PATENT DOCUMENT

Publication Number: US-10300557-B2
Application Number: US-201715712646-A
Country: US
Kind Code: B2

Title: Hybrid substrate processing

Abstract:
A hybrid laser modulation and acid etch process for the creation of a patterned substrate. According to some embodiments, a hole is formed in a glass substrate by first modulating a portion of the substrate in the desired shape. A mask is coated on the glass substrate and is patterned to expose the modulated portion. The glass substrate is then acid etched to remove the modulated portion. Once the modulated portion has been etched, the desired shape may be removed from the glass substrate and the mask may be stripped.

Claims:
What is claimed is: 
     
       1. A method of forming a hole in a substrate comprising material transparent to a laser, the method comprising:
 forming a modulated area according to a first predetermined pattern in the substrate by exposing the substrate to a pulsed laser beam according to the first predetermined pattern, wherein the first predetermined pattern defines a perimeter of the hole and surrounds a first portion of the substrate, and wherein a wavelength, power and pulse duration of the laser beam are selected to modify properties of the substrate in the modulated area without ablating the substrate; 
 depositing a mask over the substrate including the modulated area, the first portion of the substrate and a second portion of the substrate that surrounds the modulated area; 
 patterning the mask according to a second predetermined pattern that corresponds with the first predetermined pattern to form a patterned mask area; 
 etching through the mask and the substrate in the patterned mask area; 
 stripping the mask from the substrate; and 
 separating the first portion of the substrate from the second portion of the substrate. 
 
     
     
       2. The method of  claim 1  wherein the first portion of the substrate is exposed to pulses from a picosecond laser during the modulating. 
     
     
       3. The method of  claim 2  wherein the laser creates a Bessel beam. 
     
     
       4. The method of  claim 2  wherein the laser modulates the first portion of the substrate at a power level below an ablation threshold of the substrate. 
     
     
       5. The method of  claim 1  wherein modulating the first portion of the substrate changes a refractive index of the first portion of the substrate. 
     
     
       6. The method of  claim 1  wherein modulating the first portion of the substrate changes a microstructure of the first portion of the substrate. 
     
     
       7. The method of  claim 1  wherein the substrate is transparent. 
     
     
       8. The method of  claim 1  wherein etching the first portion of the substrate comprises exposing the substrate to acid. 
     
     
       9. The method of  claim 1  further comprising:
 etching the second portion of the substrate, wherein the first portion of the substrate etches at a faster rate than the second portion of the substrate. 
 
     
     
       10. The method of  claim 1  wherein the mask is patterned using photolithography. 
     
     
       11. The method of  claim 1  wherein the mask comprises a hard mask. 
     
     
       12. The method of  claim 1  wherein the mask comprises a photoresist. 
     
     
       13. The method of  claim 1  wherein after the first portion of the substrate is separated from the second portion of the substrate, edges of the first and second portion have a smooth curved surface. 
     
     
       14. The method of  claim 1  wherein the substrate is glass. 
     
     
       15. The method of  claim 1  wherein the laser beam has a collimated portion that is collimated in a focal region and the collimated portion is focused on the substrate. 
     
     
       16. The method of  claim 1  further comprising, after the mask is removed from the substrate:
 applying force to the substrate at a location within the patterned area to remove a section of the substrate corresponding to the hole. 
 
     
     
       17. The method of  claim 1  wherein the mask comprises a photoresist layer and the patterning comprises a photolithography process. 
     
     
       18. A method of forming a hole in a substrate comprising material transparent to a laser, the method comprising:
 forming a modulated area in the substrate according to a first predetermined pattern that defines a perimeter of the hole by exposing the substrate to laser beam pulses from a picosecond laser according to the first predetermined pattern, wherein the laser pulses are shaped with optics into an elongated beam shape focused within the substrate and wherein a wavelength, power and pulse duration of the laser beam are selected to modify properties of the substrate in the modulated area without ablating the substrate; 
 depositing a mask over the substrate including the modulated area, the first portion of the substrate and a second portion of the substrate that surrounds the modulated area; 
 patterning the mask according to a second predetermined pattern that corresponds with the first predetermined pattern to form a patterned mask area; 
 etching through the substrate in the modulated area; and 
 separating the first portion of the substrate from the second portion of the substrate. 
 
     
     
       19. The method of  claim 18  wherein the laser beam is collimated in a depth of focus between 0.1 to 3 mm. 
     
     
       20. The method of  claim 19  wherein forming the modulated region is done with a single pass of the laser along the first predetermined pattern. 
     
