KR20050095320A - Washing methods based on pulse laser-induced shock wave and evaporation of liquid film and apparatus thereof - Google Patents

Abstract

The present invention relates to a method for removing impurities adhered to a surface of a cleaning product, the method comprising: applying a liquid film to the cleaning product; Generating a plasma by focusing a laser pulse that has passed through at least one optical unit at a predetermined distance on the cleaning material to generate a plasma; Vaporizing the liquid film by irradiating a laser onto the surface of the cleaning film to which the liquid film is applied; Synchronizing a time at which the shock wave reaches the impurity and a time at which evaporation of the liquid film occurs on the cleaning material; And removing impurities by the evaporation pressure and the shock wave whose arrival time is synchronized.

Description

Cleaning method based on pulse laser-induced shock wave and evaporation of liquid film and Apparatus

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cleaning method for removing impurities, and more particularly, to a cleaning method and apparatus for removing impurities by synchronizing a laser organic shock wave and an evaporation pressure induced in a liquid film.

One method of removing impurities in the form of particles adhering to the surface of cleaning materials is a chemical method.

A typical chemical method is a wet chemical process in which an acidic solution such as hydrochloric acid is used to remove impurities from the metal surface.

However, chemical processes require a lot of water and sometimes cause environmental pollution due to wastewater generated in the cleaning process. In addition, the acid (eg, hydrochloric acid) used as the cleaning solution has disadvantages such as poor reliability of the product and a long washing time.

For this reason, there are active researches on megasonic cleansing, cryogenic cleansing, and laser shock cleansing techniques that can remove impurities in an environmentally friendly manner.

Megasonic cleaning is a cleaning method that uses hydrodynamic lift and drag caused by uneven flow. The method uses ultrasonic waves at the megahertz level to reduce the thickness of the flow boundary layer formed near the wall of the cleaning material to the particle size, but when the particle size is reduced to the nanometer level, the adhesion of impurities increases relatively. . Therefore, the removal force obtained by the homogeneous flow decreases in inverse proportion to the adhesion force, so this megasonic cleaning technique has a problem that the bandwidth of the ultrasonic wave becomes larger as the particle size decreases.

In addition, the cryogenic cleaning is a method of removing impurities using a cleaning gas stored in a liquid state of low temperature and high pressure, and the gas injected into the air causes a state change with dry ice or aerosol due to thermodynamic change of pressure and temperature. The thermodynamic energy and particle momentum generated are used to remove impurities. However, this cleaning method has a high risk of damaging the cleaning material due to surface damage and thermal shock due to mechanical particle collision.

The laser shock cleansing technique generates a shock wave by using the breakdown effect of air caused by a laser pulse in a dry state, and uses it as a removal force.

Another cleaning technique using a laser is liquid film assisted laser cleaning. A cleaning method that removes impurities by directly irradiating a laser pulse on a thin liquid film-coated cleaning product to remove evaporation pressure generated at the interface between the cleaning material and impurities. This is how you use it.

On the other hand, in the semiconductor industry that produces products at the nano level, impurities have a fatal effect on product performance. Therefore, a cleaning process for removing impurities in the process of manufacturing a semiconductor is one of the essential elements, and the cleaning methods proposed to date are not preferable for removing impurities at the nano level. For example, megasonic cleaning uses ultrasonic waves of several gigahertz (GHz) to remove impurities having a small particle size, and in this case, it is difficult to expect reliability of the work efficiency. In addition, cryogenic cleaning techniques are more likely to cause physical damage to the cleaning materials due to mechanical collisions, and it is also difficult to accurately aim at dozens of nanoscale impurities.

Therefore, the present invention was devised to solve the above-mentioned problems, and an object of the present invention is to use a laser to synchronize a laser organic shock wave and an evaporation pressure induced by a liquid film, and to use the cleaning method and apparatus for removing the impurities. To provide.

