Method for manufacturing a bonded SOI wafer

Abstract

A method for manufacturing a bonded SOI wafer by bonding a bond wafer and a base wafer, each composed of a silicon single crystal, via an insulator film, including the steps of: depositing a polycrystalline silicon layer on the bonding surface side of the base wafer, polishing a surface of the polycrystalline silicon layer, forming the insulator film on the bonding surface of the bond wafer, bonding the polished surface of the polycrystalline silicon layer of the base wafer and the bond wafer via the insulator film, and thinning the bonded bond wafer to form an SOI layer; As a result, it is possible to provide a method for manufacturing a bonded SOI wafer which can prevent single-crystallization of polycrystalline silicon while suppressing an increase of the warpage of a base wafer even when the polycrystalline silicon layer to function as a carrier trap layer is deposited sufficiently thick.

Claims

1. A method for manufacturing a bonded SOI wafer by bonding a bond wafer and a base wafer, each composed of a silicon single crystal, via an insulator film, comprising, in sequential order, the steps of: depositing a polycrystalline silicon layer on the bonding surface side of the base wafer, polishing a surface of the polycrystalline silicon layer, forming the insulator film on the bonding surface of the bond wafer, forming an ion-implanted layer in the bond wafer, bonding the polished surface of the polycrystalline silicon layer of the base wafer and the bond wafer via the insulator film, and thinning the bonded bond wafer by delaminating along the ion-implanted layer in the bond wafer to form an SOI layer; wherein, as the base wafer, a silicon single crystal wafer having a resistivity of 100 .Math.cm or more is used, the step for depositing the polycrystalline silicon layer further comprises a stage for previously forming an oxide film on the surface of the base wafer on which the polycrystalline silicon layer is deposited, the polycrystalline silicon layer is deposited by a method consisting of two growth stages, a first growth performed at a first temperature of 900 C. or more and 1010 C. or less, and a second growth performed at a second temperature of 1100 C. or more to deposit the polycrystalline silicon layer thicker than in the first growth, deposition of the polycrystalline silicon layer is performed using trichlorosilane as a source gas at atmospheric pressure in the first growth and the second growth, the oxide film is formed by wet cleaning, the oxide film has a thickness of 0.3 nm or more and 10 nm or less, and the polycrystalline silicon layer has a thickness of 2 m or more when the base wafer and the bond wafer are bonded.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a production flow exemplifying an example of an embodiment of the method for manufacturing a bonded SOI wafer of the present invention;

(2) FIG. 2 is a sectional process view exemplifying an example of an embodiment of the method for manufacturing a bonded SOI wafer of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(3) Hereinafter, the present invention will be explained in detail as an example of the embodiment with reference to the drawings, but the present invention is not restricted thereto.

(4) As described above, it comes to be necessary to form a carrier trap layer under a BOX layer of an SOI wafer in order to manufacture a device which can cope with higher frequency. The polycrystalline silicon layer is required to have a relatively thick film thickness in order to function as a carrier trap layer, and is suitable to be grown only on the one side as rapidly as possible. However, when a polycrystalline silicon layer is deposited thickly only on the one side, there arises a problem that the warpage of a wafer becomes larger as the thickness increases, thereby causing a bond failure. Moreover, in order to deposit a polycrystalline silicon layer as rapidly as possible, the growth temperature is required to be higher. However, when the growth temperature becomes higher, there arises a problem that a part of a native oxide film on the surface of a base wafer disappears and at the above portion a polycrystalline silicon layer does not grow and single crystallizes.

(5) Accordingly, the present inventors have diligently investigated on the method for manufacturing a bonded SOI wafer which can prevent single-crystallization of polycrystalline silicon while suppressing an increase of the warpage of a base wafer even when the polycrystalline silicon layer to function as a carrier trap layer is deposited with sufficiently thick thickness.

