JP2012222113A - Method of processing wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wafer processing method that is capable of avoiding the occurrence of chipping over a laser processing groove and has no risk of damaging a device.SOLUTION: Provided is a method of processing a wafer in which a laminate including a low dielectric constant insulating film is stacked on the surface, and devices are formed by the laminate in each region partitioned by a plurality of predetermined division lines crossing in a lattice form. The method comprises the steps of: forming a laser processing groove for dividing the laminate by irradiating a laser beam in a wavelength having absorbency to the laminate along the predetermined division line; forming a strain on the bottom surface of the laser processing groove by irradiating the wafer with a laser beam along the laser processing groove formed in the step of forming the laser processing groove; and cutting the wafer along the laser processing groove with a cutting blade after implementing the step of forming the strain.

Description

  The present invention relates to a wafer processing method using a low dielectric constant insulating film as an interlayer insulating film.

  In the semiconductor device manufacturing process, a plurality of regions are defined by dividing lines called streets formed in a lattice shape on the surface of a semiconductor wafer such as a silicon wafer or a gallium arsenide wafer having a substantially disk shape. A device such as an IC or LSI is formed in the region.

  After such a semiconductor wafer is ground to a predetermined thickness by a grinding device and then processed into a predetermined thickness, it is divided into individual devices by a cutting device or a laser processing device, and the divided devices are various electric devices such as mobile phones and personal computers. Widely used in equipment.

  As a cutting device, a cutting device generally called a dicing device is used. In this cutting device, a cutting blade having a cutting blade having a thickness of 20 to 30 μm is obtained by hardening superabrasive grains such as diamond and CBN with metal or resin. Cutting is performed by cutting into a semiconductor wafer while rotating at a high speed such as 30000 rpm.

A semiconductor device formed on the surface of a semiconductor wafer has a plurality of layers of metal wirings that transmit signals, and each metal wiring is insulated by an interlayer insulating film formed mainly of SiO ₂ . .

  In recent years, with the miniaturization of the structure, the distance between wirings has become shorter, and the electric capacity between adjacent wirings has increased. Due to this, a problem that signal delay occurs and power consumption increases has become prominent.

In order to reduce the parasitic capacitances between the layers, the device (circuit) prior to each layer when forming an interlayer insulating film for insulating primarily had adopted the SiO ₂ insulating film, than recently become SiO ₂ insulating film dielectric A low dielectric constant insulating film (Low-k film) having a low rate has been adopted.

As the low dielectric constant insulating film, a material having a dielectric constant lower than that of the SiO ₂ film (dielectric constant k = 4.1) (for example, about k = 2.5 to 3.6), for example, an inorganic material such as SiOC, SiLK, etc. Examples thereof include organic films such as films, polyimide-based, parylene-based, and polytetrafluoroethylene-based polymer films, and porous silica films such as methyl-containing polysiloxane.

  When a laminated body including such a low dielectric constant insulating film is cut along a line to be divided by a cutting blade, the low dielectric constant insulating film is very brittle like mica, which causes a problem that the laminated body is peeled off.

  In order to solve this problem, for example, in Japanese Patent Application Laid-Open No. 2003-320466 or Japanese Patent Application Laid-Open No. 2005-209719, prior to cutting with a cutting blade, the laminated body on the planned division line is removed in advance by laser beam irradiation. Semiconductor wafer processing methods have been proposed.

JP 2003-320466 A JP 2005-209719 A

  However, after removing the laminated body including the low dielectric constant insulating film on the planned division line by irradiating a laser beam along the predetermined division line to form a laser processing groove, a cutting blade is formed along the laser processing groove. In some cases, chipping beyond the laser-processed groove may occur even when cutting is performed with the above method. If chipping occurs beyond the laser processed groove, the device will be damaged, which is a problem.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a wafer processing method that suppresses the occurrence of chipping beyond the laser processing groove and does not damage the device. Is to provide.

