Method for recycling carrier wafer

Abstract

A carrier wafer recycling method is disclosed. The disclosed carrier wafer recycling method comprises the steps of: irradiating an infrared laser beam onto the surface of an adhesive attached to a carrier wafer; spraying CO2 dry ice to remove reaction residues of the adhesive caused by the irradiation of the infrared laser beam; and removing fine residues present on the surface of the carrier wafer using an organic solvent. According to the carrier wafer recycling method of the present invention, when carrier wafers are recycled and used, expensive carrier wafers, which are currently entirely discarded due to problems in recycling quality, can be recycled, thereby significantly reducing semiconductor production costs.

Description

Carrier wafer regeneration method

[0001] The present invention relates to a method for regenerating a carrier wafer used in a semiconductor manufacturing process, and more particularly, to a technique for removing an adhesive attached to a carrier wafer using a laser beam, CO2 dry ice, an organic solvent, or the like.

[0002]

[0003] Recently, the application of 3D packaging technology, which stacks semiconductor chips using the Through Silicon Via (TSV) process, has been rapidly increasing. In particular, the production of High Bandwidth Memory (HBM) devices requires vertical stacking of DRAM chips, making the TSV process essential. This process also necessitates the use of carrier wafers.

[0004] Figure 1 is a diagram illustrating a representative example of a process in which a carrier wafer is used in a semiconductor manufacturing process. As shown in Figure 1, in order to manufacture a stackable semiconductor device, a silicon via hole is drilled in a wafer for forming a semiconductor device (hereinafter referred to as the "device wafer") and the interior is filled with copper (Cu), and then solder bumps are formed on the front surface (the upper surface in Figure 1 (a)) of the device wafer to form external contact terminals ((a)). Then, a temporary bonder is applied to the upper surface of the device wafer on which the solder bumps have been formed, and a carrier wafer is attached. Thereafter, the back surface (the lower surface in Figure 1 (b)) of the device wafer is ground to open up the via holes ((c)), and then microbumps are formed on the back surface of the device wafer through exposure, etching, and plating processes ((d)). After forming contact terminals on both the front and back surfaces of the wafer in this way, the carrier wafer is separated from the device wafer, thereby completing a stackable device wafer ((e)). At this time, expensive silicon wafers used in the production of general devices are used as carrier wafers, and these expensive silicon wafers are currently being disposed of entirely after being used in the processes (a) to (e) of Fig. 1. In order to remove the adhesive attached to these expensive silicon wafers used as carrier wafers, stripping using a strong acid (e.g., sulfuric acid) may be attempted, but if a strong acid is used, the strong acid causes damage to the silicon oxide film formed on the surface of the carrier wafer, which causes serious problems such as breakage in the middle of the process when reused after stripping.In addition, as disclosed in Korean Patent Publication No. 10-2020-0085056 (published on July 14, 2020), a chemical mechanical polishing (CMP) process is used to remove the inorganic film layer formed during the process to regenerate the carrier wafer. However, this method requires expensive CMP equipment and has the problem that it is not suitable for continued recycling of the regenerated carrier wafer unless the silicon oxide film is re-formed.

[0005] Therefore, in order to solve this problem in the regeneration of silicon wafers used as carrier wafers, an environmentally friendly adhesive removal method that does not cause any damage to the silicon oxide film is needed.

[0006]

[0007] The present invention was created to solve the above-mentioned problems, and the problem to be solved by the present invention is to provide a method for regenerating a carrier wafer, which removes adhesive attached to the surface of a separated carrier wafer in an environmentally friendly manner without damaging a silicon oxide film, by using an infrared wavelength laser beam, CO2 dry ice, and an organic solvent such as alcohol.

[0008] It should be noted that the problem to be solved by the present invention is further described in the 'Specific contents for carrying out the invention' below, and the above-mentioned purpose and various advantages of the present invention will become more apparent to those skilled in the art from the preferred embodiments of the invention described below with reference to the attached drawings.

[0009]

[0010] A method for regenerating a carrier wafer according to one aspect of the present invention for solving the above problem comprises the steps of (a) irradiating an infrared laser beam onto the surface of an adhesive attached to a carrier wafer, (b) spraying CO2 dry ice to remove a reaction residue of the adhesive caused by the irradiation of the infrared laser beam, and (c) removing a fine residue present on the surface of the carrier wafer using an organic solvent.

