JP6859964B2 - Manufacturing method of high frequency SOI wafer - Google Patents

Description

The present invention relates to a method for manufacturing an SOI wafer for a high frequency device, which has a semiconductor layer formed on an insulating layer.

A substrate having a semiconductor layer such as a silicon layer on an insulating layer is known as an SOI (Silicon on Insulator) wafer. Several methods are known as a method for manufacturing an SOI wafer.

With the development of mobile terminals, Internet communication, etc., the demand for information volume and communication speed for wireless information exchange is increasing endlessly. In recent years, as a high-frequency device such as an RF switch, a single element previously manufactured of SOS (Silicon On Sapphire) or a GaAs substrate has been replaced with a device integrated on a Si substrate. As a result, miniaturization and integration technology has been actively adopted. In particular, a method of manufacturing a high-frequency device using an SOI wafer has greatly expanded the market.

As the performance of high-frequency devices, suppression of second-order harmonics and third-order harmonics is a major requirement in order to prevent communication crosstalk. For this purpose, the substrate needs to be an insulator. In SOI wafers, increasing the thickness of the embedded oxide film (BOX (Buried Oxide) layer), which is an insulating layer, is considered to be one method, but the oxide film has poor thermal conductivity and operates high-frequency devices. The problem is that the heat generated at the time cannot be removed. Therefore, a method of using a high resistance Si substrate as a support substrate for the SOI wafer has been considered. As a result, the conduction of electricity below the BOX layer can be suppressed, and the harmonics of the high-frequency device can be suppressed. However, when an electric potential is applied to the SOI layer, a depletion layer is generated at the interface between the BOX layer and the Si substrate to form an inversion layer, and electrical conduction is generated in this portion, so that harmonics cannot be suppressed. In order to solve this problem, a method is adopted in which a layer for trapping carriers is embedded directly under the BOX layer (Patent Documents 1 to 3).

The polysilicon layer (polycrystalline silicon layer) is the most common layer for trapping carriers. The polysilicon layer traps carriers at grain boundaries and suppresses electrical conduction. As a method of incorporating a polysilicon layer, a polysilicon layer is laminated on a support substrate wafer (base wafer), and this is bonded to a wafer with an oxide film (bonded wafer) to form an SOI having a polysilicon layer. There is a method of manufacturing a wafer. However, at this time, in order to realize the wafer bonding, the surface of the polycrystalline silicon layer needs to be smooth, and a method of removing the surface roughness by polishing and performing the bonding is considered. Patent Document 4).

In this case, the wafer is bonded to the poly layer (polysilicon layer) in this way, but since the poly layer with a large surface area is exposed on the surface in the manufacturing process, it is affected by environmental pollution (especially environmental boron) and is originally It may not be able to function as a trap layer. Further, even if a poly layer having a fine particle size is formed (the finer the poly, the larger the surface area and the higher the trap efficiency of the carrier), the heat treatment (bonding heat treatment) in the bonding process is performed. , Poly may grow and trap efficiency may decrease.

Special Table 2007-507093 Japanese Patent Application Laid-Open No. 2013-513234 Japanese Patent Application Laid-Open No. 2014-509087 Japanese Unexamined Patent Publication No. 2016-136591

The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for manufacturing an SOI wafer having high carrier trap efficiency as an SOI wafer for high frequencies.

In order to achieve the above object, the present invention is a method for manufacturing a high frequency SOI wafer including a structure in which a base wafer, a polysilicon layer, a BOX layer, and an SOI layer are laminated in this order, wherein the base wafer and the BOX layer are used. , And a method for manufacturing a high-frequency SOI wafer in which a silicon SOI wafer including a structure in which the SOI layers are laminated in this order is irradiated with a laser, and a part of the base wafer is made of polysilicon to form a polysilicon layer. To do.

This method prevents environmental pollution caused by the manufacturing process of SOI wafers and deterioration of the trap function due to alteration (single crystallization) of the poly layer (polysilicon layer) due to bond heat treatment (for example, 1050 ° C. for 2 hours). It is possible.

