JP6007553B2 - Wafer polishing method - Google Patents

Description

  The present invention relates to a method in which a wafer is slid in contact with a polishing cloth affixed to a surface plate while holding the wafer with a polishing head and supplying slurry.

  Due to the miniaturization of semiconductor elements, customer demand for flatness of semiconductor wafers is increasing day by day, and in particular, flatness near the edge (outer periphery) has a strong demand for improvement to prevent yield reduction due to defocusing. In recent years, the outer exclusion area (Edge Exclusion) has become 2 mm, and demands such as 1.5 mm and 1 mm have begun to appear.

In the conventional polishing method, mainly, a surface plate to which a polishing cloth is stuck, a polishing head for holding the wafer from the back side, a polishing apparatus having a nozzle for supplying slurry, and rotating the surface plate and the polishing head, Further, while supplying slurry onto the polishing cloth, polishing is performed by sliding the surface of the wafer against the polishing cloth with a polishing head (see Patent Document 1).
The wafer polishing mechanism is divided into a mechanical polishing action by contact with abrasive grains contained in a slurry supplied during polishing and a chemical polishing action by an alkali component added to the slurry.

JP 2001-334454 A

  As a result of intensive studies by the present inventors, the polishing rate at the center of the wafer is generally affected by the chemical polishing action due to heat generated by frictional heat between the wafer and the polishing cloth, and is near the wafer edge (outer periphery). It was found that the effect of the mechanical polishing action due to the increase in polishing pressure due to elastic deformation of the polishing cloth was great. The polishing allowance near the center of the wafer and the vicinity of the edge tends to be large. In particular, the increase in the allowance near the edge is called an outer peripheral sag, which is a major factor in deterioration of flatness.

  In order to improve the peripheral sag, a polishing method using a high-hardness polishing cloth with little elastic deformation and a polishing head having a retainer mechanism have been proposed.

  However, when a high-hardness abrasive cloth with little elastic deformation is used, there is a drawback that scratches are likely to occur. Even when a polishing head having a retainer mechanism is used, the improvement effect is limited when a relatively soft polishing cloth is selected to reduce scratches.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a polishing method capable of polishing the outer peripheral portion of a wafer as desired, for example, suppressing the occurrence of outer peripheral sag. To do.

  In order to achieve the above object, the present invention provides a wafer that is polished by bringing the surface of a wafer held by a polishing head into sliding contact with the polishing cloth while supplying slurry onto the polishing cloth affixed to a surface plate. A polishing method, characterized by controlling the polishing rate of the outer periphery of the wafer by changing the supply temperature of the slurry to a lower temperature than at the start of polishing during the polishing after the polishing of the wafer is started. A wafer polishing method is provided.

  According to the wafer polishing method of the present invention, low temperature slurry stays around the polishing head (that is, near the outer periphery of the wafer) after the slurry supply temperature is changed, and the temperature near the outer periphery of the wafer is lowered. Can do. Since the chemical polishing action is greatly affected by temperature, the polishing rate at the outer periphery of the wafer subjected to the cooling effect can be controlled and suppressed as desired. In particular, it is possible to suppress the occurrence or the degree of the outer sag, and improve the flatness near the outer periphery. And it can carry out simply.

  At this time, when the supply temperature of the slurry is changed, the slurry can be lowered by 5 ° C. or more from the start of polishing.

  In this way, the vicinity of the outer peripheral portion of the wafer can be cooled more efficiently. For this reason, the polishing rate of the outer peripheral portion of the wafer can be further suppressed, and the degree of occurrence of the outer peripheral sag can be further effectively suppressed.

  Moreover, the average polishing rate can be further controlled by adjusting the supply temperature at the start of polishing of the slurry.

  By supplying a low temperature slurry during polishing, the average polishing rate for the entire wafer decreases, but the supply rate at the start of polishing is adjusted in advance to control the polishing rate from the start of polishing until the slurry supply temperature is changed to a low temperature. It is possible to control the average polishing rate throughout the polishing process. Thereby, it can prevent that productivity falls. In addition, this method does not cause surface roughness due to etching, which is a concern when raising the polishing rate by raising the supply temperature of the slurry, and therefore does not cause Haze unevenness.

