Preparation method of indium column

Abstract

The invention relates to the technical field of micro-nano machining, in particular to a preparation method of an indium column. The preparation method comprises the following steps: sequentially forming a first photoresist coating and a second photoresist coating on the surface of a substrate from bottom to top; covering a partial region of the second photoresist coating with a mask; the area, not covered by the mask, of the second photoresist layer is exposed and then baked; after the baked second photoresist layer and the first photoresist layer are subjected to flooding exposure, developing is carried out, and indium plating holes are formed in the second photoresist layer and the first photoresist layer; and depositing an indium material on the surface of the second photoresist layer and in the indium plating hole to form an indium column. According to the method, one-time overlay exposure is matched with one-time extensive exposure operation, the indium plating hole with the undercut is prepared, back-and-forth switching of samples among different devices is reduced, and the utilization rate of the devices and the productivity of workpieces are improved.

Description

Technical Field

[0001] The present invention relates to the field of micro-nano processing technology, and in particular to a method for preparing indium pillars. Background Art

[0002] With the rapid development of superconducting quantum technology, people urgently hope to achieve the practical application of quantum computing, which requires integrating a larger scale and more qubit numbers, posing higher requirements for the chip integration process. Referring to the application of traditional semiconductor advanced packaging technology in large-scale chip integration, the effective integration of multi-chips with different functions can be realized. For example, in an infrared focal plane array detector, the focal plane array chip and the readout circuit chip are connected together through an indium pillar flip-chip interconnection process. In the large-scale integration of superconducting quantum chips, realizing flip-chip interconnection of multi-plane chips through indium pillars is also the most mainstream solution at present. In order to prepare indium pillars with good morphology and uniform distribution, technicians have optimized and adjusted the preparation process of indium pillars. For example, Chinese Patent CN112652540B discloses a double-layer resist process of an electron beam resist and an ultraviolet resist. The evaporation holes of indium pillars are defined by lithography of the upper layer resist through ultraviolet lithography, and the undercut morphology is achieved by removing the bottom layer resist using an etching process to facilitate cleaning and stripping after indium pillar evaporation. Chinese Patent CN112645276B discloses a double-layer resist process of a single positive resist. The bottom layer resist is completely exposed to act as a sacrificial layer to achieve undercutting for the purpose of facilitating stripping. Chinese Patent CN102136484B and Chinese Patent CN118016683A prepare inverted T-shaped indium pillar evaporation holes by performing exposure and development on the double-layer resist with different areas respectively, for the purpose of facilitating stripping.

[0003] In the current double-layer photoresist process for preparing indium pillars, a multiple lithography exposure process is generally used to achieve an inverted T-shaped or undercut morphology. Inevitably, multiple lithography exposures and spin coating baking operations need to be interspersed during this process, and it is necessary to switch operations between different devices. The process flow is rather cumbersome and time-consuming, which will reduce production capacity. In the solutions disclosed in patents CN102136484B and CN118016683A, multiple lithography exposure steps are required. On the one hand, the long operation time of lithography exposure affects production capacity, and at the same time, the lithography deviation will also affect the morphology and stability of the final inverted T-shaped structure, thus affecting the effect of preparing indium pillars. Patent CN112652540B adopts a double-layer photoresist solution with an electron beam photoresist as the bottom photoresist. However, the electron beam photoresist has a high cost, and at the same time, 2 exposures, 4 baking operations and 1 etching interspersed operation are required during the whole operation process. The operation process is cumbersome and time-consuming, seriously affecting production capacity. In the solution of patent CN 112645276 B, there are also 2 exposures and 2 spin coating operations interspersed. At the same time, for the bottom photoresist that has been fully exposed, since its molecular chain structure has been damaged by ultraviolet light, it is easy to have problems such as blistering and cracking during high-temperature baking before development, seriously affecting subsequent lithography and indium plating effects.

