JPH0691058B2 - Semiconductor wafer polishing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polishing method for polishing a semiconductor wafer in a mirror surface with high accuracy, and particularly to a semiconductor wafer or a holding method for holding the semiconductor wafer by using negative pressure. The present invention relates to a semiconductor wafer polishing method for performing a predetermined polishing while adsorbing a carrier to the plate surface.

“Conventional Technology” Conventionally, a semiconductor wafer that should be a base for manufacturing a semiconductor device such as a diode, a transistor, an IC (integrated circuit), and an LSI (large-scale integrated circuit) is a semiconductor single crystal such as silicon or germanium. The ingot is sliced into a thin plate, and at least one side surface of the ingot is mirror-polished based on a so-called mechanochemical polishing method (a polishing method combining mechanical polishing and chemical polishing).

As shown in FIG. 2, for example, such a polishing apparatus has a turntable (hereinafter referred to as a surface plate 2) having a polishing cloth 1 stuck on the upper surface thereof and rotated by receiving a driving force from the outside, and the polishing cloth sticking surface. A plate 4 located above (hereinafter referred to as polishing surface 1A) and having one or a plurality of semiconductor wafers 3 fixed to the lower surface thereof, and a pressing shaft 50 are used to apply a pressing force from the upper surface side of the plate 4. The semiconductor wafer 3 and the polishing cloth are composed of a mount head (hereinafter referred to as a head portion 5), and while using the abrasive disperser 6 or the like to disperse the abrasive containing, for example, SiO ₂ abrasive grains on the polishing cloth 1. 1 (polishing agent) is configured to generate a rubbing motion to perform a predetermined polishing. However, the mirror-finishing accuracy of the semiconductor wafer 3 depends on the miniaturization of the semiconductor element formed on the IC or LSI. As the level of integration increases, it gets severer year by year, especially per chip In the current number of elements it has entered the era of more than 100,000 VLSI, flatness of the finished wafer 3 surface mirror are being set below submicron.

Therefore, when the wafer 3 is fixed to the lower surface of the plate 4, it is necessary to fix the wafer 3 with extremely high flatness.

Generally, such a fixing means includes a method of adhering the semiconductor wafer 3 to the plate 4 surface using wax and a non-wax method of directly adsorbing the wafer 3 on the plate 4 surface by a suction means using negative pressure. In the above, since the wafer 3 is an indirect fixing method via the wax film, the following problems occur in improving the flatness of the wafer 3 and the like.

That is, such fixing means fixes the wafer 3 on the heat-melted wax surface by pressure bonding, and then cools and solidifies the wax film to fix the wax film. It is extremely difficult to make uniform the pressure applied when the wafer 3 is pressure-bonded, and to make the temperature distribution uniform at the time of cooling and solidification, and some variations may occur in the wax film thickness distribution or the wafer itself. Cause deformation. Therefore, it is difficult to maintain the flatness of the wafer 3 as compared with the latter non-wax method in which the wafer 3 is directly adsorbed on the surface of the plate 4 which is a rigid body.

On the other hand, in the latter non-wax method, if a single-wafer plate is assumed for the sake of simplicity, for example, as shown in FIG. 2, the head unit 5 and the head unit 5 are provided through a large number of suction holes 41 ′ formed in the plate 4. Since the wafer 3 is directly attracted to the rigid plate 4 surface by vacuum suction in the closed space 51 'between the plates 4, the above-mentioned drawback can be solved. Since it is necessary to always perform vacuum suction for fixing the wafer 3 to the wafer, the abrasive often penetrates into the contact surface of the plate 4 on the back side of the wafer 3, which reaches the decompression system pipe through the suction hole 41 '. But
Before that, since the inside of the suction hole 41 'of the plate 4 is in a depressurized state, when the invading polishing liquid reaches the end of the adsorption hole, the water is immediately evaporated and concentrated at the inlet portion of the polishing liquid to be concentrated. The colloidal silica contained in the liquid gels and then becomes a solid substance, which adheres to the inlet of the suction hole 41 'and solidifies.

Further, the back surface of the wafer 3 is chemically corroded due to the invading polishing liquid, resulting in subtle unevenness and unfavorable appearance. Further, like the end of the adsorption hole 41 'of the plate 4, the gel is fixed to the wafer 3 in the vicinity thereof.

The solid matter thus adhered cannot be completely removed by the subsequent washing, and as shown in FIG. 3, a part of the solid matter forms a projection at the inlet of the suction hole 41 '. Causes a slight swelling of the wafer 3 at a corresponding portion at the time of adsorbing the next wafer 3, and as a matter of course, when the raised portion is removed by the polishing process and the adsorption of the wafer 3 is released after polishing. Only that portion becomes a depression, and the flatness of the wafer is partially deteriorated.

In order to solve such a drawback, a technique is disclosed in which a ring-shaped rubber elastic body is closely adhered to and surrounded by the outer edge side of the lower surface of the plate 4 which is in contact with the wafer 3, and the elastic body is projected from the lower surface of the plate 4 by a small dimension. There is. (Japanese Patent Publication No. 63-4937) "Problems to be solved by the invention" However, according to such a conventional technique, since the elastic body is made to project from the lower surface of the plate by a small dimension, the central portion of the wafer and the peripheral area thereof are polished. The pressing force of is inevitably non-uniform, and highly accurate flat polishing cannot be performed.

