JP2015115538A - Wafer processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wafer processing method capable of dividing a wafer into individual chips with excellent processing quality, while achieving enhancement of productivity and cost reduction.SOLUTION: A wafer processing method is a method for dividing a wafer, where multiple chips are formed in the regions sectioned by dividing lines of a device layer formed on the surface of a semiconductor substrate, into individual chips along the dividing lines, and includes a grooving step for removing the device layer in the dividing lines from the surface side of the wafer where the device layer is formed, by irradiating along the dividing lines with laser light guided by a liquid beam, and grooving the semiconductor substrate, and a back processing step for thinning the wafer by processing the back of the wafer.

Description

  The present invention relates to a wafer processing method for dividing a wafer such as a semiconductor device or an electronic component into individual chips, and in particular, from a laminate in which an insulating film (for example, a low-k film) and a functional film are laminated on the surface of a semiconductor substrate. The present invention relates to a method for processing a wafer on which a device layer is formed.

  In semiconductor manufacturing processes, etc., wafers with semiconductor devices or electronic parts formed on the surface are subjected to electrical tests in the probing process and then divided into individual chips (also called dies or pellets) in the dicing process. The individual chips are then die bonded to the component base in a die bonding process. After die bonding, wire bonding is performed, and after wire bonding, resin molding is performed to obtain a finished product such as a semiconductor device or an electronic component.

  After the probing process, as shown in FIG. 13, the back surface of the wafer is attached to a dicing tape (also called a dicing sheet) S having a thickness of about 100 μm with an adhesive layer formed on one side, and a rigid ring shape. Is mounted on the frame F. In this state, the wafer W is transferred in the dicing process, between the dicing process and the die bonding process, and in the die bonding process.

  In the dicing process, a dicing apparatus that cuts the wafer by inserting a grinding groove into the wafer W with a thin grindstone called a dicing blade formed of fine diamond abrasive grains is used.

  In the dicing apparatus, the dicing blade is rotated at a high speed of 30,000 to 60,000 rpm and cut into the wafer W to completely cut the wafer W (full cut). At this time, since the dicing tape S affixed to the back surface of the wafer W is cut only about 10 μm from the front surface, the wafer W is cut into individual chips T, but the individual chips T are separated. In other words, since the arrangement of the chips T is not collapsed, the wafer state is maintained as a whole.

  In recent years, with the high integration and miniaturization of devices such as IC and LSI, an inorganic film such as SiOF or BSG (SiOB) or a polymer film such as polyimide or parylene is used on the surface of a semiconductor substrate such as silicon. A wafer on which a device layer made of a laminated body in which a low dielectric constant insulating film (Low-k film) made of a certain organic film and a functional film forming a circuit are laminated has been put into practical use.

  However, dicing of a wafer having such a device layer is likely to cause film peeling and burrs, which is a serious problem in the dicing process. In particular, when a low-k film is included in the device layer, the low-k film is very fragile. Therefore, when the device layer is cut by a dicing blade, there is a problem that the low-k film is likely to be peeled off. That is, if the low-k film is broken by cutting with a dicing blade, and the broken area spreads over the device forming area (chip forming area), the chip becomes defective, and the yield of the semiconductor device to be manufactured is lowered. It will be a factor.

  In order to solve the above problem, a method of cutting with a dicing blade after dividing the device layer by forming a laser processing groove along a planned dividing line called a street prior to cutting with a dicing blade is proposed. (For example, refer to Patent Document 1).

  In the method described in Patent Document 1, as shown in FIG. 14, first, a protective film is formed on the surface of a wafer on which a laminate (device layer) in which an insulating film and a functional film are laminated is formed. A protective film forming step is performed (step S100). Next, a laser beam irradiation process is performed in which the laser beam is irradiated on the surface of the wafer through the protective film (step S102). In this laser beam irradiation process, the laser beam is reciprocated along the streets, so that a laser processing groove having a width wider than the width of the dicing blade (cutting blade) along the streets is formed on the laminated body forming the streets of the wafer. Is formed.

