JP6406048B2 - Wafer processing method - Google Patents

Description

  The present invention relates to a wafer processing method, and more specifically, after the wafer is set in a processing block, the wafer is polished by a polishing apparatus, the orientation of the wafer is changed, and the polishing is further repeated, thereby flattening the vicinity of the end portion. The present invention relates to a wafer processing method capable of obtaining a wafer having a high degree.

  In a semiconductor element, various thin films are formed on a semiconductor wafer such as a sapphire substrate, which is a material substrate, and high flatness is required for the semiconductor wafer.

  Therefore, for mirror polishing of sapphire substrates, CMP (Chemical Mechanical Polishing) technology is used to flatten the polishing surface, that is, the surface to be polished is mechanically polished with an abrasive and a polishing cloth while chemically changing the surface layer. The technology is widely adopted, and while supplying a CMP polishing agent containing silicon oxide particles and water between the polishing cloth and the sapphire substrate, the sapphire substrate and the polishing platen are moved to flatten one side of the sapphire substrate. To be polished.

  However, as the degree of integration of elements increases, semiconductor wafers are required to have a higher level of flatness, and the level becomes stricter as the years progress. In particular, since the flatness near the edge of the wafer affects the yield, the flatness is evaluated using an index called edge roll-off. Here, the edge roll-off is a sag amount measured at a fixed position from the wafer edge with reference to the wafer surface height.

For the reasons described above, the following methods have been studied in the industry as methods for processing wafers so as to reduce edge roll-off.
That is, a method of using a pad with high hardness at a low compression rate (Patent Document 1), a method of performing an etching process with different material removal locally (Patent Document 2), and flattening the polishing platen shape during polishing A method of designing in advance (Patent Document 3), a method of managing the abrasive concentration of the polishing liquid (Patent Document 4), a method of keeping the bevel angle within a certain range (Patent Document 5), and the like.

However, the above-described edge roll-off improving method has the following problems and is not practical.
That is, in Patent Document 1, the cost is increased because a primer is applied to a processing pad. In Patent Document 2, a silicon substrate is a target, and a material such as a chemically stable sapphire substrate is processed by etching. In Patent Document 3, it is necessary to correct the shape of the polishing surface plate that is already held. In Patent Document 4, the processing speed is decreased due to the concentration change of the polishing liquid. In Patent Document 5, the silicon substrate is targeted. In the case of a chemically stable material such as a sapphire substrate, there is a problem that the frequency of bevel grinding wheel management increases.

  Therefore, the present applicant pays attention to the positional relationship between the outer periphery and inner periphery of the region where the wafer passes on the surface plate during polishing and the end surface of the polishing cloth, and the minimum value and the maximum value of the distance are in a specific range. The method of making it become like this was proposed (refer patent document 6). By doing so, a portion of the polishing cloth that does not come into contact with the wafer was not generated, but the edge roll-off could not be improved sufficiently.

  Under such circumstances, using a relatively inexpensive processing pad, it can be applied to chemically stable substrate materials, and it is not necessary to change the design of the polishing surface plate, and processing by changing the concentration of the polishing liquid There has been a need for a processing method that does not cause a decrease in speed and does not require an increase in the frequency of bevel grinding wheel management.

JP 2006-043811 A JP 2006-140484 A JP 2007-007748 A JP 2007-053298 A JP 2012-129416 A JP 2003-257916 A

  The problem of the present invention is that, in view of the above-mentioned problems of the prior art, the wafer is set in a processing block, and after polishing the wafer with a polishing apparatus, the direction of the wafer is changed and further polishing is repeated, so that An object of the present invention is to provide a wafer processing method capable of obtaining a wafer having high flatness.

  Therefore, as a result of intensive investigations to solve the problems of the prior art and observing in detail the polishing surface of the wafer fixed to the processing block, the present inventor found that edge roll-off particularly on the polishing surface on the outer peripheral side of the processing block. Large, this is because the peripheral speed on the outer peripheral side is higher than the central side of the processing block, and the supply amount of abrasive grains in the central part is smaller than the outer peripheral side when viewed in processing block units. Investigating the cause, found that if the wafer is rotated at a specific angle in the circumferential direction and changed in direction and polished, the edge roll-off on the polishing surface on the outer peripheral side of the processing block can be reduced, and the present invention is completed. It came.

