CN115026060A

CN115026060A - Photomask cleaning apparatus and photomask cleaning method

Info

Publication number: CN115026060A
Application number: CN202110614930.6A
Authority: CN
Inventors: 高哈尔; 林宪维
Original assignee: M&r Nano Technology Co ltd
Current assignee: M&r Nano Technology Co ltd
Priority date: 2021-03-08
Filing date: 2021-06-02
Publication date: 2022-09-09
Anticipated expiration: 2041-06-02
Also published as: CN115026060B; TWI760133B; TW202236005A

Abstract

The invention relates to a photomask cleaning device, which is applied to a photomask box, wherein the photomask box comprises an upper cover and a chassis, a photomask is accommodated on the chassis and is provided with a photomask protective film, the photomask cleaning device comprises a main shell, a primary shell, a photomask cover opening device, a conveying device and at least one air knife device, and the secondary shell is connected with the main shell. The cover opening device of the light shield comprises a lifting element and a cover opening element, wherein the cover opening element comprises a back connecting part and a cover part, and the lifting element is used for lifting the back connecting part. The cover part is embedded in the secondary shell, the cover part and the back connecting part form a light cover inlet, and the upper cover is propped against the cover part. The conveying device comprises a slide rail and a mask box carrying platform. The reticle pod stage is moved to the reticle entrance via a slide. When the lifting element lifts the cover opening element, the upper cover, the cover part, the main shell and the secondary shell form a closed space.

Description

Photomask cleaning apparatus and photomask cleaning method

Technical Field

The present invention relates to a mask cleaning apparatus and a mask cleaning method, and more particularly, to a mask cleaning apparatus and a mask cleaning method for removing contaminants from a pellicle.

Background

The semiconductor process includes an exposure process, in which a mask having a pattern is placed on a wafer, and an exposure light is then emitted onto the wafer through the mask. Then, the wafer is immersed in a developing solution, so that the pattern of the mask can be seen on the wafer.

The mask has a layer of pellicle that prevents the mask from being scratched. In addition, since the pellicle is attached with contaminants (contaminant particles), chemicals, etc. due to static electricity, the pellicle needs to be cleaned so as not to affect the yield of the semiconductor process. However, there is still a need to improve the dust removal effect and dust removal efficiency of the pellicle. In addition, in the process of taking out the photomask, external contamination particles are also easily attached to the pellicle.

Therefore, it is worth the thinking of those skilled in the art to improve the above-mentioned problems.

Disclosure of Invention

The present invention is directed to a reticle cleaning apparatus that has an excellent dust removal effect on pellicle and prevents external contaminant particles from adhering to the pellicle during removal of the reticle.

The invention relates to a photomask cleaning device, which is applied to a photomask box, wherein the photomask box comprises an upper cover and a chassis, a photomask is accommodated on the chassis and is provided with a photomask protecting film, the photomask cleaning device comprises a main shell, a primary shell, a photomask opening device, a conveying device and at least one air knife device, and the secondary shell is connected with the main shell. The cover opening device comprises a lifting element and a cover opening element, the cover opening element comprises a back connecting part and a cover part, and the lifting element is used for lifting the back connecting part and the cover part. In addition, the cover part is embedded in the secondary shell, the cover part and the back connecting part form a light shield inlet, and the upper cover is abutted against the cover part. In addition, the conveying device comprises a slide rail and a reticle box carrying platform. The mask box carrying platform moves to the mask inlet through the slide rail, and the chassis is arranged on the mask box carrying platform. In addition, the air knife device is used for generating air flow to the photomask protective film. When the lifting element lifts the cover opening element, the upper cover, the cover part, the main shell and the secondary shell form a closed space.

In the above-mentioned mask cleaning apparatus, the air knife device includes an orientation adjusting element and an air knife nozzle, and the air knife nozzle is connected to the orientation adjusting element.

In the above-mentioned mask cleaning apparatus, the orientation adjustment element includes a first axis, the air knife nozzle includes a second axis, and the first axis is perpendicular to the second axis.

In the above-mentioned mask cleaning apparatus, the number of the air knife devices is plural, and the air knife devices are arranged in an n-shape.

The apparatus further includes an electrostatic neutralizing device, which produces a plurality of charged particles from the alpha particles, and the charged particles are transported to the pellicle membrane via a clean gas.

