JPH0682753B2 - Method for manufacturing semiconductor device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and more particularly to an element isolation method using a dielectric.

[0002]

2. Description of the Related Art The so-called dielectric isolation method, in which elements are separated from each other in an IC or LSI by an insulator, can (1) make the leakage current extremely small, as compared with pn junction isolation. (2) The breakdown voltage can be increased, (3)
It has the advantage that it is not necessary to pay attention to the direction of voltage application.

Ideal dielectric isolation is achieved by completely wrapping each element with an insulator except for the electrode connections.
Such an element can be formed using, for example, an SOS substrate in which silicon is epitaxially grown on sapphire. However, sapphire is expensive,
In addition, there are limitations on the types of elements that can be manufactured because the crystal matching with silicon is not perfect, a high-quality single crystal film cannot be obtained, and the film thickness cannot be made sufficiently thick.

Many dielectric isolation methods that do not use an insulating substrate such as sapphire have been proposed so far. One example thereof will be described with reference to FIG. First, as shown in FIG.
An element in which a desired diffusion layer 43 (43 ₁ , 43 ₂ ) is formed on a silicon single crystal layer 42 (42 ₁ , 42 ₂ ) formed on a silicon single crystal substrate 41 by an epitaxial method is manufactured, and further, by mesa etching. The elements are separated from each other and the entire surface is covered with an insulating film 44 such as SiO ₂ . After this, FIG. 4 (b)
As shown in FIG. 4, a polycrystalline silicon support layer 45 is deposited on these elements, and then the silicon substrate 41 is ground by polishing or etching as shown in FIG. 4C until each element is completely separated. It is dropped and the surface is covered with the insulating film 46. Thereafter, as shown in FIG. 4D, a polycrystalline silicon support layer 47 is deposited again on the insulating film 46 side. And Figure 4
As shown in (e), the support layer 45 is removed by etching to obtain a dielectrically separated element.

The biggest problem with such a conventional method is that the formation of a support layer is essential. Not only extra steps such as deposition and removal of the support layer are required, but also in the case of commonly used polycrystalline silicon, since the deposition rate is slow, a sufficient thickness to withstand the steps such as polishing is obtained. It takes a very long time. For the purpose of omitting the step of depositing the support layer, for example, element isolation is completed in the step of FIG.
It has also been proposed to take out the wiring from the back surface of the device.
However, in this method, the wiring structure becomes complicated and various constraints are newly added. A method of attaching a silicon substrate or the like as a support through an adhesive layer such as oxide or glass has been proposed (Japanese Patent Laid-Open Nos. 53-30283, 48-10081, and 51). -21793, JP-A-53-128285, JP-A-53-
30284, etc.), this method requires a temperature higher than 1300 ° C. or a high pressure of 10 kg / cm ² or more. Under such a condition, the substrate may be deformed due to creep or the like, and the impurity distribution of the diffusion layer formed in the element region may be changed. Also, Japanese Patent Publication No. 39-17869 and Japanese Patent Publication No. 50-13155.
Although there is a method of bonding while growing an oxide film between the bonding surfaces as described in Japanese Patent Publication, considering uniform bonding of the entire substrate, it is difficult to obtain uniform and good bonding over a large area. is there. Further, there is also a method of applying pressure by an external force to perform thermocompression bonding (JP-A-51-150282, JP-B-49-45195, JP-B-48-40).
No. 372), and pressure application is not preferable as described above.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object thereof is to provide a method of manufacturing a semiconductor device capable of highly reliable dielectric isolation in a simple process. To do.

[0007]

According to the present invention, when the surfaces of two semiconductor single crystal substrates are mirror-polished to be sufficiently smooth, the polished surfaces are directly adhered to each other in a sufficiently clean atmosphere. This technique is applied to dielectric isolation based on the finding that a strong substrate bonded body can be obtained. That is, the essence of the present invention is that two semiconductor single crystal substrates, at least one surface to be bonded of which is covered with an insulating film such as an oxide film, are brought into close contact in a clean atmosphere to melt the insulating film at 200 ° C. or higher. In a temperature range not to do not heat substantially without growing an oxide film or the like on the bonding surface and bonding, forming an active element on at least one of the bonded semiconductor single crystal substrates,
The element isolation is performed by removing the semiconductor single crystal in the isolation region of the formed element to a depth reaching the insulating film at the junction, and forming an insulating film such as an oxide film on the semiconductor single crystal exposed by this removal.

According to the present invention, it is possible to obtain a semiconductor device in which element isolation is performed very easily without using a step of depositing or removing a support layer such as polycrystalline silicon. Moreover, high temperature and high pressure for joining the substrates are not required, and the reliability of the element is not impaired.

Since the thickness of the substrates to be bonded is not limited, the substrate thickness can be selected according to the breakdown voltage of the device, the power, etc., and the device can be designed with a high degree of freedom.

Further, the present invention is based on the fact that the two mirror-polished substrates are adhered by themselves by simply adhering the surfaces to each other in a clean atmosphere, and an oxide film grows slightly on the outer edge. However, the oxide film does not substantially grow on the entire bonding surface.

According to the bonding mechanism of the present invention, OH groups are present on the surface of the substrate which has been subjected to a mirror-polished cleaning treatment, and when these substrates are brought into contact with each other, the OH groups are bonded to each other so that the substrate is self-supporting. It is considered that a dehydration condensation reaction is caused by the heat treatment, the H ₂ O is removed from the hydrogen-bonded OH groups to form a Si—O—Si bond, and the adhesion becomes stronger.

This is basically different from the technique of growing an oxide film and performing adhesion, and as a result, good and uniform adhesion can be realized over the entire substrate. Therefore, even if the elements are separated, since the bonding state varies from island to island, there is no characteristic variation and a highly reliable semiconductor device can be obtained.

