Drying detection method and drying detection device

Abstract

[The technical problem to be solved] A drying detection method and apparatus are provided that can determine the dryness of liquid resin at appropriate time points. Technical means to solve the problem A drying detection method for detecting the drying of a liquid resin containing a solvent, the drying detection method comprising the following steps: a wavelength selection step, selecting a light absorption wavelength of the solvent; a light source selection step, selecting a light source, the light source including light of the selected wavelength; a light receiving step, irradiating the liquid resin with light from the light source and receiving the light that has passed through the liquid resin; and a determination step, determining that the solvent has evaporated and dried when the amount of light of the wavelength that can be absorbed by the solvent in the light receiving step exceeds a predetermined threshold.

Description

[Technical Field]

[0001] This invention relates to a drying detection method and a drying detection device for detecting the drying of liquid resin. [Previous Technology]

[0002] A wafer formed on the front side by dividing multiple devices such as ICs and LSIs by multiple intersecting predetermined dividing lines is divided into individual device chips by a dicing device or a laser processing device, and the divided device chips are used in electrical machines such as mobile phones and personal computers.

[0003] A laser processing apparatus generally consists of a work chuck that holds a wafer, a laser beam irradiation unit that irradiates the wafer held on the work chuck with laser beams, and a feed mechanism that feeds the work chuck and the laser beam irradiation unit relative to each other, and can process wafers with high precision.

[0004] Furthermore, when forming cleavage trenches on predetermined cleavage lines by irradiation with laser light of a wavelength that absorbs the wafer, a protective film is pre-applied to the front side of the wafer to prevent flying debris from adhering to the front side of the device and degrading its quality (see, for example, Patent Document 1). Previous Art Documents Patent Documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2004-188475 [Summary of the Invention]

[0006] Problem to be Solved by the Invention However, when a protective film is formed by coating the front side of a wafer with liquid resin, if laser light is applied before the protective film is sufficiently dried and hardened, the protective film cannot function properly, resulting in the peeling off of metal films such as TEG (Test Element Group) formed on the predetermined dicing lines, thus reducing the quality of the device. The aforementioned problem is not limited to the case where a protective film is formed on the front side of a wafer with a device formed using liquid resin, as described above. In various applications using liquid resin, it is necessary to determine whether the liquid resin has dried sufficiently; therefore, there is a requirement to reliably determine the drying of the liquid resin.

[0007] Accordingly, the object of the present invention is to provide a drying detection method and drying detection device that can reliably determine the dryness of liquid resin.

[0008] Means for solving the problem According to one aspect of the present invention, a drying detection method is provided to detect the drying of a liquid resin containing a solvent. The drying detection method includes the following steps: a wavelength selection step, selecting the light absorption wavelength of the solvent; a light source selection step, selecting a light source, the light source including light of the selected wavelength; a light receiving step, irradiating the liquid resin with light from the light source and receiving the light that has passed through the liquid resin; and a determination step, determining that the solvent has evaporated and the liquid resin has dried when the amount of light of the wavelength absorbed by the solvent in the light receiving step exceeds a predetermined threshold.

[0009] Ideally, the light from the light source selected in the light source selection step is irradiated onto the liquid resin whose solvent has evaporated and has been sufficiently dried, and the light intensity is measured by receiving the light that has passed through the liquid resin, and a value lower than this light intensity is selected as the threshold. Ideally, the liquid resin is a water-soluble resin, and the solvent is water. Ideally, the wavelengths of light absorbed by water are 1450 nm, 1940 nm, and 2900 nm, and in the light source selection step, a light source containing any of the aforementioned wavelengths is selected.

[0010] According to other aspects of the present invention, a drying detection apparatus is provided, comprising a drying detector for detecting the drying of a liquid resin, the drying detector comprising: a light source containing light of the wavelength absorbed by the solvent contained in the liquid resin; a light receiver receiving light irradiated from the light source and passing through the liquid resin; and a determination unit stored in a controller, which determines whether the amount of light of the wavelength absorbed by the solvent has exceeded a threshold based on the amount of light received by the light receiver, and determines that the liquid resin has dried.

