JP2009111147A - Semiconductor chip and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor chip manufactured by a manufacturing method including a step of cutting a semiconductor substrate through a dicing process using laser light, the semiconductor chip being capable of preventing a fine fragment in a reformed region from peeling off the cut surface of a semiconductor chip, and to provide the method of manufacturing the same. <P>SOLUTION: In an etching step after cutting a wafer 21, a semiconductor substrate 21 having been cut into a semiconductor chip 22 is disposed in a chamber for performing isotropic dry etching in a state that the substrate 21 is stuck on a sheet 411. Then XeF<SB>2</SB>as a reactive gas is introduced to etch the semiconductor substrate under predetermined conditions. Consequently, isotropic etching is carried out on the cut surface 21d to remove the reformed region K, so the reformed region K is prevented from scattering as a fine fragment. Because of the dry process, there is no risk of causing the sticking on the movable portion of an MEMS 23 due to surface tension of liquid. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a semiconductor chip manufactured by cleaving a semiconductor substrate in the thickness direction and a manufacturing method thereof.

In recent years, in a dicing process for separating a silicon wafer (hereinafter referred to as a wafer) on which a semiconductor integrated circuit or a MEMS (Micro Electro Mechanical Systems) is formed into each semiconductor chip, a dicing process (laser dicing) using a laser beam is considered. For example, Patent Document 1 below discloses a wafer processing technique using a laser. FIG. 6 is an explanatory diagram showing a dicing process using laser light. FIG. 6A is an explanatory diagram of a modified region forming process by laser light irradiation, and FIG. 6B is an explanatory diagram of a cleaving process.
As shown in FIG. 6A, the laser head H that irradiates the laser light L includes a condensing lens CV that condenses the laser light L, and condenses the laser light L at a predetermined focal length. Can do. In the modified region forming step, the planned cutting line DL for cutting the wafer W under the laser light irradiation conditions set so that the condensing point P of the laser light L is formed at a depth d from the substrate surface of the wafer W. The laser head H is moved along the top (front side in the figure), and the laser beam L is irradiated from the substrate surface of the wafer W. As a result, a modified region K by multiphoton absorption is formed in a path of depth d where the condensing point P of the laser beam L is scanned.
Here, multiphoton absorption means that a substance absorbs a plurality of the same or different photons. Due to the multiphoton absorption, a phenomenon called optical damage occurs at the condensing point P of the semiconductor substrate W and in the vicinity thereof. Due to optical damage, a modified region K is formed, which is a region once melted and then solidified to change into an amorphous structure or a polycrystalline structure.
When the laser beam L is a pulse wave, the intensity of the laser beam L is determined by the peak power density (W / cm ² ) at the focal point P. For example, the peak power density is 1 × 10 ⁸ (W / cm ² ) or more. Multiphoton absorption occurs under conditions where the pulse width is 1 μs or less. As the laser beam L, for example, a laser beam by a YAG (Yttrium Aluminum Garnet) laser is used. The wavelength of the laser beam L is, for example, a wavelength in the infrared light region of 1064 nm.
Subsequently, as shown in FIG. 6B, by applying a stress in the in-plane direction of the semiconductor substrate W (directions indicated by arrows F2 and F3 in the figure), the substrate thickness starts from the modified region K. The crack C is advanced in the vertical direction, and the semiconductor substrate W is cleaved along the cleaved line DL.
Japanese Patent No. 3408805

Here, since the strength of the modified region K is reduced, a part of the modified region K exposed in the fractured surface is peeled off and scattered as a minute piece when the semiconductor substrate W is cleaved or in a later process. There is a risk. If the minute piece adheres to an element formed on the chip, it causes a malfunction of the semiconductor device, resulting in a problem that the yield and quality of the semiconductor chip cut and separated from the wafer is lowered.
In particular, in the case where various sensor elements (pressure sensors, acceleration sensors, ultrasonic sensors, etc. composed of piezoelectric elements or capacitance elements) and micromachines formed using MEMS technology are formed, the sensor elements and micromachines If a minute piece adheres to the movable part that constitutes, the movement of the movable part is hindered by the minute piece, which may cause a decrease in yield and quality of sensor elements and micromachines.

  Accordingly, the present invention provides a semiconductor chip manufactured by a manufacturing method including a process of cleaving by a dicing process (laser dicing) using laser light, and a small piece of a modified region is peeled from a fractured surface of the semiconductor chip. An object of the present invention is to realize a semiconductor chip and a method for manufacturing the semiconductor chip that can prevent this.

