JP2003017428A - Method for diffusing impurity in semiconductor wafer, semiconductor wafer and silicon epitaxial wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for diffusing impurity in a semiconductor wafer by which dispersion of sheet resistance and generation of surface defect can be restrained, even when high concentration impurity diffusion is conducted. SOLUTION: The method for carrying out thermal diffusion of boron as an impurity to a semiconductor wafer has a deposition process for forming a B2 O3 layer on the major surface of a semiconductor wafer and forming a boron diffusion layer by diffusing boron from the B2 O3 layer into a semiconductor wafer surface layer, a wet oxidation process for forming an SiO2 layer, which is sufficiently thick to stop diffusion of boron from a B2 O3 layer to a boron diffusion layer between a B2 O3 layer and a boron diffusion layer through wet oxidation, immediately after the deposition process and a drive-in process which includes a process for carrying out heat treatment in inert gas atmosphere, when a boron diffusion layer is extended by diffusing boron until a boron diffusion layer attains to prescribed resistance and depth.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for diffusing impurities into a semiconductor wafer, a semiconductor wafer and a silicon epitaxial wafer.

[0002]

2. Description of the Related Art A polyboron film (PBF: Tokyo) serving as a coating diffusion source as an impurity source when manufacturing a semiconductor element, for example, impurity diffusion for forming a base region or a buried layer of a bipolar transistor or a photodiode. Oka Kogyo Co., Ltd.) and spin on
A glass (SOG) coating film is used. Here, the PBF or SOG coating film as the coating diffusion source is formed on the semiconductor wafer by the spin coating method and subjected to heat treatment to diffuse the impurities into the surface layer of the semiconductor wafer.

As a method of diffusing impurities into a semiconductor wafer, for example, a method of diffusing boron (boron: B) into a silicon single crystal wafer (hereinafter, simply referred to as a wafer) will be described. Generally, first, a boron compound and a polyhydric alcohol will be described. A coating solution (boron coating solution) in which the reaction product of a compound is dissolved in a solvent is dropped on the main surface of the wafer, and the wafer is rotated to spin the coating solution on the main surface of the wafer by centrifugal force. After being spread over the entire surface, the wafer is placed in a thermal diffusion furnace. Then, as shown in FIG. 5, the boron-containing coating layer on the main surface of the wafer is baked by heat treatment at a constant temperature (for example, 700 ° C.) in an atmosphere of nitrogen (N ₂ ) and trace oxygen (O ₂ ). And boron oxide (B
₂ O ₃ ) layer is formed (firing step). Next, after purging the inside of the thermal diffusion furnace under a nitrogen atmosphere, the temperature is raised to a constant temperature (for example, 9
70 ° C.), boron is diffused from the B ₂ O ₃ layer to the wafer surface layer to form a boron diffusion layer (so-called deposition step). At this time, the B ₂ O ₃ layer reacts with the wafer to form a boron silicide layer (Si _x + B _y ) on the wafer.
And a boron silicate glass layer (B ₂ O ₃ + SiO ₂ ) is formed.

Then, after purging the inside of the thermal diffusion furnace with oxygen, the temperature of the thermal diffusion furnace is raised to a predetermined temperature (1050 to 1200 ° C.) while oxidizing the boron silicate glass layer in an oxygen atmosphere, and the boron diffusion layer is removed. Boron is diffused deeper into the wafer to extend the boron and form a diffusion layer (so-called drive-in process). Here, the drive-in process is performed in an oxygen atmosphere because the sheet resistance of the wafer (ρs)
And for adjusting the diffusion depth (Xj). Then, the temperature is lowered to 700 ° C. in a nitrogen atmosphere and the wafer is taken out from the thermal diffusion furnace. The coating liquid is, for example, PBF or the like.

As described above, boron can be diffused in the semiconductor wafer. In the above description, the case where PBF is used as the impurity source is described, but the impurity diffusion can be similarly performed when using SOG. In the case of SOG, impurities other than boron impurities, such as phosphorus (P) or arsenic (As) impurities, can be similarly diffused into the semiconductor wafer.

