JP3719217B2 - Manufacturing method of silicon epitaxial wafer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a silicon epitaxial wafer.
[0002]
[Prior art]
As one method of manufacturing a silicon epitaxial wafer (hereinafter also simply referred to as an epitaxial wafer), a dopant such as antimony is diffused on the main surface side of a silicon single crystal substrate (hereinafter also simply referred to as a silicon substrate). Conventionally known is a method for producing a silicon epitaxial wafer (hereinafter also simply referred to as an epitaxial wafer) by vapor-phase growth of a silicon epitaxial layer (hereinafter also referred to as an epitaxial layer) on the main surface of the resulting diffusion wafer. It has been.
More specifically, for example, after forming a first p ⁻ -type epitaxial layer doped with a low concentration of p-type dopant on the main surface of a p ⁺ -type silicon substrate doped with a high concentration of p-type dopant, diffusing the dopant in the surface layer portion of the type epitaxial layer, Thereafter, the first p ^{- -} first p type epitaxial on the second layer p ^- with the type epitaxial layer is laminated, a buried diffusion region An epitaxial wafer having the same may be manufactured.
In this case, for example, when the second p ⁻ type epitaxial layer whose resistivity is about two orders of magnitude higher than that of the silicon substrate is vapor-phase grown, a silicon oxide film for preventing auto-doping is formed on the main back surface of the silicon substrate. It is desirable to perform vapor phase growth while forming in advance and suppressing autodoping from the main back surface to the main surface side.
As a method of forming a silicon oxide film for preventing auto-doping, for example, a method of forming a CVD oxide film on the main back surface by a CVD method or a method of forming a thermal oxide film on the main surface and the main back surface by a thermal oxide film method A method of removing only the thermal oxide film on the main surface side is known.
[0003]
[Problems to be solved by the invention]
However, the formation of the CVD oxide film by the CVD method is performed while the diffusion wafer is placed on, for example, a belt conveyor with the main back surface facing upward, and is conveyed by the belt conveyor. There is a problem that the surface state of the main surface may deteriorate.
On the other hand, when the thermal oxide film is formed by the thermal oxide film method, the dopant in the diffusion wafer (dopant diffused in the first p ⁻ type epitaxial layer) is diffused by heating for forming the thermal oxide film. There is a problem that it is difficult to adjust to the intended diffusion region depth because the diffusion (thermal diffusion) deepens inside (inside the first p ⁻ -type epitaxial layer).
Moreover, in any of the above cases, it is necessary to form an oxide film specially by the CVD method or the thermal oxide film method only for preventing auto-doping.
[0004]
The present invention has been made to solve the above problems, and provides a method for manufacturing a silicon epitaxial wafer by suitably forming an oxide film for preventing autodoping on a diffusion wafer. Objective.
[0005]
[Means for Solving the Problems]
In order to solve the above-described problems, the silicon epitaxial wafer manufacturing method of the present invention automates the remaining portion of the main back side oxide film formed on the main back side of the diffusion wafer at the end of diffusion after removing the surface layer portion. A silicon epitaxial wafer is manufactured by vapor-phase growth of a silicon epitaxial layer on the main surface of the diffusion wafer, which is used for preventing doping.
[0006]
According to the present invention, the main back surface side oxide film that is simultaneously formed on the main back surface side of the diffusion wafer when the dopant is diffused on the main surface side of the silicon wafer is used for preventing auto-doping. Since a silicon epitaxial wafer is manufactured by vapor-phase growth of a silicon epitaxial layer on the surface, it is not necessary to newly form an oxide film for preventing autodoping after diffusion.
However, since the diffused dopant remains in the surface layer portion of the main back surface side oxide film, it is necessary to remove the surface layer portion. On the other hand, the remaining portion of the main backside oxide film from which the surface layer portion has been removed is hardly doped with dopant, so that the dopant can be substantially released from the remaining portion even by heating. Absent. Therefore, by performing vapor phase growth using the remaining portion of the main backside oxide film for preventing autodoping, it is possible to suitably suppress the occurrence of autodoping in the silicon epitaxial layer.
