JP2003311371A - Method for casting vacuum chamber into sand mold - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To cast a large scaled vacuum chamber hardly generating cavity in the thick thickness at a low cost without wasting a time and a material. <P>SOLUTION: The vacuum chamber is cast by pouring molten Al alloy containing 0.5-5.8 wt.% Ni and the balance Al or 0.5-2.4 wt.% Mn and the balance Al into a sand mold B. At this time, it is desirable that chillers 7 are disposed at places corresponding to the lower end of a space part 3 of the vacuum chamber shape or side walls of the vacuum chamber shape in the sand mold B and a feeder head 4 is disposed at the upper part of the sand mold B. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sand mold casting method of a vacuum chamber used as a vacuum container in a semiconductor or liquid crystal manufacturing apparatus, a vapor deposition apparatus or the like, and more particularly to a sand chamber casting method to which a vacuum chamber is cast. In this case, it relates to measures for preventing porosity.

[0002]

2. Description of the Related Art In a semiconductor manufacturing apparatus or the like, a vacuum chamber is used for forming and etching a film on a silicon wafer, moving a silicon wafer, carrying work, and inspecting a silicon wafer. At present, this vacuum chamber is manufactured by shaving an Al alloy block material made by rolling or forging, welding an Al alloy rolled plate material, and the like.

[0003]

However, in the machining of a block material, it takes time to machine and a large amount of material is wasted. Therefore, the machining cost and the material cost are high and the manufacturing unit cost is high. Especially recently, silicon wafers are shifting from the conventional 8-inch size to 12-inch size,
Along with this, the semiconductor manufacturing equipment is also increased in size, and the vacuum chamber is also increased in size, such as requiring a size of 1.5 m to 2 m square or more. Therefore, when the vacuum chamber is formed by shaving, the processing cost and the material cost are further increased, and the manufacturing unit price tends to be cumulatively increased. Also,
In a vacuum chamber manufactured by welding, weld defects such as pinholes and shrinkage cracks are likely to occur in the weld, and in particular, those weld defects are more likely to occur as the vacuum chamber becomes larger and the weld becomes longer, It becomes difficult to secure the required vacuum performance.

By the way, there is a casting method as a method for producing a product using an Al alloy as a raw material. In casting, it is only necessary to make a casting with a shape close to the final product shape and finish the surface, so much less machining is required compared to shaving from block material, so the processing cost is significantly increased. It can be lowered and less material is wasted.
However, among the casting methods, the die casting method, the gravity die casting method, the low pressure casting method, and the like that use dies require expensive dies and dedicated casting equipment, so large castings such as vacuum chambers are required. In the case of high-mix low-volume production, the casting cost will be high and the cost will be high.

On the other hand, in the sand mold casting method, since the casting is cast with a sand mold using inexpensive sand as a raw material with a simple facility, the facility cost is not so high, and the degree of freedom of the size and shape of the casting is very high. It has the advantage that it is expensive and suitable for high-mix low-volume production. If the above vacuum chamber is cast by this sand mold casting method, the vacuum chamber can be produced inexpensively and easily in a large variety of small quantities, but there is a problem that a cavity defect is likely to occur as a drawback of the sand mold casting method, When a porosity defect is generated on the surface of the vacuum chamber, particularly on the inner surface of the chamber on the vacuum side, the degree of vacuum is lowered due to gas emission from the defective part, defective vacuum sealing, etc., and the vacuum chamber cannot be used.

[0006] Here, as for the types of cavities, when the molten metal solidifies and shrinks, the molten metal is not replenished to the solidified portion and a cavity is created to cause voids, and hydrogen that has been dissolved in the molten metal. There are two types, ie, a cavity of a molecule produced by the gas generated by being released into the casting as a gas when the molten metal is solidified in the mold. With regard to the cast cavity due to the former shrinkage, when the molten metal is solidified, it is solidified by sequentially giving directionality from one end of the casting to the other so that sufficient molten metal replenishment can always be performed toward the solidification interface, so-called By adopting a casting method that causes directional solidification, it is possible to suppress the occurrence of porosity due to shrinkage. However, in the latter case, it is very difficult to take countermeasures for the porosity caused by the gas in the sand casting, and the reason is as follows.

