DE102016002553B4 - Einkristallzüchtungsvorrichtung - Google Patents

Abstract

A single crystal growing apparatus comprising a housing wall (1), an inner space (2), a crucible unit (3) and a heater (4), said inner space (2) being formed by said housing wall (1), said crucible unit (3) and said Heating device (4) in the interior (2) are arranged, wherein the heating device (4) surrounds the crucible unit (3) at least partially, wherein an inner circumferential surface of the heating device (4) of the crucible unit (3) faces, wherein an outer surface of the heating device ( 4) of the housing wall (1) facing, wherein the crucible unit (3) comprises a crucible (10) and a crucible supporting structure (11), wherein the crucible (10) is trough-shaped, wherein the crucible (10) consists of quartz and wherein in the crucible (10) is a silicon melt (7) can be accommodated, characterized in that the crucible support structure (11) radially surrounds the crucible (10) completely and that the crucible support structure (11) has an internal Keramis Supporting layer (12) and at least one band-shaped, the support layer (12) umspannde ring structure (15), wherein the support layer (12) consists of a non-oxide ceramic and is composed of a plurality of support layer elements (13) and the crucible support structure (11) Surrounds crucible (10) as a susceptor.

Description

The invention relates to a single crystal growing apparatus for pulling semiconductor crystals by the Czochralski method. The scope covers both the photovoltaic and the semiconductor industry.

Various processes are known for producing silicon monocrystals, wherein the crystal growth can be carried out from the melt, from the gas phase or from the solution. Two of the most significant processes in this regard are the Czochralski process and the float zone process. While the Czochralski process allows for the drawing of larger diameter crystals with lower manufacturing costs, a significant advantage of the float zone process is that there is a significantly lower level of impurity contamination in the crystal.

From the prior art, single crystal growth devices for pulling crystals by the Czochralski method in various structures are known.

The publication DE 198 25 745 A1 discloses an apparatus for growing silicon single crystals by the Czochralski method. Here, the crucible is composed of an inner quartz crucible for receiving the silicon melt and an outer graphite crucible for protecting the quartz crucible. The crucible is enclosed by a heating device and a thermal insulation. Disadvantage of this structure, however, is that the outer graphite crucible, in combination with the often consisting of graphite heater without appropriate countermeasures causes an increase in carbon impurities. It is known as a countermeasure from the prior art to at least reduce the concentration of carbon and carbon intermediate compounds by flowing with an inert gas, in particular argon. Moreover, from the DE 30 05 492 C2 a comparable crucible construction is known in which the quartz crucible is embedded in a graphite crucible and is seated on a graphite plate.

A similar solution results from the document DE 91 11 315 U1 , A multi-part support crucible is described so that the graphite crucible surrounding the quartz crucible consists of several segments. By anchoring the segments in a holding element located below the support crucible, the movements of the quartz crucible taking place during the crystal production should be compensated.

Also the pamphlets EP 0 781 867 B1 and WO 2013/183218 A1 disclose the known crucible construction, consisting of an inner quartz crucible and an outer graphite crucible.

Furthermore, from the document WO 98/48 085 A1 a crucible construction is known which comprises a quartz inner crucible and a graphite support crucible. Between the crucibles, a reaction barrier made of a non-oxide ceramic is described here.

The writings DE 25 09 853 A1 . DE 101 41 554 A1 . DE 103 21 785 A1 and US 2003/0 070 612 A1 also describe crucible constructions.

All the above-described solutions known from the prior art thus have in common a melt-contacting quartz crucible with surrounding graphite edging. Thus, however, there are disadvantages with respect to the contamination by carbon particles, which are ultimately incorporated into the growing crystal and adversely affect the quality of the resulting crystal. Furthermore, only a short life of the quartz crucible and thus only a small number of feasible with a quartz crucible crystal growing operations can be achieved.

Based on the disadvantages of the prior art, it is the object of the invention to provide an apparatus for the cost-effective production of silicon monocrystals while increasing the life of the crucible and a reduction of the crystal contamination by foreign substances.

The object is solved by the features listed in claim 1. Preferred developments emerge from the subclaims.

A single crystal growth device according to the invention has a housing wall, an interior, a crucible unit and a heating device.

The housing wall describes the outer edge of the single crystal growth device. This is closed and typically has the shape of a hollow cylinder with a taper section in the upper region. The interior is formed by the housing wall.

The crucible unit and the heater are arranged in the inner space. To create an optimum range of process conditions, the pressure prevailing in the interior becomes preferably regulated to a value in the range of 0 to 200 mbar absolute pressure.

