JP2023039239A - Method and apparatus for executing laser ablation - Google Patents

Abstract

To provide a method and apparatus for executing laser ablation.SOLUTION: According to one configuration, an ultraviolet laser beam 8 is oriented through a mask 10 in order to form an image of a portion of an ablation pattern defined by the mask 10 on a material layer. The laser beam 8 is scanned on the mask 10 in order to sequentially form images of different portions of the ablation pattern on different regions of a layer 4. The laser beam 8 includes an ultra-high speed pulse laser beam having the pulse length less than 20 picoseconds.SELECTED DRAWING: Figure 1

Description

The present invention relates to methods and apparatus for performing laser ablation, particularly for forming fine metal meshes.

Fine metal mesh (FMM) is used in the fabrication of organic light emitting diode (OLED) displays. Specifically, it is used as an OLED deposition mask in the manufacture of displays. The FMM defines where the OLED molecules are deposited on the display and ultimately determines the resolution of the OLED display.

Current techniques for manufacturing fine metal meshes include photolithographic and electroforming processes. However, the cost of such processes is high, and the resolution of OLED displays using FMMs manufactured using such techniques is typically less than 600 pixels per inch (ppi). Modern applications, such as mobile phones and virtual reality headsets, require higher resolutions, eg, 1000 ppi or higher. FMMs manufactured by photolithographic and electroforming processes struggle to achieve such high resolutions.

Other conventional techniques for fabricating FMMs include splitting a single laser beam into multiple laser beams and scanning these laser beams across the surface of the substrate to form FMMs by ablation. . Such techniques typically use femtosecond pulsed infrared lasers. However, such techniques require complex projection optics to obtain multiple laser beams. The difficulty, if not impossible, of scaling up this technique to thousands of laser beams limits the speed at which FMMs can be manufactured in this manner. Such systems are capable of producing FMMs with apertures having critical dimensions of 10 μm and resolutions of several hundred dots per inch (dpi).

Embodiments of the present disclosure are intended to address, at least in part, one or more of the problems discussed above and/or other problems.

According to one aspect of the invention, a method of performing laser ablation comprises directing an ultraviolet laser beam through a mask to image a portion of an ablation pattern defined by the mask onto a layer of material. and scanning the laser beam over the mask to sequentially image different portions of the ablation pattern onto different respective regions of the layer, thereby ablating structures in the layer corresponding to the ablation pattern; A method is provided wherein the laser beam comprises an ultrafast pulsed laser beam having a pulse length of less than 20 picoseconds.

Accordingly, a method is provided for defining an ablation pattern from which a mask is formed. The ablation pattern can be defined by multiple transparent areas within the mask. A single laser beam is used to simultaneously irradiate multiple transparent regions within the mask, thereby contributing to the ablation of a corresponding number of features within the layer of material being ablated, when compared to the prior art described above. can do. This is accomplished without the need for complex beam splitting and balancing optics, and can be scaled to achieve simultaneous processing of very large numbers of features. High laser power can be used because the laser power can be distributed over many different features of the ablation pattern. The use of high power lasers facilitates high throughput. By using ultraviolet irradiation, high spatial resolution can be achieved at reasonable operating costs. Using a mask to define the ablation pattern (rather than via individual beam spots directly from the laser) reduces the requirements for the laser beam used to illuminate the mask while still defining the ablation pattern with high accuracy can. The laser can simply be "flowed" over the mask at relatively low resolution.

In one embodiment, the structure corresponding to the ablation pattern includes a regular array of openings. All of the openings can have approximately the same size and shape. Therefore, an ablation pattern can be used to form an FMM.

In one embodiment, the imaged portion of the ablation pattern contributes to forming multiple openings in the layer. The plurality of apertures corresponding to each imaging portion can include at least 100 apertures. Laser pulse energy is thus spread over at least 100 apertures without the need for complex beam splitting and balancing. Further, in one embodiment, successive imaging of different portions of the ablation pattern can contribute to forming at least 100,000 openings in the layer. Therefore, simply by scanning the laser beam over the mask, the number of openings formed can be greatly increased. This approach can be scaled up to handle over 500,000 openings, over 750,000 openings, or even over a million openings using a single mask.

