Patent Publication Number: US-11040427-B2

Title: Workpiece processing method

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a method of processing a workpiece which includes metal. 
     Description of the Related Art 
     In recent years, attention has been paid to WL-CSP (Wafer Level Chip Size Package) in which operations up to packaging of a product are conducted while the product is in a wafer state. In the WL-CSP, a rewiring layer (a redistribution layer) and metal posts (electrodes) are provided on the front surface side of devices formed on a wafer, and, after sealing the wafer with resin or the like, the sealed wafer (WL-CSP substrate) is divided by such a method as cutting. The WL-CSP, in which the size of the divided chip coincides directly with the size of the package, is advantageous from the viewpoint of downsizing. 
     Meanwhile, a ductile material such as metal is plastically elongated when a stress is exerted thereon and, therefore, cannot easily be processed by such a method as grinding or polishing. Accordingly, in the case of thinning the sealing layer side of a workpiece that includes metal such as, for example, a WL-CSP substrate, it may be necessary to grind or shave off the sealing layer and the like by a method such as grinding and thereafter to process the metal by another method such as cutting with a cutting tool (see, for example, Japanese Patent Laid-Open No. 2013-8898). 
     SUMMARY OF THE INVENTION 
     However, a combination of a plurality of different methods as aforementioned leads to an intricate production process and a higher production cost. 
     Accordingly, it is an object of the present invention to provide a processing method by which a workpiece that includes metal can be suitably processed through a simple process. 
     In accordance with an aspect of the present invention, there is provided a method of processing a workpiece that includes metal at least in a work surface thereof by processing means including a grindstone or a polishing pad, the method including: a processing step of grinding or polishing the workpiece by the processing means while supplying a processing fluid to the work surface of the workpiece, wherein the processing fluid contains an organic acid and an oxidizing agent. 
     In the present invention, it is preferable that the processing fluid further contains an anticorrosive. 
     In the processing method according to the present invention, the processing fluid containing an organic acid and an oxidizing agent is supplied, whereby the workpiece can be ground or polished while suppressing the ductility of the metal included in the work surface through modification of the metal. Therefore, a workpiece that includes metal can be suitably processed through a simple process. 
     The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing a preferred embodiment of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view schematically showing a configuration example of grinding apparatus (processing apparatus) to be used in a processing method according to an embodiment of the present invention; and 
         FIG. 2  is a perspective view schematically showing a processing step. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of the present invention will be described below, referring to the attached drawings. It is to be noted that while in this embodiment a description will be made of a processing method of grinding a plate-shaped workpiece by a grinding mechanism (processing means) that includes a grindstone for grinding (grindstone), the processing method according to the present invention is not limited to this described method. For instance, the processing method of the present invention is applicable also to cases where a plate-shaped workpiece is polished by a polishing mechanism (processing means) that includes a pad for polishing (polishing pad). 
     First, an example of the configuration of a grinding apparatus (processing apparatus) used in the processing method according to this embodiment will be described.  FIG. 1  is a perspective view showing a configuration example of the grinding apparatus according to this embodiment. As shown in  FIG. 1 , a grinding apparatus (processing apparatus)  2  in this embodiment includes a rectangular parallelepiped base  4  on which to mount various components of the apparatus. At a rear end of the base  4 , a support wall  6  extending upward is disposed upright. An upper surface of the base  4  is formed with an opening  4   a  on a front side, and a conveying mechanism  8  for conveying a plate-shaped workpiece  11  is provided inside the opening  4   a . In addition, cassettes  10   a  and  10   b  for housing the workpieces  11  are mounted in regions at lateral sides of the opening  4   a.    
     The workpiece  11  is, for example, a disc-shaped WL-CSP substrate, in which metal posts (electrodes) are embedded on the side of a surface  11   a  (see  FIG. 2 ) constituting a work surface (surface to be processed). In this embodiment, besides, a protective member  13  having roughly the same diameter as that of the workpiece  11  is attached to the back side of the workpiece  11  (see  FIG. 2 ). It should be noted, however, that the configuration of the workpiece  11  is not restricted to this. Any plate-shaped body that includes metal in a work surface thereof, such as a metal plate, a TSV wafer provided with TSV (Through Silicon Via), or wafer formed with a metal film, can be suitably processed by the processing method according to this embodiment. In addition, the protective member  13  may not necessarily be attached to the back side of the workpiece  11 . 
     On the rear side of a mount region where to mount the cassette  10   a , there is provided a positioning mechanism  12  for positioning of the workpiece  11  which is temporarily placed. For instance, the workpiece  11  conveyed from the cassette  10   a  by the conveying mechanism  8  is mounted on the positioning mechanism  12 , by which centering of the workpiece  11  is conducted. On the rear side of the positioning mechanism  12  is provided a feeding-in mechanism  14  which holds the workpiece  11  by suction and swivels. 