  After the laser light irradiation process is performed, a protective film removing process for removing the protective film coated on the surface of the wafer is performed (step S104). Next, a dicing process (cutting process) is performed in which the wafer is cut with a dicing blade along the laser processing groove formed on the street of the wafer (step S106). Thereby, the cutting groove which reaches a back surface is formed in the wafer along the laser processing groove formed in the street. As a result, the wafer is cut along the laser processing grooves formed in the streets and divided into individual chips. In this dicing process, only the semiconductor substrate (silicon substrate or the like) is cut by the dicing blade.

JP 2006-140311 A

  However, the method described in Patent Document 1 requires a laser processing device (laser scriber) in addition to the dicing device. Further, in the laser irradiation process, in order to form a laser processing groove wider than the width of the dicing blade, it is necessary to perform laser beam irradiation by reciprocating along one street. For this reason, there is a problem that productivity is poor and the cost is increased.

  Moreover, in the method described in Patent Document 1, it is necessary to form a protective film on the surface of the wafer before the laser beam irradiation process is performed in order to prevent thermal damage and contamination during processing. Such costs are also a problem.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a wafer processing method that can divide a wafer into individual chips with good processing quality while improving productivity and reducing costs. To do.

  In order to achieve the above object, a wafer processing method according to a first aspect of the present invention is a wafer in which a plurality of chips are formed in a region defined by division lines in a device layer formed on the surface of a semiconductor substrate. Is divided into individual chips along the planned dividing line, and the laser beam guided by the liquid beam is irradiated along the planned dividing line from the surface side on which the device layer of the wafer is formed. And a groove forming step for removing the device layer in the division line and forming a groove in the semiconductor substrate, and a back surface processing step for reducing the thickness of the wafer by processing the back surface of the wafer.

  According to this aspect, by irradiating the laser beam guided by the liquid beam from the front surface side of the wafer in the groove forming process along the planned dividing line, the device layer in the planned dividing line is removed and the groove is formed in the semiconductor substrate. Therefore, even if a protective film is not formed on the surface of the wafer, thermal damage and contamination during processing can be prevented, yield can be improved, and reliability can be improved. Further, a dicing process such as dicing with a dicing blade or laser dicing is not required. Therefore, the wafer can be divided into individual chips with good processing quality while improving productivity and reducing costs.

  In the wafer processing method according to the second aspect of the present invention, in the first aspect, the back surface processing step processes the back surface of the wafer until the groove is exposed on the back surface of the wafer.

  According to this aspect, the wafer is divided into individual chips by the back surface processing step. Therefore, it is not necessary to perform the expanding step after the back surface processing step is performed, and the productivity can be further improved.

  In the wafer processing method according to the third aspect of the present invention, in the first aspect, the back surface processing step ends the processing of the back surface of the wafer before the grooves are exposed on the back surface of the wafer, and the back surface processing step is performed. A dicing tape attaching step of attaching a dicing tape to the front surface or the back surface of the substrate, and an expanding step of applying a tension to the dicing tape to increase the interval between individual chips.

  According to this aspect, since the groove formed on the wafer at the time of back surface processing is not exposed on the back surface of the wafer, it is possible to eliminate the risk of a chemical solution or the like used at the time of back surface processing entering the surface (device surface) of the wafer via the groove. .

  A wafer processing method according to a fourth aspect of the present invention is the wafer processing method according to any one of the first to third aspects, wherein the wafer includes a low-k film in the device layer.

  The wafer processing method according to a fifth aspect of the present invention is the wafer processing method according to any one of the first to third aspects, wherein the wafer includes a device layer containing GaN (gallium nitride).

  The fourth aspect and the fifth aspect are one of the preferable aspects from the viewpoint that the effect of the present invention becomes more remarkable. That is, even when the device layer formed on the surface of the semiconductor substrate includes a low-k film or GaN (gallium nitride), the wafer can be divided into individual chips without causing film peeling or burrs. Therefore, the yield can be improved and the reliability can be improved.

  In the wafer processing method according to the sixth aspect of the present invention, in any one of the first to fifth aspects, the liquid beam comprises an alkaline aqueous solution.

