Method and device for cleaning substrate and computer readable storage medium

Abstract

A method and apparatus for cleaning a substrate having residue to be removed on at least one surface of the substrate is described. The method comprises: scanning at least one area of ​​the surface having the residue on it with a laser, thereby heating the surface and the residue; controlling the heating so that a portion of the residue is first liquefied, so that the liquefied portion of the residue begins to flow toward a solid portion of the residue, thereby forming a meniscus with the solid portion of the residue and partially accumulating on top of the solid portion, so that the thicker residue layer produced absorbs more heat to decompose or vaporize.

Description

Technical Field

[0001] The present invention relates to a method for cleaning a substrate, a device for cleaning a substrate and a computer-readable storage medium. Background Art

[0002] The present invention relates to a device and method for cleaning a substrate, and more particularly to an immersion lithography photomask or an extreme-ultraviolet (EUV) photomask.

[0003] In many technical fields, and in particular in the field of semiconductor production, cleaning substrates can be challenging due to the required cleanliness of the cleaned substrate. One example of such a substrate requiring high cleanliness is a photomask, such as used in photolithography for mass production of integrated circuit devices.

[0004] Any particles on the surface of such a photomask (specifically, its patterned surface) can cause errors in the substrate being imaged using the photomask. Therefore, regular cleaning of the photomask is required, which, however, can reduce the useful life of the photomask. In order to protect certain surfaces of the photomask from particle contamination, pellicles have been introduced. A pellicle is a thin film or membrane that is attached, for example, to a frame glued to one side of the photomask, so that the pellicle acts as a cover to prevent particles from reaching the covered surface. The pellicle is spaced far enough from the mask that medium to small particles that may be present on the pellicle will be too far away from the focus to affect the imaging of the photomask. By using such a pellicle, the cleaning cycles of the photomask can be reduced, thereby increasing the useful life of the photomask, and at the same time the imaging results are improved.

[0005] However, after a certain number of imaging cycles, such pellicle sheets must be replaced by removing the pellicle frame glued to the mask surface. After removing the pellicle frame, some glue remains on the photomask, which must be fully removed before another pellicle sheet and frame can be attached to the photomask.

[0006] In the past, aggressive chemical cleaning solutions had to be used to remove glue residues from the surface of the photomask. For example, SPM has been used in the past few years to remove glue residues, which are usually polymers. Although SPM has good cleaning performance, SPM has caused other problems such as haze generation. Some other methods have been proposed to overcome the haze problem, such as using different chemicals that avoid haze generation. However, these chemicals often only enable partial removal of glue within an acceptable time limit, and complete removal is difficult (if it can be achieved at all). For both SPM and other chemicals, since the chemicals are not contained, it is also impossible to clean only local areas of the photomask. Therefore, the chemicals are also applied to areas that do not need to be cleaned, thereby increasing the amount of chemicals required and causing the risk of damaging these areas. Dry removal methods such as laser ablation have also been proposed to remove film glue residues, but these methods are very specific for single use and difficult to control.

[0007] There are also some other publications that use lasers to clean substrates, such as US 2012 / 0219654A and US2014 / 0345646 A. US 2012 / 0219654 A, for example, discloses a photomask cleaning device, which includes a photomask receiving station and a laser supply unit. The photomask receiving station receives and holds the photomask in a desired orientation. There is a film adhesive residue area on the front side of the photomask. The desired orientation is to position the front side so that gravity can move particles on the front side away from the front side without interference from the front side of the photomask. The laser supply unit generates a laser beam, which directly irradiates the film adhesive residue in the target area on the front side of the photomask to remove the film adhesive residue from the target area by laser ablation. During the ablation process, the laser energy is received by the film adhesive residue and causes the film adhesive residue to be substantially instantly decomposed. The photomask cleaning apparatus is configured to move the laser across the entire front surface of the photomask to irradiate the entire film adhesive residue area. Specifically, a laser beam having a wavelength ranging from about 193 nanometers to about 355 nanometers is used in the ablation process.

[0008] US 2014 / 0345646 A discloses an apparatus and method for cleaning a photomask by heating a metal plate arranged adjacent to adhesive residues on a substrate using a laser. This apparatus is suitable, for example, for removing adhesive residues from a photomask and has a holder for arranging the photomask so that the surface on which the adhesive residues remain points downward and the metal plate is positioned adjacent to the adhesive residues. The apparatus also has a laser generator for irradiating laser light onto the metal plate through the photomask and the adhesive residues to heat the metal plate to a temperature sufficient to cause the adhesive residues to decompose by the heat from the metal plate.

[0009] However, there may be problems in these prior arts that the substrate cannot be properly cleaned. For example, with conventional approaches utilizing SPM-based chemistry, the main drawback is the risk of inadvertently exposing the active area of ​​the mask to aggressive chemistry, thereby risking CD shift, causing damage to sub-resolution assist features (SRAFs), accelerating haze growth, and thus reducing mask life. Direct laser ablation as described in US 2012 / 0219654 A may result in insufficient cleaning because each particle must be fully exposed to the laser beam to be decomposed. US 2014 / 0345646 employs a metal plate and utilizes heat generated from the metal plate, and thus the configuration becomes complicated and it is difficult to efficiently and accurately heat the residue on the substrate due to the presence of a gap between the metal plate and the residue. In addition, the metal plate may be a source of undesirable contaminants.

[0010] Therefore, starting from the known prior art for cleaning substrates, it is an object of the present invention to provide a method and a device for cleaning substrates which can at least partially overcome one or more disadvantages of the prior art, some examples of which are given above. Summary of the invention

[0011] According to the invention, a method of cleaning a substrate having residues to be removed on at least one surface thereof is defined by the appended claims. Some further embodiments are disclosed in the appended claims.

