JPH0878349A - Combined jig for heat treatment of silicon wafer and its manufacture - Google Patents

Abstract

PURPOSE: To prevent a silicon wafer from being contaminated by a method wherein a jig for mounting of the silicon wafer and a support jig are constituted of quartz glass and both are combined via a silicon member. CONSTITUTION: Silicon wafers 2 are inserted into wafer insertion grooves in a cassette boat 1 which is constituted of quartz glass and which is a jig for mounting of the silicon wafers. This assembly is set on a motherboard 5 in which a silicon plate 6 is coupled by a coupling pin 4 and which is a support jig constituted of quartz glass. This assembly is brought into a core tube 7 for an electric furnace which is provided with a liner tube 8 and the core tube 7, and the oxidation treatment of the silicon wafers 2 is executed. Then, the contamination of the silicon wafers 2, especially the contamination due to the movement of sodium element, is prevented effectively, and the silicon wafers 2 in which uniform and good-quality oxide films have been formed are obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon wafer heat treatment combination jig used in a silicon wafer heat treatment process, a method of manufacturing the same, and an annealing furnace.

[0002]

2. Description of the Related Art Conventionally, quartz glass has been used as a jig for heat treatment of silicon wafers because it has a higher purity than other refractory materials and can be fused by welding. Place a silicon wafer on a high-purity quartz glass jig, carry it into an electric furnace, and then
The heat treatment of silicon wafers is performed by heating to a high temperature of around ℃, and the electric furnace used is a horizontal electric furnace that holds the silicon wafer vertically and heat-treats it, or a vertical electric furnace that holds the silicon wafer horizontally and heat-treats it. A furnace or the like is used.

However, in recent years, as the degree of integration of manufactured devices has increased, devices such as flash memory that are extremely resistant to impurities have been developed, and the purity of the wafer can be maintained simply by using a conventional high-purity quartz glass jig. Even if it does not come out. Therefore, in order to manufacture a jig having a higher purity, a more excellent raw material crystal refining technique has been developed, and a technique for manufacturing a high-purity synthetic quartz glass from a high-purity chemical industrial chemical has been developed. In particular, in synthetic quartz glass, it has become possible to industrially produce synthetic quartz glass with a remarkably high purity in which the total amount of metal impurities does not exceed 0.1 ppm. It has also become possible to dope the additive without adding other impurities (eg adding 1 ppm of aluminum element). However, even if a jig is manufactured using such high-purity quartz glass and a silicon wafer is heat-treated in a high-purity atmosphere, it is difficult to avoid contamination with alkali elements, especially sodium elements, and the yield of high-grade elements is high. Could not overcome the drawback of being low.

[0004]

In view of the current situation,
As a result of intensive studies on the cause of the contamination of the silicon wafer, the present inventor has found that the contamination of the wafer with sodium element is not the direct contamination from the atmospheric gas but the contamination of the wafer mounting jig. It was It was also confirmed that the contamination of the wafer mounting jig started not only during the heat treatment of the silicon wafer but also during the annealing treatment during the quartz glass work. Regarding the mechanism of contamination, it has been found that if a sodium contamination source such as a heat insulating material of a heat treatment furnace and a wafer constitute a direct contact path through a quartz glass jig, contamination of the wafer with sodium element occurs. Then, if a silicon member is interposed in the path of the contamination, the contamination is interrupted at this point, and the quartz glass jig above (wafer side) from the interruption point maintains high purity, and the quartz glass jig mounted on the jig is high in purity. The present invention has been completed by finding that a high-quality semiconductor device can be obtained with a high yield. Ie

An object of the present invention is to provide a combination jig for heat treatment of silicon wafers which is free from contamination of the silicon wafers.

An object of the present invention is to provide a combination jig for manufacturing flash memory.

An object of the present invention is to provide a method for manufacturing a combination jig for heat treatment of silicon wafers.

A further object of the present invention is to provide an annealing furnace for manufacturing a combination jig for heat treatment of silicon wafers.

