JPH11277413A - Wafer polishing machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of deflection of a wafer polishing machine due to the pushing force at the time of polishing while remarkably lowering the generation of thermal deflection and while improving the rigidity by forming the wafer polishing machine having a specified coefficient of thermal expansion and a specified Young's modulus. SOLUTION: At least any one of a carrier plate 2 and a surface plate 5 forming a wafer polishing machine is made of the ceramics having a coefficient of thermal expansion at 10-40 of temperature at 1×10<-6> / deg.C or less and the Young's modulus at 130 GPa or more. In the polishing process of a semi-conductor wafer 1, even in the case where temperature difference is generated inside of the carrier plate 2 by the generated frictional heat or the like, since the coefficient of thermal expansion is very small, generation of thermal deflection can be restricted remarkably low. Furthermore, since the Young's modulus is raised so as to improve the rigidity, generation of deflection by the pushing force at the time of polishing is prevented. A semi-conductor wafer 1 having the excellent flatness is thereby obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a wafer polishing machine used in a polishing process of a semiconductor wafer.

[0002]

2. Description of the Related Art In a manufacturing process of a semiconductor device, there is a polishing step of polishing a surface of a semiconductor wafer smoothly before forming a large number of semiconductor elements on a semiconductor wafer such as silicon.

In this polishing step, as shown in FIGS. 1 and 2, one surface of a disc-shaped semiconductor wafer 1 is adhered to the surface of a carrier plate 2 with an adhesive 3, and the other surface of the semiconductor wafer 1 is The carrier plate 2 and the platen 5 are relatively rotated while the abrasive is supplied onto the platen 5 in a state where the semiconductor wafer 1 is pressed on the platen 5, thereby polishing the surface of the semiconductor wafer 1 on the platen 5 side. That is being done.

Incidentally, the semiconductor wafer 1 may be fixed to the carrier plate 2 by vacuum suction without using the adhesive 3 in some cases. Alternatively, the semiconductor wafer 1 is
Instead of fixing the semiconductor wafer 1 to the surface plate 5, it is also possible to polish and hold both surfaces of the semiconductor wafer 2 between the semiconductor wafer 1, the carrier plate 2, and the surface plate 5 by holding and rotating the semiconductor wafer 1. it can. Furthermore, carrier plate 2
Alternatively, a cloth may be provided on the surface of the surface plate 5 and the cloth may be slid relative to the semiconductor wafer 1 for polishing.

As described above, in the polishing step of the semiconductor wafer 1, the semiconductor wafer 1
In the present invention, polishing is performed while being held between the
The carrier plate 2 or the surface plate 5 is called a wafer polishing machine.

In the polishing step of the semiconductor wafer 1, the flatness of the polished semiconductor wafer 1 depends on the flatness of the wafer polishing board. On the other hand, the flatness required for the semiconductor wafer 1 has become extremely strict in the high integration of ICs, and accordingly, the flatness of the wafer polishing machine such as the carrier plate 2 and the surface plate 5 also needs to be strictly controlled. is there. Further, it is necessary to consider a pressing force at the time of polishing and a distortion due to a temperature change in the wafer polishing machine.

Therefore, the carrier plate 2 and the platen 5
By forming a wafer polishing machine such as alumina or silicon carbide from ceramics and smoothing the surface, the flatness is improved, and the distortion due to pressing force and temperature change is reduced. 4-17332 and JP-A-6-270055).

[0008]

However, with the recent increase in the degree of integration of ICs, distortions due to temperature changes have become a problem even with the above-mentioned wafer polishing machines made of ceramics such as alumina and silicon carbide.

