JPH0724708A - Method and device for polishing - Google Patents

Abstract

PURPOSE:To detect the working end point accurately and in-process by detecting the end point of polishing based on the temperature variation on the acting surface of polishing resulting from variation in friction heat generation mode of a work being polished. CONSTITUTION:A work to be polished vacuum-chucked on an upper surface plate 19 is brought into contact with a polishing cloth 17 stuck on a lower surface plate 16, the upper and lower surface plates 19 and 16 are rotated by a machining control mechanism 21 in R2 and R1 directions, respectively, and working liquid L is sprayed from a nozzle 22 for polishing. The surface temperature of the work to be polished increased due to polishing is detected with a radiation temperature sensor 24 as the surface temperature of the polishing cloth 17. The detected signal SA is inputted into a calculation processing part 26 through an amplifier 25. The calculation processing part 26 calculates a differential factor of surface temperature to polishing time. Using a correlation drawing showing a preset differential factor and polishing time, the advancement of polishing is judged, and the end of polishing is judged. Then the working control mechanism 21 outputs rotation stop signals SSU and SSD to stop the upper and lower surface plates 19 and 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing method and a polishing apparatus for detecting a polishing end point.

[0002]

BACKGROUND OF THE INVENTION SOI (S ilicon o n I ns
Due to the characteristics of radiation resistance, latch-up resistance, and low parasitic capacitance, the ululator) is expected to be applied to a high-speed LSI. By the way, FIG. 6, Portable gate MOS (M e
It shows a manufacturing process of the tal O xide S emiconductor) structure. That is, <Step 1>
After forming the field oxide film B on the polycrystalline Si substrate A, a back gate oxide film C and a back gate electrode D are formed by using a normal gate forming technique. <Step 2> A CVD (chemical vapor deposition) oxide film E is deposited on the back gate oxide film C. <Step 3> The CVD oxide film E is polished to flatten the steps of the back gate. <Step 4> Substrate F on which a back gate is formed and BPSG (boron-implanted silicon phosphide glass:
B oron-doped P hospho- S ilic
A supporting substrate G with an (Ate G lass) is attached by a pulse electrostatic adhesion method. <Step 5> The Si substrate A is ground and selectively polished using the field oxide film B as a stopper to form a thin film Si portion K corresponding to the step of the field oxide film B. <Step 6> By a normal process, the thin film Si portion K
Source M and drain N of the front gate MOSFET
And the front gate Q is formed.

By the way, by the selective polishing of Si in <Process 5>, the thickness of the wafer is usually 625 μm to 400 μm.
It decreases to about m. However, in this <Step 5>, since it is difficult to detect the end point of the selective polishing, overpolishing (overpolishing) often becomes a problem. Due to this excessive polishing, a dent is formed in the thin film Si portion K, which is an obstacle to improving the manufacturing yield.

Therefore, conventionally, the processing time is managed to some extent, and thereafter, the processing end point is detected by visually observing every short time. Therefore, not only is the efficiency inefficient, but there is also a lot of room for detection errors at the processing end point. On the other hand, it is possible to detect the processing end point by measuring the thickness of the wafer by an optical method or an electric capacitance method, but if the surface to be measured is contaminated with a processing liquid etc., a measurement error will occur, so on-machine in-machine It was not suitable for process measurement. Further, the method of detecting the processing end point by measuring the thickness of the wafer by the ultrasonic method is insufficient in accuracy.

[0005]

As described above, the SOI
The conventional processing end point detection device for selective polishing performed in the manufacturing process is insufficient in terms of detection accuracy and detection efficiency. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a processing end point detection method and a polishing apparatus that can perform the processing end point detection of selective polishing in-process and with high accuracy.

[0006]

SUMMARY OF THE INVENTION In the present invention, in the polishing of a workpiece made of plural kinds of materials, a temperature change of a polishing action surface due to a change of a frictional heat generation mode of the workpiece being polished. Based on the above, the end point of the polishing process is detected and the polishing process is stopped.

