Preparation method of multi-layer polymer film layer

Abstract

The invention discloses a preparation method of a multi-layer polymer film layer, which comprises the following steps: coating a polymer precursor solution on the surface of a substrate, and then carrying out soft baking, curing and plasma treatment to obtain a first polymer film layer; coating the surface of the ith polymer film layer with a polymer precursor solution, and then carrying out soft baking, curing and plasma treatment to obtain an (i + 1) th polymer film layer; the step S2 is repeated until the sum of the thicknesses of the N polymer film layers reaches the target thickness, and a multi-layer polymer film layer is obtained; wherein i and N are positive integers, and 1 < = i < i + 1 < = N. According to the method, the binding force between different polymer film layers is improved through surface plasma treatment, the soft baking and curing process is matched, the high-thickness multi-layer polymer film layer meeting the binding force requirement can be prepared, the surface of the film layer is smooth, the number of defects is small, and meanwhile the influence on deformation of the substrate is small.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor processing, and in particular to a method for preparing a multilayer polymer film layer. Background Art

[0002] Polyimide (PI) is widely used in the field of semiconductor manufacturing, especially in the field of MEMS processing. It is used as a sacrificial layer to prepare suspended structures, or as a substrate material for flexible devices. In the field of semiconductor manufacturing, the most common method to obtain a PI film layer is to obtain a film layer of uniform thickness on the surface of a wafer such as a silicon wafer by mechanical spin coating, and then solidify it at high temperature. In a specific process, a thicker PI film layer is often required to improve the mechanical strength of the film layer. At this time, a PI solution with a large viscosity coefficient is usually selected. However, as the wafer size increases to 8 inches or 12 inches, it is very difficult to prepare a PI film layer with a final thickness of more than 20um on the surface of the wafer by spin coating in one time, because the film thickness obtained under too high viscosity is poorly consistent, and even cannot be spin coated. At the same time, in some practical applications, due to the inconsistent properties of different types of PI (such as photosensitive, non-photosensitive, etc.), sometimes it is hoped to obtain a thicker film layer of the same type of PI, and its thickness has even exceeded the thickness index range of the PI product. At this time, single spin coating preparation will not be possible.

[0003] At present, one of the ways to obtain thick PI film layers is: after the first layer of PI is spin-coated and cured, the second layer of PI film layer is further prepared on the previous layer of PI film layer by the same method. However, this method has the following problems: 1. The bonding force between the PI film layers is poor, which easily leads to film separation and cannot meet some specific application requirements; 2. This method requires continuous spin coating and high-temperature curing, in which the furnace tube machine takes about 5 hours for high-temperature curing at a time, so the preparation of thicker film layers takes a long time in total, and the machine cannot effectively improve the use efficiency. In addition, in order to improve the bonding force, the prior art also adopts the method of multiple spin coatings and high-temperature curing again to obtain thick PI film layers. However, this method has the following problems: 1. The thickness of the preparation is limited. If the number of spin coatings is too many and the PI glue is too thick, subsequent high-temperature curing will be difficult; 2. If there are defects such as particles on the surface during the previous spin coating, the subsequent spin coating will amplify the defects, resulting in the final PI film layer performance not meeting the standards.

[0004] Therefore, there is an urgent need to provide a new method for preparing a multilayer polymer film to solve the above problems. Summary of the invention

[0005] The purpose of the present invention is to overcome the above technical deficiencies and propose a method for preparing a multilayer polymer film layer to solve the technical problem in the prior art that high film bonding strength and good surface quality cannot be taken into account when preparing a high-thickness multilayer polyimide film layer.

[0006] The present invention provides a method for preparing a multilayer polymer film layer, comprising the following steps: S1, coating a polymer precursor solution onto a substrate surface, followed by soft baking, curing, and plasma treatment to obtain a first polymer film layer; S2, coating the polymer precursor solution onto the surface of the i-th polymer film layer, and then performing soft baking, curing, and plasma treatment to obtain the i+1-th polymer film layer; S3, repeating the above step S2 until the sum of the thicknesses of N polymer film layers reaches the target thickness, thereby obtaining a multilayer polymer film layer; wherein i and N are both positive integers, and 1≤i<i+1≤N.