That is, by removing only the surface layer portion of the main back surface side oxide film formed on the main back surface side of the diffusion wafer at the end of diffusion, it can be suitably used for preventing auto-doping.
[0007]
Here, it is preferable to remove the surface layer portion of the main back-side oxide film by using buffered hydrofluoric acid (NH ₄ F / HF / H ₂ O). That is, the etching of the oxide film is performed using buffered hydrofluoric acid, so that the etching amount can be easily controlled, so that only the surface layer portion of the main back surface side oxide film can be removed, and the rest This part can be used for preventing autodoping during vapor phase growth.
[0008]
The silicon wafer to be used for diffusion is, for example, a primary obtained by vapor-phase growth of a low-doped first silicon epitaxial layer on the main surface of a highly-doped silicon single crystal substrate. It is a silicon epitaxial wafer (different from the silicon epitaxial wafer that is the result of the present invention). Further, a diffusion wafer is obtained by forming a diffusion region of the dopant in the surface layer portion of the first silicon epitaxial layer by diffusion. In addition, the silicon epitaxial layer that is vapor-grown on the main surface of the diffusion wafer is, for example, a second silicon epitaxial layer that is lightly doped. Then, the second silicon epitaxial layer is vapor-phase grown on the main surface of the diffusion wafer, so that a silicon epitaxial wafer which is a result of the present invention can be manufactured.
[0009]
In the present invention, when a diffusion wafer having a dopant-doped diffusion region on the main surface is selectively used, that is, in a state where a pattern opening is formed in the main surface side oxide film of the silicon wafer to be used for diffusion. The present invention may be applied when diffusion is performed, or may be applied when a diffusion wafer in which a dopant is doped on the entire main surface is used.
[0010]
Among these, when the present invention is applied to a diffusion wafer having a diffusion region in a position-selective manner, more specifically, for example, a resist is formed on the main back-side oxide film at the stage after diffusion, and then Then, the diffusion wafer is immersed in buffered hydrofluoric acid, the main surface side oxide film is removed only by its surface layer by wet etching using the buffered hydrofluoric acid, then the resist is removed, and then the diffusion wafer is buffered. By dipping in hydrofluoric acid and wet etching with the buffered hydrofluoric acid, the remaining part of the main surface side oxide film and only the surface layer part of the main back side oxide film are removed at a time, and the main back side oxidation is performed. It is preferable to perform vapor phase growth using the remaining part of the film for preventing autodoping.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
[First Embodiment]
Hereinafter, with reference to the drawings, a first embodiment of a method for producing a silicon epitaxial wafer according to the present invention will be described in detail for each step.
[0012]
<First vapor phase growth process>
First, as shown in FIG. 1A, a p ⁺ -type silicon single crystal substrate 1 (hereinafter, also simply referred to as a silicon substrate 1) is prepared, and a conventionally known gas is formed on the main surface of the silicon substrate 1. A first p ⁻ -type silicon epitaxial layer 2 (FIG. 1B; hereinafter also simply referred to as epitaxial layer 2) is formed (vapor phase growth) by the phase growth method. Thereby, as shown in FIG.1 (b), the primary silicon epitaxial wafer 3 (henceforth the epitaxial wafer 3 only) is obtained.
[0013]
<Oxide film formation process>
Next, as shown in FIG. 2, a silicon oxide film is formed on the surface of the epitaxial wafer 3 composed of the silicon substrate 1 and the epitaxial layer 2.
Specifically, this oxide film is formed by, for example, thermal oxidation. That is, while heating the epitaxial wafer 3, for example, oxygen is supplied to form a thermal oxide film over the entire surface of the epitaxial wafer 3.
Hereinafter, of the formed oxide film, the main surface side portion of the epitaxial wafer 3 is referred to as a main surface side oxide film 41, and the main back surface side portion is referred to as a main back surface side oxide film 42 (FIG. 2). .