[0012] Specifically, according to the embodiment, the method includes: using a laser to scan at least one area of ​​the surface having the residue on it, thereby heating the surface and the residue; and controlling the heating so that a portion of the residue is liquefied first, so that the liquefied portion of the residue begins to flow toward the solid portion of the residue, thereby forming a meniscus with the solid portion of the residue and partially accumulating on the top of the solid portion, so that the thicker residue layer produced absorbs more heat to decompose or vaporize.

[0013] In the present invention, the liquefied residue will move toward the unliquefied glue residue due to the surface tension differential between the liquefied part and the solid part of the meniscus (Marangoni effect). Therefore, the meniscus moves forward at about the same rate as the second movement described above, thereby piling up and being further heated during the process of being decomposed or vaporized. Therefore, the method makes it possible to properly clean the substrate. In particular, the method enables a laser-based cleaning process to be performed on the substrate, which utilizes the Marangoni effect to ensure that no material remains on the surface of the substrate. In addition, for example, since the method does not use SPM-based chemicals, the method is able to clean the substrate without the risk of inadvertently exposing the active area of ​​the mask to aggressive chemicals, which may cause CD shift, damage to sub-resolution assist features (SRAFs), accelerate haze growth, and thus reduce the mask life. At the same time, according to the defined method, since no additional metal plate is required to heat the residue to be removed, the configuration for cleaning the substrate can be relatively simple. Furthermore, the method enables efficient and accurate heating of the remaining residues compared to a method using an additional metal plate. Therefore, the method enables efficient and accurate heating of the remaining residues, and thus the substrate can be effectively cleaned.

[0014] Furthermore, according to aspects of the embodiments, the heating is at least partially controlled by at least one of the following: scanning speed, laser spot size of the laser on the substrate, pulse frequency of the laser, laser focus level, and energy of the laser. Thus, the heating can be controlled in a simple and well-defined manner during scanning to efficiently clean the substrate.

[0015] According to another aspect of the embodiment, the scanning of the laser comprises repeatedly moving the laser back and forth in a first direction at a first scanning speed, and moving the laser in a second direction perpendicular to the first direction at a second scanning speed. Thus, the method can efficiently and in a well-defined manner remove the remaining residue from the substrate while moving the liquefied residue along the defined direction.

[0016] In addition, according to an embodiment, the first scanning speed is fast enough to form the meniscus at the scanning area of ​​the surface and is faster than the second scanning speed, and the second speed is slow enough to move the meniscus forward in the second direction. Therefore, the method can efficiently remove the remaining residue without overheating the substrate.

[0017] According to another aspect of the embodiment, the surface of the substrate having the residue thereon has a central region, and the residue is located in a region of the surface radially outside the central region, and the second direction is along a direction from the radial inside of the residue to the radial outside of the residue, so that the meniscus moves away from the central region. Therefore, the method can efficiently remove the remaining residue from the substrate, especially from around the central region. In addition, any movement of the liquefied residue is away from the central region towards the edge of the substrate, thereby preventing any contamination of the central region.

[0018] The central region may have a rectangular shape, and the residue may have a linear shape approximately parallel to one side of the central region, wherein the first direction may be along the longitudinal direction of the residue, and the second direction is along the width direction of the residue. This enables efficient and organized removal of the remaining residue from the substrate.

[0019] In another embodiment, the central region may have a rectangular shape and the residue may be located outside the central region, wherein the second direction points away from the central region towards the edge of the substrate, thus ensuring that any liquefied residue moves away from the central region.

[0020] The scanning of the laser may include moving forward in a second direction at a second scanning speed, the second scanning speed being slow enough to move the meniscus formed in the scanned area of ​​the surface forward in the second direction, thereby ensuring efficient removal of all residues from the substrate.

[0021] Lasers with wavelengths between 5 and 25 microns have been found to be advantageous for many applications, particularly glue removal applications. In an embodiment, the laser is a CO2 laser with a wavelength of approximately 10.6 microns, and the substrate is any of a bare quartz substrate, a metal coated substrate, and a mixture of metal and quartz substrates. This combination of laser and substrate material is particularly advantageous in lithography mask applications for efficiently removing residues from a substrate.

[0022] To prevent overheating of the substrate at the end of each scan, the energy of the laser may be reduced towards the end of each pass in the first direction. This effect is particularly advantageous when scanning a line transverse to the residue, where the scan extends beyond the actual line of residue. A circular spot size wide enough to cover the width of the residue will have a similar effect of providing higher energy in the middle of a scan line than adjacent to the scan line.

[0023] In the method, the substrate will likely at least partially reflect the laser light. This reflection can be monitored and the irradiation of the laser light can be terminated based on the reflectivity, in particular the change in reflectivity, which can indicate that there is no more residue or only a negligible amount of residue. The monitoring can thus provide efficient endpoint detection for cleaning the substrate.

[0024] In addition, according to an embodiment, there is provided an apparatus for cleaning a substrate, wherein at least one surface of the substrate has residues to be removed. The apparatus comprises: a laser configured to scan at least one area of ​​the surface having the residues by laser light passing, thereby heating the surface and the residues; and a control unit configured to control the heating so that a portion of the residues are first liquefied, so that the liquefied portion of the residues begins to flow toward the solid portion of the residues, thereby forming a half-moon with the solid portion of the residues and partially accumulating on top of the solid portion, so that the thicker residue layer produced absorbs more heat to decompose or vaporize. The apparatus shows the advantages described above relative to the method.