     
       21. The method of  claim 19  wherein forming the modulated region is done with multiple passes of the laser along the first predetermined pattern, wherein in each of the multiple passes the laser is focused at a different depth of the substrate.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 62/398,743, filed Sep. 23, 2016, and is hereby incorporated by reference in its entirety. 
    
    
     FIELD 
     The present disclosure relates generally to the manufacturing of a patterned substrate using a hybrid laser modulation and acid etch process. 
     BACKGROUND 
     Many processes exist for patterning substrates to create holes therein. For example, according to one conventional process, mechanical drilling may be used to create holes in glass substrates. Mechanical drilling is insufficient for some applications, however. For example, mechanical drilling may undesirably weaken the mechanical strength of the substrate drilled and it may be difficult to create certain shapes in glass substrates using a mechanical drilling process. 
     Other processes to create holes in glass substrates have been developed that provide better results for some applications. For example, laser ablation may be used to create holes in glass substrates. Although laser ablation can improve upon some of the disadvantages of mechanical drilling, laser ablation also has some drawbacks that can make it undesirable for certain applications. 
     SUMMARY 
     Various embodiments of the disclosure pertain to a hybrid laser modulation and acid etch process for the creation of a patterned substrate that improve upon some or all of the above-described deficiencies. According to some embodiments of the disclosure, a hole is formed in a glass substrate by first modulating a portion of the substrate in the desired shape by exposing the substrate to a pulsed laser beam. A mask is coated on the glass substrate and is patterned to expose the modulated portion. The glass substrate is then acid etched to remove the modulated portion. Once the modulated portion has been etched, the desired shape may be removed from the glass substrate and the mask may be stripped. 
     According to some embodiments of the disclosure, improved glass substrate properties may be observed using the hybrid laser modulation-acid etch process. For example, the hybrid process may result in high mechanical strength, minimum cost, for example, due to minimum acid consumption, reduced processing time, and/or reuse of the removed portion of the substrate), controllable taper, zero heat-affected zone, small burr size (e.g., &lt;1 μm), high circularity (e.g., 99%), no chipping, excellent edge quality, and/or minimal edge roughness (e.g., ˜0 μm). In other words, some embodiments of the disclosure result in naturally smooth edges with no additional post-processing needed. In addition, some embodiments of the disclosure may be used to create an infinite number of shapes in the glass substrate. 
     In some embodiments, a method is provided. The method includes providing a substrate; modulating a first portion of the substrate by exposing the first portion to a pulsed laser while a second portion of the substrate remains unmodulated; and then etching the first portion of the substrate. 
     In some embodiments, a method of forming a hole in a glass substrate is provided. The method includes exposing the glass substrate to a pulsed laser beam according to a first predetermined pattern that defines a perimeter of the hole. A wavelength, power and pulse duration of the laser beam are selected to modify properties of the glass substrate in the area correspond to the first predetermined pattern without ablating the glass substrate, thereby forming a modulated area. The method further includes depositing a mask over the glass substrate including the modulated area. The method further includes patterning the mask according to a second predetermined pattern that corresponds with the first predetermined pattern to form a patterned mask area. The method further includes etching through the mask and the glass substrate in the patterned mask area and stripping the mask from the glass substrate. 
     In some embodiments, a method of forming a hole in a substrate comprising material transparent to a laser (e.g., a glass or sapphire substrate) is provided. The method can include exposing a first portion of the substrate to a pulsed laser beam according to a first predetermined pattern that defines a perimeter of the hole, wherein a wavelength, power and pulse duration of the laser beam are selected to modify properties of the substrate in the area corresponding to the first predetermined pattern without ablating the substrate, forming a modulated area that surrounds a second portion of the substrate; etching through the substrate in the modulated area; and removing the second portion of the substrate. 
     The following detailed description together with the accompanying drawings in which the same reference numerals are sometimes used in multiple figures to designate similar or identical structural elements, provide a better understanding of the nature and advantages of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a flow diagram of a method of processing a substrate according to an embodiment of the disclosure; 
         FIG. 2A  is a top view of a substrate that may be modulated according to an embodiment of the disclosure; 
         FIG. 2B  is a cross-sectional view of a substrate that may be modulated according to an embodiment of the disclosure; 
         FIG. 3A  is a top view of a substrate that has been modulated according to an embodiment of the disclosure; 
         FIG. 3B  is a cross-sectional view of a substrate that has been modulated according to an embodiment of the disclosure; 
         FIG. 3C  is a microscopic top view of a substrate that has been modulated according to an embodiment of the disclosure; 
         FIG. 4  is a microscopic cross-sectional view of a substrate that has been modulated according to an embodiment of the disclosure; 
         FIG. 5A  is a top view of a substrate having a multi-layered hard mask applied and patterned thereon according to an embodiment of the disclosure; 
         FIG. 5B  is a cross-sectional view of a substrate having a multi-layered hard mask applied and patterned thereon according to an embodiment of the disclosure; 
