DE102011119353A1 - Crushing semiconductor molding, comprises producing semiconductor molding having cavity, filling cavity with liquid having density anomaly effect, and cooling liquid below freezing point for producing pressure in cavity - Google Patents

Abstract

Crushing semiconductor molding, comprises (a) producing semiconductor molding (5) having a cavity (4), (b) filling the cavity with a liquid having a density anomaly effect, preferably with water, or with liquid surrounding the semiconductor molding, and (c) cooling the liquid below its freezing point for producing pressure in the cavity or on the outer surface of the semiconductor molding such that the semiconductor molding is crushed into fragments by volume expansion of the liquid, which is produced during cooling.

Description

The present invention relates to a method for comminuting semiconductor moldings, in particular silicon moldings with the aid of frozen liquid.

In the production of solar cells, silicon of high purity is required. Silicon for solar modules and also generally for semiconductors is obtained as a high-purity, rod-like polycrystal, which is formed by deposition of pure silicon on a silicon deposition body or a suitable carrier material.

Typically, such high purity polycrystalline silicon is formed by the Siemens method in CVD plants by chemical vapor deposition of a high purity gaseous chlorosilane onto a preferably heated silicon substrate. In this way, rods of polycrystalline silicon. In the conventional Siemens process, Si thin rods are used to start the process. These can be externally preheated to approx. 450 ° C and then heated to the required deposition temperature of approx. 1100 ° C by means of current flow in the CVD system.

Trichlorosilane, for example, is then fed into the reactor together with hydrogen as a reducing agent as reactants. This is reduced and pure silicon is selectively deposited on the surfaces of the Si thin rods to form a polycrystalline silicon rod.

The polycrystalline silicon rods produced in this way must be further processed for the subsequent process. The majority of the silicon present in a silicon rod thus obtained must be comminuted or split to a suitable size for further processing.

According to the currently used methods, the silicon rods are cut into sufficiently small pieces by means of a processing step, in particular by means of a machining tool. Typically, mechanical tools are used as machining tools. For example, the silicon rods can be broken by a hammer, crushing devices such as a jaw crusher or roll crusher. The silicon can also be heated by a furnace to a sufficiently high temperature and then thrown into water, so that the silicon body is broken by the shock of rapid cooling.

The prior art discloses other similar mechanical or thermal processing methods. However, the mechanical processing methods typically cause the silicon to be contaminated by contact with the processing equipment, the tools, and the materials used. The thermal processing methods often do not lead to a sufficient size reduction, they require a high energy input and can also lead to contamination. The consequence of contamination is that the broken and contaminated silicon must be cleaned consuming in a further process step. In this case, chemicals such as a mixture of nitric acid and hydrofluoric acid, with which the impurities are etched off in a downstream process, whereby any part of the silicon is lost lost.

Particularly disadvantageous are impurities by transition metals, which include, inter alia, copper, gold, iron, cobalt, nickel, chromium, tantalum, zinc and tungsten and impurities such as carbon, boron, phosphorus, aluminum and arsenic. Such impurities cause damage to a later silicon product even in small amounts, which can ultimately lead to impairment of quality and performance.

According to the present invention, therefore, a crushing and cleavage method is to be provided, which overcomes the disadvantages mentioned. It is therefore proposed a method which is less complicated and, as a result, more efficient and in which impurities are avoided or reduced to be reduced.

This object is achieved with the features of claim 1, wherein advantageous developments of the invention are specified in the dependent claims. All combinations of at least two features specified in the description, the claims and / or the figures also fall within the scope of the invention. For specified value ranges, all values lying within the stated limits should also be disclosed as intermediate values or limit values and may be claimable in any combination.

The basic idea of the present invention is to make use of the density anomaly of water (or other liquids having such) for the explosive effect of semiconductor molded bodies (also referred to in the following as silicon shaped bodies) during the transition from the liquid to the solid state of aggregation. For this purpose, a cavity is first formed in a silicon molded body and then filled with water in the liquid state of matter. Subsequently, the water is transferred to the solid state, that is frozen. The water expands from temperatures below 3.98 ° C due to its negative coefficient of expansion and generates in the cavity such a pressure that the silicon moldings shatters into fragments and thus comminuted according to the invention. The invention is described by the example of water, but without being limited thereto. With water, cooling to a temperature of about 3.98 ° C. is advantageously required to effect the transition to the solid state. Any other liquid with similar properties, that is with a density anomaly effect, could be used instead of water. Of course, different temperature ranges can apply here. As density aanomaly in the sense of this invention, the phenomenon is understood that a liquid in a defined temperature range has a negative coefficient of expansion and therefore expands during cooling within this temperature range. Water is therefore also particularly suitable for the process according to the invention, since water can be produced with high purity and does not introduce impurities into the silicon.

