Ultrasonic vibration device, ultrasonic cleaning device, cleaning method, and method for manufacturing semiconductor device

Abstract

The present invention provides a technique with which it is possible to remove foreign matter on an object being cleaned. Provided is a configuration having a vibration element part including a vibrator that generates ultrasonic vibration, and a horn part attached to the lower section of the vibration element part, the diameter of the vibration element part and the diameter of the horn part being the same.

Description

Ultrasonic vibration device, ultrasonic cleaning device, cleaning method, and method for manufacturing semiconductor device

[0001] The present disclosure relates to an ultrasonic vibration device, an ultrasonic cleaning device, a cleaning method, and a method for manufacturing a semiconductor device.

[0002] In recent years, there has been a demand for a cleaning device that can deal with increasingly complex structures of objects to be cleaned, such as semiconductor wafers. In this regard, as shown in Patent Document 1, there is a cleaning device that cleans objects by irradiating them with ultrasonic waves.

[0003] JP 2019-153638 A

[0004] The present disclosure provides a technique capable of removing foreign matter from an object to be cleaned.

[0005] According to one aspect of the present disclosure, there is provided a configuration having a vibration element portion including a vibrator that generates ultrasonic vibrations, and a horn portion attached to a lower portion of the vibration element portion, wherein the diameter of the vibration element portion and the diameter of the horn portion are the same.

[0006] According to the present disclosure, it is possible to remove foreign matter from an object to be cleaned.

[0007] FIG. 1 is a schematic diagram showing an example of an ultrasonic cleaning device according to an embodiment of the present disclosure. FIG. 2 is a schematic diagram showing an example of an ultrasonic vibration device according to an embodiment of the present disclosure. FIG. 3 is an example of a detailed view of the lower part of an ultrasonic vibration device according to an embodiment of the present disclosure. FIG. 4 is a diagram showing a comparative example (an example in which a vibrator is arranged on the bottom surface of the cleaning tank 6) of an ultrasonic cleaning device according to an embodiment of the present disclosure. FIG. 5 is a diagram showing a comparative example (an example in which a vibrator is arranged on the side surface of the cleaning tank 6) of an ultrasonic cleaning device according to an embodiment of the present disclosure. FIG. 6 is a diagram showing an example of an ultrasonic cleaning device according to an embodiment of the present disclosure. FIG. 7 is a diagram for explaining uniformity of ultrasonic irradiation. FIG. 8 is a diagram for explaining ultrasonic irradiation by a vibrator 101 according to an embodiment of the present disclosure.

[0008] <One Aspect of the Present Disclosure> One aspect of the present disclosure will be described below, mainly with reference to Figures 1 to 7. Note that all drawings used in the following description are schematic, and the dimensional relationships, ratios, etc. of elements in the drawings do not necessarily match those in reality. Furthermore, the dimensional relationships, ratios, etc. of elements between multiple drawings do not necessarily match.

[0009] The ultrasonic cleaning apparatus (hereinafter, referred to as the cleaning apparatus) 10 shown in FIG. 1 has the following configuration. Reference numeral 1 denotes a processed object to be cleaned, such as a semiconductor wafer, and 2 denotes a workpiece (e.g., a workpiece having various patterns) on the surface of the object to be cleaned 1, on which foreign matter adheres. Reference numerals 3 and 4 constitute a vibrator 101 in this embodiment, with 3 being a vibration element such as a piezoelectric element and 4 being an electrode. A horn 102 made of a vibration transmission material is attached to the bottom of the vibrator 101. Reference numeral 5 denotes an ultrasonic oscillator that supplies high-frequency power to the vibrator 101, and is connected by a cable 103 such as a cab tire or power cable. Reference numeral 6 denotes a cleaning tank 6, which is filled with cleaning liquid 7. The bottom of the horn 102 is immersed in this cleaning liquid 7. When the vibrator 101 is driven by the ultrasonic oscillator 5, the generated ultrasonic vibrations propagate through the cleaning liquid 7 via the horn 102, removing foreign matter adhering to the object to be cleaned 1 (specifically, the workpiece 2).