[0014]
<Pattern opening formation process>
Next, as shown in FIG. 3C, a pattern opening 41a is selectively formed in a desired position of the main surface side oxide film 41, that is, in the main surface side oxide film 41 by a conventionally known photolithography method. Form.
For this purpose, first, as shown in FIG. 3A, a resist pattern 51 having an opening 51a is selectively formed on the main surface side oxide film 41, and on the main back side oxide film 42. In this case, a resist 52 is formed on the entire surface so that the main backside oxide film 42 is not etched away. Next, wet etching is performed by immersing the epitaxial wafer 3 in, for example, buffered hydrofluoric acid. Then, the main surface side oxide film 41 is removed by selective etching through the openings 51a of the resist pattern 51 by the buffered hydrofluoric acid. As a result, as shown in FIG. 3B, a pattern opening 41a is formed in the main surface side oxide film 41 in a position-selective manner. Next, the silicon epitaxial wafer 3 is immersed in a resist removal cleaning solution (mixed solution of sulfuric acid and hydrogen peroxide solution) to perform conventionally known resist removal cleaning. Then, the resist pattern 51 and the resist 52 are cleaned and removed by the resist removal cleaning liquid, and the state shown in FIG.
[0015]
<Diffusion process>
Next, diffusion is performed by doping a surface layer portion of the epitaxial layer 2 of the epitaxial wafer 3 with a dopant (for example, Sb (antimony)) to obtain a diffusion wafer 7.
That is, the epitaxial wafer 3 is put into a conventionally known thermal diffusion furnace, heated to a required temperature, and a dopant is supplied to the surface of the epitaxial layer 2 through the pattern opening 41a of the main surface side oxide film 41. . Thereby, in the epitaxial layer 2, the dopant is shallowly thermally diffused into the portion exposed through the pattern opening 41 a of the main surface side oxide film 41. As a result, as shown in FIG. 4A, a diffusion layer 2 a is selectively formed in the surface layer portion of the epitaxial layer 2.
In other words, the diffusion is performed in a position-selective manner by performing the diffusion in a state where the pattern opening is formed in the main surface side oxide film of the epitaxial wafer (silicon wafer) 3 subjected to the diffusion.
Thereafter, for example, the surface of the diffusion layer 2a is oxidized by supplying oxygen or the like to the main surface of the diffusion wafer 7, and an oxide film 6 (FIG. 4B) is formed on the diffusion layer 2a. Stop supplying dopant to 2a. Furthermore, the diffusion layer 2a is expanded to a desired depth by performing so-called drive-in by heating to a predetermined temperature. At this time, the oxide film 6 functions as a cap film that prevents the dopant from being released from the diffusion layer 2a.
As described above, as shown in FIG. 4B, the diffusion wafer 7 having the diffusion layer 2a having a desired diffusion depth is obtained.
[0016]
By performing the diffusion step, a doped layer 41b doped with a dopant is formed on the surface layer portion of the main surface side oxide film 41, and similarly, the dopant is also present on the surface layer portion of the main back surface side oxide film 42. Doped doped layer 42a is formed.
[0017]
<Main surface side oxide film removal process>
Next, as shown in FIG. 5B, for example, all of the main surface side oxide film 41 is removed at once.
For this purpose, first, as shown in FIG. 5A, a resist 8 is formed on the main back surface of the diffusion wafer 7 to protect the main back side oxide film 42 from being etched. Next, by immersing the diffusion wafer 7 in, for example, buffered hydrofluoric acid and performing wet etching, the main surface side oxide film 41 is completely removed as shown in FIG. At this time, the oxide film 6 is also removed together.
[0018]
<Surface layer part removal process of main back side oxide film>
Next, as shown in FIG. 5D, only the surface layer portion of the main back surface side oxide film 42 is removed. Here, the surface layer portion is a portion including at least the doped layer 42a doped with a dopant.
