JP6387944B2 - Abrasive and polishing method - Google Patents

Description

  The present invention relates to an abrasive and a polishing method.

  A semiconductor wafer typified by a silicon wafer (hereinafter also simply referred to as a wafer) is polished by using a double-side polishing apparatus 1 as shown in FIG. 1 or a single-side polishing apparatus 21 as shown in FIG.

  As shown in FIG. 1, the double-side polishing includes an upper surface plate 2 and a lower surface plate 3 provided opposite to each other in the vertical direction, and a polishing cloth 4 is pasted on each of the upper surface plate 2 and the lower surface plate 3. It has been. A sun gear 5 is provided at the center of the upper surface plate 2 and the lower surface plate 3, and an internal gear 6 is provided at the periphery. The silicon wafer W is held by the carrier 7 and is sandwiched between the upper surface plate 2 and the lower surface plate 3.

  The teeth of the sun gear 5 and the internal gear 6 are engaged with the outer peripheral teeth of the carrier 7, and the carrier 7 rotates as the upper surface plate 2 and the lower surface plate 3 are rotated by a drive source (not shown). However, it revolves around the sun gear 5. At this time, the abrasive is supplied from the abrasive supply mechanism 8 provided on the upper surface plate 2 through the slurry tube 9 between the polishing cloths 4 attached to the upper and lower surface plates 2 and 3, and the silicon wafer Both surfaces of W are polished while being held by the carrier 7.

  Further, as shown in FIG. 2, the single-side polishing is performed by a surface plate 23 on which a polishing cloth 22 is attached, a polishing agent supply mechanism 25 for supplying a polishing agent 24 onto the polishing cloth 22, and a polishing for holding a silicon wafer W. The polishing is performed using a polishing apparatus including the head 26 and the like. The silicon wafer W is held by the polishing head 26, the polishing agent 24 is supplied from the polishing agent supply mechanism 25 onto the polishing cloth 22, and the surface of the silicon wafer W is rotated by rotating the surface plate 23 and the polishing head 26, respectively. The silicon wafer W is polished by being brought into sliding contact with 22.

  In recent years, as the miniaturization progresses, a flat wafer shape is required to the outer periphery of the wafer. As a flatness index for evaluating the vicinity of the edge, ESFQR (Edge Site front squares Range) for evaluating the site flatness of the outer periphery. , ESFQD (Edge Site Front squares Deviation), and ZDD (Z-Height Double Differentiation) that evaluates the change in curvature have been used.

  The ESFQR is evaluated with an average or maximum value of 72 cells at an angle of 5 degrees in a fan-shaped cell shape, for example, a point of 1 mm from the edge and a range of 35 mm. ESFQD represents the maximum value of the displacement amount of the ESFQR from the virtual plane. When the ESFQD is positive, the displacement amount is higher than the virtual plane, and when negative, the displacement amount is lower than the virtual plane. ESFQR is often used for wafer quality evaluation, and ESFQD is often used for shape analysis.

  By the way, in recent years, in order to improve the flatness of the outer peripheral portion with miniaturization, in double-sided polishing, improvements such as using a hard polishing cloth or making the load balance uniform during polishing have been performed. Then, for example, an ESFQR level of 30 nm or less can be obtained.

JP 2000-080350 A JP 11-080707 A

  However, with the improvement of ESFQR, flatness variation in the wafer circumferential direction has become a problem. In this way, fluctuations in the circumferential direction of the outer peripheral portion have become important, and in addition to the maximum value of ESFQR set as a standard, the average value and range of ESFQR have been discussed.

  When ESFQR and ESFQD are tabulated in the wafer circumferential direction, a 4-fold symmetrical pattern may be observed. A typical ESFQR four-fold symmetry pattern is shown in FIG. When the silicon wafer has a slice surface of <100>, a minute notch called a notch is processed in the <011> direction of the circumferential portion as shown in FIG. 4, for example, and alignment is performed based on this notch. . In the pattern of FIG. 3, the position of the notch is set to 0 °, the measurement result of the notch position is excluded, and the amount of displacement from the average value is displayed.

