JPH0786540A - Laminated soi and its manufacture - Google Patents

Abstract

PURPOSE:To provide a laminated SOI wafer in which an oxide film has a sufficiently high withstand voltage when devices are incorporated in it and which facilitates the improvement of the yield of the devices and its manufacturing method. CONSTITUTION:An epitaxial layer 7 whose laser scattering element density is not larger than 5X10<5>/cm<3> is made to grow on a first wafer 6 and an insulating layer 8 is formed at least on one of the first wafer 6 and a second wafer 9. Then the first wafer 6 and the second wafer 9 are bonded to each other with the epitaxial layer 7 and the insulating layer 8 therebetween. After that, whole of the first wafer 6 and a part of the epitaxial layer 7 are removed to form a semiconductor wafer 5.

Description

Detailed Description of the Invention

[0001]

This invention relates to a bonded SOI (Silico
n On Insulator) and its manufacturing method, especially bonding S
The present invention relates to improvement of breakdown voltage of oxide film of OI.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 9, a bonded SOI has an oxide film (SiO ₂ ) 18 of about 1 μm formed on a first wafer (active wafer) 16 and the oxide film 18 is formed.
The first wafer (active wafer) 16 on which is formed is superposed on the second wafer (substrate wafer) 19, and the temperature is about 1100 ° C.
Heat treatment is performed to bond the two wafers 16 and 19 together, and the surface of the first wafer (active wafer) 16 opposite to the adhesion side is removed by polishing or the like to a desired thickness, and the bonded SOI1
5 was formed. The thickness of the first wafer (active wafer) 16 remaining after removal, that is, the thickness of the active layer 16a is about 1 to 2 μm when applied to a bipolar device.

[0003]

[Problems to be Solved by the Invention] The above bonded SOI15
Various devices are incorporated in the surface layer of 1., but in order for each device to operate favorably electrically, the value of the oxide film breakdown voltage of the bonded SOI must exceed the reference value. However, the factors affecting the oxide film breakdown voltage of the device have not been sufficiently clarified so far, and as a result, the bonded SOI that is regarded as a defective product because the oxide film breakdown voltage of the incorporated device has not reached the reference value. Existed, and the device yield was deteriorated. It is an object of the present invention to provide a bonded SOI and a method for manufacturing the same, which has a sufficiently high breakdown voltage of an oxide film when the device is incorporated therein and can improve the yield of the device.

[0004]

Means for Solving the Problems The present inventor has conducted extensive research in order to achieve the above object, paying attention to scattered light when a semiconductor wafer is irradiated with a laser, and a laser scatterer which causes this scattered light is a semiconductor. It has been found that the oxide film withstand voltage deteriorates if it is present in a large amount in the surface layer of the wafer. Further, when the density of the laser scatterer was measured for an epitaxial wafer in which an epitaxial layer was grown on a substrate of a semiconductor wafer, the density of the laser scatterer was 0 on the surface side of the epitaxial layer, but the interface with the substrate. On the other hand, they have found that they grow by inheriting the laser scatterer density of the substrate, and thus completed the present invention.

That is, the present invention is a bonded SOI in which an epitaxial layer having a laser scatterer density of 5 × 10 ⁵ pieces / cm ³ or less is bonded on a substrate through an insulating layer.
Is. According to the present invention, an epitaxial layer is grown on a first wafer, an insulating layer is formed on at least one of the first wafer and the second wafer, and the first epitaxial layer side is used as a bonding surface. This is a method of manufacturing a bonded SOI in which a wafer is overlaid on a second wafer, the two wafers are bonded to each other, and the entire first wafer and part of the epitaxial layer are removed to form a semiconductor wafer. The present invention also provides
A first wafer is formed by the floating zone melting method, and an epitaxial layer is grown on the first wafer.
An insulating layer is formed on at least one of the second wafer and the second wafer, and the first wafer is superposed on the second wafer with the epitaxial layer side as a bonding surface to bond the two wafers together. Is a method for manufacturing a bonded SOI in which the entire wafer is removed to form a semiconductor wafer. At that time, instead of the floating zone melting method, the first wafer was
It can be formed by the Czochralski method with a pulling speed of 0.6 mm / min or less, and after the first wafer is manufactured by the Czochralski method, 133
It can also be formed by performing heat treatment at 0 to 1400 ° C. for 0.5 hour or more. Regarding the heat treatment, it is also possible to perform heat treatment at 1180 ° C. or higher for 30 min or longer in an H ₂ atmosphere.