  According to the present invention, a multilayer body including a low dielectric constant insulating film is laminated on the surface, and a device is formed in each of the regions divided by the multilayer body and a plurality of division lines that intersect with the division line. A laser processing groove for forming a laser processing groove for dividing a laminated body by irradiating the laminated body with a laser beam having a wavelength that absorbs the laminated body along the planned division line Forming a strain, forming a strain on the bottom surface of the laser processed groove by irradiating the wafer with a laser beam along the laser processed groove formed in the laser processed groove forming step, and the strain forming step. And a cutting step of cutting the wafer with a cutting blade along the laser processing groove.

  Preferably, the output of the laser beam irradiated in the strain forming step is set larger than the output of the laser beam irradiated in the laser processing groove forming step. As an alternative, the processing feed rate in the strain forming step may be made faster than the processing feed rate in the laser processing groove forming step without changing the output of the laser beam in both steps.

  According to the present invention, the strain forming step forms a minute strain (microcrack) on the bottom surface of the laser processing groove to make the surface state of the groove bottom rough, and then the cutting is performed with the cutting blade. It is possible to prevent the occurrence of large chips and cracks exceeding the groove.

  This is presumably because the progress of chips and cracks generated during cutting by the cutting blade stops at this strain (microcrack), and as a result, large chips and cracks exceeding the laser processed groove do not occur.

It is a perspective view of a laser processing apparatus. It is a perspective view of the semiconductor wafer supported by the annular frame via the dicing tape. It is a block diagram of a laser beam generation unit. 4A is a cross-sectional view of the semiconductor wafer adhered to the dicing tape, FIG. 4B is a cross-sectional view after the laser processing groove forming step of the first embodiment, and FIG. 4C is a strain forming step. It is sectional drawing after implementation. FIG. 5A is a cross-sectional view after performing the laser processing groove forming step of the second embodiment, and FIG. 5B is a cross-sectional view after performing the strain forming step. It is a perspective view which shows a cutting step. It is sectional drawing which shows a cutting step.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Referring to FIG. 1, there is shown a perspective view of a laser processing apparatus 2 suitable for carrying out the wafer processing method of the present invention. The laser processing apparatus 2 includes a first slide block 6 mounted on a stationary base 4 so as to be movable in the X-axis direction.

  The first slide block 6 is moved in the machining feed direction, that is, the X-axis direction along the pair of guide rails 14 by the machining feed means 12 including the ball screw 8 and the pulse motor 10.

  A second slide block 16 is mounted on the first slide block 6 so as to be movable in the Y-axis direction. That is, the second slide block 16 is moved in the indexing direction, that is, the Y-axis direction along the pair of guide rails 24 by the indexing feeding means 22 constituted by the ball screw 18 and the pulse motor 20.

  A chuck table 28 is mounted on the second slide block 16 via a cylindrical support member 26, and the chuck table 28 can be moved in the X-axis direction and the Y-axis direction by the processing feed means 12 and the index feed means 22. . The chuck table 28 is provided with a clamp 30 for clamping the semiconductor wafer sucked and held by the chuck table 28.

  A column 32 is erected on the stationary base 4, and a laser beam irradiation unit 34 is attached to the column 32. The laser beam irradiation unit 34 includes a laser beam generation unit 35 shown in FIG. 4 housed in a casing 33, and a condenser 37 attached to the tip of the casing 33.

  As shown in FIG. 3, the laser beam generating unit 35 includes a laser oscillator 62 that oscillates a YAG laser or a YVO4 laser, a repetition frequency setting unit 64, a pulse width adjusting unit 66, and a power adjusting unit 68. . Although not particularly shown, the laser oscillator 62 has a Brewster window, and the laser beam emitted from the laser oscillator 62 is a linearly polarized laser beam.

  An image pickup means 39 for detecting a processing region to be laser processed in alignment with the condenser 37 and the X-axis direction is disposed at the tip of the casing 33. The image pickup means 39 includes an image pickup device such as a normal CCD that picks up an image of a processing area of a semiconductor wafer with visible light.