It is a method for comminution of semiconductor moldings, in particular of silicon rods specified, in which first a cavity having a semiconductor molded body is produced. Subsequently, the cavity is filled with a liquid having a density anomaly, in particular with water or the semiconductor molded body is surrounded by such, and the liquid is then cooled below the freezing point. As a result, such a pressure is generated from the inside out in the cavity or from the outside in the direction of the cavity due to the volume expansion of the liquid during cooling, that the semifinished molded article is comminuted into fragments.

The method can be subdivided essentially into the two following method steps explained in more detail.

A first step relates to the production of a semiconductor molded body, in particular a silicon molded body, in which a cavity is formed which, so to speak, constitutes a kind of "explosive chamber" for the subsequent process step of comminution.

A second step relates to the comminution of the shaped body using a liquid having a sealing anomaly, which undergoes such a volume expansion on cooling that it bursts the semi-conductor shaped body. The pressure that arises in the volume expansion of the liquid can attack either from the inside or from the outside of the semiconductor moldings. In the first case, a pressure from inside the cavity is built up by the volume expansion when cooling down the water and the semiconductor molded body is blown outwards. In the second case, the cavity is used so that an externally attacking pressure of the water can ever act in the direction of a cavity inwards, such that the semiconductor molded body collapses or decays into fractions. These two cases can also be combined. Highly pure water, in particular a water having an electrical conductance of 20 μScm or less, is preferably used as the liquid.

In an advantageous embodiment of the method, the semiconductor molded body is produced in a CVD reactor by means of deposition of semiconductor material on a deposition body. It is used to deposit the semiconductor material in the reactor, a hollow, tubular or cylindrical Abscheidekörper. This has the advantage that already a suitable and preferably elongated cavity for filling with liquid is formed.

The deposition body may, for example, be a hollow semiconductor tube, in particular of the same semiconductor material that is deposited. If a hollow semiconductor tube having a sufficiently high degree of purity is used, for example, the cavity formed by the semiconductor tube can be directly used for filling with the liquid, and no separation between the semiconductor molded body and the separator body is necessary.

Alternatively, the separation body can also be any other internally heatable body that does not provide contamination to the semiconductor material. Thus, for example, a solid or even hollow separator made of silicon nitride can be provided, which can be arranged freely suspended in the CVD reactor. The cavity in the semiconductor molded body can then be formed for example by heating the Abscheidekörpers to a temperature above the melting temperature of the semiconductor material, this causes a melting of the semiconductor molded body from the Abscheidekörper to form a cavity, preferably in the form and size of the Abscheidekörpers. The separation body is heated in this process step by a suitable heating device. The semiconductor molded body, which is heated by the Abscheidekörperseite then dissolves when reaching or exceeding its melting temperature at its interface to the Abscheidekörper of this and slips due to its gravity on the outer jacket of the free-hanging Abscheidekörperes down along away. This gives a semiconductor molded body which has the required cavity.

By a suitable choice of the shape and size of the Abscheidekörpers can be for the Blasting effect of the water produce particularly suitable cavity in the semiconductor molded body. Preference is given to a tubular elongated shape of the separation body, which is attached as possible in the sliding direction of the semiconductor molded body in the reactor hanging or directed downwards. Thus, when the deposition body heats up, the semiconductor molded body can slide off as smoothly as possible.

Preferably, the cavity is open on one side and formed closed on the opposite side, as a filling of the cavity is directly possible. When using a tube, it can be closed pressure-tight before filling with liquid at one or both ends.

In the step relating to the comminution of a semisolid molded article produced in this way, an additional pressure can be exerted externally on the liquid-filled cavity, advantageously to enhance the blasting effect. The external pressure can optionally be applied directly or indirectly to the liquid column.

One way to enhance the blast effect is to use a crystallization seed that can act as a freeze accelerator to induce a spontaneous phase transition. In particular, the formation of areas of supercooled liquid can be prevented. Such a freezing accelerator may be, for example, semiconductor material dust, which is supplied to the liquid before the phase transition.

Alternatively, to blast the semiconductor molding, the cavity may remain empty and external pressure may be generated. The semiconductor molded body is introduced into a container filled with liquid, so that the liquid surrounds the semiconductor molded body. Subsequently, by cooling down the liquid below its freezing point, the liquid is transferred to the solid state of matter. As a result, a pressure from the outside on the semiconductor molded body due to the volume change, that is, volume expansion of the liquid is generated and the semiconductor molded body is crushed into fragments. Advantageously, this is a pressure and dimensionally stable container is used, the material strength and construction is such that the volume expansion of the liquid acts almost exclusively in the direction of the semiconductor molded body. The use of a high-grade VA steel or, in general, a stainless steel has proved to be advantageous.

