Composition for improving undercut of photoresist pattern and photoetching process

Abstract

The invention provides a composition for improving photoresist pattern bottom internal cutting and a photoetching process, the composition comprises 80 wt%-95 wt% of photoresist resin, 1 wt%-5 wt% of a photoacid generator, 0.1 wt%-5 wt% of an alkaline additive and the balance of a solvent, the molecular weight of the alkaline additive is 200 Da-5000 Da, and the decomposition temperature is higher than 150 DEG C. The alkaline additive is migrated to the bottom of the photoresist in the developing stage, and is subjected to a neutralization reaction with excessive H < + > released by the photoacid generator to form a pH buffer layer, so that excessive dissolution of a developing solution to the bottom of photoresist resin is inhibited, the problem of bottom inscribed defects caused by non-uniform acid diffusion in the developing process of the photoresist is solved, and meanwhile, the resolution ratio and the developing efficiency are kept.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor technology, in particular to a composition for improving the undercut of a photoresist pattern and a photoetch process. BACKGROUND

[0002] In the semiconductor photoetch process, the undercut of a photoresist pattern is a key problem affecting the line width uniformity and device performance. After exposure, the acid released by the photoacid generator (PAG) catalyzes the deprotection reaction of the resin to form a soluble product. However, the uneven vertical diffusion of acid during the development process leads to an excessively high acid concentration in the bottom region, and the dissolution rate of the resin bottom by the developer (such as TMAH aqueous solution) is significantly higher than that of the top, forming an undercut structure. The undercut leads to pattern line width deviation, bridging defects, and reduces the accuracy of subsequent etching or ion implantation. SUMMARY

[0003] In view of the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a composition for improving the undercut of a photoresist pattern and a photoetch process, which is used to solve the problem of the undercut of a photoresist pattern existing in the prior art photoetch process.

[0004] To achieve