JP3776820B2 - Dry surface cleaning device using laser - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a dry surface cleaning apparatus using a laser, and more particularly to cleaning a substrate with improved cleaning speed and efficiency without causing surface damage regardless of the type of surface contaminants and the size of the base material. The present invention relates to a dry surface cleaning apparatus using a laser that can be used.
[0002]
[Prior art]
In the semiconductor industry, sub-micrometer contaminants cause serious problems such as circuit failure and yield loss on semiconductor surfaces. For example, particles of 0.06 μm or less may cause a fatal device defect in the next household dynamic random access memory and the microprocessor. Therefore, contamination control for silicon wafers has become a serious problem in the manufacturing related field. As the density of chip elements increases, a technique is needed to effectively remove the smallest particles from the semiconductor surface, but the smaller the particles, the greater the cohesive force on the surface, and the more It becomes even more difficult. Traditional cleaning techniques such as gas jets, scrubbing, supersonics and chemical fluxes cannot effectively remove small sub-micrometer particles and can cause mechanical damage on the surface. The use of excessive amounts of water and compounds can cause environmental pollution.
[0003]
Recently, laser cleaning techniques are known to provide a new method that can effectively remove smaller particles in an environmentally friendly manner because it is a dry process. However, since removing particles is related to the laser absorption of the particle surface that produces a different cleaning force, the cleaning efficiency of the particle surface is strongly dependent on the laser wavelength and the physical properties of the particle. Become. This makes it difficult to remove all particles having different optical and thermal properties using a specific wavelength, since the interaction between the laser and the particles is different. Further, since the laser spot is small, there is a disadvantage that the cleaning speed becomes relatively slow.
[0004]
In order to solve the problems of conventional laser cleaning methods, Vaught (US Pat. No. 5,023,424) discloses a shock wave particle removal method and apparatus for removing particles from a wafer surface using laser induced shock waves. Yes. A laser beam for removing particles is collected in the atmosphere by a focus lens to ionize air particles around the laser focus and generate a laser-induced plasma shock wave. The wafer surface is cleaned using the laser-induced plasma shock wave generated at this time.
[0005]
However, a part of the laser beam generated together with the laser-induced plasma shock wave may be directly irradiated on the wafer surface, and the wafer surface may be damaged.
[0006]
In addition, the conventional laser-induced plasma shock wave described above can effectively remove inorganic dry particles, but removes organic contaminated particles and layers remaining on the wafer surface. There are drawbacks that cannot be removed effectively.
[0007]
Furthermore, since conventional laser-induced plasma shock waves are generated in the air, the intensity of the generated shock waves is small, and elements such as oxygen present in the air are ionized, causing surface damage such as oxidation on the wafer surface. It can happen.
[0008]
[Problems to be solved by the invention]
The present invention has been made paying attention to such a problem, and the object is to provide a first laser beam for generating a laser-induced plasma shock wave for removing inorganic surface contaminants from one laser, and To provide a dry surface cleaning apparatus capable of effectively removing organic and inorganic surface contaminants on a wafer surface by generating a second laser beam for effectively removing organic surface contaminants. It is in.
[0009]
Another object of the present invention is to prevent the laser beam from being applied to the surface of the work object by changing the advancing direction of the laser beam that causes damage to the wafer surface. Still another object of the present invention that essentially prevents laser beam and enables an effective cleaning operation by a laser-induced shock wave is to install a beam expander and a laser nozzle. It is possible to prevent damage to the surface of the base material and effectively remove surface contaminants.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, according to one aspect of the present invention, there is provided a dry surface cleaning apparatus for removing contaminants on the surface of a workpiece, the laser generating a laser beam, and the laser beam. Is divided into first and second laser beams so that the first and second laser beams travel in different directions, and the second laser beam is modulated to modulate the wavelength of the second laser beam. Frequency modulation means for generating a short wavelength laser beam having a shorter wavelength and directly removing contaminants on the surface using the short wavelength laser beam, and focusing the first laser beam on a laser focus around the surface of the work piece A plasma shock wave around the laser focus and using the plasma shock wave to clean surface contaminants on the surface. Dry surface cleaning apparatus comprising a chromatography focusing lens is provided.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic view showing a dry surface cleaning apparatus according to the present invention.
[0012]
A laser beam 2 generated by one laser oscillating means 1 includes a first laser beam 15 for generating a plasma shock wave 25 and a second laser beam 16 for generating a short wavelength laser beam 14 through two different paths. It is divided and transmitted. Preferably, the pulse period of the laser beam 2 is about 1 nanosecond to about 100 nanoseconds, the pulse energy is about 0.1 J to about 100 J, and the wavelength is about 500 nm to about 2000 nm. . The beam transmission control means 11 can use a switching mirror 12 that operates in an on-off method or a beam separator (not shown) that operates in a beam separation method.
