JP2011119514A - Cleaning method of substrate, and cleaning device of substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cleaning method of a substrate and a cleaning device of a substrate which can suppress damage on a semiconductor device or the like formed on the surface of a substrate, and can remove foreign matter from the surface of the substrate. <P>SOLUTION: A first cleaning liquid layer of a first cleaning liquid, and a second cleaning liquid layer of a second cleaning liquid having smaller specific gravity than the first cleaning liquid, formed on the first cleaning liquid layer, are formed on a substrate to be treated. Ultrasonic wave is applied on the second cleaning liquid layer to clean the substrate to be treated. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a substrate cleaning method and a substrate cleaning apparatus.

  Semiconductor devices are always required to be miniaturized. Needless to say, it is essential to manufacture such a fine semiconductor device with a high yield.

  In the process of manufacturing a fine semiconductor device, in order to ensure a high yield, it is necessary to remove foreign substances from the surface of the wafer on which the fine semiconductor device is formed. With the miniaturization of semiconductor devices, it is necessary to remove even finer foreign matters. In other words, it is necessary to remove even fine foreign matters having a size difficult to detect with a foreign matter detection device, for example, foreign matters having a diameter of 20 to 30 nm from the surface of the wafer. However, it is very difficult to remove such fine foreign matters because they are fine.

  Furthermore, it is very difficult to remove such fine foreign substances from the surface of the wafer without damaging the fine semiconductor devices formed on the surface of the wafer.

  Under such circumstances, there is a cleaning method using cavitation as one of methods for removing foreign substances from the surface of a wafer. This cleaning method is as follows.

  First, the surface of the wafer on which fine semiconductor devices are formed is covered with a cleaning solution in which a gas is dissolved. Further, an ultrasonic wave is applied to the cleaning liquid. If it does in this way, a micro cavity (cavity: cavity) will generate in cleaning fluid, and this cavity will burst immediately. The impact force generated at that time is called cavitation. Then, using the cavitation energy, foreign substances are lifted from the surface of the wafer to clean the wafer.

  However, since cavitation has large energy, when removing foreign matter from the surface of the wafer, fine semiconductor devices formed on the surface of the wafer may be damaged.

  For this reason, various improvements have been made to the cleaning method using cavitation in order to remove foreign matters from the surface of the wafer without damaging the fine semiconductor devices formed on the surface of the wafer (patents). References 1 to 4).

JP-A 64-4285 JP-A-2-281625 JP-A-8-108157 JP 2007-150164 A

  An object of the present invention is to provide a substrate cleaning method and a substrate cleaning apparatus capable of suppressing damage to a semiconductor device or the like formed on the surface of the substrate and removing foreign substances from the surface of the substrate.

  In the substrate cleaning method according to one embodiment of the present invention, a first cleaning liquid layer formed of a first cleaning liquid on a substrate to be processed and a specific gravity smaller than that of the first cleaning liquid formed on the first cleaning liquid layer. A second cleaning liquid layer is formed with a second cleaning liquid, and the substrate to be processed is cleaned by applying ultrasonic waves to the second cleaning liquid layer.

  ADVANTAGE OF THE INVENTION According to this invention, the washing | cleaning method of a board | substrate and the washing | cleaning apparatus of a board | substrate which can suppress the damage to the semiconductor device etc. which were formed in the surface of a board | substrate, and can remove a foreign material from the board | substrate surface can be provided. .

A photograph of a hole-like scratch formed on the surface of an aluminum film by cavitation by a scanning electron microscope. The figure for demonstrating the mechanism of cavitation. The figure for demonstrating embodiment which concerns on this invention (the 1). The figure for demonstrating embodiment which concerns on this invention (the 2). The figure for demonstrating embodiment which concerns on this invention (the 3). The figure for demonstrating embodiment which concerns on this invention (the 4). The figure for demonstrating embodiment which concerns on this invention (the 5). The figure for demonstrating embodiment which concerns on this invention (the 6). The figure for demonstrating embodiment which concerns on this invention (the 7). The figure for demonstrating embodiment which concerns on this invention (the 8).

  Before describing the embodiments of the present invention, the background of how the present inventor made the present invention will be described.