In order to achieve the above object, according to the first aspect of the present invention, in the method for manufacturing a semiconductor chip, in the semiconductor chip manufacturing method, a cleaving line for cleaving a semiconductor substrate having elements formed on the substrate surface in the thickness direction. A laser head for irradiating laser light is moved relative to the semiconductor substrate, and a laser beam is irradiated with the condensing point inside the semiconductor substrate, and the condensing point is absorbed by multiphoton absorption. A modified region forming step for forming a modified region, and the semiconductor substrate that has undergone the modified region forming step is cleaved in the thickness direction along the planned cutting line, starting from the modified region. A cleaving step for obtaining a chip, and an etching step for etching, by an isotropic dry etching method, a modified region exposed in the cleaved surface formed in the semiconductor chip by the cleaving step. , Using the technical means of.
In addition, the said condensing point is a location where the laser beam condensed.

  According to the first aspect of the present invention, since the isotropic etching is performed on the fractured surface by the etching process and the modified region is removed, the modified region peeled off from the fractured surface of the semiconductor chip is scattered as fine pieces. Can be prevented. Thereby, since a micro piece does not adhere to a semiconductor chip, it is possible to prevent a decrease in product yield and quality due to scattering of the micro piece.

  According to a second aspect of the present invention, in the method for manufacturing a semiconductor chip according to the first aspect, the technical means that the dry etching method is a reactive gas etching method is used.

  As in the invention described in claim 2, a reactive gas etching method can be used as the dry etching method. According to this, etching can be performed with a simple apparatus configuration including a chamber and a heating apparatus.

  According to a third aspect of the present invention, in the semiconductor chip manufacturing method according to the first aspect, the technical means that the dry etching method is a plasma etching method is used.

  As in the third aspect of the invention, the plasma etching method can be used as the dry etching method. According to this, since the temperature of the semiconductor substrate does not rise, there is no possibility that adverse effects such as distortion due to thermal stress occur on the semiconductor chip. Furthermore, since the etching rate is high, the processing time can be shortened.

  According to a fourth aspect of the present invention, in the method for manufacturing a semiconductor chip according to the first aspect, the technical means that the dry etching method is a chemical dry etching method is used.

  As in the fourth aspect of the invention, a chemical dry etching method can be used as the dry etching method. Since the chemical dry etching method is damage-free etching in which the etching portion and the plasma generation portion are separated, it is possible to prevent damage to the semiconductor chip due to the etching.

  According to a fifth aspect of the present invention, in the semiconductor chip manufacturing method according to any one of the first to fourth aspects, the etching step is performed together with the cleaving of the semiconductor substrate in the cleaving step. Use appropriate means.

  According to the invention described in claim 5, since the etching process is performed together with the cleaving of the semiconductor substrate in the cleaving process, the modified region can be etched immediately after cleaving, so that the separation of the minute pieces can be prevented more efficiently. can do.

  According to a sixth aspect of the present invention, in the semiconductor chip manufacturing method according to any one of the first to fifth aspects, the surface of the element formed on the substrate surface is formed before the etching step. A technical means is used that further includes a protective film forming step of forming a protective film for protecting the semiconductor element from etching by the dry etching method.

  According to invention of Claim 6, before performing an etching process, the protective film formation process of forming the protective film which protects the said semiconductor element from the etching by the dry etching method on the surface of the element formed in the board | substrate surface Since the protective film is formed on the element surface, the element can be protected from etching.

  According to a seventh aspect of the present invention, in the method for manufacturing a semiconductor chip according to any one of the first to sixth aspects, the element formed on the substrate surface is formed by a MEMS (Micro Electro Mechanical Systems) technique. The technical means of being an element having a movable part formed is used.

  When the element formed on the substrate surface is an element having a movable part formed by the MEMS technology as in the invention described in claim 7, the movement of the movable part is caused by a minute piece being sandwiched between the movable parts. Therefore, the present invention can be preferably used because the device performance can be prevented from being deteriorated.

  According to an eighth aspect of the present invention, there is provided a semiconductor chip manufactured by the method for manufacturing a semiconductor chip according to any one of the first to seventh aspects, wherein the modified region is removed from the split section. The technical means is used.