[0013]
In order to perform cleaning using a plasma shock wave, a Q-switching Nd: YAG laser beam 2 having a fundamental wavelength of approximately 1064 nm is continuously reflected by the switching mirror 12 and the reflecting mirror 3 and then the first laser beam 15 as a work piece. 6 progresses on the surface. When the first laser beam 15 is focused using the focus lens 22, a plasma shock wave 25 is generated around the laser focus 24 from the air-induced plasma generated by the laser spark in the air. Using the plasma shock wave 25, the surface contaminant 5 attached on the surface of the work 6 can be removed. It is desirable that the intensity of the first laser beam 15 at the laser focus 24 is approximately 10 ¹² W / cm ² . When gas particles in the air begin to separate due to a strong electric field induced by the focused laser beam, they are ionized and then heated rapidly to generate a plasma shock wave.
[0014]
The intensity of the first laser beam 15 can be increased around the laser focal point 4 by expanding the beam size of the first laser beam 15 using the beam expander 21. Further, the laser nozzle 23 can be used to inject additional gas along the traveling direction of the first laser beam 15, as shown in detail in FIG. Using the transparent waveguide as the surface damage prevention means 31, the first laser beam that is not used for generating the plasma shock wave 25 in the first laser beam 15 is dispersed to damage the surface of the work 6 Can be prevented.
[0015]
In order to accurately remove organic particles and layers remaining on the surface of the work 6, the switching mirror 12 is turned off, and the second laser beam 16 having a fundamental wavelength is passed through the frequency harmonic generating means 13. The second laser beam 16 having a fundamental wavelength (1064 nm) is converted into a half wavelength (532 nm) laser beam, a 1/3 wavelength (approximately 355 nm) laser beam, or a 1/4 wavelength (266 nm) laser beam by the frequency harmonic generation means 13. After being modulated into a short wavelength laser beam 14 (preferably, the wavelength range of the short wavelength laser beam is approximately 100 nm to 600 nm) , the short wavelength laser beam 14 is reflected on the surface of the work 6 by using the reflection mirror 9. The surface contaminants 5 such as organic substances attached to the surface of the work 6 can be effectively removed by direct irradiation. Further, by changing the order of the cleaning methods, the organic material is first removed using the short wavelength laser beam 14, and then any other particles can be removed using the plasma shock wave 25. Furthermore, when the beam transmission control means 11 is replaced with a beam separator, the surface cleaning can be performed using the plasma shock wave 25 and the short wavelength laser beam 14 simultaneously. Therefore, as described above, multi-purpose cleaning can be performed using only one laser without a large additional burden in price.
[0016]
On the other hand, the work 6 is attached to the work attachment means 41. The work attachment means 41 includes a vacuum chuck 43 having a cavity that is close to the other surface of the work 6, that is, the back surface side, and a vacuum pump 51 that evacuates the cavity to attach the work 6. And a vacuum line 52 connecting the vacuum chuck 43 and the vacuum pump 51.
[0017]
The system controller 71 controls the laser 1 via the laser control line 72, controls the beam transmission control means 11 via the beam transmission control line 73, and controls the gas supplier 61 via the gas supply control line 76. Then, the vacuum pump 51 is controlled via the vacuum pump control line 75. The system controller 71 also allows the workpiece attachment means 41 to be moved horizontally and / or vertically via the workpiece movement control line 74 or to be rotated relative to the vertical axis of the workpiece 6. To control. When the work attachment means 41 is rotated, the surface contaminant 5 removed from the surface of the work 6 is scattered by centrifugal force.
[0018]
FIG. 2 is a schematic diagram showing the laser nozzle means 23 shown in FIG. 1 according to the present invention.
