CN103715082A - Processing method of wafer - Google Patents

Abstract

The invention provides a processing method of a wafer capable of forming an adequate modified layer on a proper position in a short time by aiming at a water having an insulation film on a back surface. The processing method of the wafer is a processing method of a wafer W having the insulation film (15) on the back surface (13), and comprises the following steps: the insulation film removing step, the insulation film can be removed by a cutting blade (22) from the back surface of the wafer along a cutting predetermined line (14) to form a cutting groove (25); a modified layer forming step, the laser having a transmittable wavelength with respect to the wafer can be irradiated along the cutting groove (25) to form the modified layer in the wafer; and a cutting step, by applying the external force to the modified layer (35)by the cutting motion, a plurality of device chips can be formed by taking the modified layer (35) as the cutting starting points. The groove bottom (26) of the cutting groove (25) is characterized in that groove bottom is flat, the surface roughness Ra is under 0.1(mu)m, and the width is more than the diameter of the laser point.

Description

Wafer processing method

technical field

The present invention relates to a wafer processing method for dividing a semiconductor wafer or an optical device wafer into individual chips.

Background technique

Conventionally, as a processing method for dividing a wafer into individual chips, a technique of dividing a wafer by laser processing has attracted attention. As this laser processing, a processing method has been proposed in which a fragile layer (modified layer) is formed inside the wafer by irradiating laser light which is transparent to the wafer, and the modified layer with reduced strength is used as a starting point for division (e.g. , refer to Patent Document 1). In the processing method of Patent Document 1, laser beams are irradiated along grid-like partitions on the front surface of the wafer to form a linear modified layer inside the wafer. And, by applying an external force to the fragile modified layer, the wafer is divided into individual chips along the modified layer.

In addition, when the thickness of the wafer is reduced to several tens of μm or less, laser light passes through the wafer, making it difficult to form an appropriate modified layer at an appropriate position inside the wafer. Therefore, a processing method has been proposed in which a modified layer is formed inside a wafer before thinning, and the wafer is ground to a finished thickness after forming the modified layer (for example, refer to Patent Document 2). In the processing method of Patent Document 2, the modified layer is formed on the side of the ground surface at a position higher than the thickness of the finished product. Therefore, an appropriate modified layer can be formed at an appropriate position inside the wafer, and since the modified layer can also be removed, the brightness can be improved during processing of an optical device wafer, and the bending strength can be improved during processing of a semiconductor wafer.

prior art literature

Patent Document 1: Japanese Patent No. 3408805

Patent Document 2: Japanese Unexamined Patent Publication No. 2012-49164

In addition, an insulating film such as a nitride film or an oxide film is often formed on the back side of the wafer in order to prevent metal contamination. In the laser processing before grinding, due to the influence of the insulating film, it is impossible to form an appropriate thickness inside the wafer. modified layer. At this time, a method of removing the insulating film from the rear surface of the wafer by grinding before forming the modified layer is also considered. When removing the insulating film, in order to prevent the clogging of the pores of the grinding tool, it is necessary to process in the order of rough grinding, fine grinding, and grinding. Since the same process is required when the wafer is thinned after the modified layer is formed, there is a process. Time increases the problem.

Contents of the invention

The present invention was made in view of such a situation, and an object of the present invention is to provide a wafer processing method capable of forming an appropriate modified layer at an appropriate position in a short time for a wafer on which an insulating film is formed on the back surface.

The method for processing a wafer according to the present invention is a method for processing a wafer in which devices are formed on the front side in a plurality of regions divided by planned division lines and an insulating film is formed on the back side. The method for processing the wafer is characterized in that it has: In the film removal process, a cutting groove having a flat groove bottom is formed with a cutting tool along the planned dividing line from the back side of the wafer, and the insulating film is removed along the planned dividing line; After the removal process, alignment is completed from the back surface of the wafer with the above-mentioned cutting groove as a reference, and the laser light beam with a wavelength that is transparent to the wafer is positioned from the above-mentioned cutting groove to the inside near the front surface of the wafer, and along the above-mentioned cutting groove Irradiating to form a modified layer in the vicinity of the front surface of the wafer; and a dividing step, after implementing the above-mentioned modified layer forming step, grinding from the back surface of the wafer with a grinding member to thin the thickness of the finished product, and passing The grinding operation starts from the modified layer and divides the wafer along the planned dividing line. In the cutting groove, the surface roughness of the flat groove bottom is 0.1 μm or less, and the width of the flat groove bottom is formed in the groove. The diameter of the laser spot above the bottom.

