 times or more, generation of irregularities on the surface is reduced.

[Embodiment] FIGS. 1A to 1C are schematic process sectional views showing an embodiment of the present invention.

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

First, the thickness of 1 μm on the main surface of the single crystal silicon substrate 1.
An oxide film 2 made of a silicon dioxide film is formed, and polycrystalline silicon 3 is further deposited on the oxide film 2 by the CVD method to a thickness of 1500Å.
(See Figure 1A).

Next, the name crystal silicon 3 is irradiated with an argon laser beam 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 to become molten silicon 5, which is solidified and recrystallized to form single crystallized silicon 6 (see FIG. 1B).

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

By the way, in this case, the shape of the molten silicon and the shape of the single-crystallized silicon are basically the same as those described in FIGS. 4 to 6 by the same mechanism as the conventional method. However, since the melted polycrystalline silicon 3 is thin, the laser light 4 is not completely absorbed by the polycrystalline silicon 3 (the amount of argon laser light penetrating into silicon is 0.7
μm, that is, the thickness of the polycrystalline silicon 3 is 1500Å (0.
15 μm), the penetration length (that is, the reciprocal of the absorption coefficient) of the argon laser light depends on the thickness of the polycrystalline silicon 3.
It can be said that it is a light energy ray having a characteristic of 4.67 times), and most of it passes through the polycrystalline silicon 3 to heat the silicon substrate 1. Since the heat of the silicon substrate 1 quickly diffuses downward, the temperature distribution in the molten silicon 5 becomes gentle as compared with the conventional example. As a result, the amount of movement of the peripheral portion of the molten silicon 5 is almost proportional to the film thickness of the polycrystalline silicon 3 (film thickness 1000
(Within the range of ~ 10000Å), the surface unevenness after recrystallization is suppressed to within 150Å, which is a level that does not pose a problem when forming a later device.

Although the laser beam is used as the energy beam in the above embodiment, the same effect can be obtained by using the electron beam.

Further, in the above example, the element was formed as it was after single crystallization of 1500 Å polycrystalline silicon, but the thickness of the single crystallized silicon was further reduced by oxidizing the surface of the single crystallized silicon before forming the element. Good.

Further, in the above-mentioned embodiments, the atmosphere of laser light irradiation is not particularly described, but it is desirable to use a vacuum atmosphere in order to avoid the influence of oxidation of the surface of the single crystal silicon due to high heat during irradiation.

Furthermore, in the above-mentioned embodiment, the laser light was directly irradiated onto the polycrystalline silicon to melt it, but the melting is not necessarily direct.

FIG. 2 is a structural sectional view before laser light irradiation according to another embodiment of the present invention.

In the figure, an insulating film 7 is further formed on the 1500Å-thick polycrystalline silicon 3 shown in FIG.
The upper second polycrystal silicon 8 is irradiated with an energy ray such as a laser beam in the structure provided with the polycrystal silicon 8 (the thickness of this layer does not need to be 1500 Å or less). Since the second polycrystalline silicon 8 melts, its heat indirectly
The same effect can be obtained even if the polycrystalline silicon 3 is melted to a thickness of 1500Å. In this case, the second polycrystalline silicon 8 and the insulating film 7 are formed by etching after the irradiation of the laser beam isoenergy rays.
1500 Å made of single crystal after removing
The element is to be formed in.

According to this embodiment, single crystallization is performed in the state where the insulating film is formed on the polycrystalline silicon, so that there is an advantage that the influence in the atmosphere is lessened.

As described above, according to the present invention, the film layer of the non-single-crystal semiconductor layer to be melted and single-crystallized is set to 1500 Å or less, and the penetration length into the first semiconductor layer is the first. The thickness of the semiconductor layer 4.
Irradiating while scanning with a light energy ray having a characteristic of 67 times or more, a single crystal semiconductor layer with less unevenness can be obtained on the insulator, and it contributes greatly to improving the performance of the circuit element formed on this semiconductor layer. Has the effect of

[Brief description of drawings]

1A to 1C are schematic process sectional views showing an embodiment of the present invention, FIG. 2 is a structural sectional view before laser light irradiation according to another embodiment of the present invention, and FIGS. 3A to 3E are Fig. 4 is a schematic process sectional view showing a conventional manufacturing method, Fig. 4 is a plan view showing a conventional wafer upon laser light irradiation, Fig. 5 is a VV sectional view of Fig. 4,
FIG. 6 is a sectional view taken along line VI-VI in FIG. In the figure, 1 is a silicon substrate, 2 is an oxide film, 3 is polycrystalline silicon, 4 is laser light, 5 is molten silicon, 6 is single crystallized silicon, 7 is an insulating film, and 8 is polycrystalline silicon. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (4)

(57) [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. And the step of forming the non-single-crystal first semiconductor layer, and the penetration depth into the first semiconductor layer, which is represented by the reciprocal of the absorption coefficient, is 4.67 times or more the film thickness of the first semiconductor layer. A method of manufacturing a multi-layer semiconductor substrate, comprising the steps of irradiating the first semiconductor layer with light energy rays having characteristics while melting and re-crystallizing the first semiconductor layer to form a single crystal. . 2. The method for manufacturing a multilayer semiconductor substrate according to claim 1, wherein the first semiconductor layer is silicon, and the light energy rays are continuous wave argon laser light. 3. The step of single-crystallizing the first semiconductor layer, the step of forming a second insulating film on the non-single-crystal first semiconductor layer, and the step of forming a second insulating film on the second insulating film. A step of forming a non-single-crystal second semiconductor layer on the second semiconductor layer, and the second semiconductor layer is melted by applying a light energy ray to the second semiconductor layer while scanning the second semiconductor layer, and heat of the melting is applied to the second semiconductor layer. A step of melting and recrystallizing the first semiconductor layer to form a single crystal through the second insulating film; and a step of removing the melted second semiconductor layer and the second insulating film. A method for manufacturing a multi-layer semiconductor substrate according to claim 1 or 2. 4. The method for manufacturing a multilayer semiconductor substrate according to claim 1, wherein the step of single-crystallizing the first semiconductor layer is performed in a vacuum atmosphere.