In order to remove the surface layer portion, first, the main wafer side oxide film 42 is exposed as shown in FIG. 5C by immersing the diffusion wafer 7 in a resist removal cleaning solution to remove the resist 8. Next, wet etching is performed by immersing the diffusion wafer 7 in, for example, buffered hydrofluoric acid. The length of time for performing this etching is limited to the surface layer portion including the doped layer 42a of the main backside oxide film 42. It is set to a predetermined removable time. By performing such etching, as shown in FIG. 5D, only the surface layer portion including the doped layer 42a in the main back surface side oxide film 42 can be removed.
The remaining portion of the main backside oxide film 42 from which the surface layer portion including the doped layer 42a has been removed becomes an autodope preventing film 42b having an autodope suppressing function in a second vapor phase growth step described later. . That is, the auto-dope prevention film 42b of the main back surface side oxide film 42 does not include the doped layer 42a doped with the dopant (does not include a dopant that affects the characteristics of the silicon epitaxial layer 9 to be grown next). Therefore, the dopant is not substantially released during the vapor phase growth, and the auto-dope suppressing function can be suitably achieved.
[0019]
<Second vapor phase growth process>
Next, a p-type silicon epitaxial layer 9 (hereinafter also simply referred to as the epitaxial layer 9) is formed on the main surface of the diffusion wafer 7 by a well-known vapor deposition method, as shown in FIG. In addition, a silicon epitaxial wafer 10 (hereinafter also simply referred to as the epitaxial wafer 10) having a buried diffusion region (that is, the diffusion layer 2a) can be manufactured.
During this vapor phase growth, it is possible to prevent the dopant from being diffused out of the silicon substrate 1 into the vapor phase by the auto-dope preventing film 42b. Therefore, autodoping to the epitaxial layer 9 can be prevented.
[0020]
According to the first embodiment as described above, the main back side formed at the end of the diffusion on the main back side of the diffusion wafer 7 obtained by diffusing the dopant on the main surface side of the silicon epitaxial wafer 3. Of the oxide film 42, the auto-dope prevention film 42 b, which is the remaining part from which the surface layer portion including the doped layer 42 a has been removed, is used for preventing auto-doping, and the silicon epitaxial layer 9 is deposited on the main surface of the diffusion wafer 7. Since the silicon epitaxial wafer 10 is manufactured by phase growth, it is not necessary to newly form an oxide film only for preventing autodoping after diffusion.
Further, the anti-dope preventing film 42 b does not contain a dopant that affects the characteristics of the silicon epitaxial layer 9. Accordingly, by performing vapor phase growth using a part of the oxide film formed in the diffusion process as an auto-doping prevention film 42b for preventing auto-doping, generation of auto-doping in the silicon epitaxial layer 9 is suitably suppressed. can do.
Furthermore, since the surface layer portion of the main back surface side oxide film 42 is removed using buffered hydrofluoric acid, the etching amount can be easily controlled, and only the surface layer portion of the main back surface side oxide film 42 is removed. As a result, the auto-dope preventing film 42b can be left.
In short, according to the present embodiment, the main back side oxide film 42 (a part of the auto dope preventing film 42b) formed on the main back side of the diffusion wafer 7 at the end of diffusion is used for preventing auto dope. It can be suitably applied to.
[0021]
[Second Embodiment]
By the way, if all of the main surface side oxide film 41 is removed by wet etching at once after the diffusion step as in the first embodiment, the etching becomes uneven, and the main surface of the diffusion wafer 7 becomes deep. A step 101 (FIG. 8) having an unspecified shape may be formed at a thickness of about 18 nm. In addition, there is no reproducibility in the formation position of this level | step difference.
In the second embodiment, a method of manufacturing a silicon epitaxial wafer that can prevent the formation of the step in the present invention will be described.
[0022]
Since the second embodiment is the same as the first embodiment except for the points described below, the same components are denoted by the same reference numerals and the description thereof is omitted. .
That is, in the second embodiment, the steps up to the diffusion step (FIG. 4) are performed in the same manner as in the first embodiment.
