Patent Application
20120024317
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2010-168442, filed on Jul. 27, 2010; the entire contents of which are incorporated herein by reference.
Embodiments described herein relate generally to a cleaning apparatus and a cleaning method.
Conventionally, a photolithography is used in a manufacturing process of semiconductor devices. In the dimensional accuracy of a resist pattern formed on a wafer in the photolithography, an exposure amount, an exposure focus position (focus position), and the like at the time of exposure are important factors. Therefore, it is needed to realize an accurate focus position for forming a resist pattern as designed.
However, when foreign matter, dust, or the like is adhered to the back surface of a wafer at the time of exposure, the position of a light receiving surface is displaced from a focus position in an optical axis direction, i.e., defocusing occurs, so that a resist pattern is not formed as designed. For removing foreign matter or the like adhered to the surface of a wafer, a cleaning apparatus is used that removes foreign matter or the like on the surface of a wafer by using a brush. However, it is usually not performed to remove protrusions present on the back surface of a wafer.
The Chemical Mechanical Polishing (CMP) process is performed to planarize the whole surface of a wafer by grinding the whole surface. However, the CMP process uses abrasive such as slurry, so that the configuration of an apparatus and the process become complicated.
Therefore, in the cleaning apparatus and the cleaning method, a technology for efficiently removing protrusions present on the back surface of a wafer is desired.
In general, according to one embodiment, a cleaning apparatus includes a holding unit capable of holding a semiconductor wafer, a removing unit whose tip portion is harder than a constituent material of a surface layer on a back surface side of the semiconductor wafer and which is configured to clean a semiconductor-wafer back surface to be a process target surface of the semiconductor wafer held by the holding unit, and a moving mechanism that relatively moves the removing unit and the semiconductor wafer in a direction parallel to the semiconductor-wafer back surface. The removing unit grinds and removes a protrusion that is formed of a material same as the surface layer of the semiconductor-wafer back surface, by the moving mechanism relatively moving the removing unit and the semiconductor wafer in the direction parallel to the semiconductor-wafer back surface and causing the tip portion of the removing unit to come into contact with the protrusion.
The embodiments of a cleaning apparatus will be explained below in detail based on the drawings. In the drawings illustrated below, the scale of each member is different from a realistic one in some cases for easy understanding. The same thing can be said between the drawings.
The wafer holding unit 2 can hold a semiconductor wafer 10 (hereinafter, wafer 10), which is a process target substrate, by gripping the periphery of the wafer 10 with the back surface facing upward. The back surface is a surface on the opposite side of the surface of the wafer 10 on which a semiconductor device is formed. The wafer holding unit 2 grips the periphery of the side surface of the wafer 10 by a wafer gripping unit (not shown) at least at two positions.
The wafer rotation driving unit 3 horizontally rotates the wafer holding unit 2 holding the wafer 10 at a given rotation speed in a circumferential direction with the center of the wafer 10 in a plane direction as an axis. The rotation speed of the wafer 10 is appropriately set depending on the condition such as a material of a protrusion on the back surface of the wafer 10 to be a removing target and a material of brush bristles 4a. As will be described later, the sensor unit 6 provides length measurement information to the control unit 8 that controls elevation of the brush 4 to keep the distance from the back surface of the wafer 10 approximately constant. At this time, the rotation speed of the wafer 10 can be set to the rotation speed at which length measurement of the sensor unit 6 and control of the control unit 8 follow the rotation of the wafer 10 and does not necessarily need to be high speed.
In the brush 4 as a removing unit of foreign matter and protrusions on the wafer 10, a plurality of the brush bristles 4a is supported and arranged to have, for example, a columnar shape on the surface of its main body facing the wafer 10. The arrangement of the brush bristles 4a is not limited to the above-described columnar shape and various forms can be employed, such as a form in which the brush bristles 4a are arranged to have a ring shape on the surface facing the wafer 10 and a form in which the brush bristles 4a are arranged to have a line shape on the surface facing the wafer 10. The tip portions of the brush bristles 4a are formed of a material whose hardness is higher than the constituent material of the back surface of the wafer 10. Moreover, the brush bristles 4a formed of a plurality of materials can be used.
