JPS597675B2 - How to make mold parts - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for drawing crystals from a melt, and more particularly to providing a capillary type member for use in growing compacts of materials such as silicon.

HaroldE Label Juni 7
U.S. Patent Nos. 3,471,266 and 3,591,348 issued to Mr. La Belle Jr., La Belle Jr., disclose a method in which a single crystal with a controlled cross-sectional shape and a predetermined shape is produced by capillary action of the melt consumed during crystal growth. A method is described for growing by means of so-called mold parts which are intended to be replenished.

In the method described in US Pat. No. 3,471,266, crystal growth occurs at a liquid-solid interface created at the top of a capillary.

According to the method of the patent, crystals of arbitrary cross sections can be grown from capillary tubes.

In the method described in U.S. Pat. No. 3,591,348, crystals are drawn from a thin film of melt supported on the upper surface of a mold member, which stores the melt so as to automatically replenish said film. It has one or more capillary tubes for sending the fluid from the reservoir to the upper surface of the member.

Since the thin film covers the entire end surface of the mold member and crystal growth occurs from the entire extent of the thin film, the growing crystal has a cross-sectional shape corresponding to the side edge shape of the upper end surface of the mold member.

The method described in U.S. Pat. No. 3,591,348 is often referred to as the "EFG"method;
``is an abbreviation meaning ``growth where the film is fed with a zero edge defined''.

With both of Lovell's methods, it is possible to grow crystals in a wide variety of geometrical forms, especially the rod-shaped tube and the thousand-ribbon Q-shape.

Both of these methods also work with a wide range of materials such as sapphire, ruby, silicon, barium titanate and yttrium aluminum garnet.
t) may be used to grow a single crystal.

The mold members employed in Lovell's method must be able to withstand use at temperatures above and beyond the melting point of the material to be grown.

In addition, these mold parts must be made of a material that is wetted by, does not react with, and does not dissolve in the molten material, and yet has a very high purity.

As a result, materials suitable for this mold material are usually expensive.

Moreover, the cost of manufacturing mold parts is quite high due to the nature of the mold material and the close tolerances that have to be provided.

This is especially true of the silicon carbide type used in growing silicon.

Therefore, a substantially single-crystal silicon body can be used in US Pat.
It is the main object of the present invention to find a relatively simple and inexpensive method of producing high-purity mold parts for use in growing by the methods described in US Pat.

Another object is to provide a relatively inexpensive high purity silicon carbide type member of the above nature.

Yet another object is to provide a capillary-type member that includes a capillary tube filled with a solid body of material that is grown as a crystal.

The above-listed objects consist of providing a suitably shaped core piece made of a material that is grown as a crystal, and covering said suitably shaped core piece with a selected mold material;
This is achieved by a manufacturing method which basically comprises steps which make it possible to obtain a mold part of a predetermined shape.

A suitably shaped core piece defines the shape of the capillary tube and may be removed before the mold member is mounted in the crucible.

Preferably, the core piece is retained and the mold part is used directly as a prefilled mold part.

Other objects, features and many attendant advantages of the invention are set forth in or made apparent from the following description, which should be considered in conjunction with the accompanying drawings.

Like reference numbers refer to similar parts in the accompanying drawings.

Although the present invention can be used to provide mold members for use in growing crystals of a variety of materials, the detailed description below provides a mold member for growing silicon. Pertains to.

In this regard, it should be understood that molten silicon is a solvent for a wide variety of materials, so the selection of materials that can be used to produce mold parts for growing silicon is limited. It is something that can be done.

However, silicon carbide is suitable as a mold material for silicon, and the following description relates to producing silicon carbide mold parts.

Referring now to FIGS. 1 to 4 of the accompanying drawings, in the EFG type used for growing silicon flat ribbons, a core piece or molded member 2 made of single crystal or polycrystalline silicon is first prepared. Manufactured by

The core piece 2 has a rectangular cross section and both wide Uki4 pieces of the same piece.
An elongated recess 6 is formed in each as shown in the figure.

The depression 6 here does not need to be particularly elongated.

