JPH0385725A - Heat treatment of wafer - Google Patents

Abstract

PURPOSE:To realize expansion of soaking length inside a tube with a wafer loaded therein by arranging heat insulating blocks which are a little smaller than the tube diameter on the atmospheric gas inflow side apart from a region by a specified distance or more and on the atmospheric gas outflow side closely or part, respectively. CONSTITUTION:The heat diffusion furnace is provided with an oblong tube 1 (e.g. inner diameter of 6 in.) which is composed of SiC or quartz. One end of the tube 1 has an open structure. A gas introduction tube 3 is connected to the inner end of the tube 1 and introduces N2 and O2 gases therethrough. A heat resistant heat insulating block 7b which consists of single crystalline silicon (high purity silicon), that is, a material of less possibility of wafer contamination is provided at an interval of at least 10mm or more outside a group of wafers 4 (5 in. diameter) on the atmospheric gas inflow side inside the tube 1. A heat insulating block 7a of the same material is provided closely outside the group of wafers 4 on the atmospheric gas outflow side (using a silicon block of outer diameter of 5 in. and a length of 5 in., for example).

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a wafer heat treatment method, and more specifically, a wafer is placed in a quartz or SIC tube of a heat diffusion furnace, and the wafer is heat treated. When applying
The present invention relates to a wafer heat treatment method that can effectively utilize the soaking length.

[Prior Art] Thermal diffusion of impurities into a wafer is usually performed in two stages: deposition and drive-in.

Among these, in the drive-in, for example, a Si wafer with a glass layer containing impurities formed on the surface is heat-treated at a predetermined temperature (approximately 000 to 1300 degrees Celsius) in an atmosphere of N2, 02, or a mixture of these gases. , the impurities contained in the glass layer are diffused into the Si wafer.

FIG. 5 shows a heat diffusion furnace used in this drive-in.

This thermal diffusion furnace includes a horizontally long tube 1 made of SiC or quartz. This tube 1 is connected to the wafer 4 (
(See Figures 3 and 4) is open at one end for taking in and out, and around the tube there is a heater 2.
is located. The heater 2 includes, for example, a main heater placed in the center of the tube 1 and two auxiliary heaters placed on both sides of the main heater. Further, a gas introduction pipe 3 is connected to the back side of the tube 1, and N2 and 02 gases are introduced through this gas introduction pipe 3.

The wafer 4 as the object to be processed is placed inside the tube 1.
When preparing the wafer 4, as shown in Figure 3,
Lay them together without any gaps to form a ball and place them on boat 5.
In this state, it is pushed into the tube 1. At this time, some boats 5 do not have supports on both sides of the wafers 4, as shown in FIG. There is.

3 Then, for example, under an atmosphere of N2 and a small amount of 02, about 1
The wafer 4 is heated to about 000 to 1300° C. and subjected to heat treatment, and drive-in is performed.

[Problems to be Solved by the Invention] However, in the heat diffusion furnace as described above, the temperature distribution inside the tube l is different between the state where the wafer 4 is not charged (FIG. 5) and the state where the wafer 4 is charged.

That is, when wafers 4 are placed in a soaking area created by adjusting the main heater and auxiliary heater without wafers 4 being placed, the temperature of the wafers 4 decreases near both ends of the group of wafers 4 (the wafers The temperature drop of 4 reaches a maximum of 10 to 20 degrees Celsius compared to the soaking temperature, for example, 1200 degrees Celsius.), the processing temperature of the entire four groups of wafers becomes uneven, and
The impurity diffusion depth into the wafer 4 becomes non-uniform, resulting in a decrease in yield. That is, when a group of wafers 4 in the shape of a lump are placed in the tube l, the length of the portion where the temperature distribution appears to be approximately uniform, the so-called soaking length, becomes shorter. As a result, it becomes impossible to prepare wafers 4 over the entire soaking area without wafers 4 being prepared, and 20
~30% of the soaking area is wasted.

Such problems occur not only when using a boat 5 with supports as shown in FIG. This also occurs when using baud 1-5.

By the way, the total length of the heat diffusion furnace is 2000++y++, whereas the soaking length when no wafer is loaded is only 800mm at most.Why does the temperature drop near both ends of the wafer 4 when the wafer 4 is loaded? Although it is difficult to understand, it is assumed that a major cause of this is thermal radiation loss from both end faces of the four groups of wafers to the outside of the furnace. Incidentally, with regard to the influence of gas flowing into the tube 1 at room temperature, it has been found from past experience that the cooling phenomenon caused by this atmospheric gas can be almost ignored.