Further, when the supply temperature of the slurry is changed, a plurality of nozzles for separately supplying slurry having different temperatures can be provided, and the plurality of nozzles can be switched.
Or when changing the supply temperature of the said slurry, it can also carry out by selecting the slurry of the different temperature separately stored in the some tank by the switching operation of a valve | bulb, and sending it to a nozzle.

  In this way, the slurry supply temperature can be easily changed by supplying slurry at different temperatures from separate nozzles, or by sharing the nozzles and supplying the slurry at different temperatures by switching the valve.

  As described above, according to the wafer polishing method of the present invention, it is possible to polish while cooling the vicinity of the outer periphery of the wafer, and to control and suppress the polishing rate of the outer periphery of the wafer. In particular, it is possible to suppress the degree of occurrence of the outer peripheral sag and to improve the flatness near the outer peripheral part.

It is the schematic which shows an example of the grinding | polishing apparatus (no nozzle shared type) which can be used for the grinding | polishing method of the wafer of this invention. (A) The whole polishing apparatus, (B) The position of the nozzle. It is the schematic which shows another example of the grinding | polishing apparatus (no nozzle shared type) which can be used for the grinding | polishing method of the wafer of this invention. (A) The whole polishing apparatus, (B) The position of the nozzle. It is the schematic which shows an example of the grinding | polishing apparatus (nozzle shared type) which can be used for the grinding | polishing method of the wafer of this invention. (A) Whole polishing apparatus, (B) (C) Nozzle position. It is a flowchart which shows an example of the grinding | polishing method of the wafer of this invention. It is a graph which shows an example of the machining allowance shape of a 300 mm diameter wafer outer peripheral part when the supply temperature of a slurry is made low during grinding | polishing. It is a graph which shows the supply temperature conditions of a slurry, and the machining allowance difference of a position of 147 mm and 149 mm from the wafer center with a diameter of 300 mm. The relationship between the slurry supply temperature condition and the average polishing rate is shown. It is a graph which shows the evaluation result of the flatness of the wafer of diameter 300mm after grinding | polishing of an Example and a comparative example. (A) SFQR, (B) ESFQR. It is a graph which shows the Haze map of the wafer surface after grinding | polishing of an Example and a comparative example. (A) Example, (B) Comparative example. It is explanatory drawing which shows an example of the grinding | polishing method of a wafer. It is a temperature distribution figure which shows an example of the temperature distribution on the polishing cloth during grinding | polishing. (A) The case where the slurry is supplied to one place in the center and (B) the slurry is supplied to two places. It is a graph which shows the relationship between the supply temperature of a slurry, the rotation speed of a surface plate and a polishing head, and a polishing rate. It is a graph which shows the relationship between the supply temperature of a slurry, and the machining allowance shape of a wafer outer peripheral part with a diameter of 300 mm. This is the case where the platen rotation number / polishing head rotation number is (A) 60 rpm / 20 rpm, (B) 40 rpm / 40 rpm, and (C) 20 rpm / 60 rpm. It is a graph which shows the relationship between the supply temperature of a slurry, and the machining allowance difference of the position of 147 mm and 149 mm from the wafer center with a diameter of 300 mm.

As described above, the conventional polishing method tends to cause the outer periphery sagging. The inventors first investigated the cause of this.
FIG. 10 is an explanatory view showing an example of a wafer polishing method. Here, an example in which the polishing head uses two polishing apparatuses is given. In the case of such a two-head type polishing apparatus, the slurry is usually supplied from a nozzle installed near the center of the polishing pad. Here, in the vicinity of the edge portion (outer peripheral portion) of the wafer, the polishing pressure tends to be high due to the elastic deformation of the polishing cloth, and the mechanical polishing action is higher than that in the central portion, which is one of the causes of the occurrence of the outer peripheral sag. .

On the other hand, polishing includes mechanical polishing action and chemical polishing action. This chemical polishing action is considered to be affected by the supply temperature of the slurry if the slurry has the same polishing conditions and the same composition.
Here, the slurry is supplied between the wafer and the polishing cloth, but most of the slurry is discharged out of the system without contributing to polishing. Slurry that does not contribute to polishing has an effect of cooling the surface of the polishing cloth whose temperature rises due to friction between the wafer and the polishing cloth. Further, since the excess slurry stays around the polishing head for a certain time due to the rotation of the polishing head, the outer peripheral portion of the wafer is also cooled.