In the reticle cleaning apparatus described above, the base plate includes a rotary switch, and the reticle pod carrying stage includes a rotary unit corresponding to the rotary switch.

The apparatus further comprises an ultrasonic resonance device for generating an ultrasonic wave to the pellicle.

The apparatus further comprises at least one flow control device for controlling the flow of air into the air knife nozzle.

In the above-described reticle cleaning apparatus, the frequency of the ultrasonic wave is not less than 20 kHz.

In the above mask cleaning apparatus, the ultrasonic resonance device includes a height adjustment platform and an ultrasonic oscillation head, and the ultrasonic oscillation head is connected to the height adjustment platform.

The apparatus further includes a pellicle monitor for monitoring the amplitude of the pellicle.

The mask cleaning apparatus further includes at least one air filter for filtering the contamination particles in the main housing.

Another object of the present invention is to provide a method for cleaning a photomask, which has an excellent dust removal effect on the pellicle and can prevent the external contamination particles from adhering to the pellicle during the process of taking out the photomask.

The photomask cleaning method of the invention is applied to the photomask cleaning equipment, and comprises the following steps. Firstly, a mask box is placed to the mask inlet, the mask box comprises an upper cover and a chassis, and a mask is accommodated on the chassis. Then, the upper cover is separated from the base plate, so that the mask box carrying platform only carries the base plate and the mask. Then, the chassis and the mask are moved into the main housing. Then, an air flow is generated to a photo-mask protection film of the photo-mask. Thereafter, the tray and mask are returned to the mask access. Then, the upper cover is combined with the chassis to store the light shield in the light shield box.

The method further includes an electrostatic neutralization step for producing a plurality of charged particles from the plurality of alpha particles, and the charged particles are transported to the pellicle via a clean gas.

The method for cleaning a photomask further comprises an ultrasonic resonance step for generating an ultrasonic wave to the pellicle.

The invention has the following advantages: has excellent dust removing effect and can prevent external pollution particles from being attached to the photomask protective film in the process of taking out the photomask.

The invention is described in detail below with reference to the drawings and specific examples, but the invention is not limited thereto.

Drawings

FIG. 1A is a schematic view of the air knife device, the conveyor, the ultrasonic resonance device, the electrostatic neutralization device and the flow control device inside the main housing;

FIG. 1B is a perspective view of the mask cleaning apparatus;

FIG. 1C is a perspective view of the cover and chassis of the reticle pod;

FIG. 1D is a schematic view of the bottom surface of the mask box;

FIG. 2A is a schematic view of a mask opening device;

FIG. 2B is a schematic view showing the cap removing member lifted;

FIG. 3A is a schematic view of a conveyor;

FIG. 3B is a schematic view of the mask box inserted into the mask entrance;

FIG. 3C is a schematic view of the lid opening device opening the lid;

FIG. 3D is a schematic view of the base plate disposed on the reticle pod stage;

FIG. 4 is a schematic view of the chassis and the mask moving into the main housing;

FIG. 5 is a schematic view of three sets of air knife devices;

FIG. 6 is a schematic view of an electrostatic neutralization apparatus;

FIG. 7 is a schematic view of an ultrasonic resonance apparatus;

FIG. 8 is a flowchart illustrating a method of cleaning a mask according to the present embodiment;

FIG. 9 is a flowchart illustrating a method for cleaning a mask according to another embodiment.

Wherein the reference numerals

10: photomask cleaning equipment

11: main shell

12: secondary shell

13: cover opening device for photomask

131: lifting element

132: cover opening element

132B: back connecting part

132C: cover part

132E: mask entrance

14: conveying device

141: sliding rail

142: reticle box carrying platform

142S: rotary unit

15: air knife device

151: azimuth adjustment element

151A: first axle center

152: air knife nozzle

152A: second axle center 152A

16: electrostatic neutralization device

161: ion nozzle

162: alpha ionizer

17: ultrasonic resonance device

171: height adjusting platform

172: ultrasonic oscillation head

18: flow rate control device

19: photomask protective film monitoring device

21: air filter

8: light shield box

81: upper cover

81T: tenon seat

82: chassis

82T: clamping tenon

82S: rotary switch

83: light shield

83F: photo-mask protection film

S1-S8: step (ii) of

Detailed Description

The structural and operational principles of the present invention are described in detail below with reference to the accompanying drawings:

referring to fig. 1A, 1B, 1C and 1D, fig. 1A is a schematic diagram of the air knife device 15, the conveying device 14, the ultrasonic resonance device 17, the static neutralization device 16 and the flow control device 18 located in the main housing 11, fig. 1B is a perspective view of the mask cleaning apparatus 10, fig. 1C is a perspective view of the upper cover 81 and the bottom plate 82 of the mask box 8, and fig. 1D is a schematic diagram of the bottom surface of the mask box 8. The mask cleaning device 10 of the present embodiment is applied to a mask box 8, the mask box 8 includes an upper cover 81 and a bottom plate 82, the upper cover 81 includes a plurality of tenon seats 81T, the side of the bottom plate 82 includes a plurality of tenons 82T, and the adjacent tenon 82T corresponds to one tenon seat 81T. Also, the bottom surface of the chassis 82 includes a rotary switch 82S. When the top cover 81 is combined with the chassis 82, the chassis 82 is covered by the top cover 8, and the tenon 82T is embedded in the corresponding tenon seat 81T. In addition, a mask 83 is received on the upper portion of the bottom plate 82, and the mask 83 has a pellicle 83F thereon. .

The mask cleaning apparatus 10 of the present embodiment includes a main housing 11, a sub-housing 12, a mask opening device 13, a conveying device 14, three sets of air knife devices 15, an electrostatic neutralization device 16, an ultrasonic resonance device 17, a plurality of flow control devices 18, a pellicle monitor 19, and a plurality of air filter devices 21, wherein the sub-housing 12 is connected to the main housing 11, and the sub-housing 12 and the main housing 11 are conducted with each other. The air knife device 15, the static electricity neutralizing device 16, the ultrasonic resonance device 17, the flow control device 18 and the pellicle monitoring device 19 are disposed in the main housing 11, and the transport device 14 is disposed across the main housing 11 and the sub-housing 12.

Referring to fig. 1B again and fig. 2A and 2B simultaneously, fig. 2A is a schematic diagram of the mask uncovering device 13, and fig. 2B is a schematic diagram of the uncovering element 132 during the rising process. The mask uncapping device 13 includes a lifting element 131 and an uncapping element 132, the uncapping element 132 includes a back connecting part 132B and a cover part 132C, the back connecting part 132B is connected with the cover part 132C, and the appearance of the cover part 132C is in the shape of an inverted-U-shaped partition plate. It is noted that the lifting member 131 is used to lift or lower the back connecting portion 132B and the cover portion 132C. In addition, the cover portion 132C of the mask uncapping device 13 is embedded in the sub-housing 12, the cover portion 132C and the back connecting portion 132B form a mask inlet 132E, and the mask inlet 132E is a location area where the mask box 8 is located.

Referring to fig. 3A and 3B, fig. 3A is a schematic diagram of the transport device 14, and fig. 3B is a schematic diagram of the mask box 8 inserted into the mask inlet 132E. The carrying device 14 includes a slide rail 141 and a reticle pod carrying stage 142, one end of the slide rail 141 is in the main housing 11, the other end of the slide rail 141 is in the sub-housing 12, and the reticle pod carrying stage 142 includes a rotating unit 142S, and the rotating unit 142S corresponds to the rotating switch 82S of the chassis 82. In detail, when the rotating unit 142S rotates the rotating switch 82S, the tenon 82T is retracted into the chassis 82, and is not inserted into the corresponding tenon seat 81T. In this way, the upper cover 81 and the chassis 82 of the mask case 8 can be separated.

In addition, the mask box carrying stage 142 is movably connected to the slide rail 141, so that the mask box carrying stage 142 can be moved to the mask entrance 132E by the slide rail 141. Specifically, when the mask box carrying stage 142 moves into the sub-housing 12 via the slide rail 141, the mask box carrying stage 142 is exposed to the mask inlet 132E (see fig. 1B again). Thus, the mask box 8 can be set on the mask box carrying stage 142 (the mask box 8 is set on the mask box carrying stage 142 via the base plate 82).

