JPH05217894A - Semiconductor substrate and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a good semiconductor substrate with advantages in productivity, controllability and uniformity, by forming an Si layer on an Si substrate with an insulating film in between, and providing an empty space that extends to the insulating film in the Si substrate. CONSTITUTION:A semiconductor substrate comprises an insulating film 4 formed on a silicon substrate 2 having an empty space therein, and a silicon layer 8 formed on the insulating film 4. In the insulating film 4, an interfacial part next to the silicon layer 8 is made of a silicon compound richer in oxygen than that of the other interfacial part next to the silicon substrate 2 while the latter is richer in nitrogen than that of the former. The silicon layer 8 formed on a surface of a porous silicon 6 is bonded to the insulating film 4 formed on the silicon substrate 2. Then, the porous silicon 6 is removed in an etch step, and the empty space 10 is formed partly in the silicon substrate 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor substrate and a method for manufacturing the same, and in particular, a silicon layer is formed on a silicon substrate via an insulating film and part of the silicon substrate reaches the insulating film. The present invention relates to a semiconductor substrate having a cavity and a method for manufacturing the semiconductor substrate.

[0002]

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 it has been achieved in a bulk Si substrate for producing an ordinary Si integrated circuit. Much research has been done because devices that use SOI technology have a number of unprecedented advantages. That is, SO
By using I technology, 1. 1. Dielectric isolation is easy and high integration is possible. 2. It has excellent radiation resistance. 3. Stray capacitance is reduced and high speed is possible. 4. The well process can be omitted, Latch-up can be prevented, 6. It is possible to obtain a complete depletion type field effect transistor 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: "
Single-crystal silicon onnon-single-crystal insula
tors "; edited by GWCullen, Journal of CrystalGro
wth, volume 63, no 3, pp 429-590 (1983).

In addition, on old single crystal sapphire substrates,
SOS (Silicon on Sapphire), which is formed by heteroepitaxy Si by CVD (Chemical Vapor Deposition), is known, and although it succeeded as the most mature SOI technology, the Si layer and the underlying sapphire substrate A large number of crystal defects due to the lattice mismatch of the interface, the mixing of aluminum from the sapphire substrate into the Si layer, and above all, the high cost of the substrate and the delay in increasing the area hinder the spread of its application. ..

In recent years, attempts have been made to realize an SOI structure without using a sapphire substrate. This attempt is broadly divided into the following two: After the surface of the Si single crystal substrate is oxidized, a window is opened to partially expose the Si substrate, and that portion is used as a seed for lateral epitaxial growth to form a Si single crystal layer on SiO ₂ (in this case). Involves the deposition of a Si layer on SiO _2. ); The Si single crystal substrate itself is used as the active layer, and SiO ₂ is formed thereunder (this method does not involve deposition of the Si layer).

Various semiconductor devices and integrated circuits including them have been produced in a silicon layer on an insulator formed by these methods.

As means for realizing the above 1, a method of directly epitaxially growing a single crystal layer Si laterally by CVD, a method of depositing amorphous Si and performing solid phase lateral epitaxial growth by heat treatment, an amorphous or ,
Energy beam such as electron beam and laser light is applied to the polycrystalline Si layer.
The single crystal layer is converted to Si by fusion recrystallization.
A method of growing on O ₂ and a method of scanning the melting region in a band shape by a rod-shaped heater (Zone melting recryst
allization) is known. Each of these methods has merits and demerits, but there are still many problems in controllability, productivity, uniformity, and quality, and none of them has been industrially put into 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. In the beam anneal method, there are problems in the processing time for convergent beam scanning, the degree of beam overlap, and the controllability such as focus adjustment. Of these, Zone Melting R
Although the ecrystallization method is the most mature, and relatively large-scale integrated circuits have been prototyped, many crystal defects such as sub-grain boundaries still remain, leading to the creation of minority carrier devices. Not not.

