Method for removing metal layer on back surface of substrate

Abstract

The invention relates to a method for removing a metal layer on the back of a substrate. The method for removing the metal layer on the back face of the substrate comprises the following steps that a base is provided, the base comprises the substrate and the metal layer located on the back face of the substrate, and the metal layer at least comprises a metal titanium layer, a metal nickel layer and a metal silver layer; the metal titanium layer, the metal nickel layer and the metal silver layer in the metal layer are removed at the same time through a wet cleaning process, and corrosive liquid used in the wet cleaning process is a mixed solution containing concentrated sulfuric acid, hydrofluoric acid and concentrated nitric acid. According to the method, the metal titanium layer, the metal nickel layer and the metal silver layer in the metal layer are removed at the same time, multiple times of corrosion operation are not needed, operation is easy, and risks caused by using aqua regia are avoided.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor manufacturing, and in particular to a method for removing a metal layer on the back side of a substrate. Background Art

[0002] In the manufacturing process of integrated circuits, in order to form an electrode (such as a drain electrode on the back of a field effect transistor) or a metal heat dissipation layer to improve the heat dissipation effect of a semiconductor device, it is often necessary to perform a metallization process on the back of the substrate to form a multi-layer metal layer. The most common metal layers currently include titanium-nickel-silver (Ti-Ni-Ag) layer and aluminum-titanium-nickel-silver (Al-Ti-Ni-Ag) layer.

[0003] In the actual semiconductor manufacturing process, the metal layer on the back of the substrate is often removed according to the needs. The method of removing the metal layer on the back of the substrate usually includes: first using aqua regia (concentrated hydrochloric acid and concentrated nitric acid in a volume ratio of V 浓盐酸 :V 浓硝酸 =3:1 mixture) to etch away the silver and nickel layers in the metal layer, and then use hydrofluoric acid to etch away the titanium layer. If there is an aluminum layer, then after the hydrofluoric acid etching, nitric acid is also used to etch away the aluminum layer. This is because metallic titanium is insoluble in aqua regia, so hydrofluoric acid needs to be used to etch away the titanium layer alone. It can be seen that currently etching away the metal layer on the back of the substrate requires multiple etching operations, and the operation is relatively cumbersome. Moreover, aqua regia is highly corrosive, and there is a certain risk when the staff uses aqua regia to etch the metal layer on the back of the substrate.

[0004] Therefore, how to simplify the removal operation of the metal layer on the back of the substrate, improve the removal efficiency of the metal layer on the back of the substrate, and at the same time improve the safety of removing the metal layer on the back of the substrate to avoid the risks brought by the use of aqua regia is a technical problem that needs to be solved urgently. Summary of the invention

[0005] The present invention provides a method for removing a metal layer on the back side of a substrate, which is used to simplify the removal operation of the metal layer on the back side of the substrate, improve the removal efficiency of the metal layer on the back side of the substrate, and simultaneously improve the safety during the removal of the metal layer on the back side of the substrate, thereby avoiding the risks caused by the use of aqua regia.

[0006] According to some embodiments, the present invention provides a method for removing a metal layer on the back side of a substrate, comprising the following steps:

[0007] Providing a base, the base comprising a substrate and a metal layer located on the back side of the substrate, the metal layer at least comprising a metal titanium layer, a metal nickel layer and a metal silver layer;

[0008] The metal titanium layer, the metal nickel layer and the metal silver layer in the metal layer are removed simultaneously by a wet cleaning process, and the etching solution used in the wet cleaning process is a mixed solution including concentrated sulfuric acid, hydrofluoric acid and concentrated nitric acid.

[0009] In some embodiments, the metal layer further comprises a metal aluminum layer.

[0010] In some embodiments, before the metal titanium layer, the metal nickel layer and the metal silver layer in the metal layer are removed simultaneously by a wet cleaning process, the following steps are also included:

[0011] The volume ratio of the concentrated sulfuric acid, the hydrofluoric acid and the concentrated nitric acid is obtained according to the relationship between the thickness of the metal titanium layer, the thickness of the metal nickel layer and the thickness of the metal silver layer, and the etching solution is prepared.

[0012] In some embodiments, before the metal titanium layer, the metal nickel layer and the metal silver layer in the metal layer are removed simultaneously by a wet cleaning process, the following steps are also included:

[0013] The volume ratio of concentrated sulfuric acid, hydrofluoric acid and concentrated nitric acid is V 浓硫酸 :V 氢氟酸 :V 浓硝酸 =8:1:1 to prepare the corrosive liquid.