At this time, it is preferable to control the formation depth of the polysilicon layer by adjusting the depth of focus of the laser.

By using such a method, it is very easy to set the manufacturing conditions, and it becomes a manufacturing method of the high-frequency SOI wafer with high accuracy.

Further, after the laser irradiation, the silicon SOI wafer on which the polysilicon layer is formed can be subjected to RTA treatment within a temperature range of 1000 ° C. to 1300 ° C. to anneal out defects in the SOI layer. preferable.

By using such a method, defects introduced into the SOI layer by laser irradiation can be eliminated.

As described above, according to the present invention, it is possible to provide a method for manufacturing an SOI wafer having high carrier trap efficiency as a high frequency SOI wafer, and it is possible to realize good high frequency characteristics.

It is a figure which showed an example of the flow of the manufacturing method of the high frequency SOI wafer of this invention together with the schematic diagram of a wafer.

As described above, there has been a demand for the development of a method for manufacturing an SOI wafer having high carrier trap efficiency as an SOI wafer for high frequencies.

As a result of diligent studies on the above problems, the present inventors irradiate an SOI wafer (silicon SOI wafer) whose base wafer is a silicon single crystal with a laser to form a polysilicon layer under the BOX layer. , They have found that a high frequency SOI wafer having high carrier trap efficiency can be manufactured, and have completed the present invention.

That is, the present invention is a method for manufacturing a high-frequency SOI wafer including a structure in which a base wafer, a polysilicon layer, a BOX layer, and an SOI layer are laminated in this order, and the base wafer, the BOX layer, and the SOI layer are the base wafer, the BOX layer, and the SOI layer. This is a method for manufacturing a high-frequency SOI wafer in which a silicon SOI wafer including a structure in which the wafers are laminated in order is irradiated with a laser, and a part of a region of the base wafer is made of polysilicon to form a polysilicon layer.

Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.

FIG. 1 shows an outline example of the method for manufacturing a high frequency SOI wafer of the present invention. First, a silicon SOI wafer 1 including a structure in which a base wafer 3 made of a silicon single crystal, a BOX layer 5, and an SOI layer 6 are laminated in this order is prepared (FIG. 1 (A)). An oxide film 7 may be formed in advance on the surface of the silicon SOI wafer 1 to protect the surface to form the silicon SOI wafer 1'(FIG. 1 (B)). Next, the depth of focus of the laser is adjusted to a part of the region in the base wafer 3 (the region near the interface with the BOX layer 5), and the laser is irradiated from the surface side of the SOI layer, for example, so that the polysilicon layer 4 Is formed to prepare a high-frequency SOI wafer 2'(FIG. 1 (C)). After that, the oxide film 7 can be removed, and if necessary, defects in the SOI layer 6 (surface layer) can be removed by RTA treatment described later, and the high-frequency SOI wafer 2 can be manufactured (FIG. 1 (D)). ).

That is, by irradiating the silicon SOI wafer 1 with a laser, the silicon single crystal in a part of the base wafer 3 (the region irradiated with the laser) is made polysilicon, and the polysilicon layer 4 made of a silicon polycrystal is formed. To form. By laser irradiation, a part of the base wafer 3 which is a single crystal becomes a polysilicon layer 4. In the high-frequency SOI wafers 2 and 2', the polysilicon layer 4 is formed between the base wafer 3'and the BOX layer 5 (immediately below the BOX layer 5).

The silicon SOI wafer prepared here is not particularly limited, and any one can be used. For example, the bond wafer and the base wafer are bonded to each other via an oxide film formed on the surface of the bond wafer. A wafer manufactured by applying a heat treatment (bonding heat treatment) for increasing the bond strength can be used.

Further, as described above, the silicon SOI wafer to be prepared is formed with a thin oxide film on the surface of the silicon SOI wafer in the same manner as screen oxidation when ion-implanting dopant ions in the device manufacturing process. It is possible to reduce contamination of silicon SOI wafers.

