JPS6152564B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improvement in an impurity penetration diffusion process in semiconductor device manufacturing. The following will explain the case of manufacturing a planar thyristor as an example. In general, a planar thyristor is manufactured by coating a semiconductor substrate 1 made of silicon with a silicon dioxide (SiO ₂ ) film, as shown in the cross-sectional view of the main part in FIG.
A window opening 3 is formed by photolithography, and separation and diffusion is first performed to produce individual chips to form a separation diffusion zone 4. Next, similar photolithography is repeated to form a P-type emitter (P _E ) layer 5, a P-type base (P
_E ) layer 6 and N-type emitter (N _E ) layer 7 are sequentially formed. The remaining portion of the semiconductor substrate 1 becomes an N-type base (N _B ) layer 8. Now, small power thyristors with a current carrying capacity of about 0.2 to 3 A are usually manufactured with a reverse withstand voltage of about 100 to 1000 V, and the semiconductor substrate 1 used in this case has a specific resistance of 5 to 3 A. N-type silicon with a resistance of 40 Ωcm and a thickness of 130 to 200 μm is suitable. Therefore, as shown in FIG.
In order to process efficiently, a deep diffusion depth of 70 to 100 μm is required even if diffusion is performed from both main surfaces of the semiconductor substrate 1. Now, when forming a P-type layer on N-type silicon using the planar manufacturing method, boron is used as a selective diffusion impurity in most cases, but boron nitride ( Well-known examples include BN), boron oxide (B ₂ O ₃ ), and boron tribromide (BB _r ³ ). When separating and diffusing using the SiO ₂ film 2 as a mask, after forming the window opening 3, a precipitated layer of B ₂ O ₃ is formed using, for example, BN on both main surfaces of the semiconductor substrate 1, and then A method is used to penetrate the boron deeper into the semiconductor substrate 1 from the above-mentioned precipitated layer by using a high temperature, that is, by increasing the diffusion coefficient. In this case, the semiconductor substrate 1
In conventional diffusion furnaces, a schematic cross-sectional view of which is illustrated in FIG. 2, a quartz glass tube has been widely used as the furnace core tube in which diffusion is carried out. In FIG. 2, 10 is a furnace body, 20 is a quartz tube, 20a is a gas inlet through which carrier gas is introduced, and 20b is a gas outlet through which carrier gas is discharged. The carrier gas is introduced from the inlet 20a as shown by the arrow in the figure, and is introduced from the gas outlet 20a.
Ejected from 0b. Reference numeral 30 denotes a boat on which the semiconductor substrate 1 is placed, and the boat 30 with the semiconductor substrate 1 placed thereon is inserted into the soaking section of the quartz tube 20. By the way, as mentioned above, the formation of the separation diffusion zone 4 requires a diffusion depth of 70 to 100 μm, so empirically, the boron penetration time is 100 to 250 hours at a substrate temperature of 125°C. A long period of time is required. However, when processing is performed using the conventional quartz tube 20 as shown in FIG. 2, as shown in FIG.
Abnormal defects often occurred in the SiO ₂ film 2, making it impossible to expect an improvement in manufacturing yield. Figure 3 shows abnormal defects that occur in the SiO ₂ film 2 during the long-term penetration process of boron. Occurs in crowds. In addition, irregular cracks sometimes occur, which may also crack the surrounding normal SiO ₂ film 2. As shown in the graph of FIG. 4, such abnormal defects were generally observed when boron was penetrated for 30 hours or more. As a result of investigating the abnormal defect that occurred in this SiO ₂ film, the inventor estimated that it was local high-cristobalite deformation of the SiO ₂ film with alkali as the core. By the way, if alkali metals are detected in the cross section of the quartz tube 20 after 150 hours of boron penetration, as shown in the table, the devitrified area after penetration is different from the undevitrified area before penetration. The content rate has changed to 10 to 100 times that of the previous one.

[Table] In other words, for long-term diffusion, the quartz tube 20
A higher concentration of alkali diffuses into the semiconductor substrate 1,
It can be easily inferred that this adversely affects the SiO ₂ film 2, which originally has a strong affinity for alkali. In addition, when a quartz tube is subjected to heat treatment such as diffusion for a long time at a high temperature of 1200℃ or higher, the bending point (generally known as the sagging point) of the quartz tube
point) is 1200℃,
It is not uncommon for the quartz tube to be significantly deformed, making it difficult to pull out the semiconductor substrate during diffusion, or for the quartz tube to be damaged, resulting in significant contamination of the semiconductor substrate. This invention was made in view of the above points, and uses a polycrystalline silicon tube as a furnace core tube in which a semiconductor substrate is housed and penetration diffusion of impurities takes place therein, and oxygen is added to the carrier gas at 10%. By performing penetration diffusion while oxidizing the inner surface of this polycrystalline silicon tube by containing more than vol. _% , abnormal defects and The object of the present invention is to provide a method for manufacturing a semiconductor device that prevents the occurrence of cracks. This invention is an application of the fact that the reaction for precipitating single crystal or polycrystalline silicon is extremely difficult to mix with alkali. The hydrogen reduction reaction of silicon tetrachloride (SiCl ₄ ) and trichlorosilane (SiHCl ₃ ) is well known as a means to precipitate silicon, and this reaction reduces the alkali content.
It is said that it can be suppressed to the order of 10 ppm. The silicon material for the furnace core tube is usually deposited on a high-purity graphite round rod by chemical decomposition of SiCl ₄ or SiHCl ₃ (referred to as "CVD").