[0010] 1, the cleaning apparatus 10 has a stage STG on which the object 1 to be cleaned is placed. However, this is merely an example, and the cleaning apparatus 10 is not limited to this configuration.

[0011] The ultrasonic vibration device 100 shown in FIG. 2 has the following configuration. Specifically, 104 denotes a vibration element unit serving as an ultrasonic generator that generates ultrasonic waves. The vibration element unit 104 includes a vibrator 101 (vibration element 3, electrode 4), a backing plate 107 serving as an adjustment plate, and a front plate 108. When power is applied from an ultrasonic oscillator 5 via a plate-shaped electrode 4, the vibration element 3 vibrates by expansion and contraction, and the expansion and contraction vibration is transmitted to a horn unit (vibration transmission material) 102. Note that in FIG. 2 , the vibration element 3 is sandwiched between two electrodes 4. The vibration element unit 104 may also include a discharge resistor 106 for discharging power charged to the vibrator 101. 105 denotes a cover that houses the vibration element unit 104, and includes an upper cover 105a and a lower cover 105b. The lower part of the horn unit 102 is immersed in the cleaning solution 7, and ultrasonic waves are transmitted to the object 1 to be cleaned via the horn unit 102. Although not shown, ultrasonic vibrations pass through the cleaning liquid 7 due to the transmission characteristics of ultrasonic waves, and ultrasonic vibrations are also generated in the object 1 to be cleaned, making it possible to remove foreign matter on the object 1 to be cleaned.

[0012] As shown in Figure 2, the ultrasonic vibration device 100 as a vibrator unit has a cover 105 in which a vibration element section 104 including a vibrator 101 that generates ultrasonic vibrations is installed, and a horn section 102 attached to the lower part of the vibration element section 104, with the vibration element section 104 (particularly the vibrator 101) and the horn section 102 having the same diameter. With this configuration, ultrasonic vibrations can be generated only in the longitudinal direction (vertical direction), making adjustments easy. Therefore, it is expected that uneven cleaning of the object 1 to be cleaned will be eliminated.

[0013] Generally, since the size of the vibration element 104 cannot be changed, the horn 102 is made trumpet-shaped (with the output side flaring out) to make the diameter of the horn 102 the same or close to the same depending on the size of the object 1. However, if the horn 102 is made into such a shape, the ultrasonic waves emitted from the horn 102 are generated not only in the vertical direction but also in the horizontal direction, which results in the strength (energy) of the ultrasonic waves being dispersed.

[0014] 2, the tip of the horn part 102 protrudes from the lower end of the cover 105 (lower cover part 105b). Specifically, the tip of the horn part 102 protrudes from the cover 105 (lower cover part 105b) so that only the tip of the horn part 102 is immersed in the liquid to clean the object to be cleaned 1 (for example, a wafer having a pattern formed on its surface) as the processing object. This prevents the cover 105 from being immersed in the cleaning liquid 7.

[0015] For example, a PZT element made of lead zirconate titanate (hereinafter referred to as PZT) can be used as the vibration element 3. Furthermore, for example, the vibration transmitting material that makes up the horn portion 102 transmits the vibration of the vibration element 3, and is preferably made of a material that has high ultrasonic propagation properties, is free from the risk of dust generation due to deterioration during use, and does not leach metal components.

[0016] FIG. 3 shows the detailed attachment of flange portion 102a, which constitutes part of horn portion 102. Flange portion 102a is fixed to cover 105 (lower cover 105b) via cushioning material 110, a resin material such as a packing or O-ring, so that flange portion 102a does not come into direct contact with cover 105 (lower cover 105b). The use of cushioning material 110 prevents metal-to-metal contact, reducing the loss of ultrasonic vibration energy (heat energy loss) caused by frictional heat generated at the connection (fixing portion) between flange portion 102a and cover 105 (lower cover 105b). The material of cushioning material 110 may be any material with a low coefficient of friction so as not to impede vibration energy. For example, it may be an elastic material used in rubber products, such as silicone rubber.