The constituent material of the back surface of the wafer 10, for example, includes a silicon film, a carbon film, an organic material film, a silicon oxide film, and a silicon nitride film. For surely removing protrusions formed of these films, the hardness of the brush bristle 4a is preferably 30 degrees or more. Moreover, a superhard brush with diamond chips can be used. The hardness in this example is a measured value by a type A durometer according to JIS K 6253 (Rubber. vulcanized or thermoplastic-Determination of hardness) or JIS K 7215 (Testing Methods for Durometer Hardness of Plastics). Moreover, when this hardness is 90 degrees or higher, the hardness can be measured by a type D durometer of the same standard.
Moreover, when the outermost-layer film of the back surface of the wafer 10 is thin, a lower-layer film under the outermost-layer film of the back surface of the wafer 10 may be present in a protrusion. In this case, it is possible to appropriately select the hardness of the brush bristles 4a, for example, for the harder material between the material of the outermost-layer film and the material of the lower-layer film thereunder of the back surface of the wafer 10.
Furthermore, in this example, the brush 4 is illustrated as the removing unit of foreign matter and protrusions on the wafer 10, however, a deburring cutter for the back surface of the wafer 10 can be used other than the brush 4. In the cutter, for example, a plurality of cutter blades is arranged on the surface facing the wafer 10 to have a shape such as a columnar shape, a ring shape, and a line shape. The tip portions of the cutter blades, which are in contact with foreign matter and protrusions on the wafer 10, are formed of a material whose hardness is higher than the constituent material of the back surface of the wafer 10. The brush bristle 4a, although hard, has some flexibility in the tip portion thereof. Therefore, the brush 4 has a responsiveness to warpage of the back surface of the wafer 10 higher than a cutter blade.
The brush driving unit 5 raises and lowers the brush 4 to a given height above the wafer 10 held by the wafer holding unit 2. Moreover, the brush driving unit 5 rotates the brush 4 at a given rotation speed and moves the brush 4 in a predetermined direction over the surface of the wafer 10 held by the wafer holding unit 2. The brush driving unit 5 can move the brush 4, for example, in a radial direction of the wafer 10 while horizontally rotating the blush 4.
The sensor unit 6 is composed of a length measurement sensor capable of measuring the distance to the wafer 10, for example, by instantly calculating the time for light such as laser to be reflected from the wafer 10. The sensor unit 6 can be raised and lowered above the wafer 10 in the height direction by being driven by the sensor driving unit 7 and can move also in a given direction in the plane direction of the wafer 10.
The control unit 8 performs control of the wafer rotation driving unit 3, the brush driving unit 5, the sensor unit 6, and the sensor driving unit 7. The cleaning-water supplying unit 9 supplies, for example, cleaning water as cleaning liquid onto the wafer 10 during the cleaning process or after the cleaning process and washes out grinding swarf generated in the cleaning process from the back surface of the wafer 10.
Next, the cleaning process by the cleaning apparatus 1 is explained with reference to
First, the wafer 10, which is a process target substrate, is held by the wafer holding unit 2 so that the back surface faces upward. As shown in
A foreign matter 21 is adhered to part of the first coating 11 of the back surface of the wafer 10. The region over the foreign matter 21 in the second coating 12 and the third coating 13 has a shape conforming to the shape of the foreign matter 21. Therefore, on the third coating 13 that is the outermost layer of the back surface of the wafer 10, a protrusion 13a is formed in the region over the foreign matter 21. In other words, the protrusion 13a is a protrusion formed of a material same as the third coating 13 that is the surface layer of the back surface of the wafer 10. In
Next, the brush 4 is arranged in the center portion of the back surface of the wafer 10 by the brush driving unit 5. The brush 4 is arranged in a state of floating by a constant separation distance t from the flat surface of the third coating 13 at the height at which the tip portions of the brush bristles 4a can come into contact with the protrusion 13a. Specifically, the brush 4 is arranged to be separated from the flat surface of the third coating 13 at the height at which the position of the tip portions of the brush bristles 4a is lower than the height of the protrusion 13a and the tip portions is not in contact with the flat surface of the third coating 13. The brush 4 is rotated by being driven by the brush driving unit 5.