In a further preferred embodiment, in addition to the pressure generated by the freezing liquid, a pressure can be exerted externally on the semiconductor molded body for blasting the semiconductor molded body.

In an alternative method step, the liquid can be pressurized alternately by expanding liquid in the inner cavity and by the liquid surrounding the semiconductor molded body by means of cold expansion of the liquid for comminuting the semiconductor molded body.

Preferably, when creating a pressure with a container filled with liquid, the container is formed internally with straightening and guiding structures for the liquid. The purpose of these straightening and guiding structures is to direct the pressure during the expansion of the liquid in the direction of defined attack points. This has the consequence that the liquid undergoes forced guidance in its volume expansion during freezing, whereby the resulting forces can be directed specifically to defined areas.

Preferably, the liquid used is water, in particular DI water, which, on the one hand, has a sufficient volume change in order to achieve an explosive effect and, on the other hand, does not produce any impurities in the semiconductor material. In a preferred embodiment, the semiconductor molded body is a silicon molded body.

The invention will be explained in more detail with reference to the drawings. In the drawings show:

1 : A schematic representation of a reactor for carrying out the method according to the invention;

2 : Schematic sequence of the manufacturing steps of the separation of a silicon shaped body from the separation body to form a cavity;

3 FIG. 2: shows a schematic sectional view of a shaped silicon body produced by means of the method according to the invention and having a cavity; FIG.

4 : A schematic representation of a surrounding a silicon moldings filled with water container for pressurizing from the outside onto the silicon moldings.

1 shows a schematic representation of a reactor 1 with a CVD chamber 2 , In the CVD chamber 2 is a separator 3 arranged. The separator body 3 serves to deposit silicon, to make one, a cavity 4 having silicon shaped body 5 from the vapor phase.

In an advantageous embodiment, the CVD chamber 2 , with a tubular separator body 3 , as in the 1 represented, equipped. Advantageously, the deposition of silicon in the reactor 1 a hollow, tubular separating body 3 used, which preferably consists of high-purity silicon. The tubular separator body 3 is in the reactor 1 arranged upright at the bottom thereof. The separator body 3 has a cavity 4 on top of a cylindrical separation surface 6 is surrounded.

In the CVD chamber 2 becomes first a silicon moldings 5 by deposition of silicon, preferably by chemical vapor deposition from the gas phase on the separation body 3 produced. The deposition can z. Example, be carried out according to the conventional Siemens method in which a tubular Abscheidekörper 3 is used instead of a Si thin rod.

The deposition process takes place over a period of time until at the separation surface 6 of the separator body 3 Silicon has deposited in the required amount and is a rod or ingot-shaped silicon moldings 5 has formed. The silicon moldings produced in this way 5 encloses the separation body 3 and thus has the cavity 4 on.

Alternatively to the hollow, tubular separating body 3 can also be one as in 2 shown, possibly solid cylindrical separator body 3 be used. This is suspended in the CVD chamber 2 at one end 7 attached. As in 2 also shown, is the separation body 3 directly with a heater 8th connected to this heating up. The separator body 3 becomes thermally from the silicon moldings following the deposition process of the silicon 5 dissolved out to form a cavity 4 in the silicon moldings 5 , In the basic procedure is in 2 shown how the formation of a cavity 4 in the silicon moldings 5 he follows. First, the separator body 3 brought by heating to a temperature above the melting temperature of the silicon. The heating leads to a melting of the silicon molding 5 at the separation area 6 of the separator body 5 , thus at the interface between the separator body 3 and the silicon molding 5 , The silicon molding 5 slides due to the melting silicon composite and due to its gravity on the separator body 3 down and dissolves at the end of this completely off to form a cavity 4 , The so in the silicon moldings 5 generated cavity 4 corresponds in shape and size in about the shape and size of the Abscheidekörpers 3 from which it was thermally melted off.

An advantage of this manufacturing method is the possibility of a separation body 3 instead of using pure silicon also from a suitable and possibly more cost-effective silicon composition, such as silicon nitride. Another advantage is that the separation body 3 possibly reused after the thermal separation.

In 3 is a schematic sectional view of a silicon molding produced by the method according to the invention 5 with a cavity 4 shown.

In a further method step, the cavity 4 filled with water, for example with ultrapure DI water. Advantageously, the water at the time of filling a temperature of about 4 ° C, preferably of 3.98 ° C. In order to achieve a particularly efficient pressure generation in the next step, the cavity is filled as completely as possible and possibly closed the open ends by closure means at the openings. The cavity should preferably be filled to at least 98% (based on its volume), more preferably to 99.5% or more.

