WO2011050945A1

WO2011050945A1 - Wire saw comprising a wire web and cleaning nozzles

Info

Publication number: WO2011050945A1
Application number: PCT/EP2010/006541
Authority: WO
Inventors: Antonio Deagostini; Simon Habegger
Original assignee: Meyer Burger Ag
Priority date: 2009-10-28
Filing date: 2010-10-27
Publication date: 2011-05-05

Abstract

The present application relates to a wire saw (1) comprising a wire web (2) equipped with cutting means, wherein at least one nozzle (5) blasts the cutting chips from the wire web (2) at least over the width of the cutting surface of the wire web (2) using liquid. Furthermore, the application relates to related cutting methods and to uses of said wire saw (1).

Description

Wire saw with wire field and cleaning nozzles

The present invention relates to a wire saw with a cutting wire-equipped wire field in which at least one nozzle radiates the cutting chips from the wire field at least over the width of the cut surface of the wire field with liquid. In addition, the

Invention directed to appropriate cutting methods and uses with this wire saw.

The semiconductor and photovoltaic industries use crystalline silicon for the manufacture of computer chips and photovoltaic systems. The by the manufacturer as a single crystal (ingot) or polycrystalline block (brick) with weights of up to several hundred kilograms provided raw silicon undergoes a series of cutting processes that convert the crude crystals into a parallelepiped, which then cut into thin to gauzy slices (wafers) which are cleaned, post-treated and then finally processed for the respective application.

After cutting the ingots or bricks by means of so-called inner hole, outer, band, wire and dicing saws in cuboid and surface treatment, these are then usually cut with wire saws (DS265, DS264 and DS271) into thousands of thin to very thin slices.

A wire saw typically consists of two wire guide rollers with high-precision and fine grooves which guide a thin steel or bladed steel wire. The wire tension between the guide rollers creates a wire field that turns into one or alternating by quickly turning the guide rollers

Moved directions and so the ingots and Bricks using bonded cutting means or entrained Läppsuspension (also called Zerspanungsuspension) in gossamer slices. In wire saws, a distinction is made between wire-coated wire saws and separating liquid (eg DS 261, 264, 265 and 266 from Meyer Burger AG, Thun, Switzerland), which mostly consist of the cutting agent silicon carbide or diamond powder and viscous, aqueous or organic carrier liquids such as glycol. as well as wire saws with cutting-wire-studded wire, usually a diamond-studded wire (eg DS 265 and DS 264 equipped with diamond wire, CR 200 from Meyer Burger AG, Thun, Switzerland). In slurry wire sawing, separation is effected by the lapping (chipping) action of the cutting means entrained in the suspension by the wire and by wire sawing through the cutting means fixedly connected to the wire.

CONFIRMATION COPY Since silicon is an extremely hard and brittle metal and is also very expensive to manufacture, it is essential to minimize the loss of sawing by notching and rejects. In order to achieve consistent sawing performance and not overheat the cutting means such as wires, tapes and disks in contact with the silicon, a cooling fluid is used in all cutting processes. This takes depending on the type of saw in addition to the cooling performance also other tasks such as the transport of the cutting means, such as diamond or silicon carbide powder in slurries based wire saws, serves as a lubricant or lubricant and / or cleaning agent for receiving and transporting cutting material. The compositions of these liquids vary depending on the task and need from thin to highly viscous or thixotropic, aqueous, organic or mixed, and often contain conventional additives such as lubricants or anti-caking agents, stabilizers, preservatives, so-called EP additives (extreme pressure additives ), Viscosity or thixotropy-promoting substances, emulsifiers, solubilizers, etc.

The surface finish of thin-sliced wafers using wire saws is critical to the quality of the resulting products for the semiconductor and photovoltaic industries. Post-processing of surface irregularities is cost-intensive and, due to the small layer thickness and brittleness of the wafers, is only possible to a limited extent.