[0009]

SUMMARY OF THE INVENTION The present invention for achieving the above object provides a silicon wafer heat treatment combination jig comprising a silicon wafer placement jig and a support jig for supporting the jig. A jig for heat treatment of a silicon wafer, characterized in that the jig for use and the support jig are made of quartz glass, and they are combined with each other through a silicon member, a method for producing the same, and a method for implementing the method. Related to the annealing furnace.

The combination jig of the present invention includes a wafer mounting jig made of quartz glass, a support jig made of quartz glass, and a silicon member interposed between the supporting jig and the quartz glass jig for preventing contact between the jigs. It is a jig assembled with. When a horizontal heat treatment furnace is used, it is easy and convenient to handle if the wafer mounting jig is a cassette boat and the supporting jig is a mother boat. When a vertical heat treatment furnace is used, a supporting table on which a wafer boat is placed and a lower lid that prevents heat energy from escaping under the furnace may be considered as a supporting jig of the present invention. The wafer mounting jig is provided with grooves, claws and the like for mounting a silicon wafer. A plurality of silicon wafers are placed on this wafer placement jig, placed on a support jig via a silicon member, loaded into a furnace core tube of an electric furnace, and heated to a high temperature of about 1000 ° C. to oxidize the silicon wafer. Perform processing such as processing.

According to the research conducted by the present inventor, lithium element is released from all the quartz glass jigs such as the furnace core tube and the wafer boat which are usually placed in the electric furnace for heating, while potassium element is released. Elements and sodium are absorbed. Among the elements to be absorbed, the absorption rate of the potassium element is 1/10 or less of the absorption rate of the sodium element, and it can be considered that the absorption rate does not substantially move. Since sodium element has a high absorption rate and a high movement rate in quartz glass, it contaminates the silicon wafer and deteriorates its quality. This sodium element contamination route is not in the ambient gas surrounding the silicon wafer directly to the silicon wafer, but in the solid or in the solid surface in direct contact therewith. For example, in a horizontal furnace, it has been found that the mainstream is through a direct contact path of an electric furnace body, a liner tube, a quartz glass furnace core tube, a quartz glass boat, and a silicon wafer. Further, if the wafer mounting jig is significantly contaminated with sodium element, there are also harmful effects such as contaminating the hydrofluoric acid in the cleaning tank of the jig and devitrification of the quartz glass. The problem to be solved by the present invention is to prevent the wafer mounting jig from being contaminated at a smaller amount and process a high quality wafer.

The migration of the sodium element can be blocked by interposing a silicon member in the middle of the contamination path. Since the breaking point is preferably close to the wafer, in the combination jig of the present invention, a silicon member is provided at the contact portion between the wafer mounting jig and the supporting jig. The thickness of the silicon member may be within a range that blocks the movement of alkali elements, and is not particularly limited, but from the mechanical strength and the ease of handling, it is 0.3 to
It may be about 10 mm.

The quartz glass of the supporting jig constituting the combination jig of the present invention has an aluminum element content of 5 to 20 pp.
m, a lithium element content of 0.1 ppm or less, and a sodium element content of 0.1 ppm or less, so-called low-alkali varieties of quartz glass are preferable. By using such quartz glass, the sodium element is captured before the breaking point (on the opposite side of the wafer), and the contamination of the silicon wafer can be prevented. If the aluminum content in the quartz glass of the supporting jig is less than the above range, the supplemental force of sodium element is poor, and if it exceeds the above range, the quartz glass is likely to devitrify. Further, if the content of the sodium element exceeds the above range, the sodium element of the quartz glass approaches a saturated state, and thus it is not possible to sufficiently supplement the sodium element. According to the experiments conducted by the inventor of the present invention, when the material is heated in an annealing furnace at 1100 ° C. for 1000 hours, the saturation point is approached, but even if the annealing is carried out for about 1 hour, an increase in sodium element can be reliably observed by performing high sensitivity analysis. Furthermore, if the content of the lithium element exceeds the above range, in-furnace contamination occurs due to the release of the lithium element, which is not preferable.

