JP2002166357A - Wafer polishing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To polish a wafer 3 in a shape with a high flatness by setting off the effect of the deformation of a surface plate caused under a thermal environment when polishing the wafer. SOLUTION: The deformations of upper and lower surface plates 1 and 2 at the time of polishing are detected beforehand, the upper and lower surface plates 1 and 2 are worked in such a shape that the deformation thereof in a process of manufacturing the upper surface plates 1 and 2 can be set off, and an abrasive cloth 4 is stuck on the upper and lower surface plates 1 and 2. Then, the wafer 3 is held between the upper and lower surface plates I and 2, and the water 3 is polished from both surfaces thereof. The effect of deformation of the surface plates at the time of polishing can be set off also by radially adjusting the amount of dressing of the abrasive cloth 4 instead of correcting the shape of the upper and lower surface plates 1 and 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for polishing a wafer while controlling the shape of the surface plate so that the upper and lower surfaces of the surface plate match in a thermal environment during wafer polishing.

[0002]

2. Description of the Related Art A wafer sliced from an ingot is lapped and polished into a flat shape.
In the polishing of wafers, a double-side polishing apparatus that sandwiches a carrier containing a plurality of wafers between a lower surface plate and an upper surface plate and surface-processes each wafer with a polishing cloth attached to the upper and lower surface plates is often used. I have. In order to increase the flatness of the polished wafer, it is necessary that the degree of coincidence between the upper and lower platens be increased and that the mechanical action such as the viscoelasticity of the polishing cloth acts on the wafer evenly. Therefore, in a conventional polishing machine, for example, a pressure-sensitive paper having a different degree of discoloration according to the intensity of pressure is sandwiched between the upper and lower platens, and the upper and lower platens are finished so that the degree of discoloration is constant. The shape of the board is matched.
Inspection of the degree of conformity is performed after the polishing machine has been left in the room for a long time until it reaches room temperature.

[0003]

When a wafer is polished with a polishing machine whose degree of conformity between the upper and lower platens has been inspected, the polishing machine is exposed to a complicated thermal environment, and the upper and lower platens are exposed to the thermal environment. Heat deformation. Thermal deformation of the upper and lower platens has a large effect on the flatness of the polished wafer.However, in the conventional lower platen with relatively small rigidity, the thermal deformation is canceled out by bending deformation, and the elasticity of the polishing cloth is also increased. Not so big,
Variations in the clamping pressure acting on both surfaces of the wafer are suppressed, and the wafer is polished into a flat shape without being affected by thermal deformation.

However, in order to increase the diameter of the wafer and increase the flatness of the wafer, high-rigidity polishing machines including upper and lower platens have begun to be used, and hard polishing cloths have been used as polishing cloths. Is coming. A platen having high rigidity is effective in suppressing the bending deformation that lowers the flatness, but the conventional platen is strongly affected by the thermal deformation that has been canceled by the bending deformation. Moreover, the thermal deformation of the surface plate is further reflected on the shape of the polished wafer due to the reduction of the buffering effect due to the hardening of the polishing pad.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been devised to solve such a problem. The upper and lower platens are formed in a shape in which thermal deformation due to heat generated during wafer polishing has been taken in advance. Or, by adjusting the dressing amount of the polishing cloth, the upper and lower platens are matched so that the forces acting on both surfaces of the wafer being polished are equalized, and the purpose is to polish and finish the wafer into a highly flat shape. I do.

In order to achieve the object, the wafer polishing method according to the present invention grasps in advance the deformation of the upper and lower platens during polishing, and forms the upper and lower platens in a shape to cancel the deformation during polishing in the process of manufacturing the platen. After the polishing, a polishing cloth is attached to the upper and lower platens, the wafer is sandwiched between the upper and lower platens, and the wafers are polished on both sides.

By adjusting the amount of dressing of the polishing cloth instead of adjusting the shape of the upper and lower platens, it is possible to maintain the degree of matching between the upper and lower platens during polishing. In this case, after attaching the polishing cloth to the upper and lower platens, the dressing tool is sandwiched between the upper and lower platens, and the same deformation as the upper and lower platens during wafer polishing is applied to the upper and lower platens. The dressing of the polishing cloth is continued until the applied contact pressure becomes uniform, and then the wafer is sandwiched between the upper and lower platens in place of the dressing tool, and the wafer is polished on both sides.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A wafer 3 is placed between an upper surface plate 1 and a lower surface plate 2.
When both sides are polished across the surface, the factors of thermal deformation vary in accordance with the polishing conditions, and various thermal deformations occur on the upper and lower stools 1 and 2 (FIG. 1). Since the upper and lower stools 1 and 2 are complicatedly deformed as a result of the combination of these thermal deformations, even if the upper and lower stools 1 and 2 are matched with high accuracy at the time of attaching the polishing pad 4, the upper and lower stools 1 and 2 can be precisely adjusted. Deforms into a conical or inverted conical shape. Upper and lower surface plate 1,
In many cases, the deformation 2 is such that the inner circumference approaches and the outer circumference separates (FIG. 2). On the other hand, there is also a configuration in which the inner circumference separates and the outer circumference approaches. In any case, the distance between the upper and lower stools 1 and 2 fluctuates in the radial direction, the polishing pressure applied to the wafer 3 varies, and the flatness of the polished wafer 3 decreases.