         FIG. 6A  is a top view of a substrate that has been acid etched according to an embodiment of the disclosure; 
         FIG. 6B  is a cross-sectional view of a substrate that has been acid etched according to an embodiment of the disclosure; 
         FIG. 7A  is a top view of a substrate with a portion removed according to an embodiment of the disclosure; 
         FIG. 7B  is a cross-sectional view of a substrate with a portion removed according to an embodiment of the disclosure; 
         FIG. 8A  is a top view of a substrate with a hole according to an embodiment of the disclosure; and 
         FIG. 8B  is a cross-sectional view of a substrate with a hole according to an embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference is now made to  FIG. 1 , which depicts a flow diagram  100  of a method for hybrid laser modulation-acid etch substrate processing according to some embodiments of the disclosure. At step  110 , a substrate is modulated to change the microstructure and refractive index of the substrate in an area defining where a hole is to be formed in the substrate.  FIG. 2A  depicts a top view of a substrate  200  that may be modulated according to some embodiments of the disclosure.  FIG. 2B  depicts a cross-sectional view of the substrate  200 . Substrate  200  may be made of any material that does not block laser beams, such as transparent materials. For example, substrate  200  may comprise glass, plastic, acrylic, sapphire, and/or the like. Although shown as being a particular size, shape, and thickness, it is contemplated that substrate  200  may be of any size, shape, and/or thickness, and have any suitable dimensions. 
     The substrate may be modulated in a desired portion to be removed from substrate  200 . In some embodiments, the entire area to be removed from the substrate is modulated in step  110 , while in other embodiments, the substrate is modulated according to a predetermined pattern that defines a perimeter of the area to be removed.  FIG. 3A  depicts a top view of a substrate  200  that has been modulated according to a circular pattern in portion  312  per the latter approach as part of a process to form a circular hole in the substrate defining a portion  316  of substrate  200  that can be removed. Although portion  312  is shown in a particular pattern, it is contemplated that portion  312  may be of any size, shape, and/or thickness, and have any suitable dimensions. 
       FIG. 3B  depicts a cross-sectional view of the substrate  200  that has been modulated in portion  312 . Portion  312  may be modulated with a laser beam to structurally change substrate  200  in portion  312 . In some embodiments, the laser beam may be a ultra-short, ultra-fast high-intensity pulse laser emitting bursts of pulses. Short pulse wavelengths may be employed to modulate the substrate  200 , as opposed to ablating, vaporizing and/or burning off the substrate  200 , which may occur with longer pulse wavelengths. Exemplary laser wavelengths that may be used include those in the green spectrum (e.g., 532 nm), those in the infrared spectrum (e.g., 1064 nm), and/or those in the blue spectrum (e.g., 355 nm). In some embodiments, the laser may be a picosecond laser, and in some embodiments the picolaser can emit bursts of 12-24 nanosecond pulses at a frequency of approximately 200 KHz. 
     During step  110 , the laser can be moved across substrate  200  according to a path that defines portion  312 . The speed at which the laser is moved along the path may result in a path of closely spaced circular exposure regions  312 ( 1 )- 312 ( n ) in portion  312  as shown in  FIG. 3C , which illustrates a simplified top view of path  312  shown in  FIG. 3A , created by moving the laser along the circular path  312  in the direction indicated by arrow  320 . 
     The laser may employ particular optics to generate an elongated beam shape, such as Bessel optics, axicon lenses, diffraction lenses, and the like. Due to the elongated beam shape and the ultra-fast pulses, the laser may structurally change portion  312  of substrate  200  in a single pass, such that each area of portion  312  may receive one pulse in some embodiments. For example, in the case of a glass substrate  200 , a thickness of up to about 3 mm may be modulated in one pass with the laser beam collimated in a depth of focus between 0.1 to 3 mm. In some embodiments, the laser beam may make more than one pass over portion  312  and be focused at different depths of the substrate in each pass. The laser may operate at a power level below the ablation threshold of the material of substrate  200 . 
     Once modulated, dotted and/or hourglass structures  312 ( i ) may be seen in portion  312  under a microscope at each location that the substrate was exposed to a pulsed laser beam.  FIG. 4  depicts a cross-sectional view of portion  312  as seen under a microscope. Each individual hourglass-like structure  312 ( i ) shown in  FIG. 4  can be representative of one of the exposure regions  312 ( 1 )- 312 ( n ) shown in  FIG. 3C . As the pulsed laser enters the substrate to forms each individual structure  312 ( i ), the light modifies physical properties of the substrate changing its refractive index. The laser beam thus sees the substrate as having a different refractive index at different depths of each structure  312 ( i ) and bends and refocus accordingly to an extent that a plasma can be generated within the substrate. The plasma can then interfere with the focusing process and thus defocusing the light. At very high intensities that can be used by the picosecond laser according to embodiments of the disclosure, this process can be self-induced. 
     Regions in which the light bends and refocuses can be referred to as regions of Kerr-lens focusing and are shown as regions  330 ,  334  and  338  in  FIG. 4 . The regions at which a plasma can be formed that defocuses the light are shown as regions  332  and  336 . At the conclusion of the process, transparent substrate  200 , the modulated portion of substrate  200  formed by the combined structures  312 ( i ) can change the refraction index of substrate  200  in the area of portion  312 . In some embodiments, the individual regions  332 ,  336 , represented in  FIG. 4  by dots, created in each structure  312 ( i ) may have a diameter in the range of about 1 micron to about 10 microns. 
