DE102007028439A1 - Separating flat-parallel silicon wafers from cuboid crystalline or polycrystalline silicon ingot using wire saw for photo-voltaic applications, comprises moving wire around rolls, and attaching the ingot to reception of the wire saw - Google Patents

Abstract

The method for separating flat-parallel silicon wafers from a cuboid crystalline or polycrystalline silicon ingot (1) using a wire saw for photo-voltaic applications, comprises moving a self-moving wire around rolls provided with grooves for forming a wire group (3), attaching the ingot to a reception (5, 6) of the wire saw, adjusting an angle of inclination of the plane lateral surfaces relative to a plane stretched by the wire sections, and separating the wafers by relative motion of the ingot and the wire groups. The ingot is connected with the reception over an intermediate plate (4). The method for separating flat-parallel silicon wafers from a cuboid crystalline or polycrystalline silicon ingot (1) using a wire saw for photo-voltaic applications, comprises moving a self-moving wire around rolls provided with grooves for forming a wire group (3), attaching the ingot to a reception (5, 6) of the wire saw, adjusting an angle of inclination of the plane lateral surfaces relative to a plane stretched by the wire sections, and separating the wafers by relative motion of the ingot and the wire groups. The ingot is connected with the reception over a wedge-shaped intermediate plate (4) such as an adhesive connection or an adhesive joint, and has uniform surface area. An acute angle (alpha ) is enclosed between plane lateral surfaces of the ingot turned to the wire groups and the plane stretched by the wire sections for beginning the separation. For beginning the separation, the sections of the moving wire touch the edge of the plane lateral surfaces in a series of point manner. The point-contacting takes place under formation of an angle given by the acute angle and the mechanical pre-stressing of the sections, where the angle is enclosed between the plane stretched by the wire sections and the lateral surfaces of the ingot. A tilting of the plane lateral surfaces to the plane stretched by the wire sections is maximum 1 mm on 200-800 mm breadth of the plane lateral surfaces. The reception is aligned parallel to the plane stretched by the wire sections. The angle of inclination and/or the acute angle are given by a wedge angle of the intermediate plate. An inclination mechanism is arranged to the reception. The reception is inclined by the adjustment of the inclination mechanism relative to the plane stretched by the wire sections. The ingot has another uniform surface area, which lies opposite to the plane lateral surfaces, is aligned parallel to the lateral surfaces and is connected over the flat-parallel intermediate plate with the reception. An angle of inclination of the plane lateral surface of the ingot and/or the front surface of the intermediate plate is determined relative to the plane stretched by the wire sections and is adjusted on the basis of the regulation. The reception is tilted by adjusting the inclination mechanism after the beginning of separation of the wafer in such a way that a front surface of the intermediate plate turned to the ingot is parallel to the plane for ending the separation process. The inclination device is adjusted so that wire sections stretching the plane of the group of wires are merged over the entire width of the ingot.

Description

Field of the invention

The The present invention relates generally to a method of separation a plurality of thin semiconductor wafers of one Semiconductor raw material block using a multiwire saw and more particularly relates to a simultaneous separation method a plurality of semiconductor wafers of a cuboid Semiconductor raw material block with small deviations and reduced surface damage, in particular at the edges of the semiconductor wafers.

Background of the invention

silicon and comparable semiconductor materials are characterized by a comparatively high brittleness. To separate from Semiconductor wafers made of a silicon blank therefore become common used a multiwire saw, in which a moving Wire of about a plurality of grooved rollers for formation a wire group runs, a plurality of parallel mutually extending and a plane spanning sections of the moving wire.

blanks of single or polycrystalline silicon or other semiconductor materials often have a circular cross-section. At the beginning of the separation of semiconductor wafers from such a blank cylinder Therefore, with a multiwire saw comes to a point contact of wire group and blank cylinder. This allows a comparatively precise "erosion" of the wire group in the blank cylinder.

Especially for applications in photovoltaics it is preferred single or polycrystalline silicon ingots with a produce rectangular cross-section, because so the Cuttings when cutting the silicon wafer to the usual Rectangular solar cell elements are reduced can. When separating silicon wafers from such cuboid Silicon ingots using a multiwire saw, However, it is difficult, small deviations and a high surface quality of silicon wafers, in particular on the edges, to achieve. Elaborate investigations of the inventors have shown that it is especially when sawing cuboid Silicon ingots due to the linear contact of the Wire group with a flat side surface of the ingot to uncontrolled lateral evasive movements of the saw wire comes. This is associated with a widening of the sawing gap and thus higher deviations and a reduction in the Surface quality, especially at the edge areas the silicon wafer. This is especially in the production of thin Wafern and in the achievement of low tolerances a problem.