According to this configuration, by removing the insulating film from the rear surface of the wafer along the planned division line with the cutting blade, the cut grooves having flat groove bottoms are formed on the rear surface of the wafer. In addition, by irradiating laser beams so as to pass through the cut grooves, a reformed layer can be formed inside the wafer without being affected by the insulating film. At this time, since the surface roughness of the cutting groove is 0.1 μm or less and the width of the groove bottom is equal to or larger than the laser spot diameter, scattering of laser light at the groove bottom can be suppressed. Therefore, an appropriate modified layer can be formed at an appropriate position inside the wafer, and the wafer can be divided satisfactorily along the planned dividing line. In addition, since the insulating film is partially removed from the back surface of the wafer by the cutting blade, the processing time can be shortened compared with the configuration in which the entirety of the insulating film is removed from the back surface of the wafer by grinding.

According to the present invention, a flat cutting groove with a small surface roughness is formed on the back surface of the wafer by a cutting tool, and laser light is irradiated to the inside of the wafer through the cutting groove, thereby enabling the wafer with an insulating film formed on the back surface to be processed in a short time. Appropriate modifying layers are formed in appropriate locations.

Description of drawings

1A and 1B are diagrams showing an example of the insulating film removal step of the present embodiment.

FIG. 2 is a diagram showing an example of a modified layer forming step of the present embodiment.

3A and 3B are diagrams showing an example of the dividing step in this embodiment.

Label description

11 devices

12 Front side of chip

13 The back side of the chip

14 split reservation line

15 insulating film

22 cutting tools

25 cutting slots

26 tank bottom

35 modified layer

42 grinding components

W chip

Detailed ways

Hereinafter, the wafer processing method of this embodiment will be described. In the wafer processing method of this embodiment, an insulating film removal step by a cutting device, a modified layer formation step by a laser processing device, and a dividing step by a grinding device are performed on a wafer on which an insulating film is formed on the back surface. In the insulating film removal step, the insulating film formed on the back surface of the wafer is removed along the planned dividing line with a cutting blade. Cutting grooves having a flat groove bottom with a small surface roughness are formed on the back surface of the wafer along planned dividing lines by cutting processing with the cutting tool.

In the modified layer forming step, a modified layer is formed along the planned division line inside the wafer by laser processing. In this laser processing, the laser light beam is irradiated along the cutting groove by positioning the converging point of the laser beam having a wavelength that is transparent to the wafer from the cutting groove to the inside near the front surface of the wafer. Thereby, the reformed layer along the planned dividing line is formed inside the wafer without the insulating film obstructing the irradiation of the laser light. In the splitting step, the wafer is thinned to a finished thickness by a grinding member, and the wafer is split along planned splitting lines by a grinding operation starting from the reformed layer.

Hereinafter, details of the wafer processing method of this embodiment will be described. Referring to FIG. 1 , the insulating film removal step will be described. FIG. 1 is a diagram showing an example of the insulating film removal step of the present embodiment. In addition, in the present embodiment, the structure in which cut grooves are formed by one cutting process is not limited to this structure. For example, cutting grooves may be formed in multiple stages using blades having different grain diameters depending on the material of the wafer. In addition, FIG. 1A shows the state where the back surface of a wafer faces upward.

As shown in FIG. 1A , a wafer W is configured by disposing a plurality of devices 11 on a semiconductor substrate such as silicon or gallium arsenide. The wafer W is formed in a substantially disc shape, and is divided into a plurality of regions by grid-like dividing lines 14 arranged on the front surface 12 . Devices 11 such as IC (Integrated Circuit) and LSI (Large Scale Integration) are formed in each region. An insulating film 15 such as a nitride film or an oxide film is formed on the back surface 13 of the wafer W in order to prevent metal contamination due to penetration of copper or the like. In addition, on the outer edge of the wafer W, a notch 16 indicating a crystal orientation is formed.

