METHOD FOR SLICING INGOT AND WIRE SAW

Abstract

A method for slicing an ingot, including: forming a wire row by a wire spirally wound between a plurality of wire guides and configured to travel in an axial direction; and pressing an ingot against the wire row while supplying a contact portion between the ingot and the wire with a slurry from a nozzle, thereby slicing the ingot into wafers. The slurry is supplied such that slurries whose temperatures are separately controlled by two or more lines of heat exchangers are respectively supplied from two or more sections of the nozzle which are orthogonal to a travelling direction of the wire row. Consequently, a wire saw and a method for slicing an ingot are provided which enable separate control of wafer shapes depending on ingot-slicing positions.

Claims

1-7. (canceled)

8. A method for slicing an ingot, comprising: forming a wire row by a wire spirally wound between a plurality of wire guides and configured to travel in an axial direction; and pressing an ingot against the wire row while supplying a contact portion between the ingot and the wire with a slurry from a nozzle, thereby slicing the ingot into wafers, wherein the slurry is supplied such that slurries whose temperatures are separately controlled by two or more lines of heat exchangers are respectively supplied from two or more sections of the nozzle which are orthogonal to a travelling direction of the wire row.

9. The method for slicing an ingot according to claim 8, wherein the temperatures of the slurries are separately controlled depending on slurry-supply positions of the ingot to be sliced.

10. The method for slicing an ingot according to claim 8, wherein the slurry is supplied such that after an ingot is sliced in advance to check wafer shapes at sliced positions of the ingot, slurries whose temperatures are separately controlled depending on the shapes at the respective positions are supplied.

11. The method for slicing an ingot according to claim 9, wherein the slurry is supplied such that after an ingot is sliced in advance to check wafer shapes at sliced positions of the ingot, slurries whose temperatures are separately controlled depending on the shapes at the respective positions are supplied.

12. The method for slicing an ingot according to claim 8, wherein the slurry is supplied such that, of the two or more sections of the nozzle, at least one section supplies a slurry whose temperature is controlled to be changed during the ingot slicing, and at least one section supplies a slurry whose temperature is controlled to be unchanged during the ingot slicing.

13. The method for slicing an ingot according to claim 9, wherein the slurry is supplied such that, of the two or more sections of the nozzle, at least one section supplies a slurry whose temperature is controlled to be changed during the ingot slicing, and at least one section supplies a slurry whose temperature is controlled to be unchanged during the ingot slicing.

14. The method for slicing an ingot according to claim 10, wherein the slurry is supplied such that, of the two or more sections of the nozzle, at least one section supplies a slurry whose temperature is controlled to be changed during the ingot slicing, and at least one section supplies a slurry whose temperature is controlled to be unchanged during the ingot slicing.

15. The method for slicing an ingot according to claim 11, wherein the slurry is supplied such that, of the two or more sections of the nozzle, at least one section supplies a slurry whose temperature is controlled to be changed during the ingot slicing, and at least one section supplies a slurry whose temperature is controlled to be unchanged during the ingot slicing.

16. A wire saw comprising: a wire row formed of a wire spirally wound between a plurality of wire guides and configured to travel in an axial direction; an ingot-feeding means configured to press an ingot against the wire row while holding the ingot; and a nozzle configured to supply a slurry to a contact portion between the ingot and the wire, wherein the ingot-feeding means presses the ingot against the wire row while the nozzle supplies the slurry to the contact portion between the ingot and the wire, thereby slicing the ingot into wafers, the wire saw comprises two or more lines of heat exchangers configured to separately control a temperature of the slurry, the nozzle is divided in two or more sections in a direction orthogonal to a travelling direction of the wire row, and the divided sections are respectively supplied with the separately controlled slurries from the heat exchangers.

17. The wire saw according to claim 16, wherein the two or more lines of heat exchangers separately control the temperature of the slurry depending on slurry-supply positions of the ingot to be sliced.

18. The wire saw according to claim 16, wherein the two or more lines of heat exchangers separately control the temperature of the slurry depending on wafer shapes checked at positions of an ingot sliced in advance.