DE 197 23 083 A1 discloses a multiwire saw and a cutting method wherein a crystal orientation of the semiconductor material ingot is determined and an inclination angle of the semiconductor material ingot is adjusted based on the determined crystal orientation outside the wire saw. Then, the semiconductor material ingot is attached to a receptacle of the wire saw, and the cutting work is started. In this way, a predetermined orientation of the crystal axes with respect to the surfaces of the semiconductor wafer is provided. The cutting processing can also take place in relation to the orientation of a predetermined crystal axis. The semiconductor ingot is cylindrical and has a circular cross-section. For adjusting the inclination angle, the semiconductor material ingot outside the wire saw may be inclined horizontally and vertically with respect to the plane defined by the wire group, so that the area of the cut wafer is a predetermined crystal face.

EP 1 320 438 B1 discloses a multiwire saw in which a receiving block receiving the cylindrical ingot may be tilted periodically with respect to a bisector perpendicular to the plane defined by the wire group. An application for rectangular cuboid blocks is not disclosed.

JP 10-249699 discloses a multiwire saw in which, for sawing a block-shaped semiconductor material ingot, the inclination angle of the planar side surface of the ingot to the plane defined by the wire group is periodically changed between + 45 ° and -45 ° so as to reduce the stress on the saw wire during to reduce sawing.

JP 11-320381 discloses a method for sawing a cylindrical semiconductor material ingot by means of a multiwire saw. In order to suppress variations in the mechanical bias of the saw wire at the beginning of separating the wafers from the ingot, the bias of the saw wire is varied during the start of the separation and set to a value higher than the mechanical bias during the further separation.

Another multiwire saw whose orientation can be periodically changed relative to a cylindrical semiconductor ingot is shown in FIG EP 0 885 679 A1 disclosed.

DE 10 2005 040 343 A1 and EP 1 110 652 A1 reveal multiwire saws, where the mechanical preload of the saw wire can be varied.

EP 0 716 910 A2 discloses a method for separating wafers from a semiconductor material ingot by means of a multiwire saw. The ingot is cuboid. The wire group facing flat side surface of the ingot is aligned parallel to the plane spanned by the wire group, so that it comes at the beginning of the separation to a linear contact of the wire group with this facing the flat side surface of the ingot and thus uncontrolled lateral evasive movements of the saw wire Subsections, which a wider kerf and a deterioration of the tolerances and surface properties of the wafer, especially at the edges, due.

Summary of the invention

task The present invention is a method according to the Further develop preamble of claim 1, so that the simultaneous Separating a plurality of semiconductor wafers from a cuboid Ingot with smaller tolerances and higher surface quality, especially at the edges of the rectangular wafers, can be done. Further aspects of the present invention concern appropriate uses.

These and further objects are according to the present Invention by a method according to claim 1 and by uses solved according to one of claims 12 to 14. Further advantageous embodiments are the subject of the referenced Dependent claims.

The invention is therefore based on a method as in DE 197 23 083 A1 or EP 0 716 910 A2 , the contents of which are hereby expressly incorporated by reference into the present application. According to the invention, at the beginning of the separation of the wafer, an acute angle is included between the planar side surface of the ingot facing the wire group and the plane defined by the wire group, at least at the beginning of the separation, so that the wire group first saws the ingot at an edge of the planar side surface of the ingot starts.

By the punctiform contact of the wire group with the edge of the ingot join in accordance with the invention Less inclination of the saw wire sections no uncontrolled lateral evasive movements when sawing the ingot on, what compared to the state of the art, where due to the parallel Alignment of the plane spanned by the wire group to be seeded Surface of the ingot according to the invention to lower Tolerances and less surface damage leads to the edge areas.

by virtue of the punctiform contact of the wire group with the edge of the cuboid ingot is also according to the invention realized a higher contact pressure, so the wire group when advancing faster penetrates into the ingot and in less Extent lateral evasive movements performs.