Further, it is difficult to set the above-mentioned minute dimensions and to form the elastic body with a uniform size in the circumferential direction, and the inside of the ring-shaped elastic body is always under negative pressure during polishing and is in direct contact with the polishing liquid. In addition, it is impossible to completely prevent the penetration of polishing liquid,
In the case of polishing the next wafer, the same trouble as the above-mentioned solidified gel occurs.

In view of the above-mentioned drawbacks of the prior art, the present invention provides a polishing method capable of completely preventing the intrusion of an abrasive into the plate contact surface on the back surface side of the wafer while maintaining the uniformity of the pressing force in each region of the wafer. The purpose is to provide.

[Means for Solving the Problems] In order to achieve the technical object, the present invention forms the plate with a single plate and forms a negative plate in the central region of the back surface of the wafer on which the plate surface is sucked. A fluid seal layer, particularly a seal layer using water, is formed between the plate and the semiconductor wafer surface so as to surround the pressure generating portion, and the pressure of the fluid forming the seal layer is set to 0.1 to 0.4.
We propose a method for polishing semiconductor wafers, which is characterized by preventing the suction of abrasives while controlling in the range of Kgf / cm ² (gauge pressure).

[Operation] According to such technical means, since the negative pressure generating portion is formed in the central region of the back surface of the wafer sucked on the plate surface, the wafer can be sucked and held smoothly and the negative pressure generation can be performed. Since a positive pressure fluid seal layer is formed on the outer peripheral side of the portion so as to surround the generation portion, the seal layer can completely prevent the abrasive from entering the back surface of the wafer.

Further, since the present invention has a structure in which the sealing layer is formed by a fluid, especially water, the structure is extremely simple and
Unlike the prior art shown in No. 4937, it is not necessary to project the elastic body that is the sealing layer from the bottom surface of the plate by a small dimension, and since the entire surface on the back side of the wafer can be held by the rigid and flat plate surface, the pressing force It is possible to perform highly accurate flat polishing without any unevenness of

The fluid sealing layer must be maintained in a positive pressure state in order to achieve the desired sealing effect.

Even if the wafer and the plate are in close contact with each other, the sealing layer exists in a gap that is slightly present between the wafer and the plate, but when the water pressure becomes higher than the pressing force of the wafer, that is, the polishing pressure, Since the close contact of the plates cannot be maintained, the accuracy of pressing the wafer is reduced. Therefore, even if the water pressure is positive, the polishing pressure is generally lower than 0.5 Kgf / cm ² because it is 0.5 Kgf / cm ² or more.
Must be in the range of ² (gauge pressure).

Further, even if the fluid forming the fluid sealing layer enters the negative pressure generating portion side, if the fluid is water or air, there is no particular problem, but especially by making the plate rotatable. The fluid that forms the sealing layer under the action of centrifugal force does not enter the negative pressure generation site side,
It is preferable to be configured to be able to leak from the outer edge side between the wafer and the plate surface.

Thereby, because the fluid is constantly leaked to the outside while maintaining the sealing property between the fluid seal layer and the negative pressure generating portion,
It is possible to maintain cleanliness on the back side of the wafer.

In addition, when the fluid forming the seal layer is composed of water, there is no problem even if the fluid is mixed into the abrasive, and the sealing effect is increased as compared with the case of air.

[Embodiment] Hereinafter, a preferred embodiment of the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative positions, and the like of the components described in this embodiment are not intended to limit the scope of the present invention thereto unless otherwise specified, and are merely descriptions. It's just an example.

FIG. 1 shows a polishing apparatus according to an embodiment of the present invention, in particular, a single-wafer polishing apparatus, in which a polishing cloth 1 is stuck on the upper surface and receives a driving force from the outside as in the prior art. A rotating surface plate 2, a plate 4 located on the polishing surface 1A and concentrically fixing the semiconductor wafer 3 on the lower surface, and the plate 4
It is the same as the above-mentioned conventional art in that it includes a head portion 5 configured to be rotatable by a rotary shaft while urging a pressing force from the upper surface side.

Next, of these members, the configuration of the main part of this embodiment will be described in detail.

The head portion 5 has a circular recess 51 in the center area on the lower surface side and a partition wall.
A ring-shaped recess 54 is formed on the outer peripheral side of the vacuum pump 61 via a central hole 55 bored in the rotary shaft 52, and a ring-shaped recess 54 is formed in the circular recess 51. The water pressure source 63 is connected via the side hole 56 and the fluid regulating valve 62, respectively.

The plate 4 has the same outer diameter as that of the head portion 5 and is formed of a circular plate made of stainless steel whose upper and lower surfaces are smooth and has a flat surface. A large number of pores 41 and a plurality of fluid introduction pores 42 are formed at positions corresponding to the ring-shaped recesses 54.

The position of the holes 42 for introducing the fluid is determined by the distance from the holes 42 to the outer end of the wafer 3 and the holes 42 to the outermost suction holes.
It is preferable to set a large distance to 41.