19. The wire saw according to claim 17, wherein the two or more lines of heat exchangers separately control the temperature of the slurry depending on wafer shapes checked at positions of an ingot sliced in advance.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0051] FIG. 1 is a schematic view showing an example of a wire saw according to the present invention.

[0052] FIG. 2 is a top view showing an example of a nozzle in the inventive wire saw.

[0053] FIG. 3 is a graph for illustrating the slurry temperature condition for making a cut wafer have concave shape in Example, Comparative Example, and Reference Example.

[0054] FIG. 4 is a graph for illustrating the slurry temperature condition where the temperature is unchanged in Example and Comparative Example.

[0055] FIG. 5 is a graph for illustrating the slurry temperature condition for making a cut wafer have convex shape in Example, Comparative Example, and Reference Example.

[0056] FIG. 6 shows graphs for illustrating warp forms in an ingot feeding direction of sliced wafers in Comparative Example 1.

[0057] FIG. 7 shows graphs for illustrating warp forms in an ingot feeding direction of sliced wafers in Comparative Example 2.

[0058] FIG. 8 shows graphs for illustrating warp forms in an ingot feeding direction of sliced wafers in Comparative Example 3.

[0059] FIG. 9 shows graphs for illustrating warp forms in an ingot feeding direction of sliced wafers in Example 1.

[0060] FIG. 10 shows graphs for illustrating warp forms in an ingot feeding direction of sliced wafers in Example 2.

[0061] FIG. 11 shows graphs for illustrating warp forms in an ingot feeding direction of sliced wafers in Reference Example.

[0062] FIG. 12 is a schematic view showing an example of a conventional wire saw.

[0063] FIG. 13 is a top view showing an example of a nozzle in the conventional wire saw.

DESCRIPTION OF EMBODIMENTS

[0064] As described above, there have been demands for the development of a method for slicing an ingot, the method enabling separate control of wafer shapes depending on ingot-slicing positions.

[0065] The present inventor and colleagues have earnestly studied the above-described problems and consequently found that the reason why conventional methods for slicing an ingot cannot separately control wafer shapes depending on ingot-slicing positions is that the slurry temperature is controlled uniformly irrespective of ingot-slicing positions and cannot be changed. The inventor has arrived at controlling the slurry temperature with two or more lines separately instead of conventional one line. Thus, the present invention has been completed.

[0066] Specifically, the present invention provides a method for slicing an ingot, comprising:

[0067] forming a wire row by a wire spirally wound between a plurality of wire guides and configured to travel in an axial direction; and

[0068] pressing an ingot against the wire row while supplying a contact portion between the ingot and the wire with a slurry from a nozzle, thereby slicing the ingot into wafers, wherein

[0069] the slurry is supplied such that slurries whose temperatures are separately controlled by two or more lines of heat exchangers are respectively supplied from two or more sections of the nozzle which are orthogonal to a travelling direction of the wire row.

[0070] In addition, the present invention provides a wire saw comprising:

[0071] a wire row formed of a wire spirally wound between a plurality of wire guides and configured to travel in an axial direction;

[0072] an ingot-feeding means configured to press an ingot against the wire row while holding the ingot; and

[0073] a nozzle configured to supply a slurry to a contact portion between the ingot and the wire, wherein

[0074] the ingot-feeding means presses the ingot against the wire row while the nozzle supplies the slurry to the contact portion between the ingot and the wire, thereby slicing the ingot into wafers,

[0075] the wire saw comprises two or more lines of heat exchangers configured to separately control a temperature of the slurry,

[0076] the nozzle is divided in two or more sections in a direction orthogonal to a travelling direction of the wire row, and

[0077] the divided sections are respectively supplied with the separately controlled slurries from the heat exchangers.

[0078] Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.

[0079] First, an example of the inventive wire saw will be described with reference to FIG. 1. As shown in FIG. 1, a wire saw 1 is mainly constituted of: a wire row 11 formed of a wire 2 wound around multiple wire guides 3 and configured to slice an ingot; an ingot-feeding means 5 configured to feed an ingot to be sliced; a nozzle 15 configured to supply, during slicing, a slurry in which abrasive grains are dispersed and mixed in a coolant; etc.