In addition, the wafer W is not limited to a semiconductor wafer, and the insulating film 15 is not limited to a nitride film, an oxide film, or the like for preventing metal contamination. The wafer W may be an optical device wafer in which optical devices such as LEDs are formed on a ceramic, glass, or sapphire-based inorganic material substrate. In addition, the insulating film 15 may be any film as long as it is formed on the back surface 13 of the wafer W, and may be formed of a resin film, for example.

As shown in FIG. 1B , in the insulating film removal step, a protective tape 17 is attached to the front surface 12 of the wafer W, and the wafer W is carried into a cutting device (not shown) with the rear surface 13 facing upward. The wafer W carried into the cutting apparatus is held on the chuck table 21 via the protective tape 17 . In addition, the cutting blade 22 is positioned on the planned dividing line 14 of the wafer W, and the cutting blade 22 rotating at high speed cuts into the wafer W from the rear surface 13 side. Then, the cutting blade 22 is relatively moved with respect to the wafer W, thereby removing the insulating film 15 from the rear surface 13 of the wafer W along the planned dividing line 14 .

As a result, cut grooves 25 having flat groove bottoms 26 are formed on the back surface 13 of the wafer W, and the back surface 13 of the wafer W is exposed to the outside from the insulating film 15 by the cut grooves 25 . The cutting groove 25 becomes an irradiation area of the laser beam in the subsequent modified layer forming step. That is, laser light is irradiated into the wafer W through the cutting groove 25 , thereby forming the modified layer 35 along the planned dividing line 14 without being affected by the insulating film 15 (see FIG. 2 ). At this time, the groove bottom 26 of the cutting groove 25 is formed flat and has a surface roughness Ra of 0.1 μm or less in order to prevent the laser light from being disturbed.

Here, as the cutting tool 22, a tool having a flat surface at the tip and having a thickness equal to or larger than the diameter of the laser spot formed on the groove bottom 26 is used. In addition, the cutting groove 25 is processed under the cutting condition that the surface roughness Ra is 0.1 μm or less. For example, use a resin cutter with a thickness of 0.6mm and agglomerate diamond abrasive grains with a diameter of 2.0 μm to 4.0 μm through resin as the cutting tool 22, the spindle speed is set to 30000 rpm, and the cutting feed rate (card The feed speed of the disc table 21) was set to 1 mm/s, and the cutting amount was set to 0.01 mm from the back surface.

In the insulating film removing step, the cutting blade 22 is used to remove the insulating film 15 on the planned dividing line 14 which is an irradiation area of the laser beam. Therefore, compared with the structure in which the insulating film 15 is removed from the entire rear surface 13 of the wafer W by grinding, the insulating film 15 can be efficiently removed in a short time. In addition, the groove bottom 26 of the cutting groove 25 may not be completely flat, but may include curvature or unevenness to an extent that does not affect the formation of the modified layer 35 . That is, the groove bottom 26 of the cutting groove 25 may be formed substantially flat.

Referring to FIG. 2 , the modified layer forming step will be described. FIG. 2 is a diagram showing an example of a modified layer forming step of the present embodiment.

As shown in FIG. 2 , the modified layer forming step is performed after the insulating film removing step. In the modified layer forming step, the wafer W is held on a chuck table 31 of a laser processing apparatus (not shown) via a protective tape 17 . In addition, the rear surface 13 of the wafer W is photographed by an imaging device (not shown), and calibration is performed with reference to the cut groove 25 on the rear surface 13 of the wafer W. Next, the injection port of the processing head 32 is positioned on the cutting groove 25 of the wafer W, and the laser beam is irradiated from the rear surface 13 side of the wafer W through the processing head 32 . The laser light has a wavelength that is transparent to the wafer W, and is adjusted so as to be condensed in the vicinity of the front surface 12 of the wafer W. As shown in FIG.

The laser light is irradiated to the inside of the wafer W through the groove bottom 26 of the cutting groove 25 , so that it is not hindered by the insulating film 15 . In addition, since the groove bottom 26 of the cutting groove 25 is formed flat and has a surface roughness Ra of 0.1 μm or less, the disturbance of the laser beam at the groove bottom 26 can be suppressed, and an appropriate position inside the wafer W can be appropriately modified. Then, by irradiating the laser beam along the cutting groove 25 while adjusting the focusing point of the laser beam, a good reformed layer 35 along the planned division line 14 is formed inside the wafer W.