That is, alumina ceramics have a thermal expansion coefficient of about 7 × 10 ⁻⁶ / ° C., and silicon carbide ceramics have a thermal expansion coefficient of about 4.0 × 10 ⁻⁶ / ° C. Therefore, during the polishing step, when the temperature of the surface of the wafer polishing plate increases due to frictional heat or the like, and a temperature difference from the inside occurs, slight distortion occurs on the surface of the wafer polishing plate in accordance with the coefficient of thermal expansion. Occurs. Then, due to this slight distortion, the flatness of the polished semiconductor wafer 1 cannot be increased, and there is a problem that it is difficult to cope with high integration.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the foregoing, and has been made in consideration of the above problem, and in a polishing process of a semiconductor wafer, a wafer polishing machine such as a carrier plate or a surface plate used for holding and polishing the wafer. , 10-4
It is characterized by being formed of ceramics having a coefficient of thermal expansion at 0 ° C. of 1 × 10 ⁻⁶ / ° C. or less and a Young's modulus of 130 GPa or more.

That is, by using ceramics having a very low coefficient of thermal expansion of 1 × 10 ⁻⁶ / ° C. or less as a material of the wafer polishing machine, a temperature difference in the wafer polishing machine due to frictional heat generated during the polishing step or the like is caused. Even if a crack occurs, it is possible to significantly reduce the occurrence of thermal strain and prevent the flatness of the surface from being impaired. In addition, the Young's modulus is 130 GPa.
As described above, by increasing the rigidity, no distortion occurs even with the pressing force at the time of polishing, so that a semiconductor wafer having excellent flatness can be obtained.

Further, in the present invention, the wafer holding surface of the polishing machine has a flatness of 1 μm in a circular area having a diameter of 200 mm.
m or less. That is, if a semiconductor wafer is held in this portion, its flatness can be polished smoothly.

Further, the present invention provides the above-mentioned ceramic,
It is characterized by containing cordierite as a main component and containing at least one selected from the group consisting of yttrium, rare earth elements and elements of the periodic table 2a and 4b in an amount of 1.5 to 15% by weight in terms of oxide. That is, the coefficient of thermal expansion as described above is 1
Ceramics having a very small value of ^10-6 / ° C or less include ceramics containing cordierite as a main component. Generally, cordierite ceramics have a low Young's modulus. Therefore, in the present invention, it has been found that by adding the above-described components to the cordierite, the Young's modulus is increased and the cordierite can be suitably used as a wafer polishing machine.

[0014]

Embodiments of the present invention will be described below in detail.

As shown in FIGS. 1 and 2, in the polishing step of the semiconductor wafer 1, one surface of the disc-shaped semiconductor wafer 1 is adhered to the surface of the carrier plate 2 with an adhesive 3, and the other surface of the semiconductor wafer 1 is formed. While pressing on the surface plate 5,
While supplying the abrasive onto the surface plate 5, the carrier plate 2
The surface of the semiconductor wafer 1 on the side of the platen 5 is polished by relatively rotating the platen 5 and the platen 5.

Although not shown, the semiconductor wafer 1
Is fixed to the carrier plate 2 by vacuum suction without using the adhesive 3 in some cases. Alternatively, instead of fixing the semiconductor wafer 1 to the carrier plate 2, the semiconductor wafer 1 is sandwiched and held between the surface plate 5 and rotated, so that the semiconductor wafer 1 is separated from the carrier plate 2 and the surface plate 5. Both surfaces of the wafer 2 can be polished. further,
A cloth may be provided on the surface of the carrier plate 2 or the surface plate 5, and the cloth may be polished by relatively sliding the cloth and the semiconductor wafer 1.

Further, a cooling water channel may be formed inside the surface plate 5, and water may flow through the water channel during the polishing step to suppress a temperature change.

In the present invention, at least one of the carrier plate 2 and the surface plate 5 forming a wafer polishing machine is
The coefficient of thermal expansion at 10 to 40 ° C. is 1 × 10 ⁻⁶ / ° C. or less,
It is formed of ceramics having a Young's modulus of 130 GPa or more.

Therefore, in the polishing step of the semiconductor wafer 1, the carrier plate 2
Even if there is a temperature difference inside, the thermal expansion coefficient is very small, so that the occurrence of thermal distortion can be suppressed extremely low, and therefore, the flatness of the semiconductor wafer 1 after polishing can be improved. is there. In addition, since the rigidity is increased by increasing the Young's modulus, no distortion is generated even by a pressing force at the time of polishing, and therefore, the semiconductor wafer 1 having excellent flatness.
Can be obtained.

