JPH0249466A - Manufacture of soi substrate - Google Patents

Abstract

PURPOSE:To enable a Si layer to have an impurity concentration required for the formation of an element by a method wherein Si is removed except a p<+> doped layer on a first Si substrate after a the p<+> doped layer on the first Si substrate has been bonded to an insulating layer on a second Si substrate, and a part of the p<+> doped layer is oxidized. CONSTITUTION:A p<+> boron doped layer 2, a SiO2 layer 3, and a BPSG film 4 are provided onto a primary face of a Si substrate 1 to form a first substrate 5. The substrate 5 is bonded to a second substrate 9, composed of an SiO2 film 7 and a BPSG film 8 which are formed on a Si substrate 6, using the films 4 and 8, and then the substrate 5 is removed except the layer 2 to make the bonded substrate a thin layer. Then, the substrate is oxided in a moistened oxygen atmosphere to form a SiO2 film 11. In this process, an SOI(Silicon on Insulator) substrate, provided with a Si layer whose boron concentration is 3-4X10<16>cm<-3> is formed through the suction of boron due to a segregation effect as the boron high concentrated layer 2 grows gradually to be a thin layer by oxidation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an SOI (Silicon On Insulator) which forms a single crystal Si film on an insulating film such as a silicon (Si) oxide film.
)) The present invention relates to a method for manufacturing a substrate, and in particular to a method for manufacturing a So-based substrate having good film thickness uniformity and crystallinity, and in which the impurity concentration in the film is at a concentration necessary for device formation.

[Conventional technology]

In recent years, single crystal S with a thickness of about 0.1 mm has been deposited on a silicon oxide film.
When an i film (SOI) is formed and a MOSFET is formed on this Si film, the mutual conductance g increases compared to a MOSFET formed on a bulk, and the short channel effect is suppressed. It has become clear that this method has advantages such as the absence of the kink phenomenon observed in the SOI substrate used, and is attracting attention.

In order to apply it to such a 5OIti-LSI board, it is necessary to satisfy the following conditions. In other words,■
The uniformity of the Si film thickness is good, ■ the crystallinity of the Si film is good, and ■ the impurity concentration in the Si film is at a value suitable for forming the device. be.

Three methods have been proposed for realizing conventional SO-engineered boards.

FIGS. 6(a) and 6(b) are process cross-sectional views showing a first method for realizing a conventional S○■ substrate.

That is, in the first conventional method, SiO is formed on the Si substrate 61 and amorphous or polycrystalline S is formed on the film 62.
After forming the i-film 63, annealing is performed by scanning an energy beam 64 such as a laser beam or an electron beam in the direction of the arrow to monocrystallize the Si film 63 and form a single-crystal film 65 (see FIG. 6). a)) Next, the Si film 65 is thinned using a dry etching method or an oxidation method to realize an SOI substrate (FIG. 6(b)).

However, although this method satisfies the appropriate impurity concentration in condition (1) above, the film thickness uniformity in condition (2) is affected by the waving phenomenon of the Si film that is characteristic of energy beam annealing. It is difficult to ensure the uniformity of the condition (2), and good crystallinity cannot be obtained due to the presence of grain boundaries or the rotation of crystal axes that occur during recrystallization.

FIGS. 7(a) to 7(c) are process cross-sectional views showing a second method for realizing a conventional SOI substrate.

That is, in the second conventional method, an n- or p- epitaxial layer 72 is formed on an n+ or p+ substrate 71, a SiO2 film 73 is formed, and then this substrate 7 is
4 is bonded to another substrate 77 on which a Si film 76 is formed on a Si substrate 75 using a known method (FIG. 7(a)).
Next, the n+ or p+ substrate 71 is removed by etching with a mixed solution of nitric acid, hydrofluoric acid, and acetic acid, in which the etch rate of a Si substrate with a high impurity concentration is higher than that of a Si substrate with a low impurity concentration (that is, the etching rate is faster). , n- or p- epitaxial layer 72 is left.

This method satisfies conditions (1) and (2), but regarding (2) uniformity of film thickness, etching is performed using a mixed solution of nitric acid, hydrofluoric acid, and acetic acid.

Less than 100 people have the disadvantage that fine irregularities occur, and
The etch rate at high impurity concentration and low impurity concentration is also about 100 times at most, so if there is an uneven thickness of 2°0- above in the Si film thickness in the high impurity concentration area, the thickness after etching will be ±300 Å or more. Samurai will occur, and n-
Alternatively, the p- epitaxial layer can be formed by 1000 layers (0, 1
, caa ) or less, the result is not negligible. Furthermore, this method uses an epitaxial growth method, which has the drawback of significantly increasing manufacturing costs and thus making the SO substrate expensive.