In particular, in wire saws having fields of wire cut wire, the cutting chips fed from the parallel cutting grooves and adhering to the wires by means of the cooling liquid cause temporary and irregular offsetting of individual or fewer wires and thus irregularities of the cutting surface as the cutting chips enter the grooves of the wire guide rollers , Usually, therefore, the wire band is sprayed with the cooling liquid to apply the liquid and cutting chip residues from the wire before reaching the wire guide rollers

wash away. Nevertheless, these sprinklers still often cause wire deflections.

It is therefore the object of the present invention to provide new and advantageous wire-saw wire saw cutting apparatus and methods, especially such apparatus and methods which provide wire deflections caused by cutting chips and associated surface irregularities. reducing or even avoiding product imperfections. In particular, these methods should lead to improved products, in particular silicon wafers, whose surfaces are advantageously suitable for use in semiconductor products such as computer chips and photovoltaic systems.

This object is achieved in a first aspect by the provision of a wire saw with schneidmittelbesetztem wire field, in which at least one nozzle radiates the cutting chips from the wire field at least over the width of the cut surface of the wire field with liquid.

It was unexpectedly found that the blasting of the wire-field surface with liquid under pressure, in contrast to the usual sprinkling, was marked

Improvement of the surface quality of the wafer leads. This is probably due to the small proportion of material to be cut in the grooves of the guide rollers.

The at least one nozzle can be arranged above and / or below the wire field. Advantageously, it is arranged above the wire field.

In a further preferred embodiment, the at least one nozzle is arranged outside, laterally of at least one of, preferably two, wire guide rollers. The at least one nozzle thus radiates from the outside left and / or right on the wire-guiding round surface of the wire guide roller (s). This lateral, outer-side arrangement avoids that the dirt and chips adhering to the nozzle and also emitted by the nozzle fall onto the wire field.

In a particularly preferred and advantageous embodiment, the at least one nozzle is arranged between the upper and the lower wire field and the wire guide rollers and preferably radiates the lower wire field towards the middle of the wire field. Preferably, the vertical beam angle is preferably 10 to 70 degrees, and more preferably about 45 or about 60 degrees toward the lower wire field, and the horizontal beam angle to the running direction of the wire field is preferably 0 degrees (ie parallel to the wire field), and the pressure of the liquid on the wire field is preferably 0.5 to 10 bar, more preferably 1 to 5 bar, and most preferably about 1, 5 or about 2 bar. In a preferred embodiment, the at least one nozzle can be arranged along the entire wire field between the wire guide rollers and the cut material, as long as the at least one nozzle is positioned so that at operating pressure, the cutting chips from the wire field at least over the width of

Cutting surface of the wire field radiates with liquid.

The position of the nozzle to the wire field is thus herein preferably by the

Radiating surface / effect on the wire field and not defined by the absolute position of the nozzle (s). However, the at least one nozzle is usually arranged in close spatial proximity to the radiating surface on the wire field in order to avoid pressure losses.

In a particularly preferred embodiment, the at least one nozzle is arranged so that it radiates the cutting chips from the wire field in the region of the central axis to the inner edge of the wire guide roller. In this case, the cutting chips need not be radiated from the entire area of the wire field, but only at least over the width of the cut surface of the wire field with liquid, so that the

Contact point of the wire field to the wire guide roller as free of cutting material is.

The above-mentioned transition region of the wire field to the wire guide roller begins where the wire field is for the first time directly above the inner edge of the guide roller, and ends where the wire field comes into contact with the guide roller, usually above the longitudinal axis of the roller. Accordingly, the width of this area is the radius of the guide roller.

Said transition region has been found to be particularly advantageous for blasting the material to be cut with nozzles, since the pressure of the nozzles has no appreciable influence on the alignment of the wire field in the material to be cut due to the distance to the material to be cut and also stabilizes the wire field already by the grooves of the guide rollers is that a significant Abstrahldruck can be exercised, which optimally cleans the wire field, but can not lead to misalignment of the wires.

Preferably, the at least one nozzle is arranged at least on the side leading away from the item to be cut, since there the new cutting chips are obtained. However, at least one, for example, additional nozzle on the cutting material facing side be advantageous to eliminate residues of cutting material or in the case of alternating directions of the wire field.