[0019]
The first laser beam 15 is incident on the laser nozzle 23. The laser nozzle 23 includes a focus lens 22 for collecting the first laser beam 15 at the laser focus 4, a protective glass 26 for protecting the focus lens 22, and a gas intake for introducing gas from the gas supply device 61. It has a mouth 27 and a nozzle end 28 for outputting gas. The gas is injected through the nozzle end 28 together with the laser beam. Desirably, the gas travels along the traveling direction of the first laser beam 15, so that the particles removed by the plasma shock wave 25 generated around the laser focal point 24 can be effectively removed. Further, the protective glass 26 is used to prevent the focal lens 22 from being damaged by the plasma shock wave 25 generated around the laser focal point 24 and to prevent the focal lens 22 from being contaminated by the gas. When an inert gas such as Ar, He, Ne, N ₂ or the like is injected through the gas inlet 27 instead of general air, the plasma is generated more easily and powerfully around the laser focal point 24. And more powerful shock waves can be generated. The use of an inert gas has the advantage of reducing surface damage such as surface oxidation due to plasma of oxygen particles contained in the air itself. The intensity of the plasma shock wave generated in the Ar atmosphere is almost doubled compared to the plasma shock wave generated in the general air composed of approximately 80% spartan and approximately 20% oxygen. This is because it is easier to generate plasma with a high-density laser beam in an Ar atmosphere than to generate plasma with a high-density laser beam in an air atmosphere.
[0020]
FIG. 3 is a schematic diagram showing the principle of surface damage caused by plasma shock waves.
[0021]
A focus lens 22 is used to form a laser focus 24 for the first laser beam 15 in the upper atmosphere above the surface of the work 6 to be cleaned. When the energy of the first laser beam 15 is greater than or equal to the threshold value around the laser focus 24, the air around the laser focus 24 is ionized to generate a powerful plasma. The plasma shock wave 25 generated at this time is propagated in all directions, and all the contaminant particles on the surface of the work 6 are removed by the propagated shock wave 25. However, the entire energy of the first laser beam 15 is not used for generating the plasma shock wave 25, and a part of the first laser beam 15 is incident on the surface of the work 6 along its traveling path. . The first laser beam 15 incident on the surface of the work 6 is converted into heat on the surface and causes surface damage 32 on the surface of the work 6. In particular, the surface of materials sensitive to heat or light such as semiconductor materials, porcelain materials, organic materials, thin film coating layers, etc. are seriously damaged.
[0022]
FIG. 4 is a schematic diagram illustrating the basic principle of the surface damage prevention method according to the present invention.
[0023]
When light travels from the transparent solid material 38 into the air 39, it can be transmitted to the air 39 or reflected by the air 39 depending on its incident angle θ. As shown in FIG. 4, when the incident angle θ of the incident light 35 is 90 degrees, most of the light is transmitted to the air 39 as the refracted light 36. When the incident angle θ of the incident light is smaller than 90 degrees and larger than the total reflection critical angle θ _C , a part of the incident light 35 is reflected by the air 39 as the reflected light 37 and the remaining part of the incident light 35 is constant refraction. It is transmitted toward the air 39 as refracted light 36 having a corner. However, when the incident angle θ is smaller than the critical angle θ _C , the incident light 35 is totally reflected from the contact surface between the transparent solid material 38 and the air 39 without leaking outside. Such a phenomenon is called total light reflection, and in the present invention, the traveling direction of the laser beam can be effectively changed by utilizing such a property. Examples of the transparent solid material 38 include glass, quartz, diamond, and sodium chloride crystal, and the total reflection critical angle of glass with respect to air is about 52 degrees, and the total reflection critical angle of quartz with respect to air is about. The total reflection critical angle of diamond with respect to air is approximately 66 degrees.
[0024]
FIG. 5 is a schematic view showing a first example of the surface damage preventing method according to the present invention.
[0025]
A transparent solid material rod 33 having a circular or polygonal cross section can be used as the surface damage preventing means 31 shown in FIG. A rod 33 is provided between the periphery of the laser focus 24 where the plasma shock wave 25 is generated and the surface of the work 6 irradiated with the laser beam. The first laser beam 15 passing through the laser focal point 24 is incident on one end of the rod 33. As shown in FIG. 5, when the incident angle θ between the first laser beam 15 and the side surface portion of the rod 33 is smaller than the total reflection critical angle θ _C , it is transmitted through the end portion of the rod 33. The entire laser beam travels into the rod 33 and is then emitted to the outside through the other end of the rod 33. As a result, by providing a rod-like transparent solid material that causes total reflection, the traveling direction of the laser beam irradiated on the surface of the work 6 can be freely adjusted. Since the first laser beam 15 has no influence on the surface of the work 6, no surface damage is caused by the first laser beam 15.
[0026]
FIG. 6 is a schematic view showing a second example of the surface damage preventing method according to the present invention.