[0013]

EXAMPLES Examples of the present invention will be described below.

As shown in FIG. 1A, a first silicon single crystal substrate 11 and a second silicon single crystal substrate 12 are prepared. In this example, on the surface of the second silicon substrate 12,
For example, an insulating film 13 such as an oxide film formed by thermal oxidation is formed. The opposite surfaces of these substrates are mirror-polished. As shown in FIG. 1B, these substrates 11 and 12 are brought into close contact with each other and heat-treated at a temperature of 200 ° C. or more to join them.
Although a considerable bonding strength can be obtained only by bringing them into close contact at room temperature, heat treatment at 200 ° C. or higher significantly improves the bonding strength. However, the upper limit of the heat treatment temperature is required to be 1300 ° C. so that creep or the like does not occur.

Of the substrate bonded bodies thus formed,
In this embodiment, elements are formed on the substrate 12. For that purpose, as shown in FIG. 1C, the substrate 12 is ground and polished to a required thickness. Depending on the device, this step is unnecessary. Thereafter, as shown in FIG. 1D, necessary diffusion layers 14 (14 ₁ and 14 ₂ ) are formed, and the element isolation regions are mesa-etched to a depth reaching the insulating film 13, so that each element region is island-shaped. To separate. Then, an insulating film 15 such as SiO ₂ or Si ₃ N _{4 is} formed on the entire surface of the substrate on which the elements are formed.
To obtain a state in which each element is completely covered with a dielectric and separated. Thereafter, although not shown, necessary wiring is provided to complete a desired semiconductor device.

As described above, according to this embodiment, a highly reliable semiconductor device having a dielectric isolation structure can be easily manufactured.

The greatest feature of the present invention is that the semiconductor single crystal substrates are directly bonded. Although the mechanism of this bonding is not yet clear, it is considered that the thin hydrophilic natural oxide film formed on the substrate surface is involved in the bonding because the bonding strength is extremely increased by the heat treatment at about 200 ° C. .
For example, it is well known that such a layer is formed on the surface of quartz glass or the like, and it is also known that a silicon substrate is quickly covered with a natural oxide film in the air.

In order to know the substrate bonding state in the present invention,
An experiment was conducted by forming an evaluation element as shown in FIG.
In FIG. 2, reference numerals 21 and 22 each have a thickness of 2 mm and a diameter of 1
It is a silicon single crystal substrate of 0 mm, the substrate 21 has a through hole formed in the center, and the substrate 22 has a remaining thickness of 2 in the center.
The recess is formed to have a thickness of about 00 μm. With the 1 μm oxide film 23 formed on one of the substrates, the substrates were directly bonded to each other in the same manner as in the example to obtain an evaluation element. Then, the element was broken by applying a hydraulic pressure P in the direction shown by the arrow in the figure, and the relationship between the heat treatment temperature and the breaking strength at the time of joining the elements was examined. FIG. 4 shows the result. At 200 ° C or lower, the breaking pressure was less than 5 kg / cm ² , and the joint part peeled off, whereas at 200 ° C or higher, the strength rapidly increased, and the breaking was the breaking of the crystal itself.

The present invention is not limited to the above embodiment, but various modifications can be made. For example, some or all of the diffusion layers of the active device may be formed before substrate bonding. In particular, if the heat treatment temperature at the time of joining the substrates is suppressed to about 1000 ° C. or less, it is possible to reduce the characteristic variation after the diffusion layer is formed in advance. In addition, in order to facilitate the wiring process, after the FIG.
It is also possible to use anisotropic etching to optimize the shape of the mesa groove. Furthermore, an insulating film may be formed on both surfaces of the two substrates to be joined, or an element may be formed on both of the joined substrates. For example, two single crystal silicon substrates are prepared, and an insulating film such as a thermal oxide film is formed on the surfaces to be bonded of these substrates and then adhered to each other.
Heat treatment is carried out at a temperature of 00 ° C. or higher to bond them. Even in this case, a sufficiently high bonding strength can be obtained.

[0020]

According to the present invention, it is possible to obtain a semiconductor device in which element isolation is extremely easily performed without using a step of depositing or removing a support layer such as polycrystalline silicon. Moreover, high temperature and high pressure for joining the substrates are not required, and the reliability of the element is not impaired.

[Brief description of drawings]

FIG. 1 is a process chart of the present invention

FIG. 2 is a schematic diagram of an evaluation element for evaluating the present invention.

FIG. 3 is a characteristic diagram showing results obtained by using the element of FIG.

FIG. 4 Conventional process diagram

[Explanation of symbols]

11 ... 1st silicon single crystal substrate 12 ... 2nd silicon single crystal substrate 13 ... Insulating film 14 ₁ , ₂ ... Diffusion layer 15 ... Insulating film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshiaki Owada 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Toshiba Research Institute Co., Ltd. (56) Reference JP-A-53-30283 (JP, A) Kai 53-128285 (JP, A) JP 39-17869 (JP, B1) JP 49-26455 (JP, B1)

Claims (1)

[Claims] 1. A semiconductor single crystal substrate, the surface of which is mirror-polished and at least one surface to be bonded is covered with an insulating film, is brought into close contact in a clean atmosphere, and a pressure is applied substantially by an external force. Without heat treatment at a temperature in the range of 200 ° C. or higher where the insulating film does not melt, a step of forming an active element on at least one of the joined semiconductor single crystal substrates, and a step of separating the formed element. A semiconductor device comprising: a step of removing a semiconductor single crystal in a region to a depth reaching the insulating film interposed in a junction; and a step of forming an insulating film on the surface of the semiconductor single crystal exposed in this step. Manufacturing method.