Therefore, the inventive wire saw also relates to those in which at least two nozzles radiate the cutting chips from the wire field, preferably in the region of the central axis to the inner edge of the preferably two wire guide rollers.

The at least one nozzle of the wire saw according to the invention radiates the cutting chips from the wire field at least over the width of the cut surface of the wire field with liquid, i. before contacting the cutting chips with the wire guide rollers.

In a preferred embodiment, the vertical angle of the nozzle (s) to the wire array is 90 ° (vertical) or less (pointed), preferably 0 to 70 or 10 to 60 °, more preferably 15 to 55 ° or 20 to 50 ° preferably about 60 ° or about 45 °. The vertical beam angle is the angle at which the fluid hits the wire field. An acute angle is due to its directional sliding effect on the

Cutting chips preferred.

The liquid can be irradiated parallel to the running direction of the wire field or laterally offset from the running direction of the wire field in order to deflect the cutting chips in a single direction sideways from the wire field. In a preferred embodiment, the horizontal angle of the at least one nozzle to the running direction of the wire field is 0 to 60 °, preferably 0 to 45 °, more preferably 0 to 30 °, most preferably 0 to 15 °. The sharper the angle, the lower the sideways deflecting forces on the wire field.

The at least one nozzle can be aligned in the direction of material to be cut (inwards) or in the direction of the wire guide roller (outwards). Preferably, the at least one nozzle is aligned in the direction of the material to be cut, and the liquid therefrom radiates the cutting chips in the direction of the material to be cut.

The at least one nozzle can be fixed at a distance to the wire field, but also in the vertical or horizontal angle of attack or be variably adjustable and optionally also discontinuously or continuously varied in position. For example, the at least one nozzle may vary continuously at a vertical angle between 90 and 30 degrees, and / or periodically move the liquid in a direction sideways from the wire field. radiate. The distance of the at least one nozzle to the wire field and the vertical and horizontal alignment to the wire field depends, inter alia, on the nozzle geometry, the fluid pressure, the cutting chips transported by the wire field in quantity and adhesion force on the wire field, etc. The expert will optimize these depending on the specification of the cutting process.

Preferably, the at least one nozzle can be adjusted manually or automatically so that it can be used for pre-cleaning the cut wafer in the wire saw apparatus.

In a preferred embodiment, the wire saw according to the invention is such that the vertical beam angle and / or the horizontal beam angle of the at least one nozzle are variable and preferably varied during cutting, more preferably are varied periodically or continuously during cutting.

In a most preferred embodiment, the vertical beam angle is about 45 ° or about 60 ° to the wire field and / or the horizontal beam angle is about 0 ° of the at least one nozzle. The at least one nozzle is preferably in the direction of food to be cut, i. aligned inward to the wire center.

The wire saw according to the invention also differs from those of the prior art in that at least one nozzle applies a liquid under pressure to the wire field at least across the width of the cut surface of the wire field. The fluid pressure on the wire field should be sufficient to radiate the unwanted cutting chips from the wire field prior to contact with the wire guide rollers. The necessary fluid pressure therefore clearly depends on the distance nozzle-wire field and the vertical and horizontal beam angle. The term blasting in the sense of the invention means that the fluid pressure strikes the cutting chips directed from the wire field in the sense of a liquid puller.

In a preferred embodiment, the pressure which the liquid exerts on the wire field in the direct contact area (incidence area) is in the range between 0.5 and 10 bar, preferably 1 and 10, more preferably 1 and 5, even more preferably 2 and 5 bar , most preferably 2 and 4 bar. The pressure here is the average pressure in the direct contact area (impact surface).

For the wire saws according to the invention with a cutting wire-occupied wire field, the cutting means fixed to the wire are preferably those which are selected from the group consisting of silicon carbide, diamond and boron carbide

Silicon carbide and diamond, most preferably diamond. For wire saws with "slurry-lapping" suspensions, liquid nozzles in the sense of the invention are less suitable because they would otherwise remove the cutting means from wire.

