Method for improving adhesion of seed layer

Abstract

The present invention belongs to the technical field of integrated circuits, and provides a method for improving the adhesion of a seed layer. In the present invention, a first Ti layer is first deposited on a substrate with through holes formed therein. Then, the substrate is bombarded with plasma, enabling the atoms of a part of the Ti layer in contact with the substrate to be embedded into the substrate to form an alloy layer as an adhesion enhancing layer, a TiCu seed layer is then deposited, such that the adhesion between the substrate and the TiCu seed layer, and the adhesion between the sidewall of a through hole and the TiCu seed layer can be improved. An electroplating photoresist layer is fabricated on the surface of the Cu layer. A Cu layer is deposited at pattern gaps of the electroplating photoresist layer to form Cu pillars. The electroplating photoresist layer is peeled off, the Cu layer, the TiCu seed layer, the first Ti layer and the alloy layer at the original position of the electroplating photoresist are etched away, and finally the fabrication of the seed layer is completed.

Description

A method to improve seed layer adhesion Technical Field

[0001] This invention relates to the field of integrated circuit technology, and more specifically, to a method for improving the adhesion of a seed layer. Background Technology

[0002] The key to the development and integration of Chiplet heterogeneous integration technology lies in the fusion of multi-scale, multi-dimensional chip interconnects, thereby improving power efficiency and reducing latency, providing smaller and higher-performance chips for high-performance computing, artificial intelligence, and smart terminals. Vertical interconnects rely on technologies such as Through Silicon Via (TSV) or Through Glass Via (TGV), while horizontal interconnects are achieved through Re-Distribution Layer (RDL) technology.

[0003] For metal filling of TGV and TSV vias, a typical method involves first depositing a Cu seed layer on the substrate and the via sidewalls using magnetron sputtering, followed by Cu electroplating to fill the via with Cu. However, when depositing TGV substrates with high aspect ratios (typically 3:1-20:1), the energy of sputtered metal particles reaching the sidewalls is reduced, resulting in weak adhesion between the seed layer and the deep via sidewalls, posing a risk of peeling.

[0004] Therefore, there is an urgent need to develop a method to improve the adhesion of the seed layer, so as to improve the adhesion between the seed layer and the substrate and reduce the risk of peeling between the seed layer and the deep hole sidewall, even when depositing TGV substrates with high aspect ratios.

[0005] Summary of the Invention

[0006] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the present invention proposes a method for improving seed layer adhesion. The method provided by the present invention can improve the adhesion between the seed layer and the substrate, and between the seed layer and the deep hole sidewalls, and can reduce the risk of peeling between the seed layer and the deep hole sidewalls, even when depositing TGV substrates with high aspect ratios.

[0007] A first aspect of the present invention provides a method for improving the adhesion of a seed layer.

[0008] Specifically, a method for improving the adhesion of a seed layer includes the following steps:

[0009] (1) Take the substrate and make through holes;

[0010] (2) Deposit a first Ti layer on the substrate surface;

[0011] (3) Perform plasma treatment on the surface of the first Ti layer to form an alloy layer;

[0012] (4) Deposit a TiCu seed layer on the surface of the first Ti layer;

[0013] (5) An electroplated photoresist layer is fabricated on the surface of the TiCu seed layer;

[0014] (6) Next, Cu is electroplated and deposited in the gaps of the pattern of the electroplated photoresist layer until the through holes are filled with Cu and the pattern of the electroplated photoresist layer is not deposited with Cu, thus forming Cu pillars.

[0015] (7) Peel off the electroplated photoresist layer;

[0016] (8) Place the substrate after stripping the electroplated photoresist layer into the etching solution for etching. When the Cu layer, TiCu seed layer, first Ti layer and alloy layer at the original location of the electroplated photoresist are etched away and the Cu pillars are retained, stop etching.

[0017] In step (3), the plasma treatment is either Xe plasma treatment or Kr plasma treatment.

