JPH06196675A - Method for forming semiconductor substrate and semiconductor device using the substrate - Google Patents

Abstract

(57) [Summary] [Object] To improve the controllability, productivity, quality, and freedom of design in a method for forming a semiconductor substrate having an SOI structure, and to use the substrate formed by the method of the present invention. The semiconductor device provides a high-performance and highly-functional device. A process of forming a diffusion layer 102 of an opposite conductivity type on one surface of a semiconductor substrate 101 of one conductivity type and a mask material 103 on a part of the other surface of the substrate 101.
And the step of forming the substrate by electrolytic etching in an organic alkaline solution to etch away the semiconductor substrate 101 in a portion not covered by the mask material until the diffusion layer 102 is reached. A method of forming a semiconductor substrate, comprising: a step of forming a hollow groove below the diffusion layer; and a step of forming an insulating layer at least below the diffusion layer in the groove after the step.

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 semiconductor substrate and a semiconductor device using the substrate, and more particularly to a method for forming a semiconductor substrate having a structure in which a single crystal silicon semiconductor layer is laminated on an insulator, and the substrate. The present invention relates to a semiconductor device using.

More specifically, the present invention relates to a method for forming a semiconductor substrate suitable for an electronic device or an integrated circuit, which is formed on a single crystal semiconductor layer on a dielectric or on an insulator.

[0003]

2. Description of the Related Art The formation of a single crystal Si semiconductor layer on an insulator is widely known as a silicon-on-insulator (SOI) technique, and has many advantages that cannot be reached by a bulk Si substrate for producing an ordinary Si integrated circuit. Much research has been done because the devices using the SOI technology have. In other words, by using SOI technology,
1. 1. Easy dielectric isolation and high integration 2. Excellent radiation resistance 3. 3. Stray capacitance is reduced and high speed is possible. 4. The well process can be omitted. Latch-up can be prevented, 6. Advantages such as a fully depleted field effect transistor can be obtained by thinning the film.

In order to realize the many advantages in device characteristics as described above, a method for forming an SOI structure has been researched for several decades. The contents are summarized in the following documents, for example.

Special Issue: "Sing
le-crystal silicon on non
-Single-crystal insulator
s ″; edited by GW Cullen, J.
individual of Crystal Growth,
volume 63, no 3, pp 429-590
(1983).

Further, SOS (silicon on sapphire) formed by heteroepitaxy Si by CVD (chemical vapor deposition) on a single crystal sapphire substrate has been known for a long time, and is the most mature SOI technology. Although it was successful for the time being, a large amount of crystal defects due to the lattice mismatch between the Si layer and the underlying sapphire substrate interface, the mixing of aluminum from the sapphire substrate into the Si layer, and above all, the high cost and large area of the substrate The delay of the application has hindered its widespread application. In recent years, attempts have been made to realize an SOI structure without using a sapphire substrate. This attempt is roughly divided into the following two.

1. After the surface of the Si single crystal substrate is oxidized, a window is opened to partially expose the Si substrate, and the portion is used as a seed for lateral epitaxial growth to form a Si single crystal layer on SiO ₂ . (In this case, a Si layer is deposited on SiO _2. ) The Si single crystal substrate itself is used as an active layer, and SiO ₂ is formed thereunder. (This method does not involve deposition of a Si layer.)

[0008]

As means for realizing the above 1, a method of directly laterally epitaxially growing a single crystal layer Si by CVD, a method of depositing amorphous Si and performing a solid phase lateral epitaxial growth by heat treatment. Method, a method in which an amorphous or polycrystalline Si layer is irradiated with an energy beam such as an electron beam or a laser beam converged, and a single crystal layer is grown on SiO ₂ by melting and recrystallization, and a strip-shaped heater is used. Method for scanning the melted area on the surface (Zone melting restalli
zation) is known. Each of these methods has advantages and disadvantages, but their controllability, productivity, uniformity,
There are still many problems in quality, and none have been industrially put to practical use. For example, the CVD method requires sacrificial oxidation to achieve a flat thin film, and the solid phase growth method has poor crystallinity. Further, the beam annealing method has problems in processing time by convergent beam scanning, controllability such as beam overlapping and focus adjustment. Of these, Zone M
The eluting recrystallization method is the most mature, and relatively large-scale integrated circuits have been prototyped. However, many crystal defects such as point defects, line defects, and plane defects (sub-grain boundaries) remain. And, we haven't made a minority carrier device.

