JPH027516A - Method of diffusing impurity in semiconductor - Google Patents

Abstract

PURPOSE:To form a diffused layer having a required thickness in a high temperature state and in a short time and void contamination caused by heavy metal ions by a method wherein, after a semiconductor substrate is covered with a silicon nitride film with an oxide film between, the substrate is subjected to a high temperature treatment for thermal diffusion. CONSTITUTION:A thermal oxide film 24 is formed over the whole surface of an N-type Si single crystal substrate 20 in which a boron deposited layer 22 is formed and the whole surface is coated with a silicon nitride film 26. The semiconductor substrates W prepared by such pretreatment are arranged on an SiC board 14 and inserted into an SiC tube 12 and an electric furnace 10 is driven to heat the substrates W at a high temperature not lower than about 1200 deg.C. For instance, if the heating temperature, i.e. a thermal diffusion temperature, is 1250 deg.C, a diffused layer 28 having a thickness about 8-10mum is formed in about 6 hours. However, if the Si single crystal substrate 20 is covered with the silicon nitride film 26 with the oxide film 24 between, even if the substrate is heated at about 1200 deg.C for several tens of hours, heavy metal ions do not reach the inside of the Si single crystal.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to doping technology in semiconductors, and particularly to a diffusion method for diffusing impurities into a semiconductor substrate by thermal diffusion.

(Prior Art) As a basic method for doping semiconductors such as MOSFETs and bipolar transistors, a thermal diffusion method using a solid or gaseous impurity containing elements such as As, P, or B as a diffusion source is well known. ing.

In this thermal diffusion method, a semiconductor substrate such as a single crystal silicon wafer to undergo impurity diffusion is loaded into a tube that generates a diffusion atmosphere, and the semiconductor substrate is heated to a high temperature using an electric furnace. ing. In this case, the semiconductor substrate to be subjected to high-temperature processing inside the tube contains F
To prevent contamination by ions of heavy metal components such as e.
Generally, it is made of high-purity quartz with extremely low heavy metal content. For the same reason, the board that holds the semiconductor substrate inside the tube is also made of quartz.

(Problem to be solved by the invention) However, when quartz tubes and quartz boards are exposed to high temperatures of 1150°C or higher for long periods of time, the quartz itself softens and deforms, which causes the wafer The problem becomes more noticeable as the size increases and the diameter of the tube increases accordingly. For example, if a quartz tube with a diameter of 180 mm and a wall thickness of about 4 mm is heated to 1200° C., it becomes unusable within several tens of hours.

For this reason, the heat diffusion temperature has conventionally been limited, and there has been a problem that a required deep diffusion layer cannot be obtained unless heat treatment is performed at a relatively low temperature for a long time.

For example, if the heat diffusion temperature is 1200℃, the thickness is 8~1
A P-type diffusion layer of about 0 μm can be obtained in about 20 hours,
If the diffusion temperature is lowered by 40°C than 1200°C, the diffusion time to obtain the same result will be 50 hours, which is 2.5 times as long as when the diffusion temperature is 1200°C. , an enormous amount of heat treatment time is required, and a deep diffusion layer of about 8 to 10 μm cannot be formed on the side bottom.

(Purpose of the Invention) In view of the above-mentioned problems in the conventional thermal diffusion method, the present invention has been developed to ensure sufficient durability of the tube as a diffusion treatment device and to enable the tube to be heated to a higher temperature than conventional methods. It is an object of the present invention to provide an improved method for diffusing impurities, which generates a diffusion layer of a required thickness in a short time and does not contaminate a semiconductor substrate with heavy metal ions.

(Means for Solving the Problems) According to the present invention, the above-mentioned object is to cover a semiconductor substrate whose surface is doped with an impurity with a silicon nitride film (S i 3 Na ) with an oxide film interposed therebetween; This semiconductor is characterized by including a step of treating the coating at high temperature in a tube made of a heat-resistant material such as SiC, which has superior heat resistance compared to quartz, and diffusing impurities into the semiconductor substrate. This is achieved by a method of impurity diffusion.

(Description of Embodiments) Next, the present invention will be described in detail with reference to embodiments with reference to the accompanying drawings. FIG. 1 shows one embodiment of an impurity diffusion device used to implement the impurity diffusion method according to the present invention.

In FIG. 1, 10 represents an electric furnace, 12 represents a tube installed in the electric furnace 10, and 14 represents a board supporting a semiconductor substrate W, which is an object to be diffused.

In the diffusion method according to the present invention, the tube 12 and the board 14 are made of a material that has better heat resistance than quartz, such as SiC.