Of the Angle between the plane defined by the wire group and the facing this flat side surface of the ingot may be identical to the predetermined acute angle or may additionally by the mechanical prestressing of the saw wire to be influenced by. In principle, however, according to the invention a comparatively high mechanical preload of the saw wire preferred to any lateral evasive movements of the sections reduce the wire group.

to Realization of a point contact at the beginning of the separation According to the invention, the wafer satisfies one comparatively small tilting of the flat side surface of the ingot with respect to that spanned by the wire group Level. On the basis of a width of the flat side surface in the range between 200 to 800 mm according to the invention a maximum tilt of 5 mm, more preferably 3 mm and more preferably by Max. 1 mm on the aforementioned width of the flat side surface prefers.

According to one Another embodiment is the ingot on a receptacle attached to the wire saw so as to provide a tilt angle of the flat side surface relative to that of the wire group spanned level at the beginning of the separation of the plurality of wafers suitable to adjust.

The Adjustment of the angle of inclination can be via a wedge-shaped Intermediate plate done so that conventional multiwire saws Can be used in which the recording is usually aligned exactly parallel to the plane spanned by the wire group is. According to this embodiment the wedge-shaped intermediate plate in the receptacle of the wire saw taken, preferably adhered to this, and is the ingot mounted on a front of the wedge-shaped intermediate plate, preferably by an adhesive or adhesive bond. In this way can also be comparatively low tilt angle easy and without much mechanical adjustment effort the wire saw are achieved.

According to one alternative embodiment is the inclusion of the wire saw associated with a tilting device which relates to the receptacle can tilt the plane spanned by the wire group vertically. In this embodiment, a plane-parallel is preferred Intermediate plate used with your one surface recorded in the recording of the wire saw and their opposite surface as a holding surface is used for the ingot, including preferably an adhesive and adhesive bond serves.

Prefers is the angle of inclination between the spanned by the wire group Plane and this facing the flat side surface of Rohblocks set once, so that more adjustment effort eliminates and the semiconductor wafer under controlled conditions can be separated.

According to one Another embodiment, the aforementioned inclination angle even after the beginning of the separation of the plurality of semiconductor wafers by vertically tilting the recording of the wire saw relative changed to the plane defined by the wire group become. In such an embodiment, on the one hand a punctiform contact between the wire group and a longitudinal edge of the ingot are achieved and on the other hand be ensured that at the end of the separation the plane spanned by the wire group parallel to that of the ingot facing front side of the intermediate plate is aligned. Consequently does not eat the wire group or not to a significant extent in the intermediate plate into what the sawing process in total shortened and quite a multiple use of wedge-shaped or plane-parallel intermediate plate allows.

Provided due to the parallel orientation of the spanned by the wire group Plane relative to the front of the intermediate plate saw nose should remain on the wafers can, according to another Embodiment be provided that the vertical tilting the inclusion of the wire saw relative to that of the wire group spanned level during the separation process is done so that against Sägeende a small residual tilting of the Wire group spanned plane relative to the front of the intermediate plate persists.

According to one Another embodiment, the inclination angle during the separation of the semiconductor wafers only then changed, if the wire group extends over the entire width in the the wire group facing flat side surface of the ingot has eaten into it. So can an unnecessary line-shaped Touch even after the first sawing of the ingot be avoided.

One Another aspect of the present invention relates to the use a wedge-shaped intermediate plate, preferably as a glass plate is formed, and / or a wedge-shaped adapter plate, the preferably formed of metal such as iron or aluminum is and as an adapter plate for connection to a machine holder the wire saw is used on a multiwire saw for adjusting the angle of inclination between that of the wire group spanned plane and a plane facing this plane side surface a cuboid semiconductor ingot. The wedge-shaped intermediate plate serves to connect to a recording of the wire saw, intermediate plate and ingot preferably via an adhesive or adhesive bond are connected together. The wedge-shaped adapter plate serves to connect the aforementioned intermediate plate with the Machine seat of the wire saw, preferably over an adhesive or adhesive bond.

Further Aspects of the present invention relate to use of the inventive method for separating a plurality of plane-parallel silicon disks of a cuboid single- or polycrystalline silicon ingot as well as the use such a separated silicon wafer for applications in photovoltaics.