  Such a four-fold symmetrical pattern as shown in FIG. 3 has been confirmed in a wafer after double-side polishing, and it is known that the pattern becomes worse in a single-side polished wafer.

  The pattern as shown in FIG. 3 has a difference in the occurrence rate depending on the model of the double-side polishing apparatus and the polishing conditions. For example, it has been found that when the load distribution in the carrier is uniform and the uneven load is difficult to be applied, the flatness level is improved, but the incidence of a 4-fold symmetrical pattern is increased. This is considered to be because when the rotation of the wafer stops in the carrier, the rotational force for starting the rotation again is small. On the contrary, under the condition where the load balance is poor, the flatness level is slightly deteriorated, but the occurrence of a 4-fold symmetrical pattern is small. This is presumably because even when the rotation of the wafer is stopped, a rotational force sufficient to start the rotation again can be obtained by the offset load.

  Incidentally, an inorganic alkali typified by potassium hydroxide is used as a base alkali in a general abrasive (hereinafter also referred to as slurry). It is known that the etching rate by the inorganic alkali depends on the crystal orientation, and the polishing rate in the <111> direction is slow in the <110> direction and the <111> direction.

  For this reason, when rotation of the wafer in the carrier is inhibited, it is considered that a four-fold symmetric pattern is generated due to the crystal orientation dependence of the etching rate of the inorganic alkali contained in the slurry.

  When such a four-fold symmetrical pattern is generated, the flatness variation in the circumferential direction of the polished wafer becomes large. Therefore, a wafer without such a pattern has been desired.

  The present invention has been made in view of the above-described problems, and in polishing a silicon wafer, it is possible to prevent a decrease in polishing rate while preventing the occurrence of variations in outer peripheral flatness depending on the crystal orientation of the silicon wafer. An object is to provide an abrasive and a polishing method.

In order to achieve the above object, according to the present invention, an abrasive used for polishing a silicon wafer,
Contains colloidal silica, contains only lithium hydroxide as the base alkali,
Provided is an abrasive characterized in that the concentration of the lithium hydroxide is 0.02 wt% or more and less than 0.05 wt% with respect to the total mass of the abrasive.

  With such an abrasive, it is possible to prevent the occurrence of variations in the outer peripheral flatness depending on the crystal orientation of the silicon wafer in polishing the silicon wafer. Furthermore, the polishing rate can be made equal to or higher than when a conventional abrasive is used.

Further, according to the present invention, a method for polishing a silicon wafer by sliding a silicon wafer against the polishing cloth while supplying an abrasive to the polishing cloth affixed to a surface plate,
As the abrasive, containing colloidal silica, and using only lithium hydroxide as the base alkali,
Provided is a method for polishing a silicon wafer, wherein a concentration of the lithium hydroxide is 0.02 wt% or more and less than 0.05 wt% with respect to a total mass of the polishing agent.

  With such a polishing method, it is possible to prevent the occurrence of variations in outer peripheral flatness depending on the crystal orientation of the silicon wafer in polishing the silicon wafer. Furthermore, the polishing rate can be made equal to or higher than when a conventional abrasive is used.

  With the polishing agent and polishing method of the present invention, it is possible to prevent the occurrence of unevenness in the outer peripheral flatness depending on the crystal orientation of the silicon wafer in polishing the silicon wafer. Furthermore, the polishing rate can be made equal to or higher than when a conventional abrasive is used.

It is the schematic which showed the general double-side polish apparatus. It is the schematic which showed the general single-side polish apparatus. It is the graph which showed the pattern of the circumferential direction of typical ESFQR. It is the schematic which showed the crystal orientation of the silicon wafer whose slice surface is <100>. It is the graph which showed the pattern of the circumferential direction of ESFQR shown in FIG. 3 with the radar chart. It is the schematic which showed the investigation method of the polishing rate. 4 is a graph showing a difference in polishing rate when slurry A or slurry B is used. 3 is a graph showing a polishing rate when slurry A or slurry B is used. It is the graph which showed the polishing rate difference at the time of changing the kind and density | concentration of the alkali to add. It is the graph which showed the polishing rate at the time of changing the kind and density | concentration of the alkali to add. It is the graph which showed the radar chart of the circumferential direction distribution of ESFQR at the time of using the abrasive | polishing agent whose density | concentration of lithium hydroxide is 0.04 wt%. It is the graph which showed the radar chart of the circumferential direction distribution of ESFQR at the time of using the abrasive | polishing agent whose density | concentration of lithium hydroxide is 0.10 wt%. It is the graph which showed the result of having compared the range of the circumferential direction of ESFQR at the time of changing the abrasive | polishing agent to be used.

