TWI863492B - A METHOD FOR REMOVING CARBON PRECIPITATION FROM SURFACE OF SiC WAFER - Google Patents

Abstract

A method for removing carbon precipitated from the surface of a SiC wafer includes the following steps. First, a SiC wafer is provided, wherein the SiC wafer isbonded to a carrier plate. The surface of the SiC wafer is coated to form a metal film. An annealing process is performed on the metal film to precipitate carbon and the precipitate carbon is accumulated on the surface of the metal film. Plasma is introduced to the surface of the metal film, and a plasma cleaning is performed on the surface of the metal film to remove the precipitated carbon.

Description

A method for removing carbon precipitation from the surface of SiC wafer

The present invention relates to wafer cleaning, and in particular to a non-contact wafer surface particle removal device for removing carbon particles precipitated on the surface of SiC wafers.

As shown in Figure 1, this is the existing BGBM process (Backside Grinding & Backside Metallization). As shown in part (A) of Figure 1, the SiC wafer 1 is first temporarily bonded or bonded to the carrier 2 with the front side (the downward part in the figure) to increase the mechanical strength of the SiC wafer 1 and prevent the SiC wafer 1 from warping or breaking during the grinding process. The back side of the SiC wafer 1 (the upward part in the figure) will be plated to form a metal film 3, as shown in part (B) of Figure 1. Then, a laser annealing process is performed on the metal film 3. The annealing process causes a chemical reaction between the silicon atoms in the SiC wafer 1 and the nickel atoms in the metal film 3 to form nickel silicide to form an ohmic contact structure, as shown in part (C) of Figure 1.

Finally, a metal layer is grown on the metal film 3 to form a back metal layer 4, as shown in part (D) of Figure 1, and the BGBM process is completed.

However, referring to parts (C) and (D) in Figure 1, the formation of nickel silicide will cause carbon particles 5 in SiC to precipitate and gradually accumulate on the surface of the metal film 3. After the back metal layer 4 is formed. The presence of carbon particles 5 weakens the bond between the back metal layer 4 and the metal film 3. Therefore, in the subsequent processing procedure, the back metal layer 4 is easily peeled off from the surface of the metal film 3, resulting in defective products, as shown in part (E) of Figure 1.

In view of the above technical problems, the present invention proposes a method for removing carbon precipitation on the surface of SiC wafers, which is used to clean the surface of SiC wafers, avoid carbon precipitation or other unnecessary compounds remaining on the surface of SiC wafers, and avoid the back metal layer from being stressed and falling off during subsequent processing.

The present invention proposes a method for removing carbon deposited on the surface of a SiC wafer, which is used to remove carbon deposited on the surface of a SiC wafer, and includes the following steps. First, a SiC wafer is provided; wherein the SiC wafer is bonded to a carrier. The surface of the SiC wafer is plated to form a metal film. An annealing process is performed on the metal film to cause carbon to precipitate and accumulate on the surface of the metal film. Plasma is introduced into the surface of the metal film, and the surface of the metal film is cleaned with plasma to remove the deposited carbon.

In at least one embodiment, the material of the metal film is nickel, titanium or aluminum.

In at least one embodiment, the annealing process is a laser annealing process.

In at least one embodiment, the method for removing carbon deposits on the surface of a SiC wafer further includes growing a metal layer on the metal film after removing the deposited carbon to form a back metal layer.

In at least one embodiment, the material of the back metal layer is titanium (Ti), nickel-vanadium alloy (NiV) or gold (Ag).

In at least one embodiment, the step of introducing plasma into the surface of the metal film includes generating a remote plasma with an inductively coupled plasma generating device and generating a near-end plasma with a capacitively coupled plasma generating device.

In at least one embodiment, the step of introducing plasma into the surface of the metal film includes simultaneously generating a distal plasma and a proximal plasma.

In at least one embodiment, the step of introducing plasma to the surface of the metal film includes first generating a proximal plasma and then generating a distal plasma.

In at least one embodiment, the method for removing carbon deposition on the surface of a SiC wafer further includes introducing a chemical working gas to chemically clean the surface of the metal film.

In view of the above technical problems, this novel invention proposes a non-contact wafer surface particle removal device for cleaning the SiC wafer surface to prevent carbon precipitation or other unnecessary compounds from remaining on the SiC wafer surface, and to prevent the back metal layer from being detached due to stress during subsequent processing.