[0014] In some embodiments, the substrate includes a front side and a back side that are relatively distributed; before the metal titanium layer, the metal nickel layer and the metal silver layer in the metal layer are simultaneously removed by a wet cleaning process, the following steps are also included:

[0015] A protective film is formed covering the front surface of the substrate.

[0016] In some embodiments, a wet cleaning process is used to simultaneously remove the metal titanium layer, the metal nickel layer, and the metal silver layer in the metal layer, and the etching solution used in the wet cleaning process is a mixed solution including concentrated sulfuric acid, hydrofluoric acid, and concentrated nitric acid. The specific steps include:

[0017] According to the actual thickness of the metal layer, the time taken by the corrosive liquid to corrode the metal layer is obtained as the target corrosion time;

[0018] The etching liquid is sprayed onto the back side of the substrate so that the metal layer is immersed in the etching liquid and the etching lasts for the target etching time.

[0019] In some embodiments, the specific steps of obtaining the time for the corrosive solution to corrode the metal layer according to the thickness of the metal layer as the target corrosion time include:

[0020] Establishing a mapping relationship, wherein the mapping relationship includes the thicknesses of the plurality of metal layers and a plurality of corrosion times corresponding to the thicknesses of the plurality of metal layers;

[0021] Obtaining the actual thickness of the metal layer in the substrate;

[0022] The corrosion time corresponding to the actual thickness of the metal layer is selected according to the mapping relationship as the target corrosion time.

[0023] In some embodiments, after spraying the etching solution onto the back side of the substrate so that the metal layer is immersed in the etching solution and the etching time is continued for the target etching time, the following steps are further included:

[0024] The metal layer is over-etched with the etching solution for a preset time.

[0025] In some embodiments, the preset time is 30% of the target corrosion time.

[0026] In some embodiments, after the metal titanium layer, the metal nickel layer and the metal silver layer in the metal layer are removed simultaneously by a wet cleaning process, the following steps are further included:

[0027] Rinse the back side of the substrate with pure water;

[0028] The substrate is dried.

[0029] The method for removing the metal layer on the back of the substrate provided by the present invention simultaneously removes the metal titanium layer, the metal nickel layer and the metal silver layer in the metal layer by adopting a wet cleaning process. The etching liquid used in the wet cleaning process is a mixed solution including concentrated sulfuric acid, hydrofluoric acid and concentrated nitric acid. There is no need to perform multiple etching operations, and the operation is relatively simple, thereby improving the removal efficiency of the metal layer on the back of the substrate. At the same time, the etching liquid used in the present invention is a mixed solution of concentrated sulfuric acid, hydrofluoric acid and concentrated nitric acid, and there is no need to prepare and use aqua regia, thereby greatly improving the safety in the process of removing the metal layer on the back of the substrate and avoiding the risks caused by the use of aqua regia. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a flow chart of a method for removing a metal layer on the back side of a substrate in a specific embodiment of the present invention;

[0031] Figure 2 is a schematic structural diagram of a substrate in a specific embodiment of the present invention;

[0032] Figure 3 It is a schematic structural diagram of the substrate after the metal layer is removed according to a specific embodiment of the present invention. DETAILED DESCRIPTION

[0033] The specific implementation of the method for removing the metal layer on the back side of a substrate provided by the present invention is described in detail below with reference to the accompanying drawings.

[0034] This specific embodiment provides a method for removing the metal layer on the back side of a substrate. Figure 1 FIG. 1 is a flow chart of a method for removing a metal layer on the back side of a substrate in a specific embodiment of the present invention. Figure 1 As shown, the method for removing the metal layer on the back side of the substrate comprises the following steps:

[0035] Step S11, providing a base, wherein the base includes a substrate and a metal layer located on the back side of the substrate, wherein the metal layer at least includes a metal titanium layer, a metal nickel layer and a metal silver layer;

[0036] Step S12, using a wet cleaning process to simultaneously remove the metal titanium layer, the metal nickel layer and the metal silver layer in the metal layer, the corrosive solution used in the wet cleaning process is a mixed solution including concentrated sulfuric acid, hydrofluoric acid and concentrated nitric acid.