  The imaging means 39 further includes an infrared irradiation means for irradiating the semiconductor wafer with infrared rays, an optical system for capturing the infrared rays irradiated by the infrared irradiation means, and an infrared CCD for outputting an electrical signal corresponding to the infrared rays captured by the optical system. Infrared imaging means composed of an infrared imaging element such as the above is included, and the captured image signal is transmitted to a controller (control means) 40.

  The controller 40 includes a central processing unit (CPU) 42 that performs arithmetic processing according to a control program, a read-only memory (ROM) 44 that stores a control program, and a random read / write that stores arithmetic results. An access memory (RAM) 46, a counter 48, an input interface 50, and an output interface 52 are provided.

  Reference numeral 56 denotes a processing feed amount detection means comprising a linear scale 54 disposed along the guide rail 14 and a read head (not shown) disposed on the first slide block 6. Is input to the input interface 50 of the controller 40.

  Reference numeral 60 denotes index feed amount detection means comprising a linear scale 58 disposed along the guide rail 24 and a read head (not shown) disposed on the second slide block 16. The detection signal is input to the input interface 50 of the controller 40.

  An image signal picked up by the image pickup means 39 is also input to the input interface 50 of the controller 40. On the other hand, a control signal is output from the output interface 52 of the controller 40 to the pulse motor 10, the pulse motor 20, the laser beam irradiation unit 34, and the like.

  As shown in FIG. 2, on the surface of the semiconductor wafer W to be processed by the laser processing apparatus 2, the first street (division planned line) S <b> 1 and the second street (division planned line) S <b> 2 are orthogonal to each other. A large number of devices D are formed in a region defined by the first street S1 and the second street S2.

  In the semiconductor wafer W of this embodiment, as shown in the cross-sectional view of FIG. 4A, a stacked body 11 including a low dielectric constant insulating film (Low-k film) is stacked on a wafer-shaped silicon substrate 5. Streets S1 and S2 and a device D are formed on the laminate 11 by patterning.

Here, the low dielectric constant insulating film (Low-k film) refers to an insulator having a dielectric constant lower than that of the SiO ₂ film having a dielectric constant k = about 4.1. For example, SiOC, SiLK, BSG (SiOB), etc. Inorganic films, polyimide films, parylene films, organic films such as polytetrafluoroethylene films, and porous silica films such as methyl-containing polysiloxane.

  The semiconductor wafer W is attached to a dicing tape T that is an adhesive tape, and the outer peripheral portion of the dicing tape T is attached to an annular frame F. As a result, the semiconductor wafer W is supported by the annular frame F via the dicing tape T, and the wafer W is sucked and held on the chuck table 28 shown in FIG. By clamping with 30, it is supported and fixed on the chuck table 28.

  In the wafer processing method of the present embodiment, first, a laser beam having a wavelength that is absorptive with respect to the laminate 11 is generated by the laser beam generating unit 35, and this laser beam is first condensed on the wafer 11 by the condenser 37. A laser processing groove forming step for forming a laser processing groove for concentrating on the stacked body 11 corresponding to the street S1 and dividing the stacked body 11 is performed.

  Before performing this laser processing groove forming step, the semiconductor wafer W is imaged by the imaging means 39, and image processing such as pattern matching is performed to detect the first street S1 to be laser processed. To do. Following the alignment of the first street S1, the chuck table 28 is rotated 90 degrees, and then the same alignment is performed for the second street S2.

  After the alignment, the chuck table 28 is shown in FIG. 1 while condensing a laser beam having a wavelength (for example, 355 nm) having an absorptivity with respect to the stacked body 11 by the condenser 37 and irradiating it along the first street S1. To move in the X-axis direction at a predetermined machining feed rate.

  As a result, as shown in FIG. 4B, the stacked body 11 of the semiconductor wafer W is divided to form the laser processed grooves 13. The width of the laser processing groove 13 is narrower than the width of the first street S1 and wider than the width (for example, 30 μm) of the cutting blade of the cutting blade described later.