  According to an eighth aspect of the present invention, there is provided a semiconductor chip manufactured by the semiconductor chip manufacturing method according to any one of the first to seventh aspects, wherein the modified region is removed from the fractured surface. Therefore, the fine pieces are not peeled off and scattered from the modified region.

[First Embodiment]
A first embodiment of a semiconductor chip and a manufacturing method thereof according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing a configuration example of a wafer to be cut by the manufacturing method of the present invention. FIG. 1A is an explanatory plan view of the surface of a wafer, and FIG. 1B is an enlarged cross-sectional view taken along the line 1B-1B in FIG. FIG. 2 is an explanatory diagram of a cleaving apparatus that irradiates a semiconductor substrate with laser light. FIG. 3 is a cross-sectional explanatory view of a semiconductor chip formed by cleaving a wafer by a cleaving process. FIG. 4 is a cross-sectional explanatory view of the semiconductor chip etched by the etching process. FIG. 5 is a cross-sectional explanatory view of a semiconductor chip on which a protective film is formed.
In each figure, a part is enlarged and exaggerated for explanation.

First, a wafer 20 as shown in FIG. The wafer 20 is provided with a thin disk-shaped semiconductor substrate 21 made of silicon, and an orientation flat indicating a crystal orientation is formed on a part of the outer periphery thereof. On the substrate surface 21 a of the semiconductor substrate 21, an element formed through a diffusion process or the like, for example, a MEMS 23 constituting a sensor element having a movable part formed in a comb shape, for example, is aligned like a grid. Has been placed.
The wafer 20 is cleaved along the planned cleaving line DL by a dicing process to become semiconductor chips 22, and the semiconductor chip 22 is completed as a packaged IC or LSI through various processes such as a mounting process, a bonding process, and an encapsulating process. To do. In the present embodiment, the semiconductor substrate 21 can form a silicon layer that serves as a support substrate for the semiconductor chip 22.
The semiconductor substrate 21 has a back surface 21b bonded to a stretchable resin sheet 41, and the outer periphery of the sheet 41 is held by an annular frame 42 in a state where the sheet 41 is stretched.
For example, as shown in FIG. 1B, six semiconductor chips 22a to 22f are formed on the 1B-1B line. Seven cutting planned lines DL1 to DL7 are set in the thickness direction of the semiconductor substrate 21, and a modified region serving as a starting point of the cutting is formed by a method described later.

  As shown in FIG. 2, the cleaving apparatus 1 for the semiconductor substrate 21 is provided with a laser head 31 that irradiates a laser beam L. The laser head 31 includes a condensing lens 32 that condenses the laser light L, and can condense the laser light L at a predetermined focal length. Here, the condensing point P of the laser beam L is set so as to be formed at a depth d from the substrate surface 21 a of the semiconductor substrate 21.

First, a modified region forming step is performed. In order to form the modified region K in the semiconductor substrate 21, first, one of the planned cutting lines DL shown in FIG. 1A is scanned with a laser beam for wafer detection, and FIG. The outer peripheral end 21c shown is detected, and the scanning range of the laser light L is set.
Subsequently, as shown in FIG. 2, the laser head 31 is scanned along the planned cutting line DL (in the direction of arrow F4 in the figure), and the laser beam L is irradiated from the substrate surface 21a, thereby condensing the laser beam L. The modified region K by multiphoton absorption is appropriately formed in the path of depth d scanned by the point P. By adjusting the depth d of the condensing point P of the laser beam L, the modified region K having an arbitrary number of layers can be formed at an arbitrary depth within the thickness range of the semiconductor substrate 21. For example, when the thickness is relatively thick, the condensing point P is moved in the thickness direction to form the modified region K continuously in the thickness direction or at a plurality of locations, thereby cleaving the semiconductor substrate 21. Can be made easier.
Here, multiphoton absorption means that a substance absorbs a plurality of the same or different photons. Due to the multiphoton absorption, a phenomenon called optical damage occurs at and near the condensing point P of the semiconductor substrate W, and once it melts, it solidifies and changes to polycrystalline silicon or amorphous silicon. A modified region K, which is a region of this size, is formed.

  Subsequently, a cleaving process is performed. In the cleaving step, as shown in FIG. 3, the sheet 41 is expanded by a known method (F direction in the figure) and stress is applied in the in-plane direction of the semiconductor substrate 21, thereby starting the modified region K as a starting point. , Cracks propagate in the substrate thickness direction. Thereby, the semiconductor substrate 21 can be easily cleaved along the cleaving line DL. The modified region K is exposed in the split section 21d formed by being cut. The strength of the modified region K is reduced due to the change of the crystal phase and the introduction of microcracks.