[0037] Figure 2 is a schematic structural diagram of a substrate in a specific embodiment of the present invention, Figure 3 Schematic diagram of the structure of the substrate after the metal layer is removed according to a specific embodiment of the present invention. In some embodiments, the metal layer further includes a metal aluminum layer.

[0038] In one example, the substrate 20 includes a front surface 201 and a back surface 202 that are oppositely distributed (see Figure 3 ), the front side 201 of the substrate 20 may include a device structure such as a source electrode, the back side 202 of the substrate 20 includes the metal titanium layer 21, the metal nickel layer 22 covering the surface of the metal titanium layer 21 away from the substrate 20, and the metal silver layer 23 covering the surface of the metal nickel layer 22 away from the metal titanium layer 21, that is, the metal titanium layer 21, the metal nickel layer 22 and the metal silver layer 23 are sequentially stacked on the back side 202 of the substrate 20, and the metal titanium layer 21, the metal nickel layer 22 and the metal silver layer 23 together constitute the metal layer on the back side 202 of the substrate 20, as Figure 2 In another example, the metal layer further includes a metal aluminum layer (not shown in the figure) located between the metal titanium layer 21 and the substrate 20 .

[0039] In some embodiments, before the metal titanium layer 21, the metal nickel layer 22 and the metal silver layer 23 in the metal layer are removed simultaneously by a wet cleaning process, the following steps are also included:

[0040] The volume ratio of the concentrated sulfuric acid, the hydrofluoric acid and the concentrated nitric acid is obtained according to the relationship between the thickness of the metal titanium layer 21 , the thickness of the metal nickel layer 22 and the thickness of the metal silver layer 23 , and the etching solution is prepared.

[0041] For example, when the thickness of the metal titanium layer 21 increases, since the hydrofluoric acid has a better corrosion effect on the metal titanium layer 21, the volume ratio of the hydrofluoric acid in the etching solution can be increased. For another example, when the thickness of the metal nickel layer 22 or the thickness of the metal silver layer 23 increases, the volume ratio of the concentrated nitric acid and the volume ratio of the concentrated sulfuric acid can be increased accordingly. According to the relationship between the thickness of the metal titanium layer 21, the thickness of the metal nickel layer 22 and the thickness of the metal silver layer 23, the volume ratio between the concentrated sulfuric acid, the hydrofluoric acid and the concentrated nitric acid in the etching solution is adjusted, so that the composition of the etching solution can be flexibly adjusted according to the actual composition of the metal layer, which can not only further fully remove the metal layer, improve the removal effect and removal efficiency of the metal layer on the back of the substrate, but also reduce the waste of etching solution and reduce the cost of semiconductor production. The concentrated sulfuric acid described in this specific embodiment refers to a sulfuric acid aqueous solution with a mass fraction greater than or equal to 98%, and the concentrated nitric acid refers to a nitric acid aqueous solution with a mass fraction greater than or equal to 68%.

[0042] In some embodiments, before the metal titanium layer 21, the metal nickel layer 22 and the metal silver layer 23 in the metal layer are removed simultaneously by a wet cleaning process, the following steps are also included:

[0043] The volume ratio of concentrated sulfuric acid, hydrofluoric acid and concentrated nitric acid is V 浓硫酸 :V 氢氟酸 :V 浓硝酸 =8:1:1 to prepare the corrosive liquid.

[0044] Specifically, the volume ratio of concentrated sulfuric acid, hydrofluoric acid and concentrated nitric acid is V 浓硫酸 :V 氢氟酸 :V 浓硝酸 =8:1:1, the etching solution has a high etching rate (for example, the etching rate is ), is not limited by the relative size relationship between the thickness of the metal aluminum layer, the thickness of the metal titanium layer 21, the thickness of the metal nickel layer 22 and the thickness of the metal silver layer 23, so that the metal layer on the back side 202 of the substrate 20 can be completely removed, and the application range is wide, and no damage is caused to the substrate 20 (for example, the material of the substrate 20 is silicon), which helps to better protect the substrate 20. In addition, with the volume ratio of concentrated sulfuric acid, hydrofluoric acid and concentrated nitric acid being V 浓硫酸 :V 氢氟酸 :V 浓硝酸 =8:1:1, the etching solution prepared has a longer effective period, thereby helping to further reduce the waste of the etching solution.