FIG. 11 is a temperature distribution diagram on the polishing pad when polishing is performed while supplying slurry. In order to easily understand the temperature change, the polishing head was not swung, and the slurry was supplied at 15 ° C. for measurement. FIG. 11A shows a case where the slurry is supplied to one center of the polishing cloth, and FIG. 11B shows a case where the slurry is supplied to two places.
Looking at the temperature distribution in FIG. 11A, the temperature decreases toward the outside in a substantially concentric shape except for the central portion where the slurry is supplied. Note that the temperature difference is particularly noticeable because the rocking motion is not performed, but the center and outer periphery of the polishing cloth are not subjected to continuous frictional resistance even when the rocking motion is performed. It became a trend.
Further, since the slurry having a temperature lower than the surface temperature of the polishing cloth at the time of polishing is excessively retained around the polishing head (near the wafer outer peripheral portion), the temperature around the polishing head is also low.
These tendencies are substantially the same in FIG.
It is considered that the cooling effect on the outer peripheral portion of the wafer can be increased by lowering the temperature of the slurry to be supplied.

  The present inventors use a low-temperature slurry that stays in the vicinity of the outer periphery of the wafer to suppress the chemical polishing action at the outer periphery of the wafer to control the polishing rate, and in particular, it is not possible to suppress the sagging of the outer periphery. I further investigated.

  FIG. 12 is a graph showing the relationship between the slurry supply temperature, the number of rotations of the surface plate and the polishing head, and the polishing rate. As the temperature of the slurry, three patterns of 15 ° C., 20 ° C., and 25 ° C. were used, and as the rotation speed, the rotation speed of the platen / polishing head was set to three patterns of 60 rpm / 20 rpm, 40 rpm / 40 rpm, and 20 rpm / 60 rpm. .

From FIG. 12, it can be seen that the polishing rate varies depending on the rotation speed of the surface plate and the polishing head and the supply temperature of the slurry.
Since the supply temperature of the slurry directly affects the chemical polishing action of the slurry, it can be seen that the polishing rate decreases as the temperature decreases.

  As for the condition of the rotational speed, when the rotational speed of the platen is increased, heat generation due to friction near the wafer center becomes stronger, and the polishing rate of the entire wafer becomes higher. Conversely, when the rotational speed of the polishing head is increased, the polishing rate is lowered by the cooling effect of the slurry around the polishing head and the hydroplane phenomenon rather than the temperature rise of the polishing surface due to friction.

FIG. 13 is a graph showing the relationship between the slurry supply temperature and the machining allowance shape of the outer periphery of the wafer. This is the case where the platen rotation number / polishing head rotation number is (A) 60 rpm / 20 rpm, (B) 40 rpm / 40 rpm, and (C) 20 rpm / 60 rpm. The measurement was made on a wafer having a diameter of 300 mm, and the horizontal axis represents the distance from the wafer center (130 to 149 mm).
When the distance from the wafer outer periphery, particularly near the center of the wafer, is around 149 mm, it can be seen that the machining allowance is lower when the slurry temperature is lower, not limited to the rotational speed of the surface plate or polishing head.

  Further, FIG. 14 shows the result of totaling the machining allowances at the positions of 147 mm and 149 mm from the wafer center of FIG. 13 (value at 149 mm−value at 147 mm). If the machining allowance is a positive value, the machining allowance at the position 1 mm from the outer circumference is larger than that at the position 3 mm from the outer circumference (150 mm from the wafer center) (that is, the outer circumference sag occurs). On the other hand, a negative value indicates that the allowance at the position of 3 mm from the outer periphery is larger than the allowance at the position of 1 mm from the outer periphery (that is, an outer periphery is generated).

  From the data on the machining allowance, it can be seen that the lower the supply temperature of the slurry, the more the outer peripheral sag tends to be suppressed. If it sees for every rotation speed conditions, since it is the comparison on the same conditions except the supply temperature of a slurry, it is thought that the allowance of a wafer outer peripheral part fell by this cooling effect of the wafer outer peripheral part by a slurry. It is thought that the chemical polishing action was suppressed.