Subsequently, an etching process is performed. In the etching process, the cut surface 21d is etched by an isotropic dry etching method, and the modified region K is removed. In this embodiment, a reactive gas etching method using XeF ₂ (xenon difluoride) gas is employed. The reactive gas etching method can perform etching with a simple apparatus configuration including a chamber and a heating apparatus.

Etching is performed in the following steps. As shown in FIG. 4, first, the semiconductor substrate 21 that has been cleaved into the semiconductor chips 22 is disposed in a chamber in which etching is performed with the semiconductor substrate 21 attached to a sheet 41. Subsequently, XeF ₂ is introduced, the temperature is raised to a predetermined temperature, for example, 70 ° C., and then etched for a predetermined time, for example, 1 hour.
As a result, isotropic etching with XeF ₂ gas is performed in the fractured surface 21d and the modified region K is removed, so that the modified region K can be prevented from being scattered as fine pieces.
Further, since the reactive gas etching method is a dry process that does not use a liquid, there is no possibility that sticking may occur in the movable portion of the MEMS 23 due to the surface tension of the liquid.

As the reactive gas, for example, a fluorine-based gas or a chlorine-based gas such as CF ₄ , SF ₆ , NF ₃ , SiF ₄ , BF ₃ , ClF ₃ , or SiCl ₄ can be used.
In particular, if a gas having a higher etching rate of polycrystalline silicon or amorphous silicon than single crystal silicon is used, the modified region K can be selectively etched, so that a region formed of single crystal silicon, for example, the MEMS 23 The influence of etching on the movable part and the like can be reduced.

(Example of change)
A protective film such as SiO ₂ or SiN, which can be a mask material for XeF ₂ , may be formed on the surface of the MEMS 23.
Further, as shown in FIG. 5, a protective film 24 may be formed on the surface of the wafer 20 before laser irradiation, for example, the surface of the MEMS 23. According to this, it is possible to prevent the by XeF ₂ and movable portion of MEMS23 is etched by XeF _2.

[Effect of the first embodiment]
In the etching step, isotropic etching with XeF ₂ gas, which is a reactive gas, is performed on the fractured surface 21d, and the modified region K is removed, so that the modified region K is prevented from being scattered as fine pieces. Can do.
Further, since the reactive gas etching method is a dry process that does not use a liquid, there is no possibility that sticking may occur in the movable portion of the MEMS 23 due to the surface tension of the liquid.
Thereby, since a micro piece does not adhere to the semiconductor chip 22, it is possible to prevent a decrease in product yield and quality due to scattering of the micro piece.

[Second Embodiment]
The semiconductor chip and the manufacturing method thereof according to the second embodiment are different from those according to the first embodiment in that a plasma etching method in which plasma is generated by applying high-frequency power to a reactive gas in an etching process is employed. Here, the plasma etching method may be either a barrel type or a parallel plate type.
Etching is performed in the following steps. As in the first embodiment, as shown in FIG. 4, first, the semiconductor substrate 21 that has been cut into the semiconductor chips 22 is placed in a chamber in which etching is performed while the semiconductor substrate 21 is attached to the sheet 41. Subsequently, CF ₄ as a processing gas is introduced so that the gas pressure becomes 1 torr, high frequency power is applied, plasma is generated, and etching is performed by radical reaction.
Thereby, isotropic etching is performed on the fractured surface 21d, and the modified region K is removed, so that it is possible to prevent the modified region K from being scattered as fine pieces.

Since the plasma etching method is a dry process that does not use a liquid, there is no possibility that sticking will occur in the movable part of the MEMS 23 due to the surface tension of the liquid.
Further, since the temperature of the semiconductor substrate does not increase, there is no possibility that the MEMS 23 may be adversely affected by distortion due to thermal stress.
Furthermore, since the etching rate is high, the processing time can be shortened.

As the processing gas, for example, fluorine-based gas or chlorine-based gas such as SF6, NF3, SiF4, BF3, ClF3, and SiCl4 can be used.
Further, similarly to the first embodiment, a protective film 24 that can be a mask material against plasma may be formed on the movable portion of the MEMS 23 or the like.

