JP2006179593A - Method of cleaning and drying semiconductor wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of cleaning and drying a semiconductor wafer capable of preventing abrasive grains for polishing from adhering to a polished surface and of roughening of the polished surface caused by adsorption of an alkali component in atmospheric gas around a membrane of super pure water remaining on the polished surface after drying a wafer. <P>SOLUTION: The silicon wafer W after polishing undergoes after-polishing cleaning by ultra pure water containing a surface active agent, and the polished surface, after being finished as hydrophilic, is rinsed with ultra pure water just before drying. Since the wafer is dried thereafter, it is possible to prevent free abrasive grains for polishing from depositing on the polished surface. Additionally, it is possible to prevent the roughening of the polished surface caused by adsorption of any alkali component contained in surrounding atmospheric gas into the membrane of a cleaning solution on the polished surface after drying. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for cleaning and drying a semiconductor wafer, and more particularly, to a method for cleaning and drying a semiconductor wafer that has few particles on the polishing surface and prevents the polishing surface from being roughened due to adhesion of an alkali component.

The final polished silicon wafer is cleaned. As one type of cleaning after polishing, a method called “water polishing” is known. Immediately after the final polishing by the polishing apparatus, the polishing apparatus is operated by rinsing the polishing surface of the silicon wafer by operating the polishing apparatus while supplying ultrapure water on the polishing cloth instead of the polishing liquid, and the polishing liquid adhered to the polishing surface. To wash away.
Conventionally, for example, Patent Document 1 is known as a method of cleaning and drying a silicon wafer using water polishing. In Patent Document 1, first, a cleaning liquid containing a surfactant is supplied onto a polishing cloth continuously with water polishing using a cleaning liquid, and the polishing apparatus is similarly operated to rinse the polishing surface of the silicon wafer. Immediately thereafter, as shown in FIG. 10, the silicon wafer W is transported to the spin drying unit 100 and spin dried.

The spin drying unit 100 has a large water receiving tank 101. Four wafer holding plates 102 having a circular shape in plan view are arranged on the bottom of the water receiving tank 101 so as to be rotatable about a vertical rotation axis. A carrier plate 103 is detachably mounted on the upper surface of each wafer holding plate 102. Each wafer holding plate 102 is rotated at a high speed by four rotating motors 104 disposed below the water receiving tank 101.
By rotating each wafer holding plate 102 by each rotation motor 104, the four silicon wafers W adhered to the corresponding carrier plate 103 are rotated at high speed in a horizontal plane. Therefore, moisture attached to the polished surface of each silicon wafer W is blown away by centrifugal force, and each polished surface is dried in a short time. After drying, each carrier plate 103 is sequentially transferred to the wafer peeling stage S, where each silicon wafer W is peeled from the corresponding carrier plate 103 by the peeling blade 105 (FIG. 11).

According to Patent Document 1, the polished surface of the silicon wafer W to be dried becomes a hydrophilic surface, and then the silicon wafer W is spin-dried as it is without scrubbing the hydrophilic polished surface. As a result, scrubbing makes it difficult for particles to adhere to the polished surface as compared to the conventional method in which the polished surface of the wafer W becomes a hydrophobic surface.
JP 2003-109931 A

  Thus, in patent document 1, it has the process order of drying the silicon wafer W immediately after the water polishing using the washing | cleaning liquid containing surfactant. That is, there is no special process other than the process of transporting the silicon wafer W between the water polishing process using a surfactant and the spin drying process. This is because in Patent Document 1, the effect of the surfactant (hydrophilicity of the polished surface of the silicon wafer W) corresponding to the amount added to the cleaning liquid is retained as much as possible, and the subsequent spin drying is performed on the wafer W. This is to comply with the gist of Patent Document 1.

  However, when spin drying is performed immediately after water polishing with a cleaning liquid containing a surfactant, particularly when the concentration of the surfactant is as high as 5 to 10% by weight described in the specification of Patent Document 1. A small amount of free abrasive grains (such as silica particles) a that could not be removed by water polishing easily remain on the polished surface of the silicon wafer W after spin drying (FIG. 12). In particular, when free abrasive grains a are present in a thin portion of the cleaning liquid film 106 formed on the polished surface of the silicon wafer W after spin drying, the high concentration of surfactant acts as an adhesive. As a result, the loose abrasive grains a are fixed to the polished surface. As a result, the number of particles on the polished surface increased.