[0018] In this invention, a first Ti layer is deposited on an open-hole substrate, followed by Xe plasma or Kr plasma treatment. Since Xe and Kr atoms have relatively large radii, they have high energy when bombarding the Ti layer. This allows the atoms of the first Ti layer in contact with the substrate to be embedded into the substrate, forming an alloy layer (TiSi alloy layer). This is similar to the principle of driving a wooden stake into the soil with a hammer. In this way, the alloy layer can serve as a connecting layer and a buffer layer between the seed layer and the substrate, thereby significantly improving the adhesion between the seed layer and the substrate, and between the seed layer and the sidewall of the through-hole (especially the sidewall of deep holes with a depth-to-width ratio of 3:3-20:1).

[0019] Preferably, in step (1), the substrate is a glass substrate.

[0020] Preferably, in step (1), the thickness of the substrate is 0.1-1 mm.

[0021] More preferably, in step (1), the thickness of the substrate is 0.4-0.6 mm.

[0022] Preferably, in step (1), the diameter of the through hole is 10-200 μm, and / or the depth-to-width ratio of the through hole is 3:1-20:1.

[0023] More preferably, in step (1), the diameter of the through hole is 80-100μm, and / or the depth-to-width ratio of the through hole is 5:1-10:1.

[0024] Preferably, in step (2), the thickness of the first Ti layer is 5-20 nm.

[0025] More preferably, in step (2), the thickness of the first Ti layer is 10-15 nm.

[0026] The thickness of the Ti layer is controlled to ensure that the bombardment energy is transferred to the Ti in contact with the substrate, allowing it to embed into the substrate. However, during plasma bombardment, some Ti atoms are ejected, causing the Ti layer to become thinner and resulting in local discontinuities. If Cu is deposited directly on top of these discontinuous Ti films, the adhesion of the Cu layer will be poor. Therefore, a second Ti layer needs to be deposited to ensure the continuity of the Ti barrier layer and the adhesion of the subsequently deposited Cu layer.

[0027] Preferably, in step (3), the thickness of the alloy layer is 1-10 nm.

[0028] More preferably, in step (3), the thickness of the alloy layer is 1-5 nm.

[0029] Preferably, in step (3), the energy of the plasma treatment is 100-2000 eV.

[0030] More preferably, in step (3), the energy of the plasma treatment is 500-1000 eV.

[0031] Preferably, in step (4), the TiCu seed layer is a second Ti layer and a Cu layer deposited sequentially. The second Ti layer and Cu layer serve as a metal seed layer. Due to the alloy layer buffer between the substrate and the TiCu seed layer, the adhesion between the substrate and the TiCu seed layer can be significantly improved.

[0032] Preferably, the thickness of the second Ti layer is 50-150 nm, and / or the thickness of the Cu layer is 250-350 nm.

[0033] More preferably, the thickness of the second Ti layer is 100-150 nm, and / or the thickness of the Cu layer is 300-350 nm.

[0034] Preferably, in step (8), the Cu layer, TiCu seed layer, and first Ti layer are first removed by etching in an etching solution, and then the alloy layer is removed by etching. This can increase the impedance of the substrate surface (requiring the impedance between two Cu pillars of adjacent substrates to be >100MΩ) and avoid signal interference between Cu pillars of two adjacent vias.

[0035] Preferably, in step (8), the etching solution is a hydrogen peroxide solution.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] This invention involves depositing a first Ti layer on a substrate with vias, followed by plasma bombardment of the substrate to embed atoms of the first Ti layer in contact with the substrate, forming an alloy layer that serves as a bonding layer, adhesion enhancement layer, and buffer layer. Next, a TiCu seed layer is deposited, significantly improving adhesion between the substrate and the TiCu seed layer, and between the via sidewalls and the TiCu seed layer. Then, an electroplated photoresist layer is fabricated on the Cu layer surface. Cu layers are deposited in the gaps between the patterns on the electroplated photoresist layer surface, while no Cu layers are deposited in the patterns on the surface of the electroplated photoresist layer. The vias are then filled with Cu to form Cu pillars. Finally, the electroplated photoresist layer is peeled off, and the Cu layer, TiCu seed layer, first Ti layer, and alloy layer at their original locations are etched away. This completes the fabrication of the seed layer on the via substrate. This process not only significantly improves adhesion between the seed layer and the substrate, and between the seed layer and the deep via sidewalls, but also reduces the risk of peeling between the seed layer and the deep via sidewalls. Furthermore, it enables the fabrication of a seed layer with strong adhesion even on substrates with high aspect ratio vias. Attached Figure Description