Next, as for the third method, recently, as a method that does not use epitaxial growth, boron-doped p"Si
A method has been proposed in which the surface of the substrate is oxidized, a p-layer is formed only on the surface of the Si substrate by utilizing the segregation of the Si substrate, SiO, and the film, and this p-layer is left. FIG. 8 is a diagram illustrating this method.

However, the p-layer obtained by this method is about 101'' row 3, and the p-layer is about 1017C1, which is necessary for device formation.
It is difficult to obtain a Si layer with an impurity concentration of 1-' or less.

[Problem to be solved by the invention]

As described above, in the conventional SOI structure, there is no suitable technology for all of the uniformity of the Si film thickness, the crystallinity of the Si film, and the impurity concentration in the Si film.

An object of the present invention is to provide a SO substrate having a thin Si film that satisfies all of these three conditions.

[Means for solving problems]

The method for manufacturing an SOI substrate of the present invention includes the steps of forming a p+ impurity doped layer on the main surface of a first substrate made of Si;
With an insulating film interposed on the p+ impurity doped layer, Si
A step of forming a second substrate or plate whose surface layer on the side of the first substrate is made of an insulator, and selectively removing the Si portion of the first substrate other than the p+ impurity doped layer. and a step of thinning the Si layer and reducing the impurity concentration by oxidizing a part of the p'' impurity doped layer from the side opposite to the second substrate. do.

[Effect]

In the present invention, an alkaline etching solution can be used instead of using a nitric-fluoric acid-based etching solution for etching Si in the conventional second method.
- and p+, the etch rate is several times higher than that of a nitric-fluoric acid-based etching solution, and as a result, a Si film with extremely good film thickness uniformity can be obtained.

In addition, since it is possible to use Si wafer bonding technology in the same way as the conventional second method, it is possible to use
Unlike the method described above, a Si film having good crystallinity can be obtained.

Furthermore, oxidation is performed to thin the pSi layer,
This thins the Si layer and reduces the boron concentration in the p+ layer, which is also done in the conventional third method, but the difference is that in the present invention, the p+ layer is already on the SOI layer. Because of this structure, the total amount of boron is constant, and the boron concentration can be reduced more effectively through oxidation than when the surface of the p+ substrate is oxidized, as in the conventional third method. , the impurity concentration in the Si layer can be set to a value suitable for forming an element.

As described above, in the method for manufacturing a So-based substrate of the present invention, all of the conditions (1), (2), and (2) can be satisfied.

〔Example〕

FIGS. 1(a) to 1(f) are cross-sectional views showing the manufacturing process of an SOI substrate according to an embodiment of the present invention.

First, prepare a Si substrate 1 whose main semiconductor surface is the (100) plane.Next, on the main surface of this Si substrate, an impurity concentration of 10''Ql-' or more at a depth of 1tlIm from the surface is prepared. A p2 boron doped layer 2 is formed (FIG. 1(a)). The p+ boron doped layer 2 can be formed by boron ion implantation or BN (boron nitride) diffusion. For example, in the ion implantation method, the implantation energy is 40 keV and the implantation amount is I
This can be achieved by using XIO "a++-" and annealing at 1100° C. for about 30 minutes. In addition, in the BN diffusion method, 10
50" C12, 0-order, which can be realized by 7 hour diffusion conditions, SiO, film, on p + boron doped JtI2,
and BPSGg4 (boro phosphorus silicate)
Glass niboro-phosphorus silicate glass) (Boro-P h
ospho-S 1licateG 1ass)).

Next, apart from the substrate 5, SiO is deposited on the surface of the Si substrate 6.
, prepare the substrate 9 on which the film 7 is formed (FIG. 1(b)),
Adhere both (5 and 9) using BPSG film 4.8 (
As shown in Fig. 1(c)), a known technique can be used for this bonding method6. However, in order to reduce changes in the impurity concentration distribution of the formed p + boron doped layer 2, it is necessary to bond at a low temperature. Yes, and here BPSG was used as the adhesive. In this case, in order to prevent impurities from diffusing from the BPSG layer 4 into the 91 layer 2, it is necessary to form a SiO film 3 on the surface of the p+ layer 2.