After adhering to a predetermined shape, the graphite is removed by burning or drawing to obtain a tubular body. Silicon at this stage is polycrystalline, and experiments have shown that it does not need to be made into a single crystal, which reduces manufacturing costs. Furthermore, in the case of polycrystalline
It is said that grain boundaries have the ability to trap impurities, and from this point of view, we have come to the conclusion that polycrystalline silicon is more preferable as a material for the furnace tube than single-crystal silicon. FIG. 5 is a schematic sectional view showing an example of a diffusion furnace for carrying out the method of the present invention. In this diffusion furnace, a polycrystalline silicon tube 40 as a furnace core tube is attached to the furnace body 10, one end 40a is covered with a cap 50 made of quartz, and nitrogen gas is used as a carrier gas for boron penetration at 4 liters of nitrogen gas. This carrier gas is introduced through the gas outlet 40b at the other end.
is discharged from. Reference numeral 60 denotes a sealing tape made of fluororesin, which hermetically seals the polycrystalline silicon tube 40 and the quartz cap 50. Using a diffusion furnace as shown in Figure 5,
For example, 150 hours of boron penetration to 1250
When the test was carried out at a temperature of .degree. C., almost no abnormal defects in the SiO ₂ film 2 as shown in FIG. 3, which often occur in the past, were found. Additionally, this has been repeatedly confirmed and a total of 5,000 hours has been obtained. In addition, in order to keep the concentration of boron on the surface of the semiconductor substrate constant each time when used for a long time and many times, boron diffuses and accumulates in the polycrystalline silicon tube 40 itself, and this prevents outward diffusion. Experience has shown that this is necessary. In order to satisfy this requirement and increase the utilization of the polycrystalline silicon tube 40, which has a low alkali content and excellent heat resistance, the inventor believes that in order to satisfy this requirement and increase the utilization of the polycrystalline silicon tube 40, which has a low alkali content and excellent heat resistance, the inventors added 10% or more by volume to the carrier gas during boron penetration. It was experimentally confirmed that mixing oxygen gas is sufficient. That is, in each boron penetration, the polycrystalline silicon tube 40 is oxidized by the oxygen gas in the carrier gas, and silicon dioxide is formed on the inner surface, so that boron can be prevented from diffusing into the interior. Even if boron is deposited on this silicon dioxide, it is considered that it is surrounded by the growth of silicon dioxide and forms borosilicate, suppressing the behavior of boron. However, there is a natural limit to the growth of the silicon dioxide film inside the polycrystalline silicon tube 40, and after use for a certain period of time, the silicon dioxide film is removed by reduction in a hydrogen stream or peeling with hydrogen fluoride, and oxygen is added again. It has been found necessary to oxidize the inner surface in a carrier gas containing As a result of experience, it was decided that the silicon dioxide film within the polycrystalline silicon tube 40 would be removed by reduction or stripping within 1000 to 1200 hours of use. In the above explanation, we have described the case of boron penetration into a semiconductor substrate using a silicon dioxide film as a mask. The present invention can also be applied to boron penetration into. Furthermore, although the present invention has been described as being applied to boron penetration, the present invention can also be applied to penetration diffusion of other impurities, such as phosphorus, using a silicon dioxide film as a mask. Furthermore, in the above explanation, the present invention was applied to the manufacture of planar thyristors, but SiO For long-term diffusion processes using _two membranes as masks for selective diffusion,
Of course, this invention can be applied. As detailed above, in the method of manufacturing a semiconductor device according to the present invention, a polycrystalline silicon tube is used as the core tube of the diffusion furnace, and oxygen is added to the carrier gas.
Penetration diffusion of impurities is performed while oxidizing the reactor core tube by containing 10% or more by volume, so even when performing penetration diffusion at high temperatures for a long time, it can be used as a mask for selective diffusion on the surface of the semiconductor substrate. Since it is possible to prevent abnormal defects and cracks from occurring in the formed SiO ₂ film due to alkali from the furnace tube, the manufacturing yield of semiconductor devices is improved. Moreover, this actual result was confirmed over a long period of time.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of the main parts of an example of a planar thyristor, Figure 2 is a schematic cross-sectional view of an example of a diffusion furnace used in a conventional method, and Figure 3 is a schematic cross-sectional view of an example of a diffusion furnace used in a conventional method.
Plan view showing abnormal defects occurring in SiO ₂ film, 4th
The figure is a graph showing the abnormal defect occurrence rate versus penetration time in penetration diffusion of boron in a conventional method, and FIG. 5 is a schematic cross-sectional view showing an example of a diffusion furnace used for carrying out the method of the present invention. . In the figure, 1 is a semiconductor substrate, 2 is a SiO ₂ film (silicon dioxide film), 10 is a furnace body, 40 is a polycrystalline silicon tube as a furnace core tube, 40b is a gas outlet for discharging carrier gas, and 50 is a carrier gas introduction port. It is a cap that can be used. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A semiconductor substrate with a silicon dioxide film mask formed on its surface is housed in the core tube of a diffusion furnace, and impurities are removed for a long time of about 30 hours or more at a temperature of 1200 to 1400°C while flowing a carrier gas. In a method comprising the step of performing penetration diffusion of
A method for manufacturing a semiconductor device, characterized in that a polycrystalline silicon tube is used as the core tube, and the penetration diffusion is performed while the carrier gas contains 10% by volume or more of oxygen to oxidize the inner surface of the core tube. 2. A method for manufacturing a semiconductor device according to claim 1, characterized in that boron is penetrated and diffused.