In order to prevent such a reduction in the soaking length, it is possible to increase the calorific value of only the auxiliary heaters at both ends of the heat diffusion furnace, but this solution cannot prevent the occurrence of localized high-temperature areas. This goes against the idea of equalizing heat. Figure 6 shows the inside of the furnace when the heat diffusion furnace is fully filled with wafers 4 over the entire soaking length with no wafers loaded, after increasing the calorific value of the auxiliary heaters at both ends of the furnace. The temperature profile is shown as a solid line. Note that the broken line indicates the soaking profile in a state where no wafer is loaded before adjusting the auxiliary heater. From FIG. 6, it can be seen that after increasing the calorific value of the auxiliary heaters at both ends of the heat diffusion furnace, if the heat diffusion furnace is fully filled with wafers 4 over the entire soaking length without wafers, It can be seen that high temperature areas are partially occurring on both sides of the area.

The present invention has been made in view of these points, and it is possible to extend the soaking length inside the tube with wafers loaded therein.
The object of the present invention is to provide a heat treatment method that can improve heat treatment efficiency, uniform diffusion, and yield at the same time.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Means for Solving the Problems] Representative inventions disclosed in this application will be summarized as follows.

That is, in order to achieve the above-mentioned object, the present invention includes wafers that are arranged side by side in a tube of a thermal diffusion furnace so that the main surfaces thereof are perpendicular to the longitudinal direction of the tube, and in which the wafers are subjected to heat treatment in that state. On both sides of the soaking area when no wafers are placed in the tube, heat insulating blocks slightly smaller than the tube diameter are placed at least 10 mm away from the area on the atmospheric gas inflow side, or closely spaced or separated on the atmospheric gas outflow side. It is arranged so that Further, in the above invention, the material of the heat insulation block is high purity silicon.

[Function] According to the invention described above, since the heat insulation blocks are installed outside both ends of the group of wafers in the tube, direct thermal radiation loss near both ends of the group of wafers does not occur, and therefore, temperature drop is prevented. . Furthermore, by using a high-purity silicon block as a heat insulation block, it is possible to prevent unintentional contamination of the wafer and at the same time, it is expected to have the effect of blocking the passage of radiation from the wafer.

As a result, uniform heat treatment can be performed over the entire wafer, and uniform diffusion allows wafer heat treatment with a high yield.

The shape of the heat insulation block is preferably cylindrical, and its outer diameter is selected to be slightly smaller than the inner diameter of the tube, leaving a gap sufficient for the flow of atmospheric gas. The length is preferably equal to or larger than the outer diameter/2. The distance between the end of the wafer group and the opposing surfaces of the heat insulation block must be at least 10+ nm on the atmospheric gas inflow side, and may be close together on the atmospheric gas outflow side, and the maximum distance between the surfaces must be subject to particularly strict restrictions. There isn't. By selecting the shape and position of the heat insulation block in this way, the soaking length without wafers can be adjusted so that even when fully filled with wafers, the temperature of the outermost wafer will fall within the range of 1000 to 1300℃. The temperature is only 0.5℃.

[Example] Hereinafter, an example of the wafer heat treatment method according to the present invention will be described.

FIG. 1 shows a part of the heat diffusion furnace and main auxiliary equipment of the embodiment.

This thermal diffusion furnace is equipped with an oblong tube 1 (for example, 6 inches in inner diameter) made of SiC or quartz. This tube 1 has an open structure at one end, and a gas introduction pipe 3 is connected to the rear end, from which N2 and 0
Two gases can be introduced. Further, a heater 2 is arranged around the tube. The heater 2 is composed of, for example, a main heater placed in the center of the tube 1- and auxiliary heaters placed on both sides of the main heater. In addition, heat-resistant, single-crystal silicon (high-purity silicon) is placed at an interval of 15IIT11 outside the group of wafers 4 (5 inches in diameter) on the inflow side of the atmospheric gas in the tube l.
That is, a heat insulating block 7b made of a material with a low possibility of wafer contamination is installed, and a heat insulating block 7a made of the same material is installed closely outside the four groups of wafers on the side where the atmospheric gas flows out (silicon block (Used one with an outer diameter of 5 inches and a length of 5 inches.) Note that in this embodiment, the wafer 4 in the tube 1
A wafer 4 is placed in a soaking area-cup in a state where no wafer is charged.

The soaking length in a heat diffusion furnace is 2000 mm, and the central portion of the heat soaking length is usually guaranteed to be 800+ am. The temperature setting when the wafer is not filled varies depending on the conditions. In the case of the present invention, the soaking temperature on the atmosphere gas inflow side of the above-mentioned soaking length is set to +2° C. with respect to the central soaking temperature, and on the atmosphere outflow side, it is set to −2 to 10° C. With this setting, if the wafers are filled and the silicon block of the present invention is installed, the temperature of the wafer group can be set within the range of ±0° to 5° C. over the entire length.

