JP6610526B2 - Single wafer polishing method for silicon wafer - Google Patents

Description

  The present invention relates to a single wafer single side polishing method for a silicon wafer.

  Silicon wafers are widely used as substrates for semiconductor devices. In general, a silicon wafer is processed into a polished wafer by starting with a pulling process of a silicon single crystal ingot, going through a slicing process, a surface grinding process, an etching process, and a polishing process, and finally being cleaned.

  Here, in the polishing process of the silicon wafer, it is common to perform polishing in a plurality of stages such as rough polishing and finish polishing. In this case, in rough polishing, both sides of the silicon wafer are simultaneously polished (referred to as “double-side polishing method”), and the flatness of the polished silicon wafer is reduced (flatness is improved). In the subsequent finish polishing, only one side of the silicon wafer is polished (referred to as “single-side polishing method”). In single-side polishing, although flatness after double-side polishing is deteriorated to some extent, processing damage that can be caused by double-side polishing is removed, and the surface roughness of the polished surface of the silicon wafer is improved. The single-side polishing method may be performed in a plurality of stages by changing the type of polishing cloth, the size of the abrasive grains in the polishing liquid, and the alkali concentration.

  Here, a general single-side polishing method by a conventionally used single-side polishing apparatus 100 will be described with reference to FIG. The single-side polishing apparatus 100 includes a polishing head 120 that holds the silicon wafer 10 and a rotating surface plate 140 to which a polishing cloth 150 is attached. The single-side polishing apparatus 100 includes a rotating mechanism that rotates the polishing head 120 and a moving mechanism that moves the polishing head 120 in and out of the rotating surface plate 140. In the single-side polishing apparatus 100, the surface to be polished of the semiconductor wafer 10 (that is, the side of the rotary platen 140 side) with respect to the polishing cloth 150 affixed to the upper surface of the rotary platen 140 while the polishing head 120 holds the semiconductor wafer 10. Surface) and rotating the polishing head 120 and the rotating surface plate 140 together to move the polishing head 120 and the rotating surface plate 140 relative to each other so that the polishing liquid 170 is supplied from the polishing liquid supply means 160 and the silicon wafer 10 The surface to be polished is subjected to chemical mechanical polishing.

  In the patent document 1, the applicant of the present application has proposed a single-side polishing method that significantly increases the relative speed between the silicon wafer and the polishing cloth as compared with the conventional technique and significantly reduces the surface roughness of the polished silicon wafer. .

JP 2000-15571 A

  By the way, in recent years, the diameter of a silicon wafer has been increased and the device formed using the silicon wafer has been miniaturized. In a silicon wafer after final polishing by a single-side polishing method, the surface flatness and surface roughness are reduced. Requests are getting stricter. Although the surface roughness of the silicon wafer can be significantly reduced by the technique described in Patent Document 1, if the single-side polishing is performed, the flatness of the silicon wafer after the double-side polishing is considerably deteriorated as described above. Therefore, there is room for improvement in terms of suppressing deterioration in flatness.

  Therefore, the present inventor examined the influence of relative speed on the flatness and surface roughness after polishing when polishing the polished surface of a silicon wafer by a polishing head equipped with a retainer ring in a single-wafer type single-side polishing method. did. In the single-wafer single-side polishing method described above with reference to FIG. 1, the polishing head 120 including the retainer ring 124 holds the silicon wafer 10, and one side of the silicon wafer (that is, the surface to be polished) is polished. A schematic diagram is shown in FIG. In FIG. 2, the polishing head 120 includes a backing plate 122 that chucks the silicon wafer 10, and a retainer ring 124 that prevents the silicon wafer 10 that is being polished from popping out is provided on the periphery of the backing plate 122. Single-sided single-side polishing is performed with one side (surface to be polished) of the silicon wafer 10 protruding from the lower end of the retainer ring 124, and the polishing cloth 150, which is an elastic body, is pressed by the polishing head 120, Sinks below 10 The polishing liquid 170 supplied onto the polishing cloth 150 is subjected to polishing by the centrifugal force generated by the rotation of the rotating surface plate 140 from the center of the rotating surface plate 140 and the polishing cloth 150 toward the peripheral edge, and the silicon wafer 10 and the retainer ring 124. It sinks and flows into a slight gap with the cloth 150.