(Example of change)
As the plasma etching method, a chemical dry etching method can be employed. For example, etching can be performed with F atoms obtained by microwave discharge using a mixed gas of CF ₄ and O ₂ . Here, since the chemical dry etching method is damage-free etching in which the etching portion and the plasma generation portion are separated, damage to the MEMS 23 can be prevented.
In the chemical dry etching method, a mixed gas of SF ₆ and O ₂ or a mixed gas of CF ₄ , N 2, Cl 2, and O 2 can be used as a processing gas.

[Effects of Second Embodiment]
(1) According to the semiconductor chip and the manufacturing method of the second embodiment, the same effect as the semiconductor chip and the manufacturing method of the first embodiment can be obtained, and the temperature of the semiconductor substrate does not increase. There is no risk of adverse effects such as distortion due to thermal stress.
Further, since the etching rate is high, the processing time can be shortened.

(2) In the configuration employing the chemical dry etching method as the plasma etching method, damage to the MEMS 23 can be prevented because it is damage-free etching in which the etching portion and the plasma generation portion are separated.

[Other Embodiments]
(1) Before performing the cleaving step, the wafer 20 may be placed in a chamber for etching and cleaved while performing the etching step. When this configuration is used, the modified region K can be etched immediately after cleaving, so that the separation of the minute pieces can be prevented more efficiently.

(2) Although the semiconductor substrate made of only silicon is used as the semiconductor substrate 21, the application of the present invention is not limited to this. For example, an oxide film made of silicon oxide is used as the substrate surface of the semiconductor substrate 21. The present invention can also be applied to those formed in 21a and SOI (Silicon On Insulator) wafers.

It is a schematic diagram which shows the structural example of the wafer cleaved with the manufacturing method of this invention. FIG. 1A is an explanatory plan view of the surface of a wafer, and FIG. 1B is an enlarged cross-sectional view taken along the line 1B-1B in FIG. It is explanatory drawing of the cleaving apparatus which irradiates a semiconductor substrate with a laser beam. It is sectional explanatory drawing of the semiconductor chip formed by cleaving a wafer by the cleaving process. It is sectional explanatory drawing of the semiconductor chip etched by the etching process. It is sectional explanatory drawing of the semiconductor chip in which the protective film was formed. It is explanatory drawing which shows the dicing process using a laser beam. FIG. 6A is an explanatory diagram of a modified region forming process by laser light irradiation, and FIG. 6B is an explanatory diagram of a cleaving process.

Explanation of symbols

20 Wafer 21 Semiconductor substrate 21a Substrate surface 21b Back surface 21c Outer peripheral edge 21d Split section 22 Semiconductor chip 23 MEMS (element)
24 Protective film 41 Sheet 42 Frame K Modified region L Laser beam

Claims (8)

A laser head for irradiating laser light is moved relative to the semiconductor substrate along a planned cutting line for cleaving a semiconductor substrate having elements formed on the substrate surface in the thickness direction of the semiconductor substrate. A modified region forming step of aligning a condensing point inside and irradiating a laser beam, and forming a modified region by multiphoton absorption at the condensing point;
The cleaving step of obtaining the semiconductor chip by cleaving the semiconductor substrate that has undergone the modified region forming step in the thickness direction along the planned cleaving line, starting from the modified region,
An etching step of etching the modified region exposed in the fractured surface formed in the semiconductor chip by the cleaving step by an isotropic dry etching method;
A method of manufacturing a semiconductor chip, comprising:   The method of manufacturing a semiconductor chip according to claim 1, wherein the dry etching method is a reactive gas etching method.   The method for manufacturing a semiconductor chip according to claim 1, wherein the dry etching method is a plasma etching method.   The method of manufacturing a semiconductor chip according to claim 1, wherein the dry etching method is a chemical dry etching method.   The method for manufacturing a semiconductor chip according to claim 1, wherein the etching step is performed together with the cleaving of the semiconductor substrate in the cleaving step.   The method further comprises a protective film forming step of forming a protective film for protecting the semiconductor element from etching by the dry etching method on the surface of the element formed on the substrate surface before performing the etching process. A method of manufacturing a semiconductor chip according to any one of claims 1 to 5.   7. The semiconductor according to claim 1, wherein the element formed on the substrate surface is an element having a movable part formed by a MEMS (Micro Electro Mechanical Systems) technique. Chip manufacturing method.   A semiconductor chip manufactured by the method for manufacturing a semiconductor chip according to claim 1, wherein the modified region is removed from the split section. .

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