Next, the wafer rotation driving unit 3 horizontally rotates the wafer holding unit 2, so that the wafer 10 held by the wafer holding unit 2 rotates. The rotation speed of the wafer 10 and the rotation speed of the brush 4 can be appropriately changed depending on the conditions such as the material of the surface layer of the back surface of the wafer 10 and the material of the brush bristles 4a. Next, as shown in
In this manner, the brush 4 horizontally moves relative to the rotating wafer 10, so that the brush bristles 4a of the brush 4 come into contact with the protrusion 13a. Consequently, the protrusion 13a is ground by the brush 4 and is removed in a state of leaving a portion with the height corresponding to the distance between the brush bristles 4a and the flat surface of the third coating 13, i.e., the thickness corresponding to the separation distance t, as shown in
Next, control of the separation distance t when warpage occurs in the wafer 10 is explained. First, the brush 4 is arranged at the position sufficiently separated from the back surface of the wafer 10 over the wafer 10 by the brush driving unit 5.
Next, the sensor unit 6 measures the distance from the sensor unit 6 to the brush 4 and the distance from the sensor unit 6 to the back surface of the wafer 10 (the third coating 13). The sensor unit 6 measures the distance from the sensor unit 6 to the brush 4 and the distance from the sensor unit 6 to the back surface of the wafer 10 (the third coating 13) in the peripheral region of the brush 4, for example, in a vertical direction. The sensor unit 6 is movable in synchronization with the brush 4 by the control unit 8 controlling the sensor driving unit 7 and can perform measurement in accordance with the movement of the brush 4. Then, the sensor unit 6 sends these length measurement information to the control unit 8.
The control unit 8 stores information on the length from the measurement reference position of the brush 4 (position of the main body of the brush 4) to the tips of the brush bristles 4a, for example, in a storing unit included in the control unit 8. The control unit 8 calculates the distance from the tips of the brush bristles 4a to the flat surface of the back surface of the wafer 10 based on this information and the length measurement information sent from the sensor unit 6. The sensor unit 6 and the control unit 8 configure a detecting unit that detects the distance from the tip portions of the brush bristles 4a to the flat surface of the back surface of the wafer 10. Then, the control unit 8 controls the height of the brush 4 so that this distance becomes appropriately the constant separation distance t excluding a portion over the protrusion 13a of the wafer 10 when performing the cleaning process by moving the brush 4 in the plane direction of the wafer 10. Consequently, the cleaning process can be performed while reflecting the warped state of the wafer 10.
The rotation speed of the wafer 10 in the case of controlling while monitoring change in the separation distance t due to the warped state of the wafer 10 in this manner is desirably a lower rotation speed. This is effective, especially, when the tendency of the warpage is uniform from the center to the periphery in the plane of the wafer 10. Moreover, the rotation speed of the wafer 10 can be increased after obtaining information on the tendency of warpage of the wafer 10 by the sensor unit 6 and the control unit 8.
Moreover, in terms of the distance to the back surface of the wafer 10 (the third coating 13) measured by the sensor unit 6, it is possible to distinguish between change in distance due to the protrusion 13a in the third coating 13 and change in distance due to warpage of the wafer 10, for example, as follows. For example, change in distance is measured at a plurality of points around the brush 4 and the average thereof or the like is calculated to distinguish between the changes. For example, when the distance to the back surface of the wafer 10 (the third coating 13) is shorter than the average value by a predetermined distance or more, it is determined that change in distance is due to the protrusion 13a. Moreover, when the distance to the back surface of the wafer 10 (the third coating 13) is longer than the average value by a predetermined range, it is determined that change in distance is due to warpage of the wafer 10.