The surfaces 8 and 9 on both sides and both ends, respectively, are flat like the front and rear surfaces 4, and the thickness of the core piece, that is, the width of both sides 80 of the core piece is the size of a capillary tube.

The length of the core piece, ie the vertical dimension of the wide surface 4 as seen in FIG. 1, is at least the same as the length of the intended capillary tube in the finished mold part.

The surfaces of the core piece 2 are subjected to a suitable surface cleaning treatment to remove impurities such as oxides, dust, oil, etc., and then the same piece is coated with a silicon carbide layer 10 of uniform thickness. Ru.

This silicon carbide layer is preferably applied by chemical vapor deposition, for example by vapor phase reaction of methylchlorosilane in hydrogen.

The coefficient of thermal expansion of silicon and the coefficient of thermal expansion of silicon carbide are similar enough to have a difference that makes it possible to prevent cracks from forming in the deposited silicon carbide coating. be.

The deposited SiC coating retains the shape of a depression 6, as shown at 6A in FIG.

After the core piece is completely coated, both the top and bottom surfaces 12 of the SiC coating are cut or ground to form the silicon core piece 20 on both end faces 9 as shown in FIG. It is removed so that it is exposed as if it were there.

In this case, by removing at least the top surface 12 of the silicon carbide coating, the front, rear and side surfaces of the coating are formed into flat, coplanar surfaces extending perpendicularly to the longitudinal axis of the core piece 2, as shown at 14. It is removed so as to form the edge on the top surface side.

In this regard, it should be understood that the silicon carbide layer constitutes the mold member, allowing the silicon ribbon to be grown by EFG, and that the silicon carbide-silicon composite is pre-filled. It may also be used as a mold member.

However, the silicon core piece 2 may be completely melted before using the silicon carbide mold member for EFG growth of silicon.

In other words, a piece of silicon core is 1 part by weight. It can be dissolved and removed by an acid such as CP4 containing 2 parts acetic acid and 3 parts nitric acid.

After the silicon core piece has been removed (or after the top and bottom surfaces 12 of the silicon carbide coating have been removed if the composite structure is to be used as a prefilled mold part); The silicon carbide shaped member is mounted on a suitable support structure for use in holding the bottom end of the member immersed in the melt-filled crucible.

As shown in FIG. 4, by way of example, a pair of aligned, radially extending, rigid pins 18 are provided in the support ring 16, which pins are located in the recesses 6A.
and therefore engages the mold member.

The ring 16 rests on the upper end of a suitable crucible 20 and holds the lower end of the silicon carbide mold member close to, but at a distance from, the bottom of the crucible, so that the interior of the mold member is contained within the crucible. As long as the source reservoir of molten silicon is sufficient to surround the bottom end of the mold member, it will remain filled with molten silicon by the wicking action of the capillary tubes.

In practice (and as described in the above-cited Lovell patent), a radiation shielding shroud surrounds the upper end of the mold member to prevent radiation heat loss from the melt contained in the crucible. It is customary to be placed.

It is already known that it is of real advantage to hold the silicon core in a silicon carbide mold part and to use this composite structure as a "prefilled mold part."

The main advantage is that in this way the initiation of the crystal growth process is facilitated.

For some other reason, the capillary in the virgin silicon carbide type, i.e., the unused silicon carbide type, is difficult to wet with molten silicon, and as a result, the capillary can absorb molten silicon only by capillary action. will not be filled quickly,
It has also been found that a thin film of melt on the top surface 14 of the mold is not easily created and/or maintained.

However, in the present invention, if the formed pre-filled mold member is mounted in a crucible, as the source of silicon in the crucible is melted, the silicon core pieces 2 will also melt. However, it will remain within the capillary passage of the mold member.

Therefore, if the seed silicon is brought onto the hot apex 14 of the mold member and maintained to begin to melt so as to cause the formation of a thin film, at the same time the seed silicon is brought into the capillary tube. The melted core piece 2 contacts and adheres to the molten column formed by melting the core piece 2, so that the molten thin film is replenished by capillary action in the manner described in Lovell's Patent No. 3,591,348, supra. Become.

Of course, the EFG type having the upper end surface having a rectangular side edge shape may be made to have a silicon core having another cross-sectional shape.