As a diffusion method other than the above-mentioned coating diffusion method, for example, there is a BN method, which is used on a boat for thermal diffusion.
Wafers are arranged on both sides of the (boron nitride) thin plate, and B ₂ O ₃ generated on the surface of the BN thin plate by firing is scattered on the substrate to form a boron diffusion layer (see FIG. 5, so-called deposition step). In this deposition process, a boron silicide layer and a boron silicate glass layer are formed on the wafer. After that, heat treatment is performed in which the boron, which has been shallowly diffused in the wafer in the deposition step, is diffused deeper in the wafer to expand the boron and form a diffusion layer (FIG. 5).
Reference, so-called drive-in process) is performed.

[0007]

However, the above-mentioned conventional technique, in particular, the deposition process and the drive-in process are performed once after the wafer is put into the heat treatment furnace (thermal diffusion furnace) and then taken out. When the process is performed, it is difficult to suppress the variation in the sheet resistance of the impurity diffusion layer in which impurities such as boron are diffused in the wafer. For example, the boron concentration is about 10 ¹⁸ / cm ³ and the depth is 3 μm.
If an attempt is made to form an impurity diffusion layer of a certain degree, the sheet resistance of the impurity diffusion layer will be about 140 Ω / □, but in the above technique, the variation of the sheet resistance of the impurity diffusion layer is 5 when 3σ.
It was difficult to keep the percentage below.

Further, according to the conventional method, when high-concentration boron diffusion is performed on a wafer, particularly when a p-type (boron-doped) wafer (resistance 20 to 40 Ωcm) is used, bright spots or stacked layers are formed after growing an epitaxial silicon layer. There is a problem that defects (SF: Stacking Fault) frequently occur particularly in a region of about 1 to 5 cm from the peripheral portion of the wafer. If surface defects such as bright spots or SFs occur on the surface of the silicon epitaxial wafer, the device characteristics are directly adversely affected, which is not preferable.

An object of the present invention is to provide a method of diffusing impurities into a semiconductor wafer capable of suppressing the variation of sheet resistance and the generation of surface defects even when performing high-concentration impurity diffusion, even for large-diameter wafers. It is to provide a high quality epitaxial wafer.

[0010]

Means for Solving the Problems The inventors of the present invention have made extensive studies in order to solve the problem of reducing the variation in the sheet resistance of an impurity diffusion layer such as boron. Then, in the oxidation step after boron deposition, the boron silicate glass layer is oxidized, but an oxide film grows at the interface between the boron silicate glass layer and the boron diffusion layer, and the boron diffusion from the boron silicate glass layer to the wafer. By the time the oxide film thickness is enough to stop the oxide film, there are pinholes, weak spots, etc. in the formed oxide film, and these serve as diffusion passages, and boron diffusion to the wafer continues partially. Therefore, I suspect that the sheet resistance may vary. Then, as a result of diligent research by paying attention to the oxidation step after the deposition of boron, it was found that the variation in the sheet resistance depends on the oxidation condition after the impurities are deposited, and the present invention was completed.

That is, the method of diffusing impurities into a semiconductor wafer according to the present invention is a method of diffusing impurities into a semiconductor wafer, wherein a glass layer containing impurities is formed on the main surface of the semiconductor wafer, and the glass layer is removed from the glass layer. An impurity diffusion layer forming step of forming an impurity diffusion layer by diffusing impurities into the surface layer of the semiconductor wafer, and a diffusion stopper for the impurity between the glass layer and the impurity diffusion layer immediately after the impurity diffusion layer forming step. And an oxide layer forming step of forming an oxide layer by wet oxidation.

According to this method, immediately after the impurity diffusion layer forming step as the deposition step, an oxide layer is rapidly formed between the impurity-containing glass layer and the semiconductor wafer by wet oxidation, and the impurity-containing glass layer is removed. Since it is possible to quickly stop the diffusion of impurities into the semiconductor wafer, it is possible to suppress variations in sheet resistance.
Here, the wet oxidation means to oxidize by including water vapor in an oxygen atmosphere, and hydrogen (H ₂ ) in an oxygen atmosphere is used.
And burn at the same time (also called burning oxidation)
There is a method or a method of bubbling dry oxygen into warm pure water (also called bubbling oxidation).

The inventors of the present invention have made extensive studies in order to solve the problem of suppressing the generation of bright spots or SF on the surface of an epitaxial wafer. Then, the boron-diffused wafer was subjected to selective chemical etching and observed by an optical microscope. As a result, OSF (oxidation-induced stacking fault: Oxid)
ation-induced Stacking Fault) was observed. Furthermore, in order to examine the depth direction distribution of the OSF in the wafer, when the inside of the wafer was observed by performing angle polishing for polishing the wafer surface at a predetermined angle,
At least up to a depth of 200 μm from the surface, even in the bulk region, the O was observed so as to correspond to the position of the OSF observed on the surface.
SF or precipitate was observed.