Further, when the cleaning liquid containing the surfactant having a high concentration and high viscosity is spin-dried, a thick cleaning liquid film 106 appears on most of the polished surface of the wafer W. Therefore, the alkali component contained in the atmospheric gas in the polishing chamber is absorbed by the thick cleaning liquid film 106 and erodes the surface layer on the polishing surface side of the silicon wafer W. b was also generated (FIG. 13).
Therefore, for example, it is conceivable to keep the concentration of the surfactant added to the cleaning liquid in advance low. However, if the surfactant concentration is reduced in advance as described above, external particles may newly adhere to the polishing surface or transfer to the polishing surface while the water-polished silicon wafer W is transported to the spin drying process. There is a risk of heavy metal contamination.

Therefore, as a result of diligent research, the inventor does not add a low-concentration surfactant to the cleaning solution in advance, but rinses the polished surface of the wafer with ultrapure water (superpure water rinse) immediately before drying. By doing so, it was found that all the problems described above were eliminated, and the present invention was completed.
The present invention can prevent adhesion of free abrasive grains for polishing to the polishing surface of a semiconductor wafer, and after drying the wafer, the ultrapure water film remaining on the polishing surface has an alkaline component in the surrounding atmospheric gas. It is an object of the present invention to provide a method for cleaning and drying a semiconductor wafer, which can prevent the polishing surface of the wafer from being generated by adsorbing water.

  According to the first aspect of the present invention, the polishing surface of the semiconductor wafer immediately after the surface polishing is cleaned with a cleaning liquid containing a surfactant, the post-polishing cleaning step, and the post-polishing cleaning step. A method for cleaning and drying a semiconductor wafer comprising a drying step for drying, wherein the semiconductor wafer is provided with an ultrapure water rinse step for rinsing the polished surface of the semiconductor wafer with ultrapure water immediately before the drying step. is there.

  According to the first aspect of the present invention, the surface-polished semiconductor wafer is cleaned with the cleaning liquid containing the surfactant. Thereby, the polished surface of the semiconductor wafer to be dried becomes a hydrophilic surface. Thereafter, the semiconductor wafer is dried while maintaining the hydrophilicity of the polished surface. However, the polishing surface is rinsed with ultrapure water immediately before the drying step. As a result, even after a small amount of free abrasive grains in the polishing liquid remains on the polishing surface of the semiconductor wafer after the post-polishing cleaning step, it can be removed by the ultrapure water rinsing step.

  Moreover, when the semiconductor wafer is rinsed with ultrapure water, the surfactant-containing cleaning liquid that forms a film on the polished surface is reduced in concentration and the viscosity decreases. Therefore, if the rinsed semiconductor wafer is dried (not completely dried), the film of the cleaning liquid on the polished surface becomes thin. As a result, after the drying process, the amount of the alkali component contained in the surrounding atmospheric gas absorbed into the cleaning liquid film is reduced. Therefore, it is possible to prevent surface roughness that occurs when the alkali component in the film of the cleaning liquid is adsorbed on the polished surface of the semiconductor wafer.

Examples of the semiconductor wafer include a silicon wafer and a gallium arsenide wafer. The diameter of the semiconductor wafer is not limited. For example, an 8-inch wafer or a 300 mm wafer may be used.
The semiconductor wafer should just be a thing by which the surface of the wafer used as a device formation surface was grind | polished at least. That is, a wafer whose surface is polished or a wafer whose front and back surfaces are polished may be used. Among these, when manufacturing a surface-polished (single-sided polished) wafer in which only the surface is mirrored, for example, a single-sided polishing apparatus can be employed. On the other hand, when manufacturing a double-side polished wafer, this single-side polishing apparatus may be adopted, or a double-side polishing apparatus such as a planetary gear system may be adopted.