[0080] The wire 2 is reeled out from one wire reel 7, and reaches the wire guides 3 through a traverser 8 and a tension mechanism 4 constituted of a powder clutch (constant torque motor 9), a dancer roller (dead weight) (not shown), etc. After wound around the wire guides 3 approximately 300 to 400 times, the wire 2 passes through another tension-imparting mechanism 4′ and is wound around a wire reel 7′.

[0081] Additionally, the wire guides 3 are rollers each obtained by press-fitting a polyurethane resin around a cylinder made of steel and forming grooves on a surface thereof at a fixed pitch. The wire 2 wound therearound can be driven in reciprocating directions in a predetermined cycle by a driving motor 10.

[0082] The wire saw 1 has two or more lines of heat exchangers configured to separately control the temperature of slurries. In the wire saw 1 shown in FIG. 1, two slurry-supplying mechanisms 6 and 6′ configured to supply slurries are linked to one slurry tank 16, and the mechanisms respectively includes heat exchangers 17 and 17′. Nevertheless, the wire saw 1 may have three or more lines of heat exchangers.

[0083] The heat exchangers 17 and 17′ are each capable of separately controlling slurry temperature and may have equal abilities. Existing heat exchangers can be used.

[0084] Moreover, the nozzle 15 according to the present invention is divided in two or more sections in a direction perpendicular to a travelling direction of the wire row 11. The divided sections are respectively supplied with separately-controlled slurries from the heat exchangers 17, 17′.

[0085] Here, the nozzle of the present invention and a slurry supply flow will be described in more details with reference to FIG. 2 and FIG. 13 that shows an example of a conventional nozzle.

[0086] As shown in FIG. 13, the nozzle 115 in the conventional wire saw 101 consists of one section. After temperature control by the heat exchanger 117, a slurry from the slurry tank 116 enters the slurry nozzle 115 through a pipe, and is supplied in free fall to the wire and the wire guides from slit in the bottom surface of the nozzle. Then, the slurry returns to the slurry tank 116 located at the bottom of the apparatus.

[0087] Meanwhile, as shown in FIG. 2, the nozzle 15 in the inventive wire saw 1 is divided into at least two sections in the direction orthogonal to the travelling directions of the wire row 11. In FIG. 2, the nozzle 15 is divided into two sections: a nozzle 15A and a nozzle 15B. The nozzle 15A is connected to a pipe through which a slurry whose temperature is controlled by the heat exchanger 17 flows. The nozzle 15B is connected to a pipe through which a slurry whose temperature is controlled by the other heat exchanger 17′ flows. Thus, different slurries whose temperatures are separately controlled can be supplied from the respective sections of the single nozzle 15. The nozzle 15 may be divided, for example, by providing a partition plate or the like at a central portion inside the nozzle 15. The nozzles 15A and 15B are structured to prevent mixing of the slurries whose temperatures are controlled by the different lines. Although FIG. 2 shows the nozzle 15 divided into two sections, it is a matter of course that the nozzle 15 may be divided into three or more sections.

[0088] The slurry-supplying mechanism 6 shown in FIG. 1 and FIG. 2 is such a mechanism that a slurry from the slurry tank 16 is subjected to the temperature control by the heat exchanger 17, enters the nozzle 15A through the pipe, and is supplied in free fall from slit in the nozzle bottom surface to the wire and the wire guides located at one side (for example, wire-supply side) in the apparatus. Then, the slurry returns to the slurry tank 16 located at the bottom of the apparatus.

[0089] Moreover, the slurry-supplying mechanism 6′ is such a mechanism that a slurry from the slurry tank 16 is subjected to the temperature control by the heat exchanger 17′, enters the nozzle 15B through the pipe, and is supplied in free fall from slit in the nozzle bottom surface to the wire and the wire guides located at the other side (for example, wire-withdrawal side) in the apparatus. Then, the slurry returns to the slurry tank 16 located at the bottom of the apparatus.

[0090] In the present invention, the temperature control by the heat exchanger 17 or the heat exchanger 17′ may differ from the other. Alternatively, it is possible to control the temperature at one side to be changeable and the temperature at the other side to remain unchanged.