[0007] Compared with the prior art, the beneficial effects of the present invention include: The present invention utilizes surface plasma treatment to improve the bonding strength between different polymer film layers, and cooperates with the soft baking + curing process to prepare a high-thickness multilayer polymer film layer that meets the bonding strength requirements. The film layer has a smooth surface and few defects, and has little effect on the deformation of the substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is a process flow chart of an embodiment of a method for preparing a multilayer polymer film provided by the present invention; Figure 2 are photos of water drop contact angles of the first polymer film layer in Examples 1-2 and Comparative Examples 1-2 of the present invention; wherein (a) is Comparative Example 1, (b) is Comparative Example 2, (c) is Example 1, and (d) is Example 2; Figure 3 1 are adhesion test diagrams of the multilayer polymer film layers obtained in Examples 1-2 and Comparative Examples 1-2 of the present invention; wherein (a) is Comparative Example 1, (b) is Comparative Example 2, (c) is Example 1, and (d) is Example 2; Figure 4 This is a diagram showing the deformation influence of a multilayer polymer film layer prepared by the method of Example 1 of the present invention on wafers with different warpage amounts; wherein the initial warpage amounts of the wafers are -4um, -24um, and -87um from top to bottom. DETAILED DESCRIPTION

[0009] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0010] See also Figure 1 The present invention provides a method for preparing a multilayer polymer film layer, comprising the following steps: S1, coating a polymer precursor solution onto a substrate surface, followed by soft baking, curing, and plasma treatment to obtain a first polymer film layer; S2, coating the polymer precursor solution onto the surface of the i-th polymer film layer, and then performing soft baking, curing, and plasma treatment to obtain the i+1-th polymer film layer; S3, repeating the above step S2 until the sum of the thicknesses of N polymer film layers reaches the target thickness, thereby obtaining a multilayer polymer film layer; wherein i and N are both positive integers, and 1≤i<i+1≤N.

[0011] The present invention utilizes surface plasma treatment to improve the bonding strength between different polymer film layers, and cooperates with the soft baking + curing process to prepare a high-thickness multilayer polymer film layer that meets the bonding strength requirements. The film layer has a smooth surface and few defects, and has little effect on the deformation of the substrate.

[0012] The present invention does not limit the type of polymer, and those skilled in the art can select according to actual conditions. For example, the polymer can be polyimide or the like.

[0013] The present invention does not limit the type of polymer precursor, and those skilled in the art can select the type according to actual conditions, as long as the type can be cured to form a corresponding polymer film.

[0014] The present invention does not limit the type of substrate, and those skilled in the art can select it according to actual conditions. For example, the substrate can be a wafer, etc.

[0015] In some specific embodiments of the present invention, the substrate is a wafer with a size ≥ 6 inches, including but not limited to 6 inches, 8 inches, 12 inches, etc.

[0016] The present invention does not limit the coating method, and those skilled in the art can select it according to the actual situation. For example, it can be spin coating, spray coating, etc. In some specific embodiments of the present invention, spin coating is adopted, and the spin coating speed is 1000-4000 r / min, and the spin coating time is 30-200 s.

[0017] The present invention can remove volatiles such as water by soft baking. The present invention does not limit the parameters of soft baking, and those skilled in the art can select according to actual conditions. In some specific embodiments of the present invention, the soft baking temperature is 100-220° C., and the soft baking time is 60-200 s.

[0018] The present invention can improve the performance of the polymer film and achieve the best performance by curing the polymer precursor to undergo a cross-linking reaction under high temperature conditions. The thickness of the polymer film layer after curing will be lower than the thickness before curing. High-temperature curing can also optimize the surface flatness of the polymer film layer and reduce defects. The present invention does not limit the parameters of curing, and those skilled in the art can choose according to actual conditions. In some specific embodiments of the present invention, curing is carried out in a nitrogen atmosphere, starting from room temperature and rising at a rate of 1-5°C / min to 220-400°C, and maintaining for 20-120 minutes, and finally lowering to room temperature to complete the entire curing process.

