JP3998781B2 - Wafer pressurization method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wafer pressurizing method for applying a desired polishing pressure to a wafer in a wafer polishing apparatus used for double-side polishing of a semiconductor wafer or the like.
[0002]
[Prior art]
Prior to forming a device on the surface, the surface of the silicon wafer collected from the single crystal rod of silicon is polished into a mirror surface. The mirror surface polishing of the wafer surface has been performed only on the device forming surface until now. However, in a wafer having a large diameter of more than 8 inches, for example, 12 inches, the back surface on which the device is not formed is comparable to the mirror polishing. Precision polishing was required, and along with this, double-sided polishing was required. This is because, in the process of forming a device on the surface of the wafer, the surface is prevented from being contaminated by fine foreign matters adhering to the back surface, and is affected by the unevenness of the back surface during exposure.
[0003]
When performing double-side polishing of a silicon wafer, a method of causing the wafer to perform planetary movement between the upper and lower surface plates is promising from the viewpoint of apparatus scale, polishing accuracy, and the like. The basic structure of this type of wafer polishing apparatus will be described with reference to FIGS.
[0004]
A wafer polishing apparatus of a type that causes a wafer to perform planetary motion between upper and lower surface plates includes an annular lower surface plate 1 supported horizontally, an upper surface plate 2 provided above the lower surface plate 1, and upper and lower surface plates. A plurality of carriers 3, 3 and 3 arranged between 1 and 2 are provided.
[0005]
The upper surface plate 2 facing the lower surface plate 1 is suspended and supported by the frame via the air cylinder 4, the joint 5 and the support frame 6, and moves up and down on the lower surface plate 1 by the operation of the air cylinder 4.
[0006]
The plurality of carriers 3, 3, 3 are rotatably supported at circumferentially equidistant positions on the lower surface plate 1. Each carrier 3 is a so-called planetary gear that meshes with a sun gear 7 provided on the inner side of the lower surface plate 1 and a ring-shaped inner gear 8 provided on the outer side, and at a position eccentric from the center of the carrier 3. 10 is an annular body formed with a circular hole into which 10 is fitted.
[0007]
In order to perform double-side polishing of the wafer 10, the wafer 10 is set in the hole of each carrier with the upper surface plate 2 raised. Next, by lowering the upper surface plate 2 while rotating the lower surface plate 1 and the sun gear 7 at a low speed, each wafer 10 is placed between the polishing pads attached to the opposing surfaces of the upper and lower surface plates 1 and 2. Is sandwiched with a predetermined polishing pressure. The lowered upper platen 2 is connected to the sun gear 7 and starts rotating. Then, the lower surface plate 1 and the sun gear 7 are increased to a predetermined speed, and polishing is started. During polishing, the polishing liquid is supplied to the polishing pad via the upper surface plate 2.
[0008]
Each carrier 3 revolves while rotating between the upper and lower surface plates 1 and 2. As a result, the wafer 10 held eccentrically in each carrier 3 rotates eccentrically and revolves between the polishing pads impregnated with the abrasive liquid. The two surfaces are uniformly polished by a combination of these movements.
[0009]
In this type of polishing apparatus, the lower surface plate 1, the upper surface plate 2, the sun gear 7 and the inner gear 8 can be rotated independently. Further, the plurality of carriers 3, 3, and 3 can be rotated in synchronization. Such multi-axis driving allows the carrier 3 and thus the wafer 10 to perform planetary motion under a variety of conditions.
[0010]
[Problems to be solved by the invention]
However, this type of polishing apparatus has the following problems regarding pressurization of the wafer 10.
[0011]
In the surface polishing of the wafer 10, it is necessary to accurately apply a predetermined polishing pressure to the wafer 10. For this purpose, in the conventional polishing apparatus shown in FIGS. 2 and 3, three load cells are placed on the lower surface plate 1 at intervals of about 120 degrees with the upper surface plate 2 retracted upward, By moving the rod of the cylinder 4 downward, the upper surface plate 2 is lowered and placed on the three load cells. At this time, the values of the three load cells are totaled to obtain a pressing force, and the relationship between the pressing force and the air pressure applied to the air cylinder 4 is obtained. In actual polishing, this relationship is used to adjust the air pressure so that a predetermined pressure (polishing pressure) is obtained.
[0012]
However, when the necessary polishing pressure is smaller than the suspended weight of the upper surface plate 2, it is necessary to lift the upper surface plate 2 by the air cylinder 4 during polishing. The air pressure when the upper surface plate 2 is pulled up by the air cylinder 4 is adjusted by a pressure adjustment valve connected to the rod side space (lower space) in the air cylinder 4. For this reason, compared with the case where the upper surface plate 2 is pressed downward by the air cylinder 4, the accuracy of adjusting the air pressure is lowered, and the fluctuation of the polishing pressure due to this causes the polishing quality of the wafer 10 to vary.