Next, to explain how to prepare the wafers 4, the wafers 4 on which the glass layer containing impurities has been formed are placed side by side on the boat 5 without any gaps as shown in FIG. put in. At this time, the distance between the wafer 4 and the heat insulating block 7b arranged on the atmospheric gas inflow side is set to be about 15 mm or more. In this case, if the gap is less than 10 nu, the soaking length with the wafer 4 loaded will be shortened.

Then, N2 and a small amount of 02 gas atmosphere, 10QQ-
Heat treatment is performed at a temperature of about 1300°C. Then, the impurities contained in the glass layer will be diffused into the wafer 4.

In this way, the wafer 4 can actually be placed inside the tube 1.
When wafers are loaded, the soaking area can be maintained as is when nothing is loaded in the tube 1, regardless of the diameter of the wafers or the number of wafers loaded. In other words, compared to the conventional method that does not use a heat insulating block, the soaking length can be substantially extended, and the number of wafers 4 to be processed can be increased.

For comparison, when the wafer is not loaded as described above, the temperature is adjusted as shown by the broken line in Figure 2 at both ends of the soaking length section, and then the wafer is loaded without using a silicon block, as shown by the solid line in Figure 2. As shown in FIG. 5-1 at 400mm position
A temperature drop of 0°C occurs.

Although the invention made by the present inventor has been specifically explained above based on Examples, it goes without saying that the present invention is not limited to the above Examples and can be modified in various ways without departing from the gist thereof. Nor.

In the above embodiment, the wafer 4 is supported by a block 6 (FIG. 4).
Although the explanation has been made regarding the case where the support block 6 is not supported, the present invention can also be applied to the case where the support block 6 is used.

If the block 7b of the embodiment is installed outside the support block and apart from it, the soaking length can be increased for the same reason as above.

In addition, although the above embodiment describes the case of a drive-in, the case is not limited to a drive-in.
The present invention can also be applied to oxidation processes and other processes.

[Effects of the Invention] The effects obtained by typical inventions disclosed in this application are briefly explained below.

That is, in the present invention, wafers are arranged side by side in a tube of a heat diffusion furnace so that the main surfaces are perpendicular to the longitudinal direction of the tube, and when performing heat treatment on the wafers in this state, the wafers are not placed in the tube. in the soaking area, at least 10 m from the area on the atmospheric gas inflow side.
By arranging heat insulating blocks slightly smaller than the tube diameter, spaced apart by at least n+ and closely or spaced apart on the atmospheric gas outlet side, heat loss from the wafer is limited.
The cooling temperature of the wafers near both ends of the group of wafers placed in the group is inhibited, and in the case of thermal diffusion, there are two wafers for all wafers, which enables uniform diffusion, resulting in the production of high-yield wafers.

[Brief explanation of drawings]

Fig. 1 is a longitudinal cross-sectional view of a heat treatment furnace used to carry out the heat treatment method according to the present invention, and a graph showing the temperature distribution inside the furnace. Fig. 2 is a longitudinal cross-sectional view of the heat treatment furnace without a heat insulating block and a graph showing the inside of the furnace. Graph showing temperature distribution. Figure 3 is a vertical cross-sectional view of a boat used for loading wafers, Figure 4 is a vertical cross-sectional view of another boat used for loading wafers, and Figure 5 is a vertical cross-section of a heat treatment furnace used for heat diffusion. Figure 6 is a vertical cross-sectional view of a heat treatment furnace used for conventional heat diffusion, and a graph showing the temperature distribution inside the furnace when no wafers are loaded. This is a graph showing. Engineering...Tube, 2...Heater, 3...Gas introduction pipe, 4...Wafer, 7a, 7b...Heat insulation block.

Claims (1)

[Claims] 1. When wafers are placed side by side in a tube of a heat diffusion furnace so that the main surfaces are perpendicular to the longitudinal direction of the tube, and when heat treatment is applied to the wafers in this state, the wafers in the tube are Insulating blocks slightly smaller than the tube diameter are arranged on both sides of the soaking area in a state where there is no tube, at least 10 mm or more away from the area on the atmospheric gas inflow side, and closely or spaced apart on the atmospheric gas outflow side. A wafer heat treatment method characterized by: 2. The wafer heat treatment method according to claim 1, wherein the wafer is placed over the entire heat soaking area in a state where no wafer is placed in the tube and the heat treatment is performed. 3. The wafer heat treatment method according to claim 1 or 2, wherein the material of the heat insulation block is high-purity silicon.