Thick film photoresist exposure pattern distortion optimization method

Abstract

The invention discloses a thick-film photoresist exposure pattern distortion optimization method, which relates to the technical field of chip packaging process, and comprises the following steps: physical vapor deposition, baking curing, exposure coating, developing and etching: carrying out chemical reaction on active particles in plasma and pollutants on the surface of a material, and carrying out accurate detection; thick-film photoresist is adopted, the thickness of the photoresist after coating is larger than the depth of field of an exposure machine, and the problems that patterns within the depth of field have distortion risks, and product lines are prone to short circuit and open circuit are solved. Patterns within the depth of field can achieve accurate recarving of the mask plate, and patterns outside the depth of field have the risk of distortion.

Description

Technical Field

[0001] The present invention specifically relates to the technical field of chip packaging processes, and specifically to a method for optimizing the distortion of thick film photoresist exposure patterns. Background Art

[0002] As Moore's Law in chip manufacturing approaches its limit, engineers have shifted the optimization of the manufacturing process for high-performance products to the optimization of packaging processes. More and more advanced packaging processes have been widely applied, but they also pose challenges to the packaging process. In the field of chip manufacturing, traditional exposure and development technologies use thin film photoresists. The thickness of the photoresist after coating is generally at the nanometer level, all of which are less than the exposure depth of field of the lithography machine. The pattern exposed on the wafer is almost the same as the pattern on the mask. However, in the field of advanced packaging, thick film photoresists are used. The thickness of the photoresist after coating is greater than the depth of field of the exposure machine, and there is a risk of distortion for patterns outside the depth of field, and short circuits and open circuits are likely to occur in the product circuit. Now, an exposure process optimization method applicable to thick film photoresists is invented, which can reduce the risk of pattern distortion during exposure;

[0003] In the semiconductor packaging exposure process, since the thickness of the thick film photoresist is greater than the depth of field of the exposure machine, the focal plane can be moved to the center of the photoresist, so that the depth of field covers more patterns. The patterns within the depth of field can achieve precise replication of the patterns on the mask, and there is a risk of distortion for patterns outside the depth of field. The wafer has a certain reflectivity. When light shines directly on the wafer, the light is reflected and hits the adjacent photoresist that should not be exposed, resulting in distortion of the photoresist pattern. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for optimizing the distortion of thick film photoresist exposure patterns. In this method, a BARC (Bottom Anti-Reflection Coating) is coated at the interface between the photoresist and the wafer, so that the light will shine on the BARC instead of the wafer. The BARC absorbs the light to prevent it from being reflected, improving the accuracy of the photoresist pattern. In addition, during the exposure and development process, the exposure focal plane needs to be moved to the center point of the thick film photoresist to expand the depth of field and avoid distortion, so as to solve the problems in the above background art.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] A method for optimizing the distortion of thick film photoresist exposure patterns specifically includes the following steps:

[0007] S1. Physical vapor deposition. After preparing the wafer, under the action of electrons, argon atoms are collided during the flight towards the substrate, causing them to ionize to produce Ar+ ions and new electrons, and then a reflective coating is applied to the surface of the wafer;

[0008] S2. Baking and curing: Cure the bottom anti-reflection layer with high temperature, dry it to remove moisture and solvents, and form a uniform and stable thin film n real , and then apply a thick film photoresist on the surface;

[0009] S3. Exposure and baking: Use an exposure machine to expose the photoresist, transfer the pattern of the mask to the photoresist, and finally perform a drying process to remove the solvents in the photoresist;

[0010] S4. Development: The photoresist in the exposed area of the positive photoresist and the non-exposed area of the negative photoresist dissolves in the developer, and the photoresist forms the corresponding pattern of the mask;

[0011] S5. Etching: A process of selectively removing unnecessary materials from the surface of the silicon wafer by physical methods, and use isopropyl alcohol to remove particulate contaminants;

[0012] S6. Decomposition and cleaning: By using the reactive particles in the plasma to chemically react with the contaminants on the material surface, decompose them into volatile substances to achieve the purpose of cleaning, and at the same time observe under a microscope whether there are still contaminants on the wafer;

[0013] S7. Precision inspection: Use an industrial microscope to precisely inspect the photoresist pattern to ensure that the pattern is correct and the size deviation is within the specifications;

