EP2139657A1

EP2139657A1 - Method and apparatus for the production of thin disks or films from semiconductor bodies

Info

Publication number: EP2139657A1
Application number: EP08748746A
Authority: EP
Inventors: Christopher Eisele
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-04-17
Filing date: 2008-04-15
Publication date: 2010-01-06
Also published as: KR20100015895A; JP2010525559A; DE112008001002A5; WO2008125098A1; US20100117199A1; DE102007018080B3

Abstract

The invention relates to a method and an apparatus for producing thin disks or films (3) from semiconductor bodies (1). Advantageously, a laser is used as a cutting tool (2). The beam of said laser is focused using suitable optical means, e.g. a cylindrical lens, in such a way that a linear intensity profile is created rather than a point-shaped one in order to cut the semiconductor film (3). Furthermore, it makes sense to place several linear intensity profiles in a row in such a way that a parting line is created across the entire width of the semiconductor body (1) such that the entire cutting line can be removed quasi continuously, at the repetition rate of the laser. Ideally, the peripheral beams of the focused laser beam which face the semiconductor body (1) should extend parallel to the edge of the semiconductor body (1). Near the tip (9) of the cutting tool (2), on the side facing the semiconductor film (3), the peripheral beams follow the bending radius of the semiconductor film (3), and an increasing gap is created as the distance from the focus (the tip of the cutting tool (2)) increases.

Description

Method and device for producing thin slices or films of semiconductor bodies

The present invention relates to a method and an apparatus for the production of thin disks or films from semiconductor bodies such as polycrystalline blocks (ingots) or monocrystalline rods.

Usually, wire saws are used to cut brittle-hard workpieces (such as silicon). In principle, two methods are used (description DE 19959414). Separating lapping involves the use of a slurry, while the cutting grains are firmly bonded to the wire during cutting. For both methods, the separation process is carried out by a relative movement of wire and workpiece. This relative movement is achieved in DE 19959474 in that the workpiece is rotated about its longitudinal axis. Usually the wire is moved and e.g. guided by pulleys several times through the workpiece so that many discs can be separated simultaneously. When cutting with brittle diamond saws, grating multi-wire saws (DE 19959414) are particularly suitable since the wire is not stressed mechanically by the deflection.

For the production of silicon wafers with a thickness of about 200 microns for photovoltaic predominantly wire saws are currently used. The minimum kerf is limited by the wire diameter and the sawing suspension.

The splitting of single crystal silicon rods as described in US 2004055634 may be an interesting alternative for the production of silicon wafers. In this case, the lateral surface of a silicon rod is irradiated locally with ion, electron or laser beams in order to generate targeted lattice defects. This is preferably along a line which is given by the crystal axes, so that the later cleavage plane corresponds to a crystal lattice plane. The splitting process takes place, for example, by mechanical shearing forces along the generated grating defects. When splitting no sawing losses. Further advantages are pure cleavage surfaces, a fast splitting process, as well as very flat surfaces. US 2004055634 indicates a potential benefit of 10,000 wafers per meter of silicon rod length.

If a laser steel is used to heat the lateral surface of the silicon rod locally, can be dispensed with the vacuum environment. DE 3403826 describes a method in which a notch in the circumferential surface of a circumferential notch is locally heated with a laser. With a thermal shock treatment, the disc is then blasted off the bar. By machining the notch, however, it is expected that the thickness of the silicon wafer is limited downwards.

In JP 2002184724 the lateral surface is locally heated with a focused eximer laser beam. The latter two methods require, as US 2004055634 a single crystal as a starting material. For gap separation processes it thus remains unclear whether an economical application for the production of thin semiconductor wafers can be realized in the future.

US 2005199592 also describes a separation method for separating silicon by means of laser radiation. However, this is the separation of silicon wafers in single chips. For example, an Nd: YAG laser is used

(1064 nm) focused so that the focus lies inside the disc. This leads to microcracks, which become a predetermined arrangement to predetermined breaking points for the disc. If, in addition, a notch is generated mechanically on the surface with a diamond tool or with a laser, the fracture line can be defined more precisely. Now the sliding can be broken by mechanical stress along the previously defined lines. US 2005199592 describes how disks with a thickness of, for example, 625 μm can be divided. The breaking edge can be specifically defined for this slice thickness, although the method can not be arbitrarily transferred to larger material thicknesses, since the working distance of the focusing optics and the absorption of the laser radiation limit the penetration depth.

