JPH0277118A - Diffusion of boron into semiconductor wafer - Google Patents

Abstract

PURPOSE:To remarkably improve the irregularity of sheet resistance (rhos) of a silicon wafer surface by using thermal decomposition boron nitride (PBN) as a boron diffusion source, and injecting H2 and/or H2O in a diffusion tube. CONSTITUTION:When boron is diffused by using PBN as a diffusion source, HBO2 is formed on a PBN wafer surface by introducing hydrogen and/or water, and boron is diffused in a silicon wafer 8 by said HBO2. As a result, boron is uniformly diffused in the silicon wafer surface with high density by the effect of HBO2 of high vapor pressure. Hence, the irregularity of sheet resistance (rhos) of the silicon wafer surface can be remarkably improved; dislocation and lattice defect of crystal, which are considered to be caused by metal impurity, carbon, etc., can be reduced by using PBN as a diffusion source; since baking binder is not used, the deformation and sagging of dopant are not caused, and further the fusion bonding of a quartz boat maintaining the dopant does not occur.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for uniformly diffusing boron into a semiconductor wafer.

(Prior art) As a method of diffusing boron into a semiconductor wafer, for example, a silicon wafer, boron nitride (BN) powder is solidified and sintered, formed into a wafer-shaped disk, and the BN sintered body is diffused. Oxidize the source to B20° 28N + 3/202 →
Bt03+Nz), this B! A method of diffusing 03 into semiconductor wafers is well known (Japanese Patent Publication No. 43-2
8722). The diffusion source (dopant) of boron nitride is the main raw material, boron nitride powder, mixed with impurities such as sodium phosphate, sodium oxide, iron oxide, calcium oxide, or carbon, which are derived from the manufacturing method. In addition, since boric anhydride, calcium oxide, aluminum oxide, sodium oxide, aluminum phosphate, silicon dioxide, etc. are used as sintered binders for making this boron nitride powder into a sintered body, these sintered binders are used in the boron nitride dopant. remains. If pyrolytic boron nitride (PBN) is used as a diffusion source instead of this boron nitride sintered body (BN),
A proposal has already been made to eliminate the effects of the above-mentioned impurities and sintered binder (Japanese Patent Laid-Open No. 1010-1989
Publication No. 26. ) On the other hand, when boron nitride is used as a diffusion source,
HB on the surface of the BN wafer by introducing hydrogen
A known method is to form O□ and diffuse boron into a silicon wafer using this HBOz (Dr.
Jay Stack et al., Electrochemical Society,
147th Meeting, Toronto, Canada, 1975
(Announced on May 16, 2017).

According to this method, the vapor pressure is Btus and HBO.

There is a difference of more than 10,000 times at 925'C, and it is far superior to B2O3 as a boron diffusion method. A high vapor pressure means that a highly concentrated atmosphere can be obtained at the same temperature, and as a result, it has the effect of being able to diffuse uniformly at a high concentration on the silicon wafer surface. Furthermore, this IIi direction remains the same even when the temperature is changed, so it is possible to diffuse it even at low temperatures, and the effect is even greater.However, even with this method of introducing hydrogen, ordinary boron nitride sintering If a body is used, volatile low oxides are formed from the contained impurities due to this reducing component,
To silicon way for this? As a result of experiments, it was found that there is a drawback that y staining is enhanced.

(Problem B to be Solved by the Invention) The present invention was invented in view of the above-mentioned prior art, and it significantly improves the variation in sheet resistance (ρS) on the surface of a silicon wafer, and The object of the present invention is to provide a method for diffusing boron into semiconductor wafers that eliminates problems caused by metal impurities, carbon, etc., and inconveniences caused by sintered binders.

(Means for Solving the Problems) In order to achieve the above object, in the method of the present invention, a large number of semiconductor wafers and a boron diffusion source are installed in a diffusion tube, maintained in an inert atmosphere and a high temperature state, and boron is applied to the semiconductor wafers. In this method, pyrolytic boron nitride (PBN) is used as a boron diffusion source, and I (□ and/or
Alternatively, H2O is injected.

Pyrolytic boron nitride (PBN) is disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 62-1
As described in Japanese Patent No. 01026, it is economical and advantageous to use a material produced by a vapor phase growth reaction using inexpensive and highly pure boron trichloride and ammonia.

