Substrate processing method and substrate processing system

Abstract

This substrate processing method for processing a substrate includes forming a reformed layer and a crack by irradiating a substrate with a laser beam, and involves: acquiring data relating to a cumulative number of substrates processed, an amount of contamination of a cover glass protecting a condensing lens for laser beam irradiation, a flow rate of a gas supplied along the lower surface of the cover glass, and a length of the crack that extends as a result of the laser beam irradiation; and controlling the laser beam irradiation on the basis of the acquired data.

Description

Substrate processing method and substrate processing system

[0001] The present disclosure relates to a substrate processing method and a substrate processing system.

[0002] Patent Document 1 discloses a processing device that performs laser processing on a workpiece using a laser irradiation means, which includes a condenser that condenses a laser beam, and the condenser includes an objective lens and a lens protection cover that blocks debris scattered from the workpiece to prevent contamination of the objective lens. In the processing device described in Patent Document 1, dirt on the lens protection cover is detected by an imaging means.

[0003] JP 2012-179642 A

[0004] The technology disclosed herein provides a substrate processing method that can appropriately manage and estimate processing quality in substrate processing in which a modified layer is formed on a substrate by laser processing and a crack propagates from the modified layer.

[0005] One aspect of the present disclosure is a substrate processing method for processing a substrate, which includes irradiating the substrate with laser light to form a modified layer and a crack extending from the modified layer in the thickness direction of the substrate, and acquires data related to the cumulative number of substrates processed, the amount of dirt on a cover glass protecting a focusing lens that irradiates the laser light, the amount of gas supplied along the underside of the cover glass, and the length of the crack that extends due to the irradiation of the laser light, and controls the irradiation of the laser light based on the acquired data.

[0006] A substrate processing method can be provided that can appropriately manage and estimate processing quality in substrate processing in which a modified layer is formed on a substrate by laser processing and a crack propagates from the modified layer.

[0007] 1 is a side view showing an example of a laminated wafer processed in a wafer processing system; FIG. 2 is a plan view showing an outline of an example configuration of a wafer processing system according to an embodiment; FIG. 3 is a plan view showing an example configuration of an internal reforming device; FIG. 4 is a side view showing an example configuration of an internal reforming device; FIG. 5 is a cross-sectional view showing details of the configuration of a laser irradiation unit; FIG. 6 is an explanatory diagram showing a series of wafer processing in a wafer processing system; FIG. 7 is a flow chart showing main steps of detecting contamination on a cover glass; FIG. 8 is a schematic diagram showing an example of an imaging result by a lens imaging mechanism; FIG. 9 is a schematic diagram showing an example of a captured image with adjusted brightness and contrast; FIG. 10 is a diagram showing an example of a histogram of brightness of a captured image; FIG. 11 is a schematic diagram showing an example result of binarizing a captured image; FIG. 12 is a histogram showing an example result of detecting contamination on a cover glass; FIG. 13 is a graph showing the relationship between estimated and actual BHC values; FIG. 14 is a graph showing the relationship between BHC and the amount of contamination on the cover glass.

[0008] In the manufacturing process of semiconductor devices, a first wafer, which is a semiconductor substrate (hereinafter referred to as a "wafer") having a plurality of devices such as electronic circuits formed on its surface, is bonded to a second wafer to form an overlapping wafer. In this case, the peripheral portion of the first wafer may be removed, i.e., edge trimming may be performed.

[0009] In the edge trimming of the first wafer, for example, a modified layer is formed by irradiating the inside of the first wafer with laser light from a laser irradiation unit, a crack is propagated in the thickness direction of the first wafer, and the peripheral portion of the first wafer is removed from the modified layer and the crack as a base point. The laser light for forming the modified layer is irradiated from a laser head to the first wafer through a lens.

[0010] When forming a modified layer on the first wafer, particles are generated by laser processing of the first wafer. If the generated particles adhere to the lens, the processing quality will deteriorate. Therefore, as disclosed in Patent Document 1, a cover glass (lens protective cover) is provided on the lens (objective lens) in the laser irradiation unit to suppress adhesion of particles (debris) to the lens, and air is supplied along the underside of the cover glass to suppress adhesion of particles to the cover glass.

[0011] Here, the inventors conducted extensive research and found a correlation between the amount of contamination due to particle adhesion to the lens, the number of processed overlapping wafers (first wafers), the air flow rate supplied to the underside of the cover glass, and BHC. Note that "BHC" refers to the length of the crack C1 extending from the peripheral modified layer M1 formed closest to the surface of the first wafer (the surface bonded to the second wafer) to the surface (see Figure 6(b) below) of the peripheral modified layer M1 formed inside the first wafer by laser processing. The inventors then discovered the possibility of appropriately managing and estimating the processing quality of the edge trim of the first wafer by utilizing this correlation. Patent Document 1 does not describe or suggest the correlation between the amount of contamination, the number of processed wafers, the air flow rate, and BHC.

[0012] The technology disclosed herein provides a substrate processing method that can appropriately manage and estimate processing quality in substrate processing that forms a modified layer on a substrate by laser processing and propagates a crack from the modified layer. Hereinafter, a wafer processing system as a substrate processing system and a wafer processing method as a substrate processing method according to the present embodiment will be described with reference to the drawings. Note that in this specification and the drawings, elements having substantially the same functional configuration are designated by the same reference numerals, and redundant description will be omitted.

[0013] 1 , a wafer processing system 1 according to this embodiment performs processing on a laminated wafer T in which a first wafer W serving as a substrate and a second wafer S are bonded together. Hereinafter, the surface of the first wafer W that is bonded to the second wafer S will be referred to as the front surface Wa, and the surface opposite the front surface Wa will be referred to as the back surface Wb. Similarly, the surface of the second wafer S that is bonded to the first wafer W will be referred to as the front surface Sa, and the surface opposite the front surface Sa will be referred to as the back surface Sb.