The term "precipitate" as used herein means an oxygen precipitate, and the oxygen precipitate nuclei introduced during the growth of a silicon single crystal grow through a heat treatment step. The OSF means a wafer at 900 ° C. to 1200 ° C.
Defects that easily occur on the wafer surface when oxidized in the temperature range of ℃, and these nuclei are grown by using mechanical damage on the wafer surface, impurities such as metal, oxygen precipitates such as SiO ₂ as nuclei. It is known. However, although the cause of the OSF generated here is not clear,
It is presumed that these OSFs are also generated on the corresponding surface in a region where OSFs and precipitates are likely to occur frequently in the bulk region, and the cause thereof is due to the oxidizing atmosphere. It was thought that the growth of the. Then, as a result of earnest research based on these assumptions, it was found that the growth of the OSF or the precipitate can be suppressed by shortening the heat treatment in the oxidizing atmosphere for a short time, and the present invention was completed.

Therefore, according to another semiconductor wafer of the present invention,
The impurity diffusion method uses boron as an impurity in the semiconductor wafer.
On the main surface of the semiconductor wafer.
To B ₂O₃Layer (impurity-containing glass layer) is formed, and B₂O₃layer
Diffuses boron from the surface to the surface of the semiconductor wafer
Deposition process for forming a diffusion layer and the deposition process
Soon after, B₂O₃Between the layer and the boron diffusion layer, B₂O₃layer
From the thickness of the boron diffusion layer to stop the diffusion of boron
SiO₂Wet Acid Forming Layer (Oxide Layer) by Wet Oxidation
Process and until the boron diffusion layer reaches the desired resistance and depth
When diffusing boron and stretching the boron diffusion layer,
Drive-in including heat treatment in an active gas atmosphere
And a process.

According to this impurity diffusion method, as described above, since the oxide film which can stop the boron diffusion is rapidly formed by the wet oxidation in the wet oxidation step immediately after the deposition step, the variation in the sheet resistance is reduced. it can. Furthermore, since the drive-in process includes a heat treatment process in an inert gas atmosphere, it is possible to suppress the growth of OSFs and precipitates, and prevent defects such as OSFs and precipitates generated on the wafer surface where impurities, especially boron are diffused. can do. Further, since defects such as OSF and precipitates do not occur on the wafer surface, even if an epitaxial silicon layer is grown on such a wafer, generation of surface defects such as bright spots or SF on the epitaxial silicon surface is suppressed. can do.

Furthermore, since the wet oxidation step is performed immediately after the deposition step, a SiO ₂ layer having a thickness capable of stopping the diffusion of boron from the B ₂ O ₃ layer to the boron diffusion layer is rapidly formed by the wet oxidation. The processing time in the oxidizing atmosphere can be shortened as compared with the conventional process. Further, the timing of switching to the inert gas atmosphere in the drive-in step, which is the next step, can be made earlier than in the conventional case. Here, the B ₂ O ₃ layer is not limited to those formed with only B ₂ O _3, also comprising B ₂ O ₃ and boron silicate glass layer formed by the SiO _2.

For the inert gas atmosphere in the drive-in step, any one of nitrogen, argon and helium or a mixture thereof can be used, and nitrogen is more preferable.

Further, the semiconductor wafer of the present invention is characterized in that it is obtained by diffusing boron by the above-mentioned method for diffusing impurities into the semiconductor wafer. After the boron diffusion, defects such as OSF and precipitates are formed on the wafer surface. It is a semiconductor wafer with almost no generation.

The silicon epitaxial wafer of the present invention is characterized in that it is obtained by forming a silicon epitaxial layer on a semiconductor wafer obtained by diffusing impurities into the above-mentioned semiconductor wafer, particularly by diffusing boron by a boron diffusion method. I am trying. That is, since a semiconductor wafer having almost no defects such as OSF and precipitates generated on the wafer surface after boron diffusion is used, the silicon epitaxial wafer has almost no defects such as bright spots or SF on the surface of the silicon epitaxial layer.