Referring to fig. 3C, fig. 3C is a schematic diagram illustrating the cover opening device 132 opening the upper cover 81, when the mask box 8 is disposed on the mask box carrying platform 142, the upper cover 81 of the mask box 8 abuts against the cover portion 132C. Therefore, when the mask cleaning apparatus 10 is going to expose the mask 83 from the mask box 8, the rotary switch 82S is turned on by the rotary unit 142S and the lifting member 131 is also lifted up the back connecting portion 132B immediately, so that the upper cover 81 is lifted up along with the cover portion 132C. Thereafter, the top cover 81 is separated from the bottom plate 82, and the reticle pod carrying stage 142 carries only the bottom plate 82 and the reticle 83 on the bottom plate 82 (see fig. 3D).

Referring to fig. 3C and also to fig. 4, fig. 4 is a schematic diagram illustrating the chassis 82 and the mask 83 moving into the main housing 11. It should be noted that, when the lifting element 131 lifts the back connecting portion 132B, the transporting device 14 also moves the base plate 82 and the mask 83 into the main housing 11 via the mask box carrying platform 142, that is, moves the mask 83 to a position below the air knife device 15, the static electricity neutralizing device 16 and the ultrasonic resonance device 17. Moreover, when the upper cover 81 and the cover portion 132C of the mask box 8 are lifted upwards, the upper cover 81, the cover portion 132C, the main housing 11 and the sub-housing 12 form a sealed space. Thus, the mask cleaning apparatus 10 can prevent the external contaminant particles from adhering to the pellicle 83F during the process of taking out the mask 83. In addition, even when the pellicle 83F is cleaned, the pellicle 83F can be secured in the closed space.

Referring to fig. 4 and also to fig. 5, fig. 5 is a schematic diagram of three sets of air knife devices 15. The air knife device 15 includes an orientation adjusting element 151 and an air knife nozzle 152, and the air knife nozzle 152 is connected to the orientation adjusting element 151. The orientation adjusting element 151 includes a first axis 151A, and the air knife nozzle 152 includes a second axis 152A, wherein the first axis 151A is perpendicular to the second axis 152A. Therefore, the air knife nozzle 152 can move up and down, left and right, and rotate through the first axis 151A and the second axis 152A, so as to adjust the height, left and right position, and the rotation angle of the air knife device 15.

In addition, the air knife device 152 is used to generate an air flow to the pellicle 83F, so that the air flow can blow the contaminant particles away from the pellicle 83F. Specifically, the air flow is ejected from the air knife nozzle 152, and the air knife nozzle 152 can change the ejection angle of the air flow through the orientation adjusting element 151. Therefore, the air knife device 152 can be adjusted according to the thickness of the mask 83 (i.e., the position of the pellicle 83F) to achieve the best dust removal effect.

In addition, the mask cleaning device 10 of the present embodiment has three sets of air knife devices 15, and the three sets of air knife devices 15 are arranged in an n-shape. In this way, the two sets of lateral air knife devices 15 have excellent dust removing effect on the objects on the lateral vertical surfaces.

In addition, each flow control device 18 corresponds to one air knife nozzle 152, and the flow control device 18 is used for controlling the air flow entering the air knife nozzle 152. Thus, the air knife nozzle 152 can perform dust removal with optimal air flow, and the best dust removal effect is achieved.

Referring again to fig. 4 and also to fig. 6, fig. 6 is a schematic diagram of the static neutralization apparatus 16. The electrostatic neutralizing device 16 includes an alpha ionizer 162 and a plurality of ion nozzles 161, wherein the alpha ionizer 162 is used for generating a plurality of alpha particles. Thereafter, the electrostatic neutralizing device 16 produces a plurality of charged particles from the α particles, and the charged particles are then transported to the pellicle 83F through the ion nozzle 161, so that the contaminant particles are easily separated from the pellicle 83F. The neutralization device 16 uses wind (clean gas) to rapidly reach the surface of the photo-mask film 83F, so that static electricity can be effectively removed compared with the conventional neutralization device.