[0007]

According to the present invention, the polishing amount can be strictly controlled. As a result, when it is applied to an ultra-precision polishing process such as ultra-thin film SOI required for high-speed MOS, processing efficiency, yield, reliability, etc. Improve dramatically.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows the polishing apparatus of this embodiment.
This polishing apparatus includes a polishing unit 2 for planarly polishing a thin plate-shaped workpiece 1 to be SOI, and a processing end point detection unit 3 for detecting a processing end point of the workpiece 1 planarly polished by the polishing unit 2. It consists of

Therefore, FIG. 2 shows the structure of the workpiece 1 before processing. That is, this workpiece 1 is
It is composed of a substrate portion 4 and a second substrate portion 5 attached to the first substrate portion 4. Thus, the first substrate portion 4 has a Si thin film 6 made of polycrystalline Si and a field oxide film 7 made of SiO ₂ formed on the Si thin film 6.
The back gate oxide film 8 formed in the opening 7a of the field oxide film 7, the back gate electrode 9 formed on the back gate oxide film 8, and the entire surface of the Si thin film 6 on the back gate electrode 6 side. CVD-SiO ₂ film for coating 1
It consists of 0. That is, in the opening 7a of the field oxide film 7, the back gate oxide film 8 is arranged in parallel with the plate surface at the center in the depth direction, and the CVD-SiO ₂ film is formed on both sides of the back gate oxide film 8. 10 and a part of the Si thin film 6 are filled. On the other hand, the second substrate portion 5 includes a support substrate 11 and a BPSG film 12 formed on the support substrate 11. Then, the BPSG film 12 and the CV
By adhering the D-SiO ₂ film 10 to the first substrate portion 4 and the second substrate portion 4.
The substrate 5 is integrally joined. In the present embodiment, the purpose is to polish the Si thin film 6 until the field oxide film 7 is exposed (the phantom line area in FIG. 2).

Therefore, the polishing section 2 includes the lower surface plate section 13 and
The upper surface plate portion 14 is disposed at an upper position so as to face the lower surface plate portion 13, and a processing control mechanism 21 that electrically controls the lower surface plate portion 13 and the upper surface plate portion 14. The polishing unit 2 includes a liquid supply unit 1 for supplying the processing liquid L to the polishing site.
5 is attached. The lower surface plate section 13 includes a lower surface plate 16 forming a disk, a polishing cloth 17 such as urethane foam adhered to the lower surface plate 16, and a lower surface plate drive mechanism for holding and rotating the lower surface plate 16. It consists of 18. Further, the lower surface plate drive mechanism 18 includes a holding shaft 18a coaxially connected to the lower surface of the lower surface plate 16 and the holding shaft 18a.
And a lower surface plate drive motor 18b for rotatably driving the shaft. Further, the upper surface plate portion 14 has an upper surface plate 19 having a diameter smaller than the radius of the lower surface plate 16 and an upper surface plate 19 which rotatably drives the upper surface plate 19 to rotate and pressurizes the lower surface plate 16. It is composed of a drive mechanism 20. Further, a polyurethane-based suction sheet (not shown) for detachably holding the work piece 1 is attached to the lower surface of the upper surface plate 19. The upper surface plate drive mechanism 20 includes a holding shaft 20b coaxially connected to the back of the upper surface plate 19 and the holding shaft 20b.
Pressurizing means 20 such as, for example, a pneumatic cylinder for attaching and detaching the upper end of b to drive the holding shaft 20b up and down.
c, an electromagnetic valve 20d that controls the application of air pressure to the pressurizing means 20c, and an upper surface plate drive motor 20e that holds the upper end of the pressurizing means 20c and rotationally drives around the axis. . Further, the liquid supply unit 15 stores a nozzle 22 that jets a processing liquid L containing free abrasive grains (for example, colloidal silica to which amine has been added) to a polishing portion, and the processing liquid L supplied to the nozzle 22. It is composed of a tank 23 that operates. On the other hand, the processing end point detection unit 3 is arranged facing the polishing cloth 17 of the lower surface plate 16 with a certain distance apart, and detects the surface temperature T of the polishing cloth 17 during polishing, for example, a radiation temperature sensor 24 such as an infrared thermometer. And an amplifier 25 for amplifying an electric signal ST indicating the surface temperature T of the polishing pad 17 output from the radiation temperature sensor 24, and an electric signal ST output from the amplifier 25, which is input and based on the electric signal ST. The arithmetic processing unit 26 calculates the relationship between the surface temperature T of the polishing pad 17 and the polishing time t. On the other hand, the processing control mechanism 21 includes the solenoid valve 20d, the upper surface plate drive motor 2
0e, the lower platen drive motor 18b, the liquid supply unit 15, and the arithmetic processing unit 26 are electrically connected and are provided to control the polishing process as described later.