The present invention proposes a non-contact wafer surface particle removal device for removing particles from the surface of a wafer to be cleaned, comprising a reaction chamber, a plasma chamber, an induction coil and a bias generating device. The reaction chamber has a containing space for containing the wafer to be cleaned. The plasma chamber is coupled to a top of the reaction chamber; the interior of the plasma chamber has a remote plasma space connected to the containing space. The induction coil surrounds the plasma chamber to provide a time-varying magnetic flux to the remote plasma space to induce an electric field, so that a working gas in the remote plasma space is ionized to generate a remote plasma. The bias generating device is used to generate a bias electric field that varies with time in the reaction chamber, so that the working gas in the reaction chamber is ionized into a proximal plasma.

In at least one embodiment, a working gas channel is opened at a top of the reaction chamber, and the bottom of the remote plasma space is connected to the working gas channel, so that the accommodating space is connected to the remote plasma space.

In at least one embodiment, the non-contact wafer surface particle removal device further includes a spray head that shields the working gas channel, and the spray head has a plurality of holes that connect the remote plasma space and the accommodating space.

In at least one embodiment, the bias generating device includes two bias electrodes and a radio frequency current source. The two bias electrodes are disposed in the reaction chamber. The radio frequency current source is connected to the two bias electrodes to provide radio frequency current so that the two bias electrodes generate a bias electric field.

In at least one embodiment, the non-contact wafer surface particle removal device further includes a carrier plate, which is accommodated in the accommodating space; the carrier plate faces the top of the reaction chamber, and the carrier plate is used to carry the wafer to be cleaned; a proximal plasma space is defined between the top of the reaction chamber and the carrier plate, and the bias generating device generates a bias electric field in the proximal plasma space.

In at least one embodiment, the non-contact wafer surface particle removal device further includes a first air inlet pipe, which is disposed in the plasma chamber and connected to the remote plasma space. The first air inlet pipe is used to receive the working gas and pass it into the remote plasma space.

In at least one embodiment, the non-contact wafer surface particle removal device further includes a vacuum pump connected to the accommodating space for evacuating the accommodating space.

In at least one embodiment, the non-contact wafer surface particle removal device further includes a second air inlet pipe connected to the plasma chamber or the reaction chamber for receiving a chemical reaction gas.

In at least one embodiment, the inner wall of the plasma chamber has a concave mixing zone, and the first air inlet pipe and the second air inlet pipe are connected to the mixing zone.

In at least one embodiment, the induction coil and the bias generating device are activated simultaneously; or the bias generating device is activated first and the induction coil is activated later.

The present invention fully removes carbon particles on the surface of the wafer before growing the back metal layer. Therefore, the back metal layer and the metal film can be more firmly bonded and are less likely to peel off when subjected to stress, thereby improving the yield rate of semiconductor device manufacturing.

1:SiC wafer

2: Carrier board

3:Metal film

4: Back metal layer

5: Carbon particles

100: Non-contact wafer surface particle removal device

110: Reaction chamber

110a: Storage space

110b: Proximal plasma space

110c: Exhaust port

111: Top

112: Working gas channel

120: Carrier plate

130: Plasma chamber

132: Mixed Zone

130a: Remote plasma space

140: Induction coil

150: Bias generating device

151: Bias electrode

152:RF current source

161: First intake pipe

162: Second intake pipe

170: Vacuum pump

180:Sprinkler head

210:SiC wafer

210a: Wafer to be cleaned

220: Carrier board

230:Metal film

240: Carbon particles

250: Back metal layer

P1: Remote Plasma

P2: Proximal plasma

S110~S150: Steps

Figure 1 is a schematic cross-sectional view of a SiC wafer in the prior art, revealing the BGBM process.

Figure 2 is a cross-sectional schematic diagram of a non-contact wafer surface particle removal device in an embodiment of the present invention.

FIG3 is a schematic cross-sectional view of a SiC wafer in an embodiment of the present invention, revealing the BGBM process.

Figure 4 is a flow chart of a method for removing carbon deposits from the surface of a SiC wafer in an embodiment of the present invention.

