JP4732934B2 - Laser dicing method - Google Patents

Description

  The present invention relates to a laser dicing method for a bonded SOI wafer in which a silicon wafer is bonded to an upper surface of a support substrate via an insulating film, and the bonded silicon wafer is thinned to form an SOI layer.

  As a semiconductor device manufacturing process technique, an SOI (Silicon On Insulator) technique is well known. In the SOI technology, a silicon single crystal layer called an SOI layer is provided on an insulating film made of silicon oxide or the like, and an element such as a transistor is formed in the SOI layer. According to such SOI technology, the insulation around the element can be improved, and the parasitic capacitance of the element and the leakage current can be reduced. As a manufacturing technique of a silicon wafer on which an SOI layer is formed, a so-called SOI wafer, oxygen atoms are ion-implanted into the silicon wafer and heat treatment is performed, so that the insulating film is placed at a certain depth from the silicon wafer surface. In addition to the thin film SOI technology for forming the buried oxide film, the following thick film SOI technology is known.

  In the thick film SOI technology, a silicon wafer in which the SOI layer is formed on an insulating film, that is, an SOI wafer is manufactured in the manner illustrated in FIG. 8, for example. First, the silicon wafer 10b on which the oxide film 10c is formed is superposed on the support substrate (silicon substrate) 10a, and then heat treatment is performed, so that the support substrate 10a and the silicon wafer 10b are integrated as shown in FIG. Paste to. Next, as shown in FIG. 8B, the silicon wafer 10b is mechanically polished until the thickness thereof becomes about 10 to 20 μm, and the outer circumference of about 5 mm is mechanically ground. Further, as shown in FIG. 8 (c), scratches and defect layers generated by the mechanical polishing and mechanical grinding are removed by mirror polishing of the upper surface of the silicon wafer 10b and alkali etching of the outer periphery thereof.

  FIG. 9A shows a planar structure of the bonded SOI wafer 10 manufactured in this way, and FIG. 9B shows an enlarged sectional structure of a part thereof. As shown in these drawings, the bonded SOI wafer 10 includes a silicon single crystal SOI layer 10d that is insulated from the support substrate 10a by an oxide film 10c. As shown in FIG. 9B, elements (transistors, etc.), electrodes, wirings, etc. are formed on the SOI layer 10d of the SOI wafer 10 and then the bonded SOI wafer 10 is divided into individual chips by dicing. Thus, a semiconductor chip can be obtained.

  Recently, as a dicing technique for silicon wafers, a dicing technique using a laser as disclosed in Patent Document 1, for example, has attracted attention. In the technique described in the document 1, a weakened modified layer is vertically grown by irradiating a laser beam inside a silicon wafer on a planned cutting line. In other words, irradiating laser light causes optical damage due to multiphoton absorption, thereby inducing thermal strain and forming cracks, forming a fragile modified layer that is easy to cleave inside the silicon wafer. is doing. With such a dicing technique, it is possible to reduce the cutting allowance, shorten the processing time, and reduce chips and heat dripping, as compared with conventional dicing techniques such as blade dicing and laser cutting.

Conventionally, a technique described in Patent Document 2 is known as a technique related to dicing of an SOI wafer using modification of the inside of the wafer by laser light irradiation as described above. In the technique described in the document 2, the variation of the reflectance of the laser beam at the interface between the silicon single crystal layer and the oxide film layer is reduced by appropriately setting the thickness of the buried oxide film of the SOI wafer. .
Japanese Patent No. 3408805 JP-A-2005-109320

  However, when the conventional SOI wafer dicing technique is applied to a bonded SOI wafer manufactured by the thick film SOI technique, there is a problem as described below, and there is still room for improvement.

  As described above, the bonded SOI wafer 10 has a terrace region having no SOI layer on the outer periphery thereof. Therefore, as shown in FIG. 10, in the region where the SOI layer 10d is formed and the terrace region where there is no SOI layer 10d, the difference in refractive index between the silicon single crystal constituting the SOI layer 10d and the air causes the laser light The depth of focus changes significantly. Specifically, the focal depth Dt of the laser beam in the terrace region without the SOI layer 10d made of a silicon single crystal having a refractive index ≈3.5 is greater than the focal depth Ds in the region where the SOI layer 10d is formed. Will also become shallower. Therefore, immediately under the terrace region, a modified layer is formed on the upper surface side of the bonded SOI wafer 10 rather than the region where the SOI layer 10 d is formed, and the modified layer is sufficiently modified to the back surface side of the bonded SOI wafer 10. There is a concern that a quality layer cannot be formed. If the formation of the modified layer becomes insufficient in this manner, the cleaving becomes incomplete and the yield is deteriorated. Incidentally, when the laser beam focal depth is reduced as described above, the formation position of the modified layer shifts to the upper surface side and the exposed upper surface of the SOI wafer 10 is modified, and dust generation occurs. Further problems will arise. However, even in the region where the SOI layer is formed, if the layer thickness of the SOI layer is not constant, the focal depth of the laser beam similarly changes, and the modified layer can be appropriately formed. Can not.