In one embodiment, each of the openings is tapered to have a decreasing cross-sectional area in the downstream direction of the laser beam. The directing and scanning steps can then be repeated for multiple mask patterns, each mask pattern defining a cross-sectional area of the tapered opening at a different depth. This approach allows efficient and precise control of the profile of the tapered opening. Optimizing the FMM aperture taper can improve the performance of OLED manufacturing processes using FMM by minimizing pattern edge blurring during deposition of the pattern of OLED molecules. Typically, the tapered opening of the FMM is positioned to face (ie, open outward from) the substrate on which the OLED molecules are deposited. Controlling the angle of the taper provides spatially accurate FMM with high resolution (which can limit the maximum amount of taper allowed) and (in general, increasing the amount of taper An optimal balance can be achieved between minimizing the redirection of OLED molecular orbitals due to undesired interactions (collisions) with the sidewalls of the FMM aperture (which can be improved).

As noted above, the layers can include metal layers (eg, to form an FMM). The metal layer can have various compositions depending on the purpose of the FMM. The metal layer can be made of a material with a very low coefficient of thermal expansion, for example Invar. Other materials can also be used, including non-metallic materials. Layers can include, for example, dielectric materials and/or polymers.

In one embodiment, the structure includes part of an evaporation mask for depositing OLED molecules during fabrication of OLED-based displays. Thus, OLED molecules are deposited by forming an evaporation mask using the method of performing laser ablation of the present disclosure and using the resulting evaporation mask to deposit organic light-emitting molecules in a pattern defined by the evaporation mask. can provide a way to

According to another aspect of the invention, an apparatus for performing laser ablation comprising:
an ultraviolet laser configured to produce an ultrafast pulsed laser beam having a pulse length of less than 20 picoseconds; a mask defining an ablation pattern; An optical system configured to image onto the layer and a laser beam scanned over the mask to sequentially image different portions of the ablation pattern onto the layer, thereby identifying structures corresponding to the ablation pattern within the layer. and a scanning device configured to ablate.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings.

1 is a schematic side view of an apparatus for performing laser ablation; FIG. 2 is a top view of a mask that can be used in the apparatus shown in FIG. 1; FIG. FIG. 4A is a top view of a mask showing how a laser beam can be scanned over the mask; 2 is a top view of the layer shown in FIG. 1 with an ablation pattern ablated into the layer; FIG. 2A-2D are cross-sectional side views showing different stages of ablation of a tapered opening; 2A-2D are cross-sectional side views showing different stages of ablation of a tapered opening; 2A-2D are cross-sectional side views showing different stages of ablation of a tapered opening; Figure 3 shows multiple mask patterns for different scans over the same area of a layer, where the mask patterns are provided on separate masks. Fig. 2 shows multiple mask patterns for different scans over the same area of a layer, where the mask patterns are provided on different areas of the same mask. FIG. 10 is a cross-sectional side view showing different aperture taper profiles formed by decreasing or increasing laser energy density (fluence). FIG. 10 is a cross-sectional side view showing different aperture taper profiles formed by decreasing or increasing laser energy density (fluence).

FIG. 1 shows an exemplary apparatus 2 for performing laser ablation. Apparatus 2 uses an ultraviolet laser 6 configured to provide an ultrafast pulsed laser beam 8 . The ultrafast pulsed laser beam 8 is less than 20 ps, optionally less than 15 ps, optionally less than 10 ps, optionally less than 8 ps, optionally less than 6 ps, optionally less than 5 ps It has a pulse length of less than a second. A mask 10 is provided that defines an ablation pattern 18 (shown in FIG. 2). A material layer 4 to be processed is provided on a support 12 (eg a substrate). Support 12 may be provided on a movable table (not shown) for stepping support 12 to different positions under laser beam 8 . An optical system 13 is provided for directing a laser beam 8 through mask 10 and onto layer 4 . Optical system 13 images a portion of ablation pattern 18 onto layer 4 .

Scanning device 14 scans laser beam 8 over mask 10 to sequentially image different portions of ablation pattern 18 defined by mask 10 onto different respective regions of layer 4 . A structure corresponding to the ablation pattern is thereby ablated in layer 4 . Laser beam 8 is typically scanned over mask 10 without corresponding movement of laser 6 or mask 10 (eg, by suitable scanning optics).

The use of ultraviolet wavelengths allows structures to be formed in layer 4 with high resolution without the need for complex and/or expensive optics. Resolutions up to 1000 dpi are typically formed, including features such as indentations or openings having critical dimensions of, for example, about 3 μm or less.

Device 2 may further include a controller 15 for controlling the overall operation of device 2 . Controller 15 controls laser 6, scanner 14 (e.g., to control when the laser is turned on and off and/or to change laser parameters such as energy per pulse or pulse repetition rate). , and optical system 13 (eg, to control focus height) and movement of support 12 relative to laser 6 (eg, via a movable table and associated motors) can be controlled.