[0011] Effects of the Invention According to the drying detection method of the present invention, the drying of liquid resin can be reliably determined. For example, it becomes possible to perform ablation processing by irradiating the wafer with laser light when the liquid resin has been reliably dried. Even if a metal film such as TEG is formed on the predetermined dividing line, the problem of device quality reduction caused by peeling due to the ablation process can still be solved.

[0012] According to the drying detection device of the present invention, the drying of liquid resin can be reliably determined. For example, it becomes possible to perform ablation processing by irradiating the wafer with laser light when the liquid resin is reliably dried. Even if a metal film such as TEG is formed on the predetermined dividing line, the problem of device quality reduction caused by peeling due to the ablation process can still be solved.

Implementation Method

[0014] The following describes the drying detection method and drying detection apparatus according to embodiments of the present invention, with reference to the accompanying drawings.

[0015] In FIG1(a), a wafer 10 for detecting the drying of liquid resin by means of the drying detection method of this embodiment is shown together with the protective film forming apparatus 20 (only a portion is shown). The wafer 10 is a disk-shaped substrate of semiconductor, on the front side 10a, in which a plurality of devices 12 are formed by dividing the area by a plurality of intersecting predetermined dividing lines 14. The wafer 10 is held in an annular frame F by means of adhesive tape T, the annular frame F having an opening Fa for accommodating the wafer 10.

[0016] In this embodiment, the wafer 10 is irradiated with laser light of a wavelength that is absorbent to the wafer 10 by a laser processing apparatus (not shown) and ablation is performed to form a slit groove along the predetermined slit line 14. Before performing the above-mentioned laser processing, the front side 10a of the wafer 10 is coated with liquid resin P to prevent debris that flies off during the laser processing of the wafer 10 from adhering to the front side of the device 12 and reducing its quality.

[0017] Liquid resin P is supplied to the front side 10a of wafer 10 by, for example, a protective film forming apparatus 20 shown in FIG. 1(a). The protective film forming apparatus 20 includes: a spinner table 22 configured to attract and hold the wafer 10 and rotate it at high speed in the direction indicated by arrow R1 in the figure; and a liquid resin supply nozzle 24 that drips a predetermined amount of liquid resin P from above the center of the spinner table 22 to below.

[0018] The wafer 10 described above is held on the rotary table 22, and liquid resin P is dripped from the liquid resin supply nozzle 24 onto the front surface 10a of the wafer 10. The rotary table 22 is then rotated at high speed in the direction indicated by arrow R1. In this embodiment, the liquid resin P is, for example, a water-soluble resin PVA (polyvinyl alcohol), and the solvent is water. By rotating the rotary table 22, the liquid resin P spreads on the front surface 10a of the wafer 10, and as can be understood from the cross-sectional view shown in Figure 1(b) with a portion enlarged, a protective film of liquid resin P is formed on the front surface 10a of the wafer 10. The protective film of liquid resin P formed on the front surface 10a of the wafer 10 dries and hardens over time due to the evaporation of the solvent, i.e., water. The purpose of the drying detection method in this embodiment is to reliably determine whether the liquid resin P that forms this protective film has reached a dry state suitable for ablation processing by laser light.

[0019] In order to detect the drying state of the above-mentioned liquid resin P, the wafer 10 is transported to the drying detection device 2 shown in FIG2, which is suitable for carrying out the drying detection method of the present invention.

[0020] Figure 2 shows an overall perspective view of the drying detection device 2. The drying detection device 2 includes: a holding unit 3 disposed on a base 2a and holding the aforementioned wafer 10; a moving mechanism 4 for moving the holding unit 3 in the X-axis and Y-axis directions; a drying detector 6 for detecting the drying of the liquid resin P on the wafer 10 held in the holding unit 3; a frame 5 consisting of a vertical wall 5a erected on the side of the moving mechanism 4 and a horizontal wall 5b extending horizontally from the upper end of the vertical wall 5a; and a controller 100. The optical system of the drying detector 6 (described in detail later) is housed inside the horizontal wall 5b.

