JPH0560668B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention is directed to SOI (Semiconductor On
The present invention relates to a method for manufacturing a semiconductor device having an insulator structure.

BACKGROUND ART Conventionally, SOI devices have been actively developed with the aim of realizing highly integrated, high-speed, and multifunctional high-performance semiconductor devices. The most basic technology for creating SOI devices is the so-called single crystallization technology, which forms a single crystal semiconductor layer on an insulating substrate [BR Appleton & GKCeller, eds., Laser and
Electron-Beam Interaction with solids, North-Holland,
[NewYork, (1982), etc.] For example, there is a method of melting and recrystallizing a polycrystalline silicon layer formed on an amorphous insulating substrate such as SiO ₂ by laser beam or electron beam irradiation, carbon heater or lamp heating, etc. be. When forming devices on SOI, the only areas that require single crystal are locally limited areas such as the gate and source/drain junction regions of MOS transistors.

Problems to be Solved by the Invention An example of fabricating an SOIMOS transistor using the conventional technique described above will be briefly described with reference to the cross-sectional process flow chart shown in FIG. On an insulating substrate, for example, SiO ₂ 1 formed on a silicon substrate 100,
A polycrystalline silicon film 2 is formed by the LPCVD method,
A continuous wave argon (CWAr) laser L is irradiated while scanning in the direction of the position mark Z to melt and recrystallize the polycrystalline silicon 2 (a in FIG. 4). Thereafter, the recrystallized silicon film is insulated and separated by a normal local oxidation method (LOCOS method) to form a recrystallized silicon island 10 on the SiO ₂ 1 (FIG. 4b). This recrystallized silicon island 10 can also be formed by the steps shown in c and d of FIG. 4. That is, a polycrystalline silicon film 2 formed on SiO ₂ 1 is
After partially selectively oxidizing by the LOCOS method to form a polycrystalline silicon island 21, laser L is scanned and irradiated in the direction of arrow Z to melt and recrystallize the polycrystalline silicon island 21 (as shown in Fig. 4). c) A recrystallized silicon island 10 is formed on the SiO ₂ 1 (FIG. 4 d).
After that, the gate oxide film 5, the gate electrode 6, and the SiO ₂
20. Source/drain regions 10s, 10d, electrodes 8s, 8d, etc. are formed to create the SOI device shown in FIG. 4e.

As described above, when creating an SOI device using the conventional method, after forming a recrystallized silicon island, the steps after gate electrode formation are performed. The mechanism by which polycrystalline silicon is melted and recrystallized has not yet been elucidated, but it is generally known that molten silicon solidifies and recrystallizes from the lowest temperature point due to heat dissipation. There is. For this,
Efforts have been made to control the laser energy distribution and create a sample structure with partial anti-reflection coatings and heat sinks, and it has become possible to form recrystallized silicon films of fairly high quality. However, at present, even when recrystallized silicon is formed under optimal conditions, there are grain boundaries, crystal defects, and partial absence of macroscopic crystal layers. Therefore, if a gate electrode or source/drain region is formed after creating a recrystallized silicon island, it is impossible to form a single crystal region that does not contain crystal defects and is aligned with the gate portion or source/drain junction. , was extremely difficult and as a result created
There is a problem that the characteristics of SOI devices deteriorate.

In addition, in the SOI device shown in Figure 4e, during transistor operation, the current flowing through the side and bottom surfaces of the Si island other than the channel that can be controlled by the gate electrode cannot be controlled, so a so-called subthreshold current occurs and the characteristics There is also the problem of deterioration.

Means for Solving the Problems In order to solve the above problems, the present invention provides a structure in which polycrystalline silicon is provided via an oxide film so as to surround the silicon island in accordance with the portion of the silicon island that will become the gate region. After forming the silicon island,
Along with recrystallization by laser irradiation, MOS
The present invention provides a structure that allows a desired potential to be applied to the polycrystalline silicon under the silicon island when a transistor is formed.

That is, the method for manufacturing a semiconductor device of the present invention includes:
a step of providing a groove of a desired size at a desired position on the insulating substrate; a step of depositing a first polycrystalline silicon in the groove; and a step of depositing a desired portion of the first polycrystalline silicon on the insulating substrate. selectively oxidizing or removing the first polycrystalline silicon so that it remains in a portion of the groove; selectively oxidizing the surface of the first polycrystalline silicon remaining on the substrate; a step of selectively oxidizing or removing the second polycrystalline silicon while leaving the second polycrystalline silicon on the groove portion; and a step of selectively oxidizing or removing the second polycrystalline silicon remaining in the groove portion in an island shape. a step of recrystallizing the polycrystalline silicon by laser irradiation, a step of forming a gate oxide film on the recrystallized silicon island and then forming a gate electrode directly above the first polycrystalline silicon, a source, forming the drain electrode
The method includes a step of forming a MOS transistor.

Effect According to the present invention, when the silicon (Si) island made of the second polycrystalline silicon is recrystallized by laser irradiation, the first polycrystalline Si located at the lower part of the Si island corresponding to the gate portion is Recrystallization of the molten Si occurs from this part of the Si island that acts as a heat sink and has large thermal diffusion, and the recrystallized Si island in the gate area tends to become a single crystal.
When operating a MOS transistor, the first polycrystalline
By applying an appropriate potential to Si, it is possible to suppress the current flowing directly under the gate, that is, to the sidewalls and bottom surface of the Si island that forms the channel region, and good electrical characteristics without subthreshold current can be obtained.

