TWI881455B - Method for bonding foreign materials to the back of wafer substrate - Google Patents

Abstract

A method for bonding a foreign material to the back side of a wafer substrate comprises the following steps: providing a wafer substrate; bonding a glass carrier above a plurality of bare dies on the front side of the wafer substrate, wherein a frame cut line is provided between the bare dies; grinding the back side of the wafer substrate; flipping the wafer substrate to face the back side upward; sputtering a seed layer on the back side; forming a thick metal layer on the seed layer. The thick metal layer has a plurality of metal blocks, and a back cut line is provided between the metal blocks; flipping the wafer substrate to face the front side upward; bonding a connection layer and an auxiliary substrate below the thick metal; and curing the connection layer to form a cured connection layer. When curing the connection layer, the moisture or organic solvents generated during baking and curing can be released through the back cutting path, avoiding the risk of explosion caused by pressure generated by the moisture or organic solvents generated during baking.

Description

Method for bonding foreign materials to the back of wafer substrate

The present invention relates to a method for bonding heterogeneous materials, and in particular to a method for bonding heterogeneous materials to the back side of a wafer substrate.

Integrated circuit (IC) chips are the core components of various electronic products, and IC chips are made through semiconductor processes. The semiconductor process forms multiple ICs on the front side of a wafer substrate, and these ICs are also called bare chips (die). After the bare chips on the wafer substrate are processed, they need to be cut by a cutting knife on the cutting path on the wafer substrate where the bare chips are not set, and the bare chips are cut into independent bare chips, and then sent to be packaged into IC chips.

However, in addition to forming the bare die on the front side of the wafer substrate, the existing semiconductor process also forms a metal layer on the back side of the wafer substrate to increase the conductivity or heat dissipation efficiency. A heterogeneous material substrate is also bonded to the metal layer on the back side of the wafer substrate through a connection layer. The connection layer used to bond the heterogeneous material substrate needs to be cured by baking to provide a stronger adhesion to prevent the heterogeneous material substrate from falling off. However, during the baking process, water vapor or organic solvents in the connection layer are easily generated, and the generated water vapor or precipitated organic solvents have no space to escape, which can easily cause the wafer substrate or the heterogeneous material substrate to burst, thereby resulting in a low process yield.

In view of the above problems, the present invention provides a method for bonding a foreign material to the back of a wafer substrate, which can improve the risk of substrate explosion caused by water vapor or precipitated organic solvents during baking when bonding a substrate with foreign materials.

The method for manufacturing the backside structure of a wafer substrate of the present invention comprises the following steps: providing a wafer substrate; wherein a front side of the wafer substrate faces upward, and a plurality of bare dies are formed on the front side, and a front side cutting line is respectively provided between the bare dies; bonding a glass carrier above the bare dies; grinding a back side of the wafer substrate; turning the wafer substrate so that the back side faces upward; sputtering a seed layer on the back side of the wafer substrate; forming a thick metal layer on the back side of the wafer substrate; wherein the thick metal layer has a plurality of thick metal blocks, and a back side cutting line is provided between the thick metal blocks; turning the wafer substrate so that the front side faces upward; attaching a connection layer and an auxiliary substrate below the thick metal layer; curing the connection layer to form a cured connection layer.

Based on the above, in the method of laminating heterogeneous materials on the back of the wafer substrate of the present invention, since the thick metal layer formed on the back of the wafer substrate has the back cutting path, when the connection layer is cured, the water vapor generated during baking or the organic solvent precipitated in the connection layer can be dispersed through the back cutting path, thereby avoiding the risk of explosion caused by the pressure generated by the water vapor or the precipitated organic solvent during baking, so as to improve the process yield.

S11~S19: Steps

S201~S215: Steps

100: Wafer substrate

101: Front cutting path

102: Back cutting path

110: Front

111: Bare crystal

112: Glass carrier

120: Back

121: Seed layer

122: Photoresist layer

122’: Photoresist

123: Thick metal layer

123’: Thick metal block

124: Connection layer

124’: Curing connection layer

125: Auxiliary substrate

126: Cutting tape

S501~S513: Steps

Figure 1 is a schematic diagram of the process of manufacturing a wafer substrate backside structure according to an embodiment of the present invention.

Figures 2A and 2B are schematic diagrams of the process of manufacturing a backside structure of a wafer substrate according to another embodiment of the present invention.