(6) As a result, the present inventors have found that by previously forming an oxide film on the surface of a silicon single crystal of a base wafer and setting the subsequent deposition temperature of a polycrystalline silicon layer to 1010 C. or less, it is possible to prevent disappearance of a part of the oxide film on the surface of the base wafer, to prevent single-crystallization of the polycrystalline silicon layer thereby, and accordingly to sustain an effect as a carrier trap layer; and furthermore, by depositing a polycrystalline silicon layer at a low temperature of 1010 C. or less and then depositing the thicker polycrystalline silicon layer at a higher temperature than that, the warpage of a wafer can be suppressed while depositing the polycrystalline silicon layer to a sufficient thickness rapidly and efficiently; thereby bringing the present invention to completion.

(7) Hereinafter, an example of an embodiment of the method for manufacturing a bonded SOI wafer of the present invention will be explained with reference to FIGS. 1 to 2.

(8) First, a bond wafer 10 composed of a silicon single crystal is prepared (see Step S11 in FIG. 1 and FIG. 2(a)).

(9) Then, on the bond wafer 10, an insulator film (e.g., an oxide film) 13, which forms a buried oxide film layer (a BOX layer) 16, is grown by thermal oxidation or CVD or the like, for example (see Step S12 in FIG. 1 and FIG. 2(b)).

(10) Subsequently, from upper side of the insulator film 13, at least one gas ion selected from a hydrogen ion and a rare gas ion is implanted to form an ion-implanted layer 17 in the bond wafer 10 with an ion-implantation apparatus (see Step S13 in FIG. 1 and FIG. 2(c)). In this case, an accelerating voltage of the ion-implantation can be selected such that a targeted thickness of an SOI layer 15 can be obtained.

(11) Then, in order to remove particles on the bonding surface of the bond wafer 10, pre-bond cleaning is performed (see Step S14 in FIG. 1).

(12) On the other hand, a base wafer 11 composed of a silicon single crystal is prepared in addition to the bond wafer (see Step S21 in FIG. 1 and FIG. 2 (d)).

(13) Then, on the base wafer 11, an oxide film (a base oxide film) 20 is formed (see Step S22 in FIG. 1 and FIG. 2(e)). The thickness of the oxide film 20 is not particularly limited. However, the thickness of the oxide film to be formed is preferably thinner, for example, the thickness of 0.3 nm or more and 10 nm or less is preferable, since the interposed oxide film 20 between the base wafer 11 and the polycrystalline silicon layer 12 can influence property of an RF device.

(14) The method to form an oxide film with such a thickness includes wet cleaning as the most convenient method. Specifically, a uniform oxide film with a thickness of approximately 0.5 to 3 nm can be formed by cleaning with SC1 (a mixed aqueous solution of NH.sub.4OH and H.sub.2O.sub.2), SC2 (a mixed aqueous solution of HCl and H.sub.2O.sub.2), sulfuric acid-hydrogen peroxide water mixture (a mixed aqueous mixed solution of H.sub.2SO.sub.4 and H.sub.2O.sub.2), ozone water, etc., or a mixture thereof.

(15) Subsequently, on the oxide film (the base oxide film) 20, a polycrystalline silicon layer 12 is deposited (see Step S23 in FIG. 1 and FIG. 2(f)). Here, the deposition of the polycrystalline silicon layer 12 is performed, being divided into two stages comprising a first growth performed at a first temperature of 1010 C. or less and a second growth (which is carried out after the first growth) performed at a second temperature being higher than the first temperature to deposit the polycrystalline silicon layer thicker than in the first growth.

(16) By previously forming an oxide film between the surface of a silicon single crystal of a base wafer and the polycrystalline silicon layer to be deposited, and by setting the deposition temperature in the subsequent first growth to 1010 C. or less, it is possible to prevent disappearance of a part of the oxide film on the surface of the base wafer. Moreover, by depositing the polycrystalline silicon layer with a prescribed film thickness (approximately 0.5 m) at a low temperature of 1010 C. or less, and then in the second growth, by depositing more thickly than in the first growth and at a higher temperature than in the first growth, the warpage of the wafer can be suppressed while depositing the polycrystalline silicon layer 12 to a sufficient thickness rapidly and efficiently.