The post-polishing cleaning step refers to the water polishing step described above. This may be cleaning using a cleaning liquid containing a surfactant from the beginning to the end of the cleaning performed subsequent to the polishing. However, a part of the cleaning process including the end of the cleaning may be cleaning using a cleaning liquid containing a surfactant. The other part of the cleaning process is cleaning with ultrapure water.
Examples of the cleaning liquid include ultrapure water and ultrapure water containing a surfactant. The kind of surfactant is not limited. However, nonionic surfactants are preferred. Alternatively, a water-soluble polymer resin may be used.
The temperature of the cleaning liquid containing the surfactant is, for example, 18 to 20 ° C.
The cleaning time for post-polishing cleaning is not limited. For example, it is 1 to 3 minutes, preferably 1 to 1.5 minutes.

The concentration of the surfactant is, for example, 1 to 10% by weight, preferably 2 to 5% by weight. If it is less than 1% by weight, the entire polished surface of the semiconductor wafer cannot be completely hydrophilized. On the other hand, when the amount exceeds 10% by weight, the surfactant component remains on the polishing cloth, the frictional resistance is lowered, and the polishing itself is affected.
The supply amount of the cleaning liquid containing the surfactant is appropriately changed depending on the size (caliber) of the semiconductor wafer to be processed. For example, 1 to 2 liters / minute.
As a method for drying the semiconductor wafer, for example, spin drying or pulling drying can be employed. In the case of spin drying, a spin drying apparatus that blows away moisture adhering to the surface of the wafer using a centrifugal force generated by high-speed rotation is used.

The ultrapure water rinsing process is performed immediately before the semiconductor wafer drying process. Therefore, for example, an ultrapure water rinsing device that supplies ultrapure water onto the polishing surface of the semiconductor wafer via a rinse nozzle may be incorporated in the drying device. Or you may arrange | position the ultrapure water rinse apparatus outside a drying apparatus.
The supply amount of ultrapure water is appropriately changed according to various conditions such as the concentration of the surfactant in the cleaning liquid containing the surfactant and the size of the semiconductor wafer. For example, 0.5 to 2 liters / minute. If it is less than 0.5 liter / minute, coating unevenness occurs. On the other hand, if it exceeds 2 liters / minute, the surfactant will flow out of the wafer surface too much and the coating effect will be reduced, or the amount of pure water used will be increased, which will be uneconomical.
The operating temperature of ultrapure water is, for example, 18 to 20 ° C.

  The rinsing time of the polished surface of the semiconductor wafer with ultrapure water is appropriately changed according to various conditions such as the size of the semiconductor wafer. For example, it is 1 to 2 minutes. Less than 1 minute will result in insufficient rinsing. Further, when the time exceeds 2 minutes, particles in the outside air atmosphere reattach.

The invention according to claim 2 is the method for cleaning and drying a semiconductor wafer according to claim 1, wherein the surfactant is a nonionic surfactant.
As the nonionic surfactant, for example, “Drynon” manufactured by Nikka Seiko Co., Ltd. can be employed.

The invention according to claim 3 is the method for cleaning and drying a semiconductor wafer according to claim 1 or 2, wherein the drying is spin drying.
The drying time by spin drying is shortened by about 20 to 25% compared to the case where the ultrapure water rinsing step is not performed because the concentration of the surfactant in the ultrapure water is low (low viscosity).

  According to the present invention, a polished semiconductor wafer is subjected to a post-polishing cleaning step with a cleaning liquid containing a surfactant, the polished surface of the semiconductor wafer is made hydrophilic, and the polished surface is ultrapure immediately before the drying step. Rinse with water. Thereafter, since the semiconductor wafer is dried, it is possible to prevent free abrasive grains (particles) for polishing from adhering to the polishing surface. In addition, it is possible to prevent the polishing surface from being roughened by adsorbing alkali components contained in the surrounding atmospheric gas into the cleaning liquid film on the polishing surface after the drying step.

  Examples of the present invention will be specifically described below.

Embodiment 1 of the present invention will be described below with reference to the drawings.
A single crystal silicon ingot having a diameter of about 200 mm pulled up by the CZ method is sliced into a number of silicon wafers (semiconductor wafers) having a diameter of 8 inches and a thickness of 860 μm in a slicing step. In the subsequent chamfering process, the obtained silicon wafer is chamfered on the outer periphery. Here, a # 800 to # 1500 metal bond chamfering grindstone is used.