[0014] As a further technical solution of the present invention, in the step S2, the thickness of the photoresist is greater than or equal to 10um;

[0015] As a further technical solution of the present invention, in the step S2, the thickness of the anti-reflection coating is one-fourth of the wavelength of light;

[0016] As a further technical solution of the present invention, in the step S1: New electrons fly towards the substrate, Ar ions are accelerated towards the cathode target under the action of an electric field, and bombard the target surface with high energy, causing sputtering of the target material; among the sputtered particles, neutral target atoms or molecules are deposited on the substrate to form a thin film;

[0017] As a further technical solution of the present invention, the sputtered particles adopt magnetron sputtering technology, and a magnetic force is increased in the PVD cavity. Since the moving electrons are affected by the Lorentz force in the magnetic field, their movement trajectories will bend or even generate spiral movements, and their movement paths become longer, increasing the number of collisions with working gas molecules and increasing the plasma density:

[0018] As a further technical solution of the present invention, the magnetron sputtering technology improves the energy of the atoms incident on the substrate surface, the number of collisions of depositing the TiW barrier layer and the Cu seed layer, and increases the plasma density;

[0019] As a further technical solution of the present invention, in step S3, after the photoresist contacts light, its properties will change, and the pattern on the photomask is accurately copied onto the wafer, endowing the wafer with the function of an electronic circuit diagram.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1. In the present invention, the focal plane is set at the center of the thick film photoresist, expanding the depth of field area of the exposure process, and there is no risk of pattern distortion within the depth of field.

[0022] 2. In the present invention, an organic anti-reflection layer is coated on the wafer before exposure, and the light is absorbed by the anti-reflection layer and will not be reflected.

[0023] 3. In the present invention, the process flow of coating the anti-reflection layer is: coating the anti-reflection layer → baking and curing → coating the photoresist → exposure → post-baking → etching → cleaning with isopropyl alcohol → plasma cleaning. Description of the Drawings

[0024] Figure 1 is a schematic diagram of setting the focus at the center of the photoresist in the present invention.

[0025] Figure 2 is a schematic diagram of moving the focus to the center of the photoresist in the present invention.

[0026] Figure 3 is a schematic diagram of the present invention without the bottom anti-reflection layer BARC.

[0027] Figure 4 is a schematic diagram of the present invention with the bottom anti-reflection layer BARC. Detailed Embodiments

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0029] Please refer to Figures 1-4 , in the embodiments of the present invention, a method for optimizing the distortion of the exposure pattern of the thick film photoresist specifically includes the following steps:

[0030] S1. Physical vapor deposition. After preparing the wafer, under the action of electrons, during the flight towards the substrate, they collide with argon atoms, causing ionization to generate Ar+ ions and new electrons, and then the reflective coating is applied to the surface of the wafer.

[0031] As described above, during the process of preparing the wafer, the wafer batch and part number are checked to match the corresponding materials, process parameters, process flows, material specifications, and inspection standards for subsequent processes. Meanwhile, the surface of the wafer is inspected for scratches, cracks, or foreign objects. Then, the critical dimensions of the wafer are measured to ensure that the dimensional errors are within the specifications. Ultrasonic cleaning is used to ensure that the surface of the wafer is free of impurities, as impurities on the wafer surface can affect the coating of the subsequent anti-reflection layer and photoresist.

[0032] S2. Baking and curing: The bottom anti-reflection layer is cured at a high temperature and dried to remove moisture and solvents, forming a uniform and stable thin film. real ;

[0033] S3. Photoresist coating: The photoresist is coated and exposed using an exposure machine to transfer the pattern on the mask to the photoresist. Finally, a drying process is carried out to remove the solvents in the photoresist.

[0034] When the photoresist is exposed to light, its properties change, and the pattern on the photomask is accurately copied onto the wafer, endowing the wafer with a function similar to an electronic circuit diagram.

[0035] The following is the formula for calculating the resolution of the exposure machine:

[0036]

[0037] R: Minimum resolution;

[0038] K1: Process coefficient, and the coefficient for the packaging process is generally 0.8 - 1.

[0039] λ: Light source wavelength (365 - 436 nm);

[0040] NA: Numerical aperture (0.3 - 0.4);

[0041] By adopting the above technical solution, an organic anti-reflection layer is coated on the wafer before exposure, and the light is absorbed by the anti-reflection layer without reflection.