In a further step, the water is cooled to a temperature below its freezing point. In this temperature range, the water expands due to its negative expansion coefficient. When cooling down, therefore, the silicon moldings 5 in his cavity 4 due to the volume expansion of the water pressurized until it shatters into fragments. This effect can be reinforced by the fact that z. B. semiconductor material dust is used as a freezing accelerator to produce a sudden change in volume.

4 shows a schematic representation of a container 9 which is filled with water. A silicon moldings 5 with a cavity 4 is in the filled container 9 brought in.

In this alternative process step, a pressure from the outside to the silicon molding is used to break the silicon 5 exercised. This is done by cooling down the water below the freezing point. In this step, thus, a pressure from the outside of the silicon moldings 5 As a result of the volume change, the silicon molding is built up 5 shatters into fragments. The container 9 is preferred as a pressure and dimensionally stable container 9 educated. The container 9 is also with straightening and leadership structures 10 designed for the water, allowing an expansion of the water towards defined points of attack 11 on the silicon molding 5 is enforced.

There are described preferred embodiments, but an exchange or the combination of single or multiple features or deviating designs are possible. So z. B. instead of silicon and another semiconductor material in the manner described as semiconductor moldings are prepared and then crushed. The cooling of the liquid used can, for. B. by means of liquid nitrogen in direct contact. When using a semiconductor dust as a freezing accelerator, it may preferably be made of the same semiconductor material to avoid contamination with foreign materials.

LIST OF REFERENCE NUMBERS

1

reactor

2

CVD chamber

3

collecting bodies

4

cavity

5

Silicon moldings

6

separation area

7

The End

8th

heater

9

container

10

Guidance and management structures

11

targets

Claims (14)

Method for comminuting semiconductor shaped bodies with the following method steps: - producing a cavity ( 4 ) having semiconductor molded body ( 5 ); - filling the cavity ( 4 ) with a liquid having a density anomaly effect, in particular with water, or surrounding the semiconductor molded body with such a liquid; Cooling the liquid below its freezing point to create a pressure in the cavity ( 4 ) or on the outer surface of the semiconductor molded body ( 5 ), such that a volume expansion of the liquid resulting from cooling down causes the semiconductor shaped body ( 5 ) is crushed into fragments. A method according to claim 1, characterized in that the semiconductor molded body in a CVD reactor ( 1 ) by deposition of semiconductor material on a separation body ( 3 ) will be produced. A method according to claim 1 or 2, characterized in that the separation body ( 3 ) is a hollow semiconductor tube, in particular of the same semiconductor material which is deposited. A method according to claim 1 or 2, characterized in that the separation body ( 3 ) is an internally heatable body that provides no contamination to the semiconductor material. Method according to one of claims 1 to 4, characterized in that for the deposition of the semiconductor in the reactor ( 1 ) the separation body ( 3 ) at an upper end ( 7 ) in the reactor ( 1 ) is arranged freely suspended. Method according to one of claims 2 to 5, characterized in that the formation of the cavity ( 4 ) in the semiconductor molded body ( 5 ) is carried out as follows: - heating in the semiconductor molded body ( 5 ) Abscheidekörper ( 3 ) to a temperature above the melting temperature of the semiconductor material and melting of the semiconductor molded body ( 5 ) from the separation body ( 3 ) forming a cavity ( 4 ). Method according to one of claims 1 to 6, characterized in that for blasting the semiconductor molded body ( 5 ) additionally an external pressure on the liquid-filled cavity ( 4 ) is exercised. Method according to one of claims 1 to 6, characterized in that for blasting the semiconductor molded body ( 5 ) this into a pressure-stable container ( 8th ) is introduced with liquid, such that the liquid is the semiconductor molded body ( 5 ), wherein subsequently by cooling the liquid below the freezing point by generating a pressure from the outside on the semiconductor molded body ( 5 ) due to the expansion of the liquid of the semiconductor moldings ( 5 ) is crushed into fragments. A method according to claim 8, characterized in that for blasting the semiconductor molded body ( 5 ) additionally an external pressure on the semiconductor molded body ( 5 ) is exercised. Method according to one of claims 8 to 9, characterized in that the container ( 9 ) with straightening and management structures ( 10 ) is designed for the liquid, for directing the pressure in the direction of defined points of attack. Method according to one of the preceding claims, characterized in that the liquid is added during cooling before reaching the freezing point, a freezing accelerator. Method according to one of the preceding claims, characterized in that a semiconductor material dust, in particular silicon dust, is used as the freezing accelerator. Method according to one of the preceding claims, characterized in that as Liquid water, especially DI water is used. Method according to one of the preceding claims, characterized in that the semiconductor material is silicon.

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