The measurement by the sensor unit 6 described above can be performed while performing the cleaning process. Moreover, it is possible to perform the measurement by the sensor unit 6 described above in advance and store the information on warpage of the back surface of the wafer 10 in the storing unit of the control unit 8 before performing the cleaning process. In this case, the control unit 8 can control the distance from the tips of the brush bristles 4a to the back surface of the wafer 10 while reflecting the state of warpage of the wafer 10 by using the information on warpage of the wafer 10 stored in the storing unit. It is possible that a function unit related to control of the separation distance t, such as the sensor unit 6, the sensor driving unit 7, and the storing unit, is an apparatus separated from the cleaning apparatus 1.
As shown in
In the similar manner to the case of the cleaning process on the back surface of the wafer 10 described above, the cleaning process is performed on the wafer 101. In this case again, as shown in
In the manufacturing process of semiconductor devices, the photolithography process is performed, for example, to form a patterned film on a wafer. The photolithography process is largely classified into a photoresist-film forming process of applying a photosensitive film on a film, which is deposited on a wafer and is to be patterned, an exposure process of exposing a pattern on the photoresist film, and a developing process of removing part of the photoresist film by developing the exposed photoresist film and thereby forming a resist pattern. In such a photolithography process, in order to form a resist pattern accurately as designed, especially, in the exposure process, it is necessary to project a mask pattern with no blur on a photoresist film. In other words, it is needed to realize an accurate focus position as designed.
Even if foreign matter on the surface side is removed at the time of exposure, when a protrusion due to the accumulated foreign matter formed on the back surface of a wafer or due to damage, such as scratch, on the back surface of a wafer is present, the height of the wafer deviates from a desired set height due to this protrusion. Therefore, the position of a light receiving surface is displaced from the focus position in the optical axis direction, i.e., defocusing occurs. When the defocusing occurs, a resist pattern as designed is not formed, so that another photolithography process (rework) is needed. Performing the rework results in decreasing the production efficiency. Moreover, the photolithography process uses an exposure apparatus, which is expensive, and therefore is a high-cost process. Thus, performing the rework results in increasing the production cost.
As described above, foreign matter adhered to the surface of a wafer among protrusions present on the wafer can be removed by a conventionally-used cleaning apparatus using a brush. However, on the other hand, there is a protrusion formed of a material same as a surface layer of the back surface as shown in
However, in the cleaning apparatus 1 in the present embodiment, it is possible to grind and remove a protrusion that is formed of a material same as a surface layer of the back surface of a wafer and is formed on the back surface of the wafer. Moreover, in the cleaning apparatus 1, foreign matter adhered to the back surface of a wafer can be also removed by grinding or stripping it from the back surface of the wafer. Consequently, planarization and cleaning of the back surface of a wafer can be realized.
The cleaning process of the back surface of a wafer by the cleaning apparatus 1 is performed, for example, on a wafer, which is a target to be subjected to the rework, before the exposure process, desirably, immediately before the exposure process. The exposure process is performed on a wafer whose back surface is subjected to the cleaning process by the cleaning apparatus 1, so that the effect of a minor protrusion on the back surface of a wafer can be reduced and whereby occurrence of another defocusing can be prevented. Moreover, the cleaning process by the cleaning apparatus 1 can be performed on all wafers every time before performing the exposure process in the photolithography process. Furthermore, the cleaning process by the cleaning apparatus 1 can be performed before forming a photoresist film or can be performed after forming a photoresist film.