  Furthermore, in the manufacturing process of the bonded SOI wafer described above, an inclined surface whose outer peripheral side surface is inclined at an acute angle with respect to the upper surface of the support substrate in the process of mechanical grinding and alkali etching of the outer periphery of the silicon wafer 10b to be the SOI layer. End up. Then, the outer peripheral side surface that has become the inclined surface in this way has irregularities formed by alkali etching due to the surface orientation dependency of etching (see FIG. 8C). Therefore, when laser light is irradiated onto such an inclined or uneven surface, irregular reflection occurs, and as a result, the laser beam is not sufficiently focused on the focal position, so that sufficient modification cannot be performed. .

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a laser dicing method capable of suitably suppressing defective formation of a modified layer in performing laser dicing of a bonded SOI wafer. There is to do.

In order to achieve the above object, in the invention described in claim 1, a silicon wafer is bonded to the upper surface of the support substrate via an insulating film, and the bonded silicon wafer is thinned to form an SOI layer. As a method of laser dicing a bonded SOI wafer, the outer peripheral edge of the SOI layer at the boundary between the terrace region, which is a region without an SOI layer formed on the outer peripheral portion of the bonded SOI wafer, and the SOI layer is supported. An etching process for etching the outer peripheral edge of the SOI layer with the direction perpendicular to the upper surface of the SOI layer as an etching direction so as to be perpendicular to the upper surface of the substrate; A laser beam irradiation step of irradiating the inside of the support substrate along the planned cutting line of the bonded SOI wafer to form a modified layer; A cleaving step of cleaving the bonded SOI wafer into a plurality of chips along the planned cleaving line in which a layer is formed, and in the laser light irradiation in the laser light irradiation step, In the terrace region outside the outer periphery with the periphery as a boundary, the distance between the condensing optical element and the upper surface of the support substrate is reduced more than the region where the SOI layer is formed inside the terrace region. The distance correction amount H is such that when the refractive index of the SOI layer is “n” and the thickness of the SOI layer is “T”,
H = (1-1 / n) × T
The correction was made so that

  As described above, in the bonded SOI wafer, the outer peripheral edge of the SOI layer is uneven and has an inclined surface inclined at an acute angle with the upper surface of the support substrate in the manufacturing process. For this reason, the layer thickness of the SOI layer changes irregularly in the boundary region between the formation region of the SOI layer and the terrace region without the SOI layer. Is difficult to grasp.

In this respect, the laser dicing method according to claim 1, as prior to laser beam irradiation, the outer peripheral side surface of the SOI layer became such inclined uneven surface is perpendicular to the upper surface of the supporting substrate, outside of the SOI layer The peripheral edge is etched with the direction perpendicular to the upper surface of the SOI layer as an etching direction, whereby the outer peripheral side surface of the SOI layer is processed substantially perpendicularly to the upper surface of the support substrate. In such a bonded SOI wafer after processing, the boundary between the formation region of the SOI layer and the terrace region becomes clear, and the deviation degree of the laser beam focal position in these boundary regions can be easily and accurately obtained. Therefore, it becomes possible to easily and accurately correct the laser beam focal position shift at the boundary, and to form a modified layer inside the support substrate, and at the boundary region between the SOI layer forming region and the terrace region. The defective formation of the modified layer due to the change in the laser beam focal depth can be suitably suppressed. By the way, even if the outer peripheral side surface of the SOI layer is not completely perpendicular to the upper surface of the support substrate, it is possible to obtain such an effect if it is processed substantially perpendicularly, for example, at an angle of 90 ± 10 °. Can do.

Further , in the bonded SOI wafer in which the outer peripheral side surface of the SOI layer is processed substantially vertically as described above, the distance of the converging optical element from the upper surface of the support substrate is corrected by the correction amount H obtained by the following equation. By doing so, it is possible to eliminate the deviation of the laser beam irradiation position at the boundary between the formation region of the SOI layer and the terrace region. In the following formula, “n” indicates the refractive index of the SOI layer, and “T” indicates the layer thickness.

H = (1-1 / n) × T

Further , according to the invention described in claim 2 , in the invention described in claim 1, prior to the laser light irradiation step, as the information regarding the shape of the bonded SOI wafer, the diameter of the bonded SOI wafer, the terrace region , The chip size, the thickness of the SOI layer, the thickness of the insulating film, the width of the orientation flat, and the thickness of the support substrate are input to a control unit that performs laser light irradiation control. In the laser light irradiation step, A step of determining an XYZ orthogonal coordinate system based on the input information relating to the shape of the bonded SOI wafer and calculating coordinates of the planned cutting line in the XY plane through the control unit; Performing a step of irradiating the laser beam along the planned cutting line and a step of irradiating the laser beam along the planned cutting line in the X-axis direction; In the step of irradiating the laser light along the planned cutting line and the step of irradiating the laser light along the planned cutting line in the X-axis direction, when the condensing point of the laser light is determined to be in the terrace region The distance between the condensing optical element and the upper surface of the support substrate may be corrected using the correction amount H.