In the method of the above-mentioned 2 which does not use the Si substrate as a seed for the epitaxial growth, there are the following four kinds of methods.

1. An oxide film is formed on a Si single crystal substrate in which V-shaped grooves are anisotropically etched on the surface, a polycrystalline Si layer is deposited on the oxide film to be as thick as the Si substrate, and then polished from the back surface of the Si substrate. Thereby forming a Si single crystal region surrounded by the V groove and dielectrically separated on the thick polycrystalline Si layer.
In this method, the crystallinity is good, but the polycrystalline S
There is a problem in terms of controllability and productivity in the step of depositing i in a thickness of several hundreds of microns thick and the step of polishing the single crystal Si substrate from the back surface and leaving only the separated Si active layer.

2. SIMOX: S epa
relation by ion- im planted o
x ygen) and by ion implantation of oxygen into the called Si single crystal substrate is a method of forming a SiO ₂ layer, which is one of the techniques currently most mature for Si process consistent good. However, in order to form a SiO ₂ layer, it is necessary to implant oxygen ions of 10 ¹⁸ ions / cm ² or more, but the implantation time is long and the productivity cannot be said to be high. -The cost is high. Furthermore, many crystal defects remain, and from an industrial point of view, the quality is not sufficient to produce a minority carrier device.

3. A method of forming an SOI structure by dielectric isolation by oxidation of porous Si. This method uses P-type Si
Proton ion implantation of N-type Si layer on the surface of single crystal substrate,
(Imai et al., J. Crystal Growth, vo
63, 547 (1983)), or an island shape is formed by epitaxial growth and patterning, and only the P-type Si substrate is made porous by anodization in a HF solution so as to surround the Si island from the surface, and then increased. This is a method of dielectrically separating N-type Si islands by rapid oxidation. In this method,
The separated Si region is determined before the device process, which may limit the degree of freedom in device design.

[Object of the Invention] It is an object of the present invention to provide controllability, productivity,
It is to realize a forming method with improved quality and design flexibility, and to provide a high-performance and highly-functional device by a semiconductor device using a substrate formed by the method of the present invention.

[0014]

As a means for solving the above-mentioned problems, the present invention provides a step of forming a diffusion layer of opposite conductivity type on one surface of a semiconductor substrate of one conductivity type. And a step of forming a mask material on a part of the other surface of the base body, and after the step, the base body is electrolytically etched in an organic alkaline solution to form a portion of the semiconductor base body not covered with the mask material. By etching to reach the diffusion layer to form a hollow groove under the diffusion layer, and after the step, forming an insulating layer at least below the diffusion layer in the groove. A method for forming a semiconductor substrate is provided.

The insulating layer below the diffusion layer may be a translucent insulating film.

According to another aspect of the present invention, there is provided a semiconductor device having a semiconductor element formed on a diffusion layer on the groove and a semiconductor element formed on a semiconductor layer other than the groove on the same semiconductor substrate. The above problem is to be solved.

[0017]

According to the method of forming a semiconductor substrate of the present invention, a diffusion layer of opposite conductivity type is formed on the substrate and the diffusion layer is formed, and a mask material (SiO ₂ , Si ₃ N ₄ etc.) is formed on the opposite surface. Then
A part of the mask material is removed, the semiconductor crystal layer of the substrate is removed by etching until it reaches the diffusion layer, a groove having a hollow structure is formed under the thin diffusion layer, and the lower portion of the diffusion layer is further oxidized. By doing so, the base body having the SOI structure can be easily formed with high controllability and high quality.

Further, the substrate can be made transparent by oxidizing a part of the diffusion layer, and an SOI structure on a light-transmitting insulator can be manufactured. Therefore, if the substrate of the present invention is used, it becomes easy to fabricate a semiconductor device such as a liquid crystal display device that requires a light transmitting portion.