     Turning back now to  FIG. 1 , at step  120 , a mask is coated on the substrate. For example, a mask may be coated entirely on substrate  200  (i.e., top, bottom, and sides, including portion  312 ). The mask may then be patterned using photolithography to expose portion  312  of substrate  200 . In some embodiments, the mask is a photoresist. Exemplary photoresists that may be used include any commercially available photoresist, such as PMMA, AZ4620, AZ4562, and the like. 
     In some embodiments, the mask is a hard mask. The hard mask may be multilayered in some embodiments.  FIGS. 5A and 5B  depict a top view and a cross-sectional view, respectively, of a substrate  200  having a multi-layered hard mask applied and patterned thereon. The multi-layered hard mask includes a lower layer  522  and an upper layer  524 . The lower layer  522  and upper layer  524  have been patterned to expose portion  312  of substrate  200 . The lower layer  522  and the upper layer  524  may be patterned according to any suitable method. Although shown in  FIG. 5B  as being applied to the top surface of the substrate  200 , it is contemplated that the lower layer  522  and the upper layer  524  may be alternatively or additionally applied to the side surfaces and bottom surfaces of the substrate  200 . In some embodiments, the lower layer  522  and the upper layer  524  may be applied to all exposed surfaces of the substrate  200 , then patterned to expose portion  312  of substrate  200 . 
     The lower layer  522  and the upper layer  524  may include any of a number of materials. In one example, the lower layer  522  may include chrome of a first thickness (e.g., 500 Å), while the upper layer  524  may include amorphous silicon of a second thickness (e.g., 5000 Å). In this example, the chrome lower layer  522  may be deposited using physical vapor deposition, for example, while the amorphous silicon upper layer  524  may be deposited using plasma-enhanced chemical vapor deposition. However, it is contemplated that any suitable materials may be used for lower layer  522  and upper layer  524  in any thicknesses and may be deposited by any suitable methods. 
     Turning back now to  FIG. 1 , at step  130 , the substrate may be acid etched, e.g., by being exposed to acid and/or placed in an acid bath. The acid etches the modulated portion of the substrate from the substrate, while the remainder of the substrate may remain protected by the mask. In some embodiments, the substrate and the patterned portion of the mask may be etched in a single step.  FIGS. 6A-6B  depict a top view and a cross-sectional view, respectively, of a substrate  200  that has been acid etched. Modulated portion  312  has been removed from substrate  200 , leaving an opening  632  that defines the shape of the desired hole to be formed in the substrate (a circular shape, in this example). While not shown in  FIG. 6B , in some embodiments, the isotropic nature of the etch process in step  130  may result in opening  632  having an hour glass shape where the opening is wider at the opposing surfaces of substrate  200  and narrower in the center. The hour glass shape may beneficially provide a smooth, curved surface along the inner perimeter of the hole defined by opening  632 . The portion of substrate  200  that was not modulated may generally not be acid etched, as it was protected by multi-layered hard mask  522 ,  524 . In addition, because portion  312  is modulated, its etch rate may be significantly higher than the unmodulated portion of substrate  200  (e.g., 10 times higher). Thus, even though a portion of substrate  200  inside opening  632  may be exposed to the acid, it may not be significantly etched. 
     Any suitable acid may be used to acid etch substrate  200 . The type of acid may be selected based on the material of the substrate (e.g., glass), the type of mask used (e.g., a photoresist or a hard mask), the material of the mask used (e.g., chrome, amorphous silicon, PMMA, etc.), and the like. For example, a glass having a higher concentration of SiO 2  may require a higher HF-rich acid in order to be etched. In another example, a glass having a lower concentration of SiO 2  may only need a diluted HF acid. Exemplary acids include HF, HFHCl, HFHNO 3 , diluted HF, HF only, NH 4 F, and the like. 
     Once substrate  200  is acid etched, portion  316  of substrate  200  within the opening  632  may be removed, forming the desired hole. In some embodiments, removing the portion of substrate  200  within the opening  632  may include applying a force to either portion  316 .  FIGS. 7A-7B  depict a top view and a cross-sectional view, respectively, of substrate  200  with the portion of substrate  200  within the opening  632  removed, leaving a hole  732  in substrate  200 , lower layer  522 , and upper layer  524 . The removed portion of substrate  200  may be reused for other purposes or applications in some embodiments. 
     Turning back now to  FIG. 1 , at step  140 , the mask may be stripped from the substrate, leaving only the patterned substrate.  FIGS. 8A-8B  depict a top view and a cross-sectional view, respectively, of substrate  200  with the hole  632 . The mask may be stripped from substrate  200  using any suitable method for that particular type of mask (e.g., the stripping method for a photoresist may differ from the stripping method for a hard mask). In some embodiments, it is contemplated that the mask may be stripped from the substrate  200  prior to the portion of substrate  200  within the opening  632  being removed. 
     Although shown and described as applying a mask for use during the acid etch process, it is contemplated that, in some embodiments, a mask may not be applied to the substrate prior to acid etching. Because the modulated portion of the substrate etches at a much faster rate than the unmodulated portion of the substrate, the modulated portion may etch through the substrate while a substantial thickness of the unmodulated portion still remains. These embodiments may result in a desirable finish on the substrate, although some substrate thickness may be lost. Nevertheless, these embodiments may be desirable from a cost-yield perspective in some situations. 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of the specific embodiments described herein are presented for purposes of illustration and description. They are not taught to be exhaustive or to limit the embodiments to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings.