[0042] S4. Development: The photoresist in the exposed area of the positive photoresist and the non-exposed area of the negative photoresist dissolves in the developer, and the photoresist forms the corresponding pattern of the mask.

[0043] S5. Etching: A process of selectively removing the unnecessary materials from the surface of the silicon wafer using physical methods, and isopropyl alcohol is used to remove particulate contaminants.

[0044] S6. Decomposition cleaning: By using the reactive particles in the plasma to chemically react with the contaminants on the material surface and decompose them into volatile substances to achieve the purpose of cleaning. Meanwhile, the wafer is observed under a microscope to check for remaining contaminants.

[0045] S7. Precision inspection: The industrial microscope precisely inspects the photoresist pattern to ensure the pattern is correct and the dimensional deviation is within the specification.

[0046] In this example, the thickness of the photoresist in step S2 is greater than or equal to 10 μm.

[0047] In this example, in step S2, the thickness of the anti-reflection coating is one-quarter of the wavelength of light.

[0048] The light reflected from the bottom and the light reflected from the surface produce coherent interference, canceling each other's effects and further reducing reflection. There are two methods to remove the anti-reflection layer, namely isopropyl acetone and developer. This patent uses the method of isopropyl acetone + plasma cleaning, which has a better removal effect. The role of BARC is to reduce the substrate reflected light through destructive interference, and its thickness needs to meet:

[0049]

[0050] nBARC: The refractive index of the BARC material (complex number, including extinction coefficient kk).

[0051] d: The physical thickness of BARC (target value).

[0052] λ: The wavelength of the lithography light source.

[0053] In this embodiment, when considering material absorption (k≠0), the thickness is corrected to:

[0054]

[0055] n real : The real part of the refractive index (related to the material composition)

[0056] k: Extinction coefficient (absorption characteristic).

[0057] By adopting the above technical solutions;

[0058] Furthermore, for common organic BARC materials, n real ≈1.6, k≈0.3. Substituting the data into the formula, we can get:

[0059]

[0060] According to the calculation results, the ideal coating thickness of BARC is approximately equal to 57.3 nm.

[0061] In this example, in step S1: The new electrons fly towards the substrate, and the Ar ions are accelerated towards the cathode target under the action of the electric field and bombard the target surface with high energy, causing sputtering of the target material. Among the sputtered particles, the neutral target atoms or molecules are deposited on the substrate to form a thin film.

[0062] In this example, the sputtering particles adopt the magnetron sputtering technology, which increases the magnetic force in the PVD cavity. Since the moving electrons are affected by the Lorentz force in the magnetic field, their movement trajectories will bend or even generate spiral motion, their movement paths become longer, the number of collisions with working gas molecules increases, and the plasma density increases:

[0063] In this example, the magnetron sputtering technology improves the energy of the atoms incident on the substrate surface and improves the quality of the thin film; the number of collisions during the deposition of the TiW barrier layer and the Cu seed layer increases, the plasma density increases, so the magnetron sputtering rate is greatly improved, and it can work at a lower sputtering voltage and gas pressure, reducing the tendency of film contamination;

[0064] In this example, in step S3; after the photoresist contacts the light, its properties will change, and the pattern on the photomask is accurately copied onto the wafer, endowing the wafer with the function of an electronic circuit diagram.

[0065] After the photoresist contacts the light, its properties will change, and the pattern on the photomask is accurately copied onto the wafer, endowing the wafer with a function similar to that of an electronic circuit diagram: Exposure machine resolution:

[0066]

[0067] R: Minimum resolution;

[0068] K1: Process coefficient, the coefficient of the packaging process is generally 0.8 - 1;

[0069] λ: Light source wavelength (365 - 436 nm);

[0070] NA: Numerical aperture (0.3 - 0.4);

[0071] By adopting the above technical solution, an organic anti-reflection layer is coated on the wafer before exposure, and the light is absorbed by the anti-reflection layer and will not be reflected;

[0072] By adopting the above technical solution, the focal plane is set at the center of the thick film photoresist to expand the depth of field area of the exposure process;