In one embodiment, apparatus 2 further includes optics 16 downstream from mask 10 (eg, including lenses). Optics 16 can focus laser radiation 8 from mask 10 onto layer 4 . In one embodiment, optical system 16 provides demagnification between mask 10 and layer 4 . Therefore, the features formed on layer 4 by ablation are smaller than the corresponding features in mask 10 . This approach allows high resolution patterns to be formed in layer 4 while distributing the laser energy over a larger area of mask 10 . Therefore, the laser energy density (fluence) is lower with the mask 10 than otherwise. This allows higher laser pulse energies and higher laser powers to be used, which improves throughput without the risk of damaging the mask 10 . Moreover, mask 10 can be manufactured at a lower resolution than the pattern required in layer 4, which facilitates manufacturing of mask 10. FIG.

In some embodiments, the ablation-producing structures in layer 4 corresponding to the ablation pattern of mask 10 comprise a regular array of openings in layer 4 . The pitch of the array of layers 4 can be very small, for example 10 microns or less. All of the at least one subset of apertures have approximately the same size and shape and/or are otherwise suitable for forming all or part of an FMM for use in manufacturing an OLED-based display. can be configured in the same way. FIG. 2 is a top view of an exemplary mask 10 for forming such an ablation pattern. Mask 10 in this example includes a regular array of transparent regions 20 . Each transparent region 20 corresponds to a respective opening formed in layer 4 . The pitch of transparent regions 20 on mask 10 is typically larger than the pitch of corresponding openings in layer 4 due to demagnification. For ease of illustration, the mask 10 of FIG. 2 includes only a relatively small number of transparent regions 20. FIG. In practice, more transparent regions 20 (eg, 100,000 or more, as discussed below) are likely to be provided per mask.

In some embodiments, each imaged portion of ablation pattern 18 in mask 10 contributes to forming multiple openings in layer 4 . The plurality of openings can preferably include at least 100 openings. For example, each opening in layer 4 can be formed (partially or completely) by directing laser radiation through a corresponding transparent region 20 on mask 10, the imaged portion of ablation pattern 18 being , can be formed by simultaneously irradiating a plurality (eg, 100 or more) of such transparent regions 20 on mask 10 . Simultaneously irradiating multiple transparent areas 20 in this manner can contribute to the formation of multiple openings in layer 4 at the same time. This maximizes the available laser pulse energy and improves throughput. Combined with the scanning step, very large numbers of openings can be formed quickly. Sequential imaging of different portions of the ablation pattern, for example, through 1000 or more portions of the ablation pattern each contributing at least 100 openings, forms at least 10000 openings in the layer. can contribute to

In the example schematically illustrated in FIG. 2, the ablation pattern 18 defined by mask 10 includes an array of square transparent regions 20. In the example shown schematically in FIG. In other embodiments, the transparent regions 20 can have other shapes, thereby forming different shaped features or openings in the layer 4 . The transparent area 20 can be rectangular, circular, or oval, for example.

FIG. 3 shows an exemplary scanning path 22 of laser beam spot 9 on mask 10 during the scanning step (as seen by laser 6). Laser beam spot 9 is illuminated by laser beam 8 at any given time on mask 10 which defines the corresponding portion of the ablation pattern imaged on layer 4 at that time (“imaged portion”). part. Scan path 22 can be described as a raster scan. Other scanning paths may be used. Scan path 22 may be adapted to avoid areas within layer 4 where no structure is desired. Scan path 22 adds other factors such as the nature of laser 6 used (eg, power and/or spot size 9 at mask 10), ablation pattern 18 in mask 10, and/or characteristics of layer 4. can be considered either objectively or alternatively.

FIG. 4 is a top view of layer 4 after ablation into layer 4 of structure 24 corresponding to ablation pattern 18 defined by mask 10 (eg, a square array of openings). Structures 24 may be formed by a single scan over mask 10 or by multiple scans over the mask. For example, in a first scan over mask 10, at least a subset of the features of the structure are ablated through layer 4 to only a portion of their intended depth, thereby partially forming features. can be provided. By repeating the scanning process, each portion is scanned until each partially formed feature is fully formed (e.g., so that the opening extends completely through layer 4). A statically formed feature can be irradiated multiple times. This approach can advantageously dissipate heat between successive ablation processes, thereby helping to prevent unwanted damage to areas outside the target area of ablation. In one embodiment, laser beam spot 9 is scanned multiple times along scan path 22 as discussed above with reference to FIG. Multiple scans can be performed without providing relative motion between mask 10 and layer 4 during the process.