[0014] The first wafer W is a semiconductor substrate such as a silicon substrate, and has a device layer Dw including a plurality of devices formed on the front surface Wa side. A bonding film Fw is further formed on the device layer Dw, and the first wafer W is bonded to the second wafer S via the bonding film Fw. The bonding film Fw may be, for example, an oxide film (THOX film, SiO２ The first wafer W may be formed of a silicon dioxide film, a TEOS film, a SiC film, a SiCN film, or an adhesive. The peripheral edge We of the first wafer W is chamfered, and the thickness of the cross section of the peripheral edge We decreases toward the tip. The peripheral edge We is a portion to be removed in edge trimming, which will be described later, and is, for example, in the range of 0.5 mm to 3 mm in the radial direction from the outer edge of the first wafer W.

[0015] The second wafer S has, for example, the same configuration as the first wafer W, and has a device layer Ds and a bonding film Fs formed on the surface Sa, and a chamfered peripheral edge. Note that the second wafer S does not necessarily have to be a device wafer on which the device layer Ds is formed, and may be, for example, a support wafer that supports the first wafer W.

[0016] 2 , wafer processing system 1 has a configuration in which a load / unload station 2 and a processing station 3 are integrally connected. In load / unload station 2, for example, a FOUP F capable of accommodating a plurality of overlapped wafers T is loaded and unloaded between the load / unload station 2 and the outside. Processing station 3 is equipped with various processing devices that perform desired processing on overlapped wafers T.

[0017] The carry-in / out station 2 is provided with a FOUP mounting table 10 on which a FOUP F capable of accommodating a plurality of overlapped wafers T is mounted. A wafer transfer device 20 is provided adjacent to the FOUP mounting table 10 on the positive X-axis side of the FOUP mounting table 10. The wafer transfer device 20 moves on a transfer path 21 extending in the Y-axis direction, and is configured to be able to transfer overlapped wafers T between the FOUP F on the FOUP mounting table 10 and a transition device 30, which will be described later.

[0018] In the loading / unloading station 2 , a transition device 30 for transferring the overlapped wafer T between the processing station 3 and the wafer transfer device 20 is provided adjacent to the wafer transfer device 20 on the positive side of the X axis of the wafer transfer device 20 .

[0019] The processing station 3 is provided with a wafer transfer device 40, an interface modification device 50, an internal modification device 60, a peripheral removal device 70, and a cleaning device 80.

[0020] The wafer transfer device 40 is provided on the positive X-axis side of the transition device 30. The wafer transfer device 40 is configured to be movable on a transfer path 41 extending in the X-axis direction, and is configured to be able to transfer the overlapped wafer T to the transition device 30, the interface modification device 50, the internal modification device 60, the edge removal device 70, and the cleaning device 80 in the carry-in / out station 2.

[0021] The interface modification device 50 applies a laser beam (interface laser beam, for example, CO ２ The interface modification device 50 is configured as desired. The interface modification device 50 also includes a control device 51, which will be described later.

[0022] The internal modification device 60 irradiates the inside of the first wafer W with laser light (internal laser light, for example, a YAG laser or a fiber laser) to form a peripheral modified layer M1 that serves as a base point for peeling off the peripheral edge portion We and divided modified layers M2 that serve as base points for dividing the peripheral edge portion We into small pieces (see FIG. 6 below). The internal modification device 60 also has a control device 61 that will be described later.

[0023] As shown in FIGS. 3 and 4 , the internal modification device 60 has a chuck 100 that holds the overlapped wafer T on its upper surface. The chuck 100 suction-holds the back surface Sb of the second wafer S, with the first wafer W on which the peripheral modified layer M1 is to be formed being placed on top and the second wafer S being placed on the bottom. The chuck 100 is supported by a slider table 102 via an air bearing 101. A rotation mechanism 103 is provided on the underside of the slider table 102. The rotation mechanism 103 incorporates, for example, a motor as a drive source. The chuck 100 is configured to be rotatable about a vertical axis by the rotation mechanism 103 via the air bearing 101. The slider table 102 is configured to be movable on rails 106 extending in the Y-axis direction on a base 105 via a movement mechanism 104 provided on the underside of the slider table 102. The drive source of the moving mechanism 104 is not particularly limited, but may be, for example, a linear motor.

[0024] A laser irradiation unit 110 is provided above the chuck 100, and irradiates a laser beam onto the overlapped wafer T (first wafer W) held by the chuck 100. As shown in Fig. 5, the laser irradiation unit 110 has a laser head 111, a condenser lens 112, a cover glass 113, and a nozzle 114. The laser beam irradiated onto the overlapped wafer T (first wafer W) from the laser irradiation unit 110 is supplied from a laser oscillator (not shown).

[0025] The laser head 111 is supported by a support member 115. The laser head 111 is configured to be able to move up and down by an elevating mechanism 117 along rails 116 extending in the vertical direction. The laser head 111 is also configured to be able to move in the Y-axis direction by a moving mechanism 118. The elevating mechanism 117 and the moving mechanism 118 are each supported by a support column 119.

[0026] The condenser lens 112 is provided on the lower surface of the laser head 111 and condenses laser light from the laser oscillator to irradiate the laser light inside the overlapped wafer T held by the chuck 100, more specifically, inside the first wafer W. This modifies the portion inside the first wafer W irradiated with the laser light, forming a peripheral modified layer M1 and divided modified layers M2. Note that, as will be described later, cracks C extend in the thickness direction of the first wafer W from the peripheral modified layer M1 and divided modified layer M2 formed by the irradiation of the laser light.

[0027] The cover glass 113 is a member provided on the underside of the condenser lens 112, and prevents particles generated by irradiating the overlapped wafer T (first wafer W) with laser light (laser processing of the first wafer W) from adhering to the condenser lens 112.

[0028] The nozzle 114 is provided below the condenser lens 112. The nozzle 114 is a hollow cylindrical member in which an internal space 114a is formed, and the laser light from the condenser lens 112 passes through the internal space 114a and is irradiated onto the first wafer W.