That is, according to the first aspect of the present invention, a step of setting a plurality of wafers in a processing block, a step of attaching the processing block on which the wafer is set to a polishing apparatus, and polishing the wafer, and a polished wafer In the wafer processing method including the step of recovering from the processing block, the wafer is sapphire having a thickness of 100 to 1500 μm, and the concentration of silicon oxide particles is adjusted to 30 to 60% by weight in the polishing step . While supplying the slurry containing colloidal silica to the polishing surface, the wafer is polished using a polishing pad, and after the first polishing, the polished wafer is rotated at an angle exceeding 45 ° in the circumferential direction. There is provided a wafer processing method characterized by resetting to a different direction and performing the second and subsequent polishing for a shorter time than the first time .

Further, according to the second invention of the present invention, in the first invention, the step of setting the wafer may be either affixing to the processing block by wax or UV curable resin, or holding to the processing block by water or vacuum adsorption. A method for processing a wafer is provided.
According to a third invention of the present invention, there is provided a wafer processing method characterized in that, in the first or second invention, a polishing pad in which a nonwoven fabric is impregnated with polyurethane is used in the polishing step. .
According to a fourth aspect of the present invention, there is provided the wafer processing method according to any one of the first to third aspects, wherein the wafer is polished 2 to 4 times.
According to a fifth aspect of the present invention, in any one of the first to fourth aspects, when the wafer is reset, the wafer is rotated at an angle of 90 ° to 180 ° per time. A method for processing a wafer is provided.
According to a sixth aspect of the present invention, in the method according to any one of the first to fifth aspects, the wafer to be polished is sapphire having a size (diameter) of 1 inch or more. Is provided.

The seventh aspect of the present invention, in any one of the first to 6, polishing, machining of the wafer edge roll off value of the wafer characterized that you reduced to less than 0.8μm A method is provided.
Furthermore, according to an eighth invention of the present invention, in any one of the first to seventh inventions, the first polishing time is 0.5 to 5 hours, and the second polishing time is 0.3 to 2. There is provided a wafer processing method characterized by time.

  According to the present invention, after the wafer is processed, the set direction of the wafer is further changed and polished, so that the wafer can be processed so that the flatness in the vicinity of the end portion becomes high. Since this method does not require a special polishing cloth or polishing liquid, it does not increase the cost and can be performed by a relatively simple operation, so that productivity can be maintained.

It is a schematic explanatory drawing explaining the concept of edge roll-off of the wafer surface by enlarging a wafer side surface. It is explanatory drawing which shows the positional relationship of the state which set the process block used for grinding | polishing, and the wafer to it. It is explanatory drawing which shows the wafer position which expands a part of FIG. 2 and measures edge roll-off. It is the graph which showed the edge roll-off measured by the conventional grinding | polishing method for every position of a wafer. It is the graph of one embodiment which showed edge roll-off measured by the polish method of the present invention for every position of a wafer. It is the graph of the other embodiment which showed the edge roll-off measured by the grinding | polishing method of this invention for every position of a wafer.

1. Polishing Method The wafer processing method of the present invention includes a step of setting a plurality of wafers in a processing block, a step of attaching the processing block on which the wafer is set to a polishing apparatus, polishing the wafer, and processing the polished wafer In a wafer processing method including a step of recovering from a block,
The wafer is sapphire having a thickness of 100 to 1500 μm, and in the polishing step, a slurry containing colloidal silica having a concentration of silicon oxide particles adjusted to 30 to 60% by weight is supplied to the polishing surface while polishing the polishing pad. After the first polishing, the polished wafer is rotated at an angle exceeding 45 ° in the circumferential direction, reset to a different direction, and the subsequent polishing is 1 It is characterized in that the time is shorter than the first time .
Hereinafter, the present invention will be described in detail with respect to mirror polishing by a single-side polishing apparatus using a sapphire substrate as a wafer.