[0038] Figure 1A is a cross-sectional view of the glass substrate after the through hole is opened in step (1) of Embodiment 1 of the present invention;

[0039] Figure 1B is a top view of the glass substrate after the through hole is opened in step (1) of Embodiment 1 of the present invention;

[0040] Figure 2 is a schematic diagram of step (2) of embodiment 1 of the present invention, in which the first Ti layer is deposited on the substrate surface;

[0041] Figure 3 is a schematic diagram of Xe plasma treatment of the Ti layer in step (3) of Embodiment 1 of the present invention;

[0042] Figure 4 is a schematic diagram of step (4) of the embodiment of the present invention, which involves depositing a TiCu seed layer.

[0043] Figure 5 is a schematic diagram of step (5) of embodiment 1 of the present invention for making the PR pattern;

[0044] Figure 6 is a schematic diagram of the Cu layer deposition in step (6) of Embodiment 1 of the present invention;

[0045] Figure 7 is a schematic diagram of step (7) of peeling off the PR pattern in Embodiment 1 of the present invention;

[0046] Figure 8 is a schematic diagram of the substrate after removing the Cu layer, TiCu seed layer, first Ti layer and alloy layer at the original location of the electroplated photoresist in step (8) of Embodiment 1 of the present invention.

[0047] Figure 9 is a flowchart of the steps of the method for improving the adhesion of the seed layer in Embodiment 1 of the present invention.

[0048] In the diagram: 101, glass; 102, TGV through-hole; 201, Ti; 301, Xe. Plasma treatment; 302, TiSi alloy layer; 401, Cu; 501, PR; S100, Take the substrate and open the via; S200, Deposit the first Ti layer on the substrate surface; S300, Perform plasma treatment on the surface of the first Ti layer to form an alloy layer; S400, Deposit a TiCu seed layer on the surface of the first Ti layer; S500, Form an electroplated photoresist layer on the surface of the TiCu seed layer; S600, Then electroplat and deposit Cu in the gaps of the pattern of the electroplated photoresist layer until the via is filled with Cu and the pattern of the electroplated photoresist layer is not deposited with Cu, and stop the deposition to form Cu pillars; S700, Peel off the electroplated photoresist layer; S800, Place the substrate after peeling off the electroplated photoresist layer in the etching solution for etching. When the Cu layer, TiCu seed layer, first Ti layer, and alloy layer at the original location of the electroplated photoresist are etched away and the Cu pillars are retained, stop the etching. Detailed Implementation

[0049] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0050] Unless otherwise specified, the raw materials, reagents or devices used in the following examples are available from conventional commercial sources or can be obtained by existing known methods.

[0051] Example 1

[0052] A method for improving seed layer adhesion includes the following steps:

[0053] (1) Take a substrate with a thickness of 0.4 mm, make a through hole with a diameter of 80 μm and a depth-to-width ratio of 8 to obtain a glass through-hole (TGV) substrate with a completed through hole; the substrate after completing step (1) is shown in Figure 1A and 1B. Figure 1A is a cross-sectional view of the glass substrate with a completed through hole, and Figure 1B is a top view of the glass substrate with a completed through hole.

[0054] (2) A first Ti layer with a thickness of 10 nm is deposited on the substrate surface; the substrate after step (2) is shown in Figure 2;

[0055] (3) Xe plasma treatment is performed on the surface of the first Ti layer to form a TiSi alloy layer with a thickness of 1-5 nm and the Xe plasma energy is 500 eV; the substrate after step (3) is shown in Figure 3.

[0056] (4) A second Ti layer with a thickness of 100 nm and a Cu layer with a thickness of 300 nm are sequentially deposited on the surface of the alloy layer as a metal seed layer (TiCu seed layer); the substrate after completing step (4) is shown in Figure 4.

[0057] (5) An electroplated photoresist pattern (PR pattern) is formed on the surface of the Cu layer by coating, exposure and development; the substrate after step (5) is shown in Figure 5;

[0058] (6) Next, Cu layers are electroplated in the gaps of the pattern of the electroplated photoresist layer (Cu is not electroplated in the areas where the pattern of the electroplated photoresist layer is located), and the TGV vias are filled with Cu to form Cu pillars; the substrate after completing step (6) is shown in Figure 6.