  As described above, as the semiconductor device is miniaturized, the conventional substrate cleaning method using cavitation does not damage the fine semiconductor device formed on the surface of the wafer. It became difficult to remove foreign objects from the surface. Specifically, if foreign matter on the wafer surface is removed using cavitation, the fine semiconductor devices formed on the wafer surface may be scratched (defects, damage, etc.) The pattern was slashed.

  As can be understood from this, the removal of foreign matter from the surface of the wafer and the scratching of the surface of the wafer are in an integrated relationship. Therefore, it has been considered that there is a limit to removing foreign substances from the surface of the wafer without damaging the semiconductor device formed on the surface of the wafer by the substrate cleaning method using cavitation. I came.

  However, the present inventor has thought that there is still room for improvement in the substrate cleaning method using cavitation. Up to now, improvements to the substrate cleaning method using cavitation have only been made from an empirical approach. From such a current situation, the present inventor has improved the cleaning method using cavitation by taking a logical approach based on the mechanism of the substrate cleaning method using cavitation. I thought that it might be more possible.

  First, the present inventor attempted to quantitatively grasp the state of cavitation energy and the like.

  Conventionally, there is a technique called sonoluminescence that can visually grasp cavitation. However, the information obtained by this method is two-dimensional information, not three-dimensional information. Therefore, there is a limit to grasping the cavitation state in detail.

  Therefore, the present inventor decided to use the following method in order to quantitatively capture the state of cavitation energy and the like in detail.

  First, an aluminum film is formed on the surface of the wafer, and the aluminum film is cleaned using cavitation. Then, the surface of the cleaned aluminum film is observed with an SEM (Scanning Electron Microscope).

  That is, the present inventor observes the surface of the aluminum film, thereby cavitation information on the surface of the aluminum film, that is, the cavitation energy and the two-dimensional position on the aluminum film. I thought that I could know information indirectly.

  At the same time, the foreign matter removal rate indicating how much foreign matter on the wafer surface was removed was also measured.

  As shown in FIG. 1, the present inventor forms specific hole-like scratches on the surface of the aluminum film, and there are a plurality of such hole-like scratches on the entire surface of the aluminum film. I knew that I was doing. It has also been found that these hole-shaped scratches vary in size and depth, and are unevenly distributed on the surface of the aluminum film.

  The present inventor has found that these hole-shaped scratches are formed by the energy of cavitation generated by applying ultrasonic waves, and the positions of these hole-shaped scratches are determined by cavitation. The generated two-dimensional position on the aluminum film is shown, and the size and depth of the hole-like scratches are considered to indicate the cavitation energy.

  Furthermore, the present inventor considered that the substrate was cleaned using cavitation under various conditions using such a method, and indirectly represents the state of cavitation generated at that time. The surface of the resulting aluminum film was scratched by SEM. As a result, even if the substrate cleaning is performed under any condition, for example, even if the substrate cleaning is performed by changing the output power of the applied ultrasonic wave, the number and distribution of scratches formed on the aluminum film, and Even though there is a slight difference in the removal rate of foreign matters, formation of scratches on the film could not be avoided.

  In the following, the inventor's consideration on the above reason will be described.

  In the experiments conducted so far, the cleaning is performed by changing one of the frequency of the ultrasonic wave applied to the cleaning liquid, the output power of the ultrasonic wave, and the like. The present inventor found that these experiments were actually performed with various parameters related to cavitation changing at the same time, and the results obtained by these experiments showed that various parameters changed at the same time. I thought that it was a result brought about by doing. In particular, in these experiments, due to the difficulty, a position where cavitation occurs (specifically, the position where cavitation occurs is the height from the surface of the wafer). Did not control.

  The present inventor has once again reviewed and considered the results obtained so far in view of the current situation.

  First, the inventor has two main parameters that greatly affect the generation of flaws on the surface of the wafer due to cavitation: the cavitation energy and the position where cavitation occurs. I thought there was.

  Furthermore, the present inventor considered a phenomenon occurring during substrate cleaning using cavitation as shown in FIG. 2 based on such a unique idea.