Another silicon epitaxial wafer of the present invention is a silicon epitaxial wafer obtained by forming a silicon epitaxial layer on a semiconductor wafer in which boron is diffused, and the silicon epitaxial layer has a stacking fault density of 10 pieces. / Cm ² or less.

Since the semiconductor wafer in which impurities are diffused by the impurity diffusion method of the present invention has almost no defects such as OSF and precipitates, even if an epitaxial layer is formed on the semiconductor wafer, it is possible to reduce Through 5
In the area of cm, stacking faults (SF) are hardly generated, and the density is 10 / cm ² or less,
More preferably, the number of epitaxial wafers is 5 / cm ² or less.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to these. First, the first embodiment of the present invention will be described. FIG. 1 is a front sectional view showing a thermal diffusion furnace used in a boron diffusion method according to the present invention, and FIG. 2 is a series of process drawings for explaining the impurity diffusion method according to the present invention. FIG. 4 is a diagram for explaining temperature and atmosphere in each step of the impurity diffusion method according to the first embodiment. In this embodiment, a p-type (boron-doped) silicon wafer is used as the wafer.
The resistance of this wafer is 20-40 Ωcm. Figure 1
Nitrogen, oxygen, and hydrogen are laterally supplied to the horizontal thermal diffusion furnace 3 shown in FIG. The loading and unloading of the wafer 1 into and from the thermal diffusion furnace 3 is performed by opening the lid 4.

In order to diffuse boron into the wafer 1, first, as shown in FIG. 2 (a), a coating solution (PB containing a reaction product of a boron compound and a polyhydric alcohol and a solvent) is used.
F) 11 is dropped on the main surface of the wafer 1. And
The wafer 1 is put into a spinner device and rotated parallel to the plate surface direction, and the coating liquid 11 on the main surface of the wafer 1 is evenly spread over the entire main surface of the wafer 1 by a centrifugal force (coating step) (FIG. 2). (B)). The wafer 1 on which the PBF 11 has been spread is placed on the boat 2 and placed in the thermal diffusion furnace 3 shown in FIG. Then, after closing the lid 4, the wafer 1 is subjected to heat treatment continuously in the order shown in FIG.

First, in the baking step, the PBF1 coated on the main surface of the wafer 1 is formed at a predetermined temperature and in the presence of oxygen.
Hydrogen (H) and carbon (C) of the PBF 11 are burnt and removed by firing 1 to form the B ₂ O ₃ layer 12 on the main surface of the wafer 1 (FIG. 2C). Here, if the oxygen concentration is high, the main surface of the wafer 1 is roughened, so nitrogen is also supplied, and for example, an atmosphere of 95% N ₂ + 5% O ₂ is used. The temperature condition in the firing step is, for example, 450 to
The temperature is 800 ° C., more specifically 700 ° C., and the treatment time is, for example, 10 minutes to several hours.

Next, after purging in a nitrogen atmosphere, for example, 9
After the temperature is raised to 50 ° C., in the deposition step (impurity diffusion layer forming step), the temperature is kept at 950 ° C. for a predetermined time, for example, 10 minutes to 2 hours in a nitrogen atmosphere. In this step, first, the boron in the B ₂ O ₃ layer 12 is shallowly diffused to the surface layer of the wafer 1 to form the high-concentration boron diffusion layer 13, and the B ₂ O ₃ layer 12 and the silicon of the wafer 1 are separated from each other. The boron silicate glass layer 14 is formed by the reaction. A predetermined amount of boron is diffused from the boron silicate glass layer 14 to the high-concentration boron diffusion layer 13 of the wafer 1. Also,
High-concentration boron diffusion layer 13 and boron silicate glass layer 1
4, a boron silicide layer (also known as boron rich layer (BRL)) 15 containing boron at a high concentration is formed (FIG. 2 (d)).

The diffusion of boron depends on temperature and time,
Here, the temperature is mainly controlled, and the boron concentration of the high-concentration boron diffusion layer, that is, the sheet resistance is controlled by the temperature of the deposition process. That is, by increasing the temperature, the boron concentration increases and the sheet resistance decreases,
Conversely, if the temperature is lowered, the sheet resistance will increase. The temperature of the deposition process can be changed within the range of 850 to 1050 ° C.