Referring again to fig. 4 and also to fig. 7, fig. 7 is a schematic diagram of the ultrasonic resonance device 17. The ultrasonic resonance device 17 includes a height adjustment platform 171 and an ultrasonic oscillation head 172, the ultrasonic oscillation head 172 is connected to the height adjustment platform 171, and the height adjustment platform 171 is used to adjust the height position of the ultrasonic oscillation head 172. In the present embodiment, the ultrasonic resonance device 17 generates an ultrasonic wave to the pellicle 83F through the ultrasonic oscillator 172, so as to resonate the pellicle 83F and the contaminant particles attached to the pellicle 83F. In this way, the contaminant particles are easily dropped from the pellicle 83F to the outside. In the above, the frequency of the ultrasonic wave is not less than 20kHz, and the optimum frequency of the ultrasonic wave is about 35 kHz.

In addition, the air knife device 15, the electrostatic neutralizing device 16, and the ultrasonic resonance device 17 are all located above the reticle carrier 142, so that the air knife device 15, the electrostatic neutralizing device 16, and the ultrasonic resonance device 17 can simultaneously remove dust from the pellicle 83F. Moreover, the reticle pod stage 142 moves back and forth on the slide rail 141, thereby further increasing the effectiveness of cleaning the pellicle 83F.

The pellicle monitor 19 is disposed beside the ultrasonic resonator 17. It is noted that the pellicle monitor 19 is used to monitor the amplitude of the pellicle 83F. Thus, the pellicle 83F is prevented from being damaged due to excessive vibration of the pellicle 83F caused by ultrasonic vibration.

In addition, an air filtering device 21 is disposed beside the flow control device 18, and the air filtering device 21 is used to filter the contaminant particles to reduce the contaminants in the mask cleaning apparatus 10.

In this embodiment, the transporter 14 also returns the chassis 82 with the mask 83 to the mask access 132E, i.e., the opening of the mask box 8, when the pellicle 83F completes the cleaning process. Then, the mask cover opening device 13 couples the top cover 81 and the bottom plate 82, and the rotation unit 142S locks the rotation switch 82S, so that the mask 83 is accommodated in the mask box 8 again.

In summary, the mask cleaning apparatus 10 has an excellent dust removing effect on the pellicle 83F via the air knife device 15, the static neutralization device 16 and the ultrasonic resonance device 17, and can prevent external contaminant particles from adhering to the pellicle 83F during the process of taking out the mask 83 and storing the mask 83.

Referring to FIG. 8, FIG. 8 is a flowchart illustrating a method for cleaning a mask according to the present embodiment. The mask cleaning method of the present embodiment is applied to the mask cleaning apparatus 10, and includes the following steps. First, referring to fig. 1C, fig. 3B and step S1, a mask box 8 is placed in the mask entrance 132E, the mask box 8 includes an upper cover 81 and a bottom plate 82, and the bottom plate 82 accommodates a mask 83.

Thereafter, referring to fig. 3C, fig. 3D and step S2, the top cover 81 and the bottom plate 82 are separated, so that the reticle pod carrying stage 142 carries only the bottom plate 82 and the reticle 83. In detail, the upper lid 81 is separated from the base 82 by opening the lid opening member 132.

Thereafter, referring to fig. 4 and step S3, the chassis 82 and the mask 83 are moved into the main housing 11 by the conveying device 14.

Thereafter, referring to fig. 6 and step S4, step S4 corresponds to an electrostatic neutralizing step, wherein a plurality of charged particles are produced from a plurality of α particles by the electrostatic neutralizing device 16, and the charged particles are transported to a pellicle 83F of the mask 83 by a clean gas, so that the contaminant particles are easily separated from the pellicle 83F.

Referring to fig. 7 and step S5, step S5 corresponds to an ultrasonic resonance step, in which an ultrasonic wave is generated by the ultrasonic resonance device 17 to the pellicle 83F, so as to resonate the pellicle 83F and contaminant particles attached to the pellicle 83F. Therefore, the contaminant particles are liable to fall out of the pellicle 83F. .

Thereafter, referring to FIG. 5 and step S6, an air flow is generated to the pellicle 83F by the air knife devices 15 to blow contaminant particles off the pellicle 83F.

Thereafter, in step S7, the tray 82 and the mask 83 are returned to the mask inlet 132E by the transporting device 14.

Then, in step S8, the cover 81 is coupled to the bottom plate 82 via the cover opening element 132, so that the mask 83 is received in the mask box 8.