[0004] Under such a background, there is an urgent need to develop a preparation scheme for indium pillars with a simplified operation process and high production capacity to meet the usage requirements in the field of superconducting quantum technology. Summary of the Invention

[0005] The present invention adopts a double-layer photoresist structure, and prepares indium plating holes through 1 lithography exposure in combination with 1 flood exposure. The spin coating of the photoresist is completed before the first exposure, which simplifies the indium pillar process flow and avoids the back-and-forth switching of samples between different devices; by utilizing the differential exposure response characteristics of positive photoresist, negative photoresist and reversal photoresist, the preparation of indium plating holes can be realized, avoiding the interspersed operation of multiple spin coating and lithography exposures; the efficiency of indium pillar processing is greatly improved.

[0006] The first aspect of the present invention provides a method for preparing indium pillars, and the preparation steps include:

[0007] Form a first photoresist coating and a second photoresist coating on the surface of the substrate in sequence from bottom to top;

[0008] Cover a part of the area of the second photoresist coating with a mask;

[0009] After exposing the area of the second photoresist layer not covered by the mask, perform baking;

[0010] After flood exposing the baked second photoresist layer and the first photoresist layer, perform development to form indium plating holes in the second photoresist layer and the first photoresist layer;

[0011] Deposit indium material on the surface of the second photoresist layer and in the indium plating holes to form indium pillars.

[0012] In some embodiments, strip the first photoresist layer and the second photoresist layer from the substrate to obtain a substrate with the indium pillars.

[0013] The first photoresist layer uses a positive photoresist.

[0014] The second photoresist layer uses a negative photoresist or a reversal photoresist.

[0015] The present invention realizes local exposure of the second photoresist layer by means of a mask. The local exposure involved is a kind of overlay exposure method, specifically referring to that in the lithography process, after accurately aligning the pattern of the layer mask with the pattern of the previous layer on the wafer (substrate), exposure is carried out to achieve effective superposition of the pattern structures. Under the action of the layer mask, both the first photoresist layer and the second photoresist layer can be divided into an exposure area and a non-exposure area. There are property differences between different types of photoresists in the exposure area and the non-exposure area (the positive photoresist becomes a soluble substance after being irradiated with light and can be dissolved by the developer; the negative photoresist undergoes a crosslinking reaction after being irradiated with light and is not dissolved by the developer; the property of the reversal photoresist is between the two and can be reversed according to requirements for flexible use), so as to realize lithography pattern processing.

[0016] The flood exposure in the present invention means that in the lithography process, without using a mask, the current layer of photoresist is exposed uniformly without discrimination.

[0017] Optionally, the step of sequentially forming a first photoresist coating and a second photoresist coating on the substrate surface from bottom to top includes: coating the first photoresist on the surface of a clean substrate and performing a first baking to obtain a first photoresist layer; coating the second photoresist on the surface of the first photoresist layer and performing a second baking to obtain a second photoresist layer; after the two bakes, a first photoresist coating and a second photoresist coating are sequentially formed on the substrate surface from bottom to top.

[0018] Optionally, the rotation speed of coating the first photoresist on the surface of a clean substrate is 1000 - 4000 rpm; more preferably 2000 rpm.

[0019] Optionally, the rotation speed of coating the second photoresist on the surface of the first photoresist layer is 500 - 5000 rpm; more preferably 1000 - 4000 rpm.

[0020] Optionally, the temperature of the first baking is 80 - 140 °C, and the time of the first baking is 1 - 10 min.

[0021] More preferably, the temperature of the first baking is 120 °C, and the time of the first baking is 2 min.

[0022] Optionally, the temperature of the second baking is 80-140°C, and the time of the second baking is 1-15 min.

[0023] More optionally, the temperature of the second baking is 100°C, and the time of the first baking is 2-10 min.

[0024] Further optionally, when the second photoresist is a positive photoresist, the rotation speed of coating the second photoresist on the surface of the first photoresist layer is 800-1200 rpm, and the time of the second baking is 1-5 min.

[0025] Further optionally, when the second photoresist is a negative photoresist, the rotation speed of coating the second photoresist on the surface of the first photoresist layer is 2000-4000 rpm, and the time of the second baking is 5-15 min.

[0026] Optionally, the conditions of the exposure are: the light intensity is 6-12 mw / cm 2 , and the exposure time is 5-10 s.