In the process of investigating and examining the shape of the upper and lower stools 1 and 2 on the flatness of the wafer 3, the present inventor considered that the thermal environment where the polishing machine is placed and the shape of the upper and lower stools 1 and 2 are different. Have a very strong correlation. The thermal environment includes the cooling water temperature of the upper and lower platens 1 and 2, the temperature of the slurry supplied to the wafer 3, the temperature of the bearing cooling water, the upper and lower platens 1 and 2,
(The amount of heat flowing from the front surface to the back surface of the upper and lower platens 1 and 2 when the back surfaces of the upper and lower platens 1 and 2 are cooled in order to remove polishing heat). The amount of heat transfer between the upper and lower platens 1 and 2 fluctuates depending on the processing heat generated according to the polishing conditions, such as the polishing pressure, the number of rotations of the platen, and the friction coefficient of the polishing pad 4. It has a quantitative relationship with the polishing conditions.

When these values are changed, the upper and lower stools 1 and 2 change in the range of concave to convex conical shapes. In addition, the upper and lower stools 1 and 2 change with extremely high reproducibility following changes in the thermal environment. This means that a change in the thermal environment can be used for controlling the shapes of the upper and lower stools 1 and 2. In addition, the upper and lower platens 1 and 2 with a high degree of matching when the polishing cloth 4 is stuck.
It is also conceivable to control the thermal environment so that the gap in the entire surface plate is maintained even during polishing, but such temperature control causes problems such as a decrease in processing ability.

In the present invention, it is assumed that the upper and lower stools 1 and 2 are deformed in a thermal environment during polishing. In the present invention, the upper and lower stools 1 and 2 are formed in a shape that allows for deformation expected from past results and heat calculations. ,
2 is prepared in advance. Specifically, the upper and lower stool 1,
When it is anticipated that the base 2 will be deformed to a shape (FIG. 2) approaching on the inner peripheral side, the upper and lower stools 1 and 2 are formed in a shape (FIG. 3a) in which the center part is depressed in the stool making stage. The central depression is the upper and lower platens 1, which are generated in a thermal environment during wafer polishing.
2 is canceled and the distance between the upper and lower stools 1 and 2 is kept constant (FIG. 3b). As a result, the polishing pressure is evenly applied to the wafer 3, and the wafer 3 is polished and finished with good flatness.

The polishing pressure applied to the wafer 3 can also be equalized by adjusting the amount of dressing of the polishing pad 4 instead of making the upper and lower stools 1 and 2 recessed (FIG. 4). In the dressing of the polishing cloth 4, the dressing tool 5 is sandwiched between the upper and lower stools 1 and 2 on which the polishing cloth 4 is stuck, and the working surface of the polishing cloth 4 is adjusted to a predetermined surface property by the dressing tool 5. At this time, the polishing pad 4 is dressed in a state where the upper and lower platens 1 and 2 are deformed into the same shape as that of the wafer polishing. The deformation of the upper and lower platens 1 and 2 can be controlled by the applied pressure, the number of rotations of the platen, the coefficient of friction of the polishing pad 4, and the like.

When the dressing is continued until the contact pressure applied to the dressing tool 5 becomes uniform, the polishing cloth 4
It is dressed in a cross-sectional shape that is thinner on the inner peripheral side and thicker on the outer peripheral side. The thickness distribution applied to the polishing cloth 4 cancels the deformation of the upper and lower stools 1 and 2 generated during wafer polishing, and equalizes the polishing pressure applied to the wafer 3. As a result, the wafer 3 is polished to a shape having a uniform thickness distribution and a high flatness.

When the wafer 3 is polished using the upper and lower stools 1 and 2 whose shape has been corrected or the polishing cloth 4 with an adjusted dressing amount, strict control of the thermal environment depends on the degree of matching between the upper and lower stools 1 and 2. Is necessary to maintain. The control factors include the temperature and flow rate of the cooling water supplied to the upper stool 1, the temperature and flow rate of the cooling water supplied to the lower stool 2, the temperature and flow rate of the slurry supplied to the wafer 3, and the temperature of the slurry supplied to the bearing 3. Cooling water temperature and flow rate.