Usually, the material processing works with focused laser beams where the working area is limited to the immediate surroundings of the focus. DE 19518263 describes a device for material processing in which the laser radiation is guided in a liquid jet onto the material surface. For this purpose, the focused laser steel is coupled by means of a special nozzle in the most laminar liquid jet possible. This method is also used when cutting silicon wafers. In this case, cutting widths of typically 50 microns are achieved, which are essentially determined by the liquid jet. However, it has been observed that in spite of the use of nanosecond pulses, this process produces melt zones which, after re-solidification, can impair the mechanical stability of the workpieces. The melting zones can be significantly reduced when working with shorter laser pulses. DE 10020559 mentions the following advantages for material processing with ultrashort laser pulses. "The special advantages of material processing with ultrashort laser pulses (fs laser pulses) are particularly evident in the extremely precise cutting and / or removal of materials which are both of minimal thermal and mechanical damage. It is possible to achieve ablation rates in the sub-μm range with cutting widths of less than 500 nm. "The minimally damaging thermal and mechanical processing represents the decisive advantage over processing with nanosecond pulses.

However, the small cutting widths can only be achieved when working within the limited depth of focus. For larger cutting depths, the gap width increases accordingly due to the beam focusing.

It is known that silicon can also be processed by utilizing femtosecond laser pulses utilizing the advantages mentioned above. Barsch et al. reached a gap width of 10-15 microns when dividing a 50 micron thick silicon wafer. They were also able to show that a line-shaped beam profile aligned along the cutting line leads to an increased removal rate compared to point-shaped beam profiles. For narrow joints, the working area remains limited to the spatially restricted area around the focus. This makes it difficult to realize narrow kerf widths in the production of rigid silicon wafers

The present invention is based on the object, a method for producing thin semiconductor films, in particular silicon films by separating semiconductor bodies and to provide a device for carrying out this method.

This object is achieved by a method according to claim 1 and with a device according to claim 15.

While a brittle-hard material, such as semiconductor material, is intrinsically rigid and brittle in nature, the method of the present invention advantageously advantageously utilizes the property that semiconductor wafers become more and more flexible the thinner they are.

Particularly advantageous is a method for the production of thin semiconductor films, in particular silicon films by separating semiconductor bodies by means of a separating tool, when the following method steps are carried out: a. providing a semiconductor body; b. bringing a separating tool to the semiconductor body; c. initiating a relative movement between the semiconductor body and the separation tool for the successive separation of the semiconductor film from the semiconductor body; d. spreading the already freely cut part of the semiconductor film away from the semiconductor body; e. optionally supporting the already freely cut part of the separated semiconductor foil and f. remove the completely separated part of the semiconductor film and spend in a further processing station or in a storage position.

Such a method is particularly advantageous if the production of the semiconductor film by separating one Surface of a semiconductor block takes place, or if the production of the semiconductor film is carried out by tangential separation from the mantle surface of a semiconductor rod. By multiple, on the circumference of the semiconductor rod offset tangential separation from the lateral surface of the semiconductor rod, several films can be separated in an advantageous manner at the same time.

The method according to the invention can be used to particular advantage if clearance for the separating tool is created by the spreading of the already separated part of the semiconductor foil from the semiconductor body, wherein the clearance is defined by the surfaces on the semiconductor body, the tip of the cutting tool and the semiconductor facing surface of the spread semiconductor film is formed.

For the separation, a pulsed, highly focused laser beam can be used, and / or a probe with liquid or gaseous etching medium. It may also be advantageous if the separation takes place under vacuum or under a special gas atmosphere.

Furthermore, it may be advantageous if, during separation, a focused laser beam modifies the semiconductor material and the modified semiconductor material is removed with a liquid or gaseous etching medium.

By the aforementioned tangential separation from the cladding surface of the semiconductor rod semiconductor films can be produced in almost any length very cheap, and by multiple, on the circumference of the semiconductor rod tangential separation simultaneously several semiconductor films can be made in almost any length. It is also very beneficial if the separation takes place at a workpiece temperature of more than 200 ⁰ C.

The method according to the invention can advantageously be carried out with a device which has means for spreading apart the free-cut part of the semiconductor film and means for supporting the freely cut part of the semiconductor film. The means for spreading apart the free-cut part of the semiconductor film may be formed as tensile and / or pressure means and act on the cut-free part of the semiconductor film. They can be designed, for example, as electrostatically operating devices and act on the cut-free part of the semiconductor film. But they can also be designed as devices which operate with negative or positive pressure. Especially with vacuum working devices that engage the cut portion of the semiconductor film, are advantageous.