  When the relative speed between the center position of the silicon wafer 10 in plan view and the rotating surface plate 140 (polishing cloth 150) (refer to the relative speed V in FIG. 3) decreases, the polishing liquid on the polishing cloth 150 is reduced. The centrifugal force to 170 is reduced. When the centrifugal force decreases, the amount of the polishing liquid 170 that spills from the rotating surface plate 140 decreases, and the height of the polishing liquid 170 on the rotating surface plate 140 increases. As the height increases, the amount of the polishing liquid 170 that is about to flow into the retainer surface 124A of the retainer ring 124 on the center side of the rotating surface plate 140 increases, and the liquid of the polishing liquid 170 that acts on the retainer surface 124A increases. The pressure (that is, the hydraulic pressure applied to the retainer surface 124A by the polishing liquid 170 flowing from the outer peripheral side to the inner peripheral side of the retainer ring 124 at the position of the retainer surface 124A, and hereinafter referred to as “retainer hydraulic pressure”) is also high. Become. As the retainer fluid pressure increases, the compressive amount (deformation amount) of the polishing pad 150 increases on the retainer surface 124A side, so that the surface pressure stress of the polishing pad 150 acting on the peripheral edge of the silicon wafer 10 decreases. Due to this phenomenon, when the relative speed is low, deterioration of the roll-off amount (edge roll-off) at the edge portion of the silicon wafer 10 due to single-side polishing is relatively easily suppressed, so that the outer peripheral flatness is increased (flatness). Is worse). However, since the action of chemical mechanical polishing is also reduced due to the decrease in the relative speed, the effect of reducing the surface roughness is also suppressed.

  On the other hand, if the relative speed is increased, the surface roughness can be greatly reduced as in Patent Document 1. However, since the retainer hydraulic pressure is reduced, the edge roll-off is increased as compared with the case where the relative speed is low, and the increase in the outer peripheral flatness is relatively fast. In this way, when the silicon wafer is single-sided polished with a polishing head equipped with a retainer ring, the present inventor found that there is a trade-off relationship between the reduction in surface roughness and the increase in outer flatness. I found it.

  Although the surface roughness and the outer peripheral flatness are in a trade-off relationship, as described above, the requirements for the surface flatness and the surface roughness on the silicon wafer are becoming increasingly severe. Although it can be expected that both the flatness and the surface roughness can be improved to some extent by optimizing the relative speed, there is a limit.

  Accordingly, an object of the present invention is to provide a single wafer single-side polishing method for a silicon wafer that can suppress an increase in outer peripheral flatness as compared with the conventional one while reducing the surface roughness of the silicon wafer.

  The inventor has intensively studied how to solve the above problems. The inventor has paid attention to a change in the surface roughness in the single-wafer single-side polishing method and a change with time in an increase in the outer flatness. Although the influence of the retainer fluid pressure on the outer peripheral flatness due to the relative speed is as described above, the influence of the relative speed on the surface roughness over time and the influence on the outer flatness over time are different. We focused on the great differences. In other words, when the single-side polishing is started, the surface roughness decreases rapidly, and as the polishing amount increases, the reduction effect is saturated, while the outer peripheral flatness deteriorates in proportion to the polishing amount. The inventor found out.

  Conventionally, in the single-wafer single-side polishing method, the polishing time is relatively short compared to other polishing processes, and therefore the relative speed between the center of the silicon wafer and the polishing cloth is constant during polishing. However, the inventor changed the relative speed in the single-wafer single-side polishing method and increased the relative speed after the change, thereby obtaining the effect of reducing the surface roughness due to the high-speed relative speed after the change, It has been found that an increase in the outer peripheral flatness due to a high relative speed can be suppressed as compared with the prior art, and the present invention has been completed. That is, the gist configuration of the present invention is as follows.

(1) A silicon wafer is held by a polishing head having a retainer ring so that one side of the silicon wafer protrudes from a lower end of the retainer ring, and a polishing cloth is adhered while rotating the silicon wafer by the polishing head. A single wafer single-side polishing method for a silicon wafer in which a polishing liquid is supplied onto the surface of the polishing cloth while pressing the one surface of the silicon wafer against a rotating surface plate to polish the one surface of the silicon wafer. ,
Single-sided silicon wafer, wherein the relative speed between the center position of the silicon wafer and the rotating platen is changed at least once, and the relative speed is increased each time the relative speed is changed. Polishing method.

  In the present specification, the relative speed between the center position of the silicon wafer and the rotating surface plate is the magnitude of the speed in the tangential direction of the locus drawn by the silicon wafer center when the silicon wafer being polished is viewed in plan. Define as pointing. 1-3 will be described in detail by way of example. 1 to 3, the silicon wafer 10 rotates (rotates) counterclockwise by the rotation of the polishing head 120. Further, with the rotation of the polishing cloth 150 affixed on the rotating surface plate 140, the center position of the silicon wafer 10 rotates counterclockwise around the center position O of the rotating surface plate 140, and the locus T is drawn. In this case, the magnitude of the tangential speed of the trajectory T corresponds to the relative speed V, and the relative speed V depends on the rotational speed of the rotating surface plate 140 and the distance from the center O of the rotating surface plate 140 to the center of the silicon wafer 10. Is determined. In addition, the center position of the silicon wafer 10 may swing in the radial direction of the rotating surface plate 140 due to the movement of the polishing head 120 in the radial direction, and the relative speed V may fluctuate periodically. As V, an average value (average speed) of tangential speeds of the trajectory T is used.