(1) Set process In the present invention, as a polishing apparatus, a general single side having a substantially disk-shaped polishing surface plate on which a polishing cloth (polishing pad) is mounted and a substantially disk-shaped processing block are detachable. A polishing apparatus can be used. The apparatus is provided with a nozzle for quickly cleaning the polished wafer.

In this step, a plurality of wafers are set in the processing block. First, the non-polished surface of the sapphire substrate is coated with wax so as not to deform the surface of the wafer as a main surface in the future. The type of wax may be either a high molecular weight synthetic resin or a natural resin, which can be diluted with an organic solvent.
Thereafter, the sapphire substrate is fixed to the processing block by thermocompression bonding the sapphire substrate and the processing block.

  The thickness of the wafer to be polished is not particularly limited. However, in the case of a sapphire substrate, if the substrate thickness is too thin, the warpage change during epitaxial growth increases, so the degree of concavity must be increased, and within the substrate surface during epitaxial growth. Temperature fluctuations are likely to occur. Therefore, the composition of the nitride semiconductor layer is easily affected, and the variation in wavelength and electrical characteristics of the light-emitting element manufactured from the obtained film increases, and a favorable light-emitting element is obtained stably and with high yield. It becomes difficult. Therefore, the thing of 100 micrometers or more is preferable.

The thicker the wafer, the less the change in warpage during epitaxial growth, so the concave degree can be reduced, and the variation in temperature distribution in the substrate surface during epitaxial growth is preferably reduced. However, in order to increase the substrate cost, a wafer of 1500 μm or less is preferable. .
Therefore, the thickness of the wafer is 100 to 1500 μm, more preferably 300 to 1500 μm, and particularly preferably 500 to 1500 μm.

  The amount of the wax applied to the non-polished surface of the sapphire substrate may be an amount that can prevent the thread from becoming a protective film between the non-polished surface and the block, and can be, for example, 1 μm or more in thickness. However, when the coating thickness is increased, not only is the cost burden, but also the uniformity of the in-plane thickness of the substrate is deteriorated. Therefore, the thickness is preferably 5 μm or less, and more preferably 3 μm or less.

  It is desirable that a ceramic polishing plate be bonded in advance to a resin-made polishing plate having a pocket shape hollowed out in the same size as the substrate shape. The size of the wafer to be polished is not particularly limited, and it can be polished from a small size of about 1 inch to a large size of 6 inches or more.

  Then, the sapphire substrate is fitted into the pocket of the polishing plate to hold the substrate. In FIG. 2, four wafers are shown, but the number of wafers may be plural, and may be 3-6.

Instead of sticking to the processing block with wax, sticking with an ultraviolet curing agent may be employed. Moreover, the holding | maintenance by water and the holding | maintenance by vacuum adsorption may be sufficient. Holding by water means holding the sapphire substrate using the surface tension of water, and holding by vacuum adsorption means that the sapphire substrate is inserted into a polishing plate whose porous layer is the substrate holding part. The substrate is held by reducing the pressure of the porous layer. In addition, holding by a backing plate can also be performed. Among these methods, sticking with wax, holding by water or vacuum adsorption is preferable, and sticking with wax is more preferable.
In either case, it is necessary to perform pasting or the like so that the substrate does not rotate during polishing of the substrate held on the template and the non-polished surface and the processing block do not rub against each other.

(2) Polishing Step Next, in the backside polishing step, a single-side polishing apparatus is used, the backside of the wafer is pressed against a polishing surface plate on which a polishing cloth is mounted, and a polishing cloth (polishing pad) and abrasive slurry are used. Mechanochemical polishing to make a mirror surface.

That is, while supplying a CMP polishing agent containing silicon oxide particles and water between the polishing cloth and the sapphire substrate, the polishing block and the polishing platen are moved to polish one side of the sapphire substrate.
For the polishing cloth (polishing pad), for example, polyurethane-based artificial leather, polyurethane-based suede-like nonwoven fabric, or the like can be used.

  As the polishing pad, in the present invention, it is preferable to use a non-woven fabric with a hardness of less than 90. If a polishing pad having a hardness of 90 or more is used, the surface may be scratched depending on the polishing conditions.