[0029] At the top of the nozzle 114, air or nitrogen (N ２The gas supply unit 114b is provided to supply a gas such as a gas supplied from the gas supply unit 114b. The gas is supplied from the gas supply unit 114b to the internal space 114a from the side along the lower surface of the cover glass 113, and then passes through the internal space 114a, flows downward through the nozzle 114, and is sprayed onto the back surface Wb of the first wafer W. This gas prevents particles generated by laser processing from adhering to the lower surface of the cover glass 113. The particles removed from the back surface Wb of the first wafer W by the gas from the nozzle 114 are collected by a dust collector (not shown).

[0030] A wafer imaging mechanism 120 is provided above the chuck 100 and on the Y-axis positive side of the laser irradiation unit 110. In the internal modification device 60, the wafer imaging mechanism 120 images the overlapped wafer T (first wafer W) held on the chuck 100, and based on the image, alignment of the first wafer W and determination of the irradiation position of the laser light are performed.

[0031] A lens imaging mechanism 130 is provided on the negative Y-axis side of the chuck 100. The lens imaging mechanism 130 includes one or more cameras. The lens imaging mechanism 130 is disposed, for example, on the slider table 102, and is configured to be movable in the Y-axis direction together with the chuck 100 by a moving mechanism 104. In the internal reforming device 60, the lens imaging mechanism 130 images the cover glass 113 of the laser irradiation unit 110 from below, and the amount of contamination on the cover glass 113 is detected based on the image.

[0032] The edge removal device 70 removes the edge portion We of the first wafer W, i.e., performs edge trimming, using the edge modified layer M1 formed in the internal modification device 60 as a base point. Any method for edge trimming can be selected. In one example, the edge removal device 70 may insert, for example, a wedge-shaped blade into the interface between the first wafer W and the second wafer S. Alternatively, for example, an impact may be applied to the edge portion We by spraying air or a water jet toward the edge portion We.

[0033] The cleaning device 80 performs a cleaning process on the first wafer W and the second wafer S after the edge trimming by the edge removal device 70, thereby removing particles from these wafers. Any cleaning method can be selected.

[0034] The wafer processing system 1 described above is provided with a control device 51, a control device 61, and a control device 90. The control device 51 individually controls the operation of the interface modification device 50. The control device 61 individually controls the operation of the internal modification device 60. The control device 90 oversees the control of a series of wafer processes in the wafer processing system 1. The control devices 51, 61, and 90 are, for example, computers equipped with a CPU, memory, etc., and each have a program storage unit (not shown). A program for controlling the processing of the laminated wafer T is stored in the program storage unit. The program may be recorded on a computer-readable storage medium H and installed from the storage medium H. The storage medium H may be temporary or non-temporary. In this embodiment, the control devices 51 and 61 are installed individually for the interface modification device 50 and the internal modification device 60, respectively. However, the control devices 51 and 61 may be integrated with the control device 90. In other words, the operations of the interface modification device 50 and the internal modification device 60 may be controlled by the control device 90.

[0035] Next, a description will be given of wafer processing performed using the wafer processing system 1 configured as described above. In this embodiment, the first wafer W and the second wafer S are bonded together to form an overlapping wafer T in advance.

[0036] First, a FOUP F containing a plurality of overlapped wafers T is placed on a FOUP mounting table 10 in the carry-in / out station 2. Next, the overlapped wafers T are removed from the FOUP F by the wafer transfer device 20 and transferred to the interface modification device 50 via the transition device 30 and the wafer transfer device 40.

[0037] In the interface modification device 50, the interior of the overlapped wafer T, specifically the interface between the first wafer W and the second wafer S, is irradiated with pulsed interface laser light while the overlapped wafer T is rotated and moved horizontally along the Y-axis direction. This modifies the interface between the first wafer W and the second wafer S (the interface between the bonding films Fw, Fs in the illustrated example) as shown in Fig. 6(a). Modification of the bonding interface in the embodiment includes amorphization of the bonding film Fw at the irradiation position of the interface laser light, peeling of the interface between the first wafer W and the second wafer S, and the like.

[0038] In the interface modification apparatus 50, by modifying the irradiation position of the interface laser light at the interface between the first wafer W and the second wafer S in this manner, a bond strength reduced region R is formed in which the bond strength between the first wafer W and the second wafer S is reduced. In the edge trimming described below, the peripheral edge portion We of the first wafer W, which is the target for removal, is removed, and the presence of the bond strength reduced region R makes it possible to appropriately remove the peripheral edge portion We. The interface laser light may be irradiated onto the overlapped wafer T from the back surface Sb side of the second wafer S or from the back surface Wb side of the first wafer W.

[0039] The overlapped wafer T, in which the bonding strength reduced region R is formed at the interface between the first wafer W and the second wafer S, is then transferred to the internal modification device 60 by the wafer transfer device 40. In the internal modification device 60, an internal laser beam is irradiated into the interior of the first wafer W to form a peripheral modified layer M1 and a divided modified layer M2, as shown in FIG. 6B . Furthermore, cracks C1 and C2 extend from the peripheral modified layer M1 and the divided modified layer M2 formed by the irradiation of the internal laser beam in the thickness direction of the first wafer W, respectively. Like the peripheral modified layer M1, the crack C1 serves as a base point for removing the peripheral portion We. Like the divided modified layer M2, the crack C2 serves as a base point for dividing the peripheral portion We into small pieces. In the drawings used in the following description, the divided modified layer M2 and the crack C2 may be omitted to avoid complicating the illustration.

[0040] It should be noted that particles are generated during the formation (laser processing) of the peripheral modified layer M1 in the internal modification device 60. As described above, particles generated during the laser processing of the first wafer W are removed from the first wafer W by the gas from the nozzle 114. However, particularly when the volume of gas supplied from the nozzle 114 is large, the particles may be blown up and adhere to the underside of the cover glass 113. When particles adhere to the cover glass 113, the processing quality deteriorates. Specifically, the length (BHC) of the crack C1 extending from the peripheral modified layer M1 formed at the lowest part inside the first wafer W (on the side of the front surface Wa to be bonded to the second wafer S) toward the front surface Wa becomes shorter, and the crack C1 does not reach the front surface Wa, making it impossible to properly remove the peripheral portion We. Therefore, in the internal reforming device 60 according to the technology of the present disclosure, correlation data is acquired between the flow rate of gas supplied from the nozzle 114, the number of processed laminated wafers T (first wafers W) (the cumulative number of processed wafers in the internal reforming device 60), the amount of contamination on the cover glass 113 (more specifically, the brightness described below), and BHC, and laser processing in the internal reforming device 60 is controlled based on the acquired correlation data. A detailed method of controlling laser processing using the correlation data will be described later.

