JPH0319336A - Polishing of semiconductor wafer - Google Patents

Abstract

PURPOSE:To perform rapidly a polishing of a semiconductor wafer, to facilitate the control of the amount of polishing and to inhibit small the irregularity of the thickness within the surface of the wafer by a method wherein the wafer which inclines to polish is bonded on the central part of the lower surface of a plate and thickness regulating members, whose surface layers consisting of a material of a polishing speed slower than that of the wafer, are arranged on the lower surface of the plate. CONSTITUTION:A semiconductor wafer 12 which inclines to polish is bonded on the central part of the lower surface of a glass plate 11 and at the same time, dummy wafers 15, whose surface layers consist of a material of a polishing speed slower than that of the wafer 12, are arranged on the periphery of the wafer 12 in the lower surface of the plate 11. For example, speaking in respect to the dummy wafers 15, whose parent materials consist of silicon and which have a thermal oxide film formed on their surface layers, the polishing speed of the wafers 15 is 1/200 or less of that of silicon according to the condition of polishing.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for polishing semiconductor wafers,
In particular, flatness of the polished surface is strongly required. This paper relates to a technique that is effective when applied to the polishing of semiconductor wafers. [Conventional technology] The final step in processing semiconductor silicon wafers is a polishing step. This polishing process is a process for forming a mirror surface, and generally a mechanochemical method is used in which an abrasive element and a chemical reaction element are combined.

FIG. 4 shows the main parts of a polishing device used for single-sided polishing.

In the figure, reference numeral 1 indicates a glass plate, and a semiconductor wafer 2 that has been subjected to lapping, grinding, beveling, etching, etc. is placed on the bottom surface of the glass plate 1 with wax interposed therebetween, as shown in FIG. Multiple pieces are glued together so that they can be attached and removed. On the other hand, a polishing cloth 3a is provided on the upper surface of the turntable 3 located below the glass plate 1. In this apparatus, the semiconductor wafer 2 is brought into pressure contact with the polishing cloth 3a by the glass plate 1, and the glass plate 1 supports the semiconductor wafer 2 by the rotation of the turntable 3.
By also rotating the polishing cloth 3a and bringing the semiconductor wafer 2 into sliding contact with the polishing cloth 3a, the main surface of the semiconductor wafer 1 bonded to the lower surface of the glass plate 1 is polished. At this time, an aqueous solution containing a weakly alkaline abrasive such as colloidal silica is supplied as a slurry to the polishing cloth 3a.

[Problem M to be solved by the invention] In recent years, as semiconductor integrated circuits have become finer and smaller, there has been a strong demand for flatness of the polished surface of semiconductor wafers. The following problems have arisen with polishing methods. In other words, in polishing using the polishing apparatus described above, changes in the polishing cloth itself over time, elastic deformation of the glass plate 1 due to pressure contact of the semiconductor substrate 2 to the polishing cloth 3a, and There are differences in the circumferential speed at each position in the radial direction, and in recent device development, the thickness variations within the polished surface due to these differences cannot be ignored. This is especially true in devices with an SO-structured structure in which the thickness of the active region is extremely thin.

Further, the polishing rate increases as the pressure force of the semiconductor wafer 2 against the polishing cloth 3a increases, but when the polishing rate is high, it is difficult to control the amount of polishing. On the other hand, when the polishing speed is slow, although it is easy to control the amount of polishing, there is a problem in that polynosing takes a long time.

The present invention has been made in view of the above points, and provides a method for polishing semiconductor wafers that can quickly polish semiconductor wafers, easily control the amount of polishing, and suppress in-plane polishing variation to a small level. It is intended to.

Other objects and novel features of this invention will become clear from the description in the Suimei Book and the attached IRFM page.