[0025] According to another aspect, a computer program product is provided, which, when run on a computer, is capable of operating an associated device to perform a method for cleaning a substrate, wherein at least one surface of the substrate has residue to be removed, the method comprising: scanning at least one area of ​​the surface having the residue on it with a laser, thereby heating the surface and the residue; controlling the heating so that a portion of the residue is liquefied first, so that the liquefied portion of the residue begins to flow toward a solid portion of the residue, thereby forming a half-moon with the solid portion of the residue and partially accumulating on top of the solid portion, so that the thicker residue layer produced absorbs more heat to decompose or vaporize. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a diagram showing an exemplary plan view of a substrate according to a first embodiment;

[0027] Figure 2 A conceptual diagram showing an example of steps involved in a method for cleaning residues from a substrate according to a first embodiment;

[0028] Figure 3 A diagram showing the transmission rate of laser light through a quartz substrate according to the first embodiment;

[0029] Figure 4 A graph showing the transmission rate of laser light through chromium oxide according to the first embodiment;

[0030] FIG. 5A to FIG. 5C is a graph showing the absorption rate of the glue to the laser according to the first embodiment;

[0031] Figure 6 A diagram showing an example of exemplary steps involved in a method of cleaning residue from a substrate according to a first embodiment;

[0032] Fig. 7A and Figure 7B A cross-sectional view showing in more detail the sequence involved in removing residue from a substrate according to a first embodiment;

[0033] Figure 8 is a diagram illustrating an example of exemplary steps involved in a method of cleaning residue from a substrate according to other embodiments. DETAILED DESCRIPTION

[0034] The preferred embodiments of the present invention will be explained with reference to the accompanying drawings. The present invention is not limited to these embodiments. The embodiments can be used in combination as appropriate as long as the processes do not conflict with each other.

[0035] For purposes of illustration, embodiments of the present invention will be described as being applied to cleaning photomasks, and in particular to removing pellicle glue lines or glue pads from photomasks, but it will become apparent that embodiments of the present invention may also be applied to cleaning different substrates and for removing different materials and particles. Such materials will be referred to as solid when they are in a state where they retain their physical shape for a long period of time, even though the amorphous state of the material may cause the reader to consider it a high viscosity liquid. In such a state, these materials have a viscosity well above 100,000 centipoise (cP) (100 Pascal·second (Pa.s)), typically 250,000 cP to 500,000 cP (250 Pa.s to 500 Pa.s). In such a state where the material begins to flow without the application of an external force, the material will be referred to as liquefied. In their liquefied state, these materials have a viscosity of less than 100,000 centipoise (100 Pascal seconds), typically 100 to 10,000 centipoise (0.1 to 10 Pascal seconds). In the liquefied state caused by heating, the higher the temperature of these materials, the lower the viscosity and surface tension of the materials.

[0036] Directional phrases used herein (eg, left, right, top, bottom, upper, lower, vertical horizontal and their derivatives) relate to the orientation of elements shown in the drawings and are not limiting on the claims unless explicitly stated herein.

[0037] (First embodiment)

[0038] Figure 1 FIG. 1 is a diagram showing an exemplary plan view of a substrate 10 according to a first embodiment. The substrate 10 has residues 20 to be removed on at least one surface. Figure 1 As shown in , the substrate 10 having the residue 20 thereon has a central region 30 , and the residue 20 is located in a region of the surface radially outside the central region 30 .

[0039] Specifically, substrate 10 is a photomask and can be any of a bare quartz substrate, a metal coated substrate, and a mixture of metal and quartz substrates. Residue 20 is a remaining adhesive residue or a remaining glue that is used to attach a thin film to the photomask and is left behind after the thin film is removed. Central area 30 is a pattern area of ​​the photomask that generates a predetermined pattern while using the photomask during a photolithography process as known in the art. As indicated above, the method and apparatus as described herein can also be used to clean different types of substrates.

[0040] If available Figure 1As seen in , the central region 30 has been illustrated as being rectangular in shape, and the residue will generally be left behind along a line approximately parallel to one side of the central region 30 .

[0041] For ease of explanation, in the following description, the x-axis and the y-axis are described as directions on the surface of the substrate 10 , and the z-axis is described as a direction in the thickness direction of the substrate 10 (perpendicular to the surface of the substrate 10 ).

[0042] In the first embodiment, the longitudinal extension of the residue 20 is also referred to as the first direction, and the width direction of the residue 20 (perpendicular to the longitudinal extension) is also referred to as the second direction. As will be understood, the first direction and the second direction are defined with respect to the extension of the residue (which changes its direction between the x-axis direction and the y-axis direction) rather than the substrate. With respect to the residue 20 located in the region 40 of the substrate 10, Figure 1 The double arrow 50 and the direction of the x-axis correspond to the first direction, and Figure 1 The illustrated double arrow 60 and the direction of the y-axis correspond to the second direction.

[0043] Figure 2 A conceptual diagram showing an example of method steps for cleaning residue 20 from substrate 10 according to the first embodiment. Figure 2 As can be seen in steps (1) and (2), a substrate 10 having residues 20 to be removed thereon is mounted relative to an apparatus 200. The apparatus 200 is an apparatus configured to clean the substrate 10 by laser radiation. Specifically, the apparatus 200 has a laser source for irradiating a laser beam 70 onto the substrate 10 to clean the substrate 10, as will be described herein below. The apparatus 200 also has a scanning device to scan the laser on a target area of ​​the substrate 10. The scanning can be provided by at least one of the movement of the laser beam 70 on the substrate 10 and the movement of the substrate 10 relative to the laser beam 70.

[0044] After mounting the substrate 10 relative to the apparatus 200, a laser source generates a laser beam 70 and directs the laser beam 70 onto the region 11 of the surface having the residue 20. Preferably, the beam 70 is directed onto the region 11 located at the edge of the residue 20. The laser beam 70 is directed onto the region 11, for example perpendicular to the region 11. Figure 2 The substrate may be moved back and forth in a plane such as in the second direction (ie perpendicular to the longitudinal extension of the residue). Figure 2 The direction of the arrow shown in is such that the laser beam 70 is also scanned through the residue in the first direction (ie in its longitudinal extension).