Further, the wafer mounting jig constituting the quartz glass jig of the present invention is formed by using various high-purity quartz glass having an iron element of 0.2 ppm or less. If the iron element exceeds the above range, the carrier life in the wafer in contact with the iron element deteriorates, which is not preferable. Here, it should be noted that the fact that the wafer mounting jig is not contaminated with the sodium element does not necessarily mean that the wafer is not contaminated with the sodium element. It is necessary to block the contamination path with a silicon member on the side of the wafer mounting jig opposite to the wafer. In the absence of this silicon member, many cases can be observed in which a large amount of sodium element passes through the wafer mounting jig and contaminates the wafer, but the sodium element content in the quartz glass of the jig hardly increases.

An example of the method of manufacturing the combination jig of the present invention will be described below. That is, a cassette boat, which is a jig for mounting a silicon wafer, is prepared by glass work using various types of high-purity silica glass having an iron element of 0.2 ppm or less. Further, the aluminum element content is 5 to 20 ppm, the lithium element content is 0.1 ppm or less, and the sodium element content is 0.
A mother boat, which is a supporting jig, is manufactured by glass work using low-alkali quartz glass of 1 ppm or less. A wafer insertion groove or the like is machined in these jigs as needed. Since the thermal strain remains in the quartz glass due to the burner processing during the glass work, an annealing treatment is required to remove the thermal strain. The annealing treatment is carried out by placing a jig in the annealing furnace. As the annealing furnace, a furnace having a structure in which a quartz glass block is placed on an aluminum board hearth plate and further a silicon base is laid is used. By carrying out the annealing treatment by mounting the jig on the silicon table, the wafer mounting jig is not contaminated by sodium element, and the sodium capturing force of the supporting jig can be maintained. The silicon base does not need to cover the entire surface of the hearth, and may be of a size such that the quartz glass jig to be annealed does not contact the hearth. Placing one silicon table at each contact point is also effective enough.

In the quartz glass jig of the present invention, it is better that the breaking point of the sodium contamination path is closer to the wafer.
The supporting jig is preferably at least 30% by weight of the total jig weight.

As described above, the combination jig of the present invention can process an object without contaminating the object to be processed. Therefore, it is not only preferably used in the step of forming a thin oxide film on a silicon wafer, but also a general wafer heat treatment treatment. It can also be used as a tool.

Further, the annealing furnace used for manufacturing the combination jig of the present invention can be applied to the manufacture of general quartz glass products which do not like alkali element contamination.

[0019]

EXAMPLES Specific examples of the combination jig for heat treatment of silicon wafers of the present invention are shown in FIGS. 1 to 4 show a cassette / motherboat type horizontal furnace combination jig, and FIG. 4 shows a cross-sectional view taken along the line AA ′ when loaded into a furnace core tube. Further, FIG. 5 shows a schematic cross-sectional view when the combination jig for a vertical furnace is inserted into a vertical electric furnace. Further, FIG. 6 shows an annealing furnace for manufacturing a combination jig for silicon wafer heat treatment for annealing each jig forming the combination jig for heat treatment of silicon wafer.

Example 1 (Method for manufacturing combination jig for heat treatment of silicon wafer) Table 1
Nos. 1-No. The quartz glass material of No. 3 was manufactured by an electric melting method. No. No. 4 was manufactured from the crystal powder of sample A by the oxyhydrogen flame method.

[0021]

[Table 1]

The quartz glass round bar was used as a material to fabricate a jig for mounting a silicon wafer and a supporting jig by glass work, and an annealing treatment was applied to remove thermal strain. Annealing treatment is performed on the alumina hearth plate 11 shown in FIG.
Annealing method using a furnace in which the quartz glass block 11 is laid and further a silicon stand 12 having a thickness of 5 mm is arranged (invention method), and a processing method using a furnace in which the silicon stand 12 is not arranged (conventional method) Respectively. Table 2 shows the results of chemical analysis of the jig that was annealed until the strain was removed.

[0023]

[Table 2]

As shown in Table 2 above, the jig treated by the method of the present invention in which the annealing furnace and the quartz glass jig were not in direct contact with each other, the purity of the material was almost maintained and the purity was high.