The laser irradiation may be performed at room temperature of the silicon SOI wafer, or may be performed, for example, in a state of being heated to about 400 ° C. At this time, if the temperature is not raised too high, the polyparticle size (particle size of the polycrystal in the polysilicon layer) will not be too large and a sufficient carrier trapping effect will not be obtained. Therefore, the temperature at the time of laser irradiation is preferably 800 ° C. or lower.

In laser irradiation, in a high-power laser such as a YAG laser, thermal energy may be transmitted not only to a predetermined depth position but also to other semiconductor wafer portions. Therefore, it is more preferable to use a low power laser, for example, an ultrashort pulse laser such as a femtosecond laser.

When an oxide film is formed on the surface, the oxide film on the surface of the SOI layer is removed after laser irradiation, and then, if defects remain in the SOI layer, a high-temperature RTA treatment is added as described later. This also allows the defect to be annealed out.

According to this method, since the polysilicon layer can be formed later on the SOI wafer having the SOI structure already, it is necessary for environmental pollution caused by the manufacturing process of the SOI wafer and after bonding as in the bonding method. It is possible to prevent deterioration of the trap function due to alteration (single crystallization) of the polysilicon layer due to bond heat treatment.

At this time, it is preferable to control the formation depth of the polysilicon layer by adjusting the depth of focus of the laser.

By using such a method, it is very easy to set the manufacturing conditions and the polysilicon layer can be formed with high accuracy, which is a method for manufacturing a high-quality SOI wafer for high frequencies.

Further, after the laser irradiation, the silicon SOI wafer on which the polysilicon layer is formed can be subjected to RTA treatment within a temperature range of 1000 ° C. to 1300 ° C. to anneal out defects in the SOI layer. preferable.

By performing RTA treatment after laser irradiation, defects introduced by laser irradiation can be eliminated. Since the RTA treatment is annealing for a short time of about 1 to 120 seconds, single crystallization of the polysilicon layer hardly occurs even if the heat treatment is performed at a relatively high temperature. If the temperature is 1000 ° C. or higher, a sufficient defect annealing effect can be obtained, and if the temperature is lower than 1300 ° C., problems such as slip dislocation and silicon melting do not occur. Therefore, the optimum temperature is around 1200 ° C., as in the case of an annealed wafer in which surface defects are eliminated by annealing.

As described above, in the prior art, as a method for manufacturing a high-frequency SOI wafer, a wafer in which a polysilicon layer is laminated (base wafer) and a wafer in which an oxide film is laminated (bond wafer) are oxidized with a polysilicon layer. A general method is to apply bond heat treatment (for example, 1050 ° C. for 2 hours) after the films are opposed to each other and bonded together. However, in this method, since the porouscon layer is exposed in the manufacturing process of the SOI wafer, it is affected by environmental pollution, particularly dopant element pollution. Further, since the polysilicon layer is exposed to a high temperature and a long-time heating state during the bond heat treatment, the silicon polycrystal contained in the polysilicon layer becomes single crystal, and the trap efficiency is lowered.

On the other hand, in the present invention, as described above, after the silicon SOI wafer is manufactured, a polysilicon layer is formed inside the wafer using a laser to manufacture a high frequency SOI wafer. That is, unlike the prior art, the polysilicon layer is not exposed, so there is no environmental pollution. Further, although bond heat treatment may be performed when the silicon SOI wafer to be used is manufactured, the polysilicon layer is exposed to a high temperature and long time heat treatment such as bond heat treatment during the formation of the polysilicon layer and the subsequent steps. Therefore, it is possible to manufacture a high-frequency SOI wafer having high trap efficiency without causing single crystallization of the polysilicon layer.