  According to this aspect, a groove with a high aspect ratio can be formed, and the processing rate is improved.

  According to the present invention, a wafer can be divided into individual chips with good processing quality while improving productivity and reducing costs.

The flowchart which shows the flow of the wafer processing method which concerns on one Embodiment of this invention. Schematic showing the configuration of the laser processing equipment Sectional view showing an example of wafer Configuration diagram showing the configuration of the laser processing section Schematic showing how the wafer is irradiated with water-guided laser light Schematic showing the state of the wafer after being irradiated with water-guided laser light Schematic showing the state where protective tape is applied to the surface of the wafer Schematic showing how wafer backside processing is performed The flowchart which shows the flow of the wafer processing method which concerns on other embodiment of this invention. Schematic showing how the backside process is performed Schematic showing how the expanding process is performed with the dicing tape affixed to the back side of the wafer Schematic showing how the expanding process is performed with the dicing tape attached to the surface of the wafer Perspective view showing wafer mounted on frame Flow chart showing flow of conventional wafer processing method

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a flowchart showing a flow of a wafer processing method according to an embodiment of the present invention.

<Water-guided laser light irradiation process>
First, a water-guided laser light irradiation process (corresponding to the “groove forming process” of the present invention) for irradiating the surface of the wafer W with water-guided laser light is performed (step S10). This water-guided laser light irradiation step is performed using a laser processing apparatus 20 shown in FIG.

  The laser processing apparatus 20 shown in FIG. 2 mainly includes a wafer moving unit 22 that moves the wafer W, an observation optical unit 24 that observes the surface of the wafer W, a laser processing unit 26 that laser processes the wafer W, and laser processing. It is comprised from the control part 28 which controls each part of the apparatus 20. FIG.

  FIG. 3 is a cross-sectional view showing an example of the wafer W. As shown in FIG. A wafer W shown in FIG. 3 is composed of a semiconductor substrate 10 such as silicon, and a device layer 12 is formed on a surface 10 a of the semiconductor substrate 10. The device layer 12 is formed of a stacked body in which a low-k film and a functional film that forms a circuit are stacked. The wafer W is divided into a plurality of areas by the division lines 14 arranged in a lattice pattern, and various devices constituting a semiconductor chip are formed in each of the divided areas. It is assumed that such a wafer W is supplied to the laser processing apparatus 20.

  The wafer moving unit 22 includes a suction stage 30 that sucks and holds the wafer W, and an XYZθ table 32 provided on the main body base 34.

  The suction stage 30 has a pump (not shown), and a plurality of suction holes are provided on the surface. The suction stage 30 sucks and holds the wafer W through the suction holes by operating a pump.

  The XYZθ table 32 includes guide rails (not shown), and moves in four directions of XYZθ under the control of the control unit 28. In the example shown in FIG. 2, the three directions of XYZ are orthogonal to each other, among which the X direction and the Y direction are horizontal directions, and the Z direction is a vertical direction. Further, the θ direction is a rotation direction with a vertical axis (Z axis) as a rotation axis.

  The observation optical unit 24 is provided so as to face the wafer W sucked and held on the suction stage 30 and has an illumination device (not shown) and a CCD camera (not shown). The observation optical unit 24 images the surface of the wafer W by irradiating the wafer W with illumination light according to an instruction from the control unit 28 and converting the reflected light from the wafer W into an electrical signal using a CCD camera. Get the data. This imaging data is sent to the control unit 28 and used for alignment of the wafer W.

  The laser processing unit 26 irradiates the surface of the wafer W with water-guided laser light according to instructions from the control unit 28.

  FIG. 4 is a configuration diagram showing the configuration of the laser processing unit 26. As shown in the figure, the laser processing unit 26 includes a laser light supply unit 36, a liquid supply unit 38, and a processing head 40.

  The laser light supply unit 36 includes a laser light source 42, and the laser light oscillated from the laser light source 42 is collected inside the processing head 40 through an optical system such as a collimator lens 44, a mirror 46, and a condenser lens 48. Lighted.