An embodiment of a laser dicing method according to the present invention will be described below with reference to FIGS.
In this embodiment, as will be described in detail below, the laser beam condensed by the condenser lens is bonded along the planned cutting line of the SOI wafer to form a modified layer inside the support substrate. Prior to the laser beam irradiation process, an etching process (processing process) is performed in which the outer peripheral edge of the SOI layer is etched in advance with the direction perpendicular to the upper surface of the SOI layer as the etching direction. Then, in the terrace region that is the region outside the outer peripheral edge with the outer peripheral edge of the SOI layer as a boundary, the distance between the condenser lens and the upper surface of the support substrate is reduced more than the SOI region that is the inner region. By correcting the same distance, the formation failure of the modified layer is suppressed.

  FIG. 1 shows the overall configuration of a laser dicing apparatus used for carrying out the laser dicing method according to this embodiment. First, the configuration of the laser dicing apparatus used here will be described with reference to FIG.

As shown in FIG. 1, the laser dicing apparatus to which this embodiment is applied is largely
A silicon wafer is bonded to the upper surface of the support substrate via a buried oxide film (insulating film), and the bonded silicon wafer is thinned to form an SOI layer. A mounting table 21 for mounting the target bonded SOI wafer 10 on the upper surface thereof.
The X-axis stage 20a for changing the position of the mounting table 21 in the X-axis direction, the Y-axis stage 20b for changing the position of the mounting table 21 in the Y-axis direction, and the position of the mounting table 21 in the Z-axis direction are variable. A stage 20 configured to include a Z-axis stage 20c.
A laser light source 40 that irradiates a support substrate constituting the bonded SOI wafer 10 mounted on the mounting table 21 through a condensing lens (condensing optical element) 30.
A control unit 50 that takes in information regarding the shape of the bonded SOI wafer 10 from the input unit 60 and performs position control of the axis stages 20 a to 20 c of the stage 20, laser light irradiation control by the laser light source 40, and the like.
And so on.

  Here, the positions of the axis stages 20a to 20c on the axes are made variable with high accuracy through, for example, a stepping motor (not shown) that receives a command from the control unit 50. Then, the position of the X-axis stage 20 a and the Y-axis stage 20 b is controlled through the control unit 50 so that the laser beam is irradiated along the planned cutting line of the bonded SOI wafer 10. Note that the variable speed of the position by the X-axis stage 20a and the Y-axis stage 20b is approximately 30 cm per second. The Z-axis direction is a direction perpendicular to the surface of the bonded SOI wafer 10, and the distance between the condenser lens 30 and the bonded SOI wafer 10 is described in detail by controlling the position of the Z-axis stage 20 c through the control unit 50. The distance between the condenser lens 30 and the upper surface of the support substrate constituting the bonded SOI wafer 10 is variable.

  Incidentally, as the laser light source 40, for example, a YAG laser is employed, and this wavelength is 1064 nm. The laser light source 40 can emit a laser beam having a frequency of about 80 KHz in response to a command from the control unit 50. The laser beam thus irradiated follows the optical path L and is collected by the condenser lens 30 as shown in FIG.

  In addition, information regarding the shape of the bonded SOI wafer 10 necessary for dicing the bonded SOI wafer 10 with laser light is input to the control unit 50 via the input unit 60. The control unit 50 calculates the coordinates of the planned cutting line of the bonded SOI wafer 10, calculates the coordinates of the starting base point, and the distance between the condensing lens 30 and the bonded SOI wafer 10 based on the input information on the shape. In addition to calculating the correction amount, the position control of each of the axis stages 20a to 20c, the laser light irradiation control by the laser light source 40, and the like are performed. The information on the shape of the bonded SOI wafer 10 includes, for example, the diameter of the bonded SOI wafer 10, the width of the terrace region, the chip size, the layer thickness of the SOI layer, the thickness of the buried oxide film, and the orientation flat information. There are width, thickness of the support substrate, and the like.

  FIG. 2 shows a side cross-sectional structure after performing an etching process performed prior to the laser beam irradiation process on the bonded SOI wafer 10 to be diced in this embodiment. Next, the etching process will be described with reference to FIG.

  As described above, in the bonded SOI wafer 10, the outer peripheral side surface of the SOI layer has an acute angle with the upper surface of the support substrate in the process of mechanical grinding and alkali etching of the outer periphery of the silicon wafer to be the SOI layer in the manufacturing process. It tends to be an inclined surface inclined at. In addition, as described above, the outer peripheral side surface that has become an inclined surface has irregularities formed by alkali etching due to the surface orientation dependency of etching. When laser light is irradiated from the laser light source 40 onto such an inclined or uneven surface, the laser light is diffusely reflected, and the light is not sufficiently focused on the desired focal position. Quality can not be done. In addition, in the boundary region between the SOI region and the terrace region, the layer thickness of the SOI layer changes irregularly, and it is difficult to easily grasp the shift amount of the laser beam focal position corresponding to the layer thickness.

  Therefore, as shown in FIG. 2 as a partially enlarged cross-sectional view corresponding to FIG. 8C, the outer peripheral edge of the SOI layer 10d is placed on the upper surface of the SOI layer 10d prior to the laser light irradiation step. By performing, for example, dry etching with the perpendicular direction as the etching direction, the outer peripheral side surface of the SOI layer 10d is processed so as to be substantially perpendicular to the upper surface of the support substrate 10a.