The boron diffusion (doping) method is generally as follows. That is, PBN is formed into a wafer shape with approximately the same diameter as a semiconductor wafer, and only the surface is oxidized with oxygen or water vapor, and then placed alternately with the semiconductor wafer in a quartz tube, and then heated with a non-oxidizing gas such as nitrogen or argon. , in a mixed atmosphere of helium and an oxidizing gas, such as oxygen, at 70%
After processing at a temperature of about 0 to 1300°C and introducing a trace amount of hydrogen and/or water during the treatment, it is then heated at the same temperature in an atmosphere containing only non-oxidizing gas (nitrogen, argon, helium, etc.). A method of processing is taken.

(Function) In the method of the present invention, when boron is diffused using PBN as a diffusion source, hydrogen and/or water is introduced.
HBO is formed on the surface of the BN wafer, and this HB
Boron is diffused into the silicon wafer using Oz. Therefore, in the method of the present invention, H with high vapor pressure
Since boron is diffused uniformly at a high concentration on the silicon wafer surface using BO, it is possible to significantly improve the variation in sheet resistance (ρS) on the silicon wafer surface. This reduces dislocations and crystal lattice defects that are thought to be caused by metal impurities, carbon, etc. Furthermore, since a sintered binder is not used, it is possible to reduce the binder specific to sintered compact dopants, which is often a problem in the diffusion process. Distortion and blurring of the dopant due to melting can be eliminated, and fusion with the quartz boat holding the dopant can be prevented.

In addition, PBN can be made pure and does not contain substantially any impurities, so when it is used in an atmosphere containing hydrogen or water vapor, undesirable impurities other than boron can be vaporized by reducing components and silicon wafers can be heated. Upward precipitation and diffusion can be kept sufficiently low.

Furthermore, when conventional boron nitride sintered bodies are used in an atmosphere containing reducing components such as hydrogen or water vapor, the boron concentration in the vaporized atmosphere is often unstable, resulting in a stable level of boron diffusion from batch to batch. However, this problem was solved by using PBN, and it became possible to reduce the batch-to-batch variation in sheet resistance on the silicon wafer surface to 10% or less. The reason for this is that sintered bodies have grain boundaries with large gaps, and especially when an atmosphere containing H2 or water vapor is used, these gaps become larger, causing surface oxidation of the sintered bodies from batch to batch to occur internally. This is because the surface area tends to become unstable. Such inconveniences did not arise with only the conventional boron oxide vaporization and precipitation process.

PBN has a dense boron nitride layer, is extremely homogeneous, and has no grain boundaries with large gaps, so the method of the present invention can be carried out stably.

The effects of H2 and water vapor on boron diffusion in the present invention can be viewed as being the same. H2 is oxidized in the oxidizing atmosphere inside the diffusion furnace and becomes water vapor, which reacts with the boron oxide previously formed on the BN surface to produce volatile HBO, which is then deposited on the silicon wafer facing the PBN. Diffuse boron into. On the other hand, Hz
When water vapor is used without using water vapor, the water vapor directly reacts with the boron oxide on the PBN, and at the same time, the volatile HBO
Produces □. Here, the PBN and the silicon wafer are opposed to each other with an appropriate interval, and in order to increase production efficiency, these intervals are adjusted to be as small as possible. For this reason, in the oxidation of PBH and its devoting process, it is important to supply oxygen in the atmosphere onto the PBN in the oxidation process, and to supply H2 or water vapor onto the PBN in the deposition process. In the oxidation process, there is usually sufficient oxygen, and the rate-determining step in the oxidation of PBN is the surface oxidation reaction, so the supply of oxygen onto the PBN is not a problem. However, in the deposition process, the amount of H2 or water vapor is small, and the supply onto the PBN is the rate-determining step, so it is important to devise ways to uniformly supply H2 or water vapor within the limited space of both the PBN and silicon wafers. Become. This can be solved by sufficiently widening the gap between the PBN and the silicon wafer, or by increasing the total flow rate of the atmospheric gas. Comparing hydrogen and water vapor, hydrogen is more easily diffused due to the difference in their molecular weights, and has a slight advantage in uniform diffusion onto PBN and therefore average deposition of boron onto silicon wafers.

(Effects of the Invention) As described above, the present invention can significantly improve the variation in sheet resistance (ρS) on the surface of a silicon wafer, and also solve problems caused by metal impurities, carbon, etc. in the boron diffusion source. In addition, it has the great effect of completely eliminating the inconveniences caused by the sintered binder.