[0019] The present invention can significantly improve the hydrophilicity of the surface of the polymer film layer by performing surface plasma treatment on the cured polymer film layer, thereby increasing the bonding force between the polymer film layer prepared in the next step. The degree of plasma treatment needs to be moderate. If the degree of plasma treatment is too strong, it is easy to cause the surface polymer film to be etched, affecting the surface roughness, etc. If the degree of plasma treatment is too weak, the hydrophilicity is not significantly improved. The present invention does not limit the parameters of plasma treatment. Those skilled in the art can adjust according to the properties of the actual polymer film, and select the process parameters that can obtain the minimum water drop angle as the optimal conditions without causing the surface polymer film to be etched. In some specific embodiments of the present invention, during the plasma treatment, the vacuum degree is <0.5 mbar, the oxygen flow rate is 40-400 sccm, the nitrogen flow rate is 0-100 sccm, the RF power is 50-300W, and the time is 10-90s.

[0020] In this embodiment, the time interval between the plasma treatment of the previous polymer film layer and the spin coating of the next polymer film layer is ≤ 24 hours. The reason is that the water drop angle of the surface of the polymer film layer after the plasma treatment will slowly change in the natural state, reducing the hydrophilicity, so the next spin coating needs to be performed within a certain time range to obtain the ideal bonding force.

[0021] In this implementation, step S1 includes: S11, coating the polymer precursor solution onto the surface of the j-th precursor film layer of the first polymer film layer, and then soft-baking to obtain the j+1-th precursor film layer of the first polymer film layer; S12, repeating the above step S11 until the mth layer of the precursor film of the first polymer film layer is obtained, and after curing and plasma treatment, the first polymer film layer is obtained; wherein j and m are both positive integers, and 0≤j<j+1≤m. Here, it should be pointed out that when j is 0, the surface of the jth layer of the precursor film of the first polymer film layer is the substrate surface.

[0022] In each polymer film layer of the present invention, by adopting the method of multiple coatings + multiple soft baking + one curing, the preparation efficiency of the multilayer polymer film layer can be further improved under the condition of satisfying the uniformity of thickness. However, the number of continuous spin coating should not be too many. If the number of continuous spin coating is too many, it will not only make the subsequent high-temperature curing difficult, but also cause large defects. For example, the inventor found in some experimental processes that when the PI layer is spin-coated, a large thickness defect will appear if the continuous spin coating exceeds 5 times, but there will be almost no defects when the spin coating is re-coated after each spin coating curing, indicating that the method of the present invention can reduce surface defects while improving the preparation efficiency. That is, the mth layer of the precursor film of the first polymer film layer must meet the following requirements: uniform thickness (STD≤5%), no obvious defects on the surface, and high-temperature curing can fully carry out cross-linking reaction. The present invention does not limit the number of precursor film layers of the first polymer film layer (or the thickness of the first polymer film layer), and those skilled in the art can choose according to the actual situation, so that the polymer film after spin coating can meet the above requirements. Under the condition of meeting the above requirements, the number of spin coating layers can be increased as much as possible, and the number of curing times can be reduced, so that the process time can be shortened and the efficiency can be improved. In some specific embodiments of the present invention, m≤5.

[0023] In this implementation, step S2 includes: S21, coating the polymer precursor solution onto the surface of the kth layer precursor film of the i+1th polymer film layer, and then soft-baking to obtain the k+1th layer precursor film of the i+1th polymer film layer; S22, repeat the above step S21 until the nth layer of precursor film of the i+1th polymer film layer is obtained, and after curing and plasma treatment, the i+1th polymer film layer is obtained; wherein k and n are both positive integers, and 0≤k<k+1≤n. Here, it should be pointed out that when k is 0, the surface of the kth layer of precursor film of the i+1th polymer film layer is the surface of the ith polymer film layer.