(2) The single wafer polishing method for a silicon wafer according to (1), wherein the relative speed is changed only once.

(3) The single wafer of the above-mentioned (2), wherein the first relative speed before changing the relative speed is 40% or less of the second relative speed after changing the relative speed. Formula single-side polishing method.

(4) Single wafer polishing of a silicon wafer according to (3) above, wherein a polishing amount of the silicon wafer at the first relative speed is larger than a polishing amount of the silicon wafer at the second relative speed. Method.

  According to the present invention, it is possible to provide a single wafer single-side polishing method for a silicon wafer that can suppress an increase in outer peripheral flatness as compared with the conventional one while reducing the surface roughness of the silicon wafer.

It is a schematic diagram explaining the single-wafer | sheet-fed single-side polishing method of the silicon wafer by a prior art. It is a schematic diagram explaining the relationship between the retainer ring of the polishing head and the polishing liquid in the conventional single-wafer single-side polishing method. It is a schematic diagram for demonstrating the relative speed in this invention. It is a conceptual diagram explaining the influence on surface roughness and outer periphery flatness accompanying the change of the relative speed according to this invention. In Experimental example 1, it is a graph which shows the surface roughness and outer periphery flatness with respect to polishing amount.

(Single-side polishing method)
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the single wafer single-side polishing method for a silicon wafer 10 according to an embodiment of the present invention, as shown in FIGS. 1 and 2, the silicon wafer 10 is held by a polishing head 120 having a retainer ring 124, and one side ( Hereinafter, the “surface to be polished” is projected from the lower end of the retainer ring 124 and the silicon wafer 10 is rotated by the polishing head 120 while the surface to be polished of the silicon wafer 10 is rotated on the rotating surface plate 140 to which the polishing cloth 150 is attached. While pressing, the polishing liquid 170 is supplied onto the surface of the polishing pad 150 to polish the surface to be polished of the silicon wafer 10. Then, the relative speed between the center position of the silicon wafer 10 and the rotating surface plate 140 is changed at least once, and the relative speed is increased each time the relative speed is changed. In FIG. 1, the polishing head 120 and the rotating surface plate 140 are rotated in the same direction (counterclockwise), but they may be rotated in different directions.

  Hereinafter, a preferred embodiment of the present invention will be described in more detail using an embodiment in which the relative speed is changed only once. For convenience of explanation, polishing at the first relative speed (relative speed at the initial stage of polishing) before changing the relative speed is referred to as a first polishing step, and polishing at the second relative speed after changing the relative speed is second. This is called a polishing process. Each of the first polishing step and the second polishing step can be performed by a general single-side polishing apparatus. In the present preferred embodiment, it is important to change the first relative speed in the first polishing step to the second relative speed in the second polishing step and increase the second relative speed more than the first relative speed. It is. It is possible to increase the relative speed by a general method such as increasing the rotational speed of the rotary platen 140 or increasing the distance of the polishing head 120 from the center of the rotary platen 140.

Now, the technical significance of increasing the above-described relative speed will be described with reference to FIG. As described above, according to the study of the present inventor, when single-side polishing is started under a predetermined relative speed, the surface roughness starts to decrease rapidly, but the reduction effect is saturated as the polishing amount increases ( The broken line in FIG. 4 was found. On the other hand, it has also been found that the outer flatness increases almost in proportion to the polishing amount (flatness deteriorates). Also, the higher the relative speed, the higher the effect of reducing the surface roughness, but the faster the peripheral flatness increases. Therefore, as shown by the solid line in FIG. 4, when starting single-side polishing, the relative speed is set to a relatively low relative speed V _L, and then the relative speed is changed to a relatively high relative speed V _H. By doing so, it is possible to obtain a reduced surface roughness due to the relative speed V _H that cannot be obtained at the relative speed V _L. On the other hand, the outer peripheral flatness, because until you change the relative speed can be increased suppression of the outer peripheral flatness by polishing by the relative velocity V _L, than was polished only at a relative speed V _H, the outer peripheral flatness The increase can be suppressed.