LIST OF FIGURES

following the invention will be described by way of example and with reference are described on the accompanying drawings, from which provide further features, advantages and tasks to be solved become. Show it:

1 in a schematic cross-sectional view of a method for separating a plurality of wafers according to the prior art;

2 in a schematic cross-sectional view of a method according to a first embodiment of the present invention;

3 in a perspective view of the method according to the 2 ;

4 in a schematic cross-sectional view of a method according to a second embodiment of the present invention; and

5 in a schematic cross-sectional view of a method according to a third embodiment of the present invention.

In the figures, identical Be identical or substantially identically acting elements or groups of elements.

Detailed description of preferred embodiments

The 3 shows in a perspective view of the basic structure of a wire saw for use in the inventive method. According to the 3 is a wire around a wire roll (not shown) and a plurality of grooved rolls 2 wrapped, leaving a horizontal wire group 3 is formed. This consists of a plurality of mutually parallel saw wire sections of the moving wire, which together, as in the 3 represented, span a plane. Opposite the wire group 3 is a cuboid silicon ingot 1 over a wedge-shaped intermediate plate 4 from a machine receiving plate 5 held, which is received in a machine seat (not shown) of the wire saw (see. 2 ). The saw wire is so around the rollers 2 guided, that a constant tension of a predetermined size acts on the wire. The wire sections of the wire group 3 are arranged equidistant to each other, for example, at a distance of 210 microns. A typical diameter of the saw wire is about 140 microns.

An engine (not shown) is with the rollers 2 coupled and moves the wire at a high speed. According to the 3 is the silicon ingot 1 above the wire group 3 arranged. After positioning the ingot 1 spaced and above the wire group 3 becomes the ingot 1 for separating a plurality of semiconductor wafers at a predetermined speed by lowering the machine mount (not shown) lowered so that the ingot 1 finally against the wire group 3 is pressed. During the sawing process, a solid-liquid dispersion is applied to the wire group 3 applied from a reservoir (not shown) via a nozzle and the ingot 1 cut by means of a lapping processing through the abrasive grains in this dispersion.

The 2 shows the arrangement according to the 3 in a schematic cross-sectional view. According to the 2 is the cuboid ingot 1 which has four substantially mutually parallel square or rectangular side surfaces with respect to that of the machine mounting plate 5 tilted plane formed by a predetermined angle. According to the 2 This tilt angle is due to the wedge angle of the wedge-shaped intermediate plate 4 specified. This consists for example of glass and is with the silicon ingot 1 connected via an adhesive or adhesive connection and with the machine receiving plate 5 connected in a suitable manner, in particular clamped. Due to the wedge angle of the wedge-shaped intermediate plate 4 will be an acute angle α between that of the wire group 3 spanned level and the wire group 3 facing side surface of the ingot 1 locked in. This acute angle α corresponds to the wedge angle of the wedge-shaped intermediate plate 4 ,

After the ingot 1 with the wedge-shaped intermediate plate (preferably a wedge-shaped glass plate) 4 connected and via the machine receiving plate (preferably made of a metal such as iron or aluminum) 5 with the machine holder 6 the wire saw is connected, preferably via an adhesive or adhesive bond, the ingot is 1 with preferably constant speed by lowering the machine holder 6 on the wire group 3 too moved. Finally, the right longitudinal edge of the wire group arrives 3 facing side surface of the ingot 1 under point contact in contact with the wire sections of the wire group 3 so the wire group 3 the raw block 1 begins to saw down on a longitudinal edge of the flat bottom of the ingot. This point contact is due to the tilting of the ingot 1 relative to the wire group 3 conditioned by the acute angle α. Optionally, the acute angle α deviates from the wedge angle of the wedge-shaped intermediate plate due to a mechanical compliance of the wire sections, corresponding to the mechanical prestressing of the saw wire.

Typically, the edge length of the silicon ingot is 5 '' to 6 '' , With such an outer dimension, the tilt of the ingot is 1 in relation to the wire group 3 typically about a maximum of 1 mm. More generally, the tilt in the inventive method is a maximum of 5 mm, based on a width of the wire group 3 facing bottom of the ingot from 200 to 800 mm, more preferably not more than 3 mm to said width of 200 to 800 mm and more preferably not more than 1 mm based on said width of 200 to 800 mm.