  The liquid supply unit 38 includes a tank 50 that stores liquid (water in this example) and a pump 52, and the liquid pressurized by the pump 52 (pressurized liquid) is supplied to the processing head 40.

  The processing head 40 includes a liquid chamber 54 that temporarily stores the liquid supplied from the liquid supply unit 38, a liquid inlet 56 for introducing the liquid supplied from the liquid supply unit 38 into the liquid chamber 54, and a laser. A window portion 58 that guides laser light supplied from the light supply portion 36 to the inside of the machining head 40 and a nozzle 60 that forms a liquid injection port are provided.

  The window 58 is provided on the upper surface (the surface opposite to the wafer W side) of the head main body 62 that is the main body of the processing head 40, and is a light that can transmit the laser light supplied from the laser light supply unit 36. Constructed from a permeable material. As the light transmissive material, for example, glass, quartz, sapphire, transparent plastic (for example, acrylic resin, hard vinyl chloride, etc.) can be used. As a result, the laser light supplied from the laser light supply unit 36 passes through the window 58 in the liquid chamber 54 formed in the processing head 40 (head body 62) (specifically, the inlet of the nozzle 60). ).

  The nozzle 60 is formed of a minute hole provided on the lower surface (surface on the wafer W side) of the head main body 62 and is disposed at a position facing the window portion 58 with the liquid chamber 54 interposed therebetween. That is, the nozzle 60 is disposed on the optical axis of the laser beam guided from the laser beam supply unit 36 through the window 58 to the inside of the liquid chamber 54, and the ejection direction of the liquid ejected from the nozzle 60 and the laser beam. The optical axes of the light coincide. As a result, the laser light guided from the laser light supply unit 36 through the window 58 to the inside of the liquid chamber 54 is totally reflected from the inside of the beam-like liquid (liquid beam) irradiated from the nozzle 60 while being reflected on the wafer W. The surface of the wafer W is irradiated. In the present specification, laser light guided along the liquid beam ejection direction while repeating total reflection inside the liquid beam is referred to as “water-guided laser light”.

  Next, a water-guided laser light irradiation process performed using the laser processing apparatus 20 configured as described above will be described.

  In this water-guided laser light irradiation step, first, the wafer W is placed on the suction stage 30 of the laser processing apparatus 20 with the surface of the wafer W (the surface on which the device layer 12 is formed) facing upward. The wafer W is sucked and held.

  In this state, the wafer W is aligned from the surface by the illumination device of the observation optical unit 24 and the CCD camera. The alignment method is performed by an alignment method using image processing. Since an alignment method using image processing is generally well known, description thereof is omitted.

  When the alignment is completed, the XYZθ table 32 moves in the XY direction, and a beam-like liquid (liquid beam) is directed from the nozzle 60 of the processing head 40 toward the wafer W along the planned division line formed on the surface of the wafer W. ) Is injected. At this time, the laser light introduced from the laser light supply unit 36 into the liquid chamber 54 inside the processing head 40 (head main body 62) through the window 58 is entirely inside the liquid beam ejected from the nozzle 60. The light is guided toward the wafer W while repeating the reflection, and is irradiated to the position where the division line 14 is formed on the surface of the wafer W as shown in FIG. As a result, as shown in FIG. 6, the device layer 12 in the division line 14 is removed without causing film peeling, burrs, or the like, and the semiconductor substrate 10 of the wafer W extends along the division line 14. Thus, a processing groove 16 having a predetermined depth is formed.

  As described above, in the present embodiment, since a high-pressure liquid (water jet) is always supplied to the processing position of the wafer W irradiated with the water-guided laser light (that is, the planned division line 14), debris generated during laser processing is used. This debris does not adhere to the periphery of the processing area even if processing scraps referred to as are generated. Further, the wafer W as the workpiece can be cooled while removing the substance melted by the water-induced laser light from the processing position to avoid contamination. Therefore, even if a protective film is not formed on the surface of the wafer W, thermal damage and contamination during processing can be effectively prevented, yield can be improved, and reliability can be improved.