The above-mentioned method 2 which does not use the Si substrate as seeds for epitaxial growth includes the following methods: 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 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, although the crystallinity is good, control is performed in the step of depositing polycrystalline Si to a thickness of several hundreds of microns, and in the step of polishing the single crystal Si substrate from the back surface and leaving only the separated Si active layer. There are problems in terms of productivity and productivity; 1. SIMOX: Separation by ion im
This is a method of forming a SiO ₂ layer by ion implantation of oxygen into a Si single crystal substrate called “planted oxygen”.
It is currently the most mature method because it has good compatibility with i-process. 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 the quality is not industrially sufficient to produce minority carrier devices. A method of forming an SOI structure by dielectric isolation by oxidation of porous Si. In this method, an N-type Si layer is proton-ion-implanted on the surface of a P-type Si single crystal substrate (Imai et al., J.Cr.
ystal Growth, vol 63, 547 (1983)), or formed into islands by epitaxial growth and patterning, and only the P-type Si substrate is porous by anodization in HF solution so as to surround the Si islands from the surface. Then, the N-type Si islands are dielectrically separated by accelerated oxidation. In this method, the separated Si region is determined before the device process, which may limit the degree of freedom in device design. Therefore, as a semiconductor integrated circuit of various SOI structures described above, Has not yet fully exhibited the features of.

On the other hand, in an SOI structure in which a silicon oxide insulating film is formed on the surface of a Si substrate and a Si layer is formed on the insulating film, a part of the Si substrate is removed so as to reach the insulating film. By forming a cavity, a semiconductor device is manufactured using a semiconductor substrate in which a part of a laminate of a silicon oxide insulating film and a Si layer is a thin film without a support. The Si substrate is etched during the production of this semiconductor substrate. It is preferable that the etching selection ratio of Si to the insulating film is as large and stable as possible during the etching. In the case of using, it cannot be said that this selection ratio is sufficiently large and a good thin film cannot be obtained.

The present invention can solve the above-mentioned problems and meet the above-mentioned requirements, and in particular, a Si layer is formed on a Si substrate through an insulating film, and a Si layer is formed on a part of the Si substrate. It is an object of the present invention to obtain a good semiconductor base material having a cavity reaching an insulating film with excellent productivity, controllability, uniformity and economy.

[0011]

According to the present invention, in order to achieve the above object, an insulating film is formed on at least a first surface of a silicon substrate, and a silicon layer is formed on the insulating film. The semiconductor substrate is formed and a part of the silicon substrate is removed from the second surface to the interface with the insulating film, and the insulating film has the silicon layer side interface portion on the silicon substrate side. A semiconductor substrate, comprising a silicon compound that is richer in oxygen than an interface portion, and the interface portion on the silicon substrate side is made of a silicon compound that is richer in nitrogen than the interface portion on the silicon layer side. It

In the semiconductor substrate of the present invention, the insulating film may be made of a silicon compound whose composition continuously changes from the interface part on the silicon layer side to the interface part on the silicon substrate side.

According to the present invention, in order to achieve the above-mentioned object, there is provided a method for producing a semiconductor substrate as described above, which comprises first relatively nitrogen-riching on a first surface of a silicon substrate. A silicon compound and finally an oxygen-rich silicon compound to form an insulating film, while forming a non-porous single crystal silicon layer on the surface of porous silicon, and the non-porous single crystal silicon layer. The surface of the insulating film on the silicon substrate is bonded to the surface of the silicon substrate, the porous silicon is removed by etching, and a part of the silicon substrate is removed by etching from the second surface side until the insulating film is exposed. A method for manufacturing a semiconductor substrate is provided.

In the manufacturing method of the present invention, the step of forming a non-porous single crystal silicon layer on the surface of the porous silicon can be performed by using epitaxial growth.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing an example of a manufacturing process of a semiconductor substrate according to the present invention.