FIG5 is a cross-sectional schematic diagram of a non-contact wafer surface particle removal device in an embodiment of the present invention, revealing the plasma cleaning process.

Figure 6 is a flow chart of another method for removing carbon deposits from the surface of SiC wafers in an embodiment of the present invention.

Figures 7 and 8 are cross-sectional schematic diagrams of a non-contact wafer surface particle removal device in an embodiment of the present invention, revealing the plasma cleaning process.

Figure 9 is a flow chart of another method for removing carbon deposits from the surface of SiC wafers in an embodiment of the present invention.

Please refer to FIG. 2 and FIG. 3, which are a non-contact wafer surface particle removal device 100 disclosed in an embodiment of the present invention, which is applied to a method for removing carbon deposition on the surface of a SiC wafer.

As shown in FIG. 2 and FIG. 3 , the non-contact wafer surface particle removal device 100 and the method for removing carbon precipitation on the surface of the SiC wafer 210 are used to treat the carbon particles precipitated in the SiC wafer 210 due to the annealing process, which causes the subsequent metal film layer to be difficult to bond and fall off.

As shown in FIG. 3 and FIG. 4 , a SiC wafer 210 is provided, as shown in step S110 and part (A) of FIG. 3 . Generally speaking, the SiC wafer 210 is first temporarily bonded to a carrier 220 by bonding or bonding on the front side (the downward facing part in the figure), so as to utilize the carrier 220 to enhance the mechanical strength of the SiC wafer 210 and prevent the SiC wafer 210 from warping, deforming or breaking due to stress during the grinding, thinning and polishing process.

As shown in FIG3 and FIG4, a coating device such as a sputtering device is used to coat the back side (the upward portion in the figure) of the SiC wafer 210 to form a metal film 230, as shown in step S120 and part (B) of FIG3. The material of the metal film 230 may be but is not limited to nickel, titanium alloy or aluminum, preferably nickel.

As shown in FIG. 3 and FIG. 4, the metal film 230 is then subjected to an annealing process to cause the carbon particles 240 to precipitate and accumulate on the surface of the metal film 230, as shown in step S130 and part (C) of FIG. 3. The annealing process can use a laser annealing process to quickly heat the shallow layer of the metal film 230 to achieve a shallow annealing effect and avoid overheating the SiC wafer 210. The annealing process causes a chemical reaction between silicon atoms and nickel atoms to form nickel silicide to form an ohmic contact structure. As shown in part (C) of FIG. 3, the formation of the aforementioned nickel silicide will cause the carbon particles 240 in the SiC to precipitate and gradually accumulate on the surface of the metal film 230.

As shown in FIG3 and FIG4, plasma is introduced to the surface of the metal film 230, and the surface of the metal film 230 is cleaned by plasma to remove the precipitated carbon particles 240, as shown in step S140 and part (D) of FIG3.

As shown in FIG. 3 and FIG. 4 , finally, a metal layer is grown on the metal film 230 to form a back metal layer 250, as shown in step S150 and part (E) of FIG. 3 , the BGBM process (Backside Grinding & Backside Metallization) is completed. The aforementioned metal layer growth may be but is not limited to metal sputtering deposition or metal evaporation deposition. The material of the back metal layer 250 may be but is not limited to titanium (Ti), nickel-vanadium alloy (NiV) or gold (Ag).

As shown in FIG. 2 , plasma is introduced into the surface of the metal film 230 , and the surface of the metal film 230 is cleaned by plasma, which can be performed by the non-contact wafer surface particle removal device 100 .

As shown in FIG. 2 , the non-contact wafer surface particle removal device 100 has a reaction chamber 110 , a supporting plate 120 , a plasma chamber 130 , an induction coil 140 , and a bias generating device 150 .

As shown in FIG. 2 , the reaction chamber 110 has a containing space 110a. The containing space 110a is used to contain a carrier plate 120, and the carrier plate 120 faces a top 111 of the reaction chamber 110. The carrier plate 120 is used to carry a wafer 210a to be cleaned, wherein the wafer 210a to be cleaned is a SiC wafer 210 temporarily bonded or bonded to a carrier plate 220, and the carrier plate 220 faces the carrier plate 120 and the SiC wafer 210 faces the top 111.