[0006]

EXAMPLES Examples of the present invention will be described below. A single crystal silicon ingot is manufactured by the pulling method, that is, the Czochralski method, and slice, lap, chamfer,
Each step of chemical polishing was performed to obtain a silicon wafer sample. The specifications of the sample are as follows: diameter 6 inches, crystal axis <100>,
P-type, boron-doped, resistivity 10 to ²⁰ Ωcm, oxygen concentration 12 to 15 × 10 ¹⁷ atoms / cm ³ (1979 edition Annual Book of ASTM Standards [the following measured values comply with this standard] display). Measure the density of the laser scatterer for this sample,
In addition, a MOS capacitor was actually created and the oxide film breakdown voltage was measured. FIG. 1 shows an apparatus for measuring the laser scatterer density of the above sample. A laser beam having a wavelength of 1.3 μm is vertically emitted from the laser emitting device 2 toward the surface of the silicon wafer 1, and the beam is focused on the surface or inside of the silicon wafer to arbitrarily determine the surface or inside of the wafer. A plurality of points are scanned by sliding the wafer. When the beam hits the defect, a slight phase shift occurs, and the defect is detected by detecting this shift.

FIG. 2 shows the vicinity of the surface (0
Shows the relationship between the density of the laser scatterer at ˜3 μm) and the B-mode defective product rate when the oxide film withstand voltage is 3 MV / cm or more and 8 MV / cm or less. As is clear from the figure, there is a significant correlation between the laser scatterer density and the B-mode defective product rate, that is, when the laser scatterer density increases, B
It is well understood that the mode defective rate increases. Further, FIG. 3 shows that the density of the laser scatterer and the breakdown voltage of the oxide film are 8 MV / c.
The relationship with the C-mode non-defective rate of m or more is shown, and as is clear from the figure, it is understood that the C-mode non-defective rate decreases as the laser scatterer density increases. As a concrete numerical value, in general, the C-mode non-defective rate of the oxide film withstand voltage is 9
Since 5% or more is required, it is understood from FIG. 3 that the laser scatterer density needs to be about 5 × 10 ⁵ pieces / cm ³ or less. Since this also applies to the bonded SOI, as a bonded SOI having a sufficiently high oxide film withstand voltage, the laser scatterer density of the active layer is 5 × 10 ⁵ pieces /
It turns out that it needs to be less than or equal to cm ³ . In the range examined by the inventors, the laser scatterer density of the active layer is 5 × 10 ⁵
The pasted SOI having the number of pieces / cm ³ or less did not exist conventionally.

Next, FIG. 4 shows the Czochralski method (CZ
Thickness of silicon wafer manufactured by
Regarding an epitaxial wafer in which 0 μm, 20 μm, 30 μm, and 60 μm epitaxial layers (Epi) are laminated, and an epitaxial wafer in which a 10 μm thick epitaxial layer is laminated on a substrate of a silicon wafer manufactured by a floating zone melting method (FZ method) Shows the results of measuring the laser scatterer density in the depth direction. First, in an epitaxial wafer in which an epitaxial layer is stacked on a silicon wafer substrate manufactured by the Czochralski method, the laser scatterer density is 0 on the surface side of the epitaxial layer, but the laser scatterer is on the interface side with the substrate. The body density is grown by taking over the laser scatterer density of the substrate. That is, in this example, the laser scatterer density of the substrate was approximately 1 × 10 ⁶ pieces / cm ³ , and the laser scatterer density was 1 × 10 ⁶ pieces / cm ³ to 5 in the transition region on the substrate side of the epitaxial layer. The number gradually decreased to × 10 ⁵ pieces / cm ³ , and further decreased to 0. FIG. 5 shows this result from another viewpoint, showing the range where the laser scatterer density is 0 and the range where it is 5 × 10 ⁵ pieces / cm ³ or less.
That is, it is understood that the density of the laser scatterers is not 0 or 5 × 10 ⁵ pieces / cm ³ or less in the entire area of the epitaxial layer. The above results relating to the laser scatterer are based on the transmission scattering method shown in FIG. On the other hand, in FIG. 6, the wavelength 1.0 is perpendicular to the crystal surface.
This is a comparison of the results obtained by the vertical scattering method in which the scattered light was observed from the direction orthogonal to the irradiation direction by irradiating the laser light of 6 μm, and the results by the above-mentioned vertical scattering method. Also, the results related to the laser scatterer show the same tendency as in the case of the transmission scattering method. However, in the vertical scattering method, it is difficult to measure the vicinity of the surface (0 to 10 μm) because it is affected by the surface scattered light. Therefore, the results of the transmission scattering method capable of measuring the entire area of the wafer are described.