[0024] In each polymer film layer of the present invention, by adopting the method of multiple coatings + multiple soft baking + one curing, the preparation efficiency of the multilayer polymer film layer can be further improved under the condition of satisfying the thickness uniformity. Similarly, the nth layer precursor film of the ith polymer film layer must meet the following requirements: uniform thickness (STD≤5%), no obvious defects on the surface, and high temperature curing can fully carry out the cross-linking reaction. Under the condition of meeting the above requirements, the number of spin-coated layers can be increased as much as possible, and the number of curing times can be reduced, so as to shorten the process time and improve efficiency. In some specific embodiments of the present invention, n≤5.

[0025] The present invention does not impose any limitation on the thickness of each layer of the precursor film, and those skilled in the art may select the thickness according to actual conditions, as long as it is within the range obtainable by the process.

[0026] In this embodiment, the thickness of the multilayer polymer film layer is ≥5 μm, preferably ≥10 μm, and more preferably ≥20 μm.

[0027] In this embodiment, the Nth polymer film layer can be selected to be plasma treated after curing according to actual conditions. For example, if only a multi-layer polymer film layer is prepared, the surface of the Nth polymer film layer does not need to be plasma treated after curing; if other processes requiring plasma treatment are to be performed later, the surface of the Nth polymer film layer needs to be plasma treated after curing.

[0028] Example 1 (1) A polymer precursor solution (model PI-2610) was spin-coated onto the surface of a substrate (8-inch silicon wafer), followed by soft baking, curing and plasma treatment to obtain a first polymer film layer; during the spin coating process, the rotation speed was 1650 r / min and the time was 95 s; during the soft baking process, the temperature was 140°C and the time was 150 s; during the curing process, the curing was carried out in a nitrogen atmosphere, the heating rate was 2°C / min, the curing temperature was 330°C, and the time was 40 min; during the plasma treatment process, the vacuum degree was 0.2 mbar, the oxygen flow rate was 80 sccm, the nitrogen flow rate was 40 sccm, the RF power was 80 W, and the time was 30 s.

[0029] (2) Spin coating a polymer precursor solution (model PI-2610) onto the surface of the first polymer film layer, followed by sequentially performing soft baking, curing and plasma treatment to obtain a second polymer film layer; wherein the process parameters used for spin coating, soft baking, curing and plasma treatment are the same as those used to prepare the first polymer film layer.

[0030] (3) Spin coating a polymer precursor solution (model PI-2610) onto the surface of the second polymer film layer, followed by soft baking to obtain a first layer precursor film of a third polymer film layer; spin coating a polymer precursor solution (model PI-2610) onto the surface of the first layer precursor film of the third polymer film layer, followed by soft baking, curing and plasma treatment to obtain a third polymer film layer; wherein the process parameters used for spin coating, soft baking, curing and plasma treatment are the same as those used for preparing the first polymer film layer.

[0031] (4) Spin coating a polymer precursor solution (model PI-2610) onto the surface of the third polymer film layer, followed by soft baking to obtain the first layer of the precursor film of the fourth polymer film layer; repeating this step to obtain the second and third layers of the precursor film of the fourth polymer film layer, and finally curing and plasma treatment to obtain the fourth polymer film layer; wherein the process parameters used for spin coating, soft baking, curing and plasma treatment are the same as those used to prepare the first polymer film layer.

[0032] (5) Spin coating the polymer precursor solution (model PI-2610) onto the surface of the fourth polymer film layer, followed by soft baking to obtain the first layer of the precursor film of the fifth polymer film layer; repeat this step to obtain the second and third layers of the precursor film of the fifth polymer film layer, and then perform curing and plasma treatment to finally obtain a multilayer polymer film layer with a thickness of >22 um. The process parameters used for spin coating, soft baking, curing and plasma treatment are the same as those for preparing the first polymer film layer.