(17) It is to be noted that these two-stage growth can be performed continuously, and can also be performed in such a way that the second growth is performed after temporarily taking out the wafer from a growing furnace.

(18) Then, the surface of the polycrystalline silicon layer 12 deposited on the base wafer 11 is flattened by polishing (see Step S24 in FIG. 1 and FIG. 2(g)). The polycrystalline silicon layer 12 deposited at a high temperature has a large surface roughness, and is difficult to bond as it is. Accordingly, it is necessary to flatten the surface of the polycrystalline silicon layer 12 by polishing.

(19) Subsequently, pre-bond cleaning is performed in order to remove particles on the surface of the polished polycrystalline silicon layer 12 (see Step S25 in FIG. 1).

(20) It is to be noted that Steps S11 to S14 in FIG. 1 and Steps S21 to S25 in FIG. 1 can be conducted in parallel.

(21) Then, the base wafer 11 on which the polycrystalline silicon layer 12 has been formed and the bond wafer 10 on which the insulator film 13 has been formed are adhered to be bonded in such a way that the implanted surface of the bond wafer 10 is in contact with the side of the base wafer 11 on which the polycrystalline silicon layer 12 has been formed (see Step S31 in FIG. 1 and FIG. 2(h)).

(22) Subsequently, the bonded wafer is subjected to a heat treatment to generate a micro bubble layer in the ion-implanted layer 17 (a delamination heat treatment), and is delaminated along the generated micro bubble layer to produce a bonded wafer 14 in which the buried oxide film layer 16 and the SOI layer 15 are formed on the base wafer 11 (see Step S32 in FIG. 1 and FIG. 2 (i)). It is to be noted that in this step, a delaminated wafer 18 having a delaminating plane 19 is derived.

(23) Then, the bonded wafer 14 is subjected to a bonding heat treatment in order to enhance the bond strength at the interface of bonding (see Step S33 in FIG. 1).

(24) As described above, a bonded SOI wafer can be manufactured.

(25) In the method for manufacturing a bonded SOI wafer of the present invention described above, it is preferable to set the first temperature in the first growth of depositing the polycrystalline silicon layer 12 to 900 C. or more. By setting the first temperature to 900 C. or more, it is possible to prevent lowering of productivity, which is caused by getting the deposition rate too low.

(26) It is preferable to set the second temperature in the second growth of depositing the polycrystalline silicon layer 12 to 1100 C. or more. By setting the second temperature to 1100 C. or more, it is possible to obtain sufficiently high deposition rate to improve the productivity, and to sufficiently suppress the warpage of a wafer after depositing the polycrystalline silicon layer. Further, even when the temperature of a heat treatment step of a step for manufacturing an SOI wafer or a heat treatment of a step for manufacturing a device is relatively high (e.g., about 1000 to 1200 C.), since the polycrystalline silicon layer is deposited at the equivalent temperature thereto, it is also possible to sufficiently suppress grain growth of the polycrystalline silicon layer and to sustain an effect as a carrier trap layer thereby.

(27) The upper limit of the second temperature is not particularly limited. This does not have to be set to higher than the maximum temperature in a step for manufacturing an SOI wafer or a step for manufacturing a device (when it is too high, slip dislocations and metal contaminations are apt to generate); and accordingly, it is preferable to set this temperature to that maximum temperature or less, for example, 1200 C. or less.

(28) In the method for manufacturing a bonded SOI wafer of the present invention described above, it is preferable to set the thickness of the polycrystalline silicon layer 12 to 2 m or more when the base wafer and the bond wafer are bonded.