As such a ceramic having a low thermal expansion and a high Young's modulus, a cordierite ceramic is most preferred. Cordierite based ceramics, typically, a main component cordierite _{(2MgO-2Al 2 O 3 -5SiO} 2), after mixing the respective metal oxides at a predetermined ratio, the oxidation resistance of the molded after 1350 to 1450 ° C. in a predetermined shape It can be prepared by firing in an atmosphere. However, conventional cordierite ceramics have a low Young's modulus of less than 130 GPa, and lack rigidity for use as a wafer polishing machine.

Therefore, in the present invention, cordierite is used as a main component, and at least one selected from the group consisting of yttrium (Y), a rare earth element, and elements of groups 2a and 4b of the periodic table has a proportion of 3 to 15% by weight in terms of oxide. By adding
As a result of improving sinterability, it has been found that the Young's modulus of cordierite ceramics can be increased to 130 GPa or more, and the cordierite ceramics can be suitably used as a wafer polishing machine.

The reason why the content of the additional component is set to 3 to 15% by weight is that if the content is less than 3% by weight, the sinterability is poor, the relative density is low, and it is necessary to fire at a high temperature. When the content exceeds 15% by weight, the coefficient of thermal expansion becomes large. Preferably, the Young's modulus can be increased to 170 GPa or more by containing these additive components at a ratio of 10% by weight or more.

It is desirable that yttrium (Y) or a rare earth element be added as an oxide, thereby improving the sinterability. Here, the rare earth elements include Er, Yb, Sm, Lu, Ce and the like.

[0024] Examples of the elements of Groups 2a and 4b of the periodic table include Mg, Ca, C, and Si.

In addition to the above-mentioned yttrium (Y), rare earth elements and elements of groups 2a and 2b of the periodic table, the cordierite ceramics may have improved sintering properties, or may have the above-mentioned coefficient of thermal expansion and Young's modulus. SiC, S in order to further improve
Other additives such as i ₃ N ₄ and B ₄ C may be added.

Further, in the wafer polishing machine of the present invention, it is preferable that the wafer holding surface has a portion having a flatness of 1 μm or less in a circular area having a diameter of 200 mm.

That is, the wafer holding surface has a diameter of 200 mm.
When the diameter is equal to or less than 1 μm, the flatness is 1 μm or less, and when the wafer holding surface exceeds 200 mm in diameter, the diameter is 200 mm in which the flatness is 1 μm or less.
It suffices if there is a portion having a circle diameter of. Therefore, if the semiconductor wafer 1 is held and polished in a portion having a flatness of 1 μm or less, it can be polished so as to have excellent flatness.

When the wafer polishing machine of the present invention is applied to a carrier plate 2 of a type for fixing a semiconductor wafer, the surface roughness of the wafer holding surface of the carrier plate 2 is as follows:
It is preferable to have a center line average roughness (Ra) in the range of 0.5 to 1.0 μm and minute irregularities.

If the Ra is less than 0.5 μm, the roughness is insufficient.
This is because the thickness of the substrate becomes uneven, and uneven mirror polishing is performed. When Ra exceeds 1.0 μm,
The unevenness of the carrier plate 2 itself is reflected in the wafer polishing, making it difficult to uniformly mirror-polish the semiconductor wafer 1, and further, the convexities on the surface of the carrier plate 2 are easily chipped,
This is because the polishing is adversely affected. Further, in order to fix a plurality of semiconductor wafers 1 to the carrier plate 2 at a time or to fix semiconductor wafers 1 having different sizes, the surface roughness of the entire surface of the carrier plate 2 is within the above range. Is preferred.