Figures 3A to 3O are schematic diagrams of the process of manufacturing a backside structure of a wafer substrate according to another embodiment of the present invention.

Figure 4 is a schematic plan view of the back surface structure of a wafer substrate according to an embodiment of the present invention.

Figures 5A and 5B are schematic diagrams of the process of manufacturing a backside structure of a wafer substrate according to another embodiment of the present invention.

Please refer to Figure 1. The present invention is a method for manufacturing a backside structure of a wafer substrate. An embodiment of the method for manufacturing a backside structure of a wafer substrate includes the following steps:

Step S11: First, a wafer substrate is provided. In the present embodiment, a front side of the wafer substrate faces upward, and a plurality of bare chips are formed on the front side, each of which has a front cutting path. In the present embodiment, the wafer substrate is a silicon substrate.

Step S12: Bond a glass carrier on top of the bare chips.

Step S13: Grind a back side of the wafer substrate to reduce the thickness of the wafer substrate.

Step S14: Flip the wafer substrate so that the back side faces upward.

Step S15: Sputtering to form a seed layer on the back side of the wafer substrate.

Step S16: forming a thick metal layer on the back side of the wafer substrate. In this embodiment, the thick metal layer has a plurality of thick metal blocks, and there is a back side cutting path between the thick metal blocks.

Step S17: Flip the wafer substrate so that the front side faces upward.

Step S18: A connection layer and an auxiliary substrate are attached below the thick metal layer.

Step S19: solidify the connection layer to form a solidified connection layer.

Since the thick metal layer formed on the back side of the wafer substrate has the back side cutting path, when the connection layer is cured, the water vapor generated during baking and curing or the organic solvent precipitated in the connection layer can be dispersed through the back side cutting path, thereby avoiding the risk of explosion caused by the pressure generated by the water vapor or the precipitated organic solvent during baking, so as to improve the process yield. In this embodiment, the thick metal layer on the back side of the wafer substrate is formed by electroplating, sputtering or evaporation.

In addition, since the present invention forms the back cutting path in the thick metal layer, in the subsequent cutting process, a cutting knife can cut through the front cutting path and the back cutting path, and can avoid the thick metal blocks, without cutting the thick metal blocks in the thick metal layer. In this way, the thickness that the cutting knife needs to cut can be reduced, and the thick metal block will not be cut, thereby reducing the probability of damage to the blade of the cutting knife. At the same time, since there is no thick metal block in the front cutting path and the back cutting path, when metal is grown on the back of the wafer substrate, the warpage of the entire wafer can be greatly reduced, thereby reducing the risk of cracking in the subsequent process and improving efficiency and yield.

Please refer to Figures 2A and 2B, and in conjunction with Figures 3A to 3O, another embodiment of the method for manufacturing the back side structure of the wafer substrate includes the following steps:

Step S201: As shown in FIG. 3A , first provide the wafer substrate 100. The front side 110 of the wafer substrate 100 faces upward, and the bare die 111 are formed on the front side 110 , and each of the bare die 111 has a front cutting path 101 .

Step S202: As shown in FIG. 3B , the glass carrier 112 is bonded on top of the bare wafers 111 .

Step S203: As shown in FIG. 3C , the back surface 120 of the wafer substrate 100 is ground to reduce the thickness of the wafer substrate 100 .

Step S204: As shown in FIG. 3D , flip the wafer substrate 100 so that the back surface 120 faces upward.

Step S205: As shown in FIG. 3E , the seed layer 121 is formed by sputtering on the back surface 120 of the wafer substrate 100 .

In this other embodiment, steps S201 to S205 are the same as steps S11 to S15, and therefore will not be described in detail. However, the step of forming the thick metal layer (step S16) includes the following sub-steps:

Step S206: As shown in FIG. 3F , a photoresist layer 122 is coated on the seed layer 121 .

Step S207: As shown in FIG. 3G , the photoresist layer 122 is patterned to retain a photoresist 122' in the front cutting path 101. In this embodiment, the photoresist layer 122 is patterned by a lithography process.

Step S208: As shown in FIG. 3H, the thick metal blocks 123' are formed in the plurality of regions of the back side 120 of the wafer substrate 100 where the photoresist 122' is not formed, so as to form the thick metal layer 123. In this embodiment, the thick metal blocks 123' are formed by electroplating, sputtering or evaporation.