[0027] Optionally, when the second photoresist is a positive photoresist, the baking is a positive baking;

[0028] After the positive baking and the flood exposure treatment, the area of the second photoresist layer covered by the mask can be dissolved by the developer.

[0029] After the flood exposure treatment, the first photoresist layer is completely exposed.

[0030] The second photoresist layer and the first photoresist layer after the flood exposure treatment are developed. After development, the partial area of the first photoresist and the area of the second photoresist layer covered by the mask are both dissolved by the developer. After cleaning, indium plating holes are formed.

[0031] Optionally, when the second photoresist is a negative photoresist, the second photoresist layer is first developed after the baking, and then the flood exposure treatment is carried out.

[0032] Specifically, when the second photoresist is a negative photoresist, the second photoresist layer is baked to completely crosslink the area not covered by the mask; the baked second photoresist layer is first developed, so that the area not covered by the mask of the second photoresist layer is dissolved by the developer. After cleaning, a part of the first photoresist layer is exposed; then the flood exposure treatment is carried out to completely expose the first photoresist; the first photoresist layer after the flood exposure treatment is second developed. After the second development, the first photoresist is partially dissolved by the developer. After cleaning, indium plating holes are formed.

[0033] Optionally, after the first photoresist layer is flood-exposed and developed, it is partially removed by the developer. The orthographic projection of the area of the second photoresist layer covered by the mask on the substrate is located within the area where the first photoresist layer is partially removed, so that the indium plating holes have an undercut structure.

[0034] Due to the effect of flood exposure, the positive photoresist on the surface of the substrate in the present invention can be completely dissolved in the developer, while the exposed area of the negative photoresist is insoluble in the developer. The soluble area of the positive photoresist grows with the delay of the development time to form an undercut structure. By controlling the development time, an indium plating hole structure with an undercut that meets the processing requirements is obtained.

[0035] Optionally, the developer is an aqueous solution of TMAH (tetramethylammonium hydroxide); the concentration of the TMAH aqueous solution is 1-5 wt%.

[0036] Optionally, the indium plating operation includes: depositing indium material on the surface of the second photoresist layer and in the indium plating holes by using a thermal evaporation device to obtain indium columns, and the evaporation thickness of the indium columns is 2-15 μm; it can be exemplified as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15 μm.

[0037] Optionally, after the indium plating operation is completed, it is transferred to an organic cleaning agent and heat-treated at 80-90 °C for 1-5 h. After taking it out, the first photoresist layer, the second photoresist layer and the excess indium plating layer on the surface of the glue layer on the substrate surface are removed; then it is cleaned to obtain the final product.

[0038] Optionally, the sample is sequentially cleaned with isopropyl alcohol and ultrapure water and blown dry with an inert gas to obtain the product.

[0039] The organic cleaning agent can be exemplified as NMP (N-methyl-2-pyrrolidone), dimethylformamide (DMF), dimethylacetamide (DMAC), methanol, ethanol, isopropyl alcohol, ethyl acetate, ethylene glycol ether, propylene glycol ether, acetone, methyl ethyl ketone, etc.

[0040] The inert gas can be exemplified as nitrogen.

[0041] Optionally, the conditions for the flood exposure are: the light intensity is 6-12 mw / cm 2 , and the exposure time is 50-80 s; more preferably, the light intensity is 9 mw / cm 2 , and the exposure time is 60 s.

[0042] The present invention does not particularly limit the thickness of the photoresist, as long as it can meet the processing requirements of the Lift-Off process. Generally, it is required that the thickness of the photoresist is more than 1.5 times the thickness of the substrate (metal layer).

[0043] The present invention does not have special requirements for the exposure equipment for exposure and flood exposure, and it is only necessary to achieve the exposure purpose. For example, contact lithography machines, laser direct writing lithography machines or step-and-repeat lithography machines can be used for exposure; contact lithography machines, laser direct writing lithography machines, step-and-repeat lithography machines or ultraviolet lamps, etc. can be used for flood exposure.