[0013]
On the other hand, when the necessary polishing pressure is larger than the suspended weight of the upper surface plate 2, it is necessary to send the compressed air to the bottom side space (upper space) in the air cylinder 4 to apply the polishing pressure. At this time, fine adjustment of the air pressure is necessary. Furthermore, hysteresis is inevitable due to the response characteristics of the pressure regulating valve. For these reasons, fluctuations in the polishing pressure are inevitable.
[0014]
Further, when obtaining the relationship between the applied pressure and the air pressure, the relationship is basically determined by the pressure applied to the air cylinder 4. When the upper surface plate 2 is lifted up, that is, when air pressure is applied to the rod side space (lower space) in the air cylinder 4, correction is made by subtracting the rod cross section from the cylinder cross section. Since the relationship between pressure and air pressure is calculated, this relationship is not an actual measurement value. For this reason, the polishing pressure varies due to an inaccurate relationship between the applied pressure and the air pressure.
[0015]
Furthermore, for the vertical swing of the upper and lower surface plates 1 and 2, it is necessary to adjust the pressure on the rod side and the bottom side of the air cylinder 4, but due to the air compressibility and the characteristics of the pressure adjustment valve, Since the response is delayed and hysteresis occurs, the variation in polishing pressure due to the fluctuation is promoted, and the variation becomes even greater.
[0016]
As described above, in the conventional polishing apparatus, the polishing quality varies due to the inaccurate polishing pressure. This problem has not been a major problem with conventional small diameter wafers (single-side polishing) with a small polishing area, but this polishing quality variation is particularly significant with large diameter wafers with a large polishing area (double-side polishing). It becomes a big problem.
[0017]
An object of the present invention is to provide a wafer pressing method capable of accurately applying a predetermined polishing pressure.
[0018]
[Means for Solving the Problems]
The wafer pressurization method of the present invention polishes both sides of a horizontally supported lower surface plate, an upper surface plate that is opposed to the lower surface plate and supported above by an elevating mechanism, and a wafer held inside. Therefore, the elevating mechanism is driven up and down in the axial direction by the rotating operation of the motor, and the upper surface plate via a spring below the elevating drive mechanism. a lifting rod for vertically movably suspended supporting, possess a load sensor for detecting between elevation drive mechanism and the spring of the axial load applied to the lifting rod, said spring, on raising the lift rod A platen holding spring that compresses under the load of the upper platen when the platen is lifted, and a lower platen that is compressed when the lifting rod is lowered while the upper platen is placed on the lower platen Pressing platen press spring In the wafer polishing apparatus is directed to a wafer pressurizing method for adding the polishing load is pressurized by the upper platen a wafer held under a platen in the carrier, the load sensor in a state in which lift the upper platen when the values and W _0, when the polishing load is W ₀ is smaller than W _1, the upper platen is raised and lowered so that the value w ₁ of the load sensor is W ₀ -W _1, the polishing load is W ₀ When W ₂ is larger , the lift rod is raised and lowered so that the load sensor value w ₂ becomes W ₂ −W ₀ .
[0019]
(Delete)
[0020]
(Delete)
[0021]
In the wafer pressurizing method of the present invention, the upper surface plate is suspended and supported by a lifting rod that is driven to move up and down in the axial direction by a rotating operation of a motor through a spring so as to be lifted and lowered. An axial load acting on the lifting rod is detected by a load sensor. When the upper surface plate is retracted upward, the load sensor is fully loaded with the suspension part including the upper surface plate, the surface plate holding spring is fully contracted, and the surface plate pressing spring is fully extended. . Therefore, the value W ₀ of the load sensor when the upper surface plate is retracted upward is the total weight of the suspension portion.
[0022]
When the upper surface plate is gradually lowered from this state and placed on the lower surface plate, finally the entire load of the suspension is added to the lower surface plate, the surface plate holding spring is fully extended and no load is applied, The value of the load sensor is 0. For this reason, the load received by the lower surface plate when the upper surface plate is lowered until the value of the load sensor becomes 0 is the total weight W ₀ of the suspension portion.
[0023]
When the lifting rod is lifted in the axial direction from this state, the surface plate holding spring contracts, and the load of the suspension portion applied to the lower surface plate decreases. A value obtained by subtracting the value w _{1 of the} load sensor from the total weight W ₀ of the suspension is the polishing pressure W ₁ . When the lifting rod is lowered in the axial direction, the surface plate pressing spring contracts, and the total weight W ₀ of the suspension part plus the value w _{2 of the} load sensor becomes the polishing pressure W ₂ .