[0091] Moreover, the heat exchangers 17, 17′ may separately control slurry temperatures depending on slurry-supply positions in an ingot to be sliced. The wire saw 1 having such heat exchangers 17, 17′ can separately supply slurries having suitable temperatures for the respective ingot-slicing positions.

[0092] Further, each of the heat exchangers 17, 17′ may also control the temperature of the slurry depending on wafer shapes checked at positions of an ingot sliced in advance. The wire saw 1 having such heat exchangers 17, 17′ can more effectively reduce wafer warps at all the sliced positions in the ingot.

[0093] As has been described above, the inventive wire saw 1 makes it possible to supply slurries having separately controlled temperatures depending on ingot-slicing positions, and thus enables separate controls of wafer shapes depending on ingot-slicing positions, and wafer warp reductions at all the sliced positions in the ingot.

[0094] Next, the inventive method for slicing an ingot will be described by taking an example where the above-described inventive wire saw 1 is used.

[0095] In the inventive method for slicing an ingot, slurries whose temperatures are separately controlled by two or more lines of heat exchangers (for example, the heat exchangers 17 and 17′) are respectively supplied from two or more sections (for example, the nozzles 15A and 15B) of the nozzle 15 which are orthogonal to the travelling directions of the wire row 11.

[0096] In the inventive ingot slicing method, the slurry may be supplied such that, of the two or more sections of the nozzle 15, at least one section supplies a slurry whose temperature is changed during the ingot slicing, and at least one section supplies a slurry whose temperature is unchanged during the ingot slicing. The present invention makes it possible to supply slurries having the temperatures controlled in this manner for the respective sections of the nozzle.

[0097] For example, a slurry controlled under slurry temperature conditions aiming at concave shape formation to flatten wafers which otherwise have convex shape can be supplied from the apparatus front side. In addition, a slurry controlled under slurry temperature conditions aiming at convex shape formation to flatten wafers which otherwise have concave shape can be independently supplied from the apparatus back side. This process prevents such an incidence that improving warps on one side degrades warps on the other side. Thus, wafer warp reductions are achieved at all the sliced positions in an ingot.

EXAMPLE

[0098] Hereinafter, the present invention will be specifically described with reference to Examples, Comparative Examples, and Reference Example. However, the present invention is not limited thereto.

Comparative Example 1

[0099] The conventional wire saw 101 as shown in FIG. 12 was used to slice an ingot under the condition as in FIG. 4 where the slurry temperature was unchanged. Then, the wafer shapes at the sliced positions were observed.

[0100] FIG. 6 shows wafer shapes thus cut out. As shown in FIG. 6, the wafer shape cut out from the apparatus front side (wire-supply side) relative to the center of the ingot was a convex shape, while the wafer shape cut out from the apparatus back side (wire-withdrawal side) relative to the center of the ingot was a concave shape. It should be noted that, in the subsequent Comparative Examples 2 and 3 and Examples 1 and 2, the warps of wafer shapes were evaluated through comparison with the wafer shapes obtained in Comparative Example 1 which were regarded as existing shapes.

Comparative Example 2

[0101] The same procedure as in Comparative Example 1 was conducted, except that an ingot was sliced under the condition as in FIG. 3 where the slurry temperature was controlled to form wafers having concave shape.

[0102] FIG. 7 shows wafer shapes thus cut out. As shown in FIG. 7, the wafer shape cut out from the apparatus front side was a flat shape instead of the existing convex shape. However, the wafer shape cut out from the apparatus back side was a deeper concave shape than the existing concave shape.

Comparative Example 3

[0103] The same procedure as in Comparative Example 1 was conducted, except that an ingot was sliced under the condition as in FIG. 5 where the slurry temperature was controlled to form wafers having convex shape.

[0104] FIG. 8 shows wafer shapes thus cut out. As shown in FIG. 8, the wafer shape cut out from the apparatus back side was a flat shape instead of the existing concave shape. However, the wafer shape cut out from the apparatus front side was a deeper convex shape than the existing convex shape.