By tilting the wire group 3 relative to the bottom of the ingot 1 it comes to the mentioned point contact between Rohblock 1 and wire group 3 , According to the invention, the ingot is 1 thus defined sawn at a longitudinal edge, wherein a lateral deflection movement of the wire sections of the wire group 3 (lateral "swimming") according to the invention does not occur or does not occur to any appreciable extent, as a result of which the plane-parallel wafers with a higher dimensional accuracy can be separated off.The wafers separated according to the invention are characterized by a higher plane parallelism and a higher surface quality out. The kerf which is formed in each case when the plurality of wafers are separated is also narrower due to the negligible lateral deflection movement of the saw wires and substantially corresponds to the diameter of the saw wire used plus a narrow gap due to the use of an abrasive for separation.

By the point contact between bottom of the ingot 1 and wire group 3 can according to the invention at a predetermined mechanical bias of the saw wire, as determined by the design of the wire saw, when announcing the ingot 1 a higher contact pressure can be realized. The sawing wire thus eats faster into the raw block material, which is also promoted by the fact that at the beginning of Ansägens less material must be removed in the kerfs. By the inventive tilting of ingot 1 in relation to the wire group 3 the feed of the ingot needs 1 or the machine holder 6 no longer be reduced or at least only to a much lesser extent than in the prior art. Since a different residence time of the saw wire in certain wafer areas causes a different length lapping in these areas and thus a different thickness in these areas, the wafer can be separated according to the invention not only with higher dimensional accuracy but also with a higher surface quality, in particular with less surface damage along the Longitudinal edges of the ingot 1 , ie in the corner regions of the square or rectangular single wafers.

According to the By contrast, it is often necessary in the prior art during the sawing process, especially during the phase of the sawing, the feed speed of the feed table and / or to change the wire speed and / or the wire tension, which is conventional to saw marks and irregularities the sawn wafer surface leads.

by virtue of The aforementioned advantages are also according to the invention a temporary increase in saw wire tension not necessary when sawing the ingot. This reduces According to the invention, the requirements for the wire saw to be used and increases their reliability and sawing quality. Since according to the invention with constant Sägedrahtspannung can be worked, is an increased wear of the Wire guide rollers and pulleys due to a temporary Saw wire voltage increase is not to be feared. In addition, this contributes to the invention a homogenization of the surface quality in, as in the prior art at temporary Increase saw wire tension during transition the saw wire tension to the standard stress with surface steps or waves is due (due to changing Deflection and dwell time of the saw wire in the semiconductor material).

Like from the 2 it can be seen, the saw wire is the end of the separation of the wafer in the wedge-shaped intermediate plate 4 hineinfressen. This must therefore be replaced after separation of the semiconductor wafer. A gnawing of the saw wire into the wedge-shaped intermediate plate 4 can be prevented in this embodiment only if the machine recording 6 during the sawing process vertically relative to that of the wire group 3 plane spanned by the wedge angle of the intermediate plate 4 can be tilted, so that at the end of the sawing process of the wire group 3 spanned plane substantially parallel to that of the ingot 1 facing front of the wedge-shaped intermediate plate 4 is. Such an embodiment with the possibility of a relative tilting of machine recording 6 and wire group 3 during sawing is the invention explicitly considered.

The 4 shows a second embodiment, in which instead of the wedge-shaped intermediate plate 5 according to the 2 a plane-parallel intermediate plate 4 is used, which may consist in particular of glass. According to the 4 becomes the inclination of the ingot 1 relative to that of the wire group 3 clamped plane by tilting the machine holder 6 achieved vertically by a corresponding angle α, as shown in the enlarged insert.

Such a tilting of the machine holder 6 relative to that of the wire group 3 spanned level needs to be made according to the invention in principle only once, for adjusting the wire saw. The tilt angle α is also selected in this embodiment as described above with reference to the first embodiment, so that here too the wire group 3 the ingot at the beginning of the separation of the semiconductor wafer on a longitudinal edge of the wire group 3 facing flat bottom of the ingot 1 begins to mark.

Also in this embodiment, the wire group becomes 3 to the end of separating the semiconductor wafers into the ingot 1 facing front of the intermediate plate 4 hineinfressen. In order to prevent this, according to a further embodiment it can be provided that the machine receptacle 6 relative to the wire group 3 during the sawing process by the tilt angle α vertically with respect to that of the wire group 3 tilted plane can be tilted. In such an embodiment, that of the wire group 3 clamped plane to the end of the separation parallel to the raw block 1 facing front of the intermediate plate 4 ,

As will be readily apparent to those skilled in the art, the machine receiving plate may alternatively be used 5 be wedge-shaped to achieve the effects achieved in the preceding section.