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0025]
As shown in FIG. 1, the wafer polishing apparatus according to this embodiment supports the lower surface plate 1, the sun gear 7 and the inner gear 8 on the lower frame 11 side, and moves the upper surface plate 2 on the upper frame 12 side. The structure is supported via the mechanism 20.
[0026]
The lower surface plate 1 is an annular body disposed concentrically with respect to the apparatus center. The sun gear 7 is disposed concentrically inside the lower surface plate 1 and the inner gear 8 is concentrically disposed outside the lower surface plate 1. On the lower surface plate 1, a plurality of carriers 3 that hold the wafer 10 are placed in mesh with the sun gear 7 and the inner gear 8.
[0027]
The upper surface plate 2 is an annular body that faces the lower surface plate 1 from above. The lifting mechanism 20 that lifts and lowers the upper surface plate 2 has a lifting rod 21 that is arranged concentrically with respect to the apparatus center. The elevating rod 21 is divided into upper and lower parts, and the load in the axial direction is measured by a load cell 22 as a load sensor interposed between the upper part 21a and the lower part 21b.
[0028]
The upper part 21a of the elevating rod 21 is, for example, a ball screw, and is driven up and down in the axial direction together with the lower part 21b using a servo motor 23 and a speed reducer 24 attached to the upper frame 12 as power sources. In order to prevent the lifting rod 21 from rotating, the lifting rod 21 is connected to a detent shaft 25 that is supported by the upper frame 12 so as to be raised and lowered. A rack and pinion or the like may be used instead of the ball screw.
[0029]
A sleeve-like slide case 26 is fitted on the lower portion 21b of the elevating rod 21 so as to be movable up and down with respect to the lower portion 21b. The upper surface plate 2 is attached to the slide case 26 via a support member 27. The upper part of the support member 27 is externally fitted to the slide case 26 via a bearing 28, and supports the upper surface plate 2 connected to the lower part concentrically below the lifting rod 21. On the other hand, springs 29, 29 ′ are interposed between the lower part 21 b of the lifting rod 21 and the slide case 26 in two upper and lower stages. The upper spring 29 is a surface plate holding spring and is compressed between the upper end portion of the slide case 26 and the large-diameter portion 21 c of the lifting rod 21. For this reason, the upper surface plate 2 is suspended from the lifting rod 21 through the spring 29 together with the support member 27 and the slide case 26.
[0030]
Further, the lower spring 29 ′ is a surface plate pressing spring, and is provided in a state of extending between the large diameter portion 21 c of the lifting rod 21 and the lower end portion of the slide case 26.
[0031]
Next, the operation of the wafer polishing apparatus according to this embodiment and the wafer pressing method according to this embodiment will be described.
[0032]
Prior to double-side polishing of the wafer 10, the servo motor 23 is operated to raise the elevating rod 21, thereby moving the upper surface plate 2 to the upper retracted position. At this time, the upper surface plate 2 is suspended from the elevating rod 21 via the surface plate holding spring 29 together with the support member 27 and the slide case 26, so that the load cell 22 has the total weight W ₀ of this suspended portion. Added.
[0033]
When a polishing load W ₁ that is lighter than the total weight W ₀ of the suspension is applied to the wafer 10, the servo motor 23 is operated until the value w _{1 of the} load cell 22 becomes W ₀ −W _1, and the lifting rod 21 Is lowered. As a result, a desired polishing pressure is accurately applied to the wafer 10 in spite of a lighter weight than the suspension. Moreover, the operation of applying this polishing force is very simple. Further, unlike the air cylinder, the spring 29 does not have hysteresis with respect to the vertical swing of the upper surface plate 2, so that variations in the polishing pressure during polishing can be reduced.
[0034]
When the elevating rod 21 is further lowered, the value of the load cell 22 becomes 0, and the polishing load W ₁ matches the total weight W ₀ of the suspended portion. When a polishing load W ₂ that is heavier than the total weight W ₀ of the suspension is applied to the wafer 10, the lifting rod 21 is further lowered until the value w _{2 of the} load cell 22 becomes W ₂ −W ₀ . However, regarding the display, the polishing loads W ₁ and W ₂ are displayed.
[0035]
Next, another pressurizing method will be described.