In order to achieve the above object, the cleaning method provided by one aspect of the present invention is

Applying a liquid film to the cleaning material;

Generating a plasma by focusing a laser pulse that has passed through at least one optical unit at a predetermined distance on the cleaning material to generate a plasma;

Vaporizing the liquid film by irradiating a laser onto the surface of the cleaning film to which the liquid film is applied;

Synchronizing a time at which the shock wave reaches the impurity and a time at which evaporation of the liquid film occurs on the cleaning material; And,

And removing impurities by the evaporation pressure and the shock wave whose arrival time is synchronized.

Moreover, the washing | cleaning method provided by another aspect of this invention is

Applying a liquid film to the washings;

Splitting the laser pulses emitted from the laser into first and second laser pulses;

Generating a shock wave by focusing a first laser pulse that has passed through at least one optical part at a predetermined distance above the cleaning material to generate a plasma;

Vaporizing the liquid film by irradiating the second laser pulse to the cleaning product to which the liquid film is applied;

Synchronizing a time at which the shock wave reaches the impurity and a time at which evaporation of the liquid film occurs on the cleaning material; And,

And removing impurities by the evaporation pressure and the shock wave whose arrival time is synchronized.

In the present invention, the synchronization step is preferably synchronized in time within an error range of ± 0.3 ±.

In the present invention, the liquid substance that forms the liquid film on the surface of the cleaning material is preferably water, alcohol or a mixture thereof.

More preferably, the liquid film is heated after the liquid film is uniformly applied to the cleaning material in time, and the laser may include Nd: YAG laser, excimer laser, pulsed gas laser, high power diode laser, pulsed solid state laser, It is preferred that it is a copper vapor laser.

In addition, in order to implement the cleaning method described above in the present invention

A liquid film forming unit for forming a liquid film on the cleaning material;

A first laser emitting a laser pulse to create an evaporation pressure directed to the liquid film;

A second laser that emits a laser pulse for generating a shock wave at a predetermined height of the cleaning product;

A pulse generator for controlling the operation of the first and second lasers such that the evaporation pressure and the shock wave reach the impurities at the same time; And,

And an optical unit for focusing the laser pulses emitted from the second laser.

Moreover, the washing | cleaning apparatus provided in another aspect of this invention is

A liquid film forming unit for forming a liquid film on the cleaning material;

A laser that emits a laser pulse;

A divider for splitting the laser pulses emitted from the laser into first and second laser pulses;

An optical unit focusing the first laser pulse at a predetermined height of a cleaning object to induce generation of a laser induced shock wave; And,

And a synchronizing unit for adjusting the advancing time of the second laser pulse such that the evaporation pressure of the liquid film is transmitted to the impurity at the same time as the time when the shock wave is transmitted to the impurity.

At this time, the liquid film forming unit,

A container for storing a liquid substance;

A solenoid valve for controlling an amount of the liquid substance discharged from the container; And,

And a nozzle for guiding the liquid film forming vapor discharged from the container to the cleaning material.

In addition, the synchronization unit,

A mirror for changing a propagation path of the laser pulse; And,

And a beam conditioner for adjusting the time for the laser pulse to reach the cleaning object by a predetermined time difference.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. 1 is a flowchart illustrating a cleaning method according to a first embodiment of the present invention, FIG. 2 is an example device for implementing the cleaning method of FIG. 1, and FIG. 3 is an enlarged view of a part of the cleaning material. Referring to this, the cleaning method according to the first embodiment of the present invention will be described.

The cleaning apparatus of the present invention includes two lasers (11, 12) for emitting a laser pulse, and a pulse generator (13) for controlling the operation of the laser, and the liquid film forming portion for applying a liquid film to the cleaning material is the pulse. It is configured to operate under the control of the generator 13.

The liquid film forming unit is provided such that a container 14 for storing a liquid substance for providing a liquid film and a solenoid valve 15 for introducing compressed gas into the container 14 operate under the control of the pulse generator 13. . The container 14 is connected with a nozzle 141 which induces vapor generated by the compressed gas to apply a liquid film to the cleaning product.

Preferably, a heater 17 (not shown) for heating the liquid material 16 to a predetermined temperature may be further provided below the container 14. Therefore, there is an advantage that can reduce the time for the liquid film applied to the cleaning material 25 is evaporated.