  In the present embodiment, the laser beam irradiation range can be easily controlled by the liquid beam ejection width (beam diameter). For example, the processing groove can be formed with a width of about 30 μm. Therefore, it is not necessary to perform a plurality of times of processing in one division line, the number of processing feeds of the wafer W is reduced, and it is possible to form a high-quality processed groove 16 with high productivity.

  In the present embodiment, the laser processing conditions in the water-guided laser light irradiation step are set as follows, for example.

Light source: UV (ultraviolet light) -pulse laser Wavelength: 400 nm or less Repetition frequency: 1 to 100 kHz
Average output: 0.5-10W
Processing feed rate: 10 to 1000 mm / s
Thus, in the present embodiment, a UV light source is preferably used as the laser light source. Light in the ultraviolet region (UV light) emitted from the UV light source has a high absorption rate by the metal and improves the metal removal performance. Therefore, even when a metal film such as TEG (Test Element Group) is formed on the division line 14, the metal film can be efficiently removed by irradiation with water-guided laser light.

  Moreover, in this embodiment, although the aspect which the liquid beam injected from the nozzle 60 of the process head 40 consists of water was shown, not only this but the aspect which consists of silicon oil, alkaline aqueous solution etc., for example is preferably employ | adopted. it can. In particular, according to the aspect in which the liquid beam is made of an alkaline aqueous solution, the processing groove 16 having a high aspect ratio can be formed compared to the aspect in which the liquid beam is made of water, and the processing rate can be improved. .

<Backside processing process>
Next, in order to protect the device layer 12 formed on the surface of the wafer W, a protective tape (BG tape) 18 having an adhesive on one side is attached to the surface of the wafer W (see FIG. 7), and then the wafer W A back surface processing step is performed to reduce the thickness of the wafer W by processing the back surface (step S12).

  In this back surface processing step, as shown in FIG. 8, the wafer W having the protective tape 18 affixed to the front surface is adsorbed to the rotating suction table 72 of the back glider device 70 with the protective tape 18 facing downward, and the back surface is removed. It is ground by a rotating grindstone 74 (FIG. 8A), processed to a predetermined thickness (400 μm or less), then polished by a polishing head (not shown) while being held on the suction table 72, and formed during grinding. The processed damaged layer is removed (FIG. 8B). Since the protective tape 18 has sufficient hardness against the grinding pressure, it can be processed with high accuracy.

  The thickness of the wafer W after such a back surface processing step is performed so that the processing groove 16 formed in the wafer W in the water-guided laser light irradiation step in step S10 is exposed (exposed) on the back surface of the wafer W. Is done. As a result, the wafer W is divided into individual chips.

  As described above, according to the present embodiment, the water-guided laser light is divided along the planned division line 14 from the surface side of the wafer W on which the device layer 12 is formed on the surface of the semiconductor substrate 10 in the water-guided laser light irradiation step. By irradiating, the device layer 12 in the planned dividing line 14 can be removed without causing film peeling or burrs, and a processed groove 16 having a predetermined depth can be formed in the semiconductor substrate 10. For this reason, even if a protective film is not formed on the surface of the wafer W, thermal damage and contamination during processing can be prevented, yield can be improved, and reliability can be improved. Further, since a dicing process such as dicing with a dicing blade or laser dicing (also referred to as stealth dicing) is not required, productivity can be improved. Therefore, the wafer W can be divided into individual chips with good processing quality while improving productivity and reducing costs.

  Further, in the present embodiment, after the water-guided laser light irradiation process is performed, the back surface processing process is performed to reduce the thickness of the wafer W by processing the back surface of the wafer W, so that chipping and cracking occur. Therefore, an extremely thin chip having a good end face shape can be manufactured.

  In the present embodiment, the case where a wafer including a low-k film in the device layer 12 is processed as the wafer W has been described. However, the present invention is not limited to this. For example, a wafer including GaN (gallium nitride) in the device layer 12 The same effect can be obtained also when processing.