[0021] As shown in FIG. 2, the holding unit 3 includes: a rectangular X-axis movable plate 31, which is movably mounted on the base 2a in the X-axis direction; a rectangular Y-axis movable plate 32, which is movably mounted on the X-axis movable plate 31 in the Y-axis direction; a cylindrical support column 33, which is fixed to the upper surface of the Y-axis movable plate 32; and a rectangular cover plate 34, which is fixed to the upper end of the support column 33. A work clamp 35 is provided on the cover plate 34, which extends upward through an elongated hole formed in the cover plate 34. The work clamp 35 is an assembly that holds the wafer 10 using the XY plane defined by the X and Y coordinates as the holding surface, and is configured to be rotatable by a rotation drive assembly (not shown) housed in the support column 33. An adsorption chuck 36 is provided on the upper surface of the work clamp 35, which is formed of the holding surface by a porous material with air permeability. The suction chuck 36 is connected to the suction assembly (not shown) via the flow path through the support column 33, and four clamps 37 are arranged at equal intervals around the suction chuck 36. The clamps 37 hold the annular frame F when holding the wafer 10 (described later) on the work chuck 35.

[0022] The moving mechanism 4 includes: an X-axis moving mechanism 4a, which moves the aforementioned worktable 35 in the X-axis direction; and a Y-axis moving mechanism 4b, which moves the worktable 35 in the Y-axis direction. The X-axis moving mechanism 4a converts the rotational motion of the motor 42a into linear motion through the ball screw 42b and transmits it to the movable plate 31 in the X-axis direction, causing the movable plate 31 in the X-axis direction to move along a pair of guide rails 2b, 2b arranged on the base 2a in the X-axis direction. The Y-axis moving mechanism 4b converts the rotational motion of the motor 44a into linear motion through the ball screw 44b and transmits it to the movable plate 32 in the Y-axis direction, causing the movable plate 32 in the Y-axis direction to move along a pair of guide rails 31a, 31a arranged on the movable plate 31 in the X-axis direction in the Y-axis direction.

[0023] FIG3(a) shows a block diagram illustrating the general structure of the optical system of the drying detector 6 of this embodiment. The drying detector 6 includes at least: a light source 62 for illuminating light L0; and a light receiver 7 for receiving light L1, wherein the light L1 is the light that the light L0 irradiates the liquid resin P on the front side 10a of the wafer 10 and passes through the liquid resin P. Further explanation: The device includes: a reflector 63, which changes the optical path of the light L0 irradiated by the light source 62 in an appropriate direction; a beam splitter 64, which allows the light L0 irradiated by the reflector 63 to pass through; a condenser 60, which includes a condensing lens 61 that focuses the light L0 to irradiate the liquid resin P of the wafer 10; a bandpass filter 65, which allows only a predetermined wavelength region contained in the light L1 to pass through, the aforementioned light L1 referring to the light L1 reflected after passing through the liquid resin P of the wafer 10 and being reflected on the front surface 10a of the wafer 10 in the beam splitter 64; and a light receiver 7, which is composed of a photodetector, which receives the light L2 after passing through the bandpass filter 65 and outputs the amount of light L2 as a voltage value (mV), and the value of the amount of light detected by the light receiver 7 is transmitted to the controller 100 and stored.

[0024] The controller 100 installed in the aforementioned drying detection device 2 is a computer-based unit, comprising: a central processing unit (CPU) for performing calculations according to a control program; a read-only memory (ROM) for storing the control program, etc.; a read-write random access memory (RAM) for temporarily storing detected values, calculation results, etc.; an input interface; and an output interface (details omitted from the illustration). At least one light receiver 7 is connected to the controller 100, and the controller 100 includes a judgment unit 110 (described in detail later). The judgment unit 110 is configured according to the control program and determines whether the liquid resin P has dried based on the amount of light L2 received by the light receiver 7. Furthermore, although not illustrated, the controller 100 can also be used to control the operation of the holding unit 3, the moving mechanism 4, etc.