  The bonded SOI wafer 10 processed in this manner has a clear boundary B between the SOI region and the terrace region on the upper surface thereof, and a laser beam focal position in these boundary regions in the laser beam irradiation step described below. The degree of deviation can be easily and accurately obtained. Further, since the irregular reflection of the laser light is reduced, the laser light output from the laser light source can be efficiently contributed in forming the modified layer inside the support substrate.

  FIG. 3 exemplifies a planar structure and a planned cutting line of a bonded SOI wafer to be diced through the dicing method according to this embodiment. Next, with reference to this FIG. 3, the process concerning calculation of a cutting planned line is demonstrated.

  Information regarding the shape of the bonded SOI wafer 10 input to the control unit 50 (FIG. 1) includes, for example, the diameter of the bonded SOI wafer 10, the width of the terrace region, and the width of the orientation flat formed on the bonded SOI wafer 10. As described above, the chip size, the SOI layer thickness, the buried oxide film thickness, the support substrate thickness, and the like. When the bonded SOI wafer 10 is mounted at a predetermined position on the mounting table 21 (FIG. 1), the control unit 50 determines the parallel X axis in contact with the orientation flat as shown in FIG. Then, a Y-axis that is in contact with the left end of the bonded SOI wafer 10 and is orthogonal to the X-axis is determined. Then, an XY plane is determined with the intersection of the X axis and the Y axis as an origin O, and a direction perpendicular to the XY plane from the origin O is defined as a Z axis. Thus, the XYZ orthogonal coordinate system is set.

  Next, the control unit 50 calculates the coordinates of the planned cutting line for the set orthogonal coordinate system on the basis of the previous origin O based on the input chip size information. Further, the control unit 50 calculates the coordinates of the planned cutting line in the terrace area based on the input information on the width of the terrace area with respect to the orthogonal coordinate system set in the same manner. As shown in FIG. 3, the planned cutting line calculated in this way has a lattice shape parallel to the X axis or the Y axis. Note that the planned cutting line in the terrace area is a part that requires position correction of the condenser lens 30 (FIG. 1) described below. In FIG. 3, the planned cutting line corresponding to this part is indicated by a bold line. Show. Further, as described above, since the etching process is performed prior to the laser light irradiation process, the boundary B between the SOI region and the terrace region on the surface of the bonded SOI wafer 10 is clear. Therefore, the control unit 50 can easily and accurately distinguish the coordinates of the planned cutting line in the SOI region of the bonded SOI wafer 10 and the coordinates of the planned cutting line in the terrace region.

  Next, with respect to the set orthogonal coordinate system, the control unit 50 sets the start base point S0 for starting laser light irradiation based on the layer thickness of the SOI layer, the thickness of the buried oxide film, and the thickness of the support substrate. (X, Y, Z) coordinates are calculated. At this time, as shown in FIG. 3, the (X, Y) coordinates of the starting base point S0 are set, for example, at a location where the outer edge of the bonded SOI wafer 10 and the lattice point of the planned cutting line coincide or in the terrace area. The Z coordinate of the start base point S0 is set at the lowermost part of the region where the modified layer is to be formed, for example, inside the support substrate constituting the bonded SOI wafer 10.

  In this way, the control unit 50 determines the condensing point of the laser light through the condensing lens 30 through the position control of each of the axis stages 20a to 20c (X, Y, Z of the start base points S0, S1, S2,. ) Coordinates are set, (X, Z) coordinates are fixed, and laser beam irradiation is performed along the planned cutting line in the Y-axis direction to form a modified layer inside the bonded SOI wafer 10. However, the condensing point of the laser beam moves up and down in the Z-axis direction due to the difference in refractive index between the silicon single crystal constituting the SOI layer 10d and air. For this reason, when the laser beam irradiation proceeds along the planned cutting line and the condensing point of the laser beam reaches the boundary B between the SOI region and the terrace region of the bonded SOI wafer 10, the condensing of the lens 30 is performed. In order to make the Z coordinate of the point unchanged, a laser beam focal position shift of the condenser lens 30 described below is corrected. That is, the position control of the Z-axis stage 20c is also performed.

  In addition, when the laser beam condensing point reaches the outer edge of the bonded SOI wafer 10, the control unit 50 controls the X-axis stage 20a and the Y-axis stage 20b to control the laser beam condensing point, for example, as a starting base point. Shift to S1. Then, the laser beam irradiation is performed in the same manner along the planned cutting line in the Y-axis direction derived from the starting base point S1. Such a series of laser light irradiations is performed along all the planned cutting lines in the Y-axis direction derived from the starting base points S0, S1, S2,. After that, the control unit 50 sets the condensing point of the laser light to the start base point S0 again, and, similarly to the case of the Y axis direction, all of the X axis direction derived from the start base points S0, S1, S2,. Laser light irradiation is performed along the planned cutting line. Thus, after irradiating all the planned cutting lines in the Y-axis direction and the planned cutting lines in the X-axis direction set on the bonded SOI wafer 10, the Z-axis direction is controlled through the position control of the Z-axis stage 20c. The condensing point of the laser beam is moved upward. Similarly, the laser beam irradiation in the Y-axis direction and the laser beam irradiation in the X-axis direction are repeated.