[0041] The overlapped wafer T, on which the peripheral modified layer M1 and the divided modified layer M2 have been formed inside the first wafer W, is then transferred by the wafer transfer device 40 to the peripheral removal device 70. In the peripheral removal device 70, as shown in FIG. 6( c), the peripheral portion We of the first wafer W is removed, i.e., edge trimming is performed. At this time, the peripheral portion We is peeled from the center of the first wafer W (the radially inner side of the peripheral portion We) using the peripheral modified layer M1 and the crack C1 as base points, and is also completely peeled from the second wafer S using the bonding strength reduced region R as base points. At this time, the removed peripheral portion We is also broken into small pieces using the divided modified layer M2 and the crack C2 as base points. To remove the peripheral portion We, for example, a wedge-shaped blade B (see FIG. 6( c)) may be inserted into the interface between the first wafer W and the second wafer S that form the overlapped wafer T.

[0042] The overlapped wafer T from which the peripheral edge portion We of the first wafer W has been removed is then transferred by the wafer transfer device 40 to the cleaning device 80. In the cleaning device 80, the first wafer W from which the peripheral edge portion We has been removed and / or the second wafer S are cleaned. In the cleaning device 80, as shown in FIG. 6( d ), for example, the first wafer W and the second wafer S may be irradiated with a cleaning laser beam to modify and remove the irradiated portions of the first wafer W and the second wafer S, thereby removing (cleaning) any remaining particles and the like.

[0043] Thereafter, the laminated wafer T that has undergone all the processing is transferred by the wafer transfer device 40 to the transition device 30, and then transferred by the wafer transfer device 20 to the FOUP F on the FOUP mounting table 10. In this way, the series of wafer processing steps in the wafer processing system 1 is completed.

[0044] Next, a detailed method for controlling laser processing using correlation data in the internal reforming device 60 will be described with reference to the drawings.

[0045] In the laser processing control according to the present disclosure, first, various data for creating the approximation formula (2) described below is acquired (step St1 in FIG. 7 ). Specifically, in this embodiment, the various data acquired for creating the approximation formula include the gas flow rate supplied from the nozzle 114 during laser processing, the number of processed overlapping wafers T (first wafers W), and the amount of contamination on the cover glass 113.

[0046] The gas flow rate from the nozzle 114 can be obtained based on, for example, the processing recipe and processing results of the overlapped wafer T (first wafer W). The number of processed overlapped wafers T (first wafer W) is the cumulative number of overlapped wafers (first wafers W) laser-processed by the internal modification device 60 between the time when the previous data was acquired and the time when the current data was acquired. The amount of contamination on the cover glass 113 can be quantified by moving the chuck 100 to position the cover glass 113 above the lens imaging mechanism 130, capturing an image of the cover glass 113 from below using the lens imaging mechanism 130, and calculating the brightness of the captured image.

[0047] A specific method for quantifying the amount of dirt on the cover glass 113 will be described.

[0048] 8, the image captured by the lens imaging mechanism 130 has contaminated areas to which particles P resulting from laser processing are attached, and non-contaminated areas to which particles P are not attached. In addition, as shown in FIG. 8, the image captured by the lens imaging mechanism 130 has a shaded area V due to the angle of view of the camera of the lens imaging mechanism 130, etc.

[0049] When quantifying the amount of dirt, first, the brightness and contrast of the captured image are adjusted to eliminate the shaded area V formed in the captured image as shown in Fig. 9. If the quantification of the amount of dirt is carried out without eliminating this shaded area V, there is a risk that this shaded area V will be erroneously detected as a dirty area.

[0050] Next, the captured color image with adjusted brightness and contrast is grayscaled to make the captured image two-tone (two colors, monochrome). In other words, the captured image, which was expressed using RGB values ​​(each 0 to 255), is now expressed using two-color black and white brightness (0 to 255). In the grayscaled captured image, the brightness is lower (black components are stronger) in contaminated areas where particles P are attached, and the brightness is higher (white components are stronger) in non-contaminated areas where particles P are not attached.

[0051] Next, a luminance histogram (frequency distribution) of the grayscaled captured image is created, as shown in FIG. 10 . In FIG. 10 , (a) shows a histogram before laser processing (initial value), and (b) shows a histogram after processing 100 overlapped wafers T (first wafers W). As shown in FIG. 10 , in the histogram before laser processing (a), the distribution is biased toward high luminance because no particles P adhere to the cover glass 113, whereas in the histogram after laser processing (b), the distribution is dispersed to low luminance because particles P adhere to the cover glass 113. In other words, new luminance is generated in the histogram due to the particles P adhering to the cover glass 113 by laser processing.

[0052] Next, the captured image is binarized using, for example, the boundary between the low-luminance side and the high-luminance side in the histogram of (b) after laser processing in FIG. 10 (for example, a luminance value of 100 in FIG. 10 ), i.e., the newly generated luminance value, as a threshold. In other words, the luminance values ​​are unified at 255 (white) on the high-luminance side of the histogram, which is considered to be the portion of the cover glass 113 where particles P are not attached, and the luminance values ​​are unified at 0 (black) on the low-luminance side of the histogram, which is considered to be the portion of the cover glass 113 where particles P are attached. As a result, the captured image is converted into a simple image in which only the dirty portions attached to the cover glass 113 are extracted in black (luminance value 0), as shown in FIG. 11 .