[0027]
The prism 34 made of a transparent solid material can be used as the surface damage preventing means 31 shown in FIG. By providing a prism 34 between the periphery of the laser focal point 24 where the plasma shock wave 25 is generated and the surface of the work 6 irradiated with the laser beam, the first laser beam 15 is incident through one surface of the prism 34. The As shown in FIG. 6, when the incident angle θ between the laser beam incident on the prism 34 and the reflecting surface of the prism 34 is smaller than the total reflection critical angle θ _C , The laser beam is totally reflected and travels to the other surface of the prism 34 before being emitted. As a result, by providing the prism 34 made of a transparent solid material that causes total reflection, the traveling direction of the laser beam irradiated on the surface of the work 6 can be freely adjusted. Since the first laser beam 15 has no influence on the surface of the work 6, no surface damage is caused by the first laser beam 15.
[0028]
As shown in FIGS. 5 and 6, the important point in the surface damage prevention method using total reflection is that the laser beam that has entered the transparent solid material is below the total reflection threshold value at which total reflection can occur inside the material. This means that the position and direction of the substances 33 and 34 must be controlled so as to maintain the angle.
[0029]
FIG. 7 is a schematic diagram showing a work moving means 40 according to the present invention.
[0030]
The work moving means 40 includes a work attaching means 41 for firmly fixing the work 6 such as a wafer, a rotating means 42 for rotating the work attaching means 41 in order to efficiently clean the surface of the work 6, The linear movement means 47 is comprised. The work attachment means 41 includes a vacuum chuck 43 for securely holding the work 6, a vacuum pump 51 for setting a vacuum between the work 6 and the vacuum chuck 43, a vacuum chuck 43 and a vacuum pump. The rotary fitting 53 for connecting 51 and the vacuum line 52 are comprised.
[0031]
The rotation means 42 is provided in the opposite direction to which the work 6 is fixed with respect to the vacuum chuck 43, and includes a bearing 44, a drive motor 46, and a power transmission member 45 that support the work attachment means 41 so as to rotate. . The linear motion means 47 is composed of a slide moving device for linearly moving the work 6.
[0032]
The surface contaminant 5 removed from the surface of the work 6 by the plasma shock wave 25 or the short wavelength laser beam 14 is effectively separated to the outside by the rotational centrifugal force of the work 6 by the drive motor 46. The surface contaminant 5 is cut downward by the blower 81. The linear motion means 47 performs a linear motion in the left-right or up-down direction so that the entire surface of the work 6 is cleaned while rotating.
[0033]
As described above, since the surface contaminant 5 is cleaned by a small movement of the laser 1, cleaning can be performed stably. Furthermore, by rotating the work 6, high-speed cleaning and effective particle blowing of surface contaminants by centrifugal force can be performed. Since the work 6 is rotating, the work 6 can be cleaned entirely even if it is moved by half the size of the work 6 along each direction of the work 6. Compared to the conventional two-dimensional bi-directional xy scanning method that requires the work piece 6 to be moved by the size of the work piece 6 along each direction of the work piece 6, the scanning method according to the present invention is temporal and spatial. Is efficient.
[0034]
In FIG. 1, the surface of the work 6 to be cleaned is kept horizontal. However, as shown in FIG. 6, when cleaning the surface of the work 6 with a tilt of 90 degrees with respect to the horizontal plane, for example, the surface contaminant 5 separated by the shock wave 25 may be reattached to the surface by gravity. The surface contaminants can be easily removed downward along the air flow of the blower 81.
[0035]
While preferred embodiments of the present invention have been described above, those skilled in the art will be able to make various modifications without departing from the scope of the claims of the present invention.
[0036]
【The invention's effect】
As described above, according to the present invention, two different laser beams can be generated using one laser, and these can be used alternately or simultaneously to perform two different cleanings. Organic particles that were difficult to remove with a plasma shock wave can be easily removed. Furthermore, it is possible to remove many pollutants with one laser device.
[0037]
Using surface damage prevention means such as bars or prisms according to the present invention to prevent work surface damage that may be caused by some laser beams directly irradiating the work surface in a conventional plasma shock wave cleaning process. Can do. Therefore, when the surface damage preventing means according to the present invention is used, surface damage of a sensitive work object such as a wafer can be essentially prevented, and plasma shock wave dry cleaning can be performed effectively.
[0038]
By using the beam expander and laser nozzle according to the present invention, the cleaning efficiency by the conventional plasma shock wave cleaning method can be substantially improved.
[0039]
By using the workpiece moving means according to the present invention, high-speed cleaning can be performed, and the contaminated particles separated can be prevented from being recontaminated, and as a result, the surface particles can be permanently removed.