[0019]

EXAMPLE FIG. 1 is a preferred embodiment of the present invention and is a schematic view showing the most characteristic structure of the substrate forming step of the present invention.

In the figure, 101 is a silicon substrate, 1
Reference numeral 02 is a diffusion layer, and 103 is a thermal oxide film as a mask material. As described above, in the semiconductor substrate of the present invention, the thin diffusion layer 102 supported by the relatively thick silicon substrate 101 can be formed on the hollow groove portion. Therefore, although not shown in FIG. 1, a semiconductor substrate having an SOI structure can be easily obtained by forming an insulating layer below the diffusion layer 102 in the groove.

An embodiment of the method for forming a semiconductor substrate according to the present invention will be described below with reference to FIG.

[Embodiment 1] First, the specific resistance is 20 to 30 Ω.
A P-type silicon single crystal substrate 201 of about cm is prepared. Oxidation of about 500Å is applied to this substrate (Fig. 2
(A)).

Next, P ⁺ (phosphorus) is added to 1 × 10 ¹¹ to 10 ¹⁴
Ion implantation is performed under the condition of cm ⁻² / 60 to 100 keV.
Then, heat treatment is performed at 1000 ° C. for 1 hour in an N ₂ atmosphere to form the n-type diffusion layer 203. The depth of the diffusion layer is about 5000Å (Fig. 2 (b)).

Next, the Si ₃ N ₄ film 204 is used as a mask material.
To form. Depending on the Si etching conditions, if KOH (80 ° C.) is used, for example, Si 1200
0 Å / min Si ₃ N ₄ film 0.5 Å / min, so if a Si ₃ N ₄ film of about 200 Å is formed, 5 ″ φ
A 625 μm Si wafer can be sufficiently etched.

Next, a resist mask is applied, and the Si ₃ N ₄ film 204 and the SiO ₂ film 203 at desired locations are etched.

Further, this is subjected to electric field etching. A conceptual diagram of electric field etching is shown in FIG.

First, the substrate 201 is brought into contact with the metal electrode 304, and a positive voltage 302 is applied. The counter electrode 305 is
A platinum plate is used and a negative voltage 303 is applied. The etching solution 301 is an ethylenediamine-pyrocatechol-water mixed solution, and the composition ratio is ethylenediamine (7.5 liters) -pyrocatechol (1.2 kg) -water (2.4 liters). In addition, the temperature is set to 110 ° C., and sufficient stirring is performed.

This electric field etching is performed by T. N. JACK
Developed by SON and others, IEEE Dev
ice Letters vol EDL-2 No.
2 (1981 / p44) for details. Other than the above-mentioned solutions, KOH, TMAH or the like can be used as the etching solution in the same manner.

By this electric field etching, the substrate 201
Has a large selection ratio with respect to the diffusion layer 203, and in effect etching stops at the junction surface of the diffusion layer 203. Etching rate is 15000Å / mi in P region
Since it is 5Å / min in n and n regions, the selection ratio is about 300.
It becomes 0.

Finally, by electric field etching, the n-type diffusion layer (thin film) 203 remains only at a desired place (FIG. 2).
(C)).

By reversing the polarity of the electric field etching, it is possible to leave the P type diffusion layer.

Then, by oxidizing the thin film diffusion layer 203, the thin film becomes the SOI substrate 206 (FIG. 2 (d)).

[Embodiment 2] In Embodiment 1, the method of forming the SOI substrate has been described. However, in Embodiment 2, further,
A method of making this substrate transparent in the visible light region will be described.

FIG. 4 is a schematic sectional view showing a preferred embodiment of the present invention.

In the figure, 401 is a silicon substrate, 4
Reference numeral 02 is a diffusion layer, 403 is a mask material during silicon etching, 404 is a thermal oxide film, and 405 is an insulating film for reinforcing the thin film.

The forming method of this embodiment is the same as that of the first embodiment up to the step described in FIG. Hereinafter, with respect to the steps characteristic of the present embodiment, particularly the step of forming the transparent insulating film 405 will be described in detail with reference to FIG.