[0044] Optionally, the thickness of the first photoresist layer is 10-15 μm; it can be exemplified as 10, 11, 12, 13, 14 or 15 μm.

[0045] Optionally, the thickness of the second photoresist layer is 2-5 μm; it can be exemplified as 1, 2, 3, 4 or 5 μm.

[0046] Beneficial effects:

[0047] The present invention provides a method for preparing indium pillars, which has the following advantages:

[0048] (1) In the whole process flow, only two-layer photoresist needs to be initially coated on the surface of the substrate, and one-time overlay exposure (local exposure) is combined with one-time flood exposure process treatment to prepare indium-plated holes with undercut structures, which simplifies the processing flow of indium pillars. After exposure, there is no need to perform processes such as coating and etching again, avoiding the back-and-forth switching of samples between different devices, and improving the equipment utilization rate and the production capacity of workpieces.

[0049] (2) In the present invention, two-layer photoresist is sequentially coated on the surface of the substrate, the first photoresist is a positive photoresist, and the second photoresist is a negative photoresist or a reversal photoresist. Under the presence of a mask, local exposure is performed. The area of the first photoresist not covered by the mask is completely exposed. After baking, the molecules in the photoresist layer crosslink to form a photoresist layer material insoluble in the developer; while the area covered by the mask is dissolved in the developer after flood exposure and development treatment, and after cleaning, indium-plated holes can be obtained, which is convenient for indium plating operation.

[0050] (3) The design of the present invention is flexible. When the second photoresist is a reversal photoresist, after local exposure, direct reversal baking is carried out, and then flood exposure treatment is carried out together with the first photoresist layer. After flood exposure, through development operation, the area of the second photoresist covered by the mask and part of the first photoresist layer are dissolved by the developer to obtain indium-plated holes; when the second photoresist is a negative photoresist, after local exposure, baking and development are first carried out to remove the area of the second photoresist layer covered by the mask to expose part of the first photoresist layer, and then flood exposure and development are carried out to remove part of the first photoresist layer to obtain indium-plated holes. Both methods do not require multiple overlay exposures and the interspersed operation of spin coating and baking, significantly improving the production efficiency of workpieces.

[0051] (4) In the overall process flow of the present invention, only one overlay exposure is required, which can significantly shorten the process, reduce the mask and the equipment time of overlay, and reduce the cost; at the same time, problems such as blistering and cracking that are prone to occur during high-temperature baking before development are avoided, and the indium plating effect is optimized.

[0052] (5) The positive photoresist on the surface of the substrate of the present invention is completely dissolved in the developer under the action of flood exposure, while the area of the negative photoresist not covered by the mask is insoluble in the developer. The soluble area of the positive photoresist grows with the delay of the development time to form an undercut structure. By controlling the development time, an indium plating hole structure with an undercut that meets the processing requirements can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 . The preparation step principle of Example 1;

[0054] Figure 2 . The flowchart of the workpiece in Example 1;

[0055] Figure 3 . The flowchart of the workpiece in Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0056] Note: The raw materials used in the present invention are all commercially available.

[0057] EXAMPLES

[0058] Example 1

[0059] This example provides a method for preparing indium pillars, including the following steps:

[0060] S1. The first photoresist (positive photoresist AZ4620) is spin-coated on the surface of a clean substrate at a speed of 2000 rpm, and the first baking is carried out at 120 °C for 2 min to obtain a first photoresist layer with a thickness of 12 μm;

[0061] S2. The second photoresist (inversion photoresist AZ5214) is spin-coated on the surface of the first photoresist layer at a speed of 1000 rpm, and the second baking is carried out at 100 °C for 2 min to obtain a second photoresist layer with a thickness of 3 μm; after the secondary baking, a sample with the first photoresist layer, the second photoresist layer and the substrate stacked in sequence can be obtained.

[0062] S3. Using a contact exposure machine, a mask is placed on the surface of the sample, and the sample is locally exposed to define the position of the indium pillars; the light intensity of the local exposure is 9 mw / cm 2 , and the exposure time is 8 s; after the local exposure, the exposed area of the second photoresist layer is completely exposed, and the first photoresist layer is not effectively exposed.