First, as shown in FIG. 1A, the Si substrate 2
Is prepared, and the insulating film 4 is formed on the upper surface thereof. The insulating film is a layer whose interface (lower surface) with the substrate 2 is made of a silicon compound relatively rich in nitrogen as compared with the upper surface portion, and whose upper surface is made of a silicon compound relatively rich in oxygen as compared with the lower surface portion. It is a layer. Examples of such a silicon compound layer include the following layers (an example of the film forming method and film forming conditions are also shown): (1) SiO ₂ layer film forming method; plasma CVD method film forming condition; gas SiH ₄ 300 SCCM temperature 300 ° C. (2) SiN _1.5 O _1.1 layer film forming method; plasma CVD method film forming conditions; gas N ₂ 600 SCCM SiH ₄ 150 SCCM N ₂ O 630 SCCM NH ₃ 270 SCCM temperature 300 ° C. (3) Si ₃ N _6.3 layer Film forming method; plasma CVD method Film forming condition; gas N ₂ 600SCCM SiH ₄ 140SCCM NH ₃ 600SCCM temperature 300 ° C. (4) Si ₃ N ₄ layer film forming method; low pressure CVD method film forming condition; gas SiH ₄ 35SCCM NH ₃ 410SCCM Temperature 780 ° C. (5) BPSG layer film forming method; atmospheric pressure CVD method film forming condition; gas N ₂ 16000SCCM PH ₃ 1000SCCM B ₂ H ₆ 1350SCCM O ₂ 4000SCCM SiH ₄ 600SCCM Temperature 400 ° C Two of these layers are appropriately selected, and the one relatively rich in nitrogen is used as the lower surface layer, which is relatively oxygen rich. One is used as the upper surface layer. For example, a Si ₃ N _6.3 layer can be used as the lower surface layer, a SiO ₂ layer can be used as the upper surface layer, and a SiN _1.5 O _1.1 layer can be used as the lower surface layer.
Layer, a SiO ₂ layer can be used as the upper surface layer, a Si ₃ N _6.3 layer can be used as the lower surface layer, and a SiN _1.5 O _1.1 layer can be used as the upper surface layer, and a lower surface layer can be used. BPS as an upper surface layer using a Si ₃ N ₄ layer
A G layer can be used.

The thickness of the lower surface layer of the insulating film 4 as described above is, for example, about 500 to 3000 Å, and the upper surface layer is, for example, about 0.3 to 1.0 μm.

In the present invention, the insulating film 4 may have at least one intermediate layer interposed between the lower surface layer and the upper surface layer as described above. As the intermediate layer, a layer whose composition continuously changes in the film thickness direction may be used, and further, the composition continuously changes in the film thickness direction even in the lower surface layer and the upper surface layer. May be. In the case of such a continuous change, it is preferable that the oxygen content and the nitrogen content change monotonously in the film thickness direction.

Here, the results of examining the etching rate of the above five layers and Si at 80 ° C. using KOH as an etchant are shown: (0) Si etching rate 70 μm / min (1) SiO ₂ layer etching rate 0. Etching selectivity ratio to 036 μm / min Si 1/2000 (2) SiN _1.5 O _1.1 layer Etching rate 0.0035 μm / min Etching selectivity ratio to Si 1/20000 (3) Si ₃ N _6.3 layer Etching rate 0.0017 μm / min Si Etching selectivity ratio to 1/40000 (4) Si ₃ N ₄ layer Etching rate 0.0003 μm / min Etching selectivity ratio to Si 1/2002 (5) BPSG layer Etching rate 0.015 μm / min Etching selectivity ratio to Si 1/4700 ..

On the other hand, as shown in FIG. 1 (b), porous Si
A single crystal Si layer 8 is formed on the surface of the substrate 6.

Here, porous silicon (Si) will be described for ease of understanding. Porous Si is Uhlir
Discovered in the process of research on electrolytic polishing of semiconductors in 1956 (A.Uhlir, Bell Syst.Tech.J., vol 3
5, p.333 (1956)). In addition, Unami et al. Studied the dissolution reaction of Si in anodization, and reported that the anodic reaction of Si in HF solution requires holes, and the reaction is as follows (T . Unagami: J. Electrochem.Soc.,
vol. 127, p.476 (1980)): Si + 2HF + (2-n) e ⁺ → SiF ₂ + 2H ⁺ + ne ^- SiF ₂ + 2HF → SiF ₄ + H ₂ SiF ₄ + 2HF → H ₂ SiF ₆ or, Si + 4HF + (4- λ) e + → SiF 4 + 4H + + λe- SiF 4 + 2HF → H 2 SiF 6 where, e ⁺ and, e ^- respectively represent a hole and an electron ing. Further, n and λ are the numbers of holes required for dissolving one silicon atom, respectively, and porous silicon is formed when the condition of n> 2 or λ> 4 is satisfied.

As described above, holes are required to produce porous Si, and p-type Si is more likely to be transformed into porous Si than n-type Si. However, it is known that n-type Si is also transformed into porous Si if holes are injected (RPHolmstorm, IJYChi Appl.Phys.Lett. Vol.42,
386 (1983)).