On the other hand, the cleaning material 25 is placed on the micro stage 18, which is a device for finely adjusting the height so that the laser pulse is focused at the desired height.

In the present invention, the lasers 11 and 12 are Nd: YAG lasers, excimer lasers, pulsed gas lasers (CO ₂ lasers, etc.), high power diode lasers, pulsed solid state lasers (Er: YAG, etc.), copper vapor. A copper vapor laser or the like may be used, and the laser pulses emitted through the laser are modified through the mirror 19 and condensed by the block lens 22.

That is, in the cleaning apparatus of the present invention, a mirror 19 is provided between the first laser 11 and the cleaning product 25 to correct the laser pulse in a desired path, and the path-modified laser pulse is applied to the liquid film 27 of the cleaning product. ) May be additionally provided with a matching unit 20 for equalizing the pulses, or an amplifier 21 for enlarging the pulses.

On the other hand, in order to collect the laser pulses emitted from the laser 12, the block lens 22 is positioned between the laser 12 and the cleaning material 25. Accordingly, the laser pulse emitted from the second laser may be focused while passing through the block lens to generate a plasma 28 near the cleaning material, thereby inducing the shock wave 29.

Meanwhile, in FIG. 1, only the block lens 22 is provided between the second laser 12 and the cleaning material 25, but the matching unit 20 and the amplifier 21 are further configured. It can be natural.

When the cleaning device configured as described above implements the cleaning method according to the first embodiment of the present invention,

In the cleaning method of the present invention, the liquid film 27 of the cleaning material 25 is heated by using the laser pulse emitted through the laser 11.12, so that the liquid film 27 at the interface between the impurity 26 and the cleaning material 25. Evaporation pressure caused by evaporation) and 'shock wave' 29 induced by breakdown of air at a predetermined height of the cleaning material are synchronized in time to remove impurities adhering to the surface of the cleaning product.

In step S11, the liquid film 27 is applied to the cleaning material 25 using the liquid material 16 contained in the container. As the liquid substance, water, alcohol or a mixture thereof may be preferably used. At this time, when the liquid film 27 is evenly applied to the cleaning material 25, the cleaning effect is better, so that the liquid film 27 is applied for a proper time depending on the size of the cleaning material. And, since the liquid film thickness also affects the cleaning effect, it is preferable to consider this too.

The liquid material 16 is contained in the container and is sprayed in the form of vapor through the nozzle 141 to form the liquid film 27 on the surface of the cleaning material. In this case, the pretreatment step of heating the liquid substance to a predetermined temperature may be preceded in order to promote the point of time when the liquid film 27 reaches the vaporization point.

In step S12, the laser 12 is used to emit a laser pulse, which can be modified to a path along the desired path using a mirror. Then, the convex lens 22 is used to condense the laser pulse at a predetermined height of the cleaning object to induce a shock wave (S13). Thus, the convex lens is used to condense the laser pulse after modifying the path of the laser pulse to the desired shape with a mirror. Meanwhile, a curved mirror may also be preferably used instead of the block lens.

Optionally, members for equalizing or enlarging the laser pulse may optionally be arranged in the path of travel of the laser pulse. In this case, the members 20 and 21 are positioned before the laser pulse is focused through the block lens.

Laser pulses focused at a predetermined height of the cleaning products cause breakdown of the atmosphere, thereby creating a plasma 28 of high temperature and high pressure. In this case, an inert gas may be provided on the space in which the plasma is generated in order to further promote the generation of the plasma. At this time, helium, argon, and the like may be used as the inert gas.

In addition, a shock wave generated at this time is generated toward the cleaning material. In this case, the time taken for the shock wave 29 to be delivered to the impurity 26 may be obtained by considering energy conversion efficiency. For example, the time taken for the shock wave W to proceed 2 mm is calculated to be about 0.77 kHz when referring to 65% of the energy conversion efficiency (see FIG. 8).

Therefore, in the next process, the vaporization of the liquid film occurs in the cleaning product 25 in consideration of the arrival time of the shock wave 29.