As shown in FIG. 2 , a working gas channel 112 is opened at the top 111 of the reaction chamber 110. The plasma chamber 130 is coupled to the top 111 of the reaction chamber 110 and covers the working gas channel 112. The plasma chamber 130 has a remote plasma space 130a inside, and the bottom of the remote plasma space 130a is connected to the working gas channel 112, so that the accommodating space 110a is connected to the remote plasma space 130a. The remote plasma space 130a is used to allow a working gas, such as nitrogen (N2), oxygen (O2) or argon (Ar), to be introduced and enter the accommodating space 110a through the working gas channel 112.

As shown in FIG. 2 , the induction coil 140 surrounds the plasma chamber 130 to provide a time-varying magnetic flux to the remote plasma space 130a to induce an electric field, so that the working gas in the remote plasma space 130a is ionized to generate a plasma beam and moves toward the accommodating space 110a. The working gas can enter the remote plasma space 130a through a first air inlet pipe 161. The remote plasma space 130a is used for the working gas to flow, and enter the accommodating space 110a through the working gas channel 112. At the same time, the working gas in the remote plasma space 130a is ionized by the electric field to generate remote plasma P1, which is released to the accommodating space 110a through the working gas channel 112. Specifically, the plasma chamber 130 and the inductive coil 140 form an inductively coupled plasma generating device (ICP).

As shown in FIG. 2 , the non-contact wafer surface particle removal device 100 further includes a spray head 180 to shield the working gas channel 112. The spray head 180 has a plurality of holes, which connect the remote plasma space 130a with the accommodating space 110a and/or the proximal plasma space 110b, so that the proximal plasma P1 is more evenly distributed.

As shown in FIG. 2 , the bias generating device 150 is used to generate a bias electric field that varies with time in the accommodation space 110a of the reaction chamber 110, so that the working gas in the accommodation space 110a is ionized into a proximal plasma P2. In particular, a proximal plasma space 110b is defined between the top 111 of the reaction chamber 110 and the supporting plate 120. The bias generating device 150 generates a bias electric field in the proximal plasma space 110b (the space between the top 111 and the supporting plate 120) of the reaction chamber 110, so that the working gas in the proximal plasma space 110b is ionized into the proximal plasma P2.

As shown in FIG2 , specifically, the bias generating device 150 includes two bias electrodes 151 and an RF current source 152. The two bias electrodes 151 are disposed in the reaction chamber 110, and the proximal plasma space 110b is located between the two bias electrodes 151. The RF current source 152 is connected to the two bias electrodes 151 to provide an RF current to the two bias electrodes 151, thereby generating a bias electric field that varies with time in the accommodating space 110a or the proximal plasma space 110b, so that the working gas in the accommodating space 110a or the proximal plasma space 110b is ionized into the proximal plasma P2. The two bias electrodes 151 can be electrical contacts, connected to the top 111 and the support plate 120 respectively; the two bias electrodes 151 can also be plate-shaped structures, combined with the top 111 and the support plate 120 respectively, or independently configured and located on both sides of the proximal plasma space 110b. Specifically, the bias generating device 150 is a capacitive coupled plasma generating device (CCP).

In addition, the reaction chamber 110 also has an exhaust port 110c, which is located below the carrier plate 120. The exhaust port 110c is connected to a vacuum pump 170. The vacuum pump 170 is used to continuously exhaust the accommodating space 110a, generating a gas flow that continuously flows from the top 111 of the reaction chamber 110 to the bottom 112 of the reaction chamber 110, and passes through the surface of the carrier plate 120, so that the far-end plasma P1 and the near-end plasma P2 can continuously act on the surface of the wafer 210a to be cleaned, perform plasma cleaning on the surface of the wafer 210a to be cleaned, and remove the precipitated carbon particles 240.