  The laser processing groove 13 is formed by irradiating the first street S1 with a plurality of laser beams while moving the chuck table 28 in the Y-axis direction.

  While indexing and feeding the chuck table 28 in the Y-axis direction by street pitch, similar laser processing grooves 13 are formed along all the first streets S1. Next, after the chuck table 28 is rotated 90 degrees, similar laser processing grooves 13 are formed along all the second streets S2 orthogonal to the first streets S1.

  The laser processing conditions in the laser processing groove forming step are set as follows, for example.

Light source: YAG pulse laser or YVO4 pulse laser Wavelength: 355 nm
Average output: 7-10W
Repetition frequency: 100 to 130 kHz
Processing feed rate: 70 to 100 mm / s

  A cross-sectional view of the semiconductor wafer W after the laser processing groove forming step is shown in FIG. The laser processed grooves 13 formed in the laser processed groove forming step may be thinly left on the substrate 5 without completely dividing the stacked body 11.

  In the wafer processing method of the present embodiment, after performing the laser processing groove forming step, a laser beam having a wavelength (for example, 355 nm) having an absorptivity with respect to the substrate 5 along the laser processing groove 13 formed in the laser processing groove forming step. Is applied along the laser processing groove 13 to perform a strain forming step for forming a strain on the bottom surface of the laser processing groove 13.

  Preferably, the wavelength of the laser beam irradiated in this strain forming step is the same as the wavelength of the laser beam irradiated in the laser processing groove forming step. Also, it is set to be larger than the output of the laser beam irradiated in the strain forming step and the output of the laser beam irradiated in the laser processing groove forming step.

  As an alternative, the output of the laser beam irradiated in the strain forming step is set to be equal to or smaller than the output of the laser beam irradiated in the laser processing groove forming step, and the processing feed rate in the strain forming step is set to the laser processing groove forming step. It may be made faster than the machining feed rate at. When the strain forming step is performed, a minute strain (micro crack) 15 is formed on the bottom surface of the laser processing groove 13 as best shown in the partial enlarged view of FIG.

  The first laser processing conditions for the strain forming step are set as follows.

Light source: YAG pulse laser or YVO4 pulse laser Wavelength: 355 nm
Average output: 11-13W
Repetition frequency: 100 to 130 kHz
Processing feed rate: 70 to 100 mm / s

  The second laser processing conditions in the strain forming step are set as follows.

Light source: YAG pulse laser or YVO4 pulse laser Wavelength: 355 nm
Average output: 7-10W
Repetition frequency: 100 to 130 kHz
Processing feed rate: 600 to 800 mm / s

  Next, the laser processing groove forming step and the strain forming step of the second embodiment of the present invention will be described with reference to FIG. In the laser processing groove forming step of this embodiment, as shown in FIG. 5 (A), a pair of laser processing grooves 13 having a width wider than the width of the cutting blade of the cutting blade is formed on both sides of the first street S1. The laminated body 11 remains on the first street S1 at the portion sandwiched between the pair of laser processing grooves 13.

  After forming a pair of laser processing grooves 13 along all the streets S1 and S2, respectively, the substrate 5 is irradiated with a laser beam having an absorptive wavelength along the laser processing grooves 13 formed in the laser processing groove forming step. Then, as shown in FIG. 5B, a strain forming step for forming the strain 15 on the bottom surface of the laser processing groove 13 is performed. The laser processing conditions for this strain forming step are the same as the strain forming step of the first embodiment described above.

  After performing the strain forming step for forming the strain 15 on the bottom surface of the laser processed groove 13, the cutting step for cutting the semiconductor wafer W along the laser processed groove 13 is performed. Referring to FIG. 6, there is shown a perspective view of a main part of a cutting apparatus 2 suitable for performing a cutting step.

  When cutting the semiconductor wafer W, the chuck table 72 of the cutting apparatus 70 sucks and holds the semiconductor wafer W via the dicing tape T. Reference numeral 74 denotes a cutting unit of the cutting apparatus 70, which includes a spindle driven by a motor (not shown) housed in a spindle housing 76, and a cutting blade 78 detachably attached to the tip of the spindle.