  Moreover, it is preferable to supply colloidal silica to a grinding | polishing surface at the process of grinding | polishing. As an abrasive | polishing agent, it is preferable in it being a slurry containing the colloidal silica by which the density | concentration of the silicon oxide particle was adjusted to 30 to 60 weight%.

  When the silica content is less than 30% by weight, pits are generated in the mirror-polished sapphire substrate, making it difficult to grow a good epitaxial film on the sapphire substrate, while the silica content is 60 When the weight percentage is exceeded, colloidal silica aggregates during polishing, and this aggregation may cause scratches on the surface of the sapphire substrate, which may propagate to the epitaxial film. For this reason, the content of silica is more preferably adjusted to 35 to 50% by weight, and particularly preferably 40 to 50% by weight.

  The average particle size of silica is desirably 10 to 100 nm. When the average particle size is less than 10 nm, there is no problem in the quality of the epitaxial film obtained using the polished sapphire substrate, but the polishing processing speed of the sapphire substrate may become extremely slow, and the average particle size When the thickness exceeds 100 nm, irregularities are formed on the surface of the sapphire substrate after the polishing treatment, and the irregularities may propagate to the epitaxial film. For this reason, the average particle diameter of silica is more preferably 20 to 80 nm.

  When the above preparation is complete, set the polishing plate on the polishing platen so that the surface to be polished is in contact with the polishing pad, and then slowly lower the top ring (rotating shaft) from directly above the polishing plate for polishing. Contact the plate, gradually pressurize while dripping and supplying the abrasive slurry onto the polishing pad from the abrasive slurry supply pipe, rotate slowly, then apply the specified pressure while maintaining the specified rotation speed, mirror surface Polishing is performed. The abrasive may be dropped on the polishing pad 2 from above the polishing pad, but may be brought into contact with the polishing surface so that the abrasive is ejected from below the polishing pad.

  Polishing conditions are determined by the type of wafer and the state of the wafer prior to the introduction of the apparatus, and are difficult to define because they depend on the type of apparatus and the degree of polishing. For example, a polishing surface plate equipped with a polishing cloth (polishing pad) The rotation speed is set to 30 to 80 rpm, the polishing load is set to 100 to 200 kPa, the supply amount of the abrasive (slurry) is set to 5 to 24 L / min, and polishing is performed until a desired flatness is achieved. The polishing time is not particularly limited, but may be 0.5 to 5 hours, preferably 1 to 3 hours.

  Conventionally, the above polishing was performed in the positional relationship of FIG. 3, but as shown in FIG. 4, the edge roll-off on the polishing surface on the processing block outer peripheral side B was large. This is because the peripheral speed on the outer peripheral side of the processing block is larger than the central side of the processing block, and the supply amount of abrasive grains in the central part is smaller than that on the outer peripheral side when viewed in processing block units. to cause.

  Here, the edge roll-off is a sag amount measured at a fixed position from the wafer edge with reference to the wafer surface height. Roll-off can be measured using a contact profiler, and the roll-off rating is M.M. It can be carried out according to the method proposed by Kimura (Jpn. J. Apply Phys. Vol. 38 (1999) Pt. 1, No. 1A).

(3) Wafer reset and polishing In the present invention, in order to reduce edge roll-off on the polishing surface, which has been a problem in the past, the processed wafer is rotated in the circumferential direction in the processing block, and in different directions. Polish after resetting.

  At this time, the rotation angle of the wafer to be reset needs to exceed 45 °. If it is 45 ° or less, the effect of improving the edge roll-off on the polished surface is small, the number of polishing increases, and the economy is impaired.

  In the present invention, the number of polishing of the wafer is preferably 2 to 4 times. The second and subsequent polishing times are also determined by the type of wafer and the state of the wafer before the apparatus is loaded, as described above, but can be made shorter than the first time. Preferred is 0.3 to 2 hours.

  Further, the rotation angle of the wafer per time is preferably 90 ° or more and 180 ° or less. Specifically, if the number of polishing times is 2, the rotation angle of one wafer is 180 °, and if the number of polishing times is 3, the rotation angle of one wafer is 120 °. If the number of times is 4, the rotation angle of one wafer is preferably 90 °.