Note that, when polishing is performed under a constant relative speed, the effect of reducing the surface roughness is saturated, so that there is a limit to the surface roughness that can be obtained with respect to the magnitude of the relative speed. Therefore, even when the relative speed is changed to the relatively high relative speed V _H when the single-side polishing is started and then the relative speed is changed to the relatively low relative speed V _L , one point in FIG. As indicated by the chain line, the surface roughness is not improved. If the relative speed V _H is changed to the relative speed V _L , it can be said that it is preferable to stop the polishing without changing the relative speed in consideration of the increase in the outer peripheral flatness.

  As described above, in this embodiment, the relative speed is changed and the relative speed is increased, so that silicon that can suppress the increase in the outer peripheral flatness while reducing the surface roughness of the silicon wafer as compared with the conventional silicon. A single wafer single side polishing method of a wafer can be provided.

  Here, it is preferable that the first relative speed before changing the relative speed is 40% or less of the second relative speed after changing the relative speed. By restricting the first relative speed to this condition, it is possible to enjoy the effect of improving the surface roughness due to the second relative speed while significantly suppressing the increase in the outer peripheral flatness as compared with the conventional case.

  In this case, the polishing amount of the silicon wafer at the first relative speed is preferably larger than the polishing amount of the silicon wafer at the second relative speed. By doing so, after the relative speed is changed, the surface roughness is rapidly reduced by the second relative speed, and the increase in the outer peripheral flatness due to the second relative speed can be minimized.

  So far, the description has been made using a preferred embodiment in which the relative speed is changed only once. Even if the relative speed is changed a plurality of times and the relative speed is changed, even if the relative speed is increased, the above-described effect of improving the surface roughness and the effect of suppressing the increase in the outer peripheral flatness by increasing the relative speed are obtained. It is understood that this is done. However, if the change is made a plurality of times, it is necessary to increase the relative speed or to decrease the first relative speed each time the change is made. In the former case, if the speed is increased indefinitely, the hydroplane phenomenon will occur, so it is necessary to increase the pressure to avoid that condition, and the polishing cloth 150 acting on the peripheral edge of the silicon wafer 10 As the surface pressure stress increases, the amount of roll-off at the edge portion increases. In the latter case, the polishing time is lowered due to the lowering of the speed, and the polishing time becomes longer and the productivity is lowered. For this reason, it is preferable to change the relative speed once.

  In the single-wafer single-side polishing method according to the present embodiment, the surface roughness of the silicon wafer is changed by changing only the relative speed without changing the type of polishing cloth, the abrasive grain size and the alkali concentration in the polishing liquid, and the like. The increase in the outer peripheral flatness can be suppressed as compared with the conventional one while reducing the thickness. Therefore, it is clearly distinguished from a single-side polishing method performed in multiple stages, which involves changing the polishing liquid. However, after the single-wafer single-side polishing method according to the present embodiment is performed, it is not excluded to change the polishing liquid or the like to perform single-side polishing, and cleaning with pure water or the like may be performed after polishing. Of course it is understood.

  Hereinafter, specific embodiments according to the present embodiment will be described in more detail.

  The single-wafer single-side polishing method according to the present embodiment is particularly suitable for use in final polishing in which single-side polishing is performed using a relatively soft polishing cloth such as a suede material, but the type of polishing cloth is not limited at all.

  In the present embodiment, the relative speed is not limited, but the final relative speed is preferably 200 m / min or less, and more preferably 100 m / min or less.

Further, the polishing load to the silicon wafer 10 is preferably set to 400 gf / cm ² or less, and more preferably to 300 gf / cm ² or less.

  As the polishing head 120, a general one used in a single-side polishing apparatus can be used, and the chucking method of the backing plate 122 is arbitrary, such as an adsorption method using a surface tension with a liquid such as water and a vacuum chuck method. Further, as described above, the attachment method of the retainer ring 124 to the polishing head 120 is arbitrary.

  Further, the type of the polishing liquid 170 is not particularly limited, and for example, an alkaline aqueous solution containing free abrasive grains or an alkaline aqueous solution containing no free abrasive grains can be used.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail using an Example, this invention is not limited to a following example at all.

[Experimental Example 1]
A silicon wafer having a diameter of 300 mm is prepared, a polishing cloth made of suede is placed on the surface of the surface plate, and an alkaline polishing liquid is supplied as the polishing liquid while using a single wafer single-side polishing apparatus according to FIGS. Single-wafer single-side polishing was performed. The rotating direction of the polishing head and the rotating surface plate was the same direction. The pressing force when pressing the silicon wafer against the rotating platen is 200 gf / cm ² , the total polishing amount is set to 1 μm, the initial relative speed is 18.8 m / min, and the polishing amount is 0.6 μm. In the stage, only the rotational speed of the rotating platen was increased and the relative speed was increased to 47 m / min.