The crucible unit is composed of a crucible and a crucible supporting structure. The crucible is trough-shaped, made of quartz and is in one piece. Within the crucible is a silicon melt absorbable, whose temperature is held only a few degrees Celsius above the melting point acts.

The heating and temperature control of the contents of the crucible unit, ie the silicon melt, takes place by means of the heating device. This surrounds the crucible unit, is preferably designed as a hollow cylinder and made of graphite. In addition, the height of the heating device preferably corresponds to the height of the crucible unit, but regularly at least the height of the silicon melt contained.

In addition to the features mentioned, a generic single crystal growing device according to the Czochralski method usually also has a rotating device and a pulling device, wherein the rotating device is arranged below and the pulling device above the crucible unit. The rotating device is connected to a drive and is used for rotation of the crucible unit, since an optimization of the crystal quality can be achieved by the opposite rotation of the crucible unit and the growing crystal. The pulling device consists of a seed crystal, an associated seed crystal holder, a suitable traction means (eg wire, rope or stick) and a lifting device at its upper end. The pulling device thereby moves away from the surface of the silicon melt at a selected pulling rate, whereby some characteristic properties of the resulting silicon ingot, such as its diameter, can be adjusted.

The crucible support structure surrounds the crucible. Since single-crystal growth usually involves process temperatures in the region of more than 1400 ° C., a fundamental task of the tie-support structure is to maintain the shape of the quartz crucible. This is necessary because the mentioned process temperatures reach the range of the softening temperature of the quartz, so that the dimensional stability of the crucible is limited by softening. In the case of a change in the crucible shape also threatens an abrupt change in the level of the silicon melt, which ultimately the preservation of a monocrystalline structure of the growing crystal is highly vulnerable.

The single-crystal growth device according to the invention is characterized in that the crucible support structure has an inner, ceramic support layer and an outer ring structure spanning the support layer.

The crucible support structure radially surrounds the crucible completely. The crucible support structure thus surrounds the crucible and covers the lateral wall regions of the crucible. In this case, both a full-surface enclosure of the outer lateral surface of the crucible and an enclosure of only partial areas is possible. The possible size of the subregions results from this, as it requires the fulfillment of the support function.

In addition to the support function, the crucible support structure also fulfills the function of a susceptor. Accordingly, the crucible supporting structure serves to transmit the heat provided by the heater toward the crucible, making the heat uniform.

The ceramic support layer of a non-oxide ceramic forms the inner portion of the crucible support structure. It is thus in direct contact with the quartz crucible on its outer wall. It is such a ceramic used, which has a sufficiently high melting temperature and thermal conductivity.

The ring structure spans the support layer and therefore forms the outer portion of the crucible support structure. In this case, the ring structure may have different configurations, for example as a cylindrical or network-like structure as well as a ring or more rings in the strict sense. The ring structure absorbs the forces transmitted by the support layer. The ring structure is preferably made of a graphite-based material which has the required for this application high temperature resistance and mechanical strength even under the existing high temperatures. Preferably, the ring structure is formed of graphite-based material. In addition to using a graphite-based material, the ring structure may also be made of another suitable material such as molybdenum, tantalum, or non-oxide ceramic fibers. However, the particular advantage of a graphite-based ring structure is the cost savings that can be achieved over the alternative materials.

The ring structure is not in direct contact with the quartz crucible. Contrary to the state of the art, the graphite-based components of the crucible support structure are thus not in direct contact with the quartz crucible. It also makes it possible to use smaller amounts of graphite.

The monocrystal growth device according to the invention thus has, in particular, the following advantages.

The bases for the advantages can be seen in particular in the subsequent reaction processes.

The interaction of the quartz (SiO ₂ ) crucible with the melt (Si) produces silicon monoxide vapor (SiO). Furthermore, a part of the SiO reacts with the graphite components of the hot zone, which subsequently leads to the formation of carbon monoxide (CO).

As part of the Czochralski process, the resulting gases are to be removed by means of an argon flow. However, the, in the vertical direction from top to bottom directed, argon flow in industrial plants but not ensure complete removal of the SiO and CO. Thus, a significant portion of the SiO reacts with the supporting crucible made of graphite and with other graphite-based components of the hot zone. This in turn leads to the formation of further CO and as a solid present silicon (Si). Due to the reaction of the crucible materials SiO ₂ and C, the wetter results in addition to further CO and the solid silicon carbide (SiC). The resulting SiC attaches to the carbon-based components of the hot zone, significantly reducing their lifetime. Over time, the SiC deposits lead to progressive damage to the carbon-based components of the hot zone, since graphite and SiC have different thermal expansion coefficients. The resulting CO molecules, however, come into contact with the Si melt, SiC and further SiO are formed. Thus, carbon particles in the form of SiC are integrated into the growing crystal, drastically increasing its carbon content. Since the described SiC clustering process significantly reduces the quality of the grown ingot or wafers, it is undesirable in both the photovoltaic and semiconductor industries.