[0011] According to one embodiment, the infrared laser beam may be an infrared laser beam having a wavelength of 9,000 nm to 11,000 nm and an output of 100 W to 500 W.

[0012] According to one embodiment, the CO2 dry ice may be CO2 dry ice having an injection pressure of 3 bar to 6 bar and a particle size of 100 um to 500 um.

[0013] In one embodiment, the organic solvent may be alcohol or acetone.

[0014] According to one embodiment, the carrier wafer regeneration method may further include a step of performing a heat treatment deposition process to strengthen the silicon oxide film of the carrier wafer after the end of step (c).

[0015] According to one embodiment, the carrier wafer regeneration method may further include a step of checking for fine foreign matter remaining on the surface of the carrier wafer using a surface scanner using a microscope or a laser after the end of step (c), and, if it is confirmed that fine foreign matter remains on the surface of the carrier wafer, a step of locally spraying CO2 dry ice on the area where the fine foreign matter exists to perform a local cleaning operation.

[0016]

[0017] The carrier wafer regeneration method according to the present invention can significantly reduce semiconductor production costs by recycling expensive carrier wafers, which are currently being discarded entirely due to quality issues. Furthermore, by regenerating and reusing carrier wafers in an environmentally friendly manner, it offers the environmental benefit of resource recycling and a dramatic reduction in the incidental costs associated with disposal.

[0018]

[0019] Figure 1 is a drawing showing a representative example of a process in which a carrier wafer is used in a semiconductor manufacturing process.

[0020] Figure 2 is a schematic diagram of a carrier wafer regeneration method according to one embodiment of the present invention.

[0021] FIG. 3 is a sample photograph of a carrier wafer at each step of a method for regenerating a carrier wafer according to one embodiment of the present invention.

[0022] Figure 4 is a flowchart of a carrier wafer regeneration method according to another embodiment of the present invention.

[0023] Figure 5 is a flowchart of a carrier wafer regeneration method according to another embodiment of the present invention.

[0024]

[0025] Hereinafter, preferred embodiments of the present invention will be described with reference to the attached drawings. It should be noted that the attached drawings and examples are simplified and illustrative, intended to assist those skilled in the art in understanding the present invention.

[0026] Figure 2 is a schematic diagram of a carrier wafer regeneration method according to one embodiment of the present invention.

[0027] Referring to Fig. 2, as shown in (a), in the first step, a laser beam is irradiated onto the surface of an adhesive (15) attached to the surface of a carrier wafer (10) using a laser beam irradiation device. For convenience, only a focusing lens and a laser beam are briefly illustrated in the drawing. As mentioned above, the carrier wafer (10) is a wafer used as a carrier in the TSV process and refers to a wafer to be regenerated. For convenience, this is hereinafter abbreviated as a carrier wafer. A silicone resin having a similar coefficient of thermal expansion to that of the carrier wafer (10) is commonly used as an adhesive. In order to effectively remove only the adhesive (15), it is necessary to irradiate a laser beam in a wavelength range in which little reaction occurs between the lower silicon oxide film on the surface of the carrier wafer (10) under the adhesive (15) and the silicon base material and the laser, but which effectively reacts with a polymer such as a silicone resin. Only then can the carrier wafer (10) be regenerated by selectively removing only the adhesive (15) without damaging the carrier wafer (10). For this purpose, the wavelength of the laser beam is preferably in the infrared range. In particular, lasers with wavelengths in the 9,000 nm to 11,000 nm range are effective. A representative example of a usable laser is the CO2 laser. The CO2 laser is a representative example of a gas laser that oscillates in the infrared region by obtaining density inversion between the vibrational levels of carbon dioxide (CO2) in a gaseous state.

[0028] At this time, the output of the laser beam is preferably 100 W to 500 W. If the output is less than this range, the cleaning speed will be slow, resulting in low productivity. On the other hand, if the output is greater than this range, the possibility of damage to the carrier wafer will increase. Therefore, it is important to use a laser beam having a wavelength and output within the appropriate range as described above, and to uniformly scan the entire surface of the carrier wafer (10) where the adhesive (15) is present during scanning.