[0025] The drying detection apparatus 2 of this embodiment has a configuration generally as described above. The drying detection method of this embodiment implemented using the drying detection apparatus 2 will be described below. In addition, the protective film forming apparatus 20 described above can also be disposed inside the drying detection apparatus 2 shown in FIG2. In this case, liquid resin P is supplied to the front side 10a of the wafer 10 to form the protective film while the wafer 10 is held in the holding unit 3.

[0026] When implementing the drying detection method of this embodiment, a wavelength selection step is performed, which involves selecting the light absorption wavelength of the solvent of the liquid resin P supplied to the wafer 10 as a protective film. More specifically, as described above, the protective film formed on the wafer 10 in this embodiment is formed by using a liquid resin P with water as the solvent. It is known that water has the characteristic of absorbing light with wavelengths longer than 700 nm, especially light with wavelengths of 1450 nm, 1940 nm, and 2900 nm. Accordingly, in the wavelength selection step of this embodiment, any one of 1450 nm, 1940 nm, and 2900 nm, for example 1940 nm, is selected as the light absorption wavelength of the solvent, i.e., water.

[0027] Next, a light source selection step is performed, which involves selecting a light source that includes light of the wavelength (1940 nm) selected in the wavelength selection step described above. As the light source 62 in this embodiment, a QTH lamp is selected, whose irradiable light includes light of the wavelength selected in the wavelength selection step described above, namely, light of the wavelength 1940 nm. A QTH lamp is a light source that includes light of a wide range of wavelengths from 350 to 4000 nm. In the wavelength selection step described above, any wavelength among the light absorption wavelengths of 1450 nm, 1940 nm, and 2900 nm, which are particularly absorbed by water, can be used.

[0028] Next, a light receiving step is performed, in which light L0 is irradiated onto the liquid resin P and the light passing through the liquid resin P is received. More specifically, the wafer 10 is held by the holding unit 3 of the drying detection device 2, which has selected the light source 62 in the above-mentioned light source selection step, and is positioned directly below the condenser 60 of the drying detector 6.

[0029] Next, the light source 62 of the drying detector 6 is activated to illuminate the light L0, and the light L0 that has passed through the beam splitter 64 is irradiated onto the liquid resin P of the wafer 10. As shown in FIG3(b), the light L0 that has been irradiated onto the liquid resin P passes through the liquid resin P and reaches the front surface 10a of the wafer 10 and is reflected, and further becomes light L1 that has passed through the liquid resin P and reaches the beam splitter 64. The light L1 that has reached the beam splitter 64 is reflected in the beam splitter 64 and is guided to the optical path side where the light receiver 7 is provided. As mentioned above, a bandpass filter 65 is provided between the beam splitter 64 and the light receiver 7. The bandpass filter 65 of this embodiment is a filter that only allows light in the wavelength region selected by the wavelength selection step to pass through. In this embodiment, for example, it is set to allow light in the wavelength region of 1900~1980nm to pass through. The light L2 passing through the bandpass filter 65 reaches the light receiver 7. The amount Q of light L2 detected by the light receiver 7 is transmitted to the controller 100 and stored, thus completing the light receiving step. The controller 100 has a determination unit 110, which performs a determination step. This determination step determines whether the liquid resin P has dried based on the amount Q of light received by the light receiver 7 and a predetermined threshold Q2. Here, the threshold Q2 is determined in advance, for example, by the following sequence, and is stored in the controller 100.