[0045] The laser beam 70 is selected to have an appropriate wavelength and intensity (which is also related in part to the spot size and the scanning speed) so that the substrate and / or the residue itself absorbs enough laser light to heat the residue to a temperature above its melting temperature in the first stage. If the residue is, for example, substantially transparent to the laser light, the laser light can be absorbed by the heated substrate and then heat the residue. In this case, the laser beam will be considered to heat the residue indirectly. The wavelength and intensity are further selected to have an appropriate wavelength and intensity so that the substrate and / or the residue itself absorbs enough laser light to heat the previously melted residue to a temperature above its decomposition temperature in the second stage.

[0046] When the residue melts in the first stage, it forms a meniscus at the edge region caused by the thermal gradient between the molten part and the solid part, which pulls the hot molten residue towards the cooler solid part of the residue. This effect is called the thermal Marangoni effect and ensures that the molten residue is pulled towards the solid part. The molten residue is thus pulled to Figure 2 The left side of the Figure 2 The meniscus shown in step (3), wherein the molten residue is further heated above its decomposition temperature during the second stage. The two stage process is thus defined by sufficiently "slow" heating of the residue so that the residue first melts, forms a meniscus in the molten state, and is finally heated to above its decomposition temperature to be decomposed and thus removed from the substrate. The pulling force on the molten residue caused by the thermal Marangoni effect ensures that the residue is completely removed. During cleaning, the laser beam is slowly moved in the direction towards the solid part of the residue, thereby defining the cleaning direction. At the same time, the laser is usually scanned (moved back and forth) in a direction perpendicular to the cleaning direction at a much faster scanning speed.

[0047] As an example, the laser used in the first embodiment may be a laser generated by a CO2 laser or other lasers such as a solid-state laser (DPSS), which generates, for example, laser light with a wavelength between 0.3 microns (300 nanometers) and 2 microns (2000 nanometers). In a specific example, the device was demonstrated to work efficiently with a CO2 laser that generates laser light with a wavelength of approximately 10.6 microns (10600 nanometers), wherein the laser light is used to remove a thin film adhesive from a photomask.

[0048] In this example, the laser has a wavelength that is almost transparent to the glue (residue 20), but the photomask (substrate 10) absorbs at least enough laser light to heat the substrate 10 and thus the residue 20 in the above-mentioned two-step manner. Compared with the previous technology in which the laser directly heats the residue to decompose the residue immediately, the laser of the above example heats the substrate 10. It is not necessary to heat the residue 20 directly by the laser in this example, and therefore a laser with a shorter wavelength than the wavelength normally required to directly heat the residue 20 can be used.

[0049] For example, when the substrate 10 is any one of a bare quartz substrate, a metal-coated substrate, and a mixture of metal and quartz substrates, the laser light may be generated by a CO 2 laser having a wavelength of approximately 10.6 micrometers (10600 nanometers).

[0050] Reference Figures 3 to 5C , an exemplary relationship among the substrate 10, the residue 20 and the laser according to the above example will be explained. Figure 3 FIG. 5 is a graph showing the transmission rate of laser light through a quartz substrate according to the above example. Figure 4 FIG. 5 is a graph showing the transmission rate of laser light through chromium oxide according to the above example. FIG. 5A to FIG. 5C FIG. 1 is a graph showing the absorption rate of the film adhesive according to the above example. Figure 3 and Figure 4 The horizontal axis represents the wave number (cm -1 ) and the vertical axis represents transmittance (%). FIG. 5A to FIG. 5C The horizontal axis also represents the wave number (cm -1 ) and the vertical axis represents the absorbance (%), which is in other words a value calculated by subtracting the transmittance (%) from "1 (in other words, 100%)".

[0051] For example, when the substrate is Figure 3 The quartz substrate is shown in FIG. 1 and when the wavelength of the laser 70 is 10.6 μm (which corresponds to 934 cm -1 ), about 20% of the radiation is absorbed. Figure 4 and FIG. 5A to FIG. 5C As shown in , on the other hand, the amount of laser light with a wavelength of 10.6 microns absorbed by the chromium oxide or glue is almost 0%. Therefore, the laser will only heat the glue indirectly through the substrate. Once the glue melts, the absorption of the glue can change and become higher, but this is not a requirement.

[0052] Taking the above example as an example, refer to Figure 2The cleaning mechanism is briefly recapitulated again. The apparatus 200 controls the laser beam and thus the heating so that the substrate is heated near or below the residue 20, causing the residue 20 to liquefy and begin to flow toward the solid portion of the residue, thereby forming a meniscus 21 with the solid portion of the residue and partially accumulating on top of the solid portion (small protrusion 22), so that the resulting thicker residue layer absorbs more heat, as shown in FIG. Figure 2 As shown in step (3) of . The liquefied residue 20 thus flows toward the solid part, and continues to be heated to a temperature higher than its decomposition temperature and then decomposes. The residue can be liquefied, for example, at a temperature in the range of 200° C. to 300° C., and can be decomposed at a temperature in the range of 350° C. to 400° C. Obviously, these temperatures for liquefaction and decomposition are much lower than the melting temperature of the substrate to be cleaned.

[0053] Specifically, the apparatus 200 controls heating at least in part by at least one of the following: scanning speed of scanning, laser spot size of the laser on the substrate 10, pulse frequency of the laser, laser focus level, and laser energy. The apparatus 200 may also control any one of the focus position, scan pitch, and number of passes, and any combination thereof.