  Based on the above investigation results, the present inventor considered that the polishing rate can be changed and controlled by lowering the supply temperature of the slurry during polishing, and completed the present invention.

Hereinafter, the wafer polishing method of the present invention will be described in detail as an example of an embodiment with reference to the drawings. However, the present invention is not limited to this.
First, FIG. 1 shows an example of a polishing apparatus that can be used when performing the wafer polishing method of the present invention. FIG. 1 (A) shows the entire polishing apparatus, and FIG. 1 (B) shows an arrangement position of a nozzle for supplying slurry.
As shown in FIG. 1, the polishing apparatus 1 includes a polishing head 2 that holds a wafer to be polished, and a surface plate 4 on which a polishing cloth 3 is attached.
The polishing head 2 is held from the back side of the wafer, and a guide ring for holding the outer peripheral portion of the wafer is provided on the holding surface side. In addition to this, the polishing head 2 may be provided with necessary members such as those using a template or a retainer ring for pressing the polishing cloth 3. The polishing head 2 itself is not particularly limited, and for example, a conventional one can be used. In this example, the number of polishing heads 2 is two. However, the number is not limited to this, and the number can be determined as appropriate.

  The polishing cloth 3 and the surface plate 4 themselves are not particularly limited, and for example, the same one as in the past can be used. Any material can be used as long as the surface of the wafer held by the polishing head 2 can be polished by being brought into sliding contact with the polishing cloth 3 on the surface plate 4.

Further, in order to supply the slurry onto the polishing cloth 3 at the time of polishing, two tanks 5a and 5b each storing slurry at different temperatures, a plurality of (here, two) nozzles 6a and 6b, and a valve 7a. , 7a ', 7b, 7b', and other pumps.
The slurry (referred to as slurry A) in the tank 5a can be supplied through the nozzle 6a, while the slurry (slurry B) in the tank 5b can be supplied through the nozzle 6b. Each of the tanks 5a and 5b is provided with a heater, a heat exchanger, etc., and the temperature of the slurry in the tank can be adjusted, and the temperature of the slurry supplied from the nozzles 6a and 6b can be appropriately controlled. . Here, the slurry B is controlled at a lower temperature than the slurry A.

  For example, for the supply system on the slurry A side, if the valve 7a is opened and the valve 7a 'is closed, the slurry A in the tank 5a can be supplied from the nozzle 6a onto the polishing pad 3 by the pump, and the valve 7a is closed. If the valve 7 a ′ is opened, the slurry A passes through the valve 7 a ′ and returns to the tank 5 a and is only circulated, and is not supplied onto the polishing pad 3. Of course, the mechanism is not limited to this, and the operation of the pump and the opening / closing of the valve may be linked. The same applies to the supply system on the slurry B side.

In addition, although an example in which two nozzles are shown in FIG. 1, the number of nozzles can be further increased.
FIG. 2A shows the entire polishing apparatus having four nozzles, and FIG. 2B shows the nozzle arrangement positions.
Two of the four nozzles 106a and 106a ′ can be arranged for supplying the slurry A, and the remaining two nozzles 106b and 106b ′ can be arranged for supplying the slurry B.
As described above, it is possible to supply a slurry at different temperatures by using a valve or the like and switching the nozzle that supplies the slurry.

1 and 2, the non-shared type in which slurry at different temperatures is supplied by separate nozzles has been described, but in addition, a shared type in which slurry at different temperatures is supplied by the same nozzle may be used. .
FIG. 3A shows the entire polishing apparatus having one nozzle, and FIG. 3B shows the nozzle arrangement positions. FIG. 3C shows the arrangement positions when there are two nozzles.
First, as shown in FIGS. 3A and 3B, one nozzle 206 is provided, and slurry at different temperatures can be supplied by switching the valves 207a, 207a ′, 207b, and 207b ′. For example, if the valves 207a and 207b ′ are opened and the valves 207a ′ and 207b are closed, the slurry B only circulates, and only the slurry A is supplied from the nozzle 206 onto the polishing cloth. On the other hand, if the valves 207a ′ and 207b are opened and the valves 207a and 207b ′ are closed, only the slurry B can be supplied from the nozzle 206 onto the polishing cloth.
Note that as shown in FIG. 3C, a plurality of nozzles (206, 206 ′) may be provided. In this case, the nozzles 206 and 206 ′ can supply the same slurry.