Then, as shown in FIG. 3, immediately after the deposition step, the wet oxidation step (oxide layer forming step) is started from the time when the gas atmosphere is oxygen and hydrogen. In this step, the temperature is kept at the same temperature as in the deposition step for a predetermined time to make a wet oxidizing atmosphere. Therefore, the boron silicide layer 15 is quickly burned and serves as a diffusion stopper.
An oxide film 16 (oxide layer) of (SiO ₂ ) is rapidly formed (FIG. 2E).

Here, the reason why the SiO ₂ oxide film 16 is rapidly formed by wet oxidation will be described. When only dry oxygen is supplied into the thermal diffusion furnace 3 in the wet oxidation step, oxygen passes through the boron silicate glass layer 14, reacts with the boron silicide layer 15, and the boron silicate glass layer 1
4 and the boron silicide layer 15 between the SiO ₂ oxide film 1
6 is formed. The SiO ₂ oxide film 16 was considered to have a sealing function of preventing boron from diffusing into the wafer 1. However, when the oxide film serving as a diffusion stopper is thin, it includes pinholes, weak spots, etc. Diffusion was proceeding. In other words, it takes time only with dry oxygen to obtain the thickness of the SiO ₂ layer that stops the progress of boron diffusion and the thickness that fills the pinholes, weak spots, etc., and causes the variation in the sheet resistance. It was. Therefore, the predetermined high-concentration boron diffusion layer 1
3 is formed, and immediately after the deposition process for making the sheet resistance of the wafer 1 within a predetermined range is completed, not only oxygen but also hydrogen is supplied in the wet oxidation process to burn the oxygen and the oxygen containing water vapor. By supplying it, it is possible to quickly obtain a thickness of the SiO ₂ layer that just stops the progress of boron diffusion.

Therefore, the SiO film rapidly formed thick between the boron silicate glass layer 14 and the boron diffusion layer 13.
_Since the diffusion of boron from the boron silicate glass layer 14 to the boron diffusion layer 13 is stopped by the ₂ oxide film 16, and boron having a required concentration or more does not diffuse to the boron diffusion layer 13,
Variation in sheet resistance of the diffusion layer can also be suppressed.
The wet oxidation time in the wet oxidation step is at least 10
It is sufficient if the length is maintained, but it may be shorter than 10 minutes if the SiO ₂ oxide film 16 having a required thickness is formed.

Then, after the SiO ₂ oxide film 16 having a thickness necessary to stop the diffusion of boron from the boron silicate glass layer 14 to the boron diffusion layer 13 is formed, after purging in an oxygen atmosphere, a predetermined amount is formed. Temperature, eg 1150 ° C
The temperature is raised to 1050 ° C. to 1200 ° C. (changeable), the drive-in process is started, and the atmosphere is switched to nitrogen. In addition, since the surface of the wafer 1 is easily attacked by the inert gas and surface roughening occurs at the beginning of the temperature rising and the drive-in process (about 10 minutes to 30 minutes), it should be performed in an oxidizing atmosphere. preferable.

In the drive-in process, under a nitrogen atmosphere,
Boron is further diffused from the boron diffusion layer 13 to the wafer 1 to extend the boron diffusion layer 13 to form a boron diffusion layer 17 having a predetermined resistance and depth (FIG. 2).
(F)). By performing a part of the drive-in process, which was conventionally performed in an oxidizing atmosphere, in a nitrogen atmosphere, the heat treatment time in the oxidizing atmosphere is shortened, and the OS in the bulk region is reduced.
OSF near the surface by suppressing the growth of F or precipitates
It is possible to prevent the growth of precipitates. The processing time of the drive-in step depends on the desired resistance and depth of the boron diffusion layer 17, but is preferably 10 minutes to several hours.

The drive-in process under the nitrogen atmosphere shortens the time of the oxygen atmosphere, so that the incorporation of boron into the oxide film 16 due to segregation is reduced and the sheet resistance of the wafer 1 is lowered, but as described above. Moreover, it is possible to increase the sheet resistance by lowering the temperature of the deposition process.

Although the conventional drive-in process includes a process of burning and burning by flowing oxygen and hydrogen for burning, a pattern is formed in a later process when the base region and the buried layer of the bipolar transistor are formed. There is a photolithography process for performing alignment, and in order to make the pattern easy to see in that process, a step is formed at the boundary between the diffused region and the non-diffused region.