[Means for Solving 'AM] In order to achieve the above object, the present invention provides a method for polishing a semiconductor wafer bonded to a plate to a predetermined thickness by pressing it against a rotating turntable. A semiconductor wafer to be polished is bonded to the plate, and a thickness regulating member, at least the surface layer of which is made of a material whose polishing speed is slower than that of the semiconductor wafer, is disposed on the plate surface, and the thickness regulating member is used to polish the semiconductor wafer. This is designed to control the thickness of the wafer. [Function] According to the present invention, a semiconductor wafer to be polished is bonded to a plate, and a thickness regulating member made of a material whose polishing rate is slower than that of the semiconductor wafer is disposed on the plate surface, and the thickness of the semiconductor wafer is Since the semiconductor wafer is polished using the regulating member as a stopper, even if the pressing force of the semiconductor wafer to the turntable side is increased to increase the polishing speed, the pressing force will be reduced just before the end of polishing. As a result, a portion of the semiconductor wafer is supported by the thickness regulating member, and as a result, the polishing speed is reduced accordingly, making it easier to control the polishing amount of the semiconductor wafer and, by extension, the thickness of the semiconductor wafer. In addition, the polishing process becomes beautiful.6 Also, the thickness regulating member placed around the semiconductor wafer functions as a stopper, and polishing is done so that it is flush with the surface of the thickness regulating member on the turntable side. Therefore, the in-plane thickness variation is also reduced.

Therefore, a half-finished wafer with high reliability can be obtained. [Example] Hereinafter, an example of the semiconductor wafer polishing method according to the present invention will be described.

The first drawing shows the main parts of a polishing device used for single-sided polishing.

In the figure, numeral 11 indicates a glass plate,
As shown in FIG. 2, a single semiconductor wafer 12 that has been subjected to lapping, grinding, beveling, etching, etc. is adhered to the center of the lower surface of the glass plate 11 via wax. Further, a total of eight dummy wafers 15 serving as thickness regulating members are arranged on the lower surface of the glass plate 11 so as to surround the semiconductor wafer 12. When wax bonding semiconductor wafer l2 and dummy wafer 15 onto glass plate l1, the variation in thickness may be 0.1 μm depending on requirements.
It is preferable to control with a precision of m or less. Such control is
Either spray molten wax uniformly onto the wafer bonding surface and then bond the wafer 12 or 15.
This can be achieved by adhering the material onto the plate 11, heating it, allowing the wax to penetrate from the periphery, and then applying pressure.

The entire dummy wafer 15 is made of a material that is more difficult to polish than the semiconductor wafer 12, or at least its surface layer is made of a material that is more difficult to polish than the semiconductor wafer 12. For example, it has a structure in which the base material is made of silicon and a silicon oxide film is formed on its surface layer. The silicon oxide film at this time may be a thermal oxide film or a CVD oxide film, but preferably a thermal oxide film whose polishing rate is slower by a mechanochemical method. The dummy wafer 15 is removably bonded to the glass plate 11 with wax, similar to the semiconductor wafer ↓2, or is firmly (semi-permanently) bonded to the glass plate 11 with epoxy resin or the like. Dummy wafer 1
5 is 'J! ．． The latter is convenient when it is extremely difficult to polish compared to the conductor wafer 12. Note that if the base material of the dummy wafer 15 is made of silicon, extremely high degree of thickness control is possible.

On the other hand, a polishing cloth 13a is attached to the upper surface of the turntable 13 arranged below the glass plate 11.

In polishing using this device,
The semiconductor wafer 12 is brought into pressure contact with the polishing cloth 13a by the glass plate 11, and the glass plate 1 supporting the semiconductor wafer 12 is also rotated by the rotation of the turntable 13, so that the semiconductor wafer 12 is brought into sliding contact with the polishing cloth 13a. By this, the main surface of the semiconductor wafer 11 bonded to the lower surface of the glass plate 11 is polished. For example, as an abrasive at that time, colloidal silica is used as an abrasive and it is dispersed in an aqueous solution, and as a chemical reaction, Na○I-L NH,OH
Those whose pH has been adjusted to be slightly alkaline are used.

If the semiconductor wafer l1 is polished by the method described above, the following effects can be obtained.

That is, according to the polishing method of the above embodiment, the semiconductor wafer 1 to be polished is
At the same time, a dummy wafer ↓ 5 made of a material whose polishing rate is slower than that of the semiconductor wafer 12 is placed around the semiconductor wafer 12 on the glass plate 11 . For example, regarding the dummy wafer t5 whose base material is silicon and has a thermal oxide film formed on its surface layer, the polishing rate is ↓/200 or less compared to silicon depending on the polishing conditions.