     On the rear side of the feeding-in mechanism  14  is formed an opening  4   b . An X-axis moving table  16 , an X-axis moving mechanism (not shown) for moving the X-axis moving table  16  in an X-axis direction (front-rear direction), and a waterproof cover  18  covering the X-axis moving mechanism are disposed inside the opening  4   b . The X-axis moving mechanism includes a pair of X-axis guide rails (not shown) parallel to the X-axis direction, and the X-axis moving table  16  is slidably disposed on the X-axis guide rails. A nut section (not shown) is fixed to the lower side of the X-axis moving table  16 , and the nut section is in screw engagement with an X-axis ball screw (not shown) parallel to the X-axis guide rails. An X-axis pulse motor (not shown) is connected to one end portion of the X-axis ball screw. With the X-axis ball screw rotated by the X-axis pulse motor, the X-axis moving table  16  is moved in the X-axis direction along the X-axis guide rails. 
     On the X-axis moving table  16  is provided a chuck table  20  by which the workpiece  11  is suction held. The chuck table  20  is connected with a rotational drive source (not shown) such as a motor, and is rotated about an axis of rotation that extends in a Z-axis direction (vertical direction). The chuck table  20  is moved, by the aforementioned X-axis moving mechanism, between a front-side feeding-in/out position where the workpiece  11  is fed in and fed out and a rear-side grinding position where the workpiece  11  is ground. A part of an upper surface of the chuck table  20  constitutes a holding surface on which the workpiece  11  is suction held. The holding surface is connected with a suction source (not shown) by way of a channel (not shown) formed inside the chuck table  20 . The workpiece  11  fed in by the feeding-in mechanism  14  is suction held onto the chuck table  20  by a negative pressure of the suction source that acts on the holding surface. 
     A Z-axis moving mechanism  22  is provided on a front surface of the support wall  6 . The Z-axis moving mechanism  22  includes a pair of Z-axis guide rails  24  parallel to the Z-axis direction, and a Z-axis moving table  26  is slidably disposed on the Z-axis guide rails  24 . A nut section (not shown) is fixed to the rear side (back side) of the Z-axis moving table  26 , and the nut section is in screw engagement with a Z-axis ball screw  28  parallel to the Z-axis guide rails  24 . A Z-axis pulse motor  30  is connected to one end portion of the Z-axis ball screw  28 . With the Z-axis ball screw  28  rotated by the Z-axis pulse motor  30 , the Z-axis moving table  26  is moved in the Z-axis direction along the Z-axis guide rails  24 . A Z-axis scale (not shown) for indicating the position (height position) of the Z-axis moving table  26  in the Z-axis direction is additionally provided in a position close to the Z-axis guide table  24 . The position of the Z-axis moving table  26  in the Z-axis direction is read by a scale reading mechanism (not shown) provided on the Z-axis moving table  26 . 
     On a front surface of the Z-axis moving table  26  is provided a grinding mechanism (processing means)  32  for grinding the workpiece  11 . The grinding mechanism  32  includes a spindle housing  34  fixed to the Z-axis moving table  26 . A spindle  36  rotatable about an axis of rotation extending in the Z-axis direction is supported on the spindle housing  34 . A disc-shaped wheel mount  38  is fixed to a lower end portion of the spindle  36 , and a grinding wheel  40  having roughly the same diameter as that of the wheel mount  38  is mounted on a lower surface of the wheel mount  38 . The grinding wheel  40  includes a disc-shaped wheel base  40   a  formed of a metallic material such as stainless steel. A plurality of grindstones  40   b  are fixed to the lower surface of the wheel base  40   a , along the whole perimeter of the lower surface. An upper end of the spindle  36  is connected with a rotational drive source (not shown) such as a motor, and the grinding wheel  40  is rotated by a rotating force transmitted from the rotational drive source. In addition, the grinding wheel  40  is pressed against the surface  11   a  of the workpiece  11  (which is suction held by the chuck table  20 ) by the aforementioned Z-axis moving mechanism  22 . 
     In a position adjacent to the grinding mechanism  32 , there is provided a nozzle  42  for supplying a processing fluid  50  (see  FIG. 2 ) to the surface  11   a  of the workpiece  11 . The nozzle  42  is connected with a processing fluid supply source (not shown). While supplying the processing fluid  50 , the grinding wheel  40  (grindstones  40   b ) in rotation is brought into contact with the surface  11   a  of the workpiece  11  that includes metal, whereby the surface  11   a  of the workpiece  11  can be suitably ground (processed). The processing fluid  50  will be detailed later. 