[0017] Furthermore, as shown in FIG. 3 , a horn nut 111 is provided as a pressing portion that holds the flange portion 102a from below. The lower cover portion 105b and the horn nut 111, which are provided to cover the flange portion 102a from above, are configured to secure the flange portion 102a via a buffer material 110. Specifically, grooves for O-rings are formed on the top and bottom of the flange portion 102a, and the horn portion 102, with the O-rings 110a and 110b attached, is pressed against the cover 105 (lower cover portion 105b). The horn nut 111 is then screwed into the lower cover portion 105b to assemble the O-rings 110c and 110d. In this way, the lower cover portion 105b and the horn nut 111 securely hold the flange portion 102a from above and below, preventing the horn portion 102 from falling off. Furthermore, the atmosphere inside the cover 105 can be sealed from the atmosphere around the tip of the horn portion 102.

[0018] Furthermore, when fastening with screws, it is necessary to insert the screws through screw holes on the outside, which requires the flange portion 102a to be large, but if the flange portion 102a is large, the edge of the flange will vibrate greatly due to the principle of leverage, resulting in a large loss of vibration energy.On the other hand, grooves are created above and below the flange portion 102a, and cushioning material 110 is embedded in these grooves, so the flange portion 102a can be made compact.

[0019] Furthermore, by using an elastic member such as an O-ring as the buffer material 110, the cover lower part 105b and the horn nut 111 are in point contact rather than surface contact, which increases the pressure on the sealing surface, improves airtightness, and reduces leakage inside the cover 105. Generally, a flammable chemical is used as the cleaning liquid 7, and there is a risk of the cleaning liquid 7 catching fire if it gets into the cover 105. However, with this configuration, in the ultrasonic vibration device 100 of this embodiment, even if the cover lower part 105b is immersed in the cleaning liquid 7 due to incorrect operation, there is no risk of the vibration element part 104 inside the cover 105 being immersed in the cleaning liquid 7.

[0020] 2, the connection between the vibration element section 104 and the horn section 102 is set to be the antinode of the ultrasonic wave. The position where the flange section 102a of the horn section 102 is fixed to the cover 105 is set to be the node of the ultrasonic wave, and the tip of the horn section 102 is set to be the antinode of the ultrasonic wave.

[0021] Specifically, the strength of the ultrasonic waves (vibrations) is configured to be the smallest at the position where the flange portion 102a and the cover 105 are fixed, and the end of the horn portion 102 is configured to be the position where the strength of the ultrasonic waves (vibrations) propagated from the vibration element portion 104 is the greatest.

[0022] In other words, when two different objects are joined, they vibrate against each other, generating frictional heat, which consumes the ultrasonic vibration energy as heat energy. To reduce the loss of heat energy due to this frictional heat, the joining portion is configured so that the ultrasonic vibration energy is minimized. In addition, although a resin member (O-ring) is used in this embodiment, any member with a low surface friction coefficient and that can be fixed can be used as the buffer material 110.

[0023] On the other hand, because ultrasonic waves must be propagated from the tip of horn portion 102 to object 1 to be cleaned, the vibration energy of the ultrasonic waves is configured to be highest at the tip of horn portion 102. The vibration energy at the tip of horn portion 102 at this time can be increased by reducing heat energy loss at the position where vibration element portion 104 and horn portion 102 are connected and at the position where flange portion 102a and cover 105 are fixed. In other words, if these heat energy losses become large, even if ultrasonic waves can be propagated to object 1 to be cleaned, the object 1 to be cleaned may not be cleaned due to insufficient vibration energy.