  The cutting blade 78 is covered with a wheel cover 80, and a pipe 82 of the wheel cover 80 is connected to a cutting fluid supply source that supplies pure water or the like. The cutting blade 78 is configured by electrodepositing a cutting edge (grinding stone portion) 82a in which diamond abrasive grains are dispersed in a nickel base material or a nickel alloy base material on the outer periphery of a circular base.

  When cutting the semiconductor wafer W, the cutting blade 78 is rotated at high speed (for example, 30000 rpm) in the direction of arrow A while jetting cutting water from the cutting water nozzle 84, and the chuck table 72 is processed and fed in the X-axis direction. Then, the semiconductor wafer W is cut along the laser processing groove 13 formed in the street S1 or S2, and the cutting groove 17 is formed.

  While indexing and feeding the chuck table 72 in the Y-axis direction, the cutting grooves 17 are formed along the laser processing grooves 13 formed in all the first streets S1 extending in the first direction. Next, after the chuck table 72 is rotated by 90 degrees, the similar cutting grooves 17 are formed along the laser processing grooves 13 formed in all the second streets S2 extending in the second direction, thereby forming the semiconductor wafer. W is divided into individual semiconductor devices D.

  A cross-sectional view at the time of cutting is shown in FIG. Since the laser processing groove 13 of the first embodiment has a width wider than the width of the cutting blade 78a of the cutting blade 78, the progress of chips and cracks generated during cutting by the cutting blade 78 is caused by this distortion (microcracking). ), And as a result, even if the interlayer insulating film of the stacked body 11 forming the semiconductor device D includes a low-k film, the device D can be formed without generating a large chip or crack exceeding the laser processed groove 13. The semiconductor wafer W can be divided into individual semiconductor devices D without being damaged.

  In the second embodiment shown in FIG. 5, a pair of laser processing grooves 13 are formed on both sides of the first street S1, and the stacked body 11 remains in a portion corresponding to the first street S1, Since the distance between the pair of laser processing grooves 13 is wider than the width of the cutting edge 78 a of the cutting blade 78, the progress of chipping and cracks generated during cutting is a strain (microcrack) 15 formed on the bottom surface of the pair of laser processing grooves 13. As a result, it is possible to prevent the occurrence of large chips or cracks exceeding the laser processed groove 13.

2 Laser processing device 5 Semiconductor substrate 11 Laminated body 13 Laser processing groove 15 Strain (micro crack)
17 Cutting groove 28 Chuck table 35 Laser beam generating unit 37 Condenser 78 Cutting blade 78a Cutting edge W Semiconductor wafer D Device

Claims (4)

A wafer processing method in which a laminate including a low dielectric constant insulating film is laminated on a surface, a plurality of division lines intersecting in a lattice shape by the laminate, and a device formed in each region partitioned by the division lines Because
A laser processing groove forming step of forming a laser processing groove for dividing the stacked body by irradiating the stacked body with a laser beam having a wavelength having an absorptivity to the stacked body, and dividing the stacked body;
A strain forming step of irradiating a wafer with a laser beam along the laser processed groove formed in the laser processed groove forming step to form a strain on a bottom surface of the laser processed groove;
A cutting step of cutting the wafer with a cutting blade along the laser processing groove after performing the strain forming step;
A wafer processing method characterized by comprising:   2. The wafer processing method according to claim 1, wherein the wavelength of the laser beam irradiated in the strain forming step is the same as the wavelength of the laser beam irradiated in the laser processing groove forming step.   3. The wafer processing method according to claim 1, wherein an output of the laser beam irradiated in the strain forming step is larger than an output of the laser beam irradiated in the laser processing groove forming step.   The wafer processing method according to claim 1, wherein a processing feed rate at the strain forming step is faster than a processing feed rate at the laser processing groove forming step.

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