[0063] S4. Place the sample after partial exposure at 100 °C for reverse baking for 2 min; then perform flood exposure on the sample using ultraviolet light, with the light intensity of flood exposure being 9 mw / cm 2 , and the exposure time being 60 s; after the flood exposure treatment, the unexposed areas of the first photoresist and the second photoresist layer are completely exposed and can be dissolved by the developer.

[0064] S5. Use a developer (2.38 wt% aqueous solution of TMAH) to develop the sample after flood exposure treatment for 120 s; during this process, some unexposed areas of the first photoresist layer and the second photoresist layer are dissolved by the developer, then wash the sample with ultrapure water, and then dry it with nitrogen to obtain a sample with indium plating holes exposed on the substrate surface.

[0065] The orthographic projection of the unexposed area of the second photoresist layer on the substrate is located within the area where part of the first photoresist layer is removed, so that the indium plating hole has an undercut structure with a narrow upper part and a wide lower part.

[0066] S6. Place the sample in a thermal evaporation equipment for indium plating operation. After the indium plating operation, indium columns are deposited in the indium plating holes (the width of the indium columns is the same as the width of the orthographic projection of the unexposed area of the second photoresist layer on the substrate), and an indium plating layer is deposited on the surface of the second photoresist; the thickness of the indium columns is 6 μm.

[0067] S7. Place the sample in an organic cleaning agent (NMP), heat it at 85 °C for 3 h; strip and remove the first photoresist, the second photoresist, and the excess indium plating layer deposited on the surface of the second photoresist; obtain a product with indium columns plated on the surface. Wash the product with isopropyl alcohol and ultrapure water in sequence, and dry it with nitrogen to obtain the product.

[0068] Figure 1 . The principle of the preparation steps of Example 1 is shown in Figure 1 ; the manufacturing process flow chart is shown in Figure 2 ;

[0069] Example 2

[0070] This example provides a method for preparing indium columns, including the following steps:

[0071] S1. Spin-coat a first photoresist (positive photoresist AZ4620) on the surface of a clean substrate at a speed of 2000 rpm, and perform the first baking at 120 °C for 2 min to obtain a first photoresist layer with a thickness of 12 μm;

[0072] S2. Coating the second photoresist (negative photoresist AZ2070) on the surface of the first photoresist layer at a rotational speed of 4000 rpm, and performing the second baking for 10 min at 100 °C to obtain the second photoresist layer, with the thickness of the first photoresist layer being 4 μm; after the secondary baking, a sample with the first photoresist layer, the second photoresist layer, and the substrate stacked in sequence can be obtained.

[0073] S3. Using a contact exposure machine to perform local exposure on the sample to define the indium pillar positions; the light intensity of the local exposure is 9 mw / cm 2 , and the exposure time is 8 s; after the local exposure, the exposed area of the second photoresist layer is completely exposed, and the first photoresist layer is not effectively exposed.

[0074] Placing the sample after local exposure in an oven at 100 °C for baking for 2 min, the locally exposed area of the second photoresist layer is completely cross-linked and insoluble in the developer, and the non-exposed area of the second photoresist layer is soluble in the developer.

[0075] S4. Using a developer (2.38 wt% TMAH solution) to perform a single development treatment on the baked sample, with the development time being 120 s; dissolving the non-exposed area of the second photoresist layer with the developer, and then cleaning the sample with ultrapure water, after cleaning, a part of the first photoresist layer is exposed.

[0076] S5. Using ultraviolet light to perform flood exposure on the sample after the single development, the light intensity of the flood exposure is 9 mw / cm 2 , and the exposure time is 60 s; after the flood exposure treatment, the non-exposed area of the second photoresist layer is completely exposed, and the first photoresist layer is completely exposed.

[0077] S6. Using a developer (2.38 wt% aqueous TMAH solution) to perform a development treatment on the sample after the flood exposure, with the development time being 120 s; in this process, the non-exposed area of the second photoresist layer and a part of the first photoresist layer are dissolved by the developer. Then cleaning the sample with ultrapure water, and then drying it with nitrogen to obtain a sample with indium plating holes exposed on the substrate surface.