On the other hand, the jig treated by the conventional method was not able to be used as a wafer mounting jig because the amount of alkali elements, especially sodium elements increased remarkably.

(Example of use for heat treatment of wafer) In FIG. 1, a silicon wafer 2 is inserted into a wafer insertion groove 3 of a cassette boat 1, and a silicon plate 6 is locked by a locking pin 4 as shown in FIG. After being set on the mother boat 5, the wafer was carried into the furnace core tube 7 of the electric furnace having the liner tube 8 and the furnace core tube 7 shown in FIG. A uniform and good quality oxide film was formed on the obtained silicon wafer. The total weight of the cassette boat and the weight of the mother boat were almost equal.

Embodiment 2 Using the round bar of Embodiment 1, as shown in FIG. 5, the silicon wafer mounting jig 1 and the supporting jig 5 are connected via a silicon plate 6, and the same is connected as shown in FIG. It was carried into the vertical electric furnace 9 shown and annealed in the same manner as in Example 1. As a result, the silicon wafer mounting jig was not contaminated with elemental sodium. The weight of the wafer mounting jig was about half the weight of the supporting jig.

[0028]

The combination jig for heat treatment of silicon wafer of the present invention can effectively prevent the contamination of the silicon wafer, especially the contamination due to the movement of sodium element, and provide a high quality silicon wafer.

The above-mentioned combination jig comprises a jig for mounting a silicon wafer and its supporting jig, and at the time of manufacturing the jig, the annealing treatment of each jig is carried out at a required portion of the hearth of a commercially available alumina-lined annealing furnace. The desired performance is exhibited by adopting an industrially simple method of carrying out in an oven laid with a liner.

[Brief description of drawings]

FIG. 1 is a perspective view of a cassette boat of a cassette / mother boat type horizontal combination jig of the present invention.

FIG. 2 is a perspective view of a mother boat of the cassette / mother boat type horizontal combination jig of the present invention.

FIG. 3 is a cross-sectional view of a cassette / motherboat type horizontal combination jig of the present invention.

FIG. 4 is a sectional view taken along the line A, A ′ when the cassette / mother boat type horizontal combination jig of the present invention is loaded into the furnace core tube.

FIG. 5 is a schematic cross-sectional view of a vertical combination jig for heat treating a silicon wafer according to the present invention.

FIG. 6 is a schematic sectional view of an annealing furnace of the present invention.

[Explanation of symbols]

 1 wafer mounting jig 2 silicon wafer 3 wafer insertion groove 4 locking pin 5 support jig 6 silicon plate 7 furnace core tube 8 liner tube 9 vertical electric furnace 10 aluminum board hearth plate 11 quartz glass block 12 silicon platform

Claims (4)

[Claims] 1. A combined jig for heat treatment of silicon wafers comprising a jig for mounting a silicon wafer and a supporting jig for supporting the jig, wherein the jig for mounting the silicon wafer and the supporting jig are made of quartz glass. A combination jig for heat treating a silicon wafer, characterized in that both are combined through a silicon member. 2. A quartz glass constituting a jig for mounting a silicon wafer is a quartz glass having an iron element content of 0.2 ppm or less,
The silica glass constituting the support jig is a silica glass having an aluminum element content of 5 to 20 ppm, a lithium element content of 0.1 ppm or less, and a sodium element content of 0.1 ppm or less. Combination jig for wafer heat treatment. 3. A silicon wafer mounting jig is formed of quartz glass having an iron element content of 0.2 ppm or less, and
Aluminum element content 5 to 20 ppm, lithium element content 0.1 ppm or less, sodium element content 0.1
In a method for manufacturing a combination jig for silicon wafer heat treatment, in which a support jig is formed by glass work from quartz glass of ppm or less, and the annealing treatment is performed on the support jig, the annealing treatment is performed on a silicon table. Manufacturing method of combination jig. 4. An annealing furnace for manufacturing a combination jig for heat treatment of silicon wafers, wherein a silicon base is arranged on the hearth.