[0036]
Prior to double-side polishing of the wafer 10, the servo motor 23 is operated to raise the elevating rod 21, thereby moving the upper surface plate 2 to the upper retracted position. In this state, the value of the load cell 23 is recorded. At this time, the upper surface plate 2 is suspended from the elevating rod 21 via the surface plate holding spring 29 together with the support member 27 and the slide case 26, so that the total weight of the suspended portion is added to the load cell 22. The
[0037]
From this state, the up-and-down rod 21 is lowered and the upper surface plate 2 is lowered until the surface plate holding spring 29 becomes unloaded. A stroke zone 13 is secured below the elevating rod 21 so that the upper surface plate 2 can continue to descend until the surface plate holding spring 29 becomes unloaded, and the lower end of the elevating rod 21 is here. By moving the elevating rod 21 down until it enters into the platen, the surface plate holding spring 29 becomes unloaded. Then, the value of the load cell 22 at this time is set to the value recorded at the retreat position. Thereby, the value of the load cell 22 accurately corresponds to the load applied to the wafer 10.
[0038]
In double-side polishing of the wafer 10, the upper surface plate 2 is moved to the upper retracted position, and the wafer 10 is set on the plurality of carriers 3. When the wafer 10 is set, polishing pressure is applied to the wafer 10. When the polishing pressure is lighter than the total weight of the suspension part, the servo motor 23 is operated in the direction in which the elevating rod 21 descends until the value of the load cell 22 reaches the pressure value necessary for polishing the wafer 10. Lower the surface plate 2. As a result, a desired polishing pressure is accurately applied to the wafer 10 in spite of a lighter weight than the suspension. Moreover, the operation of applying this polishing force is very simple. Further, unlike the air cylinder, the spring 29 does not have hysteresis with respect to the vertical swing of the upper surface plate 2, so that variations in the polishing pressure during polishing can be reduced.
[0039]
When a polishing pressure heavier than the suspension is applied to the wafer 10, the upper surface plate 2 is further lowered from the state where the upper surface plate 2 is placed on the wafer 10. As a result, the surface plate pressing spring 29 ′ contracts and the reaction force is applied to the load cell 22. Therefore, the pressure is applied to the wafer 10 by lowering the upper surface plate 2 until the value of the load cell 22 reaches a pressure value necessary for polishing the wafer 10.
[0040]
In the above embodiment, the value of the load cell 22 when the platen holding spring 29 is in an unloaded state is set to the value recorded at the retracted position so that the value of the load cell 22 matches the polishing pressure. The polishing pressure may be obtained by adding the total weight of the suspended portion to the value of the load cell 22 without performing this operation.
[0041]
【The invention's effect】
As described above, the wafer pressurizing method of the present invention supports the upper surface plate to be lifted / lowered via a spring on a lifting / lowering rod that is driven to lift / lower in the axial direction by the rotation of a motor, and lift / lower By adopting a polishing apparatus configuration in which the axial load acting on the rod is detected by a load sensor between the elevating drive mechanism and the spring, the polishing pressure required for the wafer can be applied with high accuracy and ease. Also, the variation in polishing pressure during polishing is small. For this reason, high polishing quality can be secured stably.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a wafer polishing apparatus according to an embodiment of the present invention.
FIG. 2 is a configuration diagram of a conventional wafer polishing apparatus.
FIG. 3 is a view taken along the line AA in FIG. 2;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Lower surface plate 2 Upper surface plate 3 Carrier 10 Wafer 11 Lower frame 12 Upper frame 20 Lifting mechanism 21 Lifting rod 22 Load cell 23 Servo motor 26 Slide case 29 Spring

Claims (1)

A planetary plane between the upper and lower surface plates to polish both the lower surface plate supported horizontally, the upper surface plate facing the lower surface plate via an elevating mechanism, and the wafer held inside. The lifting mechanism is lifted and lowered in the axial direction by the rotation of the motor, and lifts and supports the upper surface plate so as to be lifted and lowered via a spring below the lifting drive mechanism. possess a rod, and a load sensor for detecting between elevation drive mechanism and the spring of the axial load applied to the lifting rod, the spring is UeJo when lifting the upper platen is raised to lift rod A platen holding spring that compresses under the load of the platen, and a platen pressure spring that compresses and presses the lower platen when the lifting rod is lowered while the upper platen is placed on the lower platen Contact the wafer polishing apparatus Te, a wafer pressurizing method for adding the polishing load is pressurized by the upper platen a wafer held under a platen in the carrier, the value of the load sensor in a state where lifting the upper platen W ₀ when a, when the polishing load is W ₀ is smaller than W _1, the values w ₁ of the load sensor is allowed to lift the upper platen so that the W ₀ -W _1, the polishing load is W ₀ is greater than W ₂ The wafer pressurizing method is characterized in that the lifting rod is lifted and lowered so that the value w ₂ of the load sensor becomes W ₂ −W ₀ .

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