  Specifically, when the generation position of the cavitation 11 is close to the surface of the wafer 3, even if the energy of the cavitation 11 itself is small, the energy of the cavitation 11 is Therefore, at the same time when the foreign matter 2 is removed from the surface of the wafer 3, the surface of the wafer 3 is scratched (see FIG. 2A).

  On the other hand, when the generation position of the cavitation 11 is far from the surface of the wafer 3, even if the energy of the cavitation 11 itself is large, the energy of the cavitation 11 reaching the surface of the wafer 3 is small. Therefore, the surface of the wafer 3 is not damaged, but the foreign matter 2 is not removed from the surface of the wafer 3 (see FIG. 2B).

  In other words, because the cavitation generation position could not be controlled, cavitation occurred at various positions, regardless of the conditions under which the substrate was cleaned using cavitation. Even if the energy of the cavitation itself was controlled, the foreign matter on the wafer surface could not be removed without damaging the wafer surface.

  Therefore, based on such considerations, the inventor has developed a cleaning method using cavitation 11 that can remove foreign matter 2 from the surface of wafer 3 without damaging the surface of wafer 3. In order to obtain, as shown in FIG. 2 (c), not only the energy of the cavitation 11 is optimized, but also the position where the cavitation 11 occurs (distance from the surface of the wafer 3. For example, the wafer When the semiconductor device was formed on the surface of No. 3, it was thought that the distance from the upper surface of the semiconductor device also had to be optimized.

  However, when considering such a cleaning method, the most important issue is how to control the position where cavitation occurs. Furthermore, the present inventor considered that a substrate cleaning method using cavitation that does not require significant modification of the substrate cleaning apparatus that has been used in the semiconductor device manufacturing line so far is preferable.

  Hereinafter, a substrate cleaning method according to an embodiment of the present invention will be described with reference to FIG.

  First, a substrate (wafer) 3 that is an object to be cleaned is prepared. A fine pattern 5 made of, for example, a polysilicon film is formed on the substrate 3. The fine pattern 5 may be a line and space pattern, for example. On the substrate 3, for example, hydrofluoroether (HFE) is supplied as a first cleaning liquid to form a first cleaning liquid layer 60. As a 1st washing | cleaning liquid, compared with the 2nd washing | cleaning liquid mentioned later, the liquid with little quantity of the gas dissolved in a liquid is used.

  The amount of the first cleaning liquid to be supplied can be appropriately adjusted depending on the conditions. However, as shown in FIG. 3A, the liquid level of the first cleaning liquid layer 60 is higher than the upper surface of the fine pattern 5. In other words, it is preferable to supply the first cleaning liquid so that the surface of the fine pattern 5 is at least covered with the first cleaning liquid. Further, the supply amount of the first cleaning liquid may be adjusted as shown in FIG.

  Subsequently, for example, pure water is supplied as the second cleaning liquid to the substrate 3 supplied with the first cleaning liquid, and the second cleaning liquid layer 61 is formed on the first cleaning liquid layer 60. To do. Here, as the second cleaning liquid, a liquid having a specific gravity lighter than that of the first cleaning liquid and a large amount of dissolved gas is selected. Further, a liquid that does not mix with the first cleaning liquid is selected as the second cleaning liquid. Since the specific gravity of the second cleaning liquid is lighter than that of the first cleaning liquid, a second cleaning liquid layer 61 made of the second cleaning liquid is formed on the first cleaning liquid layer 60. In other words, a two-layer structure in which the second cleaning liquid layer 61 is formed on the first cleaning liquid layer 60 is formed on the substrate 3.

  Next, ultrasonic waves are applied to the second cleaning liquid layer 61. When the ultrasonic wave is applied, the cavity 1 is generated in the second cleaning liquid layer 61. The cavity 1 is ruptured immediately after it is generated, and cavitation 11 is generated. The generation amount of the cavity 1 has a correlation with the dissolved amount of gas in the cleaning liquid, and it is considered that the cavity 1 is more likely to be generated as the dissolved amount of gas in the cleaning liquid is larger.