The polishing pressure can be equalized by adjusting these control factors while measuring the degree of matching between the upper and lower stools 1 and 2 or the polishing pressure applied to the wafer 3 during polishing. Alternatively, it is also possible to measure the shape of the polished wafer 3 and adjust the control factor based on the measurement result. In the measurement of the degree of coincidence during polishing, it is possible to utilize a phenomenon in which the smaller the gap between the upper and lower stools 1 and 2, the greater the polishing pressure applied to the wafer 3, the greater the amount of heat generated and the temperature rises. That is, the upper and lower platens 1,
By arranging a plurality of thermometers along the radial direction 2 and measuring the temperature distribution in the radial direction of the upper and lower platens 1 and 2, it is possible to estimate the matching state of the upper and lower platens 1 and 2.

If the polishing of the wafer 3 is repeated and continued, the thermal environment fluctuates due to scale adhesion to the cooling water system, fluctuations in frictional heat due to wear and clogging of the polishing pad 4, and the like. The matching degree of No. 2 may be reduced. In such a case, one or more of the control factors described above are selected, and the level thereof is changed to restore the matching degree between the upper and lower stools 1 and 2. Even if the polishing pressure and the rotation speed of the surface plate are changed, the amount of heat transfer between the upper and lower surface plates 1 and 2 may change, and the matching degree between the upper and lower surface plates 1 and 2 may be reduced. Also in this case, the degree of coincidence between the upper and lower stools 1 and 2 can be restored by correcting the control factors so as to compensate for the decrease.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As a polishing machine, an outer diameter of 1652 mm and an inner diameter of 49 were used.
Average thickness of 1.27m on 2mm upper surface plate 1 and lower surface plate 2
A double-side polishing apparatus to which a polishing cloth 4 made of a polyurethane-impregnated polyester non-woven fabric having a Asker C hardness of 82 (manufactured by SUBA 800 Rodel Nittta Co., Ltd.) was attached was used. The wafer 3 sandwiched between the upper and lower platens 1 and 2
The two surfaces are polished by the friction generated by the rotation of No. 2, but the upper and lower platens 1 and 2 are deformed in a thermal environment during the polishing.

FIGS. 5 to 13 show the results of investigations on various factors affecting the deformation of the upper and lower stools 1 and 2. The shape of the upper stool 1 is linearly related to the temperature of the cooling water supplied to the upper stool 1 (FIG. 5) and the amount of heat transfer (FIG. 6), and the shape of the lower stool 2 is supplied to the lower stool 2. There was a linear relationship in the opposite direction to the temperature of the cooling water (FIG. 7) and the amount of heat transfer (FIGS. 8 and 9). Also,
The shape of the lower stool 2 changes linearly depending on the temperature of the cooling water supplied to the bearing that rotatably supports the lower stool 2 (FIG. 10), and according to the rotation speed of the lower stool 2 (FIG. 11). Had changed. In the figure, Hs indicates the height of the apex when the surface shape of the surface plate is approximated by a cone, and + when the vertex of the cone is above and-when it is below.

From various control factors, it can be seen that the shapes of the upper and lower stools 1 and 2 during wafer polishing can be predicted or controlled. For example, when the temperature of the cooling water supplied to the upper stool 1 and the heat removal amount are changed, the upper stool 1 is deformed into an upwardly convex or downwardly convex shape (FIG. 12), and the cooling supplied to the lower stool 2 When the temperature of the water and the heat removal amount are changed, the lower stool 2 is deformed into an upwardly convex or downwardly convex shape (FIG. 13). Here, the amount of heat removal varies depending on the number of revolutions of the platen, polishing pressure, slurry flow rate, temperature, and the like. The temperature of the cooling water supplied to the upper and lower platens 1, 2 and the bearings,
The influence of the flow rate, the heat transfer amount of the upper and lower stools 1 and 2 and the rotation speed of the upper and lower stools 1 and 2 on the deformation of the upper and lower stools 1 and 2 has a relationship determined for each polishing machine. Therefore, by setting the polishing conditions, the upper and lower platens 1 during polishing of the wafer 3
2 can be predicted.

When the polishing conditions were set as follows, the upper and lower stools 1 and 2 that had been manufactured flat were -20 μm in Hs value in the thermal environment during wafer polishing.
The shape of the lower surface plate 1 was expected to be deformed by +10 μm, and the interval between the upper and lower surface plates 1 and 2 was increased by 30 μm from the inner peripheral side to the outer peripheral side. Therefore, the shape of the upper stool 1 at the time of manufacture of the stool is +20 in Hs value so that the deformation during wafer polishing can be offset.
The lower platen 2 was formed in a conical shape so that the Hs value became −10 μm. Polishing conditions Temperature of cooling water supplied to upper platen 1 20 ° C, flow rate 7 liter / min Temperature of cooling water supplied to lower platen 2 20 ° C, flow rate 7 liter / min Slurry temperature 20 supplied to wafer polishing ° C, flow rate 4
Liter / minute Heat transfer amount of upper surface plate 1 5 kcal / minute, heat transfer amount of lower surface plate 2 7 kcal / minute Number of revolutions of upper surface plate 1 10 rpm, number of rotations of lower surface plate 2 Clockwise 30 rpm Thickness of polishing cloth 4 .27mm,
Asker C hardness 82