The liquid used in the at least one nozzle is preferably also suitable for cooling, lubrication and rinsing of the material to be cut, in addition to the mechanical removal action of the cutting chips. Preferably, it is substantially aqueous and preferably comprises additives selected from the group consisting of lubricants or lubricants, viscosity or thixotropy-promoting substances, corrosion inhibitors, stabilizers, preservatives, extreme pressure additives (EP) additives, emulsifiers, solubilizers.

The term "width of the cut surface" denotes the width of the wire field which is guided through the material to be cut, The liquid from the at least one nozzle should at least free this width of the wire field from cutting chips.

In a further aspect, the invention relates to a method for cutting hard, preferably brittle solids, preferably metals and semi-metals, preferably selected from the group of monocrystalline and polycrystalline silicon crystals, ceramics, sapphire and germanium, characterized in that the solid by the Wire field performed a wire saw according to the invention, ie respectively.

is cut.

A third aspect of the invention relates to the use of a wire saw according to the invention for cutting hard, preferably brittle solids, preferably metals and semi-metals, preferably selected from the group of monocrystalline and polycrystalline silicon crystals, ceramics, sapphire and germanium, in particular mono- or polycrystalline silicon for the production of silicon wafers. In the following, the invention will be explained with reference to non-limiting examples and figures to be interpreted.

characters

Fig. 1 shows schematically a wire saw (1) with schneidmittelbesetztem wire field (2), the two guide rollers (3a, 3b) rotates, in which the cuboid cutting material (4) from above through the wire array (2) is guided. There are two nozzle strips (5a, 5b) on both sides of the material to be cut (4) with a longitudinal axis transverse to the cutting direction (8) and parallel to the guide rollers (3a, 3b) above the wire field (2) in the region (6, radius) of the central axis (7 ) are arranged to the inner edge (8) of the wire guide roller, the nozzles of which apply the liquid as overlapping cones on the wire field (2) and thus free by blasting with pressure of adhering cutting chips.

Figs. FIGS. 2a to 2c are graphs showing the measurement results of silicon wafers cut in accordance with the wire-fence embodiments with the trickle function or nozzles of FIGS. 3a to 3c in the example. The graphic at the top left shows the average wafer thickness (thickness). The graph at the top right shows the thickness variation within the measured wafer. The graph below left shows the depth of the saw marks within 1 mm. The graphic below shows the saw marks within 5 mm.

FIG. 2a shows the measurement results when the wire saw is equipped with nozzle rows on both sides and trickle function (standard nozzles in standard position) according to FIG. 3a.

Fig. 2b shows the measurement results when equipped with the wire saw with two-sided nozzle rows with a pressure of 1, 5 bar at a vertical angle of 45 ° to the wire field and a horizontal angle of 0 ° (parallel to the wire field) according to FIG. 3b.

Fig. 2c shows the measurement results when equipping the wire saw with double-sided nozzle rows with a pressure of 1, 5 bar directly in front of the wafer drawer on the wire guide rollers at a vertical angle of 60 ° to the wire field and a horizontal angle of 0 ° (parallel to the wire field) according to Fig. 3c.

Figs. 3a to 3c show wire saw arrangements with which the results shown in FIGS. 2a to 2c have been worked out. Fig. 3a shows the photo of a conventional wire saw with conventional trickle on both sides, in particular the hexagonal Schneidgut (4), a polycrystalline ingot, which depends on the slowly lowering Schneidgutaufnahme (10), and the two trickle tubes, from which cooling and rinsing over Guiding plates on the wire field (2) is running.

Fig. 3b shows the photograph of the conventional wire saw of Figure 1 without trickle arrangement, but with double-sided nozzle assembly (5) with a vertical angle of about 45 degrees to the wire field (ie horizontal), a horizontal angle of 0 degrees (parallel to the wire field) with alignment in Direction to be cut (4) on the material to be cut (10).