[0054] Some examples of parameters controlled by the device 200 will be briefly described. The scanning speed of the scan corresponds to a first speed, i.e. the speed at which the laser beam 70 moves back and forth over the edge region of the residue 20. The scanning speed of the scan is, for example, between 5 cm / sec and 254 cm / sec. Another parameter is the number of passes along the same scan line, which must be higher with a faster scanning speed than with a slower scanning speed if a certain power is to be delivered.

[0055] The second scanning speed for scanning forwards towards (the solid part of) the residue is much slower and is, for example, 1 cm / sec to 10 cm / sec. The second scanning speed can also be defined by a scanning pitch that defines the incremental movement of each back and forth scan or each plurality of back and forth scans in the first scanning direction.

[0056] The laser spot size of the laser corresponds to the size of the diameter of the laser beam 70 on the top surface of the substrate or residue. The laser spot size of the laser beam 70 is higher than 20 microns.

[0057] If a pulsed laser is used, the pulse frequency of the laser affects the power of the laser beam 70 and hence the corresponding heating provided thereby. The pulse frequency of the laser may be between 1 Hertz (Hz) and 20,000 Hz.

[0058] The laser focus level will again affect the intensity of the laser beam 70 and hence the corresponding heating provided thereby. The laser focus is preferably set to lie between the surface of the substrate and 10 mm above the surface of the substrate.

[0059] As indicated above, the energy provided by the laser beam 70 must be sufficient to heat the residue above its decomposition temperature in the two-step process. It has been found that a high energy laser is not required and that an inexpensive 25 watt laser, for example, can be used. In normal laser ablation, a high power laser is required because instantaneous decomposition of the material to be ablated is generally required. Preferably, the laser has an energy rating of 200 watts.

[0060] The device 200 may also use other parameters to adjust the heating, such as any of the optical working distance, focus offset, flux reduction at the end of the scan, exhaust volume to capture the molten residue vapor, and any combination thereof. The optical working distance is the distance between the device 200 and the residue 20. The optical working distance is between 0.1 cm and 100 cm. Preferably, the optical distance is between 3 cm and 6 cm. The focus offset is related to the focus level and the laser spot size, and thereby defines the energy per unit area that can be delivered. The focus offset is preferably between 0 mm and 10 mm. Flux reduction at the end of the scan is a specific technique designed by the inventors that reduces the energy flux of the laser beam 70 at the end of each scan line (i.e., before changing the scan direction by 180 degrees). This reduction is used to provide a more uniform energy transfer to the heated medium. Without the flux reduction, the end region (of the scan) may receive too much energy during the reversal time of the scan direction, which may lead to local overheating, especially when the end of the scan is outside the area covered by the residue. To avoid such overheating, the flux reduction at the end of the scan may be controlled to be much lower than the normal flux during the scan. Preferably, the flux may be reduced by 50%.

[0061] Reference Figure 6 , Fig. 7A and Figure 7B , an example of a process sequence of a method for cleaning the residue 20 from the substrate 10 will be described in more detail. Figure 6 A top view onto a cleaned substrate at different times during the cleaning process is shown, wherein the cleaning direction (slow movement of the laser beam towards the solid part of the residue once the edge region liquefies) is perpendicular to the longitudinal extension of the residue 20 on the substrate 10 . Fig. 7A and Figure 7B Shown are cross-sectional views through a substrate being cleaned at different times during the cleaning process.

[0062] If Figure 6 and Fig. 7A As indicated, in a first step (1), an apparatus 200 (not shown) and a substrate to be cleaned are aligned with each other so that in a second step (2), a laser beam 70 generated by the apparatus 200 can be directed onto the residue 20 and scanned through the edge region of the residue 20 to clean the substrate 10. The scanning of the laser beam 70 includes repeatedly moving the laser 70 back and forth in a first direction at a first scanning speed, and moving the laser in a second direction (cleaning direction) perpendicular to the first direction at a second scanning speed. In the embodiment shown, the first direction is parallel to the longitudinal extension of the residue, and the second direction is perpendicular to the longitudinal extension of the residue. Specifically, the second direction is from the inside to the outside, so that the laser moves from the inner edge of the residue 20 (facing the center of the substrate 10) toward the outer edge of the residue and beyond the outer edge of the residue. The second direction is therefore in the direction from the radial inside of the residue 20 to the radial outside of the residue 20, so that the meniscus moves away from the central region 30 of the substrate (which can be, for example, a pattern region of a photomask). The corresponding scanning speed and other parameters of the laser beam are controlled to melt or liquefy the edge region, the first scanning speed being fast enough to form a meniscus at the scanning area of ​​the substrate 10 and being faster than the second scanning speed. The second speed is slow enough to move the meniscus forward in the second direction. Figure 6 , Fig. 7A and Figure 7B , the first direction is a direction in the x-axis direction, and the second direction is a direction in the y-axis direction.

[0063] As in Figure 6 and Fig. 7A In the second step (2), the apparatus 200 repeatedly scans the region 11 of the substrate 10 by moving the laser 70 back and forth between the two edges (11a, 11b) of the region 11. The laser parameters are controlled so that the edge region of the residue is heated and melted to form a meniscus between the molten and solid portions of the residue. Figure 6 In step (2), the distance between the two arrows 11c corresponds to the width of the laser beam 70. Figure 6 Steps (2) to (6) and Fig. 7A and Figure 7BAs shown in steps (2) to (9) of , the apparatus 200 slowly moves the scanning area in the y-axis at a second scanning speed. The second speed is slow enough to allow the meniscus to form and move forward in the second direction and to further heat the residue sufficiently to decompose the residue. The thermal Marangoni effect pulls the molten material upward and toward the solid portion of the residue and may even form small protrusions 22 of the molten residue 20 that extend beyond the upper surface of the solid portion of the residue, as shown in Fig. 7A The area of ​​the substrate 10 after the scanning area 11 becomes clean, i.e. any residues 20 are removed. As will be appreciated, when the scanning area 11 reaches the outer edge of the residue, the thermal Marangoni effect will no longer function as before, since the thermal gradient will decrease as no solid parts remain. However, the remaining residue that has not yet been decomposed is pulled towards the outside of the substrate, since the substrate is cooler there. By moving the scanning area 11 further in the second direction (cleaning direction), all the residues 20 will eventually be heated sufficiently to be decomposed.