The chamfered silicon wafer is then transferred to a lapping process. Here, the silicon wafer is sandwiched between a pair of upper and lower parallel lapping plates, and while supplying a lapping solution containing loose abrasive grains, the front and back surfaces of the wafer are lapped to increase parallelism. The wrapping amount is 30 μm on one side of the silicon wafer and 60 μm on both sides.
Next, the silicon wafer is etched using a mixed acid solution (35 ° C.) of hydrofluoric acid and nitric acid. The etching amount is 30 μm.
Thereafter, the surface of the silicon wafer is primarily polished. For the primary polishing, a polishing cloth for primary polishing (made by Nitta Haas Co., Ltd., trade name: SuBa800) is used. As the polishing liquid, an alkaline solution in which 1.5 to 2% by weight of 0.05 μm silica particles is mixed is used. The polishing time here is 5 to 10 minutes, and the polishing amount is 5 μm.

  Then, the surface of the silicon wafer subjected to the primary polishing is subjected to secondary polishing. For secondary polishing, a polishing cloth for secondary polishing (product name: SuBa600, manufactured by Nitta Haas Co., Ltd.) is used. As the polishing liquid, an alkaline solution in which 1.5 to 2% by weight of 0.05 μm silica particles is mixed is used. The secondary polishing time is 5 to 10 minutes, and the polishing amount is 5 μm.

Subsequently, the surface of the silicon wafer subjected to the secondary polishing is finish-polished.
Here, a finish polishing apparatus 10 as shown in FIG. 1 is used. The finish polishing apparatus 10 includes a polishing surface plate 12 having a polishing cloth 11 for finishing polishing spread on the upper surface, and a carrier plate having a silicon wafer W adhered to the lower surface, facing the upper surface of the polishing surface plate 12. And two polishing heads 14 to which 13 is attached, respectively. The final polishing time here is 5 minutes, and the polishing amount of each silicon wafer W is 0.1 μm.

As the polishing cloth 11 for finish polishing, a product name Seagull manufactured by Toray Co-tex company is used. As the polishing liquid (slurry), an alkaline solution in which 0.3 to 38 wt% of 32-38 μm silica particles are mixed is used.
The polishing cloth 11 is adhered to the upper surface of the polishing surface plate 12 with a double-sided tape. The polishing surface plate 12 is placed on the bottom plate of the large-diameter tray 12a.
Disc-shaped carrier plates 13 are detachably attached to the lower surfaces of both polishing heads 14, respectively. Four silicon wafers W are attached to the lower surfaces of both carrier plates 13 by wax.
During polishing, a polishing liquid for finish polishing is supplied onto the polishing cloth 11 through one nozzle 15, and each silicon wafer W is placed on the surface (polishing working surface) of the polishing cloth 11 with a predetermined relative rotational speed. And are brought into sliding contact with a predetermined polishing pressure. Thereby, the surface of each silicon wafer W is mirror-polished.

Next, each silicon wafer W obtained is polished by water using the polishing apparatus 10 while supplying ultrapure water in place of the polishing liquid onto the polishing pad 11 through the nozzle 15 (cleaning step after polishing). , FIG. 2). The supply amount of ultrapure water is 1 to 3 liters / minute. The total time for water polishing is 1 minute. By this water polishing, the polishing liquid remaining on the polishing surface after the final polishing is washed away. Of the water polishing, the time for water polishing with only ultrapure water is 50 seconds.
Next, while supplying ultrapure water (cleaning liquid) containing 3 to 5% by weight of a surfactant onto the polishing pad 11, another water polishing is performed on each silicon wafer W for only 10 seconds (FIG. 2). . This is the final cleaning in the post-polishing cleaning step. As the surfactant, non-ionic “Dryon” manufactured by Nikka Seiko Co., Ltd. is used. Thus, by polishing the polished surface with ultrapure water containing a surfactant, each polished surface becomes a hydrophilic surface.