Next, the wafer polishing method of the present invention using the polishing apparatus of FIG. 1 will be described.
FIG. 4 shows an example of the flow of the wafer polishing method of the present invention.
As shown in FIG. 4, polishing is started, and after a predetermined time has elapsed, during the polishing, the supply temperature of the slurry is changed to a temperature lower than that at the start of polishing, and polishing is continued. After polishing for a predetermined time, the polishing is finished. . Thus, by lowering the supply temperature of the slurry during polishing, the polishing rate at the outer peripheral portion of the wafer is controlled to be low.
More specific description will be given below.

(Polishing started)
First, the back side of the wafer is held on the polishing head 2. Then, the slurry A is supplied from the tank 5a to the polishing cloth 3 through the nozzle 6a, and the wafer is brought into sliding contact with the polishing cloth 3 while rotating the polishing head 2 and the surface plate 4 in predetermined directions, respectively. The surface of the wafer is polished by being pressed with a predetermined pressing force while rotating with respect to 3.

  The rotational speed of the polishing head 2 and the surface plate 4, the pressing force to the polishing cloth 3, the polishing time, etc. are not particularly limited and can be determined as appropriate. Further, the temperature of the slurry A in the tank 5a, that is, the supply temperature of the slurry A at the start of polishing is not particularly limited, and can be determined as appropriate. Although details will be described later, it may be determined in consideration of an average polishing rate or the like.

  In the polishing method of the present invention, the supply temperature of the slurry is lowered during the polishing as described above, but the polishing can be performed as desired in the entire polishing process in consideration of the effect of the lower temperature, productivity, and the like. Can be determined.

(Slurry supply temperature is changed to a lower temperature than at the start of polishing)
After starting polishing as described above, the slurry supply temperature is changed to a low temperature during polishing.
Here, the method for lowering the supply temperature of the slurry is not particularly limited, but in the case of the polishing apparatus 1 in FIG. 1, for example, the supply of the slurry A from the tank 5a through the nozzle 6a is stopped, and the tank 5b is used instead. Can be changed to a low temperature by supplying a slurry B having a temperature lower than that of the slurry A to the polishing pad 3 through the nozzle 6b. The nozzle for supplying the slurry may be switched from the nozzle 6 a to the nozzle 6 b by switching the opening and closing of the valves 7 a to 7 b ′, and the slurry B lower in temperature than the slurry A may be supplied.

  In the case where the slurry A is supplied from the start of polishing by the polishing apparatus of FIG. 3, the slurry B is selected instead of the slurry A by the opening / closing switching operation of the valves 207a to 207b ′, Slurry B can be supplied onto the polishing pad 3 through the same nozzle 206 (or nozzle 206 and nozzle 206 ′).

  Here, the temperature reduction of the slurry will be described in detail. The supply temperature of the slurry B may be lower than the supply temperature of the slurry A at the start of polishing, and the degree thereof is not particularly limited. For example, by lowering the temperature by 5 ° C. or more, the outer periphery of the wafer can be cooled more efficiently, and the polishing rate of the outer periphery of the wafer can be controlled to be further suppressed. As a result, it is possible to more effectively suppress, for example, the degree of occurrence of peripheral sag.

FIG. 5 is a graph showing an example of a machining allowance shape of the outer peripheral portion of the wafer having a diameter of 300 mm when the supply temperature of the slurry is lowered during polishing.
Here, the platen rotation speed / polishing head rotation speed is 40 rpm / 40 rpm, 60% of the total polishing time from the start of polishing is polished with the slurry A at 25 ° C., and the remaining 40% until the end of polishing is 20 ° C. or 15 ° C. The result of polishing with the slurry B and the result of polishing 60% of the total polishing time from the start of polishing with the slurry A at 30 ° C. and the remaining 40% until the end of polishing with the slurry B at 10 ° C. are shown.
For comparison, FIG. 5 also shows the results when polishing is performed at a constant temperature of 25 ° C. without changing the slurry supply temperature.