[0064] As reference Figure 6 , Fig. 7A and Figure 7B As explained, two relative movements between the laser beam 70 and the surface of the substrate 10 are employed. In a first direction, the movement is a fast forward and backward scan. For example, in view of other laser parameters, the first speed may be 1 meter per second or any other suitable speed, which enables the edge region of the residue to be liquefied and form a meniscus. In a second direction (shown in this embodiment as perpendicular to the first direction), the movement is along the cleaning direction (i.e., along the direction of the pulling force caused by the thermal Marangoni effect, which causes the molten material to flow toward the solid (cooler) part of the residue), thereby forming a meniscus. The second speed is selected to be slow enough for the effect to work and to enable the molten material to be further heated to above its decomposition temperature. For example, the second speed is quite slow compared to the first scanning speed, and may be, for example, in the range of 1 cm / minute to 10 cm / minute. The scanning movement in the first direction is preferably performed by movement of the laser beam (e.g., using a scanning mirror). The second movement can be performed by the device 200 or also by movement of a scanning mirror for example, but can also be achieved by moving the substrate 10. Other means can be provided to enable the laser beam to be moved appropriately.

[0065] It should be noted that the liquefied residue will move toward the unliquefied gum residue due to the surface tension difference between the liquefied and solid parts of the meniscus (Marangoni effect). Therefore, the meniscus moves forward at about the same rate as the second movement described above, thereby accumulating and being further heated during the process of being decomposed or vaporized.

[0066] In the above example, it has been indicated that the laser beam 70 heats the residue indirectly, since the residue 20 does not absorb a significant amount of the laser. Specifically, the laser is at least partially absorbed by the heated substrate and the substrate therefore heats the residue above. However, it should be appreciated that it is also possible that, depending on the material of the residue and the laser selected, the residue absorbs more of the laser, while the substrate 10 may be transparent or also absorb the laser. As long as the energy transfer into the residue is properly controlled, the same process sequence can be maintained, i.e., the edge region of the residue is locally liquefied so that a meniscus is formed due to the Marangoni effect (the liquid medium with lower surface tension (hotter molten material) moves towards the liquid medium with higher surface tension (cooler material)), which moves forward as the scanning area moves forward (second movement). The material is further heated and eventually decomposes. This process is driven by local heating of the substrate surface / edge region / menus of the residue, regardless of where the laser energy is actually absorbed.

[0067] As explained above, the embodiments enable a laser-based cleaning process for a substrate that uses the Marangoni effect to ensure that no material remains on the surface of the substrate. In contrast to normal ablation procedures, low-cost lasers can be used in this approach, and direct and instantaneous degradation of the target material to be removed is not desired. The approach can clean the substrate 10 without the use of SPM-based chemistry, and long-wave infrared lasers can be used as indicated. The approach employs direct and / or indirect heating to provide sufficient energy required for a two-step ablation process.

[0068] (Other embodiments)

[0069] Although the first embodiment has been described to illustrate the concept of the present invention, those skilled in the art will realize various changes of the present invention relative to the described implementation. Some examples of such other implementations will be given below in this article.

[0070] The components or devices shown in the drawings need not be configured as shown in the drawings and as described above. For example, in the above embodiments, substrate 10 is described as a photomask made of a bare quartz substrate, a metal-coated substrate, or a mixture of uncoated and metal-coated quartz. However, substrate 10 may be any other substrate made of any appropriate material to which the cleaning method as explained can be applied. In addition, the residue is described as a thin film glue that is generally present on the photomask in a linear shape as shown. Obviously, any other material with different shapes on the substrate can be removed in this way, and the substrate allows a two-step method including melting to form a half-moon and subsequent decomposition. However, the process is considered and proven to be particularly suitable for thin film glue applications, in which it is desired to achieve high cleanliness without the use of aggressive chemicals or high energy.

[0071] Although in the above embodiments the laser beam 70 has been irradiated onto the side of the substrate 10 having the residue 20 thereon (the front side), backside irradiation is also conceivable if the substrate is substantially transparent and / or thin enough. Again, however, the initial concept of frontside irradiation is considered particularly advantageous, since localized heating is optimally provided to achieve the desired effect without too much heat loss in the bulk material of the substrate. However, depending on the application, the method may use backside irradiation to cause a portion of the residue 20 (located on the front side) to liquefy first, so that the liquefied portion of the residue begins to flow towards the solid portion of the residue, thereby forming a meniscus with the solid portion of the residue and partially accumulating on top of the solid portion, so that the resulting thicker residue layer absorbs more heat to decompose or vaporize.

[0072] In the above embodiment, the substrate 10 has been explained as having a central area 30, and the residue 20 exists in a region of the surface radially outside the central area 30; however, the substrate is obviously not limited to this aspect. For example, the substrate 10 may not have a central area 30 or the residue may also exist in this central area 30 or only in this central area 30. In the above embodiment, the shape of the central area 30 has been explained as a rectangle and the shape of the residue 20 is a line, but these shapes are not limited to the shapes as in Figure 1 The shape of the central area 30 and the shape of the residue 20 can be any shape. For example, the central area 30 can be a rectangular shape, a triangular shape, a circular shape, or any other possible shape. The residue 20 can be a broken line shape, a single or multiple points, or any other possible shape.