[0073] Depth of field, as a key concept in optics, describes the range of distances within which a clear image can be formed when a lens focuses on an object to a sharp state. When the lens is aligned with a target and achieves clear focus, not only can the object at the position directly in front of the lens form a clear image, but also within a certain range in front of and behind it, relatively clear image points that the eye can accept can be formed. This clear imaging distance from front to back is the depth of field. During the exposure process, it is necessary to move the focal plane to the center of the photoresist so that the depth of field can cover more areas in the thick film photoresist and the photoresist can obtain a more accurate pattern. Among them, the calculation formula for the depth of field is:

[0074]

[0075] DOF: Depth of field;

[0076] λ: Wavelength of the light source (365 - 436 nm);

[0077] NA: Numerical aperture (0.3 - 0.4);

[0078] After substituting the data, it is:

[0079]

[0080] After substituting the data, the DOF range is 1.3 - 2.4 um, which is less than the thickness of the thick film photoresist (10 um);

[0081] By adopting the above technical solution, the process flow of coating the anti-reflection layer is: coating the anti-reflection layer → baking and curing → photoresist coating → exposure → post-baking → etching → isopropyl alcohol cleaning → plasma cleaning.

[0082] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention. Any reference signs in the claims should not be regarded as limiting the claims involved.

[0083] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for optimizing the distortion of thick film photoresist exposure patterns, characterized in that: The specific steps include: S1, physical vapor deposition, after the wafer is prepared, the electrons collide with argon atoms in the process of flying to the substrate under the action of the dot formation, ionizing them to produce Ar positive ions and new electrons, and then the reflective coating is applied on the wafer surface; S2, baking and curing, using high temperature to cure the bottom anti-reflection layer, drying to remove moisture and solvent to form a uniform and stable film real , subsequently coating the surface with a thick film photoresist; S3, exposure coating, using an exposure machine to expose the photoresist, transferring the pattern of the mask to the photoresist, and finally performing a drying process to remove the solvent in the photoresist; S4, developing, the photoresist in the exposed area of ​​the positive photoresist and the non-exposed area of ​​the negative photoresist is dissolved in the developer, and the photoresist forms a pattern corresponding to the mask; S5, etching, a process that uses physical methods to selectively remove unwanted materials from the surface of the silicon wafer, and uses isopropyl alcohol to remove particulate contaminants; S6, decomposition cleaning, by using the active particles in the plasma to react chemically with the pollutants on the surface of the material, decomposing them into volatile substances to achieve the purpose of cleaning, while observing the wafer with a microscope to see if there are any residual pollutants; S7. Precision inspection: industrial microscope accurately inspects the photoresist pattern to ensure that the pattern is correct and the size deviation is within the specification; 2. The method for optimizing the distortion of thick film photoresist exposure pattern according to claim 1, characterized in that: In step S2, the thickness of the photoresist is greater than or equal to 10 um.

3. The method for optimizing the distortion of thick film photoresist exposure pattern according to claim 1, characterized in that: In the step S2, the thickness of the anti-reflection coating is one quarter of the wavelength of the light.

4. The method for optimizing the distortion of thick film photoresist exposure pattern according to claim 3, characterized in that: In the step S1, new electrons fly toward the substrate, Ar ions are accelerated toward the cathode target under the action of the electric field, and bombard the target surface with high energy, causing the target material to be sputtered; among the sputtered particles, neutral target atoms or molecules are deposited on the substrate to form a thin film.

5. The method for optimizing the distortion of thick film photoresist exposure pattern according to claim 4, characterized in that: The sputtering particles adopt magnetron sputtering technology to increase magnetic force in the PVD cavity. Since the moving electrons are subjected to the Lorentz force in the magnetic field, their movement trajectories will bend or even produce spiral motion, and their movement paths will become longer, increasing the number of collisions with working gas molecules and increasing the plasma density.

6. The method for optimizing the distortion of thick film photoresist exposure pattern according to claim 5, characterized in that: The magnetron sputtering technology increases the energy of atoms incident on the substrate surface to deposit a TiW barrier layer and a Cu seed layer.

7. The method for optimizing the distortion of thick film photoresist exposure pattern according to claim 1, characterized in that: In the step S3, the properties of the photoresist change after being exposed to light, and the pattern on the mask is accurately copied onto the sheet, giving the sheet the function of an electronic circuit diagram.

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