JPH06216027A - Manufacture of semiconductor substrate - Google Patents

Abstract

PURPOSE:To obtain a highly reliable semiconductor substrate by effectively removing particles by a method wherein the semiconductor substrate is brought into a porous state, the surface layer is removed to the specific thickness by etching, and non-porous semiconductor single crystal is grown. CONSTITUTION:A porous Si layer 2 is formed by providing multiple holes on the surface of a semiconductor Si substrate 1. Then, after the surface layer is thinned off by etching to the thickness of 30Angstrom or more and less than three times of hole diameter using an etchant of 20 to 60 deg.C, a single crystal Si 3 is epitaxially grown on the porous surface. An alkaline solution, especially NH4OH or KOH, and trimethyl aluminum hydrate are considered desirable as the etchant. Thus, by using a low etching temperature and by limiting the amount of etching, the particles on the surface can be removed by etching.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor thin film which becomes an active layer in a semiconductor element substrate such as a thin film transistor.

[0002]

2. Description of the Related Art In the technology of SOI (silicon on insulator) in which a single crystal Si layer is formed on an insulating layer, in a semiconductor element substrate, single crystal Si is α (amorphous).
Since it has many advantages over -Si and polycrystalline Si, it has been widely studied and is expected to be used for a thin film transistor (TFT) or the like which has been attracting attention in recent years.

On the other hand, in the semiconductor field, since very fine processing is performed and operation at the atomic level is handled, a slight difference in the shape determines the characteristics of the final device. Therefore, in the case of a normal Si wafer, a Si substrate free from particles and scratches is obtained by a cleaning operation such as removing the wafer surface layer by wet etching.

In the process of cleaning the semiconductor substrate, NH ₄ /
Cleaning using H ₂ O ₂ / H ₂ O solution is commonly called “SC-1”.
Called cleaning (Ogawa, Kobayashi, Nakajima: Wet cleaning technology-
Focusing on particle measures-, Monthly Semicon
doctor World 1992, March issue p. 11
1-p. 115), 1970 in RCA (Radio
W of Corporation of America)
Invented by Erner Kern et al. [W. Ker
n, D. A. Putiner: "Cleaning
Solutions Based on Hydrog
en Peroxide for use in Si
licon Semiconductor Techn
"," RCA Review, vol.46,
p. 81 (1983)]. Kern et al., NH ₄ OH:
It is recommended that a solution of H ₂ O ₂ : H ₂ O = 1: 1: 5 or 1: 2: 7 be heated to 75 to 80 ° C. and cleaned for about 10 minutes.

SC-1 is an excellent processing method capable of removing particles without using mechanical force, and is most commonly used. Although the cleaning mechanism of SC-1 has not been fully clarified yet, it is considered that the etching of Si by NH ₄ OH and the decrease of zeta potential due to the increase of pH are performed. That is, each component reacts with Si as follows.

H ₂ O, NH ₄ OH: Si + 2OH ⁻ + H ₂ O → SiO ₃ ²⁻ + 2H ₂ (1) H ₂ O ₂ : Si + 2H ₂ O ₂ → SiO ₂ + 2H ₂ O (2) In solution Then, Si is etched by the reaction of (1) to remove particles on the surface, and Si is oxidized by the reaction of (2) to make the surface SiO ₂ which is not etched by NH ₄ OH. That is, the reactions of (1) and (2) are competing with each other so that the etching of Si does not proceed extremely. Further, OH ^- pH of the liquid by large becomes than 7 (1: 1: 5 pH in the solution of about 10), by lowering the zeta potential of the Si surface, once removed particles as not to adhere to the surface again I have to.

Therefore, in principle, it suffices to have an alkaline solution having a Si etching action, and KOH can be used instead of NH ₄ OH. H ₂ O ₂ is not necessary in principle, but has a function of controlling the etching reaction of NH ₄ OH.

The effects of the etching rate of bulk Si and SiO ₂ by NH ₄ OH and the concentration of H ₂ O ₂ are as follows.
Measured by Kobayashi et al. According to it, H ₂ O ₂
The higher the concentration of Si, the lower the etching rate of Si by NH ₄ OH, and the etching rate of SiO ₂ is H ₂ O.
It is determined by the NH ₄ OH concentration regardless of the concentration of ₂ . In addition, the particle removal capability is H ₂ O = 1 ≤ H ₂ O ₂ ≤
When 0.1, NH ₄ OH ≧ 0.1 is known to be sufficient for practical particle removal [Nakajima, Kobayashi, Ogawa: “NH ₄ OH / H ₂ O ₂ cleaning solution mixture ratio and its cleaning Effect ”, Hei 2 Spring Society of Applied Physics
p. 665 (1990)].