[0045] In order to avoid damaging the front side 20 of the substrate 20 and the device structure on the front side 201 of the substrate 20 when removing the metal layer on the back side 202 of the substrate 20, in some embodiments, the substrate 20 includes a front side 201 and a back side that are relatively distributed; before simultaneously removing the metal titanium layer 21, the metal nickel layer 22 and the metal silver layer 23 in the metal layer by a wet cleaning process, the following steps are also included:

[0046] A protective film is formed covering the front surface 201 of the substrate 20. The protective film does not chemically react with the etching solution.

[0047] In some embodiments, a wet cleaning process is used to simultaneously remove the metal titanium layer 21, the metal nickel layer 22 and the metal silver layer 23 in the metal layer, and the etching solution used in the wet cleaning process is a mixed solution including concentrated sulfuric acid, hydrofluoric acid and concentrated nitric acid. The specific steps include:

[0048] According to the actual thickness of the metal layer, the time taken by the corrosive liquid to corrode the metal layer is obtained as the target corrosion time;

[0049] The etching liquid is sprayed onto the back side 202 of the substrate 20 so that the metal layer is immersed in the etching liquid and the etching lasts for the target etching time.

[0050] In some embodiments, the specific steps of obtaining the time for the corrosive solution to corrode the metal layer according to the thickness of the metal layer as the target corrosion time include:

[0051] Establishing a mapping relationship, wherein the mapping relationship includes the thicknesses of the plurality of metal layers and a plurality of corrosion times corresponding to the thicknesses of the plurality of metal layers;

[0052] Obtaining the actual thickness of the metal layer in the substrate;

[0053] The corrosion time corresponding to the actual thickness of the metal layer is selected according to the mapping relationship as the target corrosion time.

[0054] For example, Table 1 is a mapping relationship table between the thickness of the metal layer and the corrosion time and corrosion rate, which is constructed based on the thickness of the multiple metal layers and the multiple corrosion times corresponding to the thickness of the multiple metal layers and the multiple corrosion rates corresponding to the thickness of the multiple metal layers. According to the overall thickness of the metal layer to be corroded in the substrate (i.e., the actual thickness of the metal layer), the corrosion time matching the actual thickness of the metal layer is selected from the mapping relationship table between the thickness of the metal layer and the corrosion time shown in Table 1 as the target corrosion time, thereby ensuring that the metal layer on the back side 202 of the substrate 20 is fully removed at a faster corrosion rate in a shorter time, and avoiding the reduction of semiconductor manufacturing efficiency due to excessively long corrosion time. Among them, the mapping relationship table between the thickness of the metal layer and the corrosion time can be obtained based on calculation or statistical analysis of historical data.

[0055] Table 1 Mapping relationship between metal layer thickness and corrosion time

[0056]

[0057] In some embodiments, after spraying the etching solution onto the back side 202 of the substrate 20 so that the metal layer is immersed in the etching solution and the etching process lasts for the target etching time, the following steps are further included:

[0058] The metal layer is over-etched with the etching solution for a preset time.

[0059] Specifically, in order to further ensure that the metal layer on the back side 202 of the substrate 20 is completely removed, the metal layer may be over-corroded by the corrosive liquid for a preset time after the corrosive liquid corrodes the metal for the target corrosion time. The over-corrosion time should not be too short to avoid the corrosive liquid failing to fully react with the entire metal layer; the over-corrosion time should not be too long to avoid a reduction in the removal efficiency of the metal layer on the back side of the substrate. In some embodiments, the preset time is 30% of the target corrosion time.

[0060] In some embodiments, after the metal titanium layer 21, the metal nickel layer 22 and the metal silver layer 23 in the metal layer are removed simultaneously by a wet cleaning process, the following steps are further included:

[0061] Rinse the back side 202 of the substrate 20 with pure water;

[0062] The substrate 20 is dried.

[0063] Specifically, after all the metal layers on the back side 202 of the substrate 20 are removed simultaneously by a wet cleaning process, the back side 202 of the substrate 20 is rinsed with pure water to remove the etching solution remaining on the back side 202 of the substrate 20. In one example, the back side 202 of the substrate 20 is rinsed with pure water for 120 seconds. Afterwards, the substrate 20 may be spun dry to remove the pure water remaining on the back side 202 of the substrate 20.