  As described above, conventionally, in polishing of a silicon wafer, variation in outer peripheral flatness depending on the crystal orientation of the silicon wafer has occurred.

  FIG. 4 shows crystal orientations and general notch positions. Further, FIG. 5 shows the result of converting the data of FIG. 3 into a radar chart. From the results of FIG. 5, it can be seen that the ESFQR value in the 45 ° direction from the notch position is large and the ESFQR value in the 90 ° direction from the notch position is small. When viewed from the <100> plane, which is the polished surface, the direction with a poor ESFQR value is the <110> plane direction, and the direction with a good ESFQR value is the <111> direction. Therefore, when the etching force is slow, the polishing rate is also slowed, so that the allowance is small in the <111> direction and the shape change is considered to be small.

  Therefore, the present inventor first investigated whether there is a difference in the polishing rate depending on the crystal direction using a commercially available potassium hydroxide-based slurry. As an investigation method, a single-side polishing apparatus 21 as shown in FIG. 2 is used, a silicon wafer W having a diameter of 300 mm is fixed to the polishing head 26, the rotation of the polishing head 26 and the swing of the surface plate 23 are stopped, and the surface plate 23 Polishing was carried out only by rotation. The polishing load was 15 kPa, and the platen rotation speed was 20 rpm.

  The same polishing head 26 is used as the polishing head 26, and the fixing position of the silicon wafer W is set when the <111> direction is aligned with the rotation direction of the surface plate and when the <110> direction is aligned as shown in FIG. These two conditions (Condition 1 and Condition 2) were used, and the average value of the difference in crystal direction under these two conditions was defined as the polishing rate difference.

  For the measurement, we used a flatness measuring machine LSW-3010FE from Kobelco Giken, and extracted thickness data of about 5mm □ of the outer circumference in the <111> direction and the <110> direction. Was calculated.

  FIG. 7 shows the results of investigation using two types of commercially available slurries, slurry A (manufactured by Fujimi Incorporated) and slurry B (manufactured by Nitta Haas Co., Ltd.). As shown in FIG. 7, both slurries have a larger allowance in the <110> direction than that in the <111> direction regardless of the notch fixing position, and it is understood that the rate difference depending on the crystal direction differs depending on the slurry. It was.

  In addition, when the polishing rate is compared with the average machining allowance in the wafer surface by a normal polishing method, the polishing rate is faster for the slurry A and the slurry having a higher polishing rate depends on the crystal direction as shown in FIG. The result was a large rate difference. The difference in rate due to the slurry is considered to be due to the difference in concentration and additive even in the same potassium hydroxide-based slurry.

  Patent Document 1 describes sodium hydroxide, potassium hydroxide, lithium hydroxide, and ammonia as inorganic alkalis. Patent Document 2 describes potassium hydroxide, ammonium hydroxide, sodium hydroxide, lithium hydroxide, beryllium hydroxide, magnesium hydroxide, and calcium hydroxide as basic compounds.

  In addition, it is known that potassium hydroxide and tetramethylammonium hydroxide are widely used as anisotropic etching solutions.

  Therefore, the present inventor is further widely used as an anisotropic etching solution, such as sodium hydroxide (NaOH), potassium hydroxide (KOH), and lithium hydroxide (LiOH), which are generally used as a base alkali. Using four types of tetramethylammonium hydroxide (TMAH), the concentration was varied to investigate whether there was a difference in the polishing rate difference depending on the crystal direction. The investigation method was the same as the evaluation method for the aforementioned commercially available slurries A and B.