[0053] The total brightness (number of pixels) of the contaminated area is then counted from the binarized captured image, and this total brightness can be quantified as the amount of contamination on the cover glass 113. FIG. 12 is a histogram showing the amount of contamination (total brightness) after processing 100 stacked wafers T (first wafers W) at gas flow rates of 10 m / s and 25 m / s from the nozzle 114 during laser processing. Note that regions 1 to 5 shown in FIG. 12 are arbitrary regions on the surface of the cover glass 113; that is, the total brightness was counted for each arbitrary region. As shown in FIG. 12, it can be seen that the amount of contamination (total brightness) on the cover glass 113 tends to increase as the air flow rate increases. This is thought to be due to the fact that the increased air flow causes particles P on the first wafer W to be stirred up, as described above. The amount of contamination on the cover glass 113 is quantified as described above.

[0054] Instead of the total brightness (number of pixels) of the dirty part counted from the binarized captured image, the amount of dirt on the cover glass 113 may be quantified by finding the area ratio of the dirty part that can be calculated from the total brightness. Specifically, after counting the total brightness (number of pixels) of the dirty part from the binarized captured image as described above, the area [pixel ２ ] to the area of ​​the counted stain [pixel ２The amount of dirt can be quantified by calculating the ratio of the number of pixels in the vertical and horizontal directions of the image based on the following formula (1). The area of ​​the entire captured image can be calculated, for example, from the product of the number of pixels in the vertical and horizontal directions of the captured image. The area of ​​the dirty part can be calculated by multiplying the unit area of ​​a pixel in which dirt can be counted by the number of pixels in the vertical and horizontal directions. ２ ] and the total brightness [-]. Dirt amount [%] = (area of ​​dirty part [pixel ２ ] / Area of ​​captured image [pixel ２ ]) × 100... (1) The area of ​​the stain [pixel ２ ] = unit area [pixel ２ ]×Total brightness[-] Area of ​​dirty area [pixel ２ ] = Number of vertical pixels in the captured image [pixel] x number of horizontal pixels [pixel]

[0055] In the above example, the amount of dirt on the cover glass 113 was quantified based on the image of the cover glass 113 captured by the lens imaging mechanism 130, but the image of the cover glass 113 does not have to be acquired by the lens imaging mechanism 130. Instead of capturing an image of the cover glass 113 by the lens imaging mechanism 130 inside the internal reforming device 60, for example, the cover glass 113 may be removed from the laser irradiation unit 110 by an operator, and the image may be acquired outside the internal reforming device 60.

[0056] Once the various data for creating the approximation equation has been acquired, the various acquired data is then input to acquire correlation data for the gas flow rate from the nozzle 114, the number of overlapping wafers T (first wafers W) processed, the amount of contamination on the cover glass 113, and BHC.

[0057] Specifically, a multiple regression analysis was performed using BHC (the length of the crack C extending from the lowermost peripheral modification layer M1 formed by laser processing toward the surface Wa) as the objective variable, and the acquired gas flow rate, number of processed wafers, and amount of dirt as explanatory variables to create the following approximate equation (2) (step St2 in FIG. 7): y = αx1 + βx2 + γx3 + δ (2) In the above equation, y is the objective variable, BHC; x1 to x3 are explanatory variables, either the gas flow rate, number of processed wafers, or amount of dirt; α to γ ​​are coefficients of the explanatory variables; and δ is the intercept. Note that the explanatory variable for the amount of dirt is a value quantified by either the total grayscale brightness or the area percentage of the dirty area.

[0058] The inventors conducted extensive research and found that there was a good agreement between the estimated BHC value (vertical axis) obtained using the above approximate formula (2) and the actual BHC value (horizontal axis) after laser processing, as shown in Figure 13. This good agreement led to the discovery of the possibility that the BHC result (length of crack C) could be estimated from the gas flow rate, number of processed sheets, and amount of dirt obtained as various data.

[0059] More specifically, the gas flow rate and the number of wafers processed, which are explanatory variables x used in the above approximate formula (2), can be treated as constants determined based on the recipe and processing results. Therefore, the above approximate formula (2) can be expressed as the following formula (3), which can be viewed as a linear function expressed by the BHC and the amount of dirt (brightness) on the cover glass 113, as shown in Figure 14: y = αx + Δ (3) In the above formula, y is the BHC, which is the response variable; x is the amount of dirt, which is the explanatory variable; α is the coefficient of the explanatory variable; and Δ is the intercept, which includes the gas flow rate and the number of wafers processed as constants.

[0060] The present inventors have discovered that by quantifying the amount of contamination on the cover glass 113 and performing multiple regression analysis, the BHC can be estimated using the above formula (3), and that the amount of contamination on the cover glass 113 (brightness or area ratio) can be determined using the above quantification method based on the gas flow rate and the number of sheets processed.

[0061] Once the above approximate formula (2) is obtained by multiple regression analysis, the target BHC specification (hereinafter sometimes simply referred to as "BHC specification") is input (step St3 in FIG. 7). The "BHC specification" is the minimum length of the crack C required to allow the crack C1 to reach the front surface Wa of the first wafer W, which is the surface opposite to the surface irradiated with the laser light. In other words, it can be said to be a threshold value of the length of the crack C (BHC) for appropriately removing the peripheral edge We. The BHC specification may be manually input by an operator or automatically input based on a process recipe, for example.

[0062] Once the BHC specifications are input into the device, laser processing of the overlapped wafer T (first wafer W) is initiated in the internal modification device 60 (step St4 in FIG. 7). That is, an internal laser beam is irradiated onto the interior of the first wafer W, thereby forming a peripheral modified layer M1. At this time, within the first wafer W, a crack C1 extends from the peripheral modified layer M1 in the thickness direction of the first wafer W. When laser processing is performed in this manner, the cumulative number of processed overlapped wafers T (first wafer W), which constitutes the various data described above, is updated.

[0063] Simultaneously with or subsequent to the start of this laser processing, an estimated BHC value after laser processing in step St4 is calculated from the above approximate formula (2) (step St5 in FIG. 7). Then, once the estimated BHC value is calculated, the estimated value is compared with the BHC specification input in step St3 (spec determination) (step St6 in FIG. 7).