In addition, it was surprisingly found that, in addition, silicon monoxide vapor (SiO ₂ ) and the gas carbon monoxide (CO) are formed directly by direct contact of the quartz crucible (SiO ₂ ) with a graphite support crucible (C). The thus additionally produced silicon monoxide vapor (SiO) and the additional carbon monoxide (CO) thus formed adversely affects the above-described further reactions with the graphite components, with the crucible material and the melt.

A first advantage of the crucible support structure according to the invention is that the life of the quartz crucible is increased and thus the possibility exists of growing several crystals sequentially with a single crucible. This is because it has been found that the reactions between the quartz crucible and the graphite as a result of the prior art direct contact cause an immediate substantial removal of material from the quartz crucible, which has a strongly life-limiting effect. The ceramic support layer according to the crucible support structure according to the invention advantageously prevents the contact of the graphite with the quartz of the crucible and thus prevents or reduces the reactions described and thus the material removal.

A second advantage is the reduction of carbon impurities within the grown single crystal and thus the increase in the quality of the single crystal. By reducing the reactions that lead to the formation of carbon monoxide, the incorporation of carbon into the crystal to be grown is also reduced.

In this context, a third advantage of the invention is that the crucible supporting structure can be provided with a lower use of graphite, which is used only in the ring structure, not in the ceramic supporting layer. In addition, as a result of this advantage, the formation of carbon monoxide with consequent contamination of the crystal to be grown is prevented.

A fourth advantage is that the crucible support structure according to the invention improves the stability of the inner quartz crucible and thus restricts a temperature-induced change in shape of the quartz crucible.

Fifth, there is a cost advantage due to the long service life of the ceramic support layer, which is not attacked by the reactions described in contrast to graphite components.

According to the invention it is provided that the support layer consists of a non-oxide ceramic. This results in advantages for use within a single crystal growth device with respect to high chemical and thermal stability as well as high strength and hardness. Suitable materials are in particular silicon carbide, silicon nitride, boron carbide, boron nitride or aluminum nitride.

According to the invention, the support layer is composed of a plurality of support layer elements. By using a plurality of small area support layer elements arise compared to a one-piece design of the support layer advantages in terms of a simplified and thus more cost-effective production with a simultaneous saving of material. In addition, individual support layer elements can thus be removed for replacement or repair purposes, without the entire support layer is costly to replace. Another particular advantage proves that the thermal stresses with the help of the multi-part construction of the support layer compared to a one-piece support layer life are reduced significantly reduced.

The support layer elements are fixed according to a further preferred variant by positive connection in their positional relationship to each other. A shift of individual support layer elements, which in particular can impair the support function of the entire support layer and can consequently limit the positive effects of the crucible support structure according to the invention, is thus prevented. The present positive connection can be realized in various designs and includes all suitable types of connections. In particular, tongue and groove joints or the like come into consideration.

According to an advantageous development, all supporting layer elements have the same shape and size. Hereby, a simplified production of the support layer elements as well as a reduction of the complexity of the overall construction of the crucible unit is brought about. In addition, this measure ensures the uniformity of the operation of the support layer, concerning the support function and the transfer of heat energy.

A further advantageous embodiment includes that the support layer elements have an overhang at their upper edge. The upper edge is formed by the directed to the top of the crucible edge of the respective support layer elements. The overhang constitutes a partial section of the ceramic support layer elements which, contrary to the rest of the support layer, is not arranged parallel to the lateral wall regions of the crucible, but forms a right angle and therefore runs orthogonal to the latter. The overhang serves in particular as an additional possibility for mechanical stabilization of the ceramic support layer and at the same time prevents undesired displacement of the tension band.

Furthermore, a further preferred development of the solution according to the invention is that the ring structure is composed of a plurality of ring structure elements.

Since the support layer is fixed in its position surrounding the crucible by means of the ring structure, it is expedient to protect the support layer against displacements or against changes in position. This protection can be improved by using a plurality of ring structure elements compared to a one-piece ring structure, since the individual ring structure elements each surround the support layer on the outside and preferably present in different axial positions along the support layer.

In addition, by using a plurality of ring structure elements a comparable attachment of the support layer as by the use of a one-piece ring structure, which spans the support layer over the entire surface, are produced. Thus, there are corresponding advantages in terms of a reduced material requirements and the costs incurred. In addition, a further reduction in the proportion of graphite-based components in the context of the crucible support structure is achieved.