[0029] For this type of full-face scanning, the carrier wafer (10) may be fixed using a fixing means and the laser beam may be scanned in the XY axes. Alternatively, in order to perform continuous cleaning inline, the carrier wafer (10) may be continuously moved in the X-axis direction and the laser beam may be moved in the Y-axis direction. In addition to these methods, the method may be performed in various other ways.

[0030] As shown in (b) in Fig. 2, after irradiating a laser beam on a carrier wafer (10), CO2 dry ice is sprayed in the second step. After the laser treatment in the first step, residues that have reacted with the laser exist on the surface of the carrier wafer (10). These residues that have reacted with the laser usually exist in an ash state, and in order to remove these ash-state residues, a separate physical method must be used, and this step is the second step. To remove the residues, a cleaning process is performed by accelerating CO2 dry ice in clean dry air (CDA) or nitrogen. Since dry ice has a Mohs hardness of about 2, which is much softer than the Mohs hardness of the wafer (generally 6), it can physically remove residues on the surface without damaging the silicon oxide film or silicon base material. The CO2 dry ice spraying pressure used at this time is preferably 3 to 6 bar. If it is smaller than this range, the cleaning power is reduced, and if it is larger than this range, there is a possibility that the carrier wafer (10) may be damaged by vibration.

[0031] In addition, it is preferable that the particle size of the CO2 dry ice used in step 2 be 100 um to 500 um. In addition, it is very important to uniformly scan the entire area of ​​the carrier wafer (10) using the CO2 dry ice spray nozzle. For this purpose, an XY-axis automatic stage can be used. Since the carrier wafer (10) may vibrate during the cleaning operation using the CO2 dry ice nozzle, it is important to firmly fix the carrier wafer (10) using a vacuum chuck from the bottom. In addition, by installing the CO2 dry ice spray nozzle together with the laser beam irradiation device used in step 1, the CO2 dry ice cleaning can be performed immediately after the laser beam irradiation, thereby efficiently using the work space and shortening the work time.

[0032] As shown in (c) in Fig. 2, after the second step of CO2 dry ice cleaning, the third step is performed using an organic solvent. That is, after the CO2 dry ice cleaning, fine residues such as stains may exist on the surface of the carrier wafer (10). At this time, a final cleaning operation is performed by applying an organic solvent such as alcohol or acetone to a clean room wiper or pad. When performing the cleaning operation using a clean room wiper or pad, it is important to use an appropriate amount of solvent because if too much solvent is applied, stains caused by the solvent may occur. In addition, care must be taken because if the applied pressure is too high, scratches may occur on the carrier wafer.

[0033] Finally, as shown in (d) in Fig. 2, after the final cleaning operation using a cleanroom wiper or pad and an organic solvent in Step 3, a final surface inspection is performed as Step 4. That is, in Step 4, a microscope or a surface scanner using a laser is used to check whether fine foreign matter such as particles remains on the surface of the carrier wafer. If it is confirmed that fine foreign matter remains on the surface of the carrier wafer, an additional local cleaning operation is performed using a CO2 dry ice cleaner. This will be further described below with reference to Fig. 5. In the process of checking for remaining fine foreign matter, it is important to closely inspect the edges and side surfaces of the carrier wafer for foreign matter and damage, in particular.

[0034] FIG. 3 is a sample photograph of a carrier wafer at each step of a method for regenerating a carrier wafer according to one embodiment of the present invention.

[0035] Referring to FIG. 3, the photo shown in (a) is a photo of a state in which an adhesive is attached to the surface of a carrier wafer, that is, a photo immediately before the regeneration process of the carrier wafer, the photo shown in (b) is a photo showing the appearance of the surface of the carrier wafer after laser beam irradiation in the first step, the photo shown in (c) is a photo showing the appearance of the surface of the carrier wafer after CO2 dry ice spraying in the second step, and the photo shown in (d) is a photo showing the appearance of the wafer surface after cleaning is completed after organic solvent treatment in the third step. In this way, it can be confirmed that the adhesive present on the surface of the carrier wafer is removed effectively and environmentally friendly through the three-step process of the carrier wafer regeneration method according to one embodiment of the present invention, and the original silicon oxide film is clearly revealed (i.e., compare the photo of (a) before regeneration with the photo of (d) after regeneration).