In the above-mentioned mask cleaning method, step S4, step S5 and step S6 are performed in sequence. However, in other embodiments, step S4, step S5 and step S6 can be performed simultaneously (see fig. 9). Specifically, the air knife device 15, the electrostatic neutralization device 16, and the ultrasonic resonance device 17 can remove dust from the pellicle 83F at the same time, and do not need to be performed sequentially. In other embodiments, the reticle pod can be moved back and forth in the main housing 11 several times on the stage 142. Thus, the steps S4, S5, and S6 are repeated for a plurality of times, which is more advantageous for cleaning the pellicle 83F.

In summary, the mask cleaning method of the present embodiment has an excellent dust removal effect on the pellicle 83F by the air knife device 15, the static electricity neutralizing device 16 and the ultrasonic resonance device 17 of the mask cleaning apparatus 10, and the cleaned mask 83 is stored in the original mask box 8.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it should be understood that various changes and modifications can be effected therein by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. The utility model provides a light shield cleaning equipment, is applied to a light shield box, and this light shield box includes an upper cover and a chassis, supplies a light shield to hold on this chassis, and this light shield has a light shield protective film, its characterized in that, this light shield cleaning equipment includes:

a main housing;

a primary housing connected to the main housing;

a cover opening device for a photomask is provided with:

a lifting element; and

a cap opening member provided with:

a back connecting part, the lifting element is used for lifting the back connecting part; and

a cover part embedded in the secondary shell, wherein the cover part and the back connecting part form a light shield inlet, and the upper cover is abutted against the cover part;

a conveyance device is provided with:

a slide rail; and

a mask box carrying platform, which moves to the mask inlet through the slide rail, and the chassis is arranged on the mask box carrying platform; and

at least one air knife device for generating an air flow to the pellicle;

when the lifting element lifts the back connecting part and the cover part, the upper cover, the cover part, the main shell and the secondary shell form a closed space.

2. The reticle cleaning apparatus of claim 1, wherein the air knife device comprises:

an orientation adjustment element; and

and the air knife nozzle is connected with the direction adjusting element, and the direction adjusting element is used for adjusting the angle of the air knife nozzle.

3. The apparatus of claim 2, wherein the orientation adjustment element comprises a first axis, the air knife nozzle comprises a second axis, and the first axis is perpendicular to the second axis.

4. The apparatus of claim 1 or 2, wherein the number of the air knife devices is plural, and the air knife devices are arranged in n-shape.

5. The apparatus of claim 1, further comprising an electrostatic neutralizing device, wherein the electrostatic neutralizing device produces a plurality of charged particles from the plurality of alpha particles, and the charged particles are transported to the pellicle by a clean gas.

6. The reticle cleaning apparatus of claim 1, wherein the chassis comprises a rotary switch and the reticle pod carrier comprises a rotary unit, the rotary unit corresponding to the rotary switch.

7. The apparatus of claim 5, further comprising an ultrasonic resonance device for generating an ultrasonic wave to the pellicle.

8. The reticle cleaning apparatus of claim 2, further comprising at least one flow control device to control the amount of air flow into the air knife nozzle.

9. The reticle cleaning apparatus of claim 7, wherein the frequency of the ultrasonic waves is not less than 20 kHz.

10. The apparatus according to claim 7, wherein the ultrasonic resonance device comprises:

a height adjusting platform; and

an ultrasonic oscillation head connected to the height adjustment platform.

11. The apparatus of claim 7, further comprising a pellicle monitor configured to monitor the amplitude of the pellicle.

12. The apparatus of claim 1, further comprising at least one air filter for filtering contaminant particles from the main housing.

13. A reticle cleaning method applied to the reticle cleaning apparatus according to claim 7, the method comprising:

placing a mask box to the mask inlet, wherein the mask box comprises an upper cover and a chassis, and the chassis is used for accommodating a mask;

separating the upper cover from the base plate to make the mask box carrying platform only carry the base plate and the mask;

moving the base plate and the mask into the main housing;

generating a gas flow to a pellicle of the photomask;

returning the platform and the mask to the mask entrance; and

combining the upper cover and the chassis to accommodate the mask into the mask box.

14. The method of claim 13, further comprising an electrostatic neutralizing step, wherein a plurality of alpha particles are used to produce a plurality of charged particles, and wherein the charged particles are transported to the pellicle by a clean gas.

15. The method of claim 13, further comprising an ultrasonic resonance step of generating an ultrasonic wave to the pellicle membrane.