In step S14, the liquid film A of the cleaning material 25 is heated by generating a laser pulse from the laser 11 at a time synchronized with the time when the shock wave 28 arrives at the impurity 26. For example, if it takes 1 ms before the shock wave 29 reaches the impurity 26, the laser pulse is irradiated to the liquid film 27 of the cleaning product after 1 ms after the generation of the laser pulse in step S12.

Therefore, the laser pulses emitted in step S12 and the laser pulses emitted in step S14 are preferably emitted from other lasers. On the other hand, the emitted laser pulse may be made to pass through the mirror and the block lens described above. In addition, the members 20 and 21 for homogenizing and amplifying the beam may also be added on the path of the laser pulse.

As a result, the impurities attached to the cleaning material are transferred to the evaporation pressure induced by the vaporization of the liquid film at a time synchronized with the time when the shock wave is transmitted to remove the impurities.

4 is a flowchart illustrating a procedure of a cleaning method according to a second embodiment of the present invention, and FIG. 5 is an example of a cleaning device equipped to implement the same. Referring to this, the cleaning method of the second embodiment is described below.

The cleaning apparatus used in this embodiment includes one laser 31 that emits laser pulses, a divider 32 that splits the laser pulses, and a beam conditioner 33 for adjusting the advancing time of the laser pulses. do. Of course, the liquid film forming unit and the same configuration as the micro stage 18 are also included, but the description is omitted here.

The divider 32 is configured to divide the incident laser pulse into the first (P ₁ ) and the second laser pulse (P ₂ ), and the present invention divides the incident laser pulse by using the polarization property of light. There is no need to be limited to this.

Meanwhile, a first laser pulse P ₁ passing through the divider 32 is focused at a predetermined height between the divider 32 and the cleansing material 25 to induce a laser organic shock wave. A block lens 34 is provided.

And a synchronization unit for synchronizing the advancing times of the first laser pulse and the second laser pulse. The synchronization unit adjusts the progress time of the second laser pulse P _{2 to} at least the same time that the shock wave 29 is transmitted to the cleaning material 25, and the progress of the second laser pulse. It includes a mirror 35 to modify the path. At this time, the adjuster 33 is located between the mirror 35 and the divider 32.

On the other hand, the second laser pulse P ₂ whose advancing time is adjusted in the controller 33 is provided between the controller 33 and the cleaning product 25 to be provided to the liquid film 27 applied to the cleaning product 25. It is preferable that the mirror 35 is further provided.

The cleaning method according to the second embodiment of the present invention using the cleaning device configured as described above is implemented as follows.

After the cleaning product is applied to the liquid film using the liquid film forming portion, the laser pulse is emitted from the laser 31 (S21). In addition, the laser pulse is split into first and second laser pulses by adjusting a propagation path using a mirror or directly entering the splitter (S22). At this time, the first laser pulse passes through the divider 32 as it is, but the second laser pulse is reflected by the divider 32 so that the traveling path is modified.

Of these, the first laser pulse is focused on the convex lens 34 at a predetermined height of the cleaning material 25 immediately after passing through the divider 32 to induce a shock wave (S23). In this case, before the first laser pulse passes through the convex lens 34, members 20 and 21 may be selectively positioned to correct the path of the laser pulse through the mirror or to uniformize or enlarge the laser pulse.

On the other hand, the second laser pulse reflected from the divider 32 modifies the traveling path to be incident on the adjuster 33 by using the mirror 35 (S24). At this time, the advancing time is adjusted while the second laser pulse passes through the controller 33. That is, as described above, the time of the second laser pulse is adjusted to the time synchronized with the time when the shock wave 29 induced by the first laser pulse is transmitted to the impurity, and is provided to the liquid film of the cleaning material 25. . In this case, the members 20 and 21 for uniformizing or enlarging the above-described laser pulse may be selectively positioned on the traveling path of the second laser pulse.

As a result, an evaporation pressure induced by vaporization of the liquid film is transmitted to the impurities attached to the cleaning material at the same time as the shock wave is delivered, thereby obtaining the effect of removing the impurities.