Since the semiconductor wafer king 2 is polished using such a dummy wafer 15 as a stopper, even when the polishing speed is increased by increasing the pressing force of the semiconductor wafer 12 toward the turntable ↓ side, Near the end of polishing, a part of the pressure contact force is supported by the dummy wafer 15, and as a result, the polishing speed is slowed down, which makes it easier to control the amount of polishing of the semiconductor wafer 12 and, ultimately, the thickness of the semiconductor wafer L2. control becomes easy. Moreover, the polished surface becomes beautiful.

In addition, the dummy wafer 15 placed around the half-captive wafer 12 functions as a stopper, and is polished so that it is flush with the surface of the dummy wafer 15 on the turntable l1 side. The variation is also reduced.

Therefore, a highly reliable semiconductor wafer 12 can be obtained.

In order to confirm the effect of reducing in-plane thickness variation, the following experiment was conducted.

In this experiment, 17 semiconductor wafers with a diameter of 150 mm were used, and a dummy wafer whose base material was silicon and had a silicon oxide film formed on its surface by thermal oxidation was used as the thickness regulating member. The thickness measurement position at this time is 9 as shown in Figure 3.
It is a point. According to this experiment, the thickness could be controlled with high precision. Incidentally, in this experiment, the percentage of wafers whose thickness deviation was within ±0.3 μm when polished by an average of about 20 μm was 75.8%. Furthermore, the percentage of wafers whose diameter was within 0.1 μm was 50%.

Above, the invention made by the present inventor has been specifically explained based on examples, but it should be noted that the present invention is not limited to the above-mentioned examples, and can be modified in various ways without departing from the gist of the invention. Of course. For example, in the above embodiment, the dummy wafer 15 made of silicon and with a silicon oxide film formed on the surface layer was used as the thickness regulating member. May be used.

Furthermore, the dummy wafer may be made of quartz, plastic, or sapphire as the thickness regulating member, or may be made of metal if contamination is not considered. Further, the shape thereof does not have to be the same as that of the wafer, and may be formed in a ring shape so as to surround the semiconductor wafer 12. In short, any material that can support part of the pressure contact force and function as a stopper during polishing is sufficient.

[Effects of the Invention] The effects obtained by typical inventions disclosed in this application are briefly explained below. In the present invention, when polishing a semiconductor wafer bonded to a plate to a predetermined thickness by pressing it against a rotating turntable, the semiconductor wafer to be polished is bonded to the plate, and the semiconductor wafer to be polished is bonded to the plate surface. A thickness regulating member, at least the surface layer of which is made of a material whose polishing rate is slower than that of the semiconductor wafer, is arranged, and the thickness of the semiconductor wafer is controlled by this thickness regulating member, so that when the polishing rate is increased. Even in this case, the amount of polishing of the semiconductor wafer can be easily controlled. In addition, when shaft runout occurs, the pressing force is supported by the thickness regulating member, and the semiconductor wafer is not polished beyond the thickness of the thickness regulating member, so variations in the in-plane thickness can be prevented. becomes less. Therefore,
A highly reliable semiconductor wafer can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view showing a part of the polishing apparatus used to carry out the polishing method of this example, and FIG. 2 shows the state of adhesion of a semiconductor wafer and a dummy wafer (thickness regulating member) to a plate. FIG. 3 is a plan view of the semiconductor wafer showing the measurement position of the semiconductor wafer in the experiment; FIG. FIG. 5 is a plan view of the plate showing the state of adhesion of the semiconductor wafer to the plate. 11...Glass plate, 12...Semiconductor wafer, 13...Turntable, 15...Dummy wafer (thickness regulating member). Figure 1 Figure 2 Figure 5 Figure 3

Claims (1)

[Claims] 1. When polishing a semiconductor wafer adhered to a plate to a predetermined thickness by pressing it against a rotating turntable, the semiconductor wafer to be polished is adhered to the plate, and the A thickness regulating member, at least the surface layer of which is made of a material whose polishing rate is slower than that of the semiconductor wafer, is disposed on the plate surface, and the thickness of the semiconductor wafer is controlled by the thickness regulating member. A method for polishing semiconductor wafers. 2. Claim 1, wherein the base material of the thickness regulating member is made of silicon, and a silicon oxide film is formed on the surface layer of the thickness regulating member on the turntable side.
The method for polishing a semiconductor wafer as described.