That is, when solidification of the Al alloy proceeds in the mold, there is a porridge-like solid-liquid coexistence region in which liquid and solid are mixed at the solidification interface, and gas release during solidification is It is known that it occurs in the solid-liquid coexistence region, and the wider the solid-liquid coexistence region, the more easily the gas-induced porosity tends to occur. The width of this solid-liquid coexistence region is inversely proportional to the solidification rate, and in sand mold casting, the solidification rate is small because the sand mold's thermal conductivity is very poor. To do. Furthermore, the solidification rate tends to decrease rapidly as the casting thickness increases and the heat capacity of the molten metal increases.
If it is more than m, it is impossible to prevent the formation of porosity due to gas by the usual sand casting method using an Al alloy for general casting even when using a chill metal or the like.

Here, the vacuum chamber generally has a wall thickness of 15 mm or more, and in the case of a large vacuum chamber, the wall thickness may exceed 50 mm. It is not possible to manufacture a sound vacuum chamber without.

The present invention has been made in view of the above points, and an object thereof is to provide a large vacuum chamber with almost no cavities even if the casting has a wall thickness of 15 mm or more by the sand mold casting method. It is to provide a sound sand casting that can be applied to, at a low cost, without wasting time and materials.

[0010]

In order to achieve the above-mentioned object, the present invention specifies the composition of an Al alloy which is a raw material for casting, and preferably puts a cold metal and a feeder in a sand mold, It is characterized by casting a sound vacuum chamber having a thickness of 15 mm or more and having almost no porosity.

[0011] Specifically, the solving means devised by the invention described in claim 1 is 0.5 to 2.4 wt% of Al alloy or Mn containing 0.5 to 5.8 wt% of Ni and the balance of Al. %, And the balance is Al. A molten aluminum alloy is poured into a sand mold to cast a vacuum chamber.

With the above-mentioned structure, in the invention according to claim 1, the Al alloy having the above-mentioned composition has a temperature range at the time of phase change from liquid to solid in the alloy phase diagram as compared with general casting Al alloys. Therefore, the width of the solid-liquid coexistence region at the solidification interface when the molten aluminum alloy solidifies in the sand mold during casting becomes smaller than that of general casting alloys.
As a result, the generation of porosity due to gas is suppressed, and a sound vacuum chamber is obtained. Moreover, since the sand mold casting method is inexpensive, the manufacturing cost is reduced.

According to a second aspect of the present invention, there is provided a solution according to the first aspect, in which the vacuum chamber is
It is characterized in that the bottom wall and the side wall have a container shape with a wall thickness of 15 mm or more.

With the above construction, according to the second aspect of the present invention, it is possible to obtain a sound vacuum chamber having no porosity despite having a thick wall.

According to a third aspect of the present invention, in the solution according to the first or second aspect of the invention, at least the lower end of the vacuum chamber-shaped space or the side wall of the vacuum chamber in the sand mold is cooled. It is characterized by arranging a metal plate and arranging a riser on the upper part of the sand mold.

With the above construction, in the invention according to claim 3, a temperature gradient is generated in the molten metal in the sand mold from the chill metal portion toward the direction of the riser having a large heat capacity, and along the temperature gradient. Then, the solid-liquid coexisting region at the solidification interface moves and the directional solidification occurs. At that time, the gas generated in the solid-liquid coexistence region moves together with the solid-liquid coexistence region and collects in the riser part which is the final solidification part, and no gas remains in the casting product part, and almost no porosity is generated.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION A sand mold casting method according to an embodiment of the present invention will be described below with reference to the drawings.

In this embodiment, a rectangular box type vacuum chamber A (see FIG. 2) used in a semiconductor manufacturing apparatus or the like is cast by a sand casting method, but the outer shape of the vacuum chamber A depends on its application. Hexagonal shapes and cylindrical shapes are also used, and the present invention can be applied to them.

At the time of casting, a molten metal made of an Al alloy as a raw material for the vacuum chamber A and a sand mold B as a casting mold as shown in FIG. 1 are prepared.