  By the way, if the generation position of the cavity 1, in other words, the generation position of the cavitation 11 is too close to the substrate 3 or the fine pattern 5, the substrate 3 or the fine pattern 5 may be damaged. Therefore, in the present embodiment, the first cleaning liquid with a small amount of dissolved gas is provided in the region close to the substrate 3 and the fine pattern 5, and the generation efficiency of the cavity 1 is high in the region to which the ultrasonic wave is applied. A second cleaning liquid containing a large amount of liquid is supplied.

  Accordingly, in the present embodiment, the first cleaning liquid layer 60 with a small amount of dissolved gas exists in the vicinity of the substrate 3 and the fine pattern 5. It is considered that the foreign matter 2 on the substrate 3 and the fine pattern 5 can be removed by propagating the energy of the cavitation 11 generated in step 1 to the first cleaning liquid layer 60. In the present embodiment, when the foreign matter 2 is removed, the distance of the position where the cavitation 11 occurs from the substrate 3 or the fine pattern 5 is controlled by adjusting the supply amount of the first cleaning liquid. Can do.

  The present embodiment is not limited to two cleaning liquid layers. For example, three different liquids may be used to form three cleaning liquid layers.

  Next, a substrate cleaning apparatus according to an embodiment of the present invention will be described in detail with reference to FIGS. FIG. 4 is a diagram showing a substrate cleaning apparatus used in the embodiment according to the present invention. 5 to 10 are views for explaining the operation of the substrate cleaning apparatus according to the embodiment of the present invention. In the present embodiment, a semiconductor wafer will be described as an example of the substrate.

  As shown in FIG. 4, the substrate cleaning device 24 includes a cleaning tank 25 on which the wafer 3 is placed and a first cleaning liquid introduction for supplying a first cleaning liquid 40 onto the surface of the wafer (substrate to be processed) 3. A second cleaning liquid introduction section 27 that supplies a second cleaning liquid 41 having a specific gravity lower than that of the first cleaning liquid 40, and an ultrasonic application section that applies ultrasonic waves. Further, the substrate cleaning device 24 includes a wafer clamp 23 for fixing the wafer 3 in the cleaning tank 25, a first drain port 31 for discharging the used cleaning liquid from the cleaning tank 25, A drainage tank 30 for collecting used cleaning liquid discharged from the drainage port 31, a second drainage port 32 for discharging the drainage liquid from the drainage tank 30, and a rotating unit for rotating the cleaning tank 25 22.

  Next, the operation of the substrate cleaning apparatus 24 of this embodiment will be described.

  First, as shown in FIG. 5A, a wafer 3 having, for example, a fine semiconductor device (element) or the like formed on its surface at a predetermined position on the cleaning tank 25 of the substrate cleaning apparatus 24. Is transported.

  Next, as shown in FIG. 5B, the cleaning tank 25 is raised and the wafers 3 are stored one by one. At that time, the surface of the wafer 3 (specifically, the upper surface of the semiconductor device when a semiconductor device (element) is formed on the surface of the wafer 3) is on the wafer clamp 23 provided in the cleaning tank 25. Place to be. Note that the wafer 3 may be placed on the wafer clamp 23 by a transfer arm (not shown) that has fixed the cleaning tank 25 and transferred the wafer 3 to the substrate cleaning device 24.

  Subsequently, as shown in FIG. 6A, the first cleaning liquid 40 is supplied to the cleaning tank 25 by the first liquid introduction unit 26. The first cleaning liquid layer 60 is formed by the first cleaning liquid 40. At this time, the first cleaning liquid layer 60 is preferably formed so as to cover at least the upper surface of the semiconductor device (element) formed on the surface of the wafer 3. Further, the thickness of the first cleaning liquid layer 60 is such that a foreign material having a predetermined size or more can be removed without damaging the fine semiconductor device or the like formed on the wafer 3. It is also possible to select an optimum value according to the shape and size. For example, the thickness of the first cleaning liquid layer 60 can be set to 100 nm to several μm.

  Further, it is assumed that the first cleaning liquid 40 has a smaller amount of dissolved gas and a higher specific gravity than a second cleaning liquid 41 described later. For example, as the first cleaning liquid 40, hydrofluoroether (HFE), polyhydric alcohol, or the like can be used.