[0064] If the comparison results in a determination that the BHC satisfies the specifications, i.e., if the estimated BHC is equal to or greater than the BHC specifications and edge trimming can be performed appropriately, operation of the internal reforming device 60 continues (step St7 in FIG. 7 ). In this case, laser processing may be performed continuously on the next overlapped wafer T (first wafer W), or the data on the number of processed wafers may be updated and the calculation of approximate formula (2) may be performed again. In other words, the calculation of approximate formula (2) may be performed for each overlapped wafer T processed in the internal reforming device 60, or may be performed for multiple wafers processed at a time (e.g., for each lot).

[0065] On the other hand, if the comparison results in a determination that the BHC does not satisfy the specifications, i.e., if the estimated BHC is below the BHC specifications and it is determined that edge trimming cannot be performed appropriately, an alarm to this effect is issued to the operator, and maintenance of the internal reforming device 60 is performed (step St8 in FIG. 7 ). Specifically, in this embodiment, based on the above approximation formula (2), it is determined that the crack C does not properly extend inside the first wafer W due to the amount of contamination on the cover glass 113. Therefore, the cover glass 113 is removed from the laser irradiation unit 110, and the cover glass 113 is replaced or cleaned. This improves the amount of contamination on the cover glass 113, and the estimated BHC is updated. Based on this, laser processing of the overlapped wafer T (first wafer W) (step St4 in FIG. 7 ) is resumed.

[0066] The management and control of laser processing in the internal modification device 60 according to this embodiment is performed as described above. According to the above embodiment, the BHC result after laser processing is estimated from the acquired gas flow rate from the nozzle 114, the number of processed laminated wafers T, and the amount of contamination on the cover glass 113. More broadly, by acquiring correlation data between the gas flow rate from the nozzle 114, the number of processed laminated wafers T (first wafers W), the amount of contamination on the cover glass 113, and the BHC result after laser processing, it is possible to determine whether edge trimming of the first wafer W can be performed appropriately prior to laser processing of the laminated wafer T. If it is determined that edge trimming of the first wafer W cannot be performed appropriately, i.e., if the estimated BHC value does not meet the BHC specifications, an alarm is issued in advance, allowing the timing of maintenance of the device to be appropriately determined.

[0067] In the above embodiment, the gas flow rate, the number of processed wafers, and the amount of contamination are used as explanatory variables for calculating the approximate formula (2), but the number of processed overlapping wafers T (first wafers W) may be omitted as appropriate when calculating the approximate formula (2).

[0068] Furthermore, in the above embodiment, the BHC estimated value is calculated (step St5) at least after the start of laser processing of the overlapped wafer T (step St4). However, in this case, if it is determined that the BHC estimated value does not satisfy the BHC specification, cracks C are not properly formed in the overlapped wafer T that has been laser processed in step St4, and edge trimming of the overlapped wafer T cannot be properly performed. Therefore, the BHC estimated value may be calculated (step St5) before the start of laser processing of the overlapped wafer T (step St4). This allows the laser processing to be started after the BHC estimated value is calculated and compared with the BHC specification, thereby suppressing a decrease in yield in the internal modification device 60.

[0069] Furthermore, in the above embodiment, whether edge trimming can be performed appropriately is determined using the estimated BHC value calculated from the above approximate formula (2). However, instead, the number of processed laminated wafers T (first wafers W) that can ensure the BHC specification may be estimated based on the estimated BHC value. In this case, processing in the internal reformer 60 may be started if the total number of laminated wafers T processed since the previous cleaning (maintenance) of the cover glass 113 and the number of laminated wafers T to be processed in the internal reformer 60 is within the estimated number of processed laminated wafers T that can ensure the BHC specification (hereinafter referred to as the "estimated number of processed wafers"). On the other hand, if the total number exceeds the estimated number of processed wafers, an alarm may be issued to the operator, and maintenance of the internal reformer 60 (cleaning of the cover glass 113) may be performed without starting processing.

[0070] Alternatively, when the total number of processed wafers exceeds the estimated number of processed wafers, instead of immediately performing maintenance on the internal reformer 60, the difference between the cumulative number of processed wafers and the estimated number of processed wafers may be used to calculate how many more polymerized wafers T can be processed before the estimated number of processed wafers is reached. In this case, processing of polymerized wafers T may be resumed in the internal reformer 60 until the cumulative number of processed wafers reaches the estimated number of processed wafers, and maintenance of the internal reformer 60 (cleaning of the cover glass 113) may be performed after the cumulative number of processed wafers reaches the estimated number of processed wafers. In this case, the timing of issuing an alarm to the operator is not limited to the timing when it is confirmed that the total number of processed wafers exceeds the estimated number of processed wafers. For example, an alarm may be issued after processing in the internal reformer 60 is resumed and the cumulative number of processed wafers reaches the estimated number of processed wafers, or an alarm may be issued after processing in the internal reformer 60 is resumed and before the cumulative number of processed wafers reaches the estimated number of processed wafers. In this case, an alarm may be issued when the cumulative number of processed sheets reaches the number obtained by subtracting the set number of sheets from the estimated number of processed sheets.

[0071] In the above embodiment, multiple regression analysis was performed using the BHC results after laser processing as the objective variable and the gas flow rate, number of processed sheets, and amount of dirt as the explanatory variables in the approximate formula (2). However, if the BHC results after laser processing can be measured or observed, or if other data is used as the objective variable based on the calculated BHC estimate, for example.

[0072] Specifically, for example, an approximation equation may be created by performing multiple regression analysis with the objective function y being the amount of contamination on the cover glass 113 and the explanatory variables x being the gas flow rate, the number of processed sheets, and BHC. In other words, the amount of contamination on the cover glass 113 may be estimated using the approximation equation in correspondence with the gas flow rate in laser processing and the actual number of processed sheets. Even in this case, the approximation equation can be expressed as a linear function of the amount of contamination on the cover glass 113 and BHC, as shown in Figure 14, so the amount of contamination on the cover glass 113 can be appropriately estimated from the BHC.