The sand mold B is composed of two sand molds, an upper mold 1 and a lower mold 2, and a vacuum chamber A to be cast at an intermediate portion where the upper mold 1 and the lower mold 2 are combined.
The vacuum chamber shape space portion 3 corresponding to the shape of is formed. In this example, the vacuum chamber A has an internal dimension of 400
mm square, depth 600 mm, wall thickness a1 and bottom wall a1
Both 2 have a container shape of 60 mm, but particularly when the wall thickness of the bottom wall a1 and the side wall a2 is 15 mm or more, a remarkable effect is exhibited. That is, when the thickness of the vacuum chamber A is 15 mm or more, a normal sand mold casting method using an Al alloy for general casting casts a sound vacuum chamber A with no cavities even when a chill is used. This is not possible, but the present invention seeks to enable this.

The vacuum chamber-shaped space 3 is in a state in which the opening a3 of the vacuum chamber A faces downward, and above the vacuum chamber-shaped space 3 of the upper mold 1, a cylindrical feeder 4 is provided. Are formed. In addition, when casting Al
The upper mold 1 is formed with a sprue 5 for supplying the molten metal to the vacuum chamber-shaped space 3 which is a product part and the riser 4, and the lower end of the spout 5 is connected to the vacuum chamber-shaped space 3 by a communication passage 6. is doing. In addition, a plurality of chills 7 made of a cast iron plate having a thickness of about 20 mm are installed at the lower end of the vacuum chamber-shaped space 3 and the inner wall of the vacuum chamber A corresponding to the inner surface of the side wall 2. There is. The above-mentioned riser 4 is a part which becomes a final solidification part in casting, and the riser 4
The effect of this is to give a temperature gradient to the molten metal in the sand mold B from the vicinity of the chill metal 7 toward the molten metal 4 to promote directional solidification, but in addition to this In addition to supplying, it also has the function of applying a molten metal pressure head to the product section to pressurize it and make the casting dense.

The molten aluminum alloy is poured into the sand mold B as described above to cast the vacuum chamber A. The molten aluminum alloy contains 0.5 to 5.8 wt% of Ni and the balance is Al. Al alloy or a melt of Al alloy containing 0.5 to 2.4 wt% of Mn and the balance of Al is used. The former Al-N
In the i-based alloy, the Ni content is 0.5 to 5.8 wt.
% Is set so that when the Ni content falls below 0.5 wt% and approaches to pure Al, the fluidity deteriorates and it becomes difficult to cast, and the strength and hardness decrease rapidly. While adverse effects will occur, the eutectic point (5.8 wt
%), The temperature range of the solid-liquid coexisting region becomes so wide that the effect of preventing porosity cannot be expected.

In the latter Al-Mn-based alloy, the Mn content is set to 0.5 to 2.4 wt% when the Mn content is less than 0.5 wt% and approaches the pure Al. As in the case of the above Al-Ni alloy, the flowability deteriorates and it becomes difficult to cast, and the strength and hardness are rapidly decreased, while the eutectic point (2 This is because the temperature range of the solid-liquid coexistence region is rapidly widened and the effect of preventing blowholes cannot be expected if the content exceeds 0.4 wt%. The width of the solid-liquid coexistence region below the eutectic point of the Al-Mn alloy is Al-Ni, as can be seen from the state diagram of FIG.
It is much narrower than the system alloys (see the state diagram in FIG. 3) and is advantageous for preventing porosity. However, this Al-Mn alloy is A
Compared to l-Ni alloys, casting cracks tend to occur during solidification shrinkage, which is disadvantageous when using a mold such as an inorganic self-hardening sand mold that has a large deformation resistance to solidification shrinkage of castings or when the wall thickness of castings is thin. Therefore, which one is used may be appropriately selected according to the purpose and application.

Next, examples will be shown.

In the first embodiment, as the material of the vacuum chamber A of FIG. 2, Al containing 4.0 wt% of Ni and the balance of Al is used.
-Ni-based alloy was used. The composition table is shown in Table 1. It should be noted that this component table contains other trace components in addition to Ni as the main component. However, this is similar to the case of the general casting alloy, but this is an impurity from the raw material Al ingot or from the molten metal treatment material. They are mixed and do not directly affect the blowhole preventing effect of the present invention. Also, for the purpose of preventing casting cracks and improving mechanical properties, Na,
In some cases, a trace amount of elements such as Ti and Mg may be added, but this also does not directly affect the blowhole prevention effect of the present invention.