Next, the polishing method of this embodiment will be described using the polishing apparatus having the above structure. First, upper platen 19
Then, the workpiece 1 is vacuum chucked so that the Si thin film 6 faces the polishing cloth 17. Next, the processing control mechanism 21 applies a rotation signal SRD to the lower surface plate drive motor 18b to rotate the lower surface plate 16 in the direction of arrow R1 at, for example, about 60 to 120 rpm. Subsequently, the machining control mechanism 21 applies the rotation signal SRU to the upper surface plate drive motor 20e, and also applies the lowering signal SD to the solenoid valve 20d.
Is rotated in the direction of arrow R2, for example, about 60 to 120 rpm, and is lowered in the direction of arrow D1 to bring the Si thin film 6 into contact with the polishing cloth 17. The lowering of the upper platen 19 is stopped when the polishing pressure is about 200 to 1,600 gf / cm ² . At this time, the processing liquid L is jetted to the polishing portion of the workpiece 1 via the nozzle 22 based on the liquid supply signal SL applied to the liquid supply unit 15 from the processing control mechanism 21. Thus, the Si thin film 6 is surface-polished by the loose abrasive grains contained in the working liquid L and the polishing cloth 17. At this time, the surface temperature T of the polishing cloth 17 gradually increases as the polishing progresses due to the frictional heat with the workpiece 1 (see FIG. 3). Therefore, the radiation temperature sensor 24 detects the surface temperature T of the polishing cloth 17 and converts it into an electric signal ST. The electric signal ST is amplified by the amplifier 25, and the arithmetic processing unit 26
To enter. Then, in the arithmetic processing unit 26, the differential coefficient θ (= dT / d) of the surface temperature T with respect to the polishing time t.
t) is calculated. Here, FIG. 4 schematically shows the relationship between the differential coefficient θ and the polishing time t. In FIG. 4, the region R1 shows the differential coefficient θ when only the Si thin film 6 is being polished. This region R1 corresponds to the region R1a in FIG. 3, and it can be seen that the surface temperature T of the polishing pad 17 increases at a substantially constant rate. However, when the polishing process of the Si thin film 6 progresses, and immediately before the field oxide film 7 is exposed and starts to contact the polishing cloth 17,
The differential coefficient θ is the region R2 in FIG. That is, the region R2 in FIG. 3 corresponding to this region R2
As indicated by a, the increase rate of the surface temperature T of the polishing pad 17 is increased as compared with the initial polishing process of the Si thin film 6. this is,
It is considered that this is because the coefficient of friction increased due to the increase in the density of the intermediate layer and higher than that of the initial layer of the Si thin film 6. Subsequently, when the polishing process of the Si thin film 6 is completed and only the field oxide film 7 is polished, the differential coefficient θ has a negative value like the region R3 in FIG. That is, as indicated by the region R3a in FIG. 3 corresponding to this region R3, the surface temperature T of the polishing pad 17 gradually decreases as the polishing process progresses. This is because the friction coefficient between the field oxide film 7 and the polishing cloth 17 is
And the friction coefficient of the polishing cloth 17 is significantly smaller than that of the polishing cloth 17. Therefore, in this embodiment, the arithmetic processing unit 26 detects the temperature change point T1 in FIG. 3 that shifts from the region R1 to the region R2 and applies the descending signal SD1 to the solenoid valve 20d, whereby the upper platen 19 Polishing cloth 17
For example, the polishing pressure is reduced by 10 to 30%. Thereby, as shown in FIGS. 3 and 4, the differential coefficient θ is corrected to the level of the region R1. As a result, overheating of the work piece 1 can be prevented. Next, in the arithmetic processing unit 26, the temperature change point T2 in FIG. 3 where the region R2 shifts to the region R3 is detected, and several minutes after the detection time point (or after the surface temperature T of the polishing pad 17 decreases by several degrees). ), Solenoid valve 20d
By applying the rising signal SD2 to the pressurizing means 20
c is operated in the reverse direction, and the upper surface plate 1 is moved through the holding shaft 20b.
The work piece 1 attached to No. 9 is separated from the polishing cloth 17 attached to the lower surface plate 16. Then, the rotation stop signal S
SU and SSD are applied to the upper platen drive motor 20e and the lower platen drive motor 18b, and the polishing process is stopped.