Metadata:
Filing Date: 20170922
Publication Date: 20190528
Grant Date: 20190528
Priority Date: 20160923
Inventors: GUPTA, NATHAN K.
LANCASTER-LAROCQUE, SIMON R.
SHARMA, Prithu
CHENG, Weibo
KANGUDE, ABHIJIT A.
POSNER, BRYAN W.
JINASUNDERA, SUDIRUKKUGE T.
BIR, KARAN
Assignee: APPLE INC
CPC Classifications: [{"code": "B23K26/08", "inventive": true, "first": false, "tree": "[]"}, {"code": "B23K26/53", "inventive": true, "first": false, "tree": "[]"}, {"code": "B23K26/0622", "inventive": true, "first": false, "tree": "[]"}, {"code": "B23K2103/54", "inventive": false, "first": false, "tree": "[]"}, {"code": "B23K26/36", "inventive": true, "first": true, "tree": "[]"}, {"code": "B23K26/0006", "inventive": true, "first": false, "tree": "[]"}, {"code": "B23K2103/54", "inventive": false, "first": false, "tree": "[]"}, {"code": "B23K26/53", "inventive": true, "first": false, "tree": "[]"}, {"code": "B23K26/53", "inventive": true, "first": true, "tree": "[]"}, {"code": "B23K2103/54", "inventive": false, "first": false, "tree": "[]"}, {"code": "B23K26/36", "inventive": true, "first": true, "tree": "[]"}, {"code": "B23K26/08", "inventive": true, "first": false, "tree": "[]"}, {"code": "B23K26/0622", "inventive": true, "first": false, "tree": "[]"}, {"code": "B23K26/0006", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 61687491