  Under the above polishing conditions, changes in the surface roughness and peripheral flatness of the silicon wafer until the polishing amount reached 1 μm were observed. That is, the polishing was terminated when the polishing time for obtaining a predetermined polishing amount was reached, and the polishing amount, surface roughness, and outer peripheral flatness in that state were measured as follows. The relationship between the polishing amount and the polishing time was determined in advance.

<Measurement of surface roughness>
In the measurement of the surface roughness, MPS manufactured by Chapman was used, and the measurement conditions were as follows: HighPass Filter 80 μm, measurement item: RMS (root mean square height).

<Measurement of outer flatness>
In the measurement of the outer flatness, Wafer Sight 1 manufactured by KLA-Tencor was used, and the measurement condition was Edge Exclusion 1 mm, and the measurement item was ESFQR Max. The graph of FIG. 5 shows the surface roughness (Å) and the maximum value (nm) of ESFQR at each polishing level.

  Note that ESFQR (Edge flatness metric, Sector based, Front surface referenced, least sQuares fit reference plane, Range of the data within sector) is an index indicating the flatness of the wafer as defined in the SEMI standard. The absolute value of the maximum displacement from the reference plane obtained by the least square method for the wafer thickness of each area of the sector (72 mm in the circumferential direction within the range of 30 mm from the outer periphery of the wafer) formed in the peripheral area of It is obtained by calculating the sum. In addition, it means that the flatness of a wafer is so favorable that the value of ESFQR is small.

  From FIG. 5, immediately before the relative speed was increased, the effect of reducing the surface roughness was becoming saturated, but it was confirmed that the surface roughness could be further reduced by increasing the relative speed. It was also confirmed that the increase in the outer peripheral flatness was faster (the deterioration of the flatness was faster) at a higher speed than at a lower relative speed.

[Experiment 2]
Single wafer polishing of a silicon wafer was performed in the same manner as in Experimental Example 1 except that the conditions for changing the relative speed were as shown in Table 1 below. That is, the total polishing amount was set to 1 μm, and when the polishing amount reached 0.6 μm, the relative speeds as shown in Table 1 were changed in Invention Examples 1 to 4. On the other hand, the relative speed was not changed in Conventional Examples 1 and 2. Further, the measurement conditions were the same as in Experimental Example 1, and the flatness and surface roughness of the outer circumferences of Invention Examples 1 to 4 and Conventional Examples 1 and 2 after 1 μm polishing was measured. The measurement results are shown in Table 1 below together with the conditions for changing the relative speed.

  From the above results, any of Invention Examples 1 to 4 can obtain the outer peripheral flatness better than that of Conventional Example 2, and the surface roughness better than that of Conventional Example 1 can be obtained. I was able to confirm. In particular, in Invention Examples 3 and 4 in which the relative speed before changing the relative speed is 40% or less of the changed relative speed, the outer periphery flatness better than that of Conventional Examples 1 and 2 is obtained. On the other hand, it was confirmed that the surface roughness could be greatly reduced, and it was confirmed that both good outer peripheral flatness and good surface roughness could be achieved.

  According to the present invention, it is possible to provide a single wafer single-side polishing method for a silicon wafer that can suppress an increase in outer peripheral flatness while reducing the surface roughness of the silicon wafer. Useful.

DESCRIPTION OF SYMBOLS 10 Silicon wafer 100 Single-side polish apparatus 120 Polishing head 122 Backing plate 124 Retainer ring 140 Rotating surface plate 150 Polishing cloth 160 Polishing liquid supply means 170 Polishing liquid O Center of rotating surface plate T Trajectory of silicon wafer center V Relative speed

Claims (1)

A rotating surface plate to which a polishing cloth is stuck while holding the silicon wafer by a polishing head having a retainer ring, causing one side of the silicon wafer to protrude from the lower end of the retainer ring, and rotating the silicon wafer by the polishing head. While pressing the one side of the silicon wafer, supplying a polishing liquid onto the surface of the polishing cloth, a single wafer single-side polishing method for a silicon wafer for polishing the one side of the silicon wafer,
Changing the relative speed between the center position of the silicon wafer and the rotating surface plate only once, when changing the relative speed , maintaining the polishing load while increasing the relative speed ,
The first relative speed before changing the relative speed is 40% or less of the second relative speed after changing the relative speed;
A single wafer single-side polishing method for a silicon wafer , wherein a polishing amount of the silicon wafer at the first relative speed is larger than a polishing amount of the silicon wafer at the second relative speed .

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