(29) By setting the thickness of the polycrystalline silicon layer to 2 m or more when the base wafer and the bond wafer are bonded, the frequency of a bond failure increases due to warpage of a wafer. However, when the second growth has been performed at a higher temperature than in the first growth in depositing the polycrystalline silicon layer, the warpage of a wafer can be suppressed, and accordingly the bond failure can be lowered while enhancing the effect as a carrier trap layer, even when the thickness of the polycrystalline silicon layer is 2 m or more when the base wafer and the bond wafer are bonded.

(30) It is to be noted that it is preferable to set the thickness of the polycrystalline silicon layer to 10 m or less when the base wafer and the bond wafer are bonded.

(31) The base wafer 11 can be preferably used for manufacturing a radio frequency device so long as it has a resistivity of 100 .Math.cm or more, which is further preferably 1000 .Math.cm or more, particularly preferably 3000 .Math.cm or more. The upper limit of the resistivity is not particularly limited, but it can be 50000 .Math.cm, for example.

EXAMPLES

(32) Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples, but the present invention is not restricted thereto.

Example 1

(33) By using a manufacturing method explained in FIGS. 1 to 2, a bonded SOI wafer was produced. Provided that a p-type single crystal silicon with a diameter of 200 mm, crystal orientation of <100>, and a resistivity of 700 .Math.cm was used as a base wafer; and formation of a base oxide film, deposition of a polycrystalline silicon layer (trichlorosilane was used as a source gas), BOX oxidation, hydrogen ion-implantation, a delamination heat treatment, and a bonding heat treatment were performed under the following conditions:

(34) formation of a base oxide film: SC1+SC2 cleaning, the film thickness of an oxide film: about 1 nm

(35) deposition of polycrystalline silicon layer: 900 C., atmospheric pressure, the film thickness: 0.3 m+1130 C., atmospheric pressure, the film thickness: 2.7 m (the total thickness after polishing: 2.2 m)

(36) BOX oxidation: 1050 C., the film thickness of an oxide film: 400 nm

(37) hydrogen ion-implantation: 105 keV, 7.510.sup.16/cm.sup.2

(38) delamination heat treatment: 500 C., 30 minutes, 100% Ar atmosphere

(39) bonding heat treatment: 900 C. pyrogenic oxidation+Ar annealing at 1100 C. for 120 minutes.

(40) The warpage of a wafer after polishing the polycrystalline silicon layer was measured, and the state of single-crystallization of the polycrystalline silicon layer after a bonding heat treatment was examined (confirmed by cross-sectional SEM observation). The results are shown in Table 1.

Example 2

(41) A bonded SOI wafer was produced in the same manner as in Example 1. Provided that the polycrystalline silicon layer was deposited under conditions of 950 C., atmospheric pressure, and a film thickness of 0.3 m+1080 C., atmospheric pressure, and a film thickness of 2.7 m (the total thickness after polishing: 2.2 m).

(42) In the same manner as in Example 1, the warpage of a wafer after polishing the polycrystalline silicon layer was measured, and the state of single-crystallization of the polycrystalline silicon layer after a bonding heat treatment was examined. The results are shown in Table 1.

Example 3

(43) A bonded SOI wafer was produced in the same manner as in Example 1. Provided that the polycrystalline silicon layer was deposited under conditions of 1010 C., atmospheric pressure, and a film thickness of 0.3 m+1130 C., atmospheric pressure, and a film thickness of 2.7 m (the total thickness after polishing: 2.2 m).

(44) In the same manner as in Example 1, the warpage of a wafer after polishing the polycrystalline silicon layer was measured, and the state of single-crystallization of the polycrystalline silicon layer after a bonding heat treatment was examined. The results are shown in Table 1.

Example 4

(45) A bonded SOI wafer was produced in the same manner as in Example 1. Provided that the base oxide film was formed under conditions of 800 C., dry O.sub.2 oxidation, the oxide film thickness: 30 nm; and the polycrystalline silicon layer was deposited under conditions of 980 C., atmospheric pressure, and a film thickness of 0.3 m+1100 C., atmospheric pressure, and a film thickness of 2.7 m (the total thickness after polishing: 2.2 m).