  When the distance from the outer periphery of the wafer, for example, the vicinity of the wafer center is about 149 mm, the allowance rises the largest when the slurry supply temperature is constant at 25 ° C. (the allowance is large). Then, it is understood that the stock removal is small in the order of changing from 25 ° C. to 20 ° C., from 25 ° C. to 15 ° C., and from 30 ° C. to 10 ° C., and the jump of the stock removal can be suppressed.

Here, FIG. 6 shows the machining allowance (value at 149 mm−value at 147 mm) at positions of 147 mm and 149 mm from the center of the wafer having a diameter of 300 mm. A positive value indicates a peripheral sag, and a negative value indicates a peripheral sag. When the temperature is constant at 25 ° C., the stock removal difference shows a large value of 39 nm, but when changing from 25 ° C. to 20 ° C., 14 nm, when changing from 25 ° C. to 15 ° C., 11 nm, from 30 ° C. to 10 ° C. When changed, it was 8 nm.
Therefore, as can be seen from FIGS. 5 and 6, the polishing rate at the wafer outer peripheral portion can be suppressed and the degree of outer peripheral sag can be reduced by lowering the temperature during polishing as in the present invention, as compared with the case where the temperature is constant at 25 ° C. I understand that And the one where the degree of temperature reduction is large can suppress the generation | occurrence | production degree of outer periphery sagging further.

FIG. 7 shows the relationship between the slurry supply temperature condition and the average polishing rate. The average polishing rate is slightly lower when the temperature is changed from 25 ° C. to 20 ° C. and from 25 ° C. to 15 ° C., compared to the case where the temperature is constant at 25 ° C. However, when the temperature was changed from 30 ° C. to 10 ° C., the average polishing rate could be improved as compared with the case where the temperature was constant at 25 ° C.
As described above, regarding the average polishing rate, when the temperature of the slurry to be supplied is changed during polishing (for example, changed from 25 ° C. to 20 ° C. or 15 ° C.), compared to the case where the polishing process is constant (eg, constant at 25 ° C.). Is slightly reduced. However, if the supply temperature at the start of polishing is adjusted (for example, polishing starts at 30 ° C. instead of 25 ° C.), the average polishing rate can be maintained or improved. Even if the supply temperature of the slurry is set higher, if the temperature is lowered later as in the present invention, surface roughness due to etching does not occur, and occurrence of Haze unevenness can be prevented.
In consideration of productivity and the like, the supply temperatures of the slurries A and B can be determined so as to obtain a desired average polishing rate.

In addition to this, the amount of slurry to be supplied is better because it affects the cooling effect, and can be preferably 3 L / min or more. In order to suppress an increase in cost due to the supply amount, it is desirable to circulate and recover the slurry.
Further, by making the slurry A and B the same type of slurry having different temperatures, it is not necessary to divide and collect the slurry strictly at the time of waste slurry collection, and the condition setting becomes easy.

Furthermore, in the examples of FIGS. 5 to 7, the lowering of the slurry supply temperature is set at the time when 60% of the total polishing time has elapsed. However, the present invention is not particularly limited thereto, and the productivity, the degree of peripheral sag and peripheral sag, etc. Can be appropriately determined in consideration of the above.
In addition, although an example in which the temperature of the slurry supply is lowered only once during polishing is shown here, the present invention is not limited to this, and the temperature may be lowered stepwise multiple times as necessary or gradually. Thus, the polishing rate of the outer peripheral portion of the wafer can be controlled more finely.

  As described above, by changing the slurry supply temperature during polishing to a temperature lower than that at the start of polishing, the polishing rate of the outer periphery of the wafer can be controlled, and the occurrence of defects such as outer peripheral sag can be suppressed. Can do. In addition, it is simple because it only lowers the supply temperature of the slurry, and scratches and the like do not occur on the wafer surface.

EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited to these.
(Example)
A polishing apparatus 1 as shown in FIG. 1 was used to carry out the polishing method of the present invention.
While supplying the slurry A onto the polishing cloth 3, while rotating the polishing head 2 holding the wafer having a diameter of 300 mm and the surface plate 4, the wafer is brought into sliding contact with the polishing cloth 3 and the wafer is rotated with respect to the polishing cloth 3. The wafer surface was polished while being pressed.
Thereafter, the slurry A was switched to the slurry B at a different temperature and supplied during polishing.
Then, after polishing for a predetermined time, the polishing was finished.