After the drive-in process is completed, the temperature is lowered to 700 ° C. in the nitrogen atmosphere, and the wafer 1 is taken out from the thermal diffusion furnace 3. By subjecting the wafer 1 after the heat treatment to hydrofluoric acid treatment, the boron silicate glass layer 14 and the SiO ₂ oxide film 16 are removed, and the wafer 1 having the boron diffusion layer 17 is obtained (FIG. 2G).

A known silicon epitaxial growth is performed on the wafer 1 obtained as described above to form an epitaxial layer, whereby a silicon epitaxial wafer is obtained.

In addition, since almost no defects such as OSF and precipitates are generated in the wafer 1 obtained by diffusing boron obtained as described above, an epitaxial layer is formed on the main surface of the wafer 1. However, the stacking fault (S
F) is hardly generated and its density is 10 pieces / c
m ² or less. Also, in a more preferable state, 5 pieces / c
It is less than m ² .

FIG. 4 is a diagram for explaining the temperature and atmosphere in each step of the impurity diffusion method according to the second embodiment of the present invention. In the present embodiment, the temperature is raised to 960 ° C. in the deposition process, and oxygen is supplied through the drive-in process, and the drive-in process includes burning oxidation. In addition, as in the first embodiment, a wet oxidation process is performed immediately after the deposition process to remove SiO 2.
_{The second} oxide film 16 is rapidly formed by wet oxidation. Others are almost the same as those in the first embodiment, and therefore will not be described in detail.

According to the impurity diffusion method of the second embodiment, since the wet oxidation process is performed immediately after the deposition process as in the first embodiment, it is possible to suppress variations in sheet resistance.

In the present invention, when the base region and the buried layer of the bipolar transistor are formed, the temperature is raised to a predetermined temperature for drive-in diffusion, and then the heat treatment is performed in the oxygen atmosphere in the drive-in process. Although it is possible to include a burning oxidation step as in the second embodiment described above, the effect of the present invention remains unchanged. Also, when forming a photodiode,
Since the impurity diffusion layer is formed on the entire surface of the wafer, it is not necessary to perform pattern matching in a later step, and the burning oxidation step in the drive-in step is unnecessary as in the first embodiment.

[0041]

EXAMPLE A boron-doped p-type wafer is used as the silicon single crystal wafer 1. The wafer 1 has a plane orientation of <100>, a diameter of 5 inches (about 12.7 cm), and a resistance of 20 to 40 Ωcm. Coating liquid containing boron 1
PBF is used as 1.

(Example 1) First, PBF11 was applied on the main surface of the wafer 1 by spin coating to form PBF.
The coating layer 11 was formed. Then, the wafer 1 on which the PBF coating layer 11 is formed is placed upright on the quartz boat 2,
It was carried into the horizontal thermal diffusion furnace 3 shown in FIG. 1, which was kept at 700 ° C. Then, in a 95% N ₂ + 5% O ₂ atmosphere, the temperature was maintained at 700 ° C., and a baking process was performed for 45 minutes to form a B ₂ O ₃ layer 12. Then, nitrogen purge is performed for 15 minutes, and the heat diffusion furnace 3
The oxygen inside was exhausted.

Next, the temperature is kept at 700 ° C. in the nitrogen atmosphere.
To 960 ° C. and held at 960 ° C. for 30 minutes to perform the deposition process. Immediately thereafter, as a wet oxidation step, hydrogen was supplied together with oxygen for 15 minutes to perform combustion, then supply of hydrogen was stopped, purging was performed for 15 minutes in an oxygen atmosphere, and then the temperature was raised to 1150 ° C., followed by a drive-in step. For 30 minutes in an oxygen atmosphere, then 4
Burning oxidation was carried out by simultaneously supplying hydrogen and oxygen for 0 minutes. Then, the atmosphere was switched to a nitrogen atmosphere, the temperature was lowered to 700 ° C., the wafer 1 on the quartz boat 2 was carried out, and the sheet resistance was measured.

Regarding the sheet resistance, it is 49 in the wafer plane.
The points were measured in a grid pattern to obtain the variation 3σ. The target sheet resistance was 135Ω / □, which was almost the target. Further, 3 [sigma] is between 2.0 and 3.0, which is within a desired range. Therefore, it is understood that the variation in sheet resistance can be suppressed by performing the wet oxidation step immediately after the deposition step, and the variation in sheet resistance can be set within a target range.