At this time, first, the laser processing is performed so that the lower end portion of the modified layer 35 is formed along all the cut grooves 25 by adjusting the focus point to the vicinity of the front surface of the wafer W. Then, the laser processing is repeated along the cutting groove 25 every time the height of the focused spot is raised, thereby forming the reformed layer 35 with a predetermined thickness inside the wafer W. In this way, the division starting point along the planned division line 14 is formed inside the wafer W. As shown in FIG.

In addition, when the wafer W becomes thinner to several tens of μm or less, the laser light is excessively transmitted, and a good modified layer 35 cannot be formed inside the wafer W in some cases. Therefore, in the present embodiment, the modified layer forming step is performed before the thinning of the wafer W by the dividing step, whereby a favorable modified layer 35 can be formed inside the wafer W.

The modified layer 35 refers to a region in which the density, refractive index, mechanical strength, and other physical properties inside the wafer W are different from those of the surrounding area due to irradiation of laser light, and the intensity is lower than that of the surrounding area. The modified layer 35 is, for example, a melt-processed region, a cracked region, a dielectric breakdown region, a refractive index change region, or a mixture of these regions.

The dividing step will be described with reference to FIG. 3 . FIG. 3 is a diagram showing an example of a dividing step in the present embodiment. In addition, in this embodiment, the structure in which the cutting groove is formed by one grinding process is not limited to this structure. For example, the wafer may be divided along the planned dividing line by performing rough grinding, finish grinding, or polishing according to the material of the wafer.

As shown in FIG. 3 , the dividing step is performed after the modified layer forming step. As shown in FIG. 3A , in the dividing step, the wafer W is held on a chuck table 41 of a grinding device (not shown) via a protective tape 17 . In addition, the grinding member 42 is positioned above the wafer W held on the chuck table 41 . Then, the grinding wheel 43 of the grinding member 42 is rotated around the Z axis while approaching the chuck table 41, and the grinding wheel 43 is in parallel rotational contact with the rear surface 13 of the wafer W, whereby the wafer W is ground. Grinding of the wafer W not only removes the insulating film 15 from the back surface 13 of the wafer W, but also removes the irregularities caused by the cutting grooves 25 .

During the grinding process, the thickness of the wafer W is measured in real time by an altimeter (not shown). And, the feeding amount of the grinding member 42 is controlled so that the measurement result of the altimeter is close to the finished thickness L. As shown in FIG. In addition, inside the wafer W, the modified layer 35 is formed at a height position exceeding the thickness L of the finished product.

As shown in FIG. 3B , by the grinding operation, the grinding load acts strongly on each modified layer 35 from the grinding wheel 43 . As a result, cracks are generated in the wafer W along the planned dividing lines 14 starting from the modified layer 35 , and the wafer W is divided into individual device chips C. And, when the wafer W is thinned to the finished thickness L, the grinding operation is stopped. In this way, the wafer W is thinned to a desired finished product thickness L and simultaneously divided into individual device chips C along the dividing line 14 .

In addition, when the applicant of the present application made the surface roughness of the cutting groove 25 to be 0.1 μm or more, formed the modified layer 35 under the same laser processing conditions and performed grinding, in the dividing process, the surface roughness of the planned dividing line Undivided regions are generated everywhere in 14. This is considered to be because the modified layer 35 was not properly formed inside the wafer W due to the roughness of the surface of the cut groove 25 due to the disturbance of the laser light in the modified layer forming step.

As described above, according to the wafer processing method of this embodiment, the insulating film 15 is removed from the back surface 13 of the wafer W along the planned division line 14 by the cutting tool 22, and the groove bottom having a flat surface is formed on the back surface 13 of the wafer W. 26 cutting slots 25 . In addition, by irradiating laser beams so as to pass through the cutting groove 25 , the modified layer 35 can be formed inside the wafer W without being affected by the insulating film 15 . At this time, since the surface roughness of the cutting groove 25 is 0.1 μm or less, and the width of the groove bottom 26 is equal to or larger than the laser spot diameter, it is possible to suppress laser beam disturbance at the groove bottom 26 . Therefore, an appropriate modified layer 35 is formed at an appropriate position inside the wafer W, and the wafer W can be divided satisfactorily along the planned dividing line 14 . In addition, since the insulating film 15 is partially removed from the rear surface 13 of the wafer W by the cutting blade 22, the processing time can be shortened compared with the structure in which the insulating film 15 is entirely removed from the rear surface 13 of the wafer W by grinding.