[0026]

[Table 1]

Here, the alloy phase diagram of this Al--Ni alloy is as shown in FIG. From this state diagram,
In the case of the Al-4.0 wt% Ni alloy of the example, about 650
Above ℃, it is in a liquid state, and when the temperature drops, it will be about 6
Solidification of the molten metal starts at 50 ° C, and then solidification progresses to a solid-liquid coexistence region where solids and liquids coexist up to about 640 ° C. Become. The porosity caused by the gas is generated when the gas molecules dissolved in the alloy liquid in this solid-liquid coexistence region are released to the outside as a gas due to the decrease in solubility due to the temperature decrease. Since it is in a porridge-like state with a very high viscosity, the gas released there is difficult to move outward and is trapped as it is to solidify and form voids in the casting to form a porosity. From this fact, the wider the solid-liquid coexistence region in the alloy phase diagram, the more the chances of gas generation increase, and the tendency of the gas to generate cavities increases. Al-Ni of the first embodiment
A comparison between the case of a system alloy and the alloy phase diagram of an Al-Si system alloy (see FIG. 5), which is the most general basic alloy system as an Al alloy for casting (see FIG. 5), shows the range of practical alloy composition (S
In the solid-liquid coexistence region of the Al-Si alloy in (i: 3 to 18 wt%), the temperature range is generally wider than in the case of the Al-Ni alloy, and gas-induced cavities are likely to occur. I understand. In the vicinity of the eutectic point of the Al-Si alloy (Si: 11.7 wt%), the temperature width becomes narrower, but the solid-liquid boundary line has a very large inclination and is sensitive to changes in the component amounts. Even if the amount of Si slightly changes, the temperature range in the solid-liquid temperature range may sharply increase. Therefore, it is difficult to obtain a stable porosity preventive effect with such an alloy system, and it is not realistic in mass production in which a certain amount of variation in alloy component amount is unavoidable. As other typical aluminum alloys for casting, FIG. 6 shows alloy state diagrams of Al-Mg alloys and FIG. 7 shows Al-Cu alloys. -Mg
In the case of the Al-based alloy, Mg: 3 to 6 wt% and the Al-Cu based alloy, Cu: 2 to 5 wt%), the temperature range of the solid-liquid coexistence region is generally wide, as in the case of the Al-Si based alloy described above. It can be seen that gas blowouts tend to occur.

First for these general casting Al alloys
In the Al—Ni alloys of the examples, the width of the solid-liquid coexistence region and the inclination of the solid-liquid boundary line in the range of the eutectic point (5.8 wt%) or less in the alloy phase diagram of FIG. Even if the component amounts vary, it is possible to always obtain a stable and high effect of preventing blowholes.

That is, in the first embodiment, Ni was added to 4.
When an Al-Ni alloy containing 0 wt% and the balance being Al is poured into the vacuum chamber-shaped space portion 3 of the sand mold B, the molten metal is cooled and the heat is forcibly taken away by the metal 7 to accelerate the solidification rate and to push the molten metal 4 Solidification toward the side (directional solidification), and at that time, the solid-liquid coexistence region existing at the solidification interface also moves toward the above-mentioned riser 4, and the gas generated in the solid-liquid coexistence region also rises along with the solidification interface 4 And finally gathers in the hot water 4. The molten metal is finally solidified by the above-mentioned feeder 4, and as a result, cavities are gathered in the solidified portion of the feeder and the vacuum chamber A which is the product part has almost no cavities. In addition, the raw material Al-Ni
In combination with the characteristic that the solid-liquid coexisting region is narrow in the molten alloy and the gas that causes the porosity is less likely to be generated, the porosity prevention effect can be reliably obtained. Since the riser solidification part and the sprue solidification part do not become products, they are cut off from the vacuum chamber A.

In the second embodiment, as the material of the vacuum chamber A of FIG. 2, Al containing 1.5 wt% of Mn and the balance of Al is used.
A —Mn-based alloy was used. The composition table is shown in Table 2. The vacuum chamber A was cast in the same manner as in the first embodiment. This A
FIG. 4 shows a phase diagram of the 1-Mn-based alloy.