[0073] In the above embodiments, the second direction has been described as being perpendicular to the first direction, however, the second direction is not limited thereto. For example, the second direction may be a direction that is not perpendicular to the first direction, but may be at a predetermined angle relative to the first direction. In addition, the laser beam may, for example, have a certain width so that scanning in the first direction is not required and movement in the second direction is sufficient, rather than scanning back and forth in the first direction. This may, for example, be a situation where the residue is linear and the laser spot is wider than the width of the line. In such a situation, movement only in the cleaning direction will be sufficient. In addition, scanning back and forth along the line allows a component of movement in the direction of the line to play a role. In reference to Figure 6 , Fig. 7A and Figure 7B In the cleaning example described, the scanning method scans the laser beam 70 back and forth in the longitudinal extension of the residue (glue line) to melt the inner edge region of the residue and causes the molten residue 20 (or half-moon) to move perpendicularly thereto in the second direction toward the outside of the substrate. However, as indicated above, other movements are obviously possible.

[0074] Figure 8 Examples of other such moves are shown, where similar Figure 6 , Figure 8 1 shows a top view on a substrate being cleaned at different times during the cleaning process. At this point, the cleaning direction (slow movement of the laser beam towards the solid part of the residue once a portion of the residue has liquefied) is along the longitudinal extension of the residue 20 on the substrate 10, and the faster back and forth scanning movement is along the width direction of the residue line. As can be seen in Figure 8 As can be seen in step (1), the device 200 (not shown in the figure) is first aligned with the residue line. When the device generates the laser beam 70, the laser beam 70 generates an irradiation area 11 on the substrate. The laser beam 70 again causes the residue to melt and forms a half-moon in the irradiation area 11. Since the melted portion is located in the middle of the residue line, two half-moons can actually be formed initially. By moving along the Figure 8 The residue line on the left moves the irradiation area 11, and the half-moon on the right side of the irradiation area will eventually solidify. The half-moon on the left will move with the irradiation area 11, and the cycle of melting, forming half-moons, and decomposing as explained above will continue along the residue line.

[0075] The apparatus 200 can generate an irradiated area 11 on the substrate 10 by moving the laser 70 back and forth along a first direction in the width direction of the residue 20, such as can be Figure 8 As can be seen in step (2), the laser beam 70 can be scanned so that the end point of the scan just exceeds the side edge of the residue line. Figure 8In step (2), the distance between the two arrows 11c corresponds to the width of the laser beam 70. It should be noted that the width is only schematically shown and it can be much smaller than that shown in the figure. Figure 8 As shown in steps (2) to (6), the irradiation zone 11 is then moved along the longitudinal extension of the residue 20 at a speed controlled to allow the process sequence as described above.

[0076] In the above embodiments, the scanning has been explained as comprising two movements again, one in the width direction of the residue line and one in the same direction. However, scanning is not limited to this. For example, the spot size of the laser beam 70 may be adjusted so that it is not necessary to scan in order to Figure 8 Irradiation is provided in the area 11 shown in step (2). The scanning of the laser beam 70 may then only include moving forward in the cleaning direction at a speed that is slow enough so that the process sequence of melting, forming a meniscus and decomposing can occur. In other words, the scanning of the laser beam 70 may not include moving the laser beam 70 back and forth in the first direction. For example, when the laser beam 70 has a width sufficient to cover the range of interest to be cleaned, the scanning may omit moving the laser beam 70 back and forth in the first direction and may move the laser beam 70 in only one direction. Figure 8 In the example in FIG. 2 , when the laser beam 70 has a spot size wider than the width of the residue 20 , the scanning is only along the residue line.

[0077] Additionally, the apparatus 200 can control the energy of the laser 70 by reducing the energy toward the end of each pass in the first direction. This can prevent overheating at the end of each scan, especially when the scan is a line transverse to the residue 20 as in the above example. A circular spot size wide enough to cover the width of the residue will have a similar effect of providing higher energy in the middle of a scan line than adjacent to the scan line.

[0078] When the substrate 10 at least partially reflects the irradiation of the laser beam 70, the cleaning method may include monitoring the reflection of the laser beam 70, which will vary depending on the remaining residue in the irradiated area. The cleaning process may then be terminated based on monitoring the reflection.

[0079] Depending on the substrate being cleaned, it is preferred to perform the cleaning method under an inert gas (e.g., nitrogen) to avoid oxidation of the surface. In addition, the parameters of the laser beam can be controlled so that the surface temperature of the substrate 10 remains below a threshold level to avoid affecting the physical or optical properties of the substrate. Specifically, the parameters can be controlled so that the surface temperature of the substrate 10 does not exceed 500° C., for example. The surface temperature can be measured during the process, or the process can be controlled according to an appropriate protocol. If a substantial deviation from the protocol is detected (e.g., scanning is not performed properly) so that the laser beam is, for example, stationary or not moving in the desired cleaning direction, the laser can be turned off or diverted to avoid overheating of the substrate.

[0080] In addition, the method of cleaning a substrate can also be implemented by causing the functions performed by the device 200 to be controlled by a known information processing device (i.e., a computer). The known information processing device may be any information device connected to the laser irradiation device and capable of controlling the laser irradiation device. The computer may include a memory configured to store therein various programs, the various programs having the same functions to implement the method of cleaning a substrate as explained above. The computer may include a CPU configured to read the various programs from the memory and execute the programs to control the associated equipment to clean the substrate.