In addition, this invention is not limited to the said embodiment, It can implement with various changes. In the above-described embodiment, the size, shape, and the like shown in the drawings are not limited thereto, and can be appropriately changed within the range in which the effects of the present invention are exhibited. In addition, unless it deviates from the scope of the objective of this invention, it can implement with a proper change.

For example, in the present embodiment, the cutting groove 25 is formed on the wafer W by a single cutting blade 22 in the insulating film removal step, but the present invention is not limited to this configuration. For example, a pair of cutting blades 22 having different abrasive grain diameters may be used, one cutting blade 22 may be used to form the cutting groove 25 , and the other cutting blade 22 may be used to adjust the surface roughness of the cutting groove 25 .

In addition, in the present embodiment, the modified layer 35 is formed continuously along the planned dividing line 14 in the modified layer forming step, but the configuration is not limited to this configuration. The modified layer 35 may be formed intermittently along the planned dividing line 14 as long as the wafer W can be divided along the planned dividing line 14 .

In addition, in the present embodiment, the modified layer 35 having a predetermined thickness is formed by floating the converging point of the laser beam, but the structure is not limited to this. The modified layer 35 can also be formed by one irradiation of laser light by adjusting the processing conditions of laser processing. In addition, not only one modified layer 35 is formed inside the wafer W, but multiple modified layers 35 may be formed in the thickness direction.

In addition, in this embodiment, a part of modified layer 35 is formed so as to extend over the finished product thickness L, but it is not limited to this structure. The reformed layer 35 may be formed on the rear surface 13 side (upper side) of the wafer W than the finished product thickness L as long as it is near the front surface of the wafer W. At this time, by grinding the wafer W to the finished thickness L to remove the modified layer 35 , it is possible to improve the flexural strength. In addition, when the wafer W is an optical device wafer, an increase in luminance is achieved.

In addition, when the wafer W is thinned by rough grinding, finish grinding, and grinding, the wafer W may be divided at any stage of the rough grinding, finish grinding, and grinding.

In addition, in this embodiment, the insulating film removal step is performed by a cutting device, the modified layer forming step is performed by a laser processing device, and the grinding step is performed by a grinding device, but some or all of the steps may be through a device.

As described above, the present invention has the effect that an appropriate modified layer can be formed at an appropriate position in a short time for a wafer having an insulating film formed on the back surface, especially for dividing a semiconductor wafer or an optical device wafer into one Wafer processing methods for individual chips are useful.

Claims (1)

1. a processing method for wafer, be in front in the processing method by cutting apart a plurality of regions that preset lines marks off and being formed with device and being formed with overleaf the wafer of dielectric film,

The processing method of above-mentioned wafer is characterised in that to have:

Dielectric film is removed operation, from the rear side of wafer, along the above-mentioned preset lines of cutting apart, utilizes cutting tool to form the cutting slot with smooth bottom land, along the above-mentioned preset lines of cutting apart, removes dielectric film;

Modified layer forms operation, remove after operation having implemented above-mentioned dielectric film, the above-mentioned cutting slot of take from the back side of wafer completes calibration as benchmark, the focal point for wafer with the laser beam of radioparent wavelength is navigated to near inside front wafer surface from above-mentioned cutting slot, and irradiate along above-mentioned cutting slot, near inside front wafer surface forms modified layer; And

Segmentation process, forms after operation having implemented above-mentioned modified layer, from the back side of wafer, utilizes grinding member to carry out grinding, and thinning is finished product thickness, and moves by grinding, and the above-mentioned modified layer of take is cut apart wafer along the above-mentioned preset lines of cutting apart as starting point,

In above-mentioned cutting slot, the surface roughness of above-mentioned smooth bottom land is below 0.1 μ m, and the width of above-mentioned smooth bottom land is more than the diameter of laser spots that is formed at above-mentioned bottom land.

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