The upper and lower stools 1 and 2 whose shapes were adjusted were assembled into a polishing machine, and the wafer 3 was polished on both sides.
Is the flatness (difference between the maximum thickness and the minimum thickness in the wafer).
It was polished to an extremely flat shape of 0010 mm. For comparison, when a polishing machine incorporating upper and lower platens 1 and 2 without a depression is used, the polished wafer 3
Had a convex lens shape and a flatness of 0.007 mm, which was inferior to the flatness.

Further, instead of correcting the shapes of the upper and lower stools 1, 2,
When dressing the polishing cloth 4 adhered to the upper and lower platens 1 and 2, the upper and lower platens 1 and 2 are changed in shape in the same manner as during polishing, until the friction pressure applied to the dressing tool 5 becomes uniform. Was dressed. When the thickness of the dressed polishing cloth 4 was measured, the inner peripheral side was 0.031 mm thinner than the outer peripheral side. When the polishing cloth 4 thus adjusted was brought into contact with the wafer 3 and polished on both sides,
The wafer 3 was polished to a flat shape with a flatness of 0.0010 mm.

[0023]

As described above, according to the present invention, the upper and lower platens are formed in a shape that allows for the deformation of the platen during polishing, or the dressing amount of the polishing pad is adjusted, whereby the polishing during polishing is performed. The polishing pressure applied to the wafer is equalized. Adjusting the shape of the upper and lower platens and adjusting the dressing amount of the polishing cloth effectively eliminates the effects of surface plate deformation caused by the thermal environment that tends to appear in polishing machines that incorporate a platen that has increased rigidity as the size increases. Counteract. The wafer polished in this manner is polished to a shape with a high degree of flatness without being affected by surface plate deformation during polishing.
It is used as a substrate for the production of various semiconductor devices with remarkably advanced functions.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram illustrating thermal deformation of a double-side polishing machine.

FIG. 2 is a view for explaining that an upper and lower platen (a) having a high degree of matching is deformed (b) during wafer polishing.

FIG. 3 is an upper and lower surface plate (a) whose shape has been corrected according to the present invention.
For maintaining uniform gap (b) during wafer polishing

FIG. 4 is an explanatory view of a method of adjusting a dressing amount of a polishing cloth so as to increase a degree of coincidence between an upper and lower platen during wafer polishing.

FIG. 5 is a graph showing that the shape of the upper stool changes depending on the cooling water temperature.

FIG. 6 is a graph showing that the shape of the upper stool changes depending on the amount of heat transfer.

FIG. 7 is a graph showing that the shape of the lower stool changes depending on the cooling water temperature.

FIG. 8 is a graph showing that the shape of the lower stool changes depending on the amount of heat transfer.

FIG. 9 is a graph showing that the shape of the lower stool changes depending on the amount of heat transfer.

FIG. 10 is a graph showing that the shape of the lower stool changes depending on the temperature of the cooling water supplied to the fluid bearing.

FIG. 11 is a graph showing that the shape of the lower stool changes with the number of rotations.

FIG. 12 is a graph showing the relationship between the cooling water temperature and the heat removal amount and the change in the shape of the upper platen based on the equations derived from FIGS.

FIG. 13 is a graph showing the relationship between the cooling water temperature and heat removal amount and the change in the shape of the lower stool based on the equations derived from FIGS.

[Explanation of symbols]

1: Upper surface plate 2: Lower surface plate 3: Wafer 4: Polishing cloth 5: Dressing tool

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 21/304 622 H01L 21/304 622M

Claims (2)

[Claims] 1. The upper and lower platens are preliminarily grasped for deformation at the time of polishing, and the upper and lower platens are processed into a shape to cancel the deformation at the time of polishing during the platen manufacturing process, and a polishing cloth is attached to the upper and lower platens. Thereafter, the wafer is sandwiched between the upper and lower platens, and the wafer is polished on both sides. 2. After attaching a polishing cloth to the upper and lower platens, a dressing tool is inserted between the upper and lower platens, and the same deformation as the platen deformation during wafer polishing is applied to the upper and lower platens. A wafer polishing method characterized by continuing dressing of a polishing cloth until an applied contact pressure becomes uniform, then sandwiching the wafer between upper and lower platens instead of a dressing tool, and polishing the wafer on both sides.