The means for supporting the free-cut portion of the semiconductor film are advantageously designed as a support roller and support the already separated part of the semiconductor film from such that a minimum bending radius of the spread semiconductor film is not exceeded.

For this purpose, it is advantageous if the support roller is formed so that the splayed semiconductor film is merely elastically deformed.

An apparatus for carrying out the method can be realized advantageously, for example, if the cutting tool is realized by a pulsed laser whose pulse length is smaller than 10e-9s, wherein the pulsed laser It should have a high beam quality and be highly focused.

For flat separation, a laser with linear intensity profile can be used.

It may also be advantageous if a laser is used whose laser beam is guided in a medium close to the processing point. This medium can be glass fibers.

Furthermore, a fiber laser can advantageously be used. Equally advantageous may be to use a frequency-multiplied laser.

With the aid of exemplary embodiments, the invention will be explained in more detail with reference to the drawings.

It shows

Figure 1 is a schematic diagram of the separation process;

Figure 2 is a schematic diagram of the tangential separation;

FIG. 3 shows a schematic diagram of the tangential separation according to FIG. 2 with free space;

Figure 4 is a schematic diagram of the multiple tangential

Separating with open spaces and

Figure 5 is a schematic diagram of the separation process according to

Figure 1 with free space.

FIG. 1 shows a highly schematic representation of a semiconductor body 1, which is arranged on a machine tool, not shown, by means of a holder (also not shown). A separating tool 2 is in engagement with the semiconductor body 1 and serves to separate a half Semiconductor body, such as a silicon block, consist of a material that is difficult to work because it has a certain brittle hardness. The common processing methods are already described in more detail in the introduction to the description. The cutting tool according to the invention may be embodied as a focused laser beam, a tapered glass fiber as the medium for the laser beam, a probe with etching medium, a mechanical tool or another suitable cutting tool. The following is based on a highly focused laser beam as a separation tool 2, which can produce a parting line 4 with only a very small gap width 5. As a result of the spreading apart of the semiconductor foil 3 produced during the separation, a free space 6 is created between the semiconductor body 1 and the separated semiconductor foil 3, between the boundary surfaces of which the separating tool 2 can act. The free space 6 is bounded by the separating surface 7 on the semiconductor body 1, the tip of the separating tool 2 and a surface 8 of the spread semiconductor film 3 facing the semiconductor 1, as will be described in more detail later on FIG.

The spread is effected by means which exert tensile or compressive forces on the already separated region of the semiconductor film 3. For clarity, these tensile or compressive forces are indicated by two arrows Pl and P2, the arrow Pl symbolizing the compressive forces and the arrow P2 the tensile forces. The means for spreading apart the semiconductor film 3 can be realized by mechanically attacking elements or by non-contact elements. It makes sense to make the spread electrostatically. But also by means of a vacuum spreading of the semiconductor film can be realized. Likewise, through a targeted air Shot the already separated area of the semiconductor film 3 are spread so that the required space 6 for the cutting tool 2 is available.

The resulting joint width 5 of the parting line 4 is no longer determined by the width of the cutting tool 2, but only by the width of the tip 9 of the cutting tool 2, which can be significantly narrower than, for example, a saw wire, as in the state the technique is used to produce silicon wafers. The separation loss of semiconductor material is accordingly reduced considerably, because the loss-determining joint width 5 can be considerably reduced compared to the prior art. When using a highly focused laser beam as a separating tool 2, the area-related silicon consumption is significantly reduced, because the working area, ie the joint width 5 is limited to the area around the focus of the cutting tool 2. The thinner the separated semiconductor foil 3 is, the more flexible it becomes and the better it can be spread apart, the limits being given by the elastic deformation of the semiconductor foil 3 are. In order to prevent kinking of the spread semiconductor film 3, means for supporting the free-cut portion of the semiconductor film 3 are provided, which are formed as a support roller 10 and support the already separated part of the semiconductor film 3 such that a minimum bending radius of the spread semiconductor film 3 does not fall below becomes. The arrangement and the geometry of the support roller 10 is chosen so that the splayed semiconductor film 3 is only elastically deformed. The arrangement of the support roller 10 may be on a non-illustrated Werk- Grooved slide so made that it can follow the separation cut. This ensures that the already separated region of the semiconductor film 3 is always optimally supported.

