JPH04282867A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To make it possible to manufacture an N-type SOI(Silicon On Insulator) substrate by a method wherein a low-cost P-type silicon wafer is laminated on other low-cost P-type silicon wafer, the other P-type silicon wafer is polished thin, the surfaces of the silicon wafers are respectively covered with silicon oxide films and the wafers are heat-treated. CONSTITUTION:Two sheets of P-type silicon wafers 1 and 2 are prepared, the surface of the wafer 1, for example, is thermally oxidized and a silicon oxide film 3 of a thickness of about 0.5mum is formed. The wafer 1 form with the film 3 is superposed on the wafer 2 and the wafers 1 and 2 are heat-treated at 1100 deg.C, for example, in an oxidizing atmosphere. Thereby, the wafer 1 is jointed on the wafer 2. Then, the wafer 2 is made thin to a thickness of 10mum or thereabouts or thinner by polishing. Then, silicon oxide films 4 and 5 of a thickness of 1000Angstrom are respectively formed on the respective open surfaces of the wafers 1 and 2. Then, when the wafers 1 and 2 are heat-treated at 1100 deg.C in a dry nitrogen atmosphere, for example, the wafer 1 is converted into an N-type.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to SOI (Silicon
The present invention relates to a method for manufacturing a semiconductor device having an n-type semiconductor layer (on insulator) structure, and particularly to a method for providing an SOI substrate having an n-type semiconductor layer at low cost.

0002

2. Description of the Related Art Semiconductor devices having an SOI structure are expected to be used to prevent soft errors caused by radiation or latch-up of CMOS transistors. Currently, SOI is achieved by bonding two silicon wafers together.
The method of manufacturing a substrate is the closest to practical application.

[0003] Conventionally, when producing an n-type SOI substrate, there is a method of bonding an n-type silicon wafer to a p-type silicon wafer that serves as a support substrate, and polishing this n-type silicon wafer to a size of several tens of micrometers or less. It is taken.

0004

[Problems to be Solved by the Invention] As mentioned above, in the conventional SOI substrate using the bonding method, it is necessary to use n-type for at least one of the silicon wafers.
As a result, there is a problem in that semiconductor devices such as integrated circuits manufactured using such an SOI substrate also become expensive. This is because when pulling the crystal that is the source of a silicon wafer, the n-type crystal is better than the p-type crystal.
This is because it requires up to three times as much time, resulting in higher costs.

The present invention aims to solve the above problems by making it possible to fabricate an n-type SOI substrate by bonding together inexpensive p-type silicon wafers.

[0006]

[Means for Solving the Problems] The above object is to form a silicon oxide film on one surface of a p-type first silicon wafer, and to connect the first silicon wafer to a second silicon wafer through the silicon oxide film. The first silicon wafer bonded to the second silicon wafer is thinned to a predetermined thickness by heat-treating the two silicon wafers while stacked on the wafer, and at least the first silicon wafer bonded to the second silicon wafer is thinned to a predetermined thickness. A second silicon oxide film is formed on the open surface of the silicon wafer, and the first silicon wafer on which the second silicon oxide film is formed and the second silicon wafer are heat-treated at a predetermined temperature to form the first silicon oxide film. This is achieved by the method for manufacturing a semiconductor device according to the present invention, which includes steps of converting a silicon wafer to n-type.

[0007]

[Operation] A p-type silicon wafer bonded to a silicon wafer as a support substrate via a silicon oxide film,
It was discovered that by polishing a thin layer and heat-treating the surface while covering it with silicon oxide, it converts to n-type. By utilizing this, it becomes possible to manufacture low-cost SOI substrates without using n-type silicon wafers.

[0008]

[Embodiment] Fig. 1 is a process explanatory diagram of an embodiment of the present invention, and shows a silicon wafer or an SO made by bonding these.
I shows a cross section of the substrate.

Referring to FIG. 3(a), two p-type silicon wafers 1 and 2 are prepared, and the surface of the silicon wafer 1 is thermally oxidized to form a silicon oxide film 3 with a thickness of about 0.5 μm. form. A silicon wafer 1 and a silicon wafer 2 on which a silicon oxide film 3 has been formed are stacked and heat treated at, for example, 1100° C. in an oxidizing atmosphere. As a result, silicon wafers 1 and 2 are bonded. Such bonding may be performed using well-known methods and conditions. In the above, the formation of the silicon oxide film 3 on the silicon wafer 1 is as follows:
The well-known CVD (chemical vapor deposition) method may be used. Further, there is no practical limit to the thickness of the silicon oxide film 3, and the thickness may range from several tens of angstroms or more to several micrometers or less that does not cause distortion to the silicon wafer 1 bonded to the silicon wafer 2. It's optional.

[0010] Next, as shown in FIG.
The silicon wafer 2 is thinned to a thickness of about 10 μm or less. This thickness may be set to an appropriate value depending on the type of semiconductor element to be formed on the SOI substrate and the desired effect to be achieved by the SOI structure.

[0011] Next, as shown in FIG. 2(c), an oxidation film with a thickness of about 1000 Å is applied to the open surfaces of each of the thinned silicon wafers 1 and 2, for example, by a well-known thermal oxidation method in a wet atmosphere. Silicon films 4 and 5 are formed. This thermal oxidation temperature is, for example, 900°C. Note that the silicon oxide films 4 and 5 are formed by the well-known CVD process.
Alternatively, the silicon oxide film 4 may be simply formed on the silicon wafer 1.