The 5 shows finally a third embodiment of a wire saw for use in the inventive method. According to the 5 is an additional unit 7 for determining the orientation of the underside of the ingot 1 or the tilt angle relative to that of the wire group 3 spanned level. Such a determination can in particular be made optically or by suitable evaluation of video images. The determining device 7 determines the inclination of the ingot 1 in relation to that of the wire group 3 spanned level, based on the machine image 6 the wire saw can be adjusted manually, for example. This adjustment can in principle also automatically based on the signal of the determination device 7 respectively. For this purpose, the machine holder 6 an adjusting device 8th be assigned, which is the machine 6 around a mid-perpendicular to the bottom of the ingot 1 corresponding pivot axis 9 can pivot by motor.

According to a further embodiment, the determination device 7 additionally or alternatively, the wire group 3 facing underside of the ingot 1 monitor during the sawing so as to determine the wire group is warming up 3 across the entire width of the ingot 1 into whose bottom has eaten. Then, a signal can be output that a pivoting of the machine recording 6 around the axis 9 releases the aforementioned tilt angle, until finally the of the wire group 3 spanned plane parallel to the raw block 1 facing front of the intermediate plate 4 is aligned. This adjustment is made by the adjusting device 8th powered by a motor. The pivoting movement required for this purpose can be distributed uniformly over the entire process time of the sawing process, which leads to no significant unevenness of the sawing speed. However, too high an adjustment speed during tilting during the sawing process can lead to the formation of saw marks and unevenness of the sawed wafer surfaces, which can be achieved by adjusting the adjustment speed according to the overall process duration.

According to a further embodiment, the determination device 7 furthermore, the orientation of the wire group 3 spanned level in relation to the raw block 1 facing front of the intermediate plate 4 monitor, so that based on such a signal, a control device, the adjusting device 8th so controls that the two said planes are aligned parallel to each other at the end of the sawing process, the wire group 3 so not in appreciable extent or not at all in the intermediate plate 4 into it eats.

Another aspect of the present invention relates to the use of a wedge-shaped intermediate plate 4 , like in the 2 shown in a multiwire saw according to the prior art, as this example in the DE 197 23 083 A1 in which the machine mount is aligned parallel to the plane defined by the wire group for realizing a tilt of the semiconductor ingot relative to that of the wire group 3 spanned level and to realize a point contact of ingot and wire group during the phase of the rough ingot. According to the invention, the aforementioned tilting is set once and in the multiwire saw, whereas according to the prior art, for example according to the DE 197 23 083 A1 , the adjustment is only the alignment of round ingots or blanks to the crystal axes.

As the skilled person will be readily apparent that is suitable inventive method, in particular for separating a plurality of plane-parallel silicon wafers of a cuboid single or polycrystalline silicon ingot, for example produced by the VGF method (Vertical Gradient Freeze Method) is. Such separated silicon wafers are particularly suitable for applications in photovoltaics. Because these are due the cuboid shape of the ingot after separation already over a rectangular or square Base area, the blend can be at the production of solar cells are minimized. The according to the invention Process separated silicon wafers are characterized by a more uniform Thickness, smaller deviations and a higher one Surface quality especially in the area of the edges. As will be readily apparent to those skilled in the art, it is suitable However, the inventive method in principle for any semiconductor materials.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 19723083 A1 [0005, 0014, 0052, 0052]
• - EP 1320438 B1 [0006]
• - JP 10-249699 [0007]
• - JP 11-320381 [0008]
• EP 0885679 A1 [0009]
• - DE 102005040343 A1 [0010]
• EP 1110652 A1 [0010]
• - EP 0716910 A2 [0011, 0014]

Claims (14)