Figure 3c shows the photograph of the conventional wire saw of Figure 1 without a trickle arrangement, but with two nozzle arrays (5) having a vertical beam angle of about 60 degrees to the lower wire field (ie horizontal), a horizontal angle of 0 degrees (parallel to the wire field) with alignment towards the lower wire center (2), these nozzle arrangements (5) are located directly in front of or on the wafer drawer, which delimits the wire guide rollers from the cutting space. The material to be cut (4) is lowered during operation from above through the upper wire field and cut so.

Example - Cutting silicon wafers with diamond wire saws with liquid nozzles according to the invention

Polycrystalline ingots were first cutted by means of a band saw of the type BS806 or BS805 (Meyer-Burger AG), the melting caps were removed, then kneaded and then "cutted" again by means of an internal hole saw type TS207 (Meyer-Burger AG) only water was used in each of these processes.

The resulting cuboid was then divided into twelve approximately equal sized bricks in the format 156 x 156 mm by means of the band saw mentioned above. Before further processing, the side surfaces were smoothed as usual.

Then each of the twelve bricks was made by means of a wire saw type DS 265 (designed as a diamond wire saw, Meyer-Burger, Thun, Switzerland, diamond wire from DWT Diamond Wire Corporation, Colorado, USA, having a diameter of 145 pm, electrodeposited diamond grains having an average size of about 20 to 25 pm, diameter of the core wire = 120 pm,) cut into wafers having a width of 200 μm. The coolant used was city water with 5% of customary additives (TP714, Meyer-Burger, Steffisburg, Switzerland) with a pH of 7.2. It was cut in pendulum mode, ie about 1000 m forward and 900 m backwards, so that continuously 100 m of new wire were inserted. Alternatively, it can also be cut continuously at the same speed of 14 m / s. The feed was 1 mm / min. During the cutting process, the coolant passed through various filter stages, 20 pm conveyor belt, 10 pm bag filter and then 5 pm filter cartridges. A cut took about three hours, depending on the recipe, regardless of the length of the bricks.

The finished cut wafers were then removed from the sawing device, immersed in clean coolant of the same concentration (5% by volume, pH value as before) and transferred to the pre-cleaning. Here, the adhesive was removed as usual with acetic acid at 40 ° C and the wafers then passed through a conventional cleaning system (Schmid Wafer cleaning plant, Gebr. Schmid GmbH + Co., Freudenstadt, Germany). Thereafter, the clean and dry wafers were inspected by means of a conventional device (measuring system HE-WIS-04 Henneke Systems GmbH, Zülpich, Germany) and examined for geometric quality features.

A total of three wire saw systems with liquid nozzle arrangements were investigated,

(i) a standard arrangement with two-sided nozzle array and trickle function (standard nozzles directed downwards (90 °), standard position over the wire field between guide rollers and brick (photo in Fig. 3a, results in Fig. 2a);

(ii) an inventive arrangement with two-sided nozzle rows arrangements with a liquid pressure of 1.5 bar at a vertical angle of 45 ° to the wire field in the direction Brick) aligned and a horizontal angle of 0 ° (parallel to the wire field) with the spray nozzles in the standard position on the wire field between guide rollers and brick (photo in Fig. 3b, results in Fig. 2b); and

(iii) an arrangement according to the invention with two-sided nozzle row arrangements with a liquid pressure of 1.5 bar directly in front of or at the wafer drawer in alignment with the middle of the lower wire field (direction cutting material) with a vertical 60 ° angle to the wire field and a horizontal angle of 0 ° (parallel to the wire field) aligned. (Photo in Fig. 3b, results in Fig. 2b).

The results of the wafers cut with these wire saws with trickle and nozzle arrangements are graphically summarized in FIGS. 2a to 2c.

In the case of the wafers cut with the standard arrangement with trickling function (FIG. 3 a), the large scattering of the measured values towards the block ends is particularly noticeable, which is apparently due to the water turbulence becoming greater towards the block ends.