FIG. 2 shows how, in a manner analogous to that described with reference to FIG. 1, a film 3 is separated from the outer surface of a semiconductor rod 11. The same or equivalent elements are provided to avoid repetition with the same reference numerals, with a detailed description of these similar elements is unnecessary. The tip 9 of a highly focused laser beam acts as a separating tool 2 separating a semiconductor film 3 from the rotating semiconductor rod 11. By using a semiconductor rod 11 as a starting material, the length of the separated film can be very large, theoretically a few kilometers. The round shape of a semiconductor rod 11 also makes it possible to simultaneously cut a plurality of semiconductor foils 3, 31, 32 from a semiconductor rod 11, which is shown schematically in FIG. The three semiconductor films 3, 31, 32 shown schematically here are supported by three support rollers 10, 101, 102 in the manner already basically described. Again, the same or equivalent elements are provided with the same reference numerals, so that a repetition of already described can be omitted.

FIG. 3 shows that a clearance 6 for the cutting tool 2 on the rotating semiconductor rod 11 is created by the separating surface 7 and the surface facing the semiconductor rod 11 on the semiconductor foil 3, without the tip of a tool being shown here.

The same applies to the free spaces shown in FIG. 4. Figure 5 shows, looking back on Figure 1, a free space 6 for a not shown separating tool according to this figure 1. Again, the same or equivalent elements with the same reference numerals.

It is within the scope of the invention that advantageously a laser is used as a separating tool 2 whose beam is focused by suitable optical means such as a cylindrical lens or a diffractive optical element such that instead of a point-shaped intensity profile a line-shaped intensity profile for separating the semiconductor film 3 is formed. Furthermore, it makes sense to line up several line-shaped intensity profiles in such a way that a dividing line is formed over the entire width of the semiconductor body 1, 11, so that the entire cutting line can be quasi-continuously removed (with the repetition rate of the laser).

Furthermore, the marginal rays of the focused laser beam which are facing the semiconductor body 1, 11 should ideally run parallel to the edge of the semiconductor body 1, 11. On the side facing the semiconductor foil 3, 31, 32, the marginal rays in the vicinity of the tip 9 of the cutting tool 2 follow the bending radius of the semiconductor foil 3, 31, 32 and with increasing distance from the focus (tip of the cutting tool 2) creates a gap that increases.

For femtosecond silicon cutting, it is an advantage to work either in a blanket gas atmosphere, an atmosphere that reacts with the vaporized silicon, or in a vacuum. This can lead to unwanted reaction pro- products are avoided and the surface quality is improved.

In addition to the direct laser ablation, the semiconductor material, generally silicon, in the parting line may initially only be modified and then selectively removed (mainly modified material) with a gaseous etching medium or an etching liquid.

Femtosecond fiber lasers are, for example, suitable as the laser source. In particular, frequency multiplication is advantageous with high efficiency because the energy density of the ablation threshold decreases for shorter wavelengths.

An increased temperature of the silicon increases the ablation rate during ablation with femtosecond lasers

Reference sign list

1 semiconductor body

2 cutting tool

3 semiconductor film

4 parting line

5 joint width

6 free space

7 separation surface

8 area on the semiconductor film

9 tip of the cutting tool 2

10 support roller

11 semiconductor rod

31 semiconductor film

32 semiconductor film

101 support roller

102 support roller

Claims

claims

1. A process for producing thin semiconductor films, in particular silicon films, by separating semiconductor bodies by means of a separating tool, characterized by the following process steps: a. providing a semiconductor body (1, 11); b. bringing a separating tool (2) to the semiconductor body (1, 11); c. initiating a relative movement between the semiconductor body (1, 11) and the separation tool (2) for the successive separation of the semiconductor film (3, 31, 32) from the semiconductor body

(1, 11); d. abspreizen the already freely cut part (8) of the semiconductor film (3, 31, 32) of the semiconductor body (1, 11); e. optionally supporting the already freely cut part (8) of the separated semiconductor film (3, 31, 32) and f. remove the completely separated part of the semiconductor film and spend in a further processing station or in a storage position.

2. The method according to claim 1, characterized in that the production of the semiconductor film (3, 31, 32) by separating from a surface (7) of a semiconductor block (1).

3. The method according to claim 1, characterized in that the production of the semiconductor film (3, 31, 32) by tangential separation from the jacket surface (7) of a semiconductor rod (11).

4. The method according to claim 3, characterized in that the production of the semiconductor film (3, 31, 32) by multiple, on the circumference of the semiconductor rod (11) offset tangential separation from the lateral surface (7) of the semiconductor rod (11).

5. The method according to claim 1, characterized in that by the spreading apart of the already separated part of the semiconductor film (3, 31, 32) from the semiconductor body (1, 11) free space (6) for the separating tool (2) is provided.