Step S209: As shown in FIG. 3I, the photoresist 122' is removed to form the backside cutting path 102. Please refer to FIG. 4, which is a top view of FIG. 3I. The backside 120 of the wafer substrate 100 is formed with the thick metal blocks 123', and the thick metal blocks 123' are arranged at intervals from each other, and the gaps between the thick metal blocks 123' form the backside cutting path 102. In this embodiment, the photoresist 122' is removed with a photoresist remover.

In addition, the method for manufacturing the back side structure of the wafer substrate further includes the following steps after forming the thick metal layer 123 (step S16):

Step S210: As shown in FIG. 3J , flip the wafer substrate 100 so that the front side 110 faces upward.

Step S211: As shown in FIG. 3K , a connection layer 124 and an auxiliary substrate 125 are attached below the thick metal blocks 123 ′. In this embodiment, the connection layer 124 is an epoxy layer or a die attach film (DAF) layer, and the auxiliary substrate 125 is a silicon substrate, a FR4-grade glass fiber board, a Qromis Substrate Technology (QST) substrate, or a silicon carbide (SiC) substrate, but is not limited thereto.

Step S212: As shown in FIG. 3L, the connection layer 124 is cured to form a cured connection layer 124'. In this embodiment, the water vapor or organic solvent in the connection layer 124 is volatilized by baking to cure the connection layer 124 to form the cured connection layer 124'.

Step S213: As shown in FIG. 3M, a cutting tape 126 is attached below the auxiliary substrate 125.

Step S214: As shown in FIG. 3N , remove the glass carrier 112.

Step S215: As shown in FIG. 3O , a cutting blade 20 is used to cut the wafer substrate 100, the seed layer 121, the solidified connection layer 124′, and the auxiliary substrate 125 in the front cutting path 101 and the back cutting path 102 to form a plurality of independent bare chips. Since the formation positions of the thick metal blocks 123′ just correspond to the positions of the bare chips 111, the back cutting path 102 between the thick metal blocks 123′ also just corresponds to the position of the front cutting path 101 between the bare chips 111, that is, the back cutting path 102 is based on the wafer substrate 100 and is mirror-symmetrical with the front cutting path 101. That is to say, when the cutting blade 20 is used to cut the front cutting line 101, the back cutting line 102 will also be cut, so the thick metal blocks 123' will not be cut.

In this embodiment, the connection layer 124 is a heterogeneous material, usually a sticky material, used to adhere the thick metal blocks 123' and the auxiliary substrate 125. And because the connection layer 124 is a heterogeneous material, it needs to be baked and cured. The water vapor or precipitated organic solvent generated during the baking and curing process needs to be volatilized. The back side 120 of the wafer substrate 100 manufactured by the manufacturing method of the back side structure of the wafer substrate is formed with the back side cutting path 102. Therefore, the water vapor or precipitated organic solvent generated during baking and curing can be dispersed through the back side cutting path 102, thereby avoiding the risk of explosion caused by the pressure generated by the water vapor or precipitated organic solvent during baking.

Furthermore, please refer to FIG. 5A and FIG. 5B , another embodiment of the method for manufacturing the back side structure of the wafer substrate includes the following steps:

Step S501: First, provide the wafer substrate 100. The front side 110 of the wafer substrate 100 faces upward, and the bare die 111 are formed on the front side 110, and each of the bare die 111 has a front cutting line 101.

Step S502: Bond the glass carrier 112 onto the bare wafers 111.

Step S503: Grinding the back side 120 of the wafer substrate 100 to reduce the thickness of the wafer substrate 100.

Step S504: Flip the wafer substrate 100 so that the back surface 120 faces upward.

Step S505: Sputtering to form the seed layer 121 on the back side 120 of the wafer substrate 100.

In this further embodiment, steps S501 to S505 are the same as steps S11 to S15, and therefore will not be described in detail. However, the step of forming the thick metal layer 123 (step S16) includes the following sub-steps:

Step S506: forming a thick metal layer 123 on the seed layer 121 of the back side 120 of the wafer substrate 100. In the present embodiment, the thick metal layer 123 is formed by electroplating, sputtering or evaporation.

Step S507: Cut the thick metal layer 123 in the front cutting path 101, cut the thick metal layer 123 into the thick metal blocks 123', and form the back cutting path 102 between the thick metal blocks 123'. In this embodiment, the thick metal layer 123 is cut with a cutting knife or a laser, but it is not limited to this.