Next, the means for adjusting the density of the laser scatterers in the active layer of the bonded SOI to 5 × 10 ⁵ pieces / cm ³ or less will be described. FIG. 7 shows a first embodiment of the method of the present invention. First, an epitaxial layer 7 is grown on a first wafer 6 and an oxide film 8 is formed on the epitaxial layer 7. Next, the first wafer 6 is superposed on the second wafer 9 with the epitaxial layer 7 side as the bonding surface, and heat treatment at about 1100 ° C. is performed to bond the two wafers 6 and 9. Next, the opposite side of the bonding surface of the first wafer 6 is thinned by surface grinding and polishing, and further subjected to finish polishing to remove all of the first wafer 6 and a part of the epitaxial layer 7, and thus the bonding S
Form to OI5. However, the oxide film 8 can be formed on the second wafer 9 side, or can be formed on both the first wafer 6 and the second wafer 9 on which the epitaxial layer 7 has been grown. As the second wafer 9, a silicon wafer formed by the Czochralski method, a silicon wafer formed by the floating zone melting method, quartz, ceramics, or the like can be used. Further, etching or the like may be used instead of polishing. This bonded SO
Although the laser scatterer density of the epitaxial layer 7 of I5 is 0 at the interface on the oxide film 8 side, it gradually increases toward the interface on the first wafer 6 side and reaches the first wafer at the interface on the first wafer 6 side. The laser scatterer density of 6 is succeeded.
Therefore, the thickness of the region in which the laser scatterer density is 5 × 10 ⁵ pieces / cm ³ or less is obtained from FIG. Scatterer density is 5 × 10
^The number is ⁵ pieces / cm ³ or less, and thus a bonded SOI 5 having a sufficiently high oxide film withstand voltage can be obtained.

Next, a second embodiment of the method of the present invention will be described. As described above, the density of the laser scatterers in the epitaxial layer is succeeded by the density of the laser scatterers in the growth substrate. Therefore, by reducing the laser scatterer density of the growth substrate, the laser scatterer density of the epitaxial layer can be reduced. As shown in FIG. 4, regarding an epitaxial wafer in which an epitaxial layer is laminated on a substrate of a silicon wafer manufactured by the floating zone melting method (FZ method), in this case, the laser scatterer density of the growth substrate is 0. Therefore, the laser scatterer density of the epitaxial layer is also zero. Therefore, in FIG. 7, by forming the first wafer 6 by the floating zone melting method, the density of the laser scatterers in the entire axial layer 7 becomes 5 × 10 ⁵ pieces / cm ³ or less, so that the oxide film withstand voltage is reduced. A sufficiently high bonded SOI5 can be obtained. In this case, since the laser scatterer density of the first wafer 6 is also 0, it is possible to remove only a part of the first wafer 6 by polishing or the like, but at least from the viewpoint of forming the epitaxial layer 7, It is preferable to remove all of the first wafer 6.

Next, a first epitaxial layer 7 is grown.
The laser scatterer density of the wafer 6 is 5 × 10 ⁵ pieces / cm ³
The second means for achieving the following will be described. Pulling speed is 0.6mm / min in Czochralski method
6 inch diameter pulled up below, crystal axis <100>, P
Mold, boron doped, resistivity 0.01 to 0.02 Ωcm,
The laser scatterer density of a crystal having an oxygen concentration of 12 to 15 × 10 ¹⁷ atoms / cm ³ is 5 × 10 ⁵ pieces / cm ³ or less. Therefore, laser scattering in an epitaxial layer in which epitaxial growth is performed using this crystal as a growth substrate is performed. The body density was also 5 × 10 ⁵ pieces / cm ³ or less. Therefore, by removing at least the entire first wafer 6,
It is possible to obtain a bonded SOI 5 having a sufficiently high breakdown voltage of an oxide film.