Hereinafter, confirming the cleaning effect on the cleaning method provided by the present invention through an experimental example.

Experimental Example 1

In Experimental Example 1, a silicon wafer contaminated with alumina (Al ₂ O ₃ ) particles having an average size of 5 μm was manufactured as a specimen, and the contaminated state is shown in FIG. And the laser pulse whose incident energy is 140 (mJ) was used for the experiment using the Nd: YAG laser.

The experiment was performed by cleaning the specimens using conventional cleaning methods (comparative examples), performing cleaning operations according to the present invention under the same conditions, and then comparing the results.

First, Figure 5 (b) shows the surface state of the specimen three times carried out by dry laser shock wave cleaning method. 5C is a view in which the specimen is washed three times by a liquid film assisted laser cleaning method (fluence: 240 mJ / cm ₂ , alcohol: water = 1: 4, temperature: 85 ° C.). D) shows the result of cleaning the specimen three times by liquid film assisted laser cleaning after performing the cleaning operation three times on the specimen by dry laser shock wave cleaning method. Finally, Figure 5 (e) shows the result of cleaning the specimen by the cleaning method according to the present invention.

As a result, in the comparative example, although a large amount of impurities are removed as a whole without any difference in the cleaning method, it can be seen partially remaining in the specimen (see (b) to (d) of FIG. 5).

In comparison, the cleaning method of the present invention completely removed impurities from the specimen (see (e) of FIG. 5). Therefore, it can be seen that the cleaning method according to the present invention exhibits higher impurity removal efficiency than the conventional cleaning method.

Experimental Example 2

Experimental Example 2 is an experiment to determine the cleaning effect according to the time difference between the shock wave and the evaporation pressure of the present invention. The experiment was conducted under the same conditions as in Experimental Example 1, where the shock wave was 2 mm away from the specimen. At this time, the liquid film was heated with a time difference of 0.20 (㎲), 0.40 (㎲), 0.80 (㎲), 1.20 (㎲), 1.60 (㎲), and 2.00 (㎲) after the shock wave was generated. It is shown in (a), (b), (c), (d), (e) and (b) of FIG.

As a result, as can be seen from (C), the cleaning efficiency was the highest when the shock wave was generated before the liquid film heating 0.80 (㎲). The time taken for the 2 mm travel of the shock wave induced by the energy 140 (mJ) Nd: YAG laser is theoretically determined to be 0.77 (mW) (see Fig. 7). Accordingly, it can be seen that the higher the time point at which the shock wave reaches the evaporation point in the specimen, the higher the cleaning efficiency.

As described above, although the present invention has been described by way of limited embodiments and drawings, the present invention is not limited thereto and is intended by those skilled in the art to which the present invention pertains. Of course, various modifications and variations are possible within the scope of equivalents of the claims to be described.

According to the cleaning method of the present invention, the impurity in the form of particles attached to the cleaning material by synchronizing the evaporation pressure caused by the liquid film on the surface of the cleaning material and the shock wave generated by concentrating a laser pulse at a predetermined height of the cleaning material in synchronization Can be removed with higher efficiency than conventional methods.

The following drawings attached to this specification are illustrative of preferred embodiments of the present invention, and together with the detailed description of the invention to serve to further understand the technical spirit of the present invention, the present invention is a matter described in such drawings It should not be construed as limited to

1 is a flowchart illustrating a cleaning method according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating an example of an apparatus for implementing a cleaning method according to the first embodiment of FIG. 1.

Figure 3 is an exemplary view showing an enlarged view of the impurities are removed from the cleaning.

4 is a flowchart illustrating a cleaning method according to a second embodiment of the present invention.

5 is a block diagram illustrating an example of an apparatus for implementing a cleaning method according to the second embodiment of FIG. 4.

Figure 6 is a photograph showing the surface state of the specimen that appears when the specimen is cleaned by the cleaning method and the conventional cleaning method according to the present invention.

Figure 7 is a photograph showing the surface state of the specimen that appears when the cleaning operation of the specimen by varying the synchronization time in the cleaning method of the present invention.

8 is a graph showing the speed according to the propagation time of the shock wave.