As shown in FIG. 4, structures 24 corresponding to ablation patterns 18 provided by one mask 10 can cover only a small portion of layer 4 to be processed. Therefore, the method can be repeated to treat other required portions of layer 4 . In one embodiment, a step-and-scan process is used whereby structure 24 is formed with layer 4 provided in a first position relative to mask 10 . Layer 4 is then moved to a second position relative to mask 10 (usually by moving layer 4 and keeping mask 10 and optics 16 in place). Relative motion is provided between 4 and mask 10 and the scanning process is repeated to form another instance of structure 24 adjacent the previously formed instance. The process can then be repeated to treat the entire layer 4 . Thus, repeating the above orienting and scanning steps for a plurality of different locations of layer 4 relative to mask 10 in order to ablate structures corresponding to the ablation pattern at a plurality of different locations on layer 4; Thereby much larger structures can be built in layer 4 than would be possible without stepping layer 4 .

In one embodiment, as shown in FIGS. 5-7, each of the openings 25 in the ablation-formed structure 24 is tapered to have a decreasing cross-sectional area in the downstream direction of the laser beam 8. ing. In one embodiment, taper is controlled by repeatedly directing laser beam 8 onto layer 4 through mask 10 and scanning laser beam 8 over mask 10 for a plurality of different mask patterns. , each mask pattern defines a cross-sectional area of tapered opening 25 at a different depth. For example, a first mask pattern may comprise a first plurality of transparent regions 20 corresponding to respective plurality of openings 25 formed in layer 4, and a second mask pattern may comprise the same respective plurality of openings 25. and the third mask pattern comprises a third plurality of transparent regions 20 corresponding to the same respective plurality of openings 25. Alternatively, the transparent areas 20 of the first mask pattern are larger than the transparent areas 20 of the second mask pattern, and the transparent areas of the second mask pattern are larger than the transparent areas 20 of the third mask pattern. An exemplary result of processing using the first mask pattern is shown schematically in FIG. 5 in which shallow depressions with diameter 26 are formed. An exemplary result of processing using the second mask pattern is shown schematically in FIG. An exemplary result of processing using the third mask pattern is shown schematically in FIG. 7 where ablation penetrates layer 4 and forms tapered openings 25 of diameter 30 at the deepest points of depressions 25. ing. Variations in the size of the transparent regions of the first, second and third mask patterns affect the diameters 26, 28 and 30 at different points along the taper, thus permitting precise control of the taper profile.

The approach of repeating the directing and scanning steps against a plurality of mask patterns defining different respective ablation patterns is such that the structure formed is a regular array of openings and the different ablation patterns correspond to the openings. is not limited to corresponding to different depths of . This approach can be applied to different or more complex structures. This approach is useful whenever there is an advantage in controlling the shape of the depressions or openings in layer 4 as a function of the depth of the depressions or openings. In order to achieve shape control as a function of depth, it is generally desirable that the repetition of the directing and scanning steps result in the application of different laser ablation patterns to the same or overlapping regions of layer 4. deaf. Typically, this involves repeating the orientation and scanning without changing the relative position between mask 10 and layer 4, e.g., so that it is the same portion of layer 4 processed each time. would include The multiple mask patterns may be on separate masks 101, 102 and 103, as schematically shown in FIG. 8, or different regions 10A, 10B and 10C.

Other approaches for controlling taper can be used in combination with or as an alternative to the above. For example, in one class of embodiments, the taper is achieved by controlling the fluence of the laser beam 8 onto the mask 10 (pulse energy density - the energy of the laser pulse divided by the area the laser pulse is illuminating). at least partially controlled. For example, laser beam 8 may be scanned multiple times over mask 10, at least two of the scans being performed at different fluences. The fluence of laser beam 8 when incident on layer 4 affects the taper angle of the walls of the ablated pocket within the layer. The higher the fluence, the smaller the taper angle (larger in the vertical direction). The lower the fluence, the larger the taper angle (smaller vertical). Providing the ability to vary the fluence as a function of depth within layer 4 provides a useful additional degree of freedom for adjusting the internal shape (e.g., tapered profile) of structures formed within layer 4. do.