[0078] The orthographic projection of the non-exposed area of the second photoresist layer on the substrate is located within the non-area where the first photoresist layer is partially removed, so that the indium plating holes have an undercut structure with a narrow upper part and a wide lower part.

[0079] S7. Placing the sample in a thermal evaporation device for indium plating operation, after the indium plating operation, indium pillars are deposited in the indium plating holes (the width of the indium pillars is the same as the width of the orthographic projection of the non-exposed area of the second photoresist layer on the substrate), and an indium plating layer is deposited on the surface of the second photoresist; the thickness of the indium pillars is 6 μm.

[0080] S8. Place the sample in an organic cleaning agent (NMP), heat-treat it at 85 °C for 3 h; strip off the first photoresist, the second photoresist, and the excess indium plating layer deposited on the surface of the second photoresist; obtain a product with indium pillars plated on the surface. Clean the product successively with isopropyl alcohol and ultrapure water, and dry it with nitrogen gas to obtain the product.

[0081] The manufacturing process flow chart of Example 2 is shown in Figure 3 .

[0082] Finally, it should be noted that the above are only optional embodiments of the present application and are not used to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing indium pillars, characterized in that, The preparation steps include: forming a first photoresist coating and a second photoresist coating on the surface of the substrate in sequence from bottom to top; covering a part of the area of the second photoresist coating with a mask; after exposing the area of the second photoresist layer not covered by the mask, baking is carried out; after flood exposure of the baked second photoresist layer and the first photoresist layer, developing is carried out to form indium plating holes in the second photoresist layer and the first photoresist layer; depositing indium material on the surface of the second photoresist layer and in the indium plating holes to form indium pillars; the first photoresist layer uses a positive photoresist; the second photoresist layer uses a negative photoresist or a reversal photoresist.

2. The method for preparing an indium pillar according to claim 1, wherein When the second photoresist is a reversal photoresist, the baking is reversal baking; after the reversal baking and the flood exposure treatment, the area of the second photoresist layer covered by the mask can be dissolved by the developer; after the flood exposure treatment, the first photoresist layer is completely exposed.

3. The preparation method of the indium pillar according to claim 1, wherein, When the second photoresist is a negative photoresist, after the baking, the second photoresist layer is developed for the first time, and then the flood exposure treatment is carried out.

4. The method for preparing an indium pillar according to claim 2 or 3, characterized in that, after the first photoresist layer is flood exposed and developed, it is partially removed by the developer, and the positive projection of the area of the second photoresist layer covered by the mask on the substrate is located within the area where the first photoresist layer is partially removed, so that the indium plating holes have an undercut structure.

5. The method for preparing an indium pillar according to claim 1, characterized in that, The conditions for the local exposure are as follows: the light intensity is 6 - 12 mw / cm 2 , and the exposure time is 5 - 10 s.

6. The method for preparing an indium pillar according to claim 1, characterized in that, The step of forming a first photoresist coating and a second photoresist coating on the surface of the substrate in sequence from bottom to top includes: coating the first photoresist on the surface of the clean substrate at a rotation speed of 1000 - 4000 rpm, and carrying out the first baking to obtain the first photoresist layer; coating the second photoresist on the surface of the first photoresist layer at a rotation speed of 500 - 5000 rpm, and carrying out the second baking to obtain the second photoresist layer.

7. The preparation method of the indium pillar according to claim 6, wherein The temperature of the first baking is 80 - 140 °C, and the time of the first baking is 1 - 10 min.

8. The method for preparing an indium pillar according to claim 6, wherein, The temperature of the second baking is 80 - 140 °C, and the time of the second baking is 1 - 15 min.

9. The method for preparing an indium pillar according to claim 1, wherein The conditions of the flood exposure are: The light intensity is 6 - 12 mw / cm 2 , and the exposure time is 50 - 80 s.

10. The preparation method of the indium column according to claim 2, characterized in that, the developer is an aqueous TMAH solution; the concentration of the aqueous TMAH solution is 1 - 5 wt%.

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