[0030] As can be seen from the graph in Figure 4, which shows the dryness (%) of the liquid resin P on the horizontal axis and the light intensity (mV) measured by the light receiver 7 on the vertical axis, when the drying of the liquid resin P supplied to the wafer 10 is completely incomplete (0%), the light intensity received by the light receiver 7 is the lowest light intensity Q1 (e.g., 1.0mV). This is because, as mentioned above, water, as a solvent, has the characteristic of absorbing light with a wavelength of 1940nm. The 1940nm wavelength light contained in light L0 will be absorbed to the maximum extent by the solvent, i.e., water, when passing through the liquid resin P. Furthermore, when the water contained in the liquid resin P evaporates, causing the liquid resin P to dry, the 1940nm wavelength light absorbed in the liquid resin P will decrease, and the light intensity Q measured by the light receiver 7 will increase as the drying process proceeds, as shown in the figure. Furthermore, once the liquid resin P is supplied to the front side 10a of the wafer 10 for a sufficient period of time, the liquid resin P becomes completely dry (100% dryness). Light with a wavelength of 1940 nm will not be absorbed by the liquid resin P due to the water, thus the maximum light intensity Q10 (e.g., 10.0 mV) can be measured. To determine the degree of dryness of the liquid resin that will not cause obstruction during wafer 10 processing via ablation, for example, a light intensity Q9 with a dryness level lower than the aforementioned light intensity Q10 is selected as a threshold Q9 for determining that the liquid resin is sufficiently dry. This threshold Q9 is determined experimentally beforehand and stored in the controller 100.

[0031] With the threshold Q9 stored in the controller 100, the flowchart of the determination unit 110 shown in FIG5 is executed in order to perform the above-mentioned determination step. More specifically, in the above-mentioned drying detection device 2, light L0 is irradiated onto the liquid resin P on the front side 10a of the wafer 10 from the light source 62 of the drying detector 6 to make it pass through the liquid resin P, and the amount of light Q detected by the above-mentioned photodetector 7 is detected (step S1). Next, it is determined whether the amount of light Q is greater than the threshold Q9 (step S2). Here, if the amount of light Q is less than or equal to the threshold Q9 (no), since the light L0 with a wavelength of 1940nm is absorbed and becomes a low value, it is determined that there is a lot of solvent, i.e., water, in the liquid resin P and the drying of the liquid resin P is insufficient (step S3), and the process returns to step S1. In contrast, in step S2, if the light intensity Q is greater than the threshold Q9 (yes), it is determined that the solvent, i.e., water, has been sufficiently reduced from the liquid resin P and has been dried to the predetermined level, and drying is deemed complete (step S4). Thus, the drying detection method of this embodiment is completed.

[0032] As described above, if the drying of liquid resin P has been detected by the drying detection method of this embodiment, the wafer 10 can be transported to a laser processing apparatus (not shown) and laser light of a wavelength that absorbs the wafer 10 is irradiated from the front side 10a of the wafer 10 along the predetermined dividing line 14 to perform an ablation process and divide the wafer 10 into individual device chips.

[0033] According to the drying detection method and drying detection apparatus of this embodiment, the drying of the liquid resin P disposed on the wafer 10 as a protective film can be reliably determined. This allows for ablation processing of the wafer 10 by irradiating it with laser light while the liquid resin P is reliably dried. Even if a metal film such as TEG is formed on the predetermined dicing line 14, the problem of device quality degradation due to peeling caused by the ablation process can be solved. Furthermore, since it is no longer necessary to spend excessive time on drying, productivity is also improved.

[0034] In the above embodiments, although the case where the solvent of the liquid resin P is water has been described, the present invention is not limited to liquid resins with water as the solvent. For example, the solvent contained in the liquid resin may also be acetone or hexane. When the solvent is acetone, since the wavelength of light absorbed by acetone is in the range of 220 to 330 nm, a deuterium lamp that irradiates light in the range of 200 to 400 nm can be selected as the light source 62, and a bandpass filter 65 that allows only light in the range of 220 to 330 nm to pass through can be provided. In addition, since the light irradiated by the deuterium lamp is mainly composed of light in the wavelength range absorbed by acetone, the bandpass filter 65 that allows only light in the range of 220 to 330 nm to pass through can also be omitted. Furthermore, when the solvent is hexane, since the wavelength of light absorbed by hexane is 350 nm and 500 nm, a short-arc xenon lamp that irradiates light in the range of 250 to 1500 nm can be selected as the light source 62. In this case, the bandpass filter 65 of the aforementioned drying detector 6 can be set to allow only wavelengths of 340-360 nm to pass through, for example, and the amount of light Q that has passed through the liquid resin P can be detected by the photodetector 7.