Next, silicon wafers 1 and 2 were
For example, in a dry nitrogen atmosphere, at 1100℃, about 100
Heat treat for minutes. As a result, silicon wafer 1 becomes
Converts to n-type. In this way, an SOI substrate having an n-type thin silicon layer is manufactured. The silicon oxide film 4 can be used as an insulating layer for forming semiconductor elements on the silicon wafer 2. For example, as shown in FIG. 4(e), an opening is formed by selectively etching the silicon oxide film 4, and a separation groove 6 is formed in the silicon layer exposed within this opening. Elements such as transistors are formed in the thus formed island-shaped silicon region 11 according to a normal process to fabricate a semiconductor device having an SOI structure.

FIGS. 2 and 3 are graphs showing the distribution of resistance and carrier concentration in the thickness direction of the silicon wafer 1, and FIG. 2 shows the distribution of silicon oxide on the open surface, as shown in FIG. As shown in FIG. 1(d), the distribution in the state where the film 4 is formed, FIG.
This is the distribution after heat treatment to convert the type to n-type. In addition, in Figures 2 and 3,
The horizontal axis is the distance (x; μm) in the silicon wafer 1 with respect to the interface with the silicon oxide film 3, and the vertical axis is the resistance (
R; ohm) and carrier concentration (number/cm3). The resistance (R) is the value between two probes that are in contact with a cross section parallel to the thickness direction with an interval of 90 μm.

As shown in FIG. 2, after the silicon oxide film 4 is formed on the surface but before heat treatment is performed, the silicon wafer 1 maintains p-type.
The carrier concentration (C) increases with distance (x) in the silicon wafer 1, and rapidly decreases at the interface with the silicon oxide film 4. Reflecting this, the resistance (R) decreases with distance (x) and increases rapidly at the interface with the silicon oxide film 4. In other words, the carrier concentration (C) and resistance (R) in the silicon wafer 1 show the initial values of the silicon wafer 1 near the interface with the silicon oxide film 4, and as they approach the silicon oxide film 3, the carrier concentration increases. (C) decreases and resistance (R) increases. Note that the parameter in FIG. 2 is the thickness of the silicon oxide film 4, and this thickness is 500 Å and 4000 Å.
, 8000 Å, the above carrier concentration (C
) and the distribution of resistance (R) are almost the same. The separation between the curves near the interface with the silicon oxide film 4 is due to the difference in the thickness of the silicon oxide film 4.

On the other hand, in a nitrogen atmosphere, 1100
After the heat treatment at ℃, as shown in Figure 3, the silicon wafer 1 has been converted to n-type, and the carrier concentration (C) is as high as that near the interface with the silicon oxide film 3 and in the silicon oxide film 4. The number of particles decreases rapidly near the interface with , but in the area between these, the value of 1013 to 1014 pieces/cm3 is maintained. This carrier concentration distribution decreases near the center of the silicon wafer 1 in the thickness direction, and
It shows maximum values on both sides. The resistance (R) shows a distribution that reflects this carrier concentration distribution. The tendency regarding the above distribution does not depend on the thickness of the silicon oxide film 4, as in the case of FIG.

The above-mentioned conversion to n-type does not occur even if the open surface of a p-type silicon wafer, which is still bonded through a silicon oxide film, is thermally oxidized. Furthermore, as shown in FIG. 2, even if the silicon wafer 1 is thinned and heat treated, conversion to n-type will not occur, and even if only a silicon oxide film 4 is formed on the thinned silicon wafer 1, n-type conversion will not occur. No conversion occurs. That is, the conversion from p-type to n-type occurs by thinning the silicon wafer 1, forming a silicon oxide film 4 on its surface, and performing heat treatment. Although it is not essential that this heat treatment be performed in a non-oxidizing atmosphere, in order to suppress the occurrence of OSF (oxygen stacking faults) and changes in crystal layer thickness due to oxidation as much as possible, it is recommended to use a non-oxidizing atmosphere such as nitrogen. It is preferable to do it inside. Further, in order to cause the conversion to the n-type, heat treatment at at least 1100° C. or higher is required.

What should be noted is that the thickness of the silicon oxide film 4 has no effect on such conversion to n-type. Including this phenomenon, the reasons why the conversion to n-type as described above and the carrier concentration distribution as shown in FIG. 3 occur are currently unknown.

In the above embodiment, a p-type silicon wafer 1 was used as the support substrate, but in the present invention, there are no limitations on the conductivity type or resistance of the silicon wafer 1.

[0019]

[Effects of the Invention] According to the present invention, since an n-type SOI substrate can be fabricated by bonding p-type silicon wafers together, it is possible to provide an inexpensive SOI substrate. It has a promoting effect.

[Brief explanation of the drawing]

[Figure 1] Process explanatory diagram of one embodiment of the present invention

[Figure 2]
Distribution diagram of carrier concentration and resistance in the SOI substrate of the present invention at an intermediate stage of fabrication

[Figure 3] Distribution diagram of carrier concentration and resistance in the SOI substrate of the present invention in the completed stage

[Explanation of symbols]

1, 2 Silicon wafer 3, 4, 5 Silicon oxide film 6 Separation groove

Claims (1)

[Claims] 1. A step of forming a silicon oxide film on one surface of a first p-type silicon wafer, and a state in which the first silicon wafer is superimposed on a second silicon wafer with the silicon oxide film interposed therebetween. a step of bonding the two silicon wafers by heat treatment, a step of thinning the first silicon wafer bonded to the second silicon wafer to a predetermined thickness, and a step of thinning at least the thinned first silicon wafer. forming a second silicon oxide film on the open surface of the silicon oxide film; and heat-treating the first silicon wafer on which the second silicon oxide film is formed and the second silicon wafer at a predetermined temperature to form the first silicon oxide film. 1. A method for manufacturing a semiconductor device, comprising the step of converting a silicon wafer to n-type.