FIG. 4 shows a laser beam irradiation mode and a laser beam condensing point correction mode from the side surface direction along the planned cutting line in the Y-axis direction in the laser beam irradiation step.
As shown in FIG. 4, the laser light emitted from the laser light source 40 (not shown) passes through the condenser lens 30, and then follows the optical path L1 to be condensed inside the support substrate 10a. At this condensing point, optical damage due to multiphoton absorption occurs, which induces thermal strain and forms cracks. That is, the fragile modified layer CL1 is formed at the focal depth Ds. Then, in order to grow the modified layer CL1, the condenser lens 30 is moved along the orbit Or1 that maintains the distance ds from the upper surface of the SOI layer 10d. In practice, this movement is also performed through position control of each of the axis stages 20a to 20c (FIG. 1). Here, for convenience, the condenser lens 30 is assumed to move.

  As described above, the bonded SOI wafer 10 has a terrace region without the SOI layer 10d on the outer peripheral portion thereof. When the condensing lens 30 that has moved along the orbit Or1 moves along the orbit Al12 at an altitude as it is, as shown in FIG. 4, the refractive index of the silicon single crystal constituting the SOI layer 10d and the air is reduced. Due to the difference, the condensing point of the laser beam is shifted upward by ΔZ, and the laser beam is condensed shallowly at the focal depth Dt. Therefore, immediately under the terrace region, a modified layer is formed on the upper surface side of the bonded SOI wafer 10 rather than the region where the SOI layer 10 d is formed, and the modified layer is sufficiently modified to the back surface side of the bonded SOI wafer 10. There is a concern that a quality layer cannot be formed.

  Therefore, in this embodiment, as shown in FIG. 4, when the condenser lens 30 moved along the orbit Or1 reaches the boundary B between the SOI region and the terrace region, the condenser lens 30 and the support substrate The distance from the upper surface of 10a is reduced by the correction amount H, and the condenser lens 30 is moved along the trajectory Or11 that maintains the distance dt from the upper surface of the support substrate 10a. As a result, the modified layer CL1 formed inside the support substrate 10a can be properly grown, and the modified layer CL1 caused by the change in the focal depth of the laser beam in the boundary region between the SOI region and the terrace region can be obtained. Formation defects can be suppressed. The correction amount H will be described in detail below.

  When the condensing lens 30 reaches the outer edge of the SOI wafer 10 along the trajectory Or1 and the trajectory Or11, the condensing point of the laser beam, that is, the condensing lens 30 is shifted upward in the Z-axis direction, and similarly the laser Repeat the light irradiation. As shown in FIG. 4, the condensing lens 30 moves along the orbit Or2 and the orbit Or21, so that the laser light is collected along the optical path L2, and the modified layer CL2 is supported by the support substrate 10a. It will be formed inside.

  FIG. 5 shows the principle of deriving the correction amount of the condenser lens distance performed in the laser beam irradiation step. Next, the correction amount H of the distance between the condenser lens 30 and the upper surface of the support substrate 10a will be described in detail with reference to FIG.

  As shown in FIG. 5, the laser light irradiated in the air from the laser light source 40 (not shown) passes through the condenser lens 30 (not shown), then travels straight along the optical path L, and passes through the air. Refraction occurs at the interface between the silicon wafer and the silicon wafer. The refracted laser light follows the optical path Ls and is condensed at the condensing point Cs. On the other hand, when the laser light irradiated in the air goes straight as it is, that is, when it is assumed that the silicon wafer does not exist and goes straight in the air, the laser light is collected along the optical path La. Condensed to the light spot Ca.

  Here, the distance from the interface between the air and the silicon wafer to the condensing point Ca is x, the distance to the condensing point Cs is y, the angle between the normal of the silicon wafer surface and the optical path La is θa, and the silicon wafer Assuming that the angle between the normal of the upper surface and the optical path Ls is θs, the following equation (1) is derived from these geometrical relationships by a trigonometric function.

そして、これらｘとｙとの関係は、上式（１）および三角関数の定義から下式（２）で表される。

The relationship between x and y is expressed by the following equation (2) from the above equation (1) and the definition of the trigonometric function.

ここで、空気の屈折率を「１．０」、シリコンウェハの屈折率を「ｎ（≒３．５）」とすると、スネルの法則により下式（３）が得られる。

Here, when the refractive index of air is “1.0” and the refractive index of the silicon wafer is “n (≈3.5)”, the following expression (3) is obtained by Snell's law.

したがって、上式（２）に上式（３）を代入することで下式（４）が導出される。

Therefore, the following expression (4) is derived by substituting the above expression (3) into the above expression (2).

さらにθａおよびθｓが微小（ほぼ零）であると仮定すると、すなわち、「ｃｏｓθａ＝１」、および「ｃｏｓθｓ＝１」であると仮定すると、上式（４）をもとに、下式（５）が導出される。

Further, assuming that θa and θs are very small (substantially zero), that is, assuming that “cos θa = 1” and “cos θs = 1”, the following expression (5 ) Is derived.