[0035] In addition, if the thickness of the protective film formed by the liquid resin P or the concentration or type of solvent contained in the liquid resin P has changed, the light source 62 and the bandpass filter 65 are changed, and the threshold Q9 used in the above-mentioned judgment step is recalculated by experiment in the above-mentioned order each time and stored in the controller 100.

[0036] Furthermore, in the above embodiment, although light L0 irradiated from the front side 10a of the wafer 10 and reflected is used to receive light from the light source 62 that has passed through the liquid resin P by means of the light receiver 7, the present invention is not limited to this. For example, when the wafer 10 and the adhesive tape T are materials through which light L0 can pass, it is also possible to: after the work stand 35 holding the wafer 10 forms an opening (not shown), as shown in FIG. 6, the above-mentioned bandpass filter 65 and light receiver 7 are arranged on the side of the adhesive tape T supporting the wafer 10, and the light L2 after passing through the liquid resin P, the wafer 10 and the adhesive tape T is received by means of the light receiver 7. However, in this case, since it is envisioned that light absorption will also occur due to the wafer 10 and the adhesive tape T, the setting of the threshold Q9 becomes more difficult, so the embodiment described in FIG. 3 above is more ideal. Furthermore, although the drying detection device 2 has been described as a separate device in the above embodiments, the present invention is not limited thereto, and a laser processing device that irradiates laser light to perform ablation processing on the wafer 10 may also be installed. [Simplified Explanation of the Diagram]

[0013] Figure 1(a) is a perspective view showing the state of forming a protective film composed of liquid resin on a wafer, and (b) is a cross-sectional view showing a portion of the wafer shown in (a) magnified. Figure 2 is an overall perspective view of the drying detection apparatus of this embodiment. Figure 3(a) is a block diagram showing the optical system of the drying detector of the drying detection apparatus shown in Figure 2, and (b) is a cross-sectional view showing a portion of the wafer in the state of performing the light receiving step. Figure 4 is a graph showing the relationship between dryness and light intensity. Figure 5 is a flowchart showing the judgment step. Figure 6 is a cross-sectional view showing another embodiment of the state of performing the light receiving step.

Claims

1. A drying detection method for detecting the drying of a liquid resin containing a solvent, the drying detection method comprising the following steps: a wavelength selection step, selecting a light absorption wavelength of the solvent; a light source selection step, selecting a light source, the light source including light of the selected wavelength; a light receiving step, irradiating the liquid resin with light from the light source and receiving light that has passed through the liquid resin; and a determination step, determining that the solvent has evaporated and the liquid resin has dried when the amount of light of the wavelength absorbed by the solvent in the light receiving step exceeds a predetermined threshold, wherein the drying detection method irradiates the liquid resin in which the solvent has evaporated and has been sufficiently dried with light from the light source selected in the light source selection step, and receives light that has passed through the liquid resin to measure the amount of light, and selects a value lower than the amount of light as the threshold.

2. The drying detection method of claim 1, which is performed before the wafer coated with the liquid resin is subjected to laser ablation, wherein the determination step is to determine whether the liquid resin has reached a dry state suitable for ablation by laser light.

3. The drying test method as claimed in claim 1 or 2, wherein the liquid resin is a water-soluble resin and the solvent is water.

4. The drying detection method of claim 3, wherein the wavelength of light absorbed by water is 1450nm, 1940nm, or 2900nm, and in the light source selection step, a light source containing any of the aforementioned wavelengths is selected.

5. A drying detection apparatus comprising a drying detector for detecting the drying of a liquid resin, the drying detector comprising: a light source containing light of a wavelength absorbed by the solvent contained in the liquid resin; a light receiver receiving light irradiated from the light source and having passed through the liquid resin; and a determination unit stored in a controller, determining, based on the amount of light received by the light receiver, whether the amount of light of a wavelength absorbed by the solvent has exceeded a threshold, and determining that the liquid resin is dry, the threshold being a value below which the light intensity is measured by irradiating the liquid resin with the light source on which the solvent has evaporated and which has been sufficiently dried, and receiving the light that has passed through the liquid resin, and selecting a value below the light intensity as the threshold value.

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