DE2800507A1 - PROCESS FOR GAS SEALING CONNECTING HIGHLY PURE SILICON MOLDED PARTS - Google Patents

Description

Process for gas-tight joining of high-purity molded silicon parts

In high-temperature processes in semiconductor technology, especially in Diffusion, oxidation and epitaxial processes, reaction chambers made of silicon are recommended due to their greater purity than quartz, higher mechanical stability and lower gas permeability.

In addition to the silicon tubes used here, silicon end pieces are used and silicon caps are used because quartz parts are connected due to their different thermal expansion coefficient from silicon can be destroyed with silicon tubes in the event of a sharp change in temperature. The use of other connecting parts made of for example Duran glass is not feasible due to the high purity requirements of the semiconductor industry.

The production of silicon urea tubes closed on one side by deposition from the gas phase, for example, according to DT-PS 18 05 970, is technically extraordinarily complex, and in the rarest cases the carrier body used here as a separator body succeeds to be separated undamaged from the molded silicon body deposited thereon. A gluing of silicon parts with common adhesives is part of the application Such silicon molded bodies cannot be used for the semiconductor industry due to the impurities contained in the adhesives, such as in particular Heavy metals or other doping substances.

From DT-PS 19 17 Οίο it is known hollow bodies made of semiconductor material to be welded together in a vacuum or inert gas. The welding of silicon, which naturally has to be carried out at temperatures above the melting point, but leads in particular due to the intrinsic brittleness to extraordinary tensions, which often lead to

909829/0060

Lead breakage of the molded silicon body treated in this way. The welding Such a silicon molded body is made according to the cited patent usually done with high frequency, whereby the process by providing numerous, from the shaping and depend on the diameter of the hollow silicon body to be welded. Induction heating coils disproportionately expensive and therefore uneconomical will.

The invention was therefore based on the object of a method for gas-tight To find the connection of high-purity silicon molded parts, which is easy to carry out and inexpensive and through which the resulting Silicon molded body not contaminated by doping foreign atoms will.

This object is achieved in that between the to be connected Siliciuraforrateile germanium is brought and the joint is cured at a temperature within 937-1,400 C.

The method can in principle be carried out in two variants will. According to the first variant, the two silicon parts, which to be connected to each other, for example two flat-ground silicon tubes placed one on top of the other with one pole of one Welding transformers connected so that with a solid electrode as the opposite pole an arc can be maintained in which a germaniura rod, the purity of which is expediently selected according to the silicon to be treated, is melted so that the molten germanium flows between the silicon moldings to be connected. The whole arrangement is for this purpose in a furnace, for example a resistance furnace heated a temperature at which silicon becomes intrinsically conductive, so for example to a temperature between 300 and 600 C. Then the two molded parts to be connected are in the specified manner soldered together under a protective gas, for example argon. The second variant of the method, which is selected in particular when Silicon molded parts with a small diameter at the point to be attached are to be placed on larger silicon surfaces, consists in that in this larger silicon surface a groove or groove corresponding to the dimensions of the attachment point of the silicon molding to be attached is milled from a depth of preferably about 0.5 to 3 mm, up into this groove

909829/0060

pure germanium powder is given and after fitting the to be prepared Silicon molding in this groove the whole arrangement in a furnace, for example in a resistance furnace, under protective gas, such as

for example argon, exposed to a temperature within 937-1 · ^ ΟΟ C. will. The time during which the silicon moldings to be joined together are at a temperature within the specified range can range from a few minutes to a few hours. It is expedient here to use the molded silicon parts connected to one another to cure at least at the temperature at which they still have a high mechanical strength in their later intended use Should have strength. Due to the unlimited miscibility of silicon and germanium, they form in this way, depending on which one is selected Temperature, more or less silicon-rich silicon-germanium phases with a melting point that increases according to the silicon content.

The germanium does not need any in the method according to the invention Flux can be added. An addition of silicon is harmless; in addition, an addition of carbon can be advantageous if a Strength of the joint up to the melting point of silicon is desirable. The addition of carbon results in the formation of Interface between extremely high-melting silicon carbide interlayers

The method according to the invention allows individual pipes to be attached to manufacture silicon tubes of practically any length. It is well known that the length of the silicon tubes available by gas deposition is limited by the dimensions of the separation systems used. According to the method according to the invention, silicon tubes can now also be used Different pipe dimensions can be produced over the length. Also silicon boats, such as those used for holding semiconductor wafers for diffusion, oxidation and epitaxial processes are required, can be connected to each other in any shape from individual parts will. It is also possible to attach silicon sections to silicon tubes and thus laboratory devices usually made of quartz or Duran glass now to be manufactured from high-purity, high-temperature-resistant, gas-tight silicon.

909829/0060

example

A disk made of polycrystalline silicon (specific resistance 20J λ cm) with a diameter of 150 mm and a thickness of 15 mm is provided with a central bore of 20 mm in diameter, ground flat on both sides. A groove approx. 2 mm deep and 1.5 mm wide is milled in at a distance of 3 mm concentrically from this hole. The plate is placed on a piece of pipe made of polycrystalline silicon of the same purity, which has an inner diameter of 135 μm and an outer diameter of 15 mm and a length of 200 mm. The silicon plate is placed flush on the upper edge of the pipe section, which was ground flat beforehand. The silicon tube piece is then connected to one pole of a welding transformer. A tungsten electrode is used as the counter electrode and a high-purity germanium rod (specific resistance 50 _n_cm) 4 mm in diameter and 300 mm in length as solder.

The entire assembly is then placed in an oven, its Heating power is sufficient to bring the silicon to a temperature of approx. 500 C. The resistance furnace used has a gas inlet for the argon used as protective gas, as well as another one at the junction between the pipe section and the silicon plate Opening of 30 χ 30 mm, the one hand for the introduction of the tungsten electrode and the germanium rod and, on the other hand, for discharging the protective gas. The workpiece can be rotated from the outside in the furnace, so that the solder seam can be applied over the entire circumference. After the silicon plate has been soldered to the pipe section, the specified Milled groove filled with germanium powder. A silicon tube with an internal diameter of 20 mm is placed flush with the hole in the plate and 32 mm outer diameter with a length of 200 mm.

The entire arrangement is now placed in an oven, in which again argon is introduced as protective gas. The oven is heated to approx. 1,200 C and held at this temperature for about 15 minutes and then cooled to room temperature over a period of one hour and the finished soldered workpiece removed. By

909829/0060

Overlapping, any unevenness that may be present is evened out, so that no unevenness can be seen at the connection points. The connection points have a high mechanical strength and absolute gas impermeability.

909829/0060

Claims (1)

Claim Process for gas-tight joining of high-purity molded silicon parts, d a characterized in that germanium is brought between the silicon moldings to be connected and the connection point is cured at a temperature within 937-1 · 4θΟ C. 909829/0060