[0064] The method for removing the metal layer on the back of the substrate provided in this specific embodiment simultaneously removes the metal titanium layer, the metal nickel layer and the metal silver layer in the metal layer by adopting a wet cleaning process. The etching liquid used in the wet cleaning process is a mixed solution of concentrated sulfuric acid, hydrofluoric acid and concentrated nitric acid. There is no need to perform multiple etching operations, and the operation is relatively simple, thereby improving the removal efficiency of the metal layer on the back of the substrate. At the same time, the etching liquid used in this specific embodiment is a mixed solution of concentrated sulfuric acid, hydrofluoric acid and concentrated nitric acid, and there is no need to prepare and use aqua regia, thereby greatly improving the safety of the process of removing the metal layer on the back of the substrate and avoiding the risks caused by the use of aqua regia.

[0065] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for removing a metal layer on the back side of a substrate, characterized in that: The steps include: Providing a base, the base comprising a substrate and a metal layer located on the back side of the substrate, the metal layer at least comprising a metal titanium layer, a metal nickel layer and a metal silver layer; The metal titanium layer, the metal nickel layer and the metal silver layer in the metal layer are removed simultaneously by a wet cleaning process, and the etching solution used in the wet cleaning process is a mixed solution including concentrated sulfuric acid, hydrofluoric acid and concentrated nitric acid.

2. The method for removing the metal layer on the back side of the substrate according to claim 1, characterized in that: The metal layer further comprises a metal aluminum layer.

3. The method for removing the metal layer on the back side of the substrate according to claim 1, characterized in that: Before simultaneously removing the metal titanium layer, the metal nickel layer and the metal silver layer in the metal layer by a wet cleaning process, the following steps are also included: The volume ratio of the concentrated sulfuric acid, the hydrofluoric acid and the concentrated nitric acid is obtained according to the relationship between the thickness of the metal titanium layer, the thickness of the metal nickel layer and the thickness of the metal silver layer, and the etching solution is prepared.

4. The method for removing the metal layer on the back side of the substrate according to claim 1, characterized in that: Before simultaneously removing the metal titanium layer, the metal nickel layer and the metal silver layer in the metal layer by a wet cleaning process, the following steps are also included: The volume ratio of concentrated sulfuric acid, hydrofluoric acid and concentrated nitric acid is V 浓硫酸 :V 氢氟酸 :V 浓硝酸 =8:1:1 to prepare the corrosive liquid.

5. The method for removing the metal layer on the back side of the substrate according to claim 1, characterized in that: The substrate comprises a front side and a back side which are relatively distributed; before the metal titanium layer, the metal nickel layer and the metal silver layer in the metal layer are removed simultaneously by a wet cleaning process, the following steps are also included: A protective film is formed covering the front surface of the substrate.

6. The method for removing the metal layer on the back side of a substrate according to claim 1, characterized in that: The specific steps of simultaneously removing the metal titanium layer, the metal nickel layer and the metal silver layer in the metal layer by a wet cleaning process, wherein the etching solution used in the wet cleaning process is a mixed solution of concentrated sulfuric acid, hydrofluoric acid and concentrated nitric acid, include: According to the actual thickness of the metal layer, the time taken by the corrosive liquid to corrode the metal layer is obtained as the target corrosion time; The etching liquid is sprayed onto the back side of the substrate so that the metal layer is immersed in the etching liquid and the etching lasts for the target etching time.

7. The method for removing the metal layer on the back side of a substrate according to claim 6, characterized in that: The specific steps of obtaining the time for the etching solution to corrode the metal layer according to the thickness of the metal layer and taking the target etching time as the target etching time include: Establishing a mapping relationship, wherein the mapping relationship includes the thicknesses of the plurality of metal layers and a plurality of corrosion times corresponding to the thicknesses of the plurality of metal layers; Obtaining the actual thickness of the metal layer in the substrate; The corrosion time corresponding to the actual thickness of the metal layer is selected according to the mapping relationship as the target corrosion time.

8. The method for removing the metal layer on the back side of a substrate according to claim 6, characterized in that: After spraying the etching liquid onto the back side of the substrate so that the metal layer is immersed in the etching liquid and the etching time is continued for the target etching time, the following steps are also included: The metal layer is over-etched with the etching solution for a preset time.

9. The method for removing the metal layer on the back side of a substrate according to claim 8, characterized in that: The preset time is 30% of the target corrosion time.

10. The method for removing the metal layer on the back side of a substrate according to claim 1, characterized in that: After the metal titanium layer, the metal nickel layer and the metal silver layer in the metal layer are removed simultaneously by a wet cleaning process, the following steps are also included: Rinse the back side of the substrate with pure water; The substrate is dried.

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