And after a diffusion process, each process explained below is performed.
[0023]
<Main surface side oxide film removal step>
That is, after the diffusion step, only the surface layer portion of the main surface side oxide film 41 is removed as shown in FIG. Here, the surface layer portion is a portion including at least the doped layer 41b doped with a dopant during diffusion.
In order to remove the surface layer portion, first, as shown in FIG. 7A, a resist 8 is formed on the main back surface of the diffusion wafer 7 to protect the main back surface side oxide film 42 from being etched. Next, wet etching is performed by immersing the diffusion wafer 7 in, for example, buffered hydrofluoric acid. The length of time for this etching is limited to the surface layer portion including the doped layer 41b of the main surface side oxide film 41. It is set to a predetermined removable time. As a result, as shown in FIG. 7B, only the surface layer portion including the doped layer 41b in the main surface side oxide film 41 can be removed.
[0024]
<Surface layer part removal process of main back side oxide film>
Next, as shown in FIG. 7D, only the surface layer portion including the doped layer 42a in the main back surface side oxide film 42 and the remaining portion in the main surface side oxide film 41 are removed at a time.
For this purpose, first, as shown in FIG. 7C, the main back side oxide film 42 is exposed by immersing the diffusion wafer 7 in a resist removal cleaning solution to remove the resist 8. Next, wet etching is performed by immersing the diffusion wafer 7 in, for example, buffered hydrofluoric acid. The length of time for performing this etching is determined based on the remaining main surface side oxide film 41 and main back side oxide film 42. Only the surface layer portion including the doped layer 42a is set to a predetermined time that can be removed at once. By performing such etching, as shown in FIG. 7D, all the remaining main surface side oxide film 41 can be removed and the main back side oxide film 42 can be doped layer 42a. It is possible to form the auto-dope prevention film 42b by removing only the surface layer portion including the.
After that, as in the first embodiment, the epitaxial wafer 10 can be manufactured by forming the epitaxial layer 9 on the main surface of the diffusion wafer 7 (FIG. 6).
[0025]
According to the second embodiment as described above, the same effect as the first embodiment can be obtained, and in the case of the first embodiment, it can be formed on the main surface of the diffusion wafer 7. Generation of a certain level difference can be prevented.
[0026]
More specifically, the method for manufacturing a silicon epitaxial wafer according to the procedure of the first embodiment is a long time for wet etching performed from the state of FIG. 5A to the state of FIG. For example, the main surface side oxide film 41 is completely removed by setting it to 9 minutes, and the time of wet etching with buffered hydrofluoric acid performed from the state of FIG. 5C to the state of FIG. For example, it may be set to 5 minutes, and only the surface layer portion of the main back-side oxide film 42 may be removed by etching. However, in this case, a step having a depth of, for example, about 18 nm is formed on the main surface of the diffusion wafer 7.
On the other hand, the method for manufacturing a silicon epitaxial wafer according to the procedure of the second embodiment is based on the length of time of wet etching with buffered hydrofluoric acid performed from the state of FIG. 7A to the state of FIG. For example, by setting only 5 minutes to remove only the surface layer portion of the main surface side oxide film 41, the length of time of wet etching performed from the state of FIG. 7C to the state of FIG. It is preferable that the remaining main surface side oxide film 41 and only the surface portion of the main back side oxide film 42 be removed by etching after 5 minutes. In this case, it is possible to suitably prevent a step from being formed on the main surface of the diffusion wafer 7 by etching and removing the main surface side oxide film 41 in two stages. It is clarified by the experiment.
Note that the etching rate of the oxide film by the buffered hydrofluoric acid used in this embodiment is about 61 nm / min. Therefore, the length of the wet etching time is appropriately calculated and set based on this etching rate. As a result, only the surface layer portion of each of the oxide films 41 and 42 can be removed.