As shown in FIG. 2-1, before the semiconductor substrate W is subjected to thermal diffusion treatment in the tube 12, an impurity boron deposit layer 22 is formed at a predetermined position on the surface of the N-type Si single crystal substrate 20. It is formed by ion implantation method.

In the diffusion method according to the present invention, a zero thermal oxide film is deposited on the entire surface of the substrate 20 on which the deposit layer 22 has been formed as described above in an oxidizing gas atmosphere, for example, an oxygen gas atmosphere, at a temperature of 1050° C. or lower by about 1000 people. Low temperature condition! First, a quartz tube "l-+" is formed, and then the entire surface is coated with a silicon nitride film of about 1,000 to 2,000 layers using the LP CVD method.

In FIG. 2-1, the thermal oxide film is indicated by the reference numeral 24, and the silicon nitride film is indicated by the reference numeral 26, and as is clear from this figure, the substrate 20 is
It will be covered with silicon nitride [26] between the two.

The covering body pretreated as described above, that is, the semiconductor substrate W
are arranged on the SiC board 14, and this is placed on the SiC tube 1.
2 and operate the electric furnace 10 to heat it at a high temperature of about 1200° C. or higher.

For example, if the heating temperature, that is, the thermal diffusion temperature is 1250° C., the diffusion layer 28 (see FIG. 2-2) having a thickness of about 8 to 10 μm is formed in about 6 hours.

SiC tubes have better heat resistance than quartz tubes, but on the other hand, they contain more heavy metals than high-purity quartz tubes; for example, high-purity quartz tubes contain less than 0.3 ppm of Fe. On the other hand, in the case of a SiC tube, it is approximately 10 to 20 Dt) m. Therefore, if a semiconductor substrate is heat-treated under the same conditions as when using a quartz tube, it will be contaminated with heavy metal ions, and the Si single crystal that makes up the semiconductor substrate will be contaminated. Defects occur in the semiconductor device, and the characteristics of the semiconductor device deteriorate.

Therefore, in the diffusion method according to the present invention, in order to avoid contamination by heavy metal ions, heat treatment is performed while the Si single crystal substrate 20 is coated with the silicon nitride film 26 via oxidation [24]. When the Si single crystal substrate 20 is covered with a silicon nitride film 26 via an oxide film 24, this is, for example, a SiC
Heavy metal ions do not reach the Si single crystal even if it is heated at about 1200° C. for several tens of hours in the tube 12. That is, the Si single crystal substrate 20 is not contaminated with heavy metal ions.

The silicon nitride film only needs to be removed after the heat treatment for diffusion, and from this point on, semiconductor devices can be manufactured using normal processing processes.

The thermal oxide film 24 between the substrate 20 and the silicon oxide film 2G is used to reduce the influence of stress that the substrate 20 receives from the silicon oxide film 26 during heat treatment. The appropriate thickness may be selected depending on the heat diffusion treatment temperature, treatment time, etc., and normally this thickness may be sufficient for about 1000 people on the entire island.

(Effect of the invention) As mentioned above, in the impurity diffusion method according to the present invention,
Since the semiconductor substrate is coated with a silicon nitride film via an oxide film and then subjected to high-temperature treatment for thermal diffusion, even if the tube contains a relatively large amount of heavy metal components, such as a SiC tube. The semiconductor substrate is not contaminated with heavy metal ions, and the tube can be made of a material with higher heat resistance than quartz or the like, making it possible to increase the diffusion treatment temperature higher than before. . As a result, deep diffusion layers can be formed in a shorter time than in the past, especially in the isolation process of the BIPIC process and the well formation process of the CMO3IC process, which greatly reduces the manufacturing cost. Costs will be reduced.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram showing a specific example of a diffusion device used in implementing the impurity diffusion method according to the present invention, and Fig. 2-1 shows a semiconductor substrate before heat treatment used in implementing the impurity diffusion method according to the present invention. FIG. 2-2 is a sectional view showing the state after heat treatment. 10... Electric furnace 12... Tube 14... Board W... Semiconductor substrate 20... N-type Si single crystal substrate 22... Impurity boron deposit layer 24... Thermal oxide film 26...・Silicon Nyl-Lite) Model 28... Diffusion layer patent applicant Nissan Motor Co., Ltd.

Claims (1)

[Claims] 1. A process in which a semiconductor substrate with impurities added to its surface is covered with a silicon nitride film with an oxide film in between, and this coating is subjected to high temperature treatment in a tube made of heat-resistant material to diffuse impurities into the semiconductor substrate. A method for diffusing impurities in a semiconductor, characterized by containing.