Next, the portion of the substrate 5 other than the p+ layer 2 (Si substrate 1) is removed by etching to make the layer thinner (FIG. 1(d)). In this method, first, the film is thinned by mechanical polishing to a film thickness of 10-2-, and then ethylenediamine 17mQ
, 3 g of pitecatechol, and 8 m Q of water were heated to 100° C. and used. This mixed solution has an etching rate of about 0.547@in for a pn- or n"Si layer, but an etching rate of 10"a
For a p+ layer having a boron concentration of s-' or more, the etching rate is less than 10 people/min, and an etch rate of 500 times or more can be obtained. Therefore, it is possible to reduce the thickness variation of the substrate having the above 2-40 variations to ±40 variations, and improve the uniformity of the film thickness. In this way 1.0-
An SOI structure with a p'' Si layer 2 of ±40 is obtained (FIG. 1(e)).

Next, this substrate was heated with humidified oxygen at 1000°C (wet 0,
) Oxidize in atmosphere for 23 hours and 55 minutes. Under these oxidation conditions, a 2.0-thick SiO2 film 11 is formed (FIG. 1(f)).As is well known, Si is oxidized to a thickness of 2.2 times. Therefore, the film thickness is 2. To form a SiO□ film of OIjm, 0.91-
In this example, as a result, a Si N2 layer with a thickness of 900 nm remains. As a result of measuring the boron concentration of this Si layer 2, it was found that 3~4X10''''Cm-
'Met. In other words, by oxidizing a 1.0-thick boron-rich layer to make it thinner and sucking out boron by utilizing the segregation effect, a layer of 3 to 4 x 10" with a thickness of 900" was formed. Si with a boron concentration of as-'
We were able to realize a S○ engineering board with layers. Here, in order to investigate how the boron concentration decreases as oxidation progresses, we measured the boron concentration distribution at each stage of oxidation.

The results are shown in FIGS. 2 to 5. Figure 2 is.

This is when the thickness t of the SiO□ film is 0.5−, and although the boron concentration in the Si film has decreased somewhat, it is still 7×1.
In addition, FIG. 3 shows a case where the SiO2 film thickness is 1.04, and the boron concentration in the Si film is about 3×10” -3. FIG. 4 shows S i
O, when the film thickness is 1.5-, and even in this case,
The boron concentration in the Si film is close to 101'an-'. However, the Si○2 film thickness t shown in FIG. 5 is 2.0. When , the boron concentration has decreased to 1017 an-'' or less.

These data show that the smaller the remaining Si film thickness, the greater the decrease in boron concentration. This is a phenomenon that occurs because the Si film thickness is limited on the SOI structure, and if it is not an SOI structure, it is difficult to significantly reduce the boron concentration due to segregation.

In the above embodiment, the thickness of the p"Si layer 2 before oxidation is 1.0
By oxidizing p Si layer 2, p
``To reduce the thickness of Si layer 2 to 0.17a+, 23
It took 55 minutes. The results are shown below when the thickness of the p'' Si layer 2 before oxidation was set to 0.48 um in order to shorten this oxidation time. The difference from the process of obtaining the Si layer 2 is shown in Fig. 1(a).
The conditions for forming the 24' boron single layer 2 are as follows: 1050°C, 24' boron nitride diffusion method
The diffusion conditions were 1.0 hours. As a result, Figure 1 (e
), thickness 0.48. A p'' Si layer 2 of p
The oxidation conditions for reducing the boron concentration in the +Si layer 2 and making the Si film thinner are as follows:
The oxidation time was 6 hours and 40 minutes, and as a result, the Si film thickness was 800 mm.

9 to 12 show how the thickness of the Si film decreases as the oxidation of p''Si/12 progresses, and how the boron concentration in the Si film decreases due to oxidation.

Figures 9 to 12 show the progress of Si oxidation.
FIG. 2 is a diagram showing the measurement results of the boron concentration in the film and the boron concentration in the SiO2 film (3 in FIG. 1(f)) below the Si film. FIG. 9 shows the state before oxidation (the state shown in FIG. 1(e)), FIG. 10 shows the state after forming a SiO2 film with a thickness of 3,000 layers, and FIG. 11 shows the state after forming a SiO2 film with a thickness of 6,500 layers. Figure 12 shows the state after forming a SiO□ film with a film thickness of 8800.
This is shown after forming the O□ film. From these figures, as oxidation progresses, the boron concentration in the SiO2 film increases to 5i-S
It can be seen that it increases at the in2 interface. This is because boron in the Si film was slightly diffused into the Si film due to segregation during the oxidation heat treatment, and this shows one feature of the present method. It can be seen that the boron concentration in the Si film shown in FIG. 12 is 4×10110l7'', which is a concentration that allows device formation.

In order to further reduce the boron concentration, the thickness of the initial p film should be reduced to 1.0 from the results shown in Figures 2 to 5 and 9 to 12.
It can be seen that it is effective to increase the length to 7 m or more and to lengthen the oxidation time.