[0024] As described above, with the configuration in which the diameter of the vibration element section 104 (particularly the vibrator 101) and the diameter of the horn section 102 are the same, vibrations are generated only in the direction from the vibration element section 104 to the horn section 102 (hereinafter sometimes simply referred to as the vertical direction) (even if vibrations in the horizontal direction, which is perpendicular to the vertical direction, occur, they are so small that they do not need to be taken into consideration), making it possible to adjust the vibration energy in such a one direction by position. Furthermore, with such a configuration, the irradiation of ultrasound from the vibrator 101 can be made uniform.

[0025] In the case of low-frequency cleaning, repeated force on the vibrating surface gradually causes wear (erosion), and as this erosion progresses, holes (pinholes) may appear in the vibrating surface (tip of horn portion 102), allowing cleaning solution 7 to enter the vibrator unit and cause a malfunction. As a countermeasure against such erosion, although not shown, it is preferable to perform surface treatment such as chrome plating or DLC coating on the tip of horn portion 102 (particularly the part that is immersed in cleaning solution 7) to increase durability.

[0026] 4A and 4B, a conventional throw-in type ultrasonic vibrator will be described as a comparative example. Note that Fig. 4A shows a configuration in which vibrator 101 is disposed on the bottom surface of cleaning tank 6, and Fig. 4B shows a configuration in which vibrator 101 is disposed on the side surface of cleaning tank 6, but both vibrators 101 are the same.

[0027] The input power from the ultrasonic oscillator 5 to the vibrator 101 varies depending on the specifications of each manufacturer, but is, for example, up to about 1200 W. At this time, the intensity of the ultrasonic waves (unit: W / cm ２ ) is at most a few W / cm ２ This is because multiple vibrators 101 are required to clean the object 1 while the vibrators 101 are fixed to the wall (bottom surface in FIG. 4A and side surface in FIG. 4B), and therefore the ultrasonic intensity cannot be increased.

[0028] Furthermore, when ultrasonic waves are applied to a workpiece such as a semiconductor wafer as the cleaning object 1, if ultrasonic waves are applied from the bottom (back side) or horizontal side (side side) of the cleaning object 1 as shown in Figures 4A and 4B, the workpiece 2 on the surface of the cleaning object 1 cannot be cleaned efficiently.

[0029] (Example) The horn-type ultrasonic vibrator of this embodiment will be described using Figure 5. Note that, unlike the comparative example shown in Figures 4A and 4B, the number of vibrators 101 in this embodiment is one. In Figure 5, ultrasonic waves are irradiated from the surface side of the object to be cleaned 1, and the ultrasonic waves radiated from the vibrator 101 are transmitted through the object to be cleaned 1, thereby directly vibrating the object to be cleaned 1 (workpiece 2).

[0030] In one example of the ultrasonic vibration device 100 in this embodiment, the diameter of the vibrator 101 is 30 mm, and the diameter of the horn part 102 is 30 mm. In this case, when the output from the ultrasonic oscillator 5 is 100 W, the ultrasonic intensity is 14.2 W / cm ２ Furthermore, since the ultrasonic intensity is higher than that of the comparative example, it is possible to provide cleaning power to the object 1 to be cleaned.

[0031] Here, when the object 1 to be cleaned is a semiconductor wafer, as shown in Figure 5, by placing the vibrator 101 on the surface side of the object 1 and irradiating ultrasonic waves from above (the surface side) of the object 1, the workpiece 2 on the surface of the object 1 can be efficiently cleaned. Specifically, the workpiece 2 can be vibrated with a strong force and cavitation can be generated, which can remove foreign matter (adherents) adhering to deep grooves (trenches) formed in the workpiece 2. Here, cavitation is generated by expanding and compressing the cleaning solution with ultrasonic waves, and the force depends on the frequency and intensity of the ultrasonic waves.