Example 1

[0105] The inventive wire saw 1 as shown in FIG. 1 was used to slice an ingot while slurries whose temperatures were separately controlled by two lines of the heat exchangers 17, 17′ were respectively supplied from the apparatus front side and the apparatus back side relative to the center of the ingot.

[0106] The temperature of the slurry supplied from the apparatus front side was changed during the ingot slicing as in FIG. 3 to form wafers having concave shape. The temperature of the slurry supplied from the apparatus back side was unchanged as in FIG. 4. FIG. 9 shows wafer shapes thus cut out.

[0107] As shown in FIG. 9, regarding the wafer shape cut out from the apparatus front side where the temperature of the supplied slurry was changed to form concave shape, a flat shape was formed by counterbalancing the warp direction of the existing convex shape. Meanwhile, regarding the wafer shape cut out from the apparatus back side where the temperature of the supplied slurry was unchanged, the resulting shape was equivalent to that in Comparative Example 1.

Example 2

[0108] An ingot was sliced as in Example 1, except that a slurry was supplied from the apparatus back side under the temperature condition as in FIG. 5 to form convex shape in place of the existing concave shape. FIG. 10 shows wafer shapes cut out from the apparatus front side and the apparatus back side.

[0109] As shown in FIG. 10, the wafer on the apparatus front side had a flat shape as in Example 1 by counterbalancing the warp direction as if the convex shape as the existing warp form was changed in a concave direction. Moreover, as to the wafer on the apparatus back side where the control was aimed in the opposite direction as well, a flat shape was formed by counterbalancing the warp direction as if the existing concave shape was changed in a convex direction.

Reference Example

[0110] An ingot was sliced while the slurry temperatures were controlled in manners opposite to those in Example 2; specifically, the temperature of a slurry supplied from the apparatus front side varied as in FIG. 5, and the temperature of a slurry supplied from the apparatus back side varied as in FIG. 3. FIG. 11 shows wafer shapes thus cut out.

[0111] As shown in FIG. 11, the wafer shape cut out from the apparatus front side was a convex shape that was sharper than the convex shape of the existing warp form. Moreover, the wafer shape cut out from the apparatus back side was a sharper concave shape, and the flatness was degraded.

[0112] Table 1 summarizes the results of Examples, Comparative Examples, and Reference Example.

TABLE-US-00001 TABLE 1 Wafer shape Apparatus front side Apparatus back side Evaluation Comparative convex concave — Example 1 Comparative flat improved sharper degraded One C Example 2 concave side was improved, the other was degraded Comparative sharper degraded flat improved One C Example 3 convex side was improved, the other was degraded Example 1 flat improved concave no change Only one B side was improved, the other was not changed Example 2 flat improved flat improved Both sides A were improved Reference sharper degraded sharper degraded Both sides D Example convex concave were degraded Evaluation A: excellent B: good C: partially problematic D: problematic

[0113] In Comparative Examples 2 and 3 where the slurry was supplied while the temperature was controlled uniformly irrespective of ingot-slicing positions, separate controls of the wafer shapes depending on ingot-slicing positions were not possible. Although the slurry temperature condition was changed to improve wafer shapes cut out from either one of the apparatus back side or the apparatus front side, this resulted in harmful effects on the wafer shapes cut out from the other side.

[0114] In contrast, in Example 1 where the temperatures of the supplied slurries were separately controlled depending on ingot-slicing positions, the change in the slurry temperature condition to improve either one of the apparatus back side or the apparatus front side did not influence the other side. Furthermore, it was possible to improve both sides as in Example 2.

[0115] The above results verified that the present invention enables separate control of wafer shapes depending on ingot-slicing positions. Particularly, in Example 2, since the slurries were separately supplied depending on the ingot positions under the temperature conditions to counterbalance the warp directions, wafer warps were successfully reduced at all the sliced positions in the ingot.

[0116] It should be noted that the present invention is not limited to the above-described embodiments. The embodiments are just examples, and any examples that have substantially the same feature and demonstrate the same functions and effects as those in the technical concept disclosed in claims of the present invention are included in the technical scope of the present invention.