[0031]

[Table 2]

In order to confirm the porosity prevention effect in the vacuum chamber A manufactured in these first and second embodiments, the manufactured vacuum chamber A was machined over its entire surface, and then each chamber had a width of 50 mm and a length of 50 mm. A test piece of 50 mm was cut out, the surface of the test piece was observed under a microscope, and an image of the appearance of the test piece was analyzed. Furthermore, in order to confirm the vacuum performance of this vacuum chamber A, the diameter of the specimen after observation was 9 m.
A sample for measuring gas emission characteristics having a length of m and a length of 30 mm was cut out and the amount of gas released from the material was measured by the Landsley method. Table 3 shows some of those survey results.
For comparison, conventional aluminum alloys for casting (JIS AC
The results of the same investigation are shown for the case of casting with 4C material and AC7A material), and also the investigation result of the material for the conventional shaving vacuum chamber is shown. Table 3
As shown in FIG. 1, casting materials of the first and second embodiments (Al-Ni alloys, Al-Mn alloys) and conventional casting materials,
When compared with (AC4C, AC7A), both of the casting materials of the first and second embodiments are much smaller in both the amount of generated porosity and the amount of gas released than the conventional casting material. It was possible to confirm the effect of preventing porosity in the example. In addition, comparing the performances of the first and second embodiments and the conventional machined material, it can be seen that the performances are almost equal.

[0033]

[Table 3]

[0034]

As described above, according to the first aspect of the present invention, the Al alloy containing 0.5 to 5.8 wt% of Ni and the balance of Al or 0.5 to 2.4 wt% of Mn is used. Since the molten metal of the Al alloy containing the remaining balance is poured into the sand mold to cast the vacuum chamber, the width of the solid-liquid coexisting region can be narrowed and a sound vacuum chamber with almost no porosity can be cast at low cost. .

According to the second aspect of the present invention, even if the vacuum chamber has a bottom wall and a side wall with a wall thickness of 15 mm or more, a sound vacuum chamber with almost no porosity can be obtained.

According to the third aspect of the present invention, it is possible to surely obtain a sound vacuum chamber having almost no porosity defects by directionally solidifying the molten metal with the chill metal and the molten metal placed in the sand mold. .

[Brief description of drawings]

FIG. 1 is a sectional view of a sand mold used in a sand mold casting method according to an embodiment of the present invention.

FIG. 2 is a perspective view of a vacuum chamber.

FIG. 3 is a phase diagram of an Al—Ni based alloy.

FIG. 4 is a phase diagram of an Al—Mn based alloy.

FIG. 5 is a phase diagram of an Al—Si alloy.

FIG. 6 is a phase diagram of an Al—Mg based alloy.

FIG. 7 is a phase diagram of an Al—Cu based alloy.

[Explanation of symbols]

3 Vacuum chamber shape space 4 hot water 7 chilled money A vacuum chamber a1 bottom wall a2 side wall B sand mold

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) B22D 27/04 B22D 27/04 F // C22C 21/00 C22C 21/00 L N (72) Inventor Hiroshi Masaki Hiroshima Prefecture Hiroshima City, Asanami-ku, Nagatsuka 3-44-17-8, Hiroshima Aluminum Industry Co., Ltd. F-term (reference) 4E093 KA10 PB01 PB15 UC10

Claims (3)

[Claims] 1. A molten metal of an Al alloy containing 0.5 to 5.8 wt% of Ni and the balance of Al or 0.5 to 2.4 wt% of Mn and the balance of Al is poured into a sand mold. A sand casting method for a vacuum chamber, which comprises casting the vacuum chamber. 2. The sand casting method for a vacuum chamber according to claim 1, wherein the vacuum chamber has a container shape having a wall thickness of 15 mm or more on the bottom wall and the side wall. 3. The sand mold casting method for a vacuum chamber according to claim 1 or 2, wherein a chill is disposed at least at a lower end of the vacuum chamber shape space portion or a side wall of the vacuum chamber in the sand mold,
In addition, a sand casting method for a vacuum chamber, characterized in that hot water is placed above the sand casting.