In such an embodiment, the negative pressure in the circular recess 51 is about −0.5 Kg / cm ² (gauge pressure), and the water supplied in the ring-shaped recess 54 resists the pressing force on the head 5 side. It is possible to form a water seal layer on the outer peripheral edge side of the back surface of the wafer 3 in a very thin film form. In other words, the water pressure is positive pressure and controlled within a range lower than the polishing pressure of the wafer, and via the rotary shaft. It is preferable to adjust the water pressure and the flow rate lower than the pressing force to such an extent that the water leaks appropriately from the outer peripheral end of the wafer 3 due to the centrifugal force generated when the head portion 5 -plate 4 is rotated.

Since the water pressure and the flow rate are directly ejected from the pores 42 to the back surface side of the wafer 3, if the water pressure is higher than the polishing pressure of the wafer, the wafer 3 around the pores 42 is locally deformed, or In some cases, the holding force from the suction pores 41 is greatly reduced, and the close contact of the wafer 3 with the plate 4 surface may not be maintained.

On the other hand, when the water pressure is less than the positive pressure, the function of the fluid seal layer is deteriorated, and the effect of the present invention cannot be achieved smoothly. Therefore, the water pressure is related to the diameter of the pores 42 and the wall thickness of the wafer 3, but specifically, it is preferable to set 0.1 to 0.4 KgF / cm ² and the flow rate to, for example, about 0.1 to 0.3 cc / min.

For example, as shown in FIG. 1A, the outflow end of the pore 42 is enlarged in the shape of a step or a mortar or a ring-shaped recess is formed, and the pore 42 and the wafer 3 are formed through a so-called hydraulic buffer means 42a. Can also be configured to contact.

In the case of the compound leaf type, it is advisable to slightly increase the fluid pressure without using the centrifugal force. Specifically, the fluid pressure and the flow rate are almost the same as in the above-mentioned single-wafer operation in the case of water.

According to this embodiment, the above-described effects of the present invention can be smoothly achieved.

FIG. 4 shows an embodiment according to the second invention, which has an inner hole slightly larger than the outer diameter of the semiconductor wafer 3, and
Carrier 71 formed with a slightly smaller wall thickness,
A plate 4 in which suction holes 71 are formed on the center side of the carrier 71 and fluid introduction holes 72, 73 are formed on both sides thereof, and a partition wall 82 is provided at a portion corresponding to the holes 71 to 73, respectively. Head portion 5 in which ring-shaped recesses 81, 83, 85 are formed concentrically with 84
The vacuum pump 61 is connected via the through holes 81a, 83a, 85a drilled in the ring-shaped recesses 81, 83, 85, respectively, and is connected to the water pressure source 63 via the fluid regulating valve 62, respectively. .

In this embodiment, while the carrier 71 is adsorbed on the side of the center area of the carrier 71, the fluid seal layers are formed on both sides of the periphery of the carrier 71, so that it is possible to prevent the abrasive from entering the back side of the carrier 71. Can be done. In the case of the present embodiment, even if an O-ring is provided on the partition wall 84, there is no particular problem in achieving flat polishing of the wafer 3 and the invasion of the fluid to the center side of the carrier 71 can be prevented, which is preferable. .

[Advantages of the Invention] As described above, according to the present invention, it is possible to completely prevent the polishing agent from entering the plate contact surface on the back surface side of the wafer while maintaining the uniformity of the pressing force in each region of the wafer. This makes it possible to polish the wafer while maintaining high flatness, and at the same time, prevent contamination of the back side of the wafer and facilitate cleaning.

It has various remarkable effects.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a polishing apparatus according to an embodiment of the present invention, FIG. 1A is an enlarged view of an essential part showing a modified example of FIG. 1, and FIG. 4 shows a polishing apparatus according to another embodiment. 2 and 3 are schematic sectional views showing a conventional polishing apparatus,
It is an operation view showing the problem.

Claims (3)

[Claims] 1. A semiconductor wafer polishing method for performing a predetermined polishing while adsorbing a semiconductor wafer onto a plate surface using a negative pressure, wherein the plate is formed of a single plate, and the adsorption wafer on the plate surface is formed. A method for polishing a semiconductor wafer, characterized in that a positive pressure fluid sealing layer is formed between the plate and the surface of the semiconductor wafer so as to surround the negative pressure generating portion formed in the central region of the back surface of the semiconductor wafer, thereby preventing the suction of the abrasive. 2. The method for polishing a semiconductor wafer according to claim 1, wherein the fluid forming the seal layer is water. 3. A semiconductor wafer polishing method for performing a predetermined polishing while adsorbing a semiconductor wafer onto a plate surface using a negative pressure, wherein a negative pressure generating portion formed in the center of the back surface of the adsorption wafer on the plate surface is formed. As if to be surrounded
While forming a positive pressure fluid seal layer between the plate and the semiconductor wafer surface, while controlling the pressure of the fluid forming the seal layer in the range of 0.1 to 0.4 Kgf / cm ² (gauge pressure), Polishing method for semiconductor wafer characterized by preventing suction