したがって、空気とシリコンウェハとの界面でレーザ光が屈折する場合の集光点Ｃｓまでの距離ｙは、レーザ光が空気中を直進した場合の集光点Ｃａまでの距離ｘに対し、シリコンウェハの屈折率だけ乗算された大きさ（およそ３．５倍の大きさ）となる。換言すれば、レーザ光が空気中からシリコンウェハへ進行して集光した場合、集光レンズの焦点距離は、透過したシリコンウェハの厚さをその屈折率倍した距離だけ長くなることを意味する。

Therefore, the distance y to the condensing point Cs when the laser light is refracted at the interface between the air and the silicon wafer is equal to the distance x to the condensing point Ca when the laser light travels straight through the air. Is a size multiplied by the refractive index of (approximately 3.5 times larger). In other words, when the laser light travels from the air to the silicon wafer and is condensed, the focal length of the condenser lens is increased by a distance obtained by multiplying the thickness of the transmitted silicon wafer by its refractive index. .

Based on the above, the correction amount H of the condenser lens 30 is derived.
In FIG. 4, when the distance from the upper surface of the SOI layer 10d when the condenser lens 30 is in the SOI region is ds, and when the condenser lens 30 is in the terrace region and the position of the condenser lens 30 is corrected. When the distance from the upper surface of the support substrate 10a is dt, the relationship between the distance ds, the distance dt, the correction amount H, and the layer thickness T of the SOI layer 10d is expressed by the following equation (6).

また、集光レンズ３０がＳＯＩ領域にある場合であれ、あるいはテラス領域にある場合であれ、その焦点距離は不変であるため、上記焦点深さＤｓおよびＤｔを用いて空気中での焦点距離にそれぞれ換算して、その幾何学的な関係を求めると、下式（７）が導出される。

Further, whether the condenser lens 30 is in the SOI region or the terrace region, the focal length is invariable, so that the focal length in the air is calculated using the focal depths Ds and Dt. When each is converted and the geometrical relationship is obtained, the following equation (7) is derived.

これら上式（６）および（７）から、上記補正量Ｈは、ＳＯＩ層１０ｄの層厚Ｔを用いて下式（８）にて表される。

From the above equations (6) and (7), the correction amount H is expressed by the following equation (8) using the layer thickness T of the SOI layer 10d.

すなわち、補正量Ｈは、ＳＯＩ層１０ｄの層厚Ｔに対し、その透過する媒体の屈折率の違いを考慮した分を減算した量となる。

That is, the correction amount H is an amount obtained by subtracting the amount considering the difference in the refractive index of the transmitting medium from the thickness T of the SOI layer 10d.

  After all, by correcting this correction amount H, it becomes possible to properly grow the modified layer CL1 formed inside the support substrate 10a, and the laser in the boundary region between the SOI region and the terrace region as described above. It is possible to suppress the formation failure of the modified layer due to the change in the optical focal depth.

  FIG. 6 shows a processing procedure of a bonded wafer dicing process applied to this embodiment, and FIG. 7 shows a processing procedure of a laser beam irradiation process performed during the dicing process. Is. Next, the laser dicing method of this embodiment will be summarized with reference to FIGS.

  In the dicing process of this embodiment, first, for example, dry etching is performed on the outer peripheral edge of the bonded SOI wafer 10 to be diced, with the direction perpendicular to the upper surface of the SOI layer 10d as the etching direction. Thus, the processing is performed so that the outer peripheral side surface of the SOI layer 10d is substantially perpendicular to the upper surface of the support substrate 10a. Then, as shown in FIG. 6, as processing of step S <b> 100, information regarding the shape of the bonded SOI wafer 10 is input to the control unit 50 via the input unit 60. Here, as information regarding the shape of the bonded SOI wafer input to the control unit 50, the diameter of the bonded SOI wafer “5 inch”, the width of the terrace region “5 mm”, the chip size “several mm”, the layer of the SOI layer The thickness is “20 μm”, the thickness of the buried oxide film is “2 μm”, the width of the orientation flat is “several cm”, and the thickness of the support substrate is “600 μm”.

  A laser beam irradiation step is performed as the subsequent step S200. At the start of the laser beam irradiation process, as shown in FIG. 7, first, as the process of step S201, the shape information of the bonded SOI wafer 10 input to the control unit 50 in the previous step S100 is used. Based on this, a coordinate axis (XYZ), that is, an orthogonal coordinate system is determined. In step S202, the coordinates (XY plane) of the planned cutting line in the Y-axis direction and the planned cutting line in the X-axis direction are calculated based on the outer shape of the bonded SOI wafer 10 and the orientation flat. And as a process of subsequent step S203, a modified layer is formed in the inside of the support substrate 10a which comprises the bonding SOI wafer 10 by irradiating a laser beam along the cutting planned line of the Y-axis direction. Note that it is determined whether or not the condensing point of the laser beam is in the terrace area through the process of step S204, and when it is determined that it is in the terrace area, that is, when “Yes” in the process of step S204. In the subsequent step S205, the distance between the condenser lens 30 and the upper surface of the support substrate 10a is corrected, and the laser light irradiation is continued. The derivation of the correction amount H at this time is as described above. On the other hand, if it is determined in the process of the previous step S204 that the laser beam condensing point is not in the terrace area but in the SOI area, that is, if “No” in the process of step S204, the light is condensed. Since it is not necessary to correct the distance between the lens 30 and the upper surface of the support substrate 10a, the laser beam irradiation is continued while maintaining the altitude as it is, and the process proceeds to the subsequent step S206. Then, through the determination process in step S206, the processes in steps S203 to S205 are repeatedly performed until the laser beam irradiation is all performed along the planned cutting line in the Y-axis direction.