Thus, for example, the silicon core can be square, and the silicon carbide coating is deposited preferentially increasing the thickness on opposite sides, so that the finished mold part is formed at the top of the part. It has a rectangular side edge shape and a capillary passage with a square cross section.

As a further example, the rectangular EFG type is produced by coating the surface of a cylindrical Si core with a silicon carbide coating of uniform thickness, and then machining a flat surface on the coating. It can be manufactured by having a shape in cross section and having a capillary tube of circular cross section.

It should be understood that the recess 6, which forms the basis of the recess 6A for receiving the pin 18, may be replaced by a recess or notch formed in the side surfaces 8.

Alternatively, protrusions may be formed in the surface 4 or 8 instead of indentations for the same purpose (see ribs 26 in FIGS. 5 to 7).

In some cases, the through holes may be substituted for the recesses in the silicon core piece.

Accordingly, the term "recess" should be considered to include through-holes where applicable.

Figures 5 through 7 show a mold for growing silicon filaments from a capillary tube, as disclosed in Lovell's U.S. Pat.
6 shows how the present invention can be used to provide according to the method of No. 6.

In this case, the silicon core piece is in the form of a cylinder 24 having a circumferentially extending rib or flange 26 near one end.

This core piece has been treated to remove oxides, oil, dust, etc. and then a sticky coating of silicon carbide 30
are provided as shown in FIG.

This coating is applied to a uniform thickness so that the ribs 26A are formed in a manner corresponding to the shape of the ribs 26.

The coating is then machined away at the upper and lower ends 32 of the core piece. In addition, the silicon carbide is cut away to form an inclined surface 34 terminating in a sharpened circular upper edge 38 (FIG. 8). Removed by machining or grinding around the upper surface.

The result is a prefilled cylindrical silicon carbide mold consisting of a silicon carbide coating 30 and a silicon core piece 24.

Assuming that the core piece 24 is sized to an appropriately sized cross-section, the inner surface of the sheath 30 will form a capillary-sized cylinder, i.e., the inner surface of the sheath 30 will be blown by the wicking action of the capillary in accordance with the requirements of Lovell, U.S. Pat. No. 3,471,266. This will define a capillary tube that is meant to be filled with the element.

The mold thus prefilled can be mounted to the crucible 40 by means of a support disk 42 having a central hole.

This hole is sized to receive the mold so that the inner circumferential edge of the disc is under the rib 26A and acts as a shoulder to support the lip.

FIG. 8 shows how this prefilled mold member looks in cross section.

If the silicon core is leached from the silicon carbide mold, the mold will have a circumferential groove on the inner surface of the mold.

This groove does not prevent the molten silicon from flowing upward through the capillary during crystal growth.

In some cases it may be desirable for the mold member to be mounted so that it rests on the bottom of the crucible.

However, in such a case, a transverse hole 44, as shown in FIGS. 7 and 8, must be provided at the bottom end of the mold member to allow the inflow of the melt.

Although these lateral holes may be formed by cutting out a portion of the mold 30, preferably these holes are formed during the coating process so that the silicon carbide coating is formed on the appropriate portions of the core piece. It is formed by covering the same area with a mask to prevent it from being exposed.

Obviously, other cross-sectional shapes of mold members may be formed in accordance with the present invention.

Therefore, for example, a mold member having a square cross section may be formed by coating the surface of a core piece with a square cross section with silicon carbide.

The removal of silicon carbide from the upper and lower end surfaces of the core piece is made unnecessary by the simple expedient of masking these surfaces of the piece before it receives the silicon carbide deposited from the gas phase. This should also be understood.

Various deposition methods familiar to those skilled in metallurgical processing may be used to form the silicon carbide coating on the surface of the silicon core.

Preferably the precipitation is performed using R.C. Marshall (R.
C. Marshall), J.W. Faust, Jr.
Mr. R) and C.E. Ryan
), South Carolina, USA
Silicon Car published by University of South Carolina Press, Columbia.
bid) 1973” (1974), from page 92 onward, W.F.
．． Knippenberg), G. Verspui and A.W.
A, W, C. Von Ke
This is accomplished by the dissociation of methylchlorobran in hydrogen as described by John Menade.