6. The method according to claim 5, characterized in that the free space (6) through the surfaces (7) on the semiconductor body (1, 11), the tip (9) of the separation tool (2) and the semiconductor body (1, 11 ) facing surface (8) of the spread semiconductor film (3, 31, 32) is formed.

7. The method according to any one of the preceding claims, characterized in that for the separation of a pulsed, highly focused laser beam is used.

8. The method according to any one of the preceding claims, characterized in that a probe with liquid or gaseous etching medium is used for the separation.

9. The method according to any one of the preceding claims, characterized in that the separation takes place under vacuum or under a special gas atmosphere.

10. The method according to any one of the preceding claims, characterized in that for the separation of a focused laser beam modifies the semiconductor material and the modified semiconductor material is removed with a liquid o- and gaseous etching medium.

11. The method according to claim 3, characterized in that by tangential separation from the jacket surface (7) of the semiconductor rod (11) semiconductor films (3, 31, 32) can be produced in almost any length.

12. The method according to claim 3 or 11, characterized in that by multiple, on the periphery of the semiconductor rod (11) offset tangential separation simultaneously a plurality of semiconductor films in almost any length can be produced.

13. The method according to any one of the preceding claims, characterized in that the separation takes place at a workpiece temperature of more than 200 ° C.

14. A process for the production of thin semiconductor films, in particular silicon films, characterized in that the production of the semiconductor film (3, 31, 32) by tangential separation from the mantle surface (7) of a semiconductor rod (11).

15. Device in particular for carrying out the method according to claim 1, characterized in that the device comprises means for spreading apart the free-cut part of the semiconductor film (3, 31, 32) and preferably means for supporting the free-cut part of the semiconductor film (3, 31, 32).

16. The apparatus according to claim 15, characterized in that the means for spreading apart the free-cut portion of the semiconductor film (3, 31, 32) are formed as tension and / or pressure means and on the free-cut portion of the semiconductor film (3, 31, 32nd attack).

17. The apparatus according to claim 16, characterized in that the means for spreading apart the free-cut part of the semiconductor film (3, 31, 32) are formed as electrostatically operating devices and the free cut portion of the semiconductor film (3, 31, 32) attack.

18. The apparatus according to claim 16, characterized in that the means for spreading apart the free-cut part of the semiconductor film (3, 31, 32) are designed as working with underpressure or overpressure devices and on the free-cut part of the semiconductor film (3, 31, 32) attack.

19. The apparatus according to claim 16, characterized in that the means for spreading apart the free-cut portion of the semiconductor film (3, 31, 32) are designed as vacuum-working devices and attack on the free-cut portion of the semiconductor film (3, 31, 32) ,

20. The apparatus according to claim 16, characterized in that the means for spreading apart the free-cutting part of the semiconductor film (3, 31, 32) are designed as working with compressed gas devices and attack on the free-cut part of the semiconductor film (3, 31, 32) ,

21. The device according to claim 15, characterized in that the means for supporting the free-cut portion of the semiconductor film (3, 31, 32) as a support roller (10) are formed and the already separated part of the semiconductor film (3, 31, 32) in such a way support that a minimum bending radius of the spread semiconductor film (3, 31, 32) is not exceeded.

22. The apparatus according to claim 21, characterized in that the support roller (10) is formed so that the splayed semiconductor film (3, 31, 32) is deformed only elastically.

23. The device according to claim 1, characterized in that the separation tool (2) is realized by a pulsed laser whose pulse length is smaller than 10e-9s.

24. The device according to claim 23, characterized in that the pulsed laser has a high beam quality and is highly focused.

25. Device according to one of the preceding claims, characterized in that a laser with linear intensity profile is used.

26. Device according to one of the preceding claims, characterized in that a laser is used whose laser beam is guided in a medium close to the processing point.

27. The device according to claim 26, characterized in that find use as a medium glass fibers.

28. Device according to one of the preceding claims, characterized in that a fiber laser is used.

29. Device according to one of the preceding claims, characterized in that a frequency-multiplied laser is used.

30. A semiconductor film produced by a process according to claims 1-14.

31. A semiconductor film according to claim 30, characterized in that the film is longer than the circumference of the silicon block or rod from which it has been separated.

32. Semiconductor film according to one of the preceding claims, characterized in that at least two of the three connecting lines between any three points on the film, which are not in line and whose surface normals are parallel, have the property that along the connecting lines, the crystal orientation changes continuously ,

33. Plant with a device according to claims 15-29 for the production of films with a method according to claims 1-14.

34. Production line with a plant according to claim 33,