[0081] The various programs may not always be stored in the computer itself, but may be stored in a computer-read-only recording medium (e.g., a CD-ROM, a DVD disk, or a USB memory), a semiconductor memory (e.g., a flash memory), a hard disk drive, or other media. In addition, the various programs may also be stored in a device connected to the apparatus via a network (e.g., the Internet, a local area network (LAN), a wide area network (WAN), etc.), and the computer may also read and execute the programs from the recording medium described above.

Claims

1. A method for cleaning a substrate having residue to be removed on at least one surface of the substrate, the method comprising: scanning at least one area of ​​the surface having the residue thereon with a laser, thereby heating the surface and the residue; as well as The heating is controlled so that a portion of the residue liquefies first, so that the liquefied portion of the residue begins to flow toward the solid portion of the residue, thereby forming a meniscus with the solid portion of the residue and partially accumulating on top of the solid portion, whereby the resulting thicker residue layer absorbs more heat to decompose or vaporize, wherein the scanning of the laser comprises repeatedly moving the laser back and forth in a first direction at a first scanning speed, and moving the laser in a second direction perpendicular to the first direction at a second scanning speed, wherein the first scanning speed is faster than the second scanning speed, wherein due to the first scanning speed the meniscus is formed at the scanning area of ​​the surface, and wherein due to the second scanning speed the meniscus is moved forward in the second direction, wherein in a first stage, the meniscus is moved, and in a second stage, the meniscus is heated to a temperature above its decomposition temperature, and The first scanning speed is between 5 cm / s and 254 cm / s, and the second scanning speed is between 1 cm / s and 10 cm / s.

2. The method of claim 1 , wherein the heating is at least partially controlled by at least one of: a scanning speed, a laser spot size of the laser on the substrate, a pulse frequency of the laser, a laser focus level, and an energy of the laser.

3. The method according to claim 1, wherein The surface of the substrate having the residue thereon has a central region, and the residue is located in a region of the surface radially outside the central region, and The second direction is along a direction from the radial inside of the remnant to the radial outside of the remnant, so that the meniscus moves away from the central area.

4. The method according to claim 1, wherein The surface of the substrate having the residue thereon has a central region, The central area has a rectangular shape, The residue has a linear shape approximately parallel to one side of the central region, The first direction is the longitudinal direction of the residue, and The second direction is the width direction of the residue.

5. The method according to claim 1, wherein The surface of the substrate having the residue thereon has a central region, The central area has a rectangular shape, The residue is located outside the central region, and The second direction points away from the central region towards an edge of the substrate.

6. The method of claim 1, wherein the scanning of the laser comprises moving forward in the second direction at the second scanning speed, the second scanning speed being slow enough to cause a meniscus formed in a scanning area of ​​the surface to move forward in the second direction.

7. The method of claim 1, wherein the laser has a wavelength between 5 microns and 25 microns.

8. The method according to claim 1, wherein The laser is a CO2 laser with a wavelength of 10.6 microns, and The substrate is any one of a bare quartz substrate, a metal coated substrate, and a mixture of metal and quartz substrates.

9. The method of claim 1, wherein the energy of the laser light decreases toward the end of each scan pass in the first direction.

10. The method according to claim 1, wherein The substrate at least partially reflects the irradiation of the laser, and the method further comprises: monitoring reflectivity of the laser from the substrate; as well as The irradiation of the laser light is terminated based on the reflectivity.

11. An apparatus for cleaning a substrate having residue to be removed on at least one surface of the substrate, the apparatus comprising: a laser configured to scan at least one area of ​​the surface having the residue thereon with the laser, thereby heating the surface and the residue; a control unit configured to control the heating so that a portion of the residue liquefies first, so that the liquefied portion of the residue begins to flow toward the solid portion of the residue, thereby forming a meniscus with the solid portion of the residue and partially accumulating on top of the solid portion, whereby the resulting thicker residue layer absorbs more heat to decompose or vaporize, wherein the scanning of the laser comprises repeatedly moving the laser back and forth in a first direction at a first scanning speed, and moving the laser in a second direction perpendicular to the first direction at a second scanning speed, wherein the first scanning speed is faster than the second scanning speed, wherein due to the first scanning speed the meniscus is formed at the scanning area of ​​the surface, and wherein due to the second scanning speed the meniscus is moved forward in the second direction, wherein the control unit is configured to move the meniscus in a first phase, to heat the meniscus to a temperature above its decomposition temperature in a second phase, and The first scanning speed is between 5 cm / s and 254 cm / s, and the second scanning speed is between 1 cm / s and 10 cm / s.

12. A computer-readable storage medium, which when executed on a computer is capable of operating an associated device to perform a method of cleaning a substrate having residue to be removed on at least one surface of the substrate, the method comprising: scanning at least one area of ​​the surface having the residue thereon with a laser, thereby heating the surface and the residue; The heating is controlled so that a portion of the residue liquefies first, so that the liquefied portion of the residue begins to flow toward the solid portion of the residue, thereby forming a meniscus with the solid portion of the residue and partially accumulating on top of the solid portion, whereby the resulting thicker residue layer absorbs more heat to decompose or vaporize, wherein the scanning of the laser comprises repeatedly moving the laser back and forth in a first direction at a first scanning speed, and moving the laser in a second direction perpendicular to the first direction at a second scanning speed, wherein the first scanning speed is faster than the second scanning speed, wherein due to the first scanning speed the meniscus is formed at the scanning area of ​​the surface, and wherein due to the second scanning speed the meniscus is moved forward in the second direction, wherein in a first stage, the meniscus is moved, and in a second stage, the meniscus is heated to a temperature above its decomposition temperature, and The first scanning speed is between 5 cm / s and 254 cm / s, and the second scanning speed is between 1 cm / s and 10 cm / s.

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