     In a position adjacent to the feeding-in mechanism  14  in a Y-axis direction (left-right direction), there is provided a feeding-out mechanism  44  which holds the workpiece  11  by suction and swivels. On the front side of the feeding-out mechanism  44  and on the rear side of the mount region where the cassette  10   b  is mounted, there is disposed a cleaning mechanism  46  for cleaning the workpiece  11  after grinding. The workpiece  11  cleaned by the cleaning mechanism  46  is conveyed by the conveying mechanism  8 , to be housed in the cassette  10   b . On the front side of the opening  4   a  is provided a control panel  48  through which to input various grinding conditions such as rotating speeds of the chuck table  20  and the spindle  36 , lowering velocity of the grinding wheel  40 , amount of the processing fluid  50  supplied, etc. 
     Now, the processing method conducted by use of the aforementioned grinding apparatus  2  will be described below. First, a holding step of holding the workpiece  11  by the chuck table  20  is conducted. In the holding step, the protective member  13  fixed to the back side of the workpiece  11  is put into contact with the holding surface of the chuck table  20 , and the negative pressure of the suction source is applied thereto. As a result, the workpiece  11  is suction held onto the chuck table  20 , with the protective member  13  therebetween. 
     After the holding step, a processing step of processing the workpiece  11  is carried out.  FIG. 2  is a perspective view schematically illustrating the processing step. In the processing step, with the chuck table  20  and the spindle  36  being rotated, the grinding wheel  40  is lowered to bring the grindstones  40   b  into contact with the surface  11   a  of the workpiece  11 . Concurrently, the processing fluid  50  is supplied from the nozzle  42  to the surface  11   a  of the workpiece  11 . 
     In the processing method in this embodiment, a processing fluid  50  that contains an organic acid and an oxidizing agent is used. By the processing fluid  50 , the grinding of the workpiece  11  can be carried out while suppressing ductility of the metal included in the surface  11   a  of the workpiece  11  through modification of the metal. Upon this grinding, burrs (projections) would not be generated from the metal. In addition, since the workpiece  11  that includes metal can be suitably processed by this grinding alone, it is unnecessary to combine this processing method with other method or methods. 
     As the organic acid, there can be used, for example, a compound that has at least one carboxyl group and at least one amino group in its molecule. In this case, it is preferable that at least one of the amino group(s) is a secondary or tertiary amino group. In addition, the compound used as the organic acid may have a substituent group. 
     As the organic acid, there can be used amino acids. Examples of the amino acids usable here include glycine, dihydroxyethylglycine, glycylglycine, hydroxyethylglycine, N-methylglycine, β-alanine, L-alanine, L-2-aminobutyric acid, L-norvaline, L-valine, L-leucine, L-norleucine, L-alloisoleucine, L-isoleucine, L-phenylalanine, L-proline, sarcosine, L-ornithine, L-lysine, taurine, L-serine, L-threonine, L-allothreonine, L-homoserine, L-thyroxine, L-tyrosine, 3,5-diiodo-L-tyrosine, β-(3,4-dihydroxyphenyl)-L-alanine, 4-hydroxy-L-proline, L-cysteine, L-methionine, L-ethionine, L-lanthionine, L-cystathionine, L-cystine, L-cystic acid, L-glutamic acid, L-aspartic acid, S-(carboxymethyl)-L-cysteine, 4-aminobutyric acid, L-asparagine, L-glutamine, azaserine, L-canavanine, L-citrulline, L-arginine, δ-hydroxy-L-lysine, creatine, L-kynurenine, L-histidine, 1-methyl-L-histidine, 3-methyl-L-histidine, L-tryptophane, actinomycin C1, ergothioneine, apamin, angiotensin I, angiotensin II, antipain, etc. Among others, particularly preferred are glycine, L-alanine, L-proline, L-histidine, L-lysine, and dihydroxyethylglycine. 
     Also, amino polyacids can be used as the organic acid. Examples of the amino polyacids usable here include iminodiacetic acid, nitrilotriacetic acid, diethylenetriaminepentaacetic acid, ethylenediaminetetraacetic acid, hydroxyethyliminodiacetic acid, nitrilotrismethylenephosphonic acid, ethylenediamine-N,N,N′,N′-tetramethylenephosphonic acid, 1,2-diaminopropanetetraacetic acid, glycol ether diaminetetraacetic acid, transcyclohexanediaminetetraacetic acid, ethylenediamineorthohydroxyphenylacetic acid, ethylenediaminedisuccinic acid (SS isomer), β-alaninediacetic acid, N-(2-carboxylatoethyl)-L-aspartic acid, N,N′-bis(2-hydroxybenzyl)ethylenediamine-N,N′-diacetic acid, etc. 