  Next, another embodiment of the present invention will be described. FIG. 9 is an explanatory diagram showing a flow of a wafer processing method according to another embodiment of the present invention. FIG. 10 is a schematic view showing a state in which the back surface processing step is performed. FIG. 11 is a schematic diagram illustrating how the expanding process is performed. 9 to 11, elements that are the same as or similar to those shown so far are assigned the same reference numerals, and descriptions thereof are omitted.

  In the wafer processing method shown in FIG. 9, in the back surface processing step, as shown in FIG. 10, the back surface processing is terminated immediately before the processing groove 16 formed in the wafer W is exposed on the back surface of the wafer W (step S12).

  After the above-described back surface processing step is performed, a dicing tape transfer step is performed in which a dicing tape S having an adhesive on one side is applied to the back surface of the wafer W, and then the protective tape 18 attached to the front surface of the wafer W is peeled off. Performed (step S14). As a result, the dicing tape S is attached to the back surface of the wafer W as shown in FIG.

  Next, as shown in FIG. 11B, an expanding process is performed in which the dicing tape S affixed to the back surface of the wafer W is stretched by applying tension to expand the distance between the chips of the wafer W. (Step S16). Thereby, the wafer W can be divided into individual chips T.

  According to this wafer processing method, since the processing groove 16 formed in the wafer W in the back surface processing step is not exposed on the back surface of the wafer W, there is a risk that the chemical used for back surface processing may enter the surface (device surface) of the wafer W. Can be eliminated.

  In the dicing tape transfer process, the number of times of transfer increases, but the dicing tape S may be attached to the surface of the wafer W as shown in FIG. Thereafter, in the expanding step, as shown in FIG. 12B, the wafer W can be divided into individual chips T by applying tension to the dicing tape S and stretching it. According to this aspect, since the processed groove 16 is formed on the wafer W on the dicing tape S side, the tension is smaller than when the expanding process is performed with the dicing tape S attached to the surface of the wafer W. Thus, the wafer W can be divided into individual chips T.

  The embodiments of the present invention have been described above. However, the present invention is not limited to the above examples, and various improvements and modifications may be made without departing from the scope of the present invention. .

  DESCRIPTION OF SYMBOLS 10 ... Semiconductor substrate, 12 ... Device layer, 14 ... Dividing line, 16 ... Process groove, ... Protection tape, 20 ... Laser processing apparatus, 22 ... Wafer moving part, 24 ... Observation optical part, 26 ... Laser processing part, 28 DESCRIPTION OF SYMBOLS ... Control part, 30 ... Suction stage, 32 ... XYZ (theta) table, 36 ... Laser light supply part, 38 ... Liquid supply part, 40 ... Processing head, 42 ... Laser light source, 50 ... Tank, 52 ... Pump, 54 ... Liquid chamber, 56 ... Liquid inlet, 58 ... Window, 60 ... Nozzle, F ... Frame, S ... Dicing sheet, T ... Chip, W ... Wafer

Claims (6)

A method of dividing a wafer formed in a region where a plurality of chips are defined by a predetermined division line in a device layer formed on a surface of a semiconductor substrate into individual chips along the predetermined division line,
By irradiating a laser beam guided by a liquid beam from the surface side of the wafer on which the device layer is formed along the division line, the device layer in the division line is removed and the semiconductor substrate Forming a groove in the groove; and
Processing the back surface of the wafer and reducing the thickness of the wafer;
A wafer processing method including:   The wafer processing method according to claim 1, wherein the back surface processing step processes the back surface of the wafer until the groove is exposed on the back surface of the wafer. The back surface processing step ends the processing of the back surface of the wafer before the groove is exposed on the back surface of the wafer,
A dicing tape attaching step of attaching a dicing tape to the front surface or the back surface of the wafer subjected to the back surface processing step;
An expanding step of applying tension to the dicing tape to expand individual chip intervals;
The wafer processing method according to claim 1, further comprising:   The wafer processing method according to claim 1, wherein the wafer is a wafer including a low-k film in the device layer.   The wafer processing method according to claim 1, wherein the wafer is a wafer containing GaN in the device layer.   The wafer processing method according to claim 1, wherein the liquid beam is made of an aqueous alkali solution.

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