(Embodiment 2) As in Embodiment 1, PBF11
The coating and baking steps are performed, and after purging in a nitrogen atmosphere, the temperature is raised from 700 ° C. to 950 ° C.
The deposition process was performed by holding at 30 ° C. for 30 minutes. Then, as a wet oxidation process, hydrogen and nitrogen are added together with oxygen.
It is supplied for 1 minute to perform combustion, and then the supply of hydrogen and nitrogen is stopped and an oxygen atmosphere is purged.
After the temperature was raised to 150 ° C., an oxygen atmosphere was kept for 30 minutes as a drive-in step, and then the atmosphere was changed to a nitrogen atmosphere and kept for 1 hour. Then, the temperature was lowered to 700 ° C. in a nitrogen atmosphere, the wafer 1 on the quartz boat 2 was carried out, and a hydrofluoric acid treatment was performed.

When the wafer 1 thus obtained was subjected to selective chemical etching (2 minutes) and the surface was observed with an optical microscope, OSF was not detected at all. In addition, when performing angle polishing and observing the inside, the wafer 1
OSF and precipitates were observed at a position deeper than 40 μm from the surface of the outer peripheral portion, but OSF and precipitates were not observed at a depth of about 40 μm from the surface. Further, the sheet resistance is 80 to 110 Ω / □, the depth of the boron diffusion layer 17 is 3 to 4 μm, the sheet resistance of the obtained wafer 1 is ρs 90 to 94 Ω / □, and the depth of the boron diffusion layer 17 is It was within a desired range of 3 to 4 μm.

As described above, it can be understood that the generation of the OSF and the precipitate in the vicinity of the surface can be suppressed by setting a part of the drive-in process in the nitrogen atmosphere. Further, it is expected that the nitrogen atmosphere will lower the sheet resistance as compared with the case of the oxidizing atmosphere, but by lowering the temperature of the deposition step, it can be within the target range.

(Embodiment 3) On the wafer 1 in which boron is diffused under the above-mentioned conditions, silicon epitaxial growth of 15 μm thickness is performed at 1090 ° C. to form an epitaxial layer, and selective chemical etching is performed to observe the surface with an optical microscope. , SF density of this epitaxial wafer is 0 /
It was cm ² . Therefore, it is understood that the formation of SF can be suppressed by forming the epitaxial layer on the semiconductor wafer of the present invention.

[0049]

[Comparative Example] (Comparative Example 1) Boron diffusion was performed under the same conditions as in Example 1 except that the heat treatment was performed only with oxygen without supplying hydrogen immediately after the deposition step, and the sheet resistance was measured. The target sheet resistance was 135 Ω / □, which was almost the same as the target as in Example 1, but 3σ varied between about 4.9 and 7.3.

Comparative Example 2 700 ° C. in the deposition process
To 970 ° C. and boron diffusion was performed under the same conditions as in Example 2 except that oxygen was supplied through the drive-in process to create an oxygen atmosphere. When the obtained wafer is subjected to selective chemical etching (2 minutes) and the surface is observed with an optical microscope,
10 to 100 OSFs / precipitates / cm ^{2 were} detected over the entire circumference in a region of about 1 to 5 cm from the peripheral portion of the wafer. When angle polishing was performed and the inside was observed, OSF and precipitates were observed from the surface to the inside at a depth of at least 200 μm. On the other hand, the sheet resistance is 80 to 110Ω / □, and the depth of the boron diffusion layer 17 is 3 to 4
μm is the target, and the sheet resistance of the obtained wafer is ρ
s80 to 110Ω / □, the depth of the boron diffusion layer 17 is 3 to
It was within a desired range of 4 μm.

(Comparative Example 3) A boron-diffused wafer was subjected to epitaxial growth under the conditions of Comparative Example 2 at 1090 ° C to a thickness of 15 µm to form an epitaxial layer, and selective chemical etching was performed to observe the surface with an optical microscope. Then,
The SF density of this epitaxial wafer was about 3000 pieces / cm ² .

The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, has substantially the same configuration as the technical idea described in the scope of the claims of the present invention, and has any similar effect to the present invention. It is included in the technical scope of the invention.