In the above present embodiment, explanation is made for the case of using the brush 4 as the removing unit of foreign matter and protrusions on the back surface of the wafer 10 as an example, however, it is also possible to use, for example, a cutter in which a plurality of cutter blades is arranged to have a columnar shape on the surface facing the wafer 10 instead of the brush 4 and perform control of the separation distance t in the similar manner to the above.
In the cleaning apparatus 1 described above, the effect of minor protrusion and recess on the back surface of a wafer at the time of exposure can be reduced by selectively grinding and planarizing only a protruded portion instead of planarizing the whole surface-layer film of a wafer by polishing it as in the conventional CMP technology. Consequently, occurrence of the rework can be suppressed and decrease in the production efficiency and increase in the production cost can be prevented. The cleaning process by such a cleaning apparatus 1 is preferable, particularly, for immersion exposure in which an effect of defocusing at the time of exposure to the accuracy of a resist pattern is large.
Moreover, the cleaning apparatus 1 described above does not use abrasive such as slurry as in the CMP, so that a planarizing process can be easily performed by an apparatus with a simple configuration.
Furthermore, other than suppression of occurrence of defocusing in the photolithography process, the cleaning process of the back surface of a wafer by the cleaning apparatus 1 has an effect of preventing occurrence of a failure due to minor protrusion and recess on the back surface by performing the cleaning process before a process that is affected by the minor protrusion and recess on the back surface.
In the above, explanation is made for the case in which the cleaning process is performed in a state where the tip portions of the brush bristles 4a are separated from the flat surface of the back surface of the wafer 10 by approximately the constant separation distance t, however, the cleaning process of the back surface of the wafer 10 can be performed in a state where the separation distance t is zero, i.e., the tip portions of the brush bristles 4a are in contact with the flat portion of the back surface of the wafer 10. The sensor unit 6 and the control unit 8 perform control of setting the separation distance t to zero in the cleaning process of the back surface of the wafer 10. In this case again, a protrusion formed of a material same as the back surface of the wafer 10 and foreign matter formed of a material different from the back surface of the wafer 10 can be removed from the back surface of the wafer 10 and cleaning of the back surface of the wafer 10 can be performed.
Then, the control unit 8 performs control so that the pressure A becomes equal to the pressure B, for example, by using an air spring such as an air suspension on the brush driving unit 5 side. By moving the brush 4 in a state of being in contact with the back surface of the wafer 10 while performing such control, a protrusion that is formed of a material same as a surface layer of the back surface side of the wafer 10 and is formed on the back surface of the wafer 10 can be ground and removed without measuring the separation distance t as in the case of the first embodiment. Moreover, foreign matter adhered to the back surface of the wafer 10 can be ground or stripped from the back surface of the wafer 10 to be removed. Consequently, in the similar manner to the case of the first embodiment, only the protruded portion can be selectively ground to be planarized.
Next, the cleaning process of the back surface of a wafer according to the second embodiment is explained with reference to
First, the wafer 10 is held by the wafer holding unit 2 so that the back surface faces upward. As shown in
Next, the brush 4 is arranged in the center portion of the back surface of the wafer 10 by the brush driving unit 5. The brush 4 is arranged in a state where the tip portions of the brush bristles 4a are in contact with the flat surface of the third coating 13 by the brush driving unit 5, i.e., in a state where the separation distance t is zero, to apply the pressure A to the back surface of the wafer 10. Moreover, on the device surface of the wafer 10, the predetermined pressure B (constant pressure) is applied to the region facing the brush 4 via the wafer 10 by the not-shown pressurizing mechanism. At this time, in the brush driving unit 5, the pressure A is set to the pressure same as the pressure B by using an air spring (pressure A=pressure B). Then, the brush 4 rotates by being driven by the brush driving unit 5.
Next, the wafer rotation driving unit 3 horizontally rotates the wafer holding unit 2, so that the wafer 10 held by the wafer holding unit 2 rotates. Next, as shown in
As shown in
Then, when the protrusion 13a and the foreign matter 22 disappear as shown in
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-168442 | Jul 2010 | JP | national |