In addition, the method for manufacturing the back side structure of the wafer substrate further includes the following steps after forming the thick metal layer 123 (step S16):

Step S508: Flip the wafer substrate 100 so that the front side 110 faces upward.

Step S509: Paste the connection layer 124 and the auxiliary substrate 125 under the thick metal blocks 123'. In this embodiment, the connection layer 124 is an epoxy layer or a die attach film (DAF) layer, and the auxiliary substrate 125 is a silicon substrate, a FR4-grade glass fiber board, a Qromis Substrate Technology (QST) substrate, or a silicon carbide (SiC) substrate, but not limited thereto.

Step S510: solidify the connection layer 124 to form the solidified connection layer 124'. In this embodiment, the water vapor or organic solvent in the connection layer 124 is volatilized by baking to solidify the connection layer 124 to form the solidified connection layer 124'.

Step S511: Paste the cutting tape 126 under the auxiliary substrate 125.

Step S512: Remove the glass carrier 112.

Step S513: Use the cutting blade 20 to cut the wafer substrate 100, the seed layer 121, the solidified connection layer 124', and the auxiliary substrate 125 in the front cutting path 101 and the back cutting path 102 to form a plurality of independent bare chips.

The above is only the preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as the preferred embodiment, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes by using the technical contents disclosed above within the scope of the technical solution of the present invention. However, any simple modification, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

S11~S19: Steps

Claims (10)

A method for bonding a foreign material to the back side of a wafer substrate comprises the following steps: Providing a wafer substrate; wherein a front side of the wafer substrate faces upward, and a plurality of bare dies are formed on the front side, and a front cutting line is respectively provided between the bare dies; Bonding a glass carrier above the bare dies; Grinding a back side of the wafer substrate; Flipping the wafer substrate so that the back side faces upward; Sputtering a seed layer on the back side of the wafer substrate; Forming a thick metal layer on the back side of the wafer substrate; wherein the thick metal layer has a plurality of thick metal blocks, and a back cutting line is provided between the thick metal blocks; Flipping the wafer substrate so that the front side faces upward; Bonding a connection layer and an auxiliary substrate below the thick metal layer; The connecting layer is cured to form a cured connecting layer. The method for bonding a foreign material to the back side of a wafer substrate as described in claim 1, wherein the step of forming the thick metal layer includes the following sub-steps: Coating a photoresist layer on the seed layer; Patterning the photoresist layer to retain a photoresist in the front cutting path; Forming the thick metal blocks in a plurality of areas on the back side of the wafer substrate where the photoresist is not formed to form the thick metal layer; Removing the photoresist to form the back cutting path. The method for bonding a foreign material to the back side of a wafer substrate as described in claim 2, wherein, in the step of patterning the photoresist layer, the photoresist layer is patterned by a lithography process. A method for bonding a foreign material to the back side of a wafer substrate as described in claim 2, wherein in the step of removing the photoresist, the photoresist is removed using a photoresist stripper. The method for bonding a foreign material to the back side of a wafer substrate as described in claim 1, wherein the step of forming the thick metal layer includes the following sub-steps: Forming the thick metal layer on the seed layer on the back side of the wafer substrate; Cutting the thick metal layer in the front cutting path to cut the thick metal layer into the thick metal blocks, and forming the back cutting path between the thick metal blocks. The method of bonding a foreign material to the back side of a wafer substrate as described in claim 5, wherein in the step of cutting the thick metal layer in the front cutting path, the thick metal layer is cut with a cutting knife or a laser. The method of laminating a foreign material on the back side of a wafer substrate as described in claim 1 further comprises the following steps: Laying a cutting tape under the auxiliary substrate; Removing the glass carrier; Cutting the wafer substrate, the seed layer, the cured connection layer, and the auxiliary substrate in the front cutting path and the back cutting path. A method for bonding a foreign material to the back side of a wafer substrate as described in claim 7, wherein the auxiliary substrate is a silicon substrate. A method for bonding a foreign material to the back side of a wafer substrate as described in claim 1, wherein the connection layer is an epoxy layer. A method for bonding a foreign material to the back side of a wafer substrate as described in claim 1, wherein the wafer substrate is a silicon substrate.

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