[0036] Meanwhile, if the carrier wafer that has been regenerated in this way is continuously used, the possibility of wear and damage to the silicon oxide film on the surface increases. Therefore, to compensate for this, a process of additionally forming a silicon oxide film through a heat treatment deposition process after the carrier wafer adhesive removal process may be performed. For example, by periodically forming an additional silicon oxide film on the regenerated carrier wafer using low-pressure chemical vapor deposition (LPCVD), the number of times the carrier wafer can be regenerated can be significantly increased. This will be described with reference to FIG. 4 below.

[0037] Figure 4 is a flowchart of a carrier wafer regeneration method according to another embodiment of the present invention.

[0038] Referring to FIG. 4, a carrier wafer regeneration method according to another embodiment of the present invention includes a step (S11) of irradiating an infrared laser beam onto a surface of an adhesive attached to a carrier wafer, a step (S12) of spraying CO2 dry ice to remove a reaction residue of the adhesive caused by the irradiation of the infrared laser beam, a step (S13) of removing a fine residue existing on the surface of the carrier wafer using an organic solvent, and a step (S14) of performing a heat treatment deposition process (e.g., LPCVD) to strengthen a silicon oxide film of the carrier wafer. By doing so, the number of times the carrier wafer can be regenerated can be greatly increased.

[0039] Finally, FIG. 5 is a flowchart of a carrier wafer regeneration method according to another embodiment of the present invention.

[0040] Referring to FIG. 5, a carrier wafer regeneration method according to another embodiment of the present invention may further include a step of irradiating an infrared laser beam on the surface of an adhesive attached on a carrier wafer (S21), a step of spraying CO2 dry ice to remove a reaction residue of the adhesive caused by the irradiation of the infrared laser beam (S22), a step of removing fine residue existing on the surface of the carrier wafer using an organic solvent (S23), a step of checking fine foreign substances remaining on the surface of the carrier wafer using a microscope or a surface scanner (S24), and a step of locally spraying CO2 dry ice on the relevant portion to perform a local cleaning operation if fine foreign substances remain on the surface of the carrier wafer (S25).

[0041] As described above, when carrier wafers are reclaimed and used using the carrier wafer regeneration method according to the present invention, expensive carrier wafers, which are currently being discarded entirely due to quality issues, can be recycled, significantly reducing semiconductor production costs. Furthermore, by regenerating and reusing carrier wafers in an environmentally friendly manner, it is expected that the environmental benefits of resource recycling and the incidental costs incurred due to carrier wafer disposal will be dramatically reduced.

[0042] It should be noted that the above description is merely an example of a preferred embodiment of the present invention, and therefore, a person skilled in the art may make modifications and changes to the present invention without changing the gist of the present invention, and the scope of the present invention is defined by the claims below.

Claims

1. As a method for regenerating a carrier wafer, (a) A step of irradiating an infrared laser beam onto the surface of an adhesive attached to a carrier wafer; (b) a step of spraying CO2 dry ice to remove the reaction residue of the adhesive caused by irradiation with the infrared laser beam; and (c) A method for regenerating a carrier wafer, characterized in that it comprises a step of removing fine residues present on the surface of the carrier wafer using an organic solvent.

2. In claim 1, A method for regenerating a carrier wafer, characterized in that the infrared laser beam has a wavelength of 9,000 nm to 11,000 nm and an output of 100 W to 500 W.

3. In claim 1, A method for regenerating a carrier wafer, characterized in that the above CO2 dry ice has an injection pressure of 3 bar to 6 bar and a particle size of 100 um to 500 um.

4. In claim 1, A method for regenerating a carrier wafer, characterized in that the organic solvent is alcohol or acetone.

5. In claim 1, A method for regenerating a carrier wafer, characterized in that it further includes a step of performing a heat treatment deposition process to strengthen the silicon oxide film of the carrier wafer after the end of the above step (c).

6. In claim 1, A step of checking for fine foreign matter remaining on the surface of the carrier wafer using a microscope or a surface scanner using a laser after the end of the above step (c); and A method for regenerating a carrier wafer, characterized in that it further includes a step of locally spraying CO2 dry ice on the area where the fine foreign matter exists to perform a local cleaning operation when it is confirmed that fine foreign matter remains on the surface of the carrier wafer.

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