The adhesive 3 for fixing the semiconductor wafer 1 to the carrier plate 2 is preferably wax, paraffin, rosin, or the like. After polishing, the adhesive 2 adhered to the semiconductor wafer 1 is washed or the like. Those that can be easily removed are preferred. Further, as a bonding method, wax or the like is diluted with a volatile solvent, formed into fine particles by spraying, and coated on the carrier plate 2 while controlling the thickness to about 1 to 2 μm. Further, the semiconductor wafer 1 is adhered while heating the carrier plate 2, the surface plate 5 is applied via an elastic sheet, pressurized, naturally cooled, and fixed. As described above, the semiconductor wafer 1 is fixed to the carrier plate 2, pressed against the platen 5, rotated, and polished with an abrasive.

However, if the carrier plate 2 is used several times in this polishing step, the portions other than the holding portion of the semiconductor wafer 1 are polished, and the initial surface roughness is lost. On the other hand, since the semiconductor wafer 1 is fixed to the carrier plate 2 by hand manually, it is difficult to fix the semiconductor wafer 1 to exactly the same place every time, and the position is slightly shifted. The surface roughness of the carrier plate 2 is not fixed. Then, by the mirror polishing of the surface of the carrier plate 2,
When the minus portion of the semiconductor wafer 1 is fixed to the portion where the surface roughness is reduced by the adhesive 3, there is a problem that the adhesive 3 is not uniformly dispersed and its thickness becomes uneven.

That is, on the original surface of the carrier plate 2, the tip of the convex portion of the fine irregularities almost directly contacts the semiconductor wafer 1, and the adhesive 3 enters the concave portion, so that the flatness of the semiconductor wafer 1 can be kept high. . However, when the surface of the carrier plate 2 becomes smooth, the thickness becomes 1 to 3 μm.
The wafer 1 is bonded with the semiconductor via the adhesive 3 of m, and the flatness when the semiconductor wafer 1 is fixed is impaired according to the unevenness of the thickness of the adhesive 3. When polishing is performed in this state,
Depending on the deterioration of the flatness of the semiconductor wafer 1, dents of several microns may occur in some cases.

On the surface of the carrier plate 2 having the reduced surface roughness, there is also a problem that particles are contaminated from the working atmosphere and dents occur on the polished surface of the semiconductor wafer 1.

Therefore, the surface roughness of the carrier plate 2 used a plurality of times can be corrected so that the carrier plate 2 can be used again. As a method of correcting the surface of the carrier plate 2,
Polishing may be performed using a wrapping material so that the entire surface has a uniform roughness. As the surface roughness of the carrier plate 2 after the surface correction, the original surface roughness, that is, Ra 0.5 to 1.0 μm
It is good. The wrapping material used is preferably Al ₂ O ₃ or SiC, which can polish the surface roughness of the carrier plate 2 to a roughness of Ra 0.5 to 1.0 μm, and these may be used alone or in combination. Can be.

[0035]

EXAMPLE 1 Next, the present invention will be described in detail with reference to examples.

As the wafer polishing machine of the present invention, cordierite is a main component, and Y, Er, Yb, S
A dense cordierite ceramic containing 10% by weight of an oxide such as m, Lu, Ce, etc., has a diameter of 250 mm,
A carrier plate 2 having a thickness of 20 mm was formed.

The above-mentioned carrier plate 2 is
Polishing was performed using a lap material in which C abrasive grains and # 240 GC abrasive grains were mixed at a ratio of 4: 1, so that the surface roughness was Ra 1.0 μm. After heating, a thin layer is formed on the carrier plate 2 using wax as an adhesive 3 and then a 6 inch diameter is formed thereon.
A silicon semiconductor wafer 1 having a thickness of 0.5 to 0.6 mm and subjected to grinding and chemical etching was mounted. As shown in FIG. 2, one semiconductor wafer 1 is arranged at equal intervals at the center and six at the periphery thereof at equal intervals, and while being heated from the back of the carrier plate 2, an iron platen of substantially the same shape is placed on the semiconductor wafer 1. 5 was placed, pressurized, held for 1 hour, and cooled.