[0033] Example 2 Compared with Example 1, only the model of the polymer precursor solution was changed from PI-2610 prepared by a foreign manufacturer to PAA-9011 prepared by a domestic manufacturer, and the parameters of spin coating and soft baking were adjusted accordingly as follows: during the spin coating process, the rotation speed was 1600 r / min, and the time was 85 s; during the soft baking process, the temperature was 130°C, and the time was 150 s; except for the spin coating and soft baking parameters, the other process conditions and parameters were the same as in Example 1, and finally a multilayer polymer film layer with a thickness of >22um was obtained.

[0034] Comparative Example 1 Compared with Example 1, the only difference is that no plasma treatment is performed in steps (1) to (5).

[0035] Comparative Example 2 Compared with Example 2, the only difference is that no plasma treatment is performed in steps (1) to (5).

[0036] Performance Testing 1. Film surface condition test The surfaces of the multilayer polymer films obtained in Example 1-2 and Comparative Example 1-2 were observed by an optical microscope to see if there were any defects. The thickness consistency of the surfaces of the multilayer polymer films obtained in Example 1-2 and Comparative Example 1-2 was detected by a film thickness meter. The test results are shown in Table 1.

[0037] 2. Wettability test The first polymer film layer after plasma treatment in Example 1-2 and the first polymer film layer not subjected to plasma treatment in Comparative Example 1-2 were tested for water drop contact angle. The test results are shown in FIG. Figure 2 .

[0038] 3. Binding strength test The adhesion of the multilayer polymer film obtained in Example 1-2 and Comparative Example 1-2 was tested by scribing and UV film tape tearing. The test results are shown in Figure 3 .

[0039] 4. Warpage test In order to test the effect of multi-layer thick PI prepared by the method of the present invention on wafer warpage, silicon oxide film layers with different stresses were first grown on an 8-inch silicon wafer substrate to prepare two wafers with warpage (the height difference between the edge of the silicon wafer and the center) of -4um, -24um, and -87um, respectively. Then, the two wafers were used as substrates to prepare multi-layer polymer film layers with a thickness of >22um using the method of Example 1. The test results are shown in FIG. Figure 4 .

[0040] Table 1

[0041] Please refer to Table 1. It can be seen from Table 1 that the multilayer polymer film layer prepared by the method of the present invention has no additional obvious defects on the surface and has uniform thickness, which can meet the requirements of subsequent semiconductor MEMS processes.

[0042] See also Figure 2 ,pass Figure 2 It can be seen that after plasma treatment, the water contact angle of the PI film decreased significantly, indicating that its hydrophilicity was greatly improved.

[0043] See also Figure 3 ,pass Figure 3 It can be seen that the film layer prepared in Comparative Example 1-2 will adhere to the tape (within the dotted box in the figure) after tearing, while the film layer prepared in Example 1-2 will not adhere to the tape (within the dotted box in the figure), reflecting its good bonding strength with the original substrate.

[0044] See also Figure 4 ,pass Figure 4 It can be seen that by comparing the warpage of PI after each high-temperature curing stage, no matter how much the initial wafer warpage is, the final change in warpage is only 13-30um, indicating that the process of the present invention can meet the strict requirements of subsequent semiconductor processes for wafer flatness. At the same time, as the number of film layers increases, the change in warpage becomes smaller and smaller, gradually tending to a stable value, indicating that the process of the present invention can meet the needs of preparing thicker film layers.

[0045] The present invention combines the plasma surface treatment method to solve the problem that the prior art cannot prepare a thicker PI film layer, and has the following advantages: (1) The present invention improves the bonding strength between polymer film layers by plasma treatment of the cured polymer film layer, laying a foundation for preparing a multi-layer high-bonding polymer film layer; at the same time, combined with the method of spin coating the next polymer film layer after curing, the defect of poor thickness uniformity caused by blindly increasing the number of polymer layers for curing together is avoided. The method of the present invention can shorten the process time for obtaining a thicker film layer and improve the preparation efficiency by combining the method of multiple spin coatings and one curing under the condition of satisfying the thickness uniformity.