[0040]
The apparatus according to the present invention is a dry surface cleaning process of a substrate wafer in a semiconductor manufacturing process, a surface cleaning process in a flat panel display manufacturing process such as LCD, TFT, PDP, OLED, ELD, microelectronic parts, porcelain parts, precision processing. It can be used for a surface cleaning process in the manufacturing process of a lens or the like.
[Brief description of the drawings]
FIG. 1 is a schematic view showing a dry surface cleaning apparatus according to the present invention.
2 is a schematic diagram showing the laser nozzle means shown in FIG. 1 according to the present invention.
FIG. 3 is a schematic diagram for explaining the principle of occurrence of surface damage by a plasma shock wave.
FIG. 4 is a schematic view for explaining the basic principle of the surface damage prevention method according to the present invention.
FIG. 5 is a schematic view showing a first example of a surface damage preventing method according to the present invention.
FIG. 6 is a schematic view showing a second example of the surface damage preventing method according to the present invention.
FIG. 7 is a schematic view showing a work moving means according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Laser 2 Laser beam 3 Reflection mirror 5 Surface contaminant 6 Workpiece 11 Beam transmission control means 12 Switching mirror 13 Frequency modulation means 14 Short wavelength laser beam 21 Beam expander 22 Focus lens 23 Laser nozzle 24 Laser focus 25 Plasma shock wave 31 Surface Damage prevention means 41 Workpiece adhesion means 43 Vacuum chuck

Claims (16)

A dry surface cleaning device for removing contaminants on the surface of a work piece,
A laser that generates a laser beam;
Beam transmission control means for dividing the laser beam into first and second laser beams so that the first and second laser beams travel in different directions;
Frequency modulating means for modulating the second laser beam to generate a short wavelength laser beam having a wavelength shorter than that of the second laser beam, and directly removing contaminants on the surface using the short wavelength laser beam;
A first laser beam to converge to a laser focus on the surface around the work product, the laser focusing lens for generating a plasma shock wave around the laser focus, to clean the surface contaminants on the surface using the plasma shock wave,
A dry surface cleaning apparatus including a transparent waveguide provided along a traveling path of the first laser beam in order to disperse a part of the first laser beam which is not used for generating the plasma shock wave.   The dry surface according to claim 1, further comprising a laser nozzle provided around the laser focus and jetting a gas in a traveling direction of the laser beam so that ionization is performed around the laser focus. Cleaning device. The dry surface cleaning apparatus according to claim 2, wherein the gas is selected from the group including Ar, He, Ne, and N ₂ .   The dry surface cleaning apparatus according to claim 1, wherein the transparent waveguide is made of a transparent solid material selected from the group including glass, quartz, diamond, and sodium chloride crystals.   The dry surface cleaning apparatus according to claim 1, wherein the transparent waveguide has a prism shape for performing total reflection on the part of the first laser beam.   2. The dry surface cleaning apparatus according to claim 1, wherein the transparent waveguide has a rod shape for performing total reflection on the part of the first laser beam.   The dry surface cleaning apparatus according to claim 1, wherein the beam transmission control means is a beam splitter.   The dry surface cleaning apparatus according to claim 1, wherein the beam transmission means is a switching mirror.   2. The dry surface cleaning apparatus according to claim 1, wherein the frequency modulator is frequency modulation means for generating the short wavelength laser beam, and the wavelength of the short wavelength laser beam is approximately 100 nm to approximately 600 nm.   The dry surface cleaning apparatus of claim 1, further comprising a beam expander that increases a power density of the first laser beam at the laser focus by increasing a size of the first laser beam.   2. The dry surface cleaning apparatus according to claim 1, wherein the laser beam has a pulse period of about 1 nanosecond to about 100 nanoseconds, a pulse energy of about 0.1 J to about 100 J, and a wavelength of about 500 nm to about 2000 nm.   The dry surface cleaning apparatus according to claim 1, wherein the wavelength of the short wavelength laser beam is 1/2, 1/3, or 1/4 of the fundamental wavelength of the laser beam.   The dry surface cleaning apparatus according to claim 12, wherein the fundamental wavelength of the laser beam is approximately 1064 nm generated by an Nd: YAG laser.   The dry surface cleaning apparatus according to claim 1, further comprising a work attachment means for attaching the work and a moving means for rotating and moving the work.   The dry surface cleaning apparatus according to claim 1, wherein a surface of the work is inclined by a certain angle with respect to a horizontal plane. The work attachment means is
A vacuum chuck comprising a cavity proximate to another surface of the work piece;
A vacuum pump that evacuates the cavity and deposits the work;
The dry surface cleaning apparatus according to claim 14, further comprising a vacuum line connecting the vacuum chuck and the vacuum pump.

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