Compared to the arrangement in FIG. 3a, substantially less water is applied to the wire field with the spray nozzles of the arrangements 3b and 3c, which leads to a reduction in the turbulence at the two block ends. The wire field is also quieter which results in a lower dispersion of the values of the average thickness variation, the saw marks within 1 mm and the saw marks within 5 mm.

Compared to the wire saw assemblies of Figs. 3a and 3b, in the results of the arrangement of FIG. 3c, the much smaller deviation of the thickness and the thickness distribution occurs. This is achieved by spraying the fluid from the inside onto the lower wire field in the direction of the wire field center. The wire guide rollers are cleaned better, which is reflected in the lower distribution.

Claims

claims

1. wire saw (1) with schneidmittelbesetztem wire field (2), characterized in that at least one nozzle (5) the cutting chips from the wire array (2) at least over the width of the cut surface of the wire array (2) radiates with liquid.

2. Wire saw according to claim 1, characterized in that the at least one nozzle (5) above the wire array (2) is arranged.

3. Wire saw according to claim 1 or 2, characterized in that the at least one nozzle (5) outside, laterally of at least one of the wire guide rollers (3) is arranged.

4. Wire saw according to one of claims 1 to 3, characterized in that the at least one nozzle (5) between the upper and the lower wire field (2) and the wire guide rollers (3a, 3b) is arranged and the lower wire field (2) preferably radiates towards the middle.

5. Wire saw according to one of claims 1 to 4, characterized in that the at least one nozzle (5) radiates the cutting chips from the wire field (2) in the region of the central axis (7) to the inner edge (8) of the wire guide roller (3).

6. wire saw according to one of claims 1 to 5, characterized in that

at least two nozzles (5), the cutting chips from the wire field (2) preferably in the region of the central axis (7) to the inner edge (8) of the preferably two wire guide rollers (3) radiate.

7. Wire saw according to one of claims 1 to 6, characterized in that the vertical angle of the at least one nozzle (5) to the wire field (2) 90 ° or less, preferably 0 to 70 °, more preferably 10 to 60 ° or 15 to 55 °, most preferably 20 to 50 °, about 45 ° or about 60 °.

8. Wire saw according to one of claims 1 to 7, characterized in that the horizontal angle of the at least one nozzle (5) to the running direction (8) of the wire field (2) 0 to 60 °, preferably 0 to 45 °, more preferably 0 to 30 °, most preferably 0 to 15 °.

9. Wire saw according to one of claims 1 to 8, characterized in that the at least one nozzle (5) in the direction of the material to be cut (4) is aligned and the liquid from the cutting chips in the direction of the material to be cut (4) emits.

10. Wire saw according to one of claims 1 to 9, characterized in that the vertical angle of radiation and / or the horizontal angle of the at least one nozzle (5) are variable and preferably varies during cutting, more preferably be varied periodically or continuously during cutting.

11. Wire saw according to one of claims 1 to 10, characterized in that the pressure through the liquid to the wire field (2) in the range between 0.5 and 10 bar, preferably 1 and 10 or 1 and 5 bar, most preferably 2 and 4 bar.

12. Wire saw according to one of claims 1 to 11, characterized in that the liquid for cooling, lubrication and flushing of the cut material (4) is suitable, preferably substantially aqueous, preferably additives selected from the group consisting of lubricants or lubricants , Viscosity or thixotropy-inducing substances, corrosion inhibitors, stabilizers, preservatives, extreme pressure additives (EP) additives, emulsifiers, solubilizers.

13. A method for cutting hard, preferably brittle solids, preferably metals and semi-metals, preferably selected from the group of monocrystalline and polycrystalline silicon crystals, ceramics, sapphire and germanium, characterized in that the solid through the wire field (2) of a wire saw after a of the present claims.

14. Use of a wire saw according to one of the preceding claims for cutting hard, preferably brittle solids, preferably metals and semi-metals, preferably selected from the group of monocrystalline and polycrystalline silicon crystals, ceramics, sapphire and germanium.

15. Use according to claim 14 for the production of silicon wafers.