  The platen rotation speed / polishing head rotation speed is 40 rpm / 40 rpm, 60% of the total polishing time from the start of polishing is supplied with 30 ° C. slurry A, and the remaining 40% until the end of polishing is 10 ° C. Slurry B was supplied and polished.

(Comparative example)
The same wafer was polished in the same manner as in Example 1 except that the slurry supply temperature was not changed and the polishing was performed at a constant temperature of 25 ° C.

About the wafer after grinding | polishing in an Example and a comparative example, flatness was measured using Wafersight made from KLA-Tencor, and SFQR and ESFQR were evaluated. The result is shown in FIG.
The SFQR was evaluated with a site size of 26 mm × 8 mm, excluding a 2 mm region from the wafer edge. In addition, ESFQR was evaluated by excluding a 1 mm region from the wafer edge, dividing the entire circumference of the wafer at 5 ° intervals, and a site size in which the length of one side in the radial direction was 35 mm.

As can be seen from FIG. 8, in the example in which the present invention is implemented, the distribution of both SFQR and ESFQR is shifted to the smaller value as compared with the comparative example. It can be seen that both SFQRmax and ESFQRmax are improved as the shape of the wafer outer periphery is improved.
The improvement rate of SFQR was about 14%, and the improvement rate of ESFQR was about 22%. As for the cross section shape, since the sagging at a position of 149 mm from the center is greatly improved, it is considered that the improvement rate of ESFQR measured with the exclusion region of 1 mm is higher than the SFQR measured with the exclusion region of 2 mm from the wafer edge. It is done.

  By carrying out the present invention, the vicinity of the outer periphery of the wafer can be effectively cooled. In addition, it can suppress the chemical polishing action and suppress the polishing rate of the outer periphery of the wafer, and can improve the flatness of the wafer (particularly the flatness near the outer periphery of the wafer) as in the embodiment. It is.

  FIG. 9 shows a Haze map of the wafer surface after polishing. It is the result confirmed with the SP-2 light-scattering measuring apparatus made from KLA-Tencor. In the example and the comparative example, no difference was observed in the Haze map, and no occurrence of Haze unevenness was observed.

Thus, the flatness can be improved by the present invention without causing Haze unevenness and the like.
Also, with respect to the average polishing rate, the same result as that obtained when the example was changed from 30 ° C. to 10 ° C. in FIG. 7 was obtained, and the same result was obtained when the comparative example was constant at 25 ° C. in FIG. It was. That is, it can be seen that the example has a higher average polishing rate than the comparative example, and polishing can be performed with high productivity.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

DESCRIPTION OF SYMBOLS 1 ... Polishing apparatus, 2 ... Polishing head, 3 ... Polishing cloth, 4 ... Surface plate,
5a, 5b ... tank,
6a, 6b, 106a, 106a ′, 106b, 106b ′,
206, 206 '... Nozzle,
7a, 7a ′, 7b, 7b ′, 207a, 207a ′,
207b, 207b '... valves.

Claims (3)

A method of polishing a wafer in which a slurry is supplied onto a polishing cloth affixed to a surface plate, and the polishing cloth is slidably brought into contact with the surface of a wafer held by a polishing head.
By controlling the supply temperature at the start of polishing of the slurry, the average polishing rate is controlled, and
After starting the polishing of the wafer, during the polishing, the slurry is switched to a slurry having a different temperature that is 5 ° C. or more lower than that at the start of polishing , so that the supply temperature of the slurry is 5 ° C. or more lower than that at the start of polishing. method for polishing a wafer, characterized in that to change, to control the polishing rate of the wafer outer peripheral portion. 2. The wafer polishing method according to claim 1 , wherein when the supply temperature of the slurry is changed, a plurality of nozzles for separately supplying slurry having different temperatures are provided, and the plurality of nozzles are switched. 2. The wafer according to claim 1 , wherein when changing the supply temperature of the slurry, the slurry having different temperatures separately stored in a plurality of tanks is selected by a valve switching operation and sent to a nozzle. Polishing method.

Images