  On the other hand, when the number of times of polishing is determined to be 2 times, if the rotation angle of the wafer is reduced to 90 °, for example, the edge roll-off is not sufficiently improved, while the number of times of polishing is determined to be 3 times. Further, when the rotation angle of one wafer is set to 180 °, for example, or when the number of times of polishing is determined to be four, if the rotation angle of one wafer is increased to, for example, 120 °, the edge roll-off is sufficiently achieved. It may not be improved.

  In other words, in the present invention, polishing is performed a plurality of times, but it is necessary to reset the wafer in a different orientation with a good balance, and therefore it is necessary to change the orientation of the wafer by an angle of about (360 ° / number of polishing times). There will be.

  In the present invention, when the orientation of the wafer is rotated by 180 ° and the processing block outer peripheral side B is reset to the inner peripheral side, the edge roll on the polishing surface D on the processing block outer peripheral side as shown in FIG. Off can be reduced.

Further, in the present invention, if the wafer is rotated by 90 ° to change the direction and the processing block outer peripheral side B is reset to be slightly inner peripheral side, for example, and the second polishing is performed, as shown in FIG. Edge roll-off of A or C that becomes the polishing surface on the outer peripheral side of the processing block can be slightly reduced.
Thereafter, in the same manner, if the fourth polishing is repeated, such as rotating 90 ° further in the same direction and setting the inner periphery to perform the third polishing, the outer periphery of the processing block Edge roll-off at the side polishing surface can be significantly reduced.

  As can be seen from the comparison between FIG. 5 and FIG. 6, the results of the case where only the polishing is performed twice and the case where the polishing is performed four times are almost the same. Although it is more economical to reduce the number of times of polishing, depending on the polishing conditions, the edge roll-off may be improved as compared with the case of two times of polishing when the number of times of polishing is three or more.

(4) Wafer collection step After polishing is completed, the top ring (rotating shaft) of the polishing apparatus is raised, and at the same time, a cleaning liquid is supplied to the wafer attached to the polishing plate to wash away the polishing agent adhering to the wafer. After cleaning, the polishing plate is removed, dried, the wafer is peeled off, and stored in a case.
The mirror polishing by the single-side polishing apparatus using the sapphire substrate as the wafer has been described above, but the present invention can be similarly applied to the case of mirror polishing by the double-side polishing apparatus. In double-side polishing, a processing block for setting a plurality of wafers is used that is thinner than the wafer.

2. Polished wafer The wafer to be polished is not limited by the type of material, but is preferably sapphire.

  When manufacturing a nitride semiconductor light emitting device for a light emitting device, it is important to grow a high quality epitaxial film. The sapphire substrate used for the growth of the epitaxial film is also required to have a smooth surface free of processing distortion and free of defects, but the wafer processed by the above method has an edge roll-off of 1 μm or less. If the polishing conditions are optimized, the edge roll-off can be 0.8 μm or less.

  Examples of the present invention will be described below together with comparative examples, but the present invention is not limited only to these examples.

  The roll-off was measured using a Tencor P-12 contact profiler. FIG. 1 shows the measurement site. Evaluation of roll-off is as follows. It was carried out by the method proposed by Kimura (Jpn. J. Apply Phys. Vol. 38 (1999) Pt. 1, No. 1A) et al.

As shown in FIG. 1, the flatness is measured by scanning the contact needle over a length of 5000 μm in the outer peripheral direction starting from a point of a part of 6000 μm from the wafer outer peripheral end surface toward the center point.
At this time, the starting point and a point 3000 μm from the starting point are set to the same level by the leveling process, and a horizontal line passing through these two points is set as a reference line. At this time, the distance h between the reference line at the 5000 μm point (end point) and the surface of the wafer was set as a roll-off value.

(Conventional example)
Polishing using a surface plate was performed using diamond abrasive grains to prepare a 6-inch diameter sapphire substrate with an edge roll-off of 0.2 μm or less.
Next, after fixing this board | substrate to the process block with wax, it set to the precision grinding | polishing apparatus and implemented precision grinding | polishing. Colloidal silica (COMPOL 505 manufactured by Fujimi Incorporated) was used as the abrasive grains, and a non-woven fabric (SUBA800 manufactured by Nitta Haas) was used as the pad.
Precision polishing was performed for 3 hours under the conditions of a rotational speed of the platen of 60 rpm and a load of 300 g / cm ² , and then edge roll-off was measured for each position of the wafer. The measurement position of the edge roll-off was grasped using an end face shape measuring device. As a result, the edge roll-off increased at the measurement positions B and D as shown in FIG.