[0027]
In the above embodiment, the example in which the present invention is applied to the case where the diffusion wafer obtained by performing the position selective diffusion is used has been described. You may do it. In this case, a silicon epitaxial wafer having a buried diffusion region (that is, diffusion layer 2a) on the entire surface can be manufactured.
[0028]
【The invention's effect】
According to the method for producing a silicon epitaxial wafer of the present invention, on the main back surface side of the diffusion wafer, the remaining portion of the main back surface side oxide film formed at the end of the diffusion after removing the surface layer portion is used for auto-doping prevention. Since the silicon epitaxial wafer is manufactured by vapor-phase growth of the silicon epitaxial layer on the main surface of the diffusion wafer, it is necessary to form an oxide film only for preventing auto-doping after the diffusion. There is no.
In addition, the remaining portion of the main backside oxide film from which the surface layer portion has been removed does not release dopants that can affect the characteristics of the silicon epitaxial layer even by heating, so the remaining portion is prevented from being auto-doped. By using this for vapor phase growth, it is possible to suitably suppress the occurrence of autodoping in the silicon epitaxial layer.
That is, in short, a part of the main back surface side oxide film formed on the main back surface side of the diffusion wafer at the end of diffusion can be suitably used for preventing auto-doping.
[Brief description of the drawings]
FIG. 1 is a series of schematic process charts for explaining a first embodiment of a method for producing a silicon epitaxial wafer according to the present invention.
FIG. 2 is a series of schematic process charts for explaining a first embodiment of a method for producing a silicon epitaxial wafer according to the present invention.
FIG. 3 is a series of schematic process charts for explaining a first embodiment of a method for producing a silicon epitaxial wafer according to the present invention.
FIG. 4 is a series of schematic process charts for explaining a first embodiment of a method for producing a silicon epitaxial wafer according to the present invention.
FIG. 5 is a series of schematic process charts for explaining a first embodiment of a method for producing a silicon epitaxial wafer according to the present invention.
FIG. 6 is a series of schematic process charts for explaining the first embodiment of the method for producing a silicon epitaxial wafer according to the present invention.
FIG. 7 is a series of schematic process charts for explaining a second embodiment of the method for producing a silicon epitaxial wafer according to the present invention.
FIG. 8 is a schematic diagram for explaining a step.
[Explanation of symbols]
7 Diffusion wafer 41 Main surface side oxide film 42 Main back surface side oxide film 42a Dope layer (at least part of surface layer portion of main back surface side oxide film)
42b Auto-dope prevention film (remaining part of main back side oxide film with surface layer removed)
9 Silicon epitaxial layer 10 Silicon epitaxial wafer 101 Step

Claims (4)

Of the main back side oxide film formed on the main back side of the diffusion wafer at the end of the diffusion, the remaining part from which the surface layer part has been removed is used for autodoping prevention, and a silicon epitaxial layer is formed on the main surface of the diffusion wafer. A method for producing a silicon epitaxial wafer, characterized in that a silicon epitaxial wafer is produced by vapor phase growth. The method for producing a silicon epitaxial wafer according to claim 1, wherein the removal of the surface layer portion of the main back-side oxide film is performed using buffered hydrofluoric acid. 3. The silicon epitaxial wafer according to claim 1, wherein the diffusion is performed in a position selective manner by performing the diffusion in a state where a pattern opening is formed in a main surface side oxide film of the silicon wafer to be subjected to the diffusion. 4. Manufacturing method. A resist is formed on the main back side oxide film at the stage after the diffusion, and then the main surface side oxide film is formed by immersing the diffusion wafer in buffered hydrofluoric acid and etching with the buffered hydrofluoric acid. And then removing the resist, and then immersing the diffusion wafer in buffered hydrofluoric acid and etching with the buffered hydrofluoric acid, and the remaining portion of the main surface side oxide film, The vapor phase growth is performed by removing only the surface layer portion of the main back-side oxide film at a time and using the remaining portion of the main back-side oxide film for preventing auto-doping. Item 4. A method for producing a silicon epitaxial wafer according to Item 3.

Images