[0046] (2) The multilayer polymer film prepared by the present invention not only has a strong bonding force between the film layers, but also has little effect on the warping deformation of the wafer, and can meet the strict requirements for wafer flatness in subsequent processes such as photolithography.

[0047] (3) The present invention improves the bonding strength by using surface plasma treatment and combines the above two methods to effectively prepare a PI film layer with a thickness of 22um on an 8-inch wafer, which is much greater than the thickness recommended in the PI product manual. The method is also applicable to the preparation of thick PI film layers on 6-inch, 12-inch and other wafers, as well as other material film layers.

[0048] The specific implementation of the present invention described above does not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing a multilayer polymer film, characterized in that: The following steps are involved: S1, coating a polymer precursor solution onto a substrate surface, followed by soft baking, curing, and plasma treatment to obtain a first polymer film layer; S2, coating the polymer precursor solution onto the surface of the i-th polymer film layer, and then performing soft baking, curing, and plasma treatment to obtain the i+1-th polymer film layer; S3, repeating the above step S2 until the sum of the thicknesses of N polymer film layers reaches the target thickness, thereby obtaining a multilayer polymer film layer; wherein i and N are both positive integers, and 1≤i<i+1≤N.

2. The method for preparing a multilayer polymer film according to claim 1, characterized in that: The polymer is polyimide.

3. The method for preparing a multilayer polymer film according to claim 1, characterized in that: The substrate is a wafer; and / or, The size of the substrate is ≥ 6 inches.

4. The method for preparing a multilayer polymer film according to claim 1, characterized in that: The coating method is spin coating, and the rotation speed of the spin coating is 1000-4000 r / min, and the spin coating time is 30-200 s.

5. The method for preparing a multilayer polymer film according to claim 1, characterized in that: During the soft baking process, the soft baking temperature is 100-220° C. and the soft baking time is 60-200 s; and / or, During the curing process, the curing is carried out in a nitrogen atmosphere, starting from room temperature and rising at a rate of 1-5°C / min to 220-400°C, and maintained for 20-120min, and finally lowered to room temperature; and / or, During the plasma treatment, the vacuum degree is <0.5 mbar, the oxygen flow rate is 40-400 sccm, the nitrogen flow rate is 0-100 sccm, the RF power is 50-300 W, and the time is 10-90 s.

6. The method for preparing a multilayer polymer film according to claim 1, characterized in that: The time interval between the plasma treatment of the previous polymer film layer and the spin coating of the next polymer film layer is ≤24 hours.

7. The method for preparing a multilayer polymer film according to claim 1, characterized in that: Step S1 includes: S11, coating a polymer precursor solution onto a surface of the j-th precursor film layer of the first polymer film layer, and then soft-baking to obtain a j+1-th precursor film layer of the first polymer film layer; S12, repeating the above step S11 until the mth layer of precursor film of the first polymer film layer is obtained, and obtaining the first polymer film layer through curing and plasma treatment; wherein j and m are both positive integers, and 0≤j<j+1≤m≤5.

8. The method for preparing a multilayer polymer film according to claim 1, characterized in that: Step S2 includes: S21, coating a polymer precursor solution onto a surface of a k-th layer precursor film of the i+1-th polymer film layer, and then soft-baking the surface to obtain a k+1-th layer precursor film of the i+1-th polymer film layer; S22. Repeat the above step S21 until the nth layer of precursor film of the i+1th polymer film layer is obtained, and obtain the i+1th polymer film layer after curing and plasma treatment; wherein k and n are both positive integers, and 0≤k<k+1≤n≤5.

9. The method for preparing a multilayer polymer film according to claim 1, characterized in that: The thickness of the multi-layer polymer film layer is ≥5 μm.

10. The method for preparing a multilayer polymer film according to claim 1, characterized in that: The Nth polymer film layer is not plasma treated after curing.

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