[0009]

The applicant of the present invention has the above-mentioned S
As one of the OI techniques, a method has been achieved in which porous Si is used and single crystal Si is epitaxially grown on the surface thereof.
According to this method, a single crystal Si substrate having almost no defects can be obtained. The method will be briefly described.

FIG. 1 shows a manufacturing process of a single crystal Si substrate using porous Si. First, the first Si substrate (bulk) 1
The surface is made porous to form a porous Si layer 2 (a),
(B). Single-crystal Si3 is epitaxially grown on this porous surface (c). On the other hand, a second Si substrate 4 is prepared, an insulating layer 5 is formed on the surface thereof, the insulating layer 5 and the single crystal Si3 are bonded (d), and the first Si substrate side is removed by etching to obtain a Si substrate. (E).

However, in reality, fine particles are present on the surface of the porous Si, and the epitaxial growth of the single crystal Si is hindered by the particles, so that FIG.
As shown in (1), defects are generated and voids are generated in the final Si substrate. The defects such as the voids generated in the single crystal Si substrate directly affect the characteristics of the semiconductor element, and cause the reliability of the semiconductor element substrate to be deteriorated. Therefore, removal of particles on the surface of porous Si is an essential requirement for producing a good-quality single crystal Si substrate.

However, the surface area of the porous substrate varies depending on the degree of porosity, but the surface area of the 5-inch wafer is 2
It extends from 00 m ^{2 to} 400 m ² . Therefore, the etching rate of Si and the etching rate of oxidized Si are 10 to 100 times as high as those in the case of bulk. Therefore, a cleaning method effective for bulk Si is not always effective even for porous materials, and it is necessary to consider a negative effect such as roughening the surface.

According to experiments conducted by the present inventors, NH ₄ OH:
H ₂ O ₂ : H ₂ O = 0.05: 1: 5 solution at 80 ° C.,
When a substrate having a porosity of 30% was washed for 10 minutes and then epitaxially grown, defects having an areal density of 1 × 10 ⁶ / cm ² were observed in the epitaxial layer. This is because although about 30 nm of Si should have been originally removed under the above conditions, it is 10 to 100 times (300 to 3000 nm) of S due to the high reactivity on the porous substrate.
Since i has been removed, the pore size of the porous (about 60
nm) has changed significantly.

Conventionally, in order to avoid such a problem due to the difference in reactivity, a method of cleaning with a diluted HF solution and pure water has been used. If a dilute HF solution is used, single crystal S
This is a convenient cleaning method because the effect of removing the surface natural oxide film immediately before the epitaxial growth, which is essential in the i substrate manufacturing process, is obtained.

However, only about 20% of the particles on the porous surface can be removed by washing only with diluted HF, and it cannot be said that the particle removing function is sufficiently fulfilled.

In view of the above problems, it is an object of the present invention to provide a highly reliable semiconductor substrate by efficiently removing particles in a method of manufacturing a semiconductor substrate.

[0017]

According to the present invention, a semiconductor substrate is made porous, and after the surface layer is removed by etching with an etching solution at 20 to 60 ° C. to a thickness of 30 Å or more and 3 times or less of the pore diameter, a non-porous material is obtained. A method of manufacturing a semiconductor substrate, which comprises growing a semiconductor single crystal. In the present invention,
The etching solution is an alkaline solution, especially N 2.
H ₄ OH or KOH or TMAH (trimethylaluminum hydrate) is preferably used, and further HN ₄
OH, H ₂ O ₂ , H ₂ O mixed solution, KOH, H ₂ O ₂ , H ₂
A mixed solution of O and a mixed solution of TMAH, H ₂ O ₂ and H ₂ O are preferably used. Hereinafter, the present invention will be described in detail by taking Si, which is most widely used in the semiconductor field, as an example.

First, the porous Si according to the present invention will be described. Porous Si was discovered by Uhir et al. In 1956 in the course of research on electrolytic polishing of semiconductors [A. Uhir, Bell System. Tech.
J. , Vol 35, 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. , Vo
l. 127, 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 ⁺ + λ
e ⁻ SiF ₄ + 2HF → H ₂ SiF ₆ Here, e ⁺ and e ⁻ respectively represent a hole and an electron. Further, n and λ are the numbers of holes necessary for dissolving Si1 atoms, respectively, and porous Si is formed when the condition of n> 2 or λ> 4 is satisfied.

As described above, holes are required to form porous Si, and P-type Si is more easily 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. [R. P. Holmstrom and J. Y.
Chi. Appl. Phys. Lett. vol. Four
2, 386 (1983)].