(Example) Examples of the method of the present invention will be described below, but before that, an outline of the apparatus used in implementing the method of the present invention will be explained based on the accompanying drawings.

Figure 1 shows the equipment used in Example 1 (NZ, 0□%H).
FIG. In the figure, 2 is a quartz tube, 4 is a quartz boat installed in the quartz tube 2, and 6 is a quartz boat 4!
! The placed PBN dopant 8 is a silicon wafer facing the PBN dopant and placed on the quartz boat 4 . R is a pressure reducing valve, F is a flow meter, ■ is a valve,
M is a mixer. The introduction of nitrogen (N), oxygen (0□), and hydrogen (H) gases is performed through a nitrogen gas introduction path IO1, an oxygen gas introduction path 12, and a hydrogen gas introduction path 14, respectively.

Figure 2 shows the equipment R (Nz, Oz,
H! 2 is a schematic explanatory diagram of a device (which can supply O (water vapor)), which is almost the same as the device shown in FIG. 1, but the hydrogen gas introduction path is omitted, and the nitrogen gas introduction path 10 is branched into two, The difference is that a bubbler 16 is provided on one of the supply lines. The bubbler 16 has pure water W sealed therein, and functions to supply moisture to the supplied nitrogen gas.

In addition, the device (NZ, 0□,
If H2 and/or H2O (water vapor) can be supplied (not shown), Examples 1 and 2 can be carried out with the same apparatus.

Furthermore, it goes without saying that the implementation of the method of the present invention is not limited to the use of the apparatus shown in the drawings.

Example 1 Six nines of high purity boron trichloride and five nines of high purity ammonia were grown in a vapor phase on high purity graphite at 2,000°C under a reduced pressure of 10 Torr to form a material with a diameter of 1.
00mm, 1.3am thick pyrolytic boron nitride (PBN)
Forty sheets of dopant were prepared. The total amount of metal impurities in this dopant was less than 1Oppm. After oxidizing the surface of this dopant in oxygen at 1,050°C, a silicon semiconductor wafer (diameter 100mm, thickness 525μ
m) and quartz boats are placed alternately at a distance of 51 W+, and the boats are inserted into a quartz tube in a nitrogen:oxygen atmosphere of 1:1, hydrogen 5Qcc/min, nitrogen 2.m) at 900°C. 51/min for 1 minute, boron was diffused for 40 minutes at the same temperature in a nitrogen atmosphere. As a result, the sheet resistance of the silicon wafer after diffusion was 55 ohms, and the variations within the wafer, between the wafers, and between the lofts were all within 5%. Further, the number of lattice defects was 10/c++1.

Comparative Example 1 When a conventional boron nitride sintered dopant was used under the same conditions as in Example 1, the sheet resistance of the silicon wafer after diffusion was 60 ohms/unit, a variation of 20%, and 30 lattice defects.
It was 0 ke/cal.

The dopant in the boron nitride sintered body sagged and fused to the quartz boat, making it difficult to handle during the diffusion process. This is thought to be due to the reaction between the quartz boat and the sintered binder in the sintered body.

In contrast, the PBN dopant used in Examples 1 and 2 did not fuse to the boat, did not sag, and was extremely easy to handle.

Example 2 A case will be described in which water vapor H2O is used instead of hydrogen (H□+0□) in Example 1.

After introducing water vapor diluted with nitrogen (96% nitrogen, 4% water vapor) at 900°C in a nitrogen atmosphere for 1 minute, boron was diffused. As a result, the sheet resistance of the silicon wafer obtained was 65 ohms/unit, with a variation of 7%.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram showing an example of an apparatus for implementing the method shown in Example 1, and FIG. 2 is a schematic explanatory diagram showing an example of an apparatus for implementing the method shown in Example 2. 2...Quartz tube, 4--Quartz boat, 6...
- PBN, 8...Silicon wafer, 10--Nitrogen gas introduction path, 12--Oxygen gas introduction path, 14--Hydrogen gas introduction path, 16--Bubbler. Patent applicant Shin-Etsu Semiconductor Co., Ltd. Figure 1

Claims (1)

[Claims] (1) Pyrolytic boron nitride (PBN) is used as the boron diffusion source in a method of installing a large number of semiconductor wafers and boron diffusion sources in a diffusion tube and maintaining them in an inert atmosphere and high temperature condition to diffuse boron into the semiconductor wafers. A method for diffusing boron into a semiconductor wafer, comprising simultaneously injecting H_2 and/or H_2O into a diffusion tube.