     Further, carboxylic acids can be used as the organic acid. Examples of the carboxylic acids usable here include saturated carboxylic acids such as formic acid, glycolic acid, propionic acid, acetic acid, butyric acid, valeric acid, hexanoic acid, oxalic acid, malonic acid, glutaric acid, adipic acid, malic acid, succinic acid, pimelic acid, mercaptoacetic acid, glyoxylic acid, chloroacetic acid, pyruvic acid, acetoacetic acid, glutaric acid, etc., unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, fumaric acid, maleic acid, mesaconic acid, citraconic acid, aconitic acid, etc., and cyclic unsaturated carboxylic acids such as benzoic acids, toluic acid, phthalic acids, naphthoic acid, pyromellitic acid, naphthalic acid, etc. 
     As the oxidizing agent, there can be used, for example, hydrogen peroxide, peroxides, nitrates, iodates, periodates, hypochlorites, chlorites, chlorates, perchlorates, persulfates, dichromates, permanganate, cerates, vanadates, ozonated water, silver(II) salts, iron(III) salts, and their organic complex salts. 
     Besides, an anticorrosive may be mixed in the processing fluid  50 . Mixing of the anticorrosive makes it possible to prevent corrosion (elution) of the metal included in the workpiece  11 . As the anticorrosive, there is preferably used a heterocyclic aromatic ring compound which has at least three nitrogen atoms in its molecule and has a fused ring structure or a heterocyclic aromatic ring compound which has at least four nitrogen atoms in its molecule. Further, the aromatic ring compound preferably includes a carboxyl group, sulfo group, hydroxyl group or alkoxyl group. Specific preferable examples of the aromatic ring compound include tetrazole derivatives, 1,2,3-triazole derivatives, and 1,2,4-triazole derivatives. 
     Examples of the tetrazole derivatives usable as the anticorrosive include those which do not have a substituent group on the nitrogen atoms forming the tetrazole ring and which have, introduced into the 5-position of the tetrazole, a substituent group selected from the group consisting of sulfo group, amino group, carbamoyl group, carbonamide group, sulfamoyl group, and sulfoneamide group, or an alkyl group substituted with at least one substituent group selected from the group consisting of hydroxyl group, carboxyl group, sulfo group, amino group, carbamoyl group, carbonamide group, sulfamoyl group, and sulfonamide group. 
     Examples of the 1,2,3-triazole derivatives usable as the anticorrosive include those which do not have a substituent group on the nitrogen atoms forming the 1,2,3-triazole ring and which have, introduced into the 4-position and/or 5-position of the 1,2,3-triazole, a substituent group selected from the group consisting of hydroxyl group, carboxyl group, sulfo group, amino group, carbamoyl group, carbonamide group, sulfamoyl group, and sulfonamide group, or an alkyl or aryl group substituted with at least one substituent group selected from the group consisting of hydroxyl group, carboxyl group, sulfo group, amino group, carbamoyl group, carbonamide group, sulfamoyl group, and sulfoneamide group. 
     Besides, examples of the 1,2,4-triazole derivatives usable as the anticorrosive include those which do not have a substituent group on the nitrogen atoms forming the 1,2,4-triazole ring and which have, introduced into the 2-position and/or 5-position of 1,2,4-triazole, a substituent group selected from the group consisting of sulfo group, carbamoyl group, carbonamide group, sulfamoyl group, and sulfonamide group, or an alkyl or aryl group substituted with at least one substituent group selected from the group consisting of hydroxyl group, carboxyl group, sulfo group, amino group, carbamoyl group, carbonamide group, sulfamoyl group, and sulfonamide group. 
     In the processing method according to this embodiment, the rotating speed of the spindle  36  is, for example, 6,000 rpm, and the rotating speed of the chuck table  20  is, for example, 300 rpm. It is to be noted, however, that the rotating speeds of the spindle  36  and the chuck table  20  are not limited to these values, and can be modified as desired. 
     When the spindle  36  is lowered at a predetermined feed rate under the aforementioned conditions, the surface  11   a  of the workpiece  11  can be ground. This grinding is carried out while measuring the thickness of the workpiece  11  by a thickness measuring sensor of a contact type or a non-contact type. When the workpiece  11  is ground to a predetermined thickness, the processing step ends. 
     As has been described above, in the processing method according to this embodiment, the workpiece  11  can be ground (or polished) while suppressing the ductility of the metal present at the surface (work surface)  11   a  of the workpiece  11  through modification of the metal by supplying the processing fluid  50  that contains the organic acid and the oxidizing agent. Therefore, the workpiece  11  that includes metal can be suitably processed through a simple process. 
     It is to be understood that the present invention is not limited to the description of the embodiment above, and the invention can be carried out with various modifications. For instance, the processing fluid  50  is not restricted to the one that is configured as aforementioned. Other amino acids, amino polyacids, carboxylic acids and the like than the aforementioned may also be used as the organic acid. Other azole compounds (tetrazoles, triazoles, benzotriazoles, etc.) than the aforementioned may be used as the anticorrosive. 
     The present invention is not limited to the details of the above described preferred embodiment. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claims are therefore to be embraced by the invention.