This porous Si has a density of single crystal Si of 2.
Compared with 33 g / cm ³ , the HF solution concentration is 50-20%
By changing the density to 1.1-0.6 g / c
It can be changed in the range of m ³ . Porous Si is
According to observation with a transmission electron microscope, holes having an average diameter of about 600 Å are formed. As described above, although the density of porous Si is less than half that of single crystal Si, single crystallinity is maintained, and it is possible to epitaxially grow a single crystal Si layer on the surface thereof. is there. In addition, since a large amount of voids are formed inside the porous Si and the density thereof is reduced to less than half, the surface area of the porous Si is dramatically increased as compared with the volume, and the chemical etching rate is higher than that of the non-porous Si. The speed is significantly increased compared to the speed.

Next, a method for forming porous Si by anodization will be described. A p-type single crystal Si substrate is prepared and set in the anodizing apparatus. That is, in the anodizing apparatus, the substrate is in contact with a hydrofluoric acid-based solution, and the negative electrode is arranged on one side of the substrate and the positive electrode is arranged on the other side in the solution. The porosity occurs from the negative electrode side of the substrate in contact with the hydrofluoric acid solution. Concentrated hydrofluoric acid (50% HF) is generally used as the hydrofluoric acid solution. For the purpose of efficiently removing bubbles generated from the surface of the substrate during anodization, alcohol such as methanol, ethanol, propanol or isopropanol can be added as a surfactant. Note that stirring with a stirrer may be used instead of adding the surfactant. As the electrode, a material which is not corroded by the hydrofluoric acid solution, such as gold (Au) or platinum (Pt), is used. An appropriate value of several hundred mA / cm ² or less is used as a current value for anodizing. This current value is appropriately selected within a range that allows high-quality epitaxial growth on the surface of porous Si. Generally, when the current value is large, the rate of anodization increases and at the same time, the density of the porous Si layer decreases. That is, the volume occupied by the voids increases. This changes the conditions for epitaxial growth.

For example, a p-type (100) single crystal Si substrate having a thickness of 200 μm is subjected to a current density of 100 mA in 50% HF solution.
The entire substrate can be made porous at a porosification rate of about 8.4 μm / min for about 24 minutes by performing anodization treatment at a rate of about 8 cm ² / cm ² .

Next, a single crystal Si layer 8 is formed on the surface of the porous Si substrate 6 by epitaxial growth. A low pressure CVD method can be used for the epitaxial growth.

Next, as shown in FIG.
On the surface of the insulating film 4 of (a), the single crystal Si of FIG.
The surfaces of layer 8 are joined. This joining is carried out, for example, by cleaning the joining surfaces, then fitting the joining surfaces together and heat-treating them. The heat treatment is performed at a temperature of 600 ° C. or higher in an atmosphere of oxygen, nitrogen, hydrogen, a rare gas, or the like. Generally, the higher the heat treatment temperature, the stronger the bond strength at the interface. In the present invention, since an oxygen-rich silicon compound such as a SiO ₂ layer is used as the insulating film 4 on the upper surface portion, good bonding with the surface of the single crystal Si layer 8 is achieved, and voids are hardly present on the bonding surface. It does not peel off even by heat treatment and has a high bonding strength.

Then, in order to remove the porous Si substrate 6, etching is performed using an etchant having a high etching selectivity ratio between non-porous Si and porous Si. An etchant preferably used is a hydrofluoric nitric acid acetic acid solution. For example, a hydrofluoric nitric acid acetic acid solution (1: 3:
The etching rate for 8) is about 1 μm / min or less in the case of non-porous single crystal Si, but the porous single crystal S
In the case of i, the speed is increased by about 100 times. Thus Figure 1
An SOI in which an epitaxially grown single crystal Si layer 8 is bonded onto a Si substrate 2 via an insulating film 4 as shown in (d).
The structure is obtained.

As an etchant for etching the porous Si, other than the hydrofluoric nitric acid acetic acid solution,
A mixed solution of hydrofluoric acid, buffered hydrofluoric acid, and hydrofluoric acid or buffered hydrofluoric acid and alcohol (ethyl alcohol, isopropyl alcohol, etc.) and / or hydrogen peroxide solution can be used. By adding alcohol, it is possible to instantaneously remove the bubbles of the reaction product gas by etching from the etching surface without stirring, and to uniformly and efficiently etch the porous Si. In addition, by adding hydrogen peroxide water, S
It becomes possible to accelerate the oxidation of i and to accelerate the reaction rate as compared with the case of no addition, and the reaction rate can be controlled by changing the ratio of hydrogen peroxide solution. The conditions of the solution concentration and the temperature are set within a range in which hydrofluoric acid, buffered hydrofluoric acid, the above hydrogen peroxide solution, alcohol, and the like each have an effect, and the etching rate does not interfere with the manufacturing process.