Next, the first epitaxial layer 7 is grown.
The laser scatterer density of the wafer 6 is 5 × 10 ⁵ pieces / cm ³
A third means for achieving the following, that is, a method of performing heat treatment after manufacturing a silicon single crystal at a normal pulling rate in the Czochralski method will be described below. FIG. 8 shows a silicon wafer 1 when various heat treatment conditions are changed.
The density of the laser scatterer in the vicinity of the surface (0 to 3 μm) is shown. As shown in the figure, when no heat treatment is performed, in this embodiment, about 3 × 10 ⁶ pieces / cm ³ of laser scatterers are present, and the density of the laser scatterers is up to about 1300 ° C. It can be seen that the laser scatterer is very stable even if it is subjected to the heat treatment or the heat treatment time is prolonged.
However, if the heat treatment temperature is set to about 1330 ° C. or higher, by performing heat treatment of at least 0.5 Hr,
The laser scatterers have disappeared almost completely. Therefore, considering the melting point of silicon, 1330 to 1400 ° C,
The laser scatterer can be almost completely erased by applying a heat treatment of 0.5 Hr or more. By stacking an epitaxial layer on the first wafer 6, a bonded SOI 5 having a sufficiently high oxide film breakdown voltage. Can be obtained. As an example performed by the inventor, a diameter of 6 inches grown at a normal pulling rate in the Czochralski method,
Crystal axis <100>, N type, antimony doped, resistivity 0.01 to 0.02 Ωcm, oxygen concentration 13 to 16 × 10
For a crystal of ¹⁷ atoms / cm ³ , the above 1330-
Even when the epitaxial heat treatment was performed at 1400 ° C. for 0.5 hr or more, the laser scatterer density in the epitaxial layer was 5 × 10 ⁵ pieces / cm ³ or less.

Since there is no particular relation between the processing of a silicon ingot into a silicon wafer and the heat treatment at 1330 to 1400 ° C. and 0.5 Hr or more, the heat treatment is performed after processing the silicon wafer as in this embodiment. In addition to the heat treatment, the silicon ingot may be heat-treated as it is and then processed into a silicon wafer. As for the apparatus for heat treatment, a dedicated apparatus for heat treatment can be used, and the pulling apparatus itself can be used as a heat treatment furnace. This method is particularly effective when heat treatment is performed on a silicon ingot as it is.
In the above embodiment, the heat treatment is performed with an inert gas, specifically A
Although it was carried out in an r gas atmosphere, it can also be carried out in an H ₂ atmosphere.
By applying a heat treatment of not less than in, for example, 1200
By performing heat treatment at 60 ° C. for 60 minutes, the laser scatterer can be almost completely extinguished.

[0014]

According to the present invention, a bonded SOI having a sufficiently high breakdown voltage of an oxide film and thus a good device yield.
And the manufacturing method can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a method for measuring a laser scatterer density.

FIG. 2 is a diagram showing the relationship between the density of laser scatterers and the B-mode defective product rate.

FIG. 3 is a graph showing a relationship with the C-mode non-defective rate.

FIG. 4 is a diagram showing a laser scatterer density in a depth direction of an epitaxial wafer.

FIG. 5 is a diagram showing a low defect region and a transition region with respect to the thickness of an epitaxial layer.

FIG. 6 is a diagram showing depth distributions of laser scatterers on an epitaxial wafer by a vertical scattering method and a transmission scattering method.

FIG. 7 is a process chart showing an embodiment of the method of the present invention.

FIG. 8 is a graph showing the relationship between heat treatment temperature and laser scatterer density.

FIG. 9 is a process diagram showing a conventional method for manufacturing a bonded SOI.

[Explanation of symbols]

1 ... Silicon wafer 2 ... Laser emitting device 5
... Bonded SOI 6 ... First wafer 7 ... Epitaxial layer 8
… Oxide film 9… Second wafer

Claims (6)

[Claims] 1. A bonded SOI, in which an epitaxial layer having a laser scatterer density of 5 × 10 ⁵ particles / cm ³ or less is bonded onto a substrate via an insulating layer. 2. An epitaxial layer is grown on a first wafer, an insulating layer is formed on at least one of the first wafer and the second wafer, and the first epitaxial layer is used as a bonding surface. The method of manufacturing a bonded SOI, wherein the wafer is overlaid on a second wafer, the two wafers are adhered to each other, and the entire first wafer and a part of the epitaxial layer are removed to form a semiconductor wafer. 3. A first wafer is formed by a floating zone melting method, an epitaxial layer is grown on the first wafer, and an insulating layer is formed on at least one of the first wafer and the second wafer. Forming a semiconductor wafer by laminating the first wafer on the second wafer with the epitaxial layer side as the adhesive surface and adhering the two wafers together, and removing at least the entire first wafer to form a semiconductor wafer. Combined SOI
Manufacturing method. 4. The method for producing a bonded SOI according to claim 3, wherein the first wafer is formed by a Czochralski method with a pulling rate of 0.6 mm / min or less, instead of the floating zone melting method. 5. In place of the floating zone melting method, after the first wafer is manufactured by the Czochralski method,
The method for manufacturing a bonded SOI according to claim 3, which is formed by performing a heat treatment at 1330 to 1400 ° C. at 0.5 Hr or higher. 6. The method for producing a bonded SOI according to claim 5, wherein instead of the heat treatment, a heat treatment at 1180 ° C. or higher for 30 min or longer is performed in an H ₂ atmosphere.