[0059] (7) The PR pattern is peeled off using a stripping solution; the substrate after step (7) is shown in Figure 7.

[0060] (8) Place the substrate in an H2O2 etching solution containing F. After etching the Cu layer, TiCu seed layer, and first Ti layer at the original location of the photoresist electroplated on the substrate, continue to etch the substrate until the TiSi alloy layer is also completely etched away. At this point, the Cu pillars are retained, and the etching is stopped. The impedance between two adjacent Cu pillars is >100MΩ. The substrate after step (8) is shown in Figure 8.

[0061] Example 2

[0062] A method for improving seed layer adhesion differs from Example 1 in that, in step (3), Xe plasma treatment is replaced with Kr plasma treatment.

[0063] Comparative Example 1

[0064] This comparative example provides a method for preparing a seed layer, which differs from Example 1 in that the Xe plasma treatment in step (3) is not performed.

[0065] Product effectiveness test

[0066] 1. Testing Method

[0067] Tensile test: This is a standard industry testing method (refer to Chinese National Standard GB / T 5210-2006, or International Standard ISO 4624-2016). The specific testing method is as follows: Using the products finally prepared in the above embodiments and comparative examples as test substrates, test spindles are attached to the test substrates with seed layer films deposited on them, and the film is scratched along the circumference where the spindle and the film are in contact. Then, the test spindle is stretched with a force perpendicular to the substrate until the test spindle and the test substrate separate. The tensile force value at this point is converted into the tensile force per unit area, which is the adhesion force between the seed layer and the substrate.

[0068] 2. Test Results

[0069] Table 1. Tensile test results for each embodiment and comparative example.

[0070] As shown in the table above, in the tensile test, the tensile force of Example 1 can reach 1.0-1.1 N / mm; while the tensile force of Comparative Example 1 is only 0.3 N / mm, indicating that the method of the present invention significantly improves the adhesion between the seed layer and the substrate.

Claims

1. A method for improving the adhesion of a seed layer, characterized in that, Includes the following steps: (1) Take the substrate and make through holes; (2) Deposit a first Ti layer on the substrate surface; (3) Perform plasma treatment on the surface of the first Ti layer to form an alloy layer; (4) Deposit a TiCu seed layer on the surface of the first Ti layer; (5) An electroplated photoresist layer is fabricated on the surface of the TiCu seed layer; (6) Next, Cu is electroplated and deposited in the gaps of the pattern of the electroplated photoresist layer until the through holes are filled with Cu and the pattern of the electroplated photoresist layer is not deposited with Cu, thus forming Cu pillars. (7) Peel off the electroplated photoresist layer; (8) Place the substrate after stripping the electroplated photoresist layer into the etching solution for etching. When the Cu layer, TiCu seed layer, first Ti layer and alloy layer at the original location of the electroplated photoresist are etched away and the Cu pillars are retained, stop etching. In step (3), the plasma treatment is either Xe plasma treatment or Kr plasma treatment.

2. The method according to claim 1, characterized in that, In step (1), the substrate is a glass substrate.

3. The method according to claim 1, characterized in that, In step (1), the thickness of the substrate is 0.1-1 mm.

4. The method according to claim 1, characterized in that, In step (1), the diameter of the through hole is 10-200 μm, and / or the depth-to-width ratio of the through hole is 3:1-20:

1.

5. The method according to claim 1, characterized in that, In step (2), the thickness of the first Ti layer is 5-20 nm.

6. The method according to claim 1, characterized in that, In step (3), the thickness of the alloy layer is 1-10 nm.

7. The method according to claim 1, characterized in that, In step (3), the energy of the plasma processing is 100-2000 eV.

8. The method according to claim 1, characterized in that, In step (4), the TiCu seed layer includes a second Ti layer and a Cu layer.

9. The method according to claim 8, characterized in that, The thickness of the second Ti layer is 50-150 nm, and / or the thickness of the Cu layer is 250-350 nm.

10. The method according to claim 1, characterized in that, In step (8), the Cu layer, TiCu seed layer and first Ti layer are first removed by etching in the etching solution, and then the alloy layer is removed by etching.

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