*** Explanation of symbols for main parts of drawings ***

11, 12, 31: laser 13: pulse generator 14: container

15: solenoid valve 16: liquid material 17: heater

18: micro stage 19: mirror 22: convex lens

25 cleaning material 26 impurity 27 liquid film

28: plasma 29: shock wave 32: divider

33: adjuster

Claims (16)

By removing impurities attached to the surface of the cleaning product, Applying a liquid film to the cleaning material; Generating a plasma by focusing a laser pulse that has passed through at least one optical unit at a predetermined distance on the cleaning material to generate a plasma; Vaporizing the liquid film by irradiating a laser onto the surface of the cleaning film to which the liquid film is applied; Synchronizing a time at which the shock wave reaches the impurity and a time at which evaporation of the liquid film occurs on the cleaning material; And, And removing impurities by the evaporation pressure and the shock wave in which the time of arrival is synchronized. Applying a liquid film to the cleaning material; Splitting the laser pulses emitted from the laser into first and second laser pulses; Generating a shock wave by focusing a first laser pulse that has passed through at least one optical part at a predetermined distance above the cleaning material to generate a plasma; Vaporizing the liquid film by irradiating the second laser pulse to the cleaning product to which the liquid film is applied; Synchronizing a time at which the shock wave reaches the impurity and a time at which evaporation of the liquid film occurs on the cleaning material; And, And removing impurities by the evaporation pressure and the shock wave in which the time of arrival is synchronized. The method according to claim 1 or 2, The synchronizing step is a cleaning method characterized in that the synchronization in time within the error range of ± 0.3㎲ The method according to claim 1 or 2, The liquid substance which forms a liquid film on the surface of the said washing | cleaning material is the cleaning method characterized by the above-mentioned. The method according to claim 1 or 2, Heating the liquid substance to a predetermined temperature. The method according to claim 1 or 2, And said optical portion comprises a convex lens for focusing said laser pulse. The method of claim 6, The optical unit further comprises a mirror for changing the path of the laser pulse. The method of claim 6, The optical unit further comprises a matching unit for equalizing the laser pulse. The method of claim 8, The optical unit further comprises amplifying unit for amplifying the laser pulse. The method according to claim 1 or 2, Heating of the liquid film is performed after the liquid film is uniformly applied to the cleaning material over time. The method according to claim 1 or 2, The laser pulse is a cleaning method, characterized in that emitted by any one of Nd: YAG laser, excimer laser, pulsed gas laser, high power diode laser, pulsed solid-state laser, copper vapor laser. Device that removes impurities attached to the surface of cleaning materials A liquid film forming unit for forming a liquid film on the cleaning material; A first laser emitting a laser pulse to create an evaporation pressure directed to the liquid film; A second laser that emits a laser pulse for generating a shock wave at a predetermined height of the cleaning product; A pulse generator for controlling the operation of the first and second lasers such that the evaporation pressure and the shock wave reach the impurities at the same time; And, And an optical unit for focusing the laser pulse emitted from the second laser. Device that removes impurities attached to the surface of cleaning materials A liquid film forming unit for forming a liquid film on the cleaning material; A laser that emits a laser pulse; A divider for splitting the laser pulses emitted from the laser into first and second laser pulses; An optical unit focusing the first laser pulse at a predetermined height of a cleaning object to induce generation of a laser induced shock wave; And, And a synchronizing unit for adjusting the advancing time of the second laser pulse so that the evaporation pressure of the liquid film is transmitted to the impurity at the same time as the time when the shock wave is transmitted to the impurity. The method according to claim 12 or 13, The liquid film forming unit, a container for storing a liquid substance; A solenoid valve for controlling an amount of the liquid substance discharged from the container; And, And a nozzle for guiding the liquid film forming vapor discharged from the container to the cleaning material. The method of claim 13, The synchronization unit may include: a mirror configured to change a propagation path of the laser pulse; And, And a beam conditioner for adjusting the time for the laser pulse to reach the cleaning object by a predetermined time difference. The method of claim 14, And a heater for heating the liquid substance to a predetermined temperature.