Based on the above, in one class of embodiments, for each of the one or more openings, the fluence of laser beam 8 at mask 10 varies during formation of the openings. A change in fluence at mask 10 causes a corresponding change in fluence at layer 4 . The variation is such that the fluence at the mask (and thus layer 4) is different during the formation of portions of the openings at different depths in layer 4, so that as a function of depth in layer 4 controls the change in the taper angle of the opening of the

In one example procedure, a first scan over mask 10 is performed with laser beam 8 providing a first fluence at mask 10 . Scanning may, for example, follow scan path 22 as described above with reference to FIG. The fluence of the laser beam 8 is such that after this first scan over the mask 10 the structures formed in layer 4 extend only part way through layer 4 (similar to the situation in FIG. 5). can do. A second scan over the mask 10 is then performed with the laser beam 8 providing a second fluence that is lower than the first fluence. This scan results in the deepening of the structures formed in the first scan. However, due to the lower fluence of laser beam 8 during the second scan, the taper angle also increases. A third scan over the mask 10 is then performed with the laser beam 8 providing a third fluence that is lower than the second fluence. The result of this scan is to deepen the structures formed in the second scan until the ablation breaks through to the opposite side of layer 4 . A lower fluence of the laser beam 8 during the third scan means that the taper angle increases further at the newly reached depth. FIG. 10 shows the profile of an opening made in such a way. This approach thus provides an alternative or additional method for controlling the shape of the aperture taper. Although this embodiment has been illustrated with reference to three scans, any number of scans can be used. Furthermore, the fluence need not necessarily be adjusted in the manner described above, but can instead be altered in any suitable manner. A gradual increase in fluence in a continuous scan produces an aperture profile of the type shown in FIG. Furthermore, the fluence of the laser beam 8 need not be different for every scan as long as it is different for at least two scans. The fluence can be increased or decreased between different scans.

Claims (19)

A method of performing laser ablation comprising:
directing an ultraviolet laser beam through a mask to image a portion of the ablation pattern defined by the mask onto a layer of material;
scanning the laser beam over the mask to sequentially image different portions of the ablation pattern onto different respective regions of the layer, thereby ablating structures in the layer corresponding to the ablation pattern. and
The method, wherein the laser beam comprises an ultrafast pulsed laser beam having a pulse length of less than 20 picoseconds. 2. The method of claim 1, wherein the structure corresponding to the ablation pattern comprises a regular array of openings. 3. The method of claim 2, wherein all of at least a subset of said openings have approximately the same size and shape. 4. A method according to claim 2 or 3, wherein each of said openings is tapered to have a decreasing cross-sectional area in the downstream direction of said laser beam. For each of one or more of said openings, the fluence of said laser beam at said mask varies during formation of said openings, said variations resulting in said openings at different depths in said layer of material. 5. The method of claim 4, wherein the fluence is varied during formation of portions of to thereby control the change in taper angle of the opening as a function of the depth of the material layer. 5. The steps of directing and scanning are repeated for a plurality of mask patterns, each mask pattern defining a cross-sectional area of the tapered opening at a different depth or 5. The method described in 5. The method of any one of claims 2-6, wherein each imaged portion of the ablation pattern contributes to forming a plurality of openings in the layer. 8. The method of claim 7, wherein the plurality of apertures corresponding to each imaging portion comprises at least 100 apertures. 9. The method of claim 8, wherein said sequential imaging of different portions of said ablation pattern contributes to forming at least 100,000 openings in said layer. A method according to any one of claims 2 to 9, wherein the pitch of said array is less than 10 microns. The method of any one of claims 1-10, wherein the directing and scanning steps are repeated for a plurality of mask patterns defining different respective ablation patterns. 12. The method of claim 11, wherein the repeating of the directing and scanning steps apply different laser ablation patterns to the same or overlapping regions of the layer. 13. The method of claim 11 or 12, wherein the plurality of mask patterns are provided on separate masks. 13. The method of claim 11 or 12, wherein the multiple mask patterns are provided in different regions of the same mask. A method according to any preceding claim, wherein said layer comprises a metal layer. The orienting and scanning steps are repeated for a plurality of different locations of the layer relative to the mask, thereby ablating the structures corresponding to the ablation pattern at a plurality of different locations on the layer. The method according to any one of claims 1 to 15, wherein A method according to any one of the preceding claims, wherein said structure comprises part of an evaporation mask for depositing organic light-emitting molecules during the manufacture of organic light-emitting molecule-based displays. A method of depositing organic light-emitting molecules comprising:
forming an evaporation mask by performing the method of claim 17;
and using the evaporation mask to deposit organic light emitting molecules in a pattern defined by the evaporation mask. An apparatus for performing laser ablation comprising:
an ultraviolet laser configured to produce an ultrafast pulsed laser beam having a pulse length of less than 20 picoseconds;
a mask defining an ablation pattern;
an optical system configured to direct the laser beam through the mask to image a portion of the ablation pattern onto a material layer;
scanning configured to scan the laser beam over the mask to sequentially image different portions of the ablation pattern onto the layer, thereby ablating structures in the layer corresponding to the ablation pattern; An apparatus, including an apparatus.

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