It is also conceivable that components made of other materials may be manufactured according to the invention.

Thus, for example, a silicon oxide mold used to grow silicon may be manufactured by depositing a coating of silicon oxide on the surface of a silicon core piece.

Silicon titanium is published in the Electrochemical Society Bulletin (J, Electrochemical Society).
No. 114 (1967), pages 717 et seq., by T. L. Chu, C. H. Lee, and G. Koichi Gruba. .A, Gruber) 3
His paper ``The Preparation and Properties of Amorphous S i 3N4''
Parties of Amorphorus
For example, as described in
It may also be deposited by chemical vapor deposition using Cl4 and NH3.

The quartz mold used in growing silicon may be manufactured by forming a Si02 coating on the surface of a silicon core piece.

The most common method for forming such coatings is by simple oxidation of silicon.

This method is used for almost all silicon device processing.

This coating can also be made by chemically vapor-deposited silicon carbide or by chemically vapor-deposited silicon carbide or on the same materials (i.e. Si3N4 to Si3N4 or SiO2 to S
i02) requires a backing coating to obtain the mechanical rigidity that can be imparted by bonding.

Of course, many alternative methods can be employed for the same end goal.

Silicon can thus be oxidized, for example directly, in methane or eg directly atomized in ammonia.

Both of these methods result in relatively thin coatings that will require auxiliary support.

Mold parts by precipitating mold material from the gas phase? Forming is preferred, especially if the mold material is formed by a gas phase reaction, such as the above-mentioned Ω, since the mold parts can be produced with almost perfect purity.

This is important because it minimizes the possibility of introducing unwanted contamination into the melt and crystalline product.

What is buried is that the mold material for growing silicon is deposited on the surface of a core piece that is not made of silicon, for example, silicon carbide is deposited on the surface of a germanium core piece. The core piece is melted and (
or) may be removed by suitable solvents or reactive chemicals.

However, the use of silicon core pieces minimizes the introduction of impurities into the crucible and crystalline product, while at the same time reducing the resistance of the capillaries of the new mold part to be wetted and filled by molten silicon. It is clearly advantageous in avoiding the problem of overcoming the problem.

The silicon core piece may be monocrystalline or polycrystalline.

However, polycrystalline core pieces are preferred because they are less expensive and can be easily obtained in various shapes.

A specific example of how the invention may be implemented is as follows.

The thickness is approximately 0.41 mm (0.016 inch) and the width is approximately 25.4 mm (13 inches) and 34.9 mm (1-3 mm).
A slab or ribbon of single crystal silicon having a length of 8 inches) is purified to remove surface impurities and then subjected to hydrogen dissociation of methylchlorosilane as described by Mr. Nitzpenberg (supra). The entire surface is coated with a 0.015 inch thick layer of silicon carbide deposited by.

The silicon carbide coating is then removed by grinding from both ends of the silicon plate, leaving a silicon carbide EFG-type member prefilled with silicon.

This mold member is then mounted in a crucible and used to grow a single crystal silicon ribbon.

If the method of the invention is modified, selected surface coatings that do not contain carbon and therefore reduce or eliminate the introduction of carbon as an impurity, such as SiO or S
A silicon carbide type with i 3 N4 can be produced.

The modified method is essentially as follows.

First, all or only selected portions of the surface of the silicon core are provided with a skin or coating of a selected material by chemical vapor deposition or by oxidation or curing.

Second, a silicon carbide mold is formed on the surface of the coated silicon core by vapor deposition as described above.

The silicon carbide is then optionally removed from selected areas of the core, such as the top and bottom ends.

Thereafter, the silicon core may be removed before the mold member is used, or it may be retained to provide a prefilled mold member.

In either case, the mold member comprises a silicon carbide body or substrate having a coating of the selected material, such as the one shown in FIG. 3 with silica-filled capillaries. ing.

If desired, an auxiliary coating of the same or a different material of choice may be applied to some or all of the outer surface of the silicon carbide body (either before or after the silicon core is removed if removed). ) can be applied.