  Next, the carrier plates 13 are separated from the lower surfaces of the two polishing heads 14, respectively. Thereafter, the arm 16a of the transfer robot 16 is operated to hold the carrier plate 13 (FIG. 3). Specifically, the upper surface of the carrier plate 13 (the surface opposite to the bonding side of the silicon wafer W) is vacuum-sucked by the suction pad 16b provided at the tip of the arm 16a. At this time, the suction port formed in the suction pad 16b and the suction part of the negative pressure generator provided outside are in communication with each other via the arm 16a and the suction pipe. Then, the arm 16a is rotated around the axis, and the carrier plate 13 is reversed. Subsequently, the transfer robot 16 is operated to transfer a large number of carrier plates 13 to a spin drying unit (spin drying apparatus) 17 that can rotate at a high speed.

  The spin drying unit 17 has a large water receiving tank 18 (FIG. 4). Four circular wafer holding plates 19 are disposed on the bottom of the water receiving tank 18 so as to be rotatable in plan view. The carrier plate 13 is detachably mounted on the top of each wafer holding plate 19. Each wafer holding plate 19 is provided so as to be rotated at high speed by four rotary motors 20 disposed on the back surface of the bottom plate of the water receiving tank 18. Further, an inverted L-shaped rinse for supplying ultrapure water used in the ultrapure water rinsing process to the polishing surface of each silicon wafer W on the portion between the wafer holding plates 19 of the bottom plate of the water receiving tank 18. Nozzles 21 are erected. From each rinse nozzle 21, a rinse solution of ultrapure water is supplied to the upper surface of the corresponding wafer holding plate 19.

  When each carrier plate 13 is transferred to the corresponding wafer holding plate 19 by the arm operation of the transfer robot 16, ultrapure water from each rinse nozzle 21 is directed to the silicon wafer W at 3 liters / minute for 1 minute. Are blown out. At this time, each wafer holding plate 19 is rotated at a low speed of 30 rpm by a corresponding rotary motor 20. As a result, in each carrier plate 13, the polished surfaces of all the bonded silicon wafers W are uniformly rinsed by the ultrapure water that has flowed out from the corresponding one rinse nozzle 21. Therefore, even when a small amount of free abrasive grains in the polishing liquid remain on each polished surface after water polishing, the free abrasive grains can be removed almost completely from each polished surface. Moreover, the surfactant concentration in the ultrapure water containing the surfactant that had formed the cleaning liquid film c on the polished surface of each silicon wafer W by rinsing with ultrapure water immediately before the drying decreased respectively. Low viscosity).

Thereafter, the silicon wafers W are simultaneously spin-dried. At the time of drying, the back surface of the silicon wafer W whose polished surface is maintained hydrophilic by the final cleaning is vacuum-adsorbed on the wafer holding plate 19 via the carrier plate 13. Then, when the wafer holding plate 19 is rotated at a high speed by the rotary motor 20, the moisture adhering to the polishing surface of the silicon wafer W is blown off by centrifugal force, and the polishing surface is dried within a short time. The rotation speed of the wafer holding plate 19 is 600 rpm. The drying time is 1 minute.
Next, each dried silicon wafer W is transferred onto the wafer peeling stage S, where it is peeled off from the corresponding carrier plate 13 by the peeling blade 22 (FIG. 5).
The peeled silicon wafer W is then SC-1 cleaned with an SC-1 cleaning liquid. Then, the silicon wafer W is sequentially subjected to flatness measurement, surface inspection, finish cleaning (HF / HCl cleaning after SC-1 cleaning), and packaging. The silicon wafer W thus commercialized is then shipped to a device factory or the like.

  Thus, by cleaning the surface-polished silicon wafer W with ultrapure water containing a surfactant, the polished surface of the silicon wafer W to be dried becomes a hydrophilic surface. Thereafter, the silicon wafer W is dried while maintaining the hydrophilicity of the polished surface. However, the polishing surface is rinsed with ultrapure water immediately before the drying step. As a result, even if a small amount of loose abrasive grains in the polishing liquid remain on the polished surface of the silicon wafer W after performing the cleaning process after polishing, the ultrapure water rinse process can remove it almost completely. Yes (Fig. 6).