[0032] However, when the object 1 to be cleaned is a semiconductor wafer, the diameter of the semiconductor wafer is approximately 150 mm to 300 mm, while the diameter of the vibrator 101 is relatively small. Therefore, cleaning multiple times while changing locations is necessary. Although not specifically described, the ultrasonic vibration device 100 is configured to be movable up, down, left, and right using a transport mechanism (not shown). Therefore, while the number of measurement points may increase and it may take time, as shown in Figure 7 (described later), it is possible to thoroughly clean even workpieces 2 that have been made with recent advances in devices. Note that in this specification, a numerical range such as "150 mm to 300 mm" means that the lower and upper limits are included within the range. Therefore, for example, "150 mm to 300 mm" means "150 mm or more and 300 mm or less." The same applies to other numerical ranges.

[0033] Fig. 6 is a diagram for explaining the range of ultrasonic irradiation in the comparative example. The area surrounded by the dashed line indicates the range (irradiation area) to which ultrasonic waves are irradiated in the comparative example. In Fig. 6, the dotted line indicates the irradiation area by one transducer 101, and an example is shown in which there are 13 transducers 101. In the embodiment, the irradiation area of ​​ultrasonic waves is the same as the irradiation area of ​​the transducer 101 shown by the dotted line.

[0034] As shown in Figure 6, in the comparative example, gaps 200 are generated, which are areas where ultrasonic waves are not irradiated by the transducer 101. This shows that uniformity within the irradiation area is poor in the comparative example. On the other hand, in the example, irradiation is performed by a single transducer 101 via the horn portion 102, so uniformity within the irradiation area is maintained.

[0035] In the embodiment, when the object 1 to be cleaned is a semiconductor wafer, the movement of the vibrator 101 and cleaning are repeated many times. An example of the ultrasonic irradiation range at this time is shown in FIG. 7. FIG. 7 shows the irradiation range after 41 cycles of movement and cleaning. In this way, by repeating movement and cleaning so as not to create gaps 200, the object 1 to be cleaned can be evenly cleaned.

[0036] As described above, according to this embodiment, at least one of the following effects (a) to (f) is achieved.

[0037] (a) According to this embodiment, the diameter of the vibration element portion 104 (vibrator 101) and the diameter of the horn portion 102 are configured to be the same, so ultrasonic waves of only longitudinal vibration can be generated, and the lengths of the flange portion 102a and the tip of the horn portion 102 can be adjusted so that the tip of the horn portion 102 has the maximum vibration energy. This allows the object 1 placed in the cleaning liquid 7 to be cleaned uniformly without unevenness in cleaning.

[0038] (b) According to this embodiment, the horn 102 is configured to protrude beyond the cover 105, so even if the tip of the horn 102 is immersed in the cleaning liquid 7, the cover 105 is not immersed in the cleaning liquid 7. Therefore, air bubbles do not accumulate in the cover 105, and the object 1 placed in the cleaning liquid 7 can be cleaned.

[0039] (c) According to this embodiment, by providing an adjustment plate, it is possible to adjust the lengths of the flange portion 102a and the tip of the horn portion 102 so that the vibration energy at the joint between the flange portion 102a and the cover 105 is minimized. This makes it possible to reduce energy loss due to frictional heat generated by vibration.

[0040] (d) According to this embodiment, grooves are formed on the top and bottom of the flange portion 102a, and the buffer material 110 is placed in these grooves, which prevents metal-to-metal contact at the connection between the flange portion 102a and the cover 105. This reduces energy loss due to frictional heat generated by vibration.

[0041] (e) According to this embodiment, ultrasonic waves are emitted by a single vibrator 101 having the same diameter as the vibration element portion 104 (vibrator 101) and the horn portion 102, so that the object 1 placed in the cleaning liquid 7 can be cleaned evenly.

[0042] (f) According to this embodiment, even if the object 1 to be cleaned is a semiconductor wafer having a recent pattern on its surface, it can be cleaned without unevenness.