  Next, as shown in FIG. 6B, the second cleaning liquid 41 is supplied by the second liquid introduction unit 27. The second cleaning liquid 41 has a specific gravity smaller than that of the first cleaning liquid 40 described above in order to form a cleaning liquid layer divided into two layers. Therefore, the second cleaning liquid layer 61 can be formed on the first cleaning liquid layer 60 by the second cleaning liquid 41. The second cleaning liquid layer 61 is a liquid layer in which cavitation is likely to occur because the amount of dissolved gas is larger than that of the first cleaning liquid 40 described above, and the thickness thereof is, for example, several From μm to several mm.

  As the second cleaning liquid 41, for example, gas-dissolved pure water can be used as the second cleaning liquid 41. Further, for example, an alkaline aqueous solution in which a gas is dissolved may be used as the second cleaning liquid 41 so that the foreign matter that has floated from the surface of the wafer 3 by cavitation does not adhere to the wafer 3 again. it can.

  Further, the type and amount of gas dissolved in the second cleaning liquid 41 can remove foreign matters of a predetermined size or more without damaging fine semiconductor devices formed on the surface of the wafer 3. Choose the best one. For example, nitrogen, oxygen, or the like can be used as the gas to be dissolved, and the dissolved amount of these gases is, for example, several ppm to several tens ppm.

  Next, as illustrated in FIG. 7A, the ultrasonic wave application unit 28 is moved so that the ultrasonic wave application unit 28 contacts the second cleaning liquid layer 61. As the shape of the ultrasonic wave application section and the type of vibrator, an optimum one can be selected from various conventional vibrators.

  Next, as shown in FIG. 7B, ultrasonic waves are applied to the second cleaning liquid layer 61 by the ultrasonic wave application unit 28.

  The output, frequency, application time, etc. of the ultrasonic wave should be optimal so that foreign matters larger than a predetermined size can be removed without damaging the fine semiconductor devices formed on the surface of the wafer 3. select. For example, an ultrasonic wave of 800 kHz to 1 MHz is applied for several minutes with an output power of several W or more.

  In this way, when an ultrasonic wave is applied, a cavity is generated in the second cleaning liquid layer 61. Since the cavity has a lifetime of about μsec, the cavity bursts and cavitation occurs immediately after the cavity is generated.

  In the present embodiment, since the first cleaning liquid 40 with a small amount of dissolved gas exists in the vicinity of the wafer 3, a cavity is hardly generated.

  Therefore, by adjusting the supply amount of the first cleaning liquid 40, the distance from the wafer 3 where cavitation is generated can be controlled, and the surface of the wafer 3 has an optimum size. The energy of the cavity formation can be adjusted to be given.

  Then, the cavitation energy generated in the second cleaning liquid layer 61 is propagated to the first cleaning liquid layer 60, and the foreign matter on the wafer 3 can be removed using the energy.

  After applying the ultrasonic wave, as shown in FIG. 8A, the ultrasonic wave application unit 28 is raised, and the first cleaning liquid 40 is discharged from the first liquid discharge port 31.

  Next, as shown in FIG. 8B, the second cleaning liquid 41 is discharged from the first drain port 31.

  Subsequently, as shown in FIG. 9A, pure water 43 is supplied to the cleaning tank 25 so as to cover the surface of the wafer 3.

  Next, as shown in FIG. 9B, the cleaning tank 25 is rotated by the rotating unit 22 in a state where the pure water 43 is supplied, and the foreign matter remaining on the surface of the wafer 3 and the first and second The cleaning liquids 40 and 41 are removed from the surface of the wafer 3.

  Then, as shown in FIG. 10A, the rotation of the cleaning tank 25 is stopped and the pure water 43 is discharged from the first drain port 31.

  Finally, as shown in FIG. 10B, the cleaning tank 25 is rotated by the rotating unit 22 to remove moisture from the surface of the wafer 3. At this time, instead of the pure water 43, for example, IPA (Isopropyl Alcohol) or the like may be supplied onto the wafer 3 to dry the wafer 3.

  As described above, the substrate cleaning method of this embodiment is performed.