Incorporation of silica onto the surface of silicon carbide type capillaries is accomplished by oxidizing the outer surface of the silicon core.

A silica coating on the exterior surface of a silicon carbide mold is similarly made by oxidizing the exterior surface of the mold.

Such oxidation is accomplished by heating the silicon core or silicon carbide body in oxygen to a temperature of about 1200 DEG C. or above 1200 DEG C., respectively.

The formation of the Si3N4 coating on the surface of the silicon core is accomplished according to known methods such as those described by Tei Erchu et al., supra.

An important feature of the invention lies in the fact that it allows monolithic designs with precisely dimensioned capillaries to be manufactured at relatively low cost.

Single-piece molds are advantageous because molds made by joining two pieces or many pieces have a tendency to "bleed", ie, leak silicon through the cracks formed between the pieces. .

Another advantage is that a pre-filled mold part is provided, with the core piece reinforcing the mold part and therefore requiring less rough handling than an unfilled mold part of comparable dimensions. This stems from the fact that it can withstand

Yet another advantage is that mold members constructed as described herein can grow silicon at a higher purity than is possible by machining the mold member from a rigid body of mold material. The fact lies in the fact that it can be manufactured (thus reducing contamination of the melt).

This high purity comes from the fact that the mold material is deposited on the surface of the core piece by a gas phase reaction.

Yet another advantage is that the wall thickness of the mold member can be varied simply by varying the amount of mold material deposited on the surface of the silicon core.

In the case of the EFG type, any desired peripheral configuration can also be created by machining or grinding the outer surface of the mold at the end surface that supports the thin film of molten silicon, while the capillary tube is simply shaped to the appropriate shape. It can be made to have any desired cross-section by using core pieces of any size.

It should also be noted that more than one core piece may be used to make a mold of the selected type.

Yet another advantage is that the present invention allows large numbers of identical molds to be manufactured relatively inexpensively.

It should be noted in this regard that, for example, a number of identical EFG-type members for growing silicon ribbons prepare a core piece having a length at least several times the length of the core piece 2; The core piece is coated with a layer of silicon carbide as previously described in connection with FIG. It can be obtained by cutting at right angles to plane 8 and constructing a prefilled mold member similar to that shown in FIG. 3, with each section thus obtained.

Of course, if an unfilled, empty mold member is desired, the core may be removed before or after the composite structure is cut into multiple parts.

[Brief explanation of the drawing]

1-3 are perspective views showing the formation of an EFG-type member according to the invention for use in growing flat ribbons; FIG.
Figure 5 is a perspective view showing the same mold member mounted on a crucible.
Figures 7 to 7 are perspective views showing the formation of a mold member used in growing a round filament, or rond, with crystal growth suspended in a capillary tube, and Figure 8 is a perspective view showing the formation of a mold member used in growing a round filament, or rond, with crystal growth suspended in a capillary tube. FIG. 8 is a sectional view showing the same mold member in FIG. 7 on a smaller scale than in the same figure; 2-... "Solid core piece", 6A... "Indentation", 10... "Solid layer" of second selected material
, or "silicon carbide member", 18... "interconnected device".

Claims (1)

Claims: 1. A method of fabricating a mold member having a capillary tube of a selected size and shape used for growing a crystal from a melt of a first selected material, comprising the steps of: providing a solid core piece made of a selected material and having a shape and size corresponding to the shape and size of the capillary tube;
(b) capable of being wetted by the melt of the first selected material; and (e) relatively soluble in the first selected material. The core piece is covered with a solid layer of a second selected material that does not react with the same material and that does not react with the same material, and both end faces of the core piece are exposed. A method of manufacturing a mold member, comprising the steps of: 2. The method of claim 1, wherein the core piece is made of silicon and the solid layer is made of silicon carbide. 3. A method according to claim 1, characterized in that the core piece is coated by vapor deposition of the solid layer. 4. The method of manufacturing a mold member according to claim 1, wherein the core piece has a rectangular cross section. 5. A method for manufacturing a mold member according to claim 1, wherein the core piece has a recess or protrusion on at least one surface thereof. 6. A method according to claim 5, characterized in that the depressions or protrusions are covered with the second coating selection material.