(46) In the same manner as in Example 1, the warpage of a wafer after polishing the polycrystalline silicon layer was measured, and the state of single-crystallization of the polycrystalline silicon layer after a bonding heat treatment was examined. The results are shown in Table 1.

Comparative Example 1

(47) A bonded SOI wafer was produced in the same manner as in Example 1. Provided that the polycrystalline silicon layer was deposited under one-stage conditions of 1000 C., atmospheric pressure, and a film thickness of 3 m (2.2 m after polishing) without dividing into two stages of a first growth and a second growth.

(48) In the same manner as in Example 1, the warpage of a wafer after polishing the polycrystalline silicon layer was measured, and the state of single-crystallization of the polycrystalline silicon layer after a bonding heat treatment was examined. The results are shown in Table 1.

Comparative Example 2

(49) A bonded SOI wafer was produced in the same manner as in Example 1. Provided that the polycrystalline silicon layer was deposited under one-stage conditions of 1020 C., atmospheric pressure, and a film thickness of 3 m without dividing into two stages of a first growth and a second growth.

(50) In Comparative Example 2, deposition of single crystal was confirmed by SEM observation after depositing a polycrystalline silicon layer, and a polycrystalline silicon layer failed to deposit thereby. Accordingly, the subsequent steps were not performed.

(51) TABLE-US-00001 TABLE 1 Comparative Comparative Example 1 Example 2 Example 3 Example 4 Example 1 Example 2 Base wafer Diameter: 200 mm, Crystal orientation: <100>, Resistivity: 700 .Math. cm, p-type Conditions for forming base oxide film SC1 + SC2 cleaning, forming 800 C. SC1 + SC2 oxide film thickness of ca. 1 nm dry O2 cleaning, forming oxidation oxide film thickness forming of ca. 1 nm oxide film thickness of 30 nm First-growth conditions Temp. 900 C. 950 C. 1010 C. 980 C. 1000 C. 1020 C. for depositing Pressure Atmospheric pressure polycrystalline-silicon layer Thickness 0.3 m 3 m Second-growth conditions Temp. 1130 C. 1080 C. 1130 C. 1100 C. Single for depositing Pressure Atmospheric pressure crystal was polycrystalline-silicon layer Thickness 2.7 m confirmed Thickness of polycrystalline-silicon 2.2 m by SEM layer after polishing (total thickness) observation Warpage of wafer after polishing 14 m 30 m 10 m 25 m 70 m Accordingly polycrystalline-silicon layer post-steps State of single-crystallization of polycrystalline No problem were not silicon layer (at completion of SOI wafer) performed

(52) As can be seen from Table 1, in Examples 1 to 4, which were performed with each deposition of a polycrystalline silicon layer divided into the first growth performed at 1010 C. or less and the second growth performed at a temperature higher than in the first growth to deposit the polycrystalline silicon layer thicker than in the first growth, single-crystallization of polycrystalline silicon was prevented while suppressing an increase of the warpage of each wafer. Particularly, in Examples 1 and 3 to 4, in which each second growth was performed at 1100 C. or more, the warpage of each wafer could be more lowered compared to Example 2, in which the second growth was performed below 1100 C.

(53) On the other hand, in Comparative Example 1, in which the polycrystalline silicon layer was deposited at 1000 C. without dividing into the first growth and the second growth, the warpage of the wafer was larger compared to Examples 1 to 4, although single-crystallization of polycrystalline silicon was prevented.

(54) Furthermore, in Comparative Example 2, in which the polycrystalline silicon layer was deposited at 1020 C. without dividing into the first growth and the second growth, the polycrystalline silicon was single-crystallized at the completion of depositing the polycrystalline silicon layer.

(55) It is to be noted that the present invention is not limited to the foregoing embodiment. The embodiment is just an exemplification, and any examples that have substantially the same feature and demonstrate the same functions and effects as those in the technical concept described in claims of the present invention are included in the technical scope of the present invention.