As described above, in this embodiment, since the processing end point detecting section 3 is provided and the polishing processing is controlled based on the detection result of the processing end point detecting section 3, the field oxide film 7 is formed. Sagging of the opening 7a (dent)
It becomes possible to polish CC <see FIG. 5> to 1 μm or less with high efficiency. In particular, since the polishing pressure of the upper surface plate 19 with respect to the polishing cloth 17 is reduced by detecting the temperature change point T1, it is possible to prevent the workpiece 1 from overheating and suppress the sag (depression). Can be further enhanced.

In the above embodiment, the polishing pressure is adjusted based on the detection of the temperature change point T1 which shifts from the region R1 to the region R2, but this process is omitted.
Alternatively, only the end point of the polishing process may be detected based on the temperature change point T2.

Further, in the above embodiment, the polishing cloth 1 when the polishing process is transferred from the Si thin film 6 to the field oxide film 7 is performed.
Although the processing end point is detected based on the decrease in the surface temperature of No. 7, depending on the material type, the surface temperature of the polishing cloth increases when the polishing processing moves from one layer to an adjacent layer. Also, the present invention can be applied.

Further, in the above embodiment, the surface temperature of the polishing cloth 17 is detected by the radiation temperature sensor without contact, but the temperature sensor is embedded in the upper surface plate 19 or the lower surface plate 16. You may do it.

The present invention is not limited to flat surface processing as long as it is a polishing processing for polishing a workpiece made of a plurality of kinds of materials having different friction heat generation modes associated with polishing. It can also be applied to other polishing processes such as groove processing.

Furthermore, in the above embodiment, polishing is exemplified as the type of polishing, but any processing method can be applied as long as it is plane polishing such as rapping and grinding. Of course, it can be applied to either single-sided polishing or double-sided polishing.

[0018]

Since the polishing apparatus of the present invention is provided with the processing end point detecting section, the processing end point can be automatically detected with high accuracy, and the polishing amount can be strictly controlled. . Therefore, when the polishing apparatus of the present invention is applied to an ultra-precision polishing process for ultra-thin film SOI or the like required for high-speed MOS, the yield, reliability, throughput, etc. are dramatically improved.

The polishing method of the present invention is based on the change in the surface temperature of the polishing action surface due to the change in the friction heat generation mode of the workpiece being polished in the polishing of the workpiece made of plural kinds of materials. Since the end point of the polishing process is detected and the polishing process is stopped, the polishing amount can be strictly controlled. Therefore, when the polishing method of the present invention is applied to, for example, an ultra-precision polishing process for ultra-thin film SOI or the like required for high-speed MOS, the yield, reliability, etc. are dramatically improved.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a polishing apparatus according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a workpiece to be polished by a polishing apparatus according to an embodiment of the present invention.

FIG. 3 is a graph showing a relationship between a polishing temperature and a polishing time for explaining an example of the present invention.

FIG. 4 is a graph showing a differential coefficient between a polishing temperature and a polishing time for explaining an example of the present invention.

FIG. 5 is a cross-sectional view of a workpiece for explaining the function and effect of one embodiment of the present invention.

FIG. 6 is an explanatory diagram of a conventional technique.

[Explanation of symbols]

1: Work piece, 2: Polishing part, 3: Processing end point detecting part, 1
7: polishing cloth, 24: radiation temperature sensor, 26: arithmetic processing unit.

Claims (4)

[Claims] 1. In a polishing method for polishing a workpiece made of a plurality of materials having different friction heat generation modes associated with polishing, based on a temperature change of a polishing action surface due to a friction heat generation mode change caused by polishing. The polishing method is characterized by detecting the end point of the polishing process and stopping the polishing process. 2. A polishing method for flat-polishing only a specific layer of a workpiece, in which at least two kinds of materials having different frictional heat generation modes due to polishing are laminated in parallel, in a plane of the specific layer. A polishing method characterized in that the end point of polishing is detected and the polishing is stopped based on the temperature change of the polishing working surface caused by the change of frictional heat generation mode generated when shifting from polishing to planar polishing of another layer. 3. A polishing unit for polishing a workpiece, a temperature sensor for detecting a surface temperature of a polishing surface of the polishing unit, and an output from the temperature sensor during polishing of the workpiece by the polishing unit. And a processing end point detector for detecting the polishing processing end point based on an electric signal indicating the surface temperature of the polishing action surface. 4. The polishing apparatus according to claim 1, wherein the temperature sensor is a radiation temperature sensor that detects a radiation temperature of the polishing action surface, and is arranged facing the polishing action surface with a space therebetween.