For example, although the case of the spin coating method has been described in the above embodiment, the present invention is not limited to this and may be applied to a known boron diffusion method such as the BN method. In addition, although the heat treatment processes of deposition, wet oxidation and drive-in are performed continuously in one thermal diffusion furnace, the heat treatment processes of deposition / wet oxidation and drive-in are performed in different thermal diffusion furnaces. May be. Furthermore, wafers with relatively low sheet resistance (ρs 80 to 110, 135
We have described the case of diffusing high-concentration boron to obtain Ω / □), but not limited to this, not only for wafers with lower sheet resistance but also for diffusing boron to obtain wafers with higher sheet resistance. The present invention can also be applied to the case.

[0054]

According to the method of diffusing impurities into a semiconductor wafer according to the present invention, an oxide film layer serving as a stopper of a diffusion source is promptly formed by wet oxidation immediately after a deposition process, which causes variations in sheet resistance. Can be suppressed. Further, the growth of the OSF or the precipitate of the semiconductor wafer can be suppressed by setting a part of the drive-in process to an inert gas atmosphere. Therefore, it is possible to suppress the variation in the sheet resistance of the impurity diffusion layer, prevent the occurrence of defects such as OSF and precipitates on the surface of the semiconductor wafer, and further, after the epitaxial silicon layer is grown, bright spots or It is possible to prevent defects such as SF from occurring.

[Brief description of drawings]

FIG. 1 is a front sectional view showing a thermal diffusion furnace used in a boron diffusion method according to the present invention.

FIG. 2 is a series of process drawings for explaining a boron diffusion method according to the present invention.

FIG. 3 is a diagram for explaining temperature and atmosphere in each step of the boron diffusion method according to the first embodiment of the present invention.

FIG. 4 is a diagram for explaining temperature and atmosphere in each step of the boron diffusion method according to the second embodiment of the present invention.

FIG. 5 is a diagram for explaining temperature and atmosphere in each step of a conventional boron diffusion method.

[Explanation of symbols]

1 wafer (silicon single crystal wafer) 2 boat 3 thermal diffusion furnace 4 lid 11 coating solution 12 B ₂ O ₃ layer 13 boron diffusion layer 14 boron silicate glass layer 15 boron silicide layer 16 SiO ₂ oxide film 17 boron diffusion layer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shoichi Fujiya             2-13-1, Isobe, Annaka-shi, Gunma Shinetsuhan             Conductor Co., Ltd. Isobe factory

Claims (6)

[Claims] 1. A method of diffusing impurities into a semiconductor wafer, comprising forming a glass layer containing impurities on a main surface of a semiconductor wafer, diffusing the impurities from the glass layer to a surface layer of the semiconductor wafer, and diffusing the impurities. Forming an impurity diffusion layer, and forming an oxide layer between the glass layer and the impurity diffusion layer by wet oxidation immediately after the impurity diffusion layer formation step by wet oxidation. A method for diffusing impurities into a semiconductor wafer, comprising: 2. A method of diffusing boron into semiconductor wafers as impurities, to form a B ₂ O ₃ layer on the main surface of the semiconductor wafer, B ₂ O ₃
Deposition step of diffusing boron from the layer to the surface layer of the semiconductor wafer to form a boron diffusion layer, and immediately after the deposition step, between the B ₂ O ₃ layer and the boron diffusion layer, the boron from the B ₂ O ₃ layer is formed. A wet oxidation step of forming a SiO ₂ layer having a thickness that can stop the diffusion of boron into the diffusion layer by wet oxidation, and diffusing boron until the boron diffusion layer has a predetermined resistance and depth to extend the boron diffusion layer. At this time, a drive-in step including a step of performing a heat treatment in an inert gas atmosphere, and a method for diffusing impurities into a semiconductor wafer. 3. The impurity diffusion into the semiconductor wafer according to claim 2, wherein any one of nitrogen, argon, helium, or a mixture thereof is used for the inert gas atmosphere in the drive-in step. Method. 4. A semiconductor wafer obtained by diffusing impurities by the method for diffusing impurities into a semiconductor wafer according to claim 1. Description: 5. A silicon epitaxial wafer obtained by forming a silicon epitaxial layer on the main surface of the semiconductor wafer according to claim 4. 6. A silicon epitaxial wafer obtained by forming a silicon epitaxial layer on a main surface of a semiconductor wafer having boron diffused therein, wherein the stacking fault density of the silicon epitaxial layer is 10 / cm ² or less. A silicon epitaxial wafer characterized by being present.