When hydrofluoric acid is used, the HF concentration in the etching solution is preferably set in the range of 1 to 95%, more preferably 5 to 90%, and further preferably 5 to 80%. When using buffered hydrofluoric acid, the HF concentration in the etching solution is preferably set in the range of 1 to 95%, more preferably 1 to 85%, further preferably 1 to 70%, and the NH ₄ F concentration is preferably set. 1-95%,
More preferably 5 to 90%, still more preferably 5 to 80%.
It is set in the range of%.

In the etching solution, the H ₂ O ₂ concentration is preferably 1 to 95%, more preferably 5 to 90%, further preferably 10 to 80%, and set within the range where the above hydrogen peroxide solution effect is exhibited. To be done. In the etching solution, the alcohol concentration is preferably 80% or less, more preferably 60% or less, still more preferably 40% or less, and set within a range in which the effect of the alcohol is exhibited.

The temperature is preferably set in the range of 0 to 100 ° C, more preferably 5 to 80 ° C, and further preferably 5 to 60 ° C.

Next, as shown in FIG. 1E, the Si substrate 2
Only the desired portion is selectively removed by etching from the lower surface side of the above to form the cavity 10. KOH can be used as an etchant for the etching for forming the cavity, in which case a mask for forming the cavity is formed on the lower surface of the Si substrate 2, and the mask is removed after etching. In the present invention, since a nitrogen-rich silicon compound such as a Si ₃ N ₄ layer is used as the insulating film 4 on the lower surface, the etching rate is extremely low compared to Si when etching the Si substrate 2 for forming a cavity, Therefore, the insulating film 4 is not substantially damaged by etching and remains as a good thin film.

[0034]

As described above in detail, according to the present invention, S
Using an insulating film in which the i-layer side interface part is an oxygen-rich Si compound compared to the Si substrate side interface part, and the Si substrate-side interface part is a nitrogen-rich Si compound compared to the Si layer side interface part Since the SOI structure is formed, the insulating film and the Si layer are bonded well, voids are hardly present in the bonding surface, and the bonding strength is high.
The insulating film is not damaged during the etching of the i substrate and remains as a good thin film. Therefore, according to the present invention, the Si layer is formed on the Si substrate through the insulating film.
A good semiconductor base material having a cavity reaching an insulating film in a part of the substrate can be obtained with excellent productivity, controllability, uniformity and economy.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of a manufacturing process of a semiconductor substrate according to the present invention.

[Explanation of symbols]

 2 Si substrate 4 Insulating film 6 Porous Si substrate 8 Epitaxial growth single crystal Si layer 10 Cavity

Claims (4)

[Claims] 1. An insulating film is formed on at least a first surface of a silicon substrate, a silicon layer is formed on the insulating film, and a part of the silicon substrate extends from the second surface to the insulating film. In the semiconductor base material that has been removed up to the interface with the insulating film, the silicon layer side interface portion is made of an oxygen-rich silicon compound as compared to the silicon substrate side interface portion, and the silicon substrate side interface portion is A semiconductor substrate comprising a silicon compound richer in nitrogen than the silicon layer side interface portion. 2. The semiconductor substrate according to claim 1, wherein the insulating film is made of a silicon compound whose composition continuously changes from the interface part on the silicon layer side to the interface part on the silicon substrate side. 3. A method of making a semiconductor substrate according to claim 1, wherein a relatively nitrogen-rich silicon compound is first deposited on a first surface of a silicon substrate and finally an oxygen-rich silicon compound. To form an insulating film, while forming a non-porous single crystal silicon layer on the surface of porous silicon, and covering the surface of the insulating film on the silicon substrate with respect to the surface of the non-porous single crystal silicon layer. Bonding, removing the porous silicon by etching, and etching away a part of the silicon substrate from the second surface side until the insulating film is exposed. 4. The method for producing a semiconductor substrate according to claim 3, wherein the step of forming a non-porous single crystal silicon layer on the surface of the porous silicon is performed by using epitaxial growth.