[0043] Although the present embodiment has been specifically described above, it goes without saying that the present embodiment is not limited to the above embodiment and examples, and various modifications are possible. For example, the present embodiment is an effect expected of high-frequency ultrasound, regardless of whether it is in liquid, and can also be applied to uses that utilize the characteristics of ultrasound propagation in gas.

[0044] As an application example of this embodiment, a cooler for suppressing heat generation from the vibrator 101 may be attached inside the cover 105 .

[0045] Furthermore, in the above-described embodiment, an ultrasonic cleaning device that performs cleaning processing on processed products including patterns, etc., which is one of the processing devices that processes semiconductor wafers for manufacturing semiconductors, has been described. However, the disclosed technology is not limited to applications in semiconductor manufacturing, and can also be applied to ultrasonic cleaning devices that perform cleaning processing on glass substrates such as liquid crystal display (LCD) devices, for example.

[0046] 100: Ultrasonic vibration device 101: Vibrator 102: Horn part (vibration transmission part) 104: Vibration element part (ultrasonic wave generation part) 105: Cover

Claims

1. An ultrasonic vibration device comprising: a vibration element section including a vibrator that generates ultrasonic vibrations; and a horn section attached to the lower part of the vibration element section, wherein the diameter of the vibration element section is the same as that of the horn section.

2. The ultrasonic vibration device according to claim 1, further comprising a cover in which the vibration element portion is provided, and a tip of the horn portion protruding from a lower end of the cover.

3. An ultrasonic vibration device according to claim 2, wherein said horn portion further comprises a flange portion which is fixed to said cover via a cushioning material, said flange portion being configured not to come into direct contact with said cover.

4. An ultrasonic vibration device according to claim 3, further comprising a pressing portion for holding said flange portion from below, said pressing portion being configured to fix said flange portion via said cushioning material.

5. An ultrasonic vibration device as claimed in claim 4, further comprising a cover lower portion constituting the lower portion of said cover, said cover lower portion and said pressing portion being configured to be capable of clamping and fixing the upper and lower portions of said flange portion.

6. The ultrasonic vibration device according to claim 3, wherein the position at which the flange portion and the cover are fixed is the position at which the intensity of the ultrasonic waves propagating from the vibration element portion is the smallest.

7. The ultrasonic vibration device according to claim 3, wherein said buffer material is a resin material.

8. The ultrasonic vibration device according to claim 7, wherein the resin member is a packing or an O-ring.

9. The ultrasonic vibration device according to claim 3, wherein said buffer material is an elastic material.

10. The ultrasonic vibration device according to claim 9, wherein said elastic member is made of rubber.

11. An ultrasonic vibration device as described in claim 1, wherein the position where the vibration element section and the horn section are connected is a position where the strength of the ultrasonic waves propagating from the vibration element section is small, and the position of the end of the horn section is a position where the strength of the ultrasonic waves propagating from the vibration element section is largest.

12. An ultrasonic cleaning device comprising: the ultrasonic vibration device according to claim 1; an ultrasonic oscillator for driving said vibrator; and a cleaning tank in which an object to be cleaned is placed and which is filled with a cleaning liquid.

13. The ultrasonic cleaning device according to claim 12, wherein the horn portion is configured to be immersed in the cleaning liquid.

14. The ultrasonic cleaning device according to claim 12, wherein the object to be cleaned is a semiconductor wafer.

15. A cleaning method using an ultrasonic cleaning device according to any one of claims 12 to 14, comprising the steps of: irradiating the surface side of the object to be cleaned with ultrasonic waves emitted from the vibrator, thereby vibrating the object to be cleaned.

16. A method for manufacturing a semiconductor device, comprising the steps of: preparing an ultrasonic cleaning device as defined in claim 14; placing the semiconductor wafer having a processed surface in the cleaning tank; and vibrating the object to be cleaned by irradiating the semiconductor wafer with ultrasonic waves emitted from the vibrator by irradiating the semiconductor wafer with ultrasonic waves from the surface side of the semiconductor wafer.

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