As shown in FIG. 2 , in addition, the non-contact wafer surface particle removal device 100 may be further provided with a second air inlet pipe 162, and the second air inlet pipe 162 is connected to the plasma chamber 130 or the reaction chamber 110. Preferably, the second air inlet pipe 162 is connected to the plasma chamber 130, and the inner wall of the plasma chamber 130 has a concave mixing zone 132, and the second air inlet pipe 162 is connected to the mixing zone 132. The first air inlet pipe 161 is also connected to the mixing zone 132. The second air inlet pipe 162 is used to be connected to a chemical reaction gas source, and is used to receive a chemical reaction gas, so as to directly or indirectly pass into the accommodating space 110a through the plasma chamber 130. The chemical reaction gas source can be a fluoride such as CF4 or SF6, which is used to perform chemical reaction cleaning on the metal film 230 of the wafer 210a to be cleaned, so as to more fully remove the precipitated carbon particles and other unnecessary compounds. The aforementioned mixing zone 132 allows the working gas and the chemical reaction gas to be fully mixed first, and then evenly dispersed in the plasma chamber 130 before being introduced into the reaction chamber 110, so as to avoid uneven distribution of the working gas and the chemical reaction gas.

Based on the non-contact wafer surface particle removal device 100, the step of plasma cleaning the surface of the metal film 230 can be divided into two modes.

As shown in Figures 5 and 6, the first mode is that the induction coil 140 and the bias generating device 150 act simultaneously to generate the remote plasma P1 and the near plasma P2 to act on the surface of the wafer 210a to be cleaned at the same time to perform plasma cleaning, as shown in steps S141 and S142. The remote plasma P1 generated by the induction coil 140 has good uniformity, but its charge is reduced and the cleaning ability is weak. The near plasma P2 provided by the bias generating device 150 has a large charge and has better cleaning ability, but poor uniformity. Therefore, the remote plasma P1 and the near plasma P2 are used for cleaning at the same time to ensure that the surface of the wafer is cleaned uniformly.

As shown in Figures 7, 8 and 9, the second mode is segmented cleaning, first using the proximal plasma P2 provided by the bias generating device 150 for better cleaning, as shown in step S143. Then, the remote plasma P1 generated by the induction coil 140 is used for cleaning, as shown in step S144. The remote plasma P1 generated by the induction coil 140 has lower charge damage to the wafer and better uniformity, which can modify the surface of the wafer so that the subsequent deposition and coating materials have better adhesion on the wafer surface.

The present invention fully removes the carbon particles on the surface of the SiC wafer before growing the back metal layer 250. Therefore, the back metal layer 250 and the metal film 230 can be more firmly bonded and are not easily peeled off when subjected to stress, thereby improving the yield rate of semiconductor device manufacturing.

210:SiC wafer

220: Carrier board

230:Metal film

240: Carbon particles

250: Back metal layer

Claims (9)

A method for removing carbon deposited on the surface of a SiC wafer, for removing carbon deposited on the surface of a SiC wafer, comprises: providing a SiC wafer; wherein the SiC wafer is bonded to a carrier; coating the surface of the SiC wafer to form a metal film; performing an annealing process on the metal film to cause carbon to precipitate and accumulate on the surface of the metal film; introducing plasma to the surface of the metal film, performing plasma cleaning on the surface of the metal film, and removing the deposited carbon. A method for removing carbon deposition on the surface of a SiC wafer as described in claim 1, wherein the material of the metal film is nickel, titanium or aluminum. A method for removing carbon deposition on the surface of a SiC wafer as described in claim 1, wherein the annealing process is a laser annealing process. The method for removing carbon deposition on the surface of a SiC wafer as described in claim 1 further includes growing a metal layer on the metal film after removing the deposited carbon to form a back metal layer. A method for removing carbon deposition on the surface of a SiC wafer as described in claim 4, wherein the material of the back metal layer is titanium (Ti), nickel-vanadium alloy (NiV) or gold (Ag). The method for removing carbon deposition on the surface of SiC wafer as described in claim 1, wherein the step of introducing plasma into the surface of the metal film comprises generating a remote plasma with an inductively coupled plasma generating device and generating a near-end plasma with a capacitively coupled plasma generating device. A method for removing carbon deposition from the surface of a SiC wafer as described in claim 6, wherein the step of introducing plasma into the surface of the metal film includes simultaneously generating the distal plasma and the proximal plasma. The method for removing carbon deposition on the surface of a SiC wafer as described in claim 6, wherein the step of introducing plasma into the surface of the metal film comprises first generating the proximal plasma and then generating the distal plasma. The method for removing carbon deposition on the surface of SiC wafer as described in claim 1 further includes introducing a chemical working gas to perform chemical reaction cleaning on the surface of the metal film.

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