Thereafter, as shown in FIG. 1, the semiconductor wafer 1 was mirror-polished using a slurry in which fine silica particles were dispersed in water as an abrasive, by pressing against the platen 5 and rotating. After the polishing, the semiconductor wafer 1 was removed from the carrier plate 2, and the wax was removed with an organic solvent and a neutral detergent. By the above polishing, a mirror-polished silicon wafer having a high degree of flatness was obtained.

Example 2 Next, the same experiment as described above was conducted by forming the carrier plate 2 from various ceramics.

As an embodiment of the present invention, the above-mentioned cordierite-based ceramics (cordierites A and B) were used. On the other hand, as a comparative example, a porous cordierite-based ceramic (cordelite C, D),
The same carrier plate 2 was made of alumina ceramics, silicon carbide ceramics, and lithia ceramics.

Table 1 shows the properties of the material of each carrier plate 2 and the flatness of the surface. The flatness of the semiconductor wafer 1 polished using each carrier plate 2 is as shown in Table 2. The coefficient of thermal expansion α is 10 to 4
The temperature was between 0 ° C., and the flatness of the carrier plate 2 was measured using a stylus straightness meter with respect to a circular area having a diameter of 200 mm.

From these results, it was found that the coefficient of thermal expansion was 1.0 × 10
^{In the case of} alumina and silicon carbide which are larger than ⁻⁶ / ° C., the flatness of the semiconductor wafer 1 could be polished only up to 1.7 μm. Further, even with ceramics having a coefficient of thermal expansion of 1.0 × 10 ⁻⁶ / ° C., those having a Young's modulus of less than 130 GPa (cordierites C, D, and lithia) are deformed by the pressing force, so that the flatness of the semiconductor wafer 1 is reduced. Could not be reduced.

On the other hand, the thermal expansion coefficient was 1.0 × 10
^{In the} embodiment of the present invention (cordierites A and B) having a Young's modulus of 130 GPa or more at ^-6 / ° C., the flatness of the semiconductor wafer 1 can be polished to 1.3 to 1.4 μm. It can be seen that a semiconductor wafer 1 having a surface can be obtained.

[0044]

[Table 1]

[0045]

[Table 2]

[0046]

According to the present invention, in the polishing step of a semiconductor wafer, a polishing plate used for holding and polishing the wafer has a coefficient of thermal expansion of 1 × at 10 to 40 ° C.
Due to being formed of a ceramic having a modulus of 10 ⁻⁶ / ° C. or less and a Young's modulus of 130 GPa or more, the coefficient of thermal expansion is very small even if a temperature difference occurs in the wafer polishing machine due to frictional heat generated during polishing. Therefore, the occurrence of thermal distortion can be significantly reduced, and the flatness of the semiconductor wafer can be improved. In addition, since the Young's modulus is large, no distortion is caused by the pressing force at the time of polishing, and a semiconductor wafer having excellent flatness can be obtained. Thereby, the flatness accuracy of the semiconductor wafer can be improved, and a semiconductor wafer for a highly integrated IC can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a polishing step of a semiconductor wafer.

FIG. 2 is a plan view showing an example of an arrangement of the semiconductor wafer on a carrier plate in a polishing step of the semiconductor wafer.

[Explanation of symbols]

 1: Semiconductor wafer 2: Carrier plate 3: Adhesive 5: Surface plate

Claims (3)

[Claims] 1. A polishing disk used for holding and polishing a wafer in a polishing step of a semiconductor wafer, wherein a coefficient of thermal expansion at 10 to 40 ° C. is 1 × 10 ⁻⁶ / ° C.
A wafer polishing machine comprising a ceramic having a Young's modulus of 130 GPa or more. 2. The polishing machine according to claim 1, wherein the wafer holding surface of the polishing machine has a diameter of 200 mm.
2. The wafer polishing machine according to claim 1, wherein a flatness in a circle area of 1 mm is 1 μm or less. 3. The ceramic according to claim 2, wherein said ceramics comprises cordierite as a main component, yttrium, a rare earth element, and a periodic table.
2. The wafer polishing machine according to claim 1, wherein at least one element selected from Group a and 4b elements is contained in an amount of 1.5 to 15% by weight in terms of oxide.