An oxidation resistant film is formed on 402. The film of the portion to be made transparent is removed by patterning. Then, by oxidizing this at a high temperature of 500 ° C. or higher, a part of the semiconductor substrate is oxidized and the light-transmitting insulating films 404, 4 are formed.
05 is formed.

With such a structure, it is possible to form an SOI device in the diffusion layer region of 406 which is not subjected to the oxidation treatment, and it is possible to form an ordinary device in the diffusion layer region of 407. Becomes

As described above, the SOI structure in which the semiconductor layer 406 is laminated on the transparent insulating film 405 can be obtained. Therefore, a structure advantageous for the structure of an optical semiconductor device such as a liquid crystal display device that requires a light transmitting portion can be easily formed.

When this is applied to a liquid crystal display device, for example, a MOS for pixel changeover switch is provided in the region 406.
Tr. And a peripheral drive circuit such as a shift register is formed in the region 407, a device capable of high speed driving can be easily obtained.

Incidentally, in the groove portion subjected to the electric field etching, silicon rubber, epoxy resin, SiN _x , SiO _x
The film strength in the region 406 can be improved by depositing the above.

[0042]

As described in detail above, according to the present invention,
In the method of forming a semiconductor substrate having an SOI structure, controllability,
It is possible to obtain the effect that a forming method with improved productivity, quality, and design flexibility can be realized.

Further, the semiconductor device using the substrate formed by the method of the present invention can provide a high-performance and highly-functional device.

In particular, according to the present invention, since the normally used single crystal substrate is present on the insulating film, there is no problem in crystallinity and the like.

Further, it becomes possible to form an SOI device and a normal device on the same substrate. A high speed device is formed on the SOI substrate and a high breakdown voltage device is formed on a normal bulk substrate. This also makes it possible to easily form a high-performance and highly-functional device.

Further, the SOI formed on the translucent insulator
Since a semiconductor substrate having a structure can be easily obtained, the effect of facilitating the manufacture of an optical semiconductor device such as a liquid crystal display device can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a semiconductor substrate showing a preferred embodiment of the present invention.

FIG. 2 is a schematic process sectional view for explaining a forming method according to an embodiment of the present invention.

FIG. 3 is a conceptual diagram of electric field etching according to an embodiment of the present invention.

FIG. 4 is a schematic cross-sectional view of a substrate having an SOI region and a bulk region formed by using the forming method of the present invention.

[Explanation of symbols]

Reference Signs List 101 silicon substrate 102 diffusion layer 103 mask material 201 P-type silicon single crystal substrate 202 oxide film 203 N-type diffusion layer 204 mask material (Si ₃ N ₄ ) 205 oxide film 304 metal electrode 305 counter electrode 401 silicon substrate 402 diffusion layer 403 mask Material 404 Thermal oxide film 405 Light-transmitting insulating film 406 Region for SOI device 407 Region for normal device

Claims (5)

[Claims] 1. A step of forming a diffusion layer of an opposite conductivity type on one surface of a semiconductor substrate of one conductivity type, and a step of forming a mask material on a part of the other surface of the substrate. After the step, the substrate is electrolytically etched in an organic alkaline solution to etch away the semiconductor substrate in a portion not covered with the mask material until the diffusion layer is reached. A method for forming a semiconductor substrate, comprising: a step of forming a groove; and a step of forming an insulating layer at least below the diffusion layer in the groove after the step. 2. The method for forming a semiconductor substrate according to claim 1, wherein, as the insulating layer below the diffusion layer, a part of the diffusion layer is a translucent insulating film. 3. The method for forming a semiconductor substrate according to claim 1, wherein a translucent insulating film is deposited as an insulating layer below the diffusion layer. 4. A semiconductor device using a semiconductor substrate formed by the method for forming a semiconductor substrate according to claim 1, 2, or 3, wherein a semiconductor element formed in a diffusion layer on the groove and a portion other than the groove are provided. A semiconductor device formed on the same semiconductor substrate as the semiconductor element formed on the semiconductor layer. 5. A semiconductor device comprising a liquid crystal display device formed by using a substrate formed by the method for forming a semiconductor substrate according to claim 2.