The porous Si produced in this way is
By changing the HF solution concentration to 50 to 20% as compared with the density of single crystal Si of 2.33 g / cm ³ , the density can be changed to the range of 1.1 to 0.6 g / cm ^3. . According to observation with a transmission electron microscope, pores having an average diameter of about 600 Å are formed in this porous Si layer. Despite its density being less than half that of single crystal Si, single crystallinity is maintained, and single crystal Si can be epitaxially grown on the upper part of the porous layer.

Generally, when single-crystal Si is oxidized, its volume is increased about 2.2 times, but it is possible to suppress the volume expansion by controlling the density of the porous material.
Warpage of the substrate and cracks introduced into the surface residual single crystal layer can be avoided. The volume ratio R of single crystal Si after being oxidized to porous Si can be expressed as follows.

R = 2.2 × (A / 2.33) where A is the density of porous Si. If R = 1,
That is, if there is no volume expansion after oxidation, A = 1.06
(G / cm ³ ), and if the density of porous Si is set to 1.06, volume expansion can be suppressed.

Further, since the porous layer has a large amount of voids formed therein, its density is reduced to less than half. As a result, the surface area increases dramatically compared to the volume,
Its chemical etching rate is significantly enhanced compared to the etching rate of the non-porous Si layer.

The manufacturing method of the present invention is characterized by the step of etching the surface of the porous Si substrate. That is, by setting the temperature of the etching solution used for wet etching to a temperature lower than that of the conventional method and limiting the etching amount within a specific range, the etching amount of the holes is set to an extent that does not affect the epitaxial growth of single crystal Si. It suppresses and removes particles on the surface by etching to prevent defects in the semiconductor substrate.

In the present invention, the conditions for making the first Si substrate porous are not particularly limited. For example, the following conditions are preferably used.

Current density J = 10 ^-3 to 10 ⁰ A / cm ² preferably 10 ^-2 to 10 ^-1 A / cm ² solution = HF (49%): C ₂ H ₅ OH: H ₂ O porous layer Film thickness of 0.1 to 100 μm, preferably 1 to 10 μm Porosity = 20 to 50% In the surface etching treatment of the porous Si substrate, which is a feature of the present invention, the conditions other than the temperature of the solution and the etching amount are: The conditions may be the same as those used when finally removing the porous Si substrate by etching. For example, the following conditions are preferably used.

Etching solution = NH ₄ OH: H ₂ O ₂ : H ₂ OH With respect to H ₂ O = 1, NH ₄ OH = 10 ⁻⁴ to 10 ⁻¹ H ₂ O ₂ = 0 to ¹ Desirably, NH ₄ OH = 10 ^{−3 to} 0.05 H ₂ O ₂ = 10 ^{−3 to} 0.5 In the present invention, the temperature of the solution is 20 to 60 ° C., preferably 30 to 50 ° C. Further, in the present invention, the etching amount is 30 Å or more and 3 times or less of the hole diameter, that is, since the hole diameter is about 600 Å as described above, the etching time and the like are set so as to be 1800 Å or less. Preferably, it is not less than 40Å and not more than twice the hole diameter.

[0029]

【Example】

(Example 1) SC-1 etching solution (NH ₄ OH: H
₂ O ₂ : H ₂ O = 0.05: 1: 5), and using the above solution in the steps of etching with the solution, washing with pure water for 10 minutes, washing with warm water (90 ° C.) for 10 minutes, and washing with pure water for 10 minutes. The temperature was changed to measure the relationship between the removal rate of particles having a diameter of 0.5 μm or more and the defect density due to excessive etching of the epitaxial layer grown on the porous surface (FIG. 2). In this example, it can be seen that in the temperature range of 20 to 60 ° C., it has a particle removing effect but does not significantly affect the porous surface. Note that washing with warm water can remove Al that tends to adhere after washing with ammonium.

Next, 800 ° C. to 110 ° C. is applied on the porous substrate.
Epitaxial growth was performed at 0 ° C. Reaction gas is SiH
₂ Cl ₂ (dichlorosilane) was used, but it is not limited to this in the present invention. The grown film thickness is 3 μm. After that, the epitaxial layer surface and the surface are 500 to 1000.
0Å Oxidized Si was stuck. At this time, the bonding interface was observed with an infrared microscope, but no void was observed.