Embodiment An embodiment of the present invention will be described with reference to FIGS. 1, 2, and 3. FIG. 3 is a schematic view of the island after formation of the gate electrode. Figure 1 is a cross-sectional process flowchart. Figure 1 is a cross-sectional process taken on the X-X' plane in Figure 3, and Figure 2 is a process cross-section taken on the Y-Y' plane in Figure 3. Yes, and also c in Fig. 1 and a in Fig. 2, 1st
d in the figure, b in FIG. 2, e in FIG. 1, and c in FIG. 2 are cross-sectional views at the same step, respectively.

For example, a SiO ₂ 1 formed on a Si substrate 100 is used as an insulating substrate, a groove 200 of a desired size is formed in the SiO ₂ 1 to a depth of, for example, 0.5 μm, and a groove 200 is formed on the SiO 2 1 by LPCVD. 1 polycrystalline Si film 2 is formed ((a in FIG. 1). Next, as shown in b in FIG.
selectively oxidizes a part of the polycrystalline Si film to form SiO ₂ 1
A buried Si layer 21 is formed by insulating and separating SiO ₂ layers 1 and 11, and a SiO ₂ layer 3 is formed on the exposed portion of the buried Si layer 21 using a conventional method such as thermal oxidation. After this, as shown in Fig. 1 c and Fig. 2 a, the thickness is approximately reduced by LPCVD method.
A second polycrystalline Si film 4 of 0.5 μm is formed. next,
As shown in Figure 1 d and Figure 2 b, the normal
Using the LOCOS method, the second polycrystalline Si film 4 is insulated and isolated by a selective oxidation method or the like to form an island 4 made of the second polycrystalline Si in the groove portion. At this time, the buried Si layer 21 is placed so as to surround the side and bottom surfaces of the polycrystalline Si island 4 via the SiO ₂ 3.

Thereafter, for example, CWAr laser L is irradiated with a power of 1 to 10 W and a scanning speed of 10 cm/sec in the direction of arrow Z. The conditions at this time are the second polycrystalline
The Si island 4 is selected so that it melts and immediately solidifies and recrystallizes after the laser scan ends. In this recrystallization, the buried Si layer 21 serves as a heat sink, and the molten Si 4 directly above the buried Si layer 21
Part a solidifies the fastest, and recrystallization proceeds from this part until the entire island is recrystallized. Therefore, even if random crystal growth occurs from other parts than directly above the buried Si layer 21, the part 41a of the recrystallized Si island 41 directly above the buried Si layer 21 has already grown into a single crystal. Because of this structure, it is a high-quality single crystal with extremely few crystal defects such as grain boundaries.

Thereafter, a MOS transistor is formed on the recrystallized Si island 41 using a normal MOS transistor manufacturing method. That is, as shown in FIG. 1 e and FIG. Gate electrode 6
is formed directly above the buried Si layer 21. Next, source and drain regions 7 and wiring 8 are formed,
Create SOI MOS transistor.

At this time, is the buried Si layer 21 connected to the control electrode so that a desired potential can be applied?
Alternatively, it is desirable to combine it with the original gate electrode 6. With this structure, during transistor operation, the periphery of the recrystallized Si island portion 41a directly below the gate electrode 6, which serves as a channel, is fixed at a desired potential by the gate electrode 6 and the buried Si layer 21. In this case, it becomes possible to suppress the subthreshold current that is thought to occur because the bulk Si is electrically floating, and good electrical characteristics can be obtained.

Furthermore, it goes without saying that the method of the present invention can be used not only for producing a single-layer SOI device but also for forming an SOI recrystallized layer for producing a so-called three-dimensional device having a device in an underlying layer.

Effects of the Invention As described above, by using the present invention, when recrystallizing a polycrystalline Si island, the area under the gate electrode, which needs to be made into a single crystal as a device, can be reliably made into a single crystal.
It is possible to provide a structure that suppresses the subthreshold current that normally occurs in the operation of SOI MOS transistors, and it is possible to form SOI MOS transistors with very good device characteristics with low leakage current. This invention can be said to be extremely useful for realizing devices.

[Brief explanation of the drawing]

FIGS. 1 and 2 are sectional views of a manufacturing process of a semiconductor device according to an embodiment of the present invention, FIG. 3 is a schematic bird's-eye view of the same semiconductor device, and FIG. 4 is a sectional view of a conventional method. 1...SiO2, _2,4 ...Polycrystalline Si, 3,11
...SiO ₂ , 5 ... gate oxide film, 6 ... gate electrode, 41 ... recrystallized Si, 21 ... buried
Si, 7...source, drain, 8...wiring, 10
0...Si substrate, 200...groove, L...laser beam.

Claims (1)

[Claims] 1. A step of providing a groove of a desired size at a desired position on an insulating substrate, a step of depositing a first polycrystalline silicon in the groove, and a step of depositing a desired portion of the first polycrystalline silicon in the insulating substrate. selectively oxidizing or removing the first polycrystalline silicon so that it remains in a part of the groove of the substrate; selectively oxidizing the surface of the first polycrystalline silicon that remains; and the substrate. depositing a second polycrystalline silicon layer thereon;
A step of selectively oxidizing or removing the second polycrystalline silicon while leaving the second polycrystalline silicon on the groove portion, and recrystallizing the second polycrystalline silicon remaining in an island shape in the groove portion by laser irradiation. a step of forming a gate oxide film on the recrystallized silicon island and then forming a gate electrode directly above the first polycrystalline silicon; and forming source and drain electrodes.
1. A method of manufacturing a semiconductor device, comprising the step of forming a MOS transistor.