Method for separating a plurality of semiconductor wafers from a semiconductor raw material block ( 1 ) having at least one flat side surface using a wire saw, in which a moving wire is wound around a plurality of grooved rollers (Fig. 2 ) to form a wire group ( 3 ), which comprises a plurality of mutually parallel and a plane-spanning portions of the moving wire, wherein the plurality of semiconductor wafers by relative movement of ingot ( 1 ) and wire group ( 3 ) are separated, characterized in that between one of the wire group ( 3 ) facing flat side surface of the ingot ( 1 ) and the plane spanned by the wire sections, at least at the beginning of the separation, includes an acute angle (α) so that the wire group begins to saw the ingot at an edge of the planar side surface. The method of claim 1, wherein at the beginning of the separation the sections of the moving wire the edge of the plane Touch the side surface punctually. Method according to Claim 2, in which the point contact is formed by forming an angle between the plane defined by the acute angle and the mechanical pretension of the subsections between the plane ( 3 ) And this facing side surface of the ingot takes place. Method according to one of the preceding claims, wherein a tilt of the flat side surface in relation to that of the sections of the moving wire spanned Level maximum 5 mm on 200 to 800 mm width of the flat side surface, more preferably 3 mm to 200 to 800 mm width of the flat side surface and more preferably at most 1 mm to 200 to 800 mm width of the flat side surface amounts. Method according to one of the preceding claims, further comprising the steps of: attaching the ingot ( 1 ) on a recording ( 5 . 6 ) of the wire saw; and setting an inclination angle of the planar side surface relative to the plane defined by the wire sections at the beginning of separating the plurality of semiconductor wafers so that the wire group starts to suture the ingot at an edge of the planar side surface. Method according to claim 5, wherein the ingot ( 1 ) with the recording ( 5 . 6 ) via a wedge-shaped intermediate plate ( 4 ), preferably by an adhesive or adhesive bond, the receptacle ( 5 . 6 ) of the wire saw is aligned parallel to the plane spanned by the wire sections and the angle of inclination or the acute angle (α) by a wedge angle of the wedge-shaped intermediate plate ( 4 ) is given. Method according to claim 5, wherein the receptacle ( 5 . 6 ) of the wire saw a tilt device ( 8th ), the raw block ( 1 ) with the inclusion of a plane-parallel intermediate plate ( 4 ), preferably by an adhesive or adhesive bond, and the receptacle ( 5 . 6 ) by adjusting the tilting device ( 8th ) is tilted relative to the plane defined by the wire sections, between the flat side surface of the ingot ( 1 ) and the plane spanned by the wire sections of the plane of the acute angle (α) is included. Method according to claim 7, wherein the ingot ( 1 ) has a further planar side surface, that of the wire group ( 3 ) facing facing planar side surface, is aligned parallel to this and via the plane-parallel intermediate plate ( 4 ) with the recording ( 5 . 6 ) connected is. Method according to one of claims 5 to 8, wherein an angle of inclination of the flat side surface of the ingot and / or the tube block ( 1 ) facing front of the intermediate plate ( 4 ) is determined relative to the plane defined by the wire sections and the inclination angle of the planar side surface of the ingot and / or the ingot ( 1 ) facing front of the intermediate plate ( 4 ) is set relative to the plane defined by the wire sections based on the determination. Method according to claim 7 or 8, wherein the receptacle ( 5 . 6 ) by adjusting the tilting device ( 8th ) is tilted after the beginning of the separation of the plurality of semiconductor wafers such that a tube block ( 1 ) facing front of the intermediate plate ( 4 ) at the end of severing parallel to the plane defined by the wire sections. Method according to claim 10, wherein the inclining device ( 8th ) is first adjusted after it has been determined that the wire group ( 3 ) spanning wire sections the facing this planar side surface of the ingot ( 1 ) have sawn over the entire width. Use of the method according to one of the preceding claims for separating a plurality of plane-parallel silicon wafers from a cuboid monocrystalline or polycrystalline silicon ingot ( 1 ). Using a method according to any one of Claims 1 to 11 separated silicon wafer from a or polycrystalline silicon for photovoltaic applications. Use of a wedge-shaped intermediate plate ( 4 ), which is preferably formed as a glass plate, or a wedge-shaped intermediate plate in a wire saw, in which a moving wire around a plurality of grooved rollers ( 2 ) to form a wire group ( 3 ) comprising a plurality of mutually parallel and a plane-spanning portions of the moving wire, for adjusting an inclination angle of the plane defined by the wire sections relative to a plane side surface of a semiconductor material ingot (FIG. 1 ), that with a recording ( 5 . 6 ) of the wire saw received intermediate plate ( 4 ), preferably via a main or adhesive connection, so that the wire group ( 3 ) the ingot ( 1 ) starts to be sawed on one edge of the flat side surface.