In addition, in order to reduce the boron concentration, oxidized Si
After removing the O2 film (11 in FIG. 1(f)), forming a non-doped amorphous or polycrystalline Si film on the p+ layer, and diffusing boron by heat treatment.

It is also effective to remove the Si layer formed later by oxidation.

Next, an n-channel MO8FET was formed using the SO substrate formed as shown in FIG. 1, and its characteristics were measured. The characteristics of this MOSFET are as follows:
A value of mutual conductance gm which is 51.5 times or more higher than that of T is obtained, which shows the characteristics of the S○ groove structure.

In this way, in the SOI substrate manufacturing method of this example, the factors that determine the film thickness are: (1) formation of the p+ layer by boron; (2)
There are three methods: wet etching using an alkaline mixture of ethylenediamine, pyrocatechol, and water, and layer thinning through oxidation.All of these methods have excellent controllability of film thickness, and are easy to use in conventional LSI manufacturing processes. Easy to introduce.

It goes without saying that the present invention is not limited to the above embodiments. For example, in the above embodiment, BP
Although the Si substrates were bonded together using SG, the method and material are not limited to this, but bonding methods that replace BPSG with other insulators, or substrates that thickly deposit polycrystalline Si or insulators are possible. can be used. That is, another Si substrate is formed on the first Si substrate on which the p+ layer is formed.
It is only necessary to form a second substrate whose substrate or at least the surface layer is an insulating layer, and finally obtain an SOI structure in which an insulating film is formed under a p+ layer.

〔Effect of the invention〕

As explained above, in the method for manufacturing an SOI substrate of the present invention, an alkaline etching solution having a high etch rate between the Si substrate and the p+ layer can be used, and the uniformity of the Si film thickness can be improved. Furthermore, since Si wafer bonding technology can be used and there is no need to perform recrystallization, the crystallinity of the Si film can be improved. In addition, by oxidizing the p+ layer, the Si layer is thinned and the boron concentration in the p+ layer is reduced at the same time.
Moreover, since the p+ layer already has an SOI structure, the impurity concentration can be effectively reduced, and the impurity concentration of the Si layer can be set to a value suitable for forming an element. Furthermore, there are three factors that determine the Si film thickness: ■ Formation of a p+ impurity layer, ■ Etching using an alkaline etching solution, and ■ Thinning the layer by oxidation. It is easy to introduce into the conventional LSI manufacturing process, and there is no need to use expensive epitaxial growth, making it possible to manufacture inexpensive SOI structures through mass production.
It is effective in realizing the

[Brief explanation of the drawing]

FIGS. 1(a) to (f) are cross-sectional views showing the manufacturing process of an SO-treated substrate according to an embodiment of the present invention, and FIGS. 2 to 5 show the progress of oxidation of the p"Si film, respectively. FIGS. 6(a) and 6(b) are diagrams showing the accompanying decrease in the boron concentration in the Si film.
Process cross-sectional diagrams showing a first manufacturing method of a conventional SOR substrate,
7(a) and 7(b) are process cross-sectional views showing the second conventional SOI substrate manufacturing method, FIG. 8 is a diagram for explaining the third conventional manufacturing method, and FIG. 9 ~Figure 12 is
FIG. 3 is a diagram showing the measurement results of the boron concentration in the Si film, the Si under the Si film, and the boron concentration in the film as the oxidation of the p''Si film progresses. 1...Si substrate 2... p boron doped layer 3.7...Sin, film 4.8.10 ・BPSG film 5...first substrate 6...Si substrate 9...second substrate 11... SiO2 film 61...Si substrate 62...SiO2 film 63...Amorphous or polycrystalline Si film 64...Energy beam 65...Si film 71...n+ or p+ substrate 72...・N- or p- epitaxial layer 73・
... 5i02 film 74 ... First substrate 75 ... Si substrate 76 ... = S x Oz film 77 ... Second substrate patent applicant Nippon Telegraph and Telephone Corporation

Claims (1)

[Claims] 1. Forming a p^+ impurity doped layer on the main surface of the first substrate made of Si, and forming the Si substrate or at least the first substrate by interposing an insulating film on the p^+ impurity doped layer. a step of forming a second substrate whose side surface layer is made of an insulator; a step of selectively removing the Si portion of the first substrate other than the p^+ impurity doped layer; A method for manufacturing an SOI substrate, comprising at least the step of thinning the Si layer and reducing the impurity concentration by oxidizing a part of the p^+ impurity doped layer from the opposite side.