[0073] In this case, if the total number of the "cumulative number of processed polymerized wafers T since the previous cleaning (maintenance) of the cover glass 113" and the "number of polymerized wafers T to be processed in the internal reforming device 60" is within the "number of processed polymerized wafers T (estimated number of processed wafers) that can ensure the amount of contamination (brightness or contamination area) of the cover glass 113 that is estimated to allow appropriate edge trimming (to form a crack C1 of the target length inside the first wafer W)," processing in the internal reforming device 60 may be started. On the other hand, if the total number of processed wafers exceeds the estimated number of processed wafers (exceeds the amount of contamination of the cover glass 113 that is estimated to allow the crack C1 of the target length to be formed inside the first wafer W), an alarm may be issued to the operator, and maintenance of the internal reforming device 60 (cleaning of the cover glass 113) may be performed without starting processing. Alternatively, when the total number of wafers exceeds the estimated number of wafers to be processed, instead of immediately performing maintenance on the internal reformer 60, the difference between the cumulative number of wafers to be processed and the estimated number of wafers to be processed may be used to calculate how many more polymerized wafers T can be processed before the estimated number of wafers to be processed is reached. In this case, processing of polymerized wafers T may be resumed in the internal reformer 60 until the cumulative number of wafers to be processed reaches the estimated number of wafers to be processed, and after the cumulative number of wafers to be processed reaches the estimated number of wafers to be processed, maintenance of the internal reformer 60 (cleaning of the cover glass 113) may be performed. Note that the timing of issuing an alarm to the operator can be determined arbitrarily, as described above.

[0074] In other words, processing may be started when it is determined that the estimated amount of contamination on the cover glass 113 after processing of the total number of laminated wafers T, which is the cumulative number of processed laminated wafers T and the number of laminated wafers T to be processed in the future, is equal to or less than the amount of contamination on the cover glass 113 that is determined to allow appropriate edge trimming (that is, allows cracks C that satisfy the BHC specifications to be formed). On the other hand, when it is determined that the estimated amount of contamination on the cover glass 113 after processing of the total number of wafers is greater than the amount of contamination on the cover glass 113 that is determined to allow appropriate edge trimming, an alarm may be issued to the operator, and maintenance of the internal reformer 60 (cleaning of the cover glass 113) may be performed without starting processing.

[0075] In the above embodiment, an example has been described in which laser processing is controlled based on the correlation data when processing a laminated wafer T in which a first wafer W and a second wafer S are bonded together in the internal reforming device 60, but the technology disclosed herein can also be applied to other wafer processing.

[0076] For example, the technology disclosed herein can be applied not only to processing a laminated wafer T in which a first wafer W and a second wafer S are bonded together, but also to wafer processing in which a single wafer (a wafer that is not bonded to another wafer) is irradiated with laser light to form a modified layer and then a crack propagates from the modified layer.

[0077] Alternatively, the technology disclosed herein can also be applied to, for example, a case where a crack is propagated in the thickness direction of a wafer by irradiation with laser light to divide the wafer into multiple chips, i.e., a case where so-called wafer dicing is performed. In this case, the variable used in the above approximate formula (2) may be simply "the length of the crack required (target) for the dicing process formed in the wafer by laser processing" instead of the above BHC (the length of the crack C extending from the peripheral modified layer M1 formed at the bottom by laser processing toward the surface Wa).

[0078] The embodiments disclosed herein should be considered illustrative in all respects and not restrictive. The above-described embodiments may be omitted, substituted, or modified in various ways without departing from the spirit and scope of the appended claims. For example, the components of the above-described embodiments may be arbitrarily combined. Such an arbitrary combination naturally provides the functions and effects of each of the components in the combination, as well as other functions and effects that would be apparent to a person skilled in the art from the description herein. Furthermore, the effects described herein are merely descriptive or exemplary and are not limiting. In other words, the technology disclosed herein may provide other effects that would be apparent to a person skilled in the art from the description herein, in addition to or in place of the above-described effects.

[0079] REFERENCE SIGNS LIST 1 wafer processing system 60 internal modification device 90 control device 112 condenser lens 113 cover glass 114 nozzle C1 crack M1 peripheral modification layer W first wafer We peripheral portion

Claims

1. A substrate processing method for processing a substrate, comprising: irradiating the substrate with laser light to form a modified layer and a crack extending from the modified layer in the thickness direction of the substrate; acquiring data relating to the cumulative number of substrates processed, the amount of dirt on a cover glass that protects a focusing lens that irradiates the laser light, the amount of gas supplied along the underside of the cover glass, and the length of the crack that extends due to the irradiation of the laser light; and controlling the irradiation of the laser light based on the acquired data.

2. A substrate processing method as described in claim 1, comprising: creating an approximate formula from the data to estimate the length of the crack that will expand due to irradiation with the laser light; inputting a specification value that is the minimum length of the crack that will reach the surface of the substrate opposite to the surface irradiated with the laser light; and calculating an estimated value of the length of the crack after irradiation with the laser light from the approximate formula.

3. The substrate processing method of claim 2, wherein the irradiation of the laser light is started when it is determined that the estimated value satisfies the specification value, and cleaning of the cover glass is started when it is determined that the estimated value does not satisfy the specification value.

4. A substrate processing method as described in claim 1, comprising: creating an approximation formula from the data to estimate the length of the crack that will expand due to irradiation with the laser light; inputting a specification value that is the minimum length of the crack that will reach the surface of the substrate opposite to the surface irradiated with the laser light; and estimating from the approximation formula the number of substrates that can be processed while ensuring the specification value.

5. A substrate processing method as described in claim 4, wherein irradiation of the laser light is initiated when it is determined that the total number of substrates processed plus the number of substrates to be processed in the future is equal to or less than the estimated processable number, and cleaning of the cover glass is initiated when it is determined that the total number of substrates exceeds the estimated processable number.

6. A substrate processing method as described in claim 4, wherein the irradiation of the laser light is initiated when it is determined that the total number of substrates processed plus the number of substrates to be processed in the future is equal to or less than the estimated processable number, and when it is determined that the total number of substrates exceeds the estimated processable number, the substrates are processed until the accumulated number of substrates processed reaches the estimated processable number, and then cleaning of the cover glass is initiated.