  Moreover, when the silicon wafer W is rinsed with ultrapure water, the concentration of the ultrapure water containing the surfactant that forms the film c on the polished surface is reduced and the viscosity thereof is lowered. Therefore, if the rinsed silicon wafer W is spin-dried, the cleaning water film (ultra pure water film) c on the polished surface becomes thin (FIG. 7). As a result, after the drying process, the amount of the alkali component contained in the surrounding atmospheric gas is absorbed in the film c of the cleaning liquid is reduced. Therefore, in the conventional case, it is possible to prevent the surface roughness (FIG. 13) that occurs due to the alkali component in the cleaning liquid film c adsorbed on the polished surface of the silicon wafer W (FIG. 7). Moreover, the drying time by spin drying can be shortened by about 20 to 25% compared to the case where the ultrapure water rinse is not performed because the concentration of the surfactant in the ultrapure water is low (low viscosity).

Here, referring to FIG. 8 and FIG. 9, the generation distribution (FIG. 8) of particles P on the polished surface of the silicon wafer W obtained by the conventional method of spin drying after cleaning (water polishing) after polishing, and the spin The generation distribution of particles P (FIG. 9) on the polished surface of the silicon wafer W obtained by the method of Example 1 which rinses with ultrapure water immediately before drying is compared.
As is apparent from FIGS. 8 and 9, the number of particles P generated by the method of Example 1 was significantly reduced by rinsing with ultrapure water immediately before spin drying as compared with the conventional method.

It is a front view which shows the final polishing process in the washing | cleaning drying method of the semiconductor wafer which concerns on Example 1 of this invention. It is a front view which shows the washing | cleaning process after grinding | polishing in the washing | cleaning drying method of the semiconductor wafer which concerns on Example 1 of this invention. It is a front view which shows the conveyance start state of the carrier plate which the washing | cleaning after grinding | polishing in the washing | cleaning drying method of the semiconductor wafer concerning Example 1 of this invention was complete | finished. It is a front view which shows the ultrapure water rinse process and drying process in the washing | cleaning drying method of the semiconductor wafer which concerns on Example 1 of this invention. It is a front view which shows the peeling process of the semiconductor wafer from the carrier plate in the washing | cleaning drying method of the semiconductor wafer which concerns on Example 1 of this invention. It is an expanded sectional view which shows the semiconductor wafer just after peeling from the carrier plate in the washing | cleaning drying method of the semiconductor wafer which concerns on Example 1 of this invention. It is an expanded sectional view which shows the semiconductor wafer manufactured by the washing | cleaning drying method of the semiconductor wafer which concerns on Example 1 of this invention. It is a top view which shows the distribution state of the particle | grains which generate | occur | produced on the grinding | polishing surface of the semiconductor wafer obtained by the washing | cleaning drying method of the semiconductor wafer which concerns on the conventional means. It is a top view which shows the distribution state of the particle | grains which generate | occur | produced on the grinding | polishing surface of the semiconductor wafer obtained by the washing | cleaning drying method of the semiconductor wafer which concerns on Example 1 of this invention. It is a front view which shows the drying process in the washing | cleaning drying method of the semiconductor wafer which concerns on the conventional means. It is a front view which shows the peeling process of the semiconductor wafer from the carrier plate in the washing / drying method of the semiconductor wafer which concerns on the conventional means. It is an expanded sectional view which shows the semiconductor wafer immediately after peeling from the carrier plate in the washing | cleaning drying method of the semiconductor wafer which concerns on the conventional means. It is an expanded sectional view which shows the semiconductor wafer manufactured with the washing | cleaning drying method of the semiconductor wafer which concerns on the conventional means.

Explanation of symbols

  W Semiconductor wafer.

Claims (3)

A post-polishing cleaning step of cleaning the polished surface of the semiconductor wafer immediately after surface polishing with a cleaning liquid containing a surfactant;
In this method for cleaning and drying a semiconductor wafer comprising a drying step for drying the semiconductor wafer after performing this post-polishing cleaning step,
A method of cleaning and drying a semiconductor wafer provided with an ultrapure water rinsing step of rinsing the polished surface of the semiconductor wafer with ultrapure water immediately before the drying step.   The method for cleaning and drying a semiconductor wafer according to claim 1, wherein the surfactant is a nonionic surfactant.   The method for cleaning and drying a semiconductor wafer according to claim 1, wherein the drying is spin drying.

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