Example 1
In the above conventional example, precision polishing was performed for 3 hours, but in Example 1, polishing was performed for 2 hours under the conditions that the rotation speed of the surface plate was 60 rpm and the load was 300 g / cm ² .
Next, after completion of precision polishing, the wax was fluidized by heating, the wafer was rotated 180 ° counterclockwise in the circumferential direction, and then fixed to the processing block, and polishing was performed for 1 hour.
The measurement position of the edge roll-off on the wafer was determined on the basis of the position facing the center direction of the processing block at the first precision polishing. Thereafter, when the edge roll-off was measured for each position of the wafer, the edge roll-off was significantly reduced at the measurement positions B and D as shown in FIG.

(Example 2)
As in Example 1, polishing was performed for 2 hours in the first precision polishing, but in the second precision polishing, the wafer was rotated 90 ° counterclockwise in the circumferential direction and then fixed to the processing block for 20 minutes. Next, in the third precision polishing, the wafer is further rotated 90 ° counterclockwise in the circumferential direction, fixed to the processing block, and polished for 20 minutes. Finally, in the fourth precision polishing, The wafer was further rotated 90 ° counterclockwise in the circumferential direction, and then fixed to the processing block, followed by polishing for 20 minutes.
Thereafter, when the edge roll-off was measured for each position of the wafer, the edge roll-off became small at the measurement positions B and D as shown in FIG.

"Evaluation"
In both the example and the conventional example, the position B of the wafer is on the outer peripheral side of the processing block, but the edge roll-off at the position B is increased after the first polishing.
In the conventional example, the edge roll-off is close to 1 μm, but in the second polishing of Example 1 and the fourth polishing of Example 2 that exceeded 1 μm at the first time, the edge roll-off was less than 0.9 μm. . This polishing method can be said to be effective in reducing edge roll-off.

  Since the wafer obtained by the present invention has a small edge roll-off, when used as a sapphire substrate, a high-quality epitaxial film can be grown by manufacturing a nitride semiconductor light-emitting element for a light-emitting device.

1 Wafer 2 Processing block 3 Wafer surface h Edge roll-off

Claims (8)

Wafer processing method comprising: setting a plurality of wafers in a processing block; attaching the processing block on which the wafer is set to a polishing apparatus; polishing the wafer; and recovering the polished wafer from the processing block In
The wafer is sapphire having a thickness of 100 to 1500 μm, and in the polishing step, a slurry containing colloidal silica having a concentration of silicon oxide particles adjusted to 30 to 60% by weight is supplied to the polishing surface while polishing the polishing pad. After the first polishing, the polished wafer is rotated at an angle exceeding 45 ° in the circumferential direction, reset to a different direction, and the subsequent polishing is 1 A wafer processing method, characterized in that the processing is performed for a time shorter than the first time .   2. The wafer processing method according to claim 1, wherein the step of setting the wafer is any one of affixing to a processing block with wax or ultraviolet curable resin, and holding on the processing block with water or vacuum adsorption.   3. The wafer processing method according to claim 1, wherein a polishing pad impregnated with polyurethane is used in the nonwoven fabric in the polishing step. Polishing times of the wafer processing method of the wafer according to any one of claims 1 to 3, characterized in that 2 to 4 times. When resetting the wafer processing method of the wafer according to any one of claims 1 to 4, characterized in that is rotated at an angle of less than 180 ° 90 ° or more per wafer. Wafer, the wafer processing methods according to any one of claims 1 to 5, characterized in that the size (diameter) of more than 1 inch sapphire is polished. The polishing method of processing a wafer according to any one of claims 1 to 6 edge roll off value of the wafer characterized that you reduced to less than 0.8 [mu] m. The wafer processing method according to claim 1, wherein the first polishing time is 0.5 to 5 hours and the second polishing time is 0.3 to 2 hours .

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