  Further, as a modification of the present embodiment, a substrate cleaning apparatus to which a cleaning liquid recycling mechanism is added so that the used cleaning liquid can be recycled and reused as the cleaning liquid may be used. In this case, the used first cleaning liquid 40 and the second cleaning liquid 41 after cleaning may be discharged to different used chemical liquid tanks (not shown), or the used first cleaning liquid 40 and the second cleaning liquid 41 may be discharged. The two cleaning liquids 41 may be collectively discharged into the same used chemical liquid tank (not shown), and then the respective cleaning liquids may be separated using specific gravity. Impurities are removed from each collected used cleaning solution and supplied again as a cleaning solution.

  By doing so, it is possible to reuse the cleaning liquid and reduce the manufacturing cost for manufacturing the semiconductor device.

  According to the embodiment of the present invention described above, the cavitation generation position is obtained by performing the substrate cleaning using cavitation using the cleaning liquid layer divided into two layers using two different cleaning liquids. However, since it is optimized by the cleaning liquid layer divided into two layers, foreign matters can be removed from the surface of the wafer without damaging fine semiconductor devices and the like formed on the surface of the wafer.

  Furthermore, according to the embodiment of the present invention, it is not necessary to significantly modify the substrate cleaning apparatus that has been used in the semiconductor device manufacturing line.

  In addition, this invention is not limited to the said embodiment, Various forms other than these can be taken. For example, although two liquid layers are used in the present embodiment, three different liquids may be used to form three layers. Further, the present invention can be used not only for cleaning a wafer on which a fine semiconductor device or the like is formed, but also for cleaning the surface of a substrate on which a soft film such as a resist film is formed. . In addition, in the above-described embodiment of the present invention, the wafer is exemplified as the object to be cleaned. However, the present invention is not limited to this, and the scope of the present invention is applicable to a processing object to be cleaned by applying ultrasonic waves. The present invention can be implemented with appropriate modifications without departing from the scope of the invention.

1 Cavity 2 Foreign object 3 Wafer (substrate, substrate to be processed)
4 Scratches 5 Fine Pattern 11 Cavitation 22 Rotating Unit 23 Wafer Clamp 24 Substrate Cleaning Device 25 Cleaning Tank 26 First Liquid Introducing Unit 27 Second Liquid Introducing Unit 28 Ultrasonic Applying Unit 29 Discharging Unit 30 Draining Tank 31 First drainage port 32 Second drainage port 40 First cleaning solution 41 Second cleaning solution 43 Pure water 60 First cleaning solution layer 61 Second cleaning solution layer

Claims (7)

On the substrate to be processed, a first cleaning liquid layer made of the first cleaning liquid, and a second cleaning liquid layer made of the second cleaning liquid formed on the first cleaning liquid layer and having a specific gravity smaller than that of the first cleaning liquid. Forming,
Cleaning the substrate to be processed by applying ultrasonic waves to the second cleaning liquid layer;
A method for cleaning a substrate.   The substrate cleaning method according to claim 1, wherein a pattern is formed on the substrate to be processed, and the first cleaning liquid layer covers at least the pattern.   3. The substrate cleaning method according to claim 1, wherein the first cleaning liquid has a smaller amount of gas dissolved in the liquid than the second cleaning liquid. A cleaning tank for placing the substrate to be processed and cleaning the substrate to be processed;
A first cleaning liquid introduction section for supplying a first cleaning liquid to the cleaning tank;
A second cleaning liquid introduction section for supplying a second cleaning liquid having a specific gravity smaller than that of the first cleaning liquid to the cleaning tank;
An ultrasonic application unit that applies ultrasonic waves to the second cleaning liquid;
A rotating unit for rotating the cleaning tank;
A substrate cleaning apparatus comprising:   The substrate cleaning apparatus according to claim 4, wherein the first cleaning liquid has a smaller amount of gas dissolved in the liquid than the second cleaning liquid.   6. The substrate cleaning apparatus according to claim 4, wherein the substrate cleaning apparatus is a single wafer processing apparatus.   The substrate cleaning apparatus according to claim 4, further comprising a cleaning liquid recycling mechanism that separates and collects the used first and second cleaning liquids.