The high-frequency SOI wafer thus produced does not cause environmental pollution or deterioration of the polysilicon layer due to heat treatment (bonding heat treatment) in the bonding process, and is a semiconductor device manufactured using such high-frequency SOI wafer. It is also possible to realize high frequency characteristics.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

[Example]
In each case, a bond wafer made of a silicon single crystal and a base wafer are bonded to each other via an oxide film formed on the surface of the bond wafer, and after performing a bond heat treatment (1050 ° C., 2 hours) in order to increase the bond strength. , A silicon SOI wafer (diameter 200 mm) having the following structure was prepared by thinning the bond wafer by grinding and polishing.
Silicon SOI wafer SOI layer: 1000 nm, boron dope 10 Ωcm, <100>
BOX layer: 500 nm
Base wafer: Boron dope 1000Ωcm, <100>

An oxide film of 20 nm was formed on the surface of this silicon SOI wafer by a treatment at 900 ° C. for 10 minutes in a Pyro atmosphere. A titanium sapphire laser was used on the silicon SOI wafer on which this oxide film was formed, and laser irradiation treatment was performed with a beam wavelength of 1080 nm, a beam diameter of about 2 μm, a pulse width of 1 nsec, and a pulse energy of 100 mJ, and directly under the BOX layer. A polysilicon layer having a wavelength of about 200 nm was formed on the wafer.

Then, in order to remove the oxide film with dilute hydrofluoric acid and further improve the crystallinity of the SOI layer, a 100% hydrogen atmosphere and RTA treatment at 1150 ° C. for 30 seconds were performed to complete a high frequency SOI wafer. After removing the active layer (SOI layer) of this high-frequency SOI wafer and forming an aluminum electrode on the surface of the BOX layer, the RF characteristics were evaluated and the second harmonic characteristics were measured. As a result, it was confirmed that the second harmonic characteristics were improved by 10% as compared with the comparative example described later.

[Comparison example]
Before the laser irradiation of Example 1, except that a polysilicon layer was deposited on the surface of the base wafer in advance by the CVD method at 2000 nm, the surface was polished to form a polysilicon layer at 1000 nm, and then bonded to the bonded wafer. The following high-frequency SOI wafers, which were not irradiated with laser under the same conditions as those for producing silicon SOI wafers, were produced.
High frequency SOI wafer SOI layer: 1000 nm, boron dope 10 Ωcm, <100>
BOX layer: 500 nm
Polysilicon layer: 1000 nm
Base wafer: Boron dope 1000Ωcm, <100>

After removing the active layer (SOI layer) of this high-frequency SOI wafer and forming an aluminum electrode on the surface of the BOX layer, the RF characteristics were evaluated and compared with the wafer of the example. It was confirmed that the wave characteristics were 10% inferior to those of the examples.

As described above, it has been clarified that the method for manufacturing a high-frequency SOI wafer of the present invention is a method for manufacturing an SOI wafer having high carrier trap efficiency as a high-frequency SOI wafer.

The present invention is not limited to the above embodiment. The above-described embodiment is an example, and any object having substantially the same configuration as the technical idea described in the claims of the present invention and exhibiting the same effect and effect is the present invention. Is included in the technical scope of.

1, 1'... Silicon SOI wafer, 2, 2'... High frequency SOI wafer,
3, 3'... base wafer, 4 ... polysilicon layer, 5 ... BOX layer,
6 ... SOI layer, 7 ... Oxide film.

Claims (4)

A method for manufacturing a high-frequency SOI wafer including a structure in which a base wafer, a polysilicon layer, a BOX layer, and an SOI layer are laminated in this order.
A silicon SOI wafer including a structure in which a base wafer, a BOX layer, and an SOI layer are laminated in this order is irradiated with laser from the surface side of the SOI layer , and a part of the area of the base wafer is made polysilicon to form a polysilicon layer. A method for manufacturing a high frequency SOI wafer, which comprises forming. The method for manufacturing a high-frequency SOI wafer according to claim 1, wherein the formation depth of the polysilicon layer is controlled by adjusting the depth of focus of the laser. After the laser irradiation, the silicon SOI wafer on which the polysilicon layer is formed is subjected to RTA treatment in a temperature range of 1000 ° C. to 1300 ° C. to anneal out defects in the SOI layer. The method for manufacturing a high-frequency SOI wafer according to claim 1 or 2. The method for manufacturing a high-frequency SOI wafer according to any one of claims 1 to 3, wherein an oxide film is formed in advance on the surface of the silicon SOI wafer before laser irradiation.

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