  On the other hand, as a process of subsequent step S207, the modified layer is formed inside the support substrate 10a constituting the bonded SOI wafer 10 by irradiating laser light along the planned cutting line in the X-axis direction. In this case as well, it is determined whether or not the condensing point of the laser beam is in the terrace area through the process of step S208. If it is determined that the laser beam is in the terrace area, that is, “Yes” in the process of step S208. If there is, in the subsequent step S209, the distance between the condenser lens 30 and the upper surface of the support substrate 10a is corrected, and the laser light irradiation is continued. On the other hand, if it is determined in the process of the previous step S208 that the laser beam condensing point is not in the terrace area but in the SOI area, that is, if “No” in the process of step S208, the light is condensed. Since it is not necessary to correct the distance between the lens 30 and the upper surface of the support substrate 10a, the laser beam irradiation is continued while maintaining the altitude as it is, and the process proceeds to the subsequent step S209. Then, through the determination process in step S210, the processes in steps S207 to S209 are repeatedly performed until the laser beam irradiation along the planned cutting line in the X-axis direction is performed.

  When all the laser beam irradiation to the XY plane is completed in this way, as a process of subsequent step S211, a predetermined amount of the laser beam condensing point is set in the upper surface direction (Z-axis direction) of the bonded SOI wafer 10. For example, it is moved upward by several tens of μm. Then, through the subsequent determination process in step S212, the laser light condensing point reaches the uppermost portion of the modified layer forming region in the support substrate 10a, that is, the modified layer in the support substrate 10a has a sufficient thickness. Thus, the processes from step S203 to step S211 are repeatedly performed until the bonded SOI wafer 10 is easily cleaved.

  When the modified layer is sufficiently formed in this way, as shown in FIG. 6, the process proceeds to the cleaving process of the bonded SOI wafer 10 as the process of step S300. In this cleaving step, for example, a resin sheet that has been in close contact with the back surface of the bonded SOI wafer 10 is stretched, and the modified layer formed as described above along the planned cutting line is used as a starting point. The combined SOI wafer 10 is cleaved for each chip. Note that the modified layer formed at this time is not exposed on the upper surface of the support substrate 10a and remains in the inside thereof. Therefore, no dust is generated when cleaving for each chip.

As described above, according to the laser dicing method of this embodiment, the following excellent effects can be obtained.
(1) Prior to the laser beam irradiation step, the outer peripheral edge of the SOI layer 10d is dry-etched with the direction perpendicular to the upper surface of the SOI layer 10d as the etching direction, so that the outer peripheral side surface of the SOI layer 10d becomes the support substrate 10a. It was decided to process it so that it was almost perpendicular to the upper surface of. As a result, the boundary B between the SOI region and the terrace region on the upper surface of the bonded SOI wafer 10 is clarified, and the degree of deviation of the laser beam focal position in these boundary regions can be easily and accurately determined in the subsequent laser beam irradiation step. Will be able to ask. Further, since the irregular reflection of the laser light is reduced, the laser light output from the laser light source can be efficiently contributed in forming the modified layer inside the support substrate.

(2) When laser light is irradiated in the laser light irradiation step, the distance between the condensing lens 30 and the upper surface of the support substrate 10a in the terrace area of the bonded SOI wafer 10 is expressed by the above equation (8) as compared with the SOI area. The correction was made so as to be shortened by the correction amount H determined in this way. Thereby, the shift of the laser beam irradiation position at the boundary B between the SOI region and the terrace region can be eliminated, and as a result, formation failure of the modified layer can be suitably suppressed.
(Other embodiments)
The laser dicing method according to the present invention is not limited to the method exemplified in the above embodiment, and can be implemented as, for example, the following form obtained by appropriately changing the embodiment.
In the laser beam irradiation process of the above embodiment, laser beam irradiation is performed from the lowermost part of the modified layer forming region inside the support substrate 10a along the planned cutting line on the XY plane until reaching the uppermost part. Although this was repeated, the laser beam irradiation mode is not limited to this. Laser irradiation may be performed along the planned cutting line on the XY plane from the uppermost part of the modified layer forming region inside the support substrate 10a, and this may be repeated until the lowermost part is reached. Alternatively, after the modified layer is grown in a direction perpendicular to the surface of the support substrate 10a (Z-axis direction), the modified layer may be grown in a parallel direction (XY plane). In short, the laser light irradiation mode is arbitrary as long as the modified layer can be accurately formed over the entire modified layer formation scheduled region inside the support substrate 10a.
In the laser beam irradiation process of the above embodiment, when the laser beam is irradiated on the terrace region of the bonded SOI wafer 10, the distance between the condenser lens 30 and the upper surface of the support substrate 10a is the laser beam irradiation on the SOI region. Instead, the correction is made so as to be shortened by the correction amount H obtained by the above equation (8), but is not limited to this. In short, if the correction is made so that the distance between the condensing lens 30 and the upper surface of the support substrate 10a is reduced in the terrace region of the bonded SOI wafer 10 than in the SOI region, the effect (2) described above can be achieved. A similar effect can be obtained.
In the above embodiment, prior to the laser light irradiation step, the outer peripheral edge of the SOI layer 10d is dry-etched with the direction perpendicular to the upper surface of the SOI layer 10d as the etching direction. However, it is not limited to dry etching. The processing method is arbitrary as long as the outer peripheral edge of the SOI layer 10d can be processed to be perpendicular to the upper surface of the support substrate 10a. Further, the outer peripheral edge of the SOI layer 10d subjected to such processing does not have to be completely perpendicular to the upper surface of the support substrate 10a. If it is processed substantially vertically, for example, at an angle of 90 ± 10 °, the effect according to the effect (1) can be obtained.
Further, in addition to correction when processing the outer peripheral edge of the SOI layer 10d, or separately, when irradiating laser light in the laser light irradiation step, the distance between the condenser lens 30 and the upper surface of the support substrate 10a is In accordance with the layer thickness of the SOI layer 10d serving as the irradiation position, the correction may be desirably performed in such a manner that the smaller the layer thickness of the SOI layer 10d serving as the irradiation position, the smaller.