7. The substrate processing method of claim 1, comprising: creating an approximate formula for estimating the amount of contamination on the cover glass from the data; and estimating the amount of contamination on the cover glass using the approximate formula in accordance with the number of substrates processed.

8. A substrate processing method as described in claim 7, wherein the irradiation of the laser light is initiated when it is determined that the estimated amount of contamination on the cover glass after processing of the total number of substrates, which is the sum of the accumulated number of substrates to be processed and the number of substrates to be processed in the future, is equal to or less than the amount of contamination on the cover glass that is determined to be able to form the crack of the target length on the substrate, and cleaning of the cover glass is initiated when it is determined that the estimated amount of contamination on the cover glass after processing of the total number of substrates is greater than the amount of contamination on the cover glass that is determined to be able to form the crack of the target length on the substrate.

9. A substrate processing method as described in claim 7, wherein the irradiation of the laser light is started when it is determined that the estimated value of the amount of contamination on the cover glass after processing of the total number of substrates, which is the sum of the accumulated number of substrates to be processed and the number of substrates to be processed in the future, is equal to or less than the amount of contamination on the cover glass that is determined to be able to form the crack of the target length on the substrate, and when it is determined that the estimated value of the amount of contamination on the cover glass after processing of the total number of substrates has been completed exceeds the amount of contamination on the cover glass that is determined to be able to form the crack of the target length on the substrate, the substrate is processed until the amount of contamination on the cover glass reaches the amount that is determined to be able to form the crack of the target length on the substrate, and then cleaning of the cover glass is started.

10. A substrate processing method according to any one of claims 1 to 9, comprising: acquiring an image of the cover glass; grayscaling the image; binarizing the grayscaled image; counting the total brightness of the binarized image; and calculating the area ratio of the total brightness to the entire area of ​​the image, wherein the amount of contamination on the cover glass is acquired from either the total brightness or the area ratio.

11. A substrate processing system for processing substrates, comprising: an internal reforming device that irradiates the substrate with laser light to form a modified layer and cracks that extend from the modified layer in the thickness direction of the substrate; and a control device, wherein the internal reforming device comprises: a focusing lens that focuses the laser light toward the substrate; a cover glass that protects the underside of the focusing lens; and a nozzle that supplies gas along the underside of the cover glass, and the control device acquires data from the internal reforming device relating to the cumulative number of substrates processed in the internal reforming device, the amount of dirt on the cover glass, the amount of gas supplied from the nozzle, and the length of the cracks that extend due to the irradiation of the laser light, and controls the irradiation of the laser light based on the acquired data.

12. The substrate processing system described in claim 11, wherein the control device performs the following control: creating an approximate equation from the data to estimate the length of the crack that will expand due to irradiation with the laser light; and calculating an estimated value of the length of the crack after irradiation with the laser light from the approximate equation.

13. The substrate processing system of claim 12, wherein the control device executes control to start irradiating the laser light when it is determined that the estimated value satisfies a specification value, which is the minimum length of the crack that reaches the surface of the substrate opposite to the surface irradiated with the laser light, and to issue an alarm to start cleaning the cover glass when it is determined that the estimated value does not satisfy the specification value.

14. The substrate processing system described in claim 11, wherein the control device performs the following control: creating an approximation formula from the data to estimate the length of the crack that will expand due to the irradiation of the laser light; and estimating, from the approximation formula, the number of substrates that can be processed while ensuring a specification value that is the minimum value of the length of the crack that will reach the surface of the substrate opposite the surface irradiated with the laser light.

15. The substrate processing system of claim 14, wherein the control device executes control to start irradiating the laser light when it is determined that the total number of substrates processed plus the number of substrates to be processed in the future is equal to or less than the estimated number of substrates that can be processed, and to issue an alarm to start cleaning the cover glass when it is determined that the total number of substrates exceeds the estimated number of substrates that can be processed.

16. The substrate processing system of claim 14, wherein the control device executes control to start irradiating the laser light when it is determined that the total number of substrates processed plus the number of substrates to be processed in the future is equal to or less than the estimated processable number, and when it is determined that the total number exceeds the estimated processable number, to process the substrates until the accumulated number of substrates processed reaches the estimated processable number, and then to sound an alarm to start cleaning the cover glass.

17. The substrate processing system of claim 11, wherein the control device performs the following control: creating an approximate equation for estimating the amount of contamination on the cover glass from the data; and estimating the amount of contamination on the cover glass using the approximate equation in accordance with the number of substrates processed.

18. The substrate processing system described in claim 17, wherein the control device executes control to start irradiating the laser light when it is determined that the estimated value of the amount of contamination on the cover glass after processing of the total number of substrates, which is the sum of the accumulated number of substrates to be processed and the number of substrates to be processed in the future, is equal to or less than the amount of contamination on the cover glass that is determined to be able to form the crack of the target length on the substrate, and to sound an alarm to start cleaning the cover glass when it is determined that the estimated value of the amount of contamination on the cover glass after processing of the total number of substrates is greater than the amount of contamination on the cover glass that is determined to be able to form the crack of the target length on the substrate.

19. The substrate processing system of claim 17, wherein the control is to start irradiating the laser light when it is determined that the estimated value of the amount of contamination on the cover glass after processing of the total number of substrates, which is the sum of the accumulated number of substrates to be processed and the number of substrates to be processed in the future, is equal to or less than the amount of contamination on the cover glass that is determined to be able to form the crack of the target length on the substrate, and when it is determined that the estimated value of the amount of contamination on the cover glass after processing of the total number of substrates has been completed exceeds the amount of contamination on the cover glass that is determined to be able to form the crack of the target length on the substrate, the control is to process the substrate until the amount of contamination on the cover glass reaches the amount that is determined to be able to form the crack of the target length on the substrate, and then issue an alarm to start cleaning the cover glass.

20. A substrate processing system as described in any one of claims 11 to 19, wherein the control device executes the following controls: acquiring an image of the cover glass; grayscaling the image; binarizing the grayscaled image; counting the total brightness of the binarized image; and calculating the area ratio of the total brightness to the entire area of ​​the image; and the amount of contamination on the cover glass is obtained from either the total brightness or the area ratio.