After that, the Si substrate in contact with the porous Si and the porous Si were sequentially removed with an H ₂ O ₂ -based etching solution to complete the SOI substrate. The single crystal layer of the obtained SOI substrate is a minute void (1 to 1) caused by particles of several particles / wafer generated and attached during epitaxial growth.
Other than 0 μm), it is almost defect-free, and large voids (≧ 1 mmφ) that have been generated in the past by several wafers and microscopic voids that have been generated by several hundred wafers / wafer can be significantly reduced. (Example 2) Next, in the same process as in Example 1, the same solution was used and the etching amount was changed to measure the change in the particle removal rate. The result is shown in FIG. Similar to bulk Si, a particle removal effect is almost completely obtained at 40 Å or more. Therefore, NH ₄ OH: H ₂ O ₂ : H ₂ O = 0.01:
The 1: 5 solution is warmed to 40 ° C, and the pore system 600 Å porous S
The i substrate was etched for 10 minutes. Etching amount is Si
With the amount of about 600Å, particles were completely removed (99.9%) in the range of> 0.3 μm.

Next, SiH ₄ gas is depressurized (0.1 to 1).
00 Torr), 0.5 at low temperature (750-900 ° C)
Epitaxial growth of ˜5 μm was performed. No defects in the single crystal layer were found by etching with the potassium dichromate solution. Furthermore, after the surface was oxidized by 500 Å, it was bonded to a Si substrate whose surface was oxidized by 500 to 10000 Å, and then heat treatment at 950 ° C. was performed, whereby a large void at the bonding interface could be eliminated. Also, the number of minute voids was reduced to a few / wafer.

The example using NH ₄ OH has been described above.
KOH can also be used because a similar effect can be obtained with an alkaline solution of high purity. However, in this case, it is necessary to optimize the concentration. Another candidate is TMAH.

The pore size of the porous Si is not limited to this.

Further, in the embodiment, the epitaxial growth using the vapor phase reaction is described, but in addition, MBE (Mo
method using a beam such as a laser beam epitaxy (PVD) or a PVD (Physical Vapor De) method such as bias sputtering using dual frequency excitation.
The method using the position method is possible,
It does not impair the effects of the present invention.

[0036]

According to the manufacturing method of the present invention, the particles on the surface of the porous Si layer of the porous layer are removed without significantly affecting the epitaxial growth such as the enlargement of the pore size by wet etching and the high quality SOI substrate. Can be stably supplied, and the manufacturing yield can be significantly increased. Further, the integrated circuit using this SOI substrate shows high performance, high yield, and high reliability, and sufficiently guarantees the validity of using the SOI substrate. INDUSTRIAL APPLICABILITY The present invention provides a driving force for industrially frequently using SOI substrates.

[Brief description of drawings]

FIG. 1 is a diagram showing a manufacturing process of a single crystal Si substrate using porous Si.

FIG. 2 is a diagram showing the results of Example 1 of the present invention.

FIG. 3 is a diagram showing the results of Example 2 of the present invention.

FIG. 4 is an explanatory diagram of generation of voids in a single crystal Si substrate.

[Explanation of symbols]

 1 Si substrate 2 Porous Si 3 Single crystal Si 4 Si substrate 5 Insulating layer 6 Particle 7 Void

Claims (10)

[Claims] 1. A semiconductor substrate is made porous to 20 to 60 ° C.
A method for manufacturing a semiconductor substrate, comprising: removing a surface layer by etching with the etching solution up to a thickness of 30 Å or more and 3 times or less of a pore diameter, and then growing a non-porous semiconductor single crystal. 2. The method of manufacturing a semiconductor substrate according to claim 1, wherein the etching solution is an alkaline solution. 3. The method of manufacturing a semiconductor substrate according to claim 2, wherein the alkaline solution contains NH ₄ OH. 4. The method of manufacturing a semiconductor substrate according to claim 2, wherein the alkaline solution contains KOH. 5. The method of manufacturing a semiconductor substrate according to claim 2, wherein the alkaline solution contains TMAH. 6. The alkaline solution is NH ₄ OH, H ₂
The method for manufacturing a semiconductor substrate according to claim 3, wherein the mixed solution is O ₂ and H ₂ O. 7. The alkaline solution is KOH, H
5. A mixed solution of ₂ O ₂ and H ₂ O. 5.
A method for manufacturing a semiconductor substrate according to claim 1. 8. The alkaline solution is TMAH, H ₂
The method for manufacturing a semiconductor substrate according to claim 5, wherein the method is a mixed solution of O ₂ and H ₂ O. 9. The method of manufacturing a semiconductor substrate according to claim 1, wherein the semiconductor is Si. 10. A porous semiconductor substrate on which the semiconductor single crystal is grown and a second substrate having an insulating layer formed on the surface of another semiconductor substrate are in contact with the semiconductor single crystal and the insulating layer. 2. The method for manufacturing a semiconductor substrate according to claim 1, wherein the SOI substrate is manufactured by pasting together as described above.