1 is a block diagram showing an overall configuration of a laser dicing apparatus used for carrying out an embodiment of a laser dicing method according to the present invention. Sectional drawing which shows the side surface cross-section of the bonding SOI wafer made into the process target in the same embodiment. The top view which shows the cleaving line of the bonding SOI wafer made into the process target of the embodiment. Sectional drawing which shows the irradiation aspect of the laser beam in the embodiment. The figure which shows the derivation | leading-out principle of the correction amount of the condensing lens distance performed in the embodiment. The flowchart which shows the process sequence of the dicing process of the bonded wafer applied to the embodiment. The flowchart which shows the process sequence of the laser beam irradiation process implemented during the said dicing process. (A)-(c) is sectional drawing which shows the manufacturing process of a bonding SOI wafer. (A) of a bonded SOI wafer is a plan view, and (b) is a partial cross-sectional view. Sectional drawing which shows the irradiation aspect of the laser beam in the conventional laser dicing method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Bonded SOI wafer, 10a ... Support substrate, 10b ... Silicon wafer, 10c ... Embedded oxide film (insulating film), 10d ... SOI layer, 20 ... Stage, 20a ... X-axis stage, 20b ... Y-axis stage, 20c DESCRIPTION OF SYMBOLS ... Z-axis stage, 21 ... Mounting stand, 30 ... Condensing lens (condensing optical element), 40 ... Laser light source, 50 ... Control part, 60 ... Input part.

Claims (2)

A method of laser dicing a bonded SOI wafer in which a silicon wafer is bonded to an upper surface of a support substrate via an insulating film, and the bonded silicon wafer is thinned to form an SOI layer.
As the outer peripheral side surface of the SOI layer in the boundary portion of the bonded terrace area which is an area having no SOI layer formed on the outer peripheral portion of the SOI wafer and the SOI layer becomes perpendicular to the upper surface of the supporting substrate, An etching process for etching the outer peripheral edge of the SOI layer with the direction perpendicular to the upper surface of the SOI layer as an etching direction, and a laser beam condensed by a condensing optical element is scheduled to cleave the bonded SOI wafer A laser beam irradiation step of irradiating the inside of the support substrate along a line to form a modified layer, and the bonded SOI wafer along a planned cutting line on which the modified layer is formed into a plurality of chips A cleaving process for cleaving,
In the laser light irradiation in the laser light irradiation step, the light condensing is performed in the terrace region outside the outer peripheral edge with the outer peripheral edge of the SOI layer as a boundary, compared with the inner region where the SOI layer is formed. The distance correction amount H is such that the refractive index of the SOI layer is “n” and the layer thickness of the SOI layer is “T” so that the distance between the optical element for use and the upper surface of the support substrate is reduced. And when
H = (1-1 / n) × T
Laser Dicing method and correcting so that.   Prior to the laser light irradiation step, information on the shape of the bonded SOI wafer includes the diameter of the bonded SOI wafer, the width of the terrace region, the chip size, the thickness of the SOI layer, the thickness of the insulating film, and the width of the orientation flat. , And the thickness of the support substrate is input to the control unit that performs laser light irradiation control,
  In the laser light irradiation step, through the control unit,
  A step of determining an XYZ orthogonal coordinate system based on the input information on the shape of the bonded SOI wafer and calculating the coordinates of the planned cutting line in the XY plane;
  Irradiating a laser beam along the planned cutting line in the Y-axis direction;
  Irradiating laser light along the planned cutting line in the X-axis direction;
Run
  In the step of irradiating the laser light along the planned cutting line in the Y-axis direction and the step of irradiating the laser light along the planned cutting line in the X-axis direction, a condensing point of the laser light is applied to the terrace region. 2. The laser dicing method according to claim 1, wherein when it is determined that there is, the distance between the condensing optical element and the upper surface of the support substrate is corrected using the correction amount H. 3.

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