• 1 einer Schnittansicht der Einkristallzüchtungsvorrichtung,
• 2 einer perspektivischen Darstellung der Tiegeleinheit näher erläutert.

The invention will be described as an embodiment with reference to

• 1 a sectional view of the single crystal growing apparatus,
• 2 a perspective view of the crucible unit explained in more detail.

1 shows a sectional view of an embodiment of the single crystal growing apparatus according to the invention. All components of the single crystal growth device are in an interior space 2 arranged, which by a housing wall 1 is delimited spatially. In the center of the arrangement is the crucible unit 3 , which in the embodiment (as shown in detail in FIG 2 ) an inside crucible 10 made of quartz and an external crucible supporting structure 11 having. In the crucible unit 3 becomes a silicon melt 7 which represents the material basis for the monocrystal to be grown. Below the crucible unit 3 is the turning device 8th arranged while the pulling device 9 above the crucible unit 3 located. The crucible unit is surrounded 3 from the heater 4 , which in turn of a heat insulating layer 5 is enclosed. Here are both between crucible unit 3 and heating device 4 as well as between heater 4 and heat insulating layer 5 Distances before. The heat insulating layer 5 is constructed in the embodiment of two different layers, wherein the heating device 4 facing layer of carbon fiber reinforced carbon (CFC) and the housing wall 1 facing layer consists of a graphite-based felt. There is also a funnel 6 above the crucible unit 3 arranged. This has the shape of a hollow truncated cone whose diameter in the direction of the crucible unit 3 decreases.

In 2 is a perspective view of the crucible unit. The crucible unit 3 sits down from the crucible 10 itself as well as the crucible support structure 11 together. While the crucible 10 is present in one piece and consists entirely of quartz, the crucible support structure 11 a two-part construction, consisting of a ceramic support layer 12 and a graphite-based ring structure 15 , on. The support layer 12 surrounds the lateral wall areas of the crucible 10 and thus is in direct contact with the crucible 10 while the ring structure 15 the outer area of the support layer 12 spans. In the illustrated embodiment, the support position is 12 from a plurality of support layer elements 13 together, extending over the entire height of the crucible 10 extend and with the lateral edges on the adjacent support layer elements 13 issue. As material for the support layer elements 13 Here, a non-oxide ceramic was used. For better illustration, the support layer elements 13 drawn only in sections. At the top of the support layer elements 13 is an overhang 14 intended. This at the top of the crucible 10 attached supernatant serves the mechanical stabilization of the support layer 13 as well as the ring structure 15 , The ring structure 15 has several ring structure elements 16 on which the support layer 12 radially span. By using four ring structure elements 16 and their vertical distribution along the support layer 13 may in the present example an undesirable shift of the support layer 13 effectively counteracted. At the same time, savings are made in terms of material quantity and material costs compared to a one-piece, all-over ring structure 15 achieved.

LIST OF REFERENCE NUMBERS

1

housing

2

inner space

3

crucible unit

4

heater

5

thermal insulating layer

6

funnel

7

melt

8th

rotator

9

puller

10

crucible

11

Pot support structure

12

support layer

13

Support base member

14

overhang

15

ring structure

16

Ring structure element

Claims (5)

A single crystal growing apparatus comprising a housing wall (1), an inner space (2), a crucible unit (3) and a heater (4), said inner space (2) being formed by said housing wall (1), said crucible unit (3) and said Heating device (4) in the interior (2) are arranged, wherein the heating device (4) surrounds the crucible unit (3) at least partially, wherein an inner circumferential surface of the heating device (4) of the crucible unit (3) faces, wherein an outer surface of the heating device ( 4) of the housing wall (1) facing, wherein the crucible unit (3) has a crucible (10) and a crucible support structure (11), wherein the crucible (10) is trough-shaped, wherein the crucible (10) consists of quartz and wherein in the crucible (10) a silicon melt (7) can be accommodated, characterized in that the crucible supporting structure (11) radially surrounds the crucible (10) completely and that the crucible supporting structure (11) has an internal ceramic The support layer (12) consists of a non-oxide ceramic and is composed of a plurality of support layer elements (13) and the crucible support structure (11) Surrounds crucible (10) as a susceptor. Single crystal growth device according to Claim 1 , characterized in that the support layer elements (13) are fixed by positive connection in their positional relationship to each other. Single crystal growth device according to Claim 1 or 2 , characterized in that all supporting layer elements (13) have the same shape and size. Single crystal growth device according to Claim 1 . 2 or 3 , characterized in that the support layer elements (13) at an upper edge have an overhang (14). Single crystal growth device according to one of the preceding claims, characterized in that the ring structure (15) consists of a plurality of ring structure elements (16).

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