  As the slurry, colloidal silica (trade name: Quatron PL-3, manufactured by Fuso Chemical Industry Co., Ltd.) having a primary particle size of 35 nm is used, and the silica concentration is 1.0 wt%, and the alkali concentrations are 0.04 wt% and 0.10 wt%. Adjusted as follows. Moreover, although the chelating agent etc. were added to the commercially available slurry, it evaluated without adding this time.

  The difference in polishing rate between the <110> direction and the <111> direction and the polishing rate are shown in FIGS. As shown in FIG. 9, the polishing rate difference varies depending on the alkali species, and when the alkali concentration is increased, the polishing rate difference tends to increase.

  Sodium hydroxide and potassium hydroxide had almost the same tendency, but potassium hydroxide had a slightly smaller polishing rate difference and a faster polishing rate.

  Tetramethylammonium hydroxide widely used as an anisotropic etching solution has the largest polishing rate difference (FIG. 9) and the fastest polishing rate (FIG. 10).

  In contrast, lithium hydroxide showed the largest change in polishing rate difference depending on the concentration, but the rate difference itself was small. Even when 0.10 wt% was added, the concentration of sodium hydroxide and potassium hydroxide was 0.04 wt%. Also, the polishing rate difference was small. Further, the polishing rate was a result that the polishing rate of 0.04 wt% of lithium hydroxide was faster than the concentration of 0.10 wt% of sodium hydroxide and potassium hydroxide.

  From this result, the present inventor considered that by using only lithium hydroxide as the base alkali, it was possible to suppress fluctuations in the outer peripheral portion of the wafer while maintaining a high polishing rate.

  Therefore, colloidal silica (trade name: Quatron PL-3, manufactured by Fuso Chemical Industry Co., Ltd.) having a primary particle diameter of 35 nm was used, and the silica concentration was 1.0 wt% and the lithium hydroxide concentrations were 0.04 wt% and 0.10 wt%. Using a slurry in which DTPA (diethylenetriaminepentaacetic acid) as a chelating agent was added to the adjusted slurry so as to have a concentration of 0.05 mol / L, a 300 mm diameter wafer was polished on both sides and investigated. The double-side polishing conditions were such that a four-fold symmetrical pattern as shown in FIG. 3 was generated, and the polishing time was adjusted so that the polishing allowance would be the same. In addition, in FIG. 3, it is a case where the above-mentioned slurry A is used.

  A representative example with a lithium hydroxide concentration of 0.04 wt% is shown in FIG. 11, and a representative example with a lithium hydroxide concentration of 0.10 wt% is shown in FIG. As a result, it was found that the four-fold symmetrical pattern of the slurry was improved when the lithium hydroxide concentration was 0.10 wt% (FIG. 12) as compared with the case where the slurry A was used (FIG. 3). Furthermore, when the lithium hydroxide concentration was 0.04 wt% (FIG. 11), the 4-fold symmetry pattern was further improved as compared with FIG. 12, and almost no 4-fold symmetry pattern was generated.

  FIG. 13 shows the result of comparing the circumferential ranges of the three ESFQRs used in FIGS. 3, 11 and 12 described above. As shown in FIG. 13, the slurry using lithium hydroxide showed an improvement of about 30% when the lithium hydroxide concentration was 0.10 wt%, compared with the slurry A in which a 4-fold symmetrical pattern was generated. On the other hand, when the lithium hydroxide concentration was 0.04 wt%, an average improvement of about 40% was observed, which was greatly improved as compared with the lithium hydroxide concentration of 0.10 wt%. In particular, it has been found that if the lithium hydroxide concentration is less than 0.05 wt%, the circumferential displacement of ESFQR can be 3 nm or less.

  Based on the above investigation results, the present inventor contains colloidal silica as the base alkali, contains only lithium hydroxide as the base alkali, and has a lithium hydroxide concentration of 0. 0 relative to the total mass of the abrasive. It has been found that if it is less than 05 wt%, it is possible to prevent the occurrence of variations in the outer peripheral flatness depending on the crystal orientation of the silicon wafer in polishing the silicon wafer. Further, it has been found that if the concentration of lithium hydroxide is 0.02 wt% or more with respect to the total mass of the abrasive, the polishing rate can be made equal to or higher than that when a conventional abrasive is used. .

  First, the abrasive | polishing agent of this invention is demonstrated. The polishing agent used for polishing the silicon wafer of the present invention contains colloidal silica, contains only lithium hydroxide as a base alkali, and the concentration of lithium hydroxide is 0.02 wt% with respect to the total mass of the polishing agent. More than 0.05 wt%.

  As described above, since the concentration of lithium hydroxide is less than 0.05 wt% with respect to the total mass of the polishing agent, in the polishing of the silicon wafer, the occurrence of variation in the outer peripheral flatness depending on the crystal orientation of the silicon wafer occurs. Can be prevented. Furthermore, since the concentration of lithium hydroxide is 0.02 wt% or more with respect to the total mass of the abrasive, the polishing rate can be made equal to or higher than that when a conventional abrasive is used.

  Moreover, since additives, such as a chelating agent, have little influence on a polishing rate difference, you may add a chelating agent etc. to an abrasive | polishing agent as needed.

  Further, although the concentration of colloidal silica is not particularly limited, in principle, the higher the colloidal silica concentration, the stronger the element of mechanical polishing, which can be advantageous for the polishing rate difference. For example, if the colloidal silica concentration is 0.2 wt% or more, the polishing rate difference is not affected, and a polishing rate equal to or higher than that of a commercially available KOH-based slurry can be obtained. In consideration of the slurry cost, it is preferably 1.0 wt% or less.

  The larger the primary particle size of colloidal silica, the slightly higher the polishing rate, but the contribution to the polishing rate is very small compared to the base alkali concentration. Moreover, since the influence on the polishing rate difference is small, the primary particle diameter of the colloidal silica may be selected in accordance with the target surface state. Since the load of final polishing can be reduced when the surface roughness is kept low, colloidal silica having a primary particle diameter of about 15 nm to 70 nm is preferable.

  Next, as an example of the polishing method of the present invention, a case where a single-side polishing apparatus 21 as shown in FIG. 2 is used will be described, but the present invention is not limited to this.

First, a silicon wafer W to be polished is prepared.
In the polishing apparatus 21 as shown in FIG. 2, the silicon wafer W is held by the polishing head 26, and the polishing agent 24 of the present invention as described above is supplied onto the polishing cloth 22 from the polishing agent supply mechanism 25. The silicon wafer W can be polished by rotating the surface plate 23 and the polishing head 26 to press and slide the surface of the silicon wafer W against the polishing pad 22.

  In this case, as described above, since the concentration of lithium hydroxide is less than 0.05 wt% with respect to the total mass of the abrasive, the polishing of the silicon wafer depends on the crystal orientation of the silicon wafer. It is possible to prevent the occurrence of unevenness in the outer peripheral flatness. Furthermore, since the concentration of lithium hydroxide is 0.02 wt% or more with respect to the total mass of the abrasive, the polishing rate can be made equal to or higher than that when a conventional abrasive is used.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples of the present invention, but the present invention is not limited to these.

(Example 1-7, Comparative Example 1-11)
In addition to the results of the investigation (Comparative Example 1-8) conducted using sodium hydroxide (NaOH), potassium hydroxide (KOH), and tetramethylammonium hydroxide (TMAH) as the base alkali as described above, water Polishing was performed using a single-side polishing machine with lithium oxide as the base alkali, varying the primary particle size and silica concentration. At this time, the case where the lithium hydroxide concentration was changed in the range of 0.02 wt% or more and less than 0.05 wt% was set as Example 1-7, and the case where the lithium hydroxide concentration was 0.10 wt% was set as Comparative Example 9 It was set to -10. Moreover, the case where the density | concentration of lithium hydroxide was 0.01 wt% was made into the comparative example 11. Table 1 shows a summary of the conditions of the abrasives in Examples and Comparative Examples, and the results of measuring polishing rate differences and polishing rates.

  The difference in polishing rate between the <110> direction and the <111> direction was determined to be 3% or less, ◎ when 5% or less, ◯, 6% or less to Δ, and 6% or more to be evaluated as ×. . A polishing rate of 5 nm / sec or less was evaluated as x, 10 nm / sec or less as Δ, 15 nm / sec or less as ◯, and when exceeding 15 nm / sec as ◎.

  As shown in Table 1, in Comparative Example 1-8 using an alkali other than LiOH, the polishing rate difference exceeded 6%, and the outer periphery variation occurred. On the other hand, in Comparative Example 9-10, the polishing rate difference was improved as compared with Comparative Example 1-8, but the polishing rate difference was still large. Moreover, in Comparative Example 11, the polishing rate difference was the same level as in the example, but the polishing rate was very low. A low polishing rate is not preferable because productivity decreases.

  On the other hand, in Example 1-7, the polishing rate difference was 3% or less, which was greatly improved as compared with Comparative Example 1-10. Further, the polishing rate in Example 1-7 was equal to or higher than that of a commercially available slurry such as Comparative Example 8.

  When the colloidal silica concentration and the lithium hydroxide concentration were lowered, the polishing rate was lowered, but the difference in the polishing rate was not affected. The primary particle size of colloidal silica also had a slight effect on the polishing rate, but had no effect on the polishing rate difference.

  From the above, it was found that the slurry with lithium hydroxide as the base alkali can suppress the polishing rate difference to 3% or less by setting the lithium hydroxide concentration to less than 0.05 wt%. It was also found that when the lithium hydroxide concentration was 0.02 wt% or more, a polishing rate equivalent to or higher than that of a commercially available KOH-based slurry (5 nm / sec under the current polishing conditions) could be secured.

  Moreover, since additives, such as a chelating agent, do not affect a polishing rate difference, it turned out that a chelating agent etc. may be added to an abrasive | polishing agent as needed.

  Moreover, since the element of mechanical polishing becomes stronger as the colloidal silica concentration is higher, it is considered that the difference in the polishing rate is superior. From this result, if the colloidal silica concentration is 0.2 wt% or higher, the polishing rate difference is not affected and a polishing rate equal to or higher than that of a commercially available KOH-based slurry can be obtained. It was sufficient that the slurry cost was taken into consideration, and it was found to be preferably 1.0 wt% or less in consideration of the slurry cost.

  Further, it was found that the larger the primary particle size of the colloidal silica, the slightly higher the polishing rate, but the contribution to the polishing rate is very small compared to the concentration of the base alkali. Moreover, since the influence on the polishing rate difference was not observed, the primary particle diameter of the colloidal silica may be selected in accordance with the target surface state. It is considered that colloidal silica having a primary particle diameter of about 15 nm to 70 nm is preferable because the surface polishing can be reduced by reducing the surface roughness.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

DESCRIPTION OF SYMBOLS 1 ... Double-side polish apparatus, 2 ... Upper surface plate, 3 ... Lower surface plate, 4 ... Polishing cloth, 5 ... Sun gear,
6 ... Internal gear, 7 ... Carrier, 8 ... Abrasive supply mechanism,
9 ... Slurry tube, 21 ... Single-side polishing device, 22 ... Polishing cloth, 23 ... Surface plate,
24 ... Abrasive, 25 ... Abrasive supply mechanism, 26 ... Abrasive head,
W: Silicon wafer.

Claims (2)

An abrasive used for polishing a silicon wafer,
Contains colloidal silica, contains only lithium hydroxide as the base alkali,
A polishing agent, wherein a concentration of the lithium hydroxide is 0.02 wt% or more and less than 0.05 wt% with respect to a total mass of the polishing agent. A method of polishing a silicon wafer by sliding the silicon wafer against the polishing cloth while supplying an abrasive to the polishing cloth affixed to a surface plate,
As the abrasive, containing colloidal silica, and using only lithium hydroxide as the base alkali,
A method for polishing a silicon wafer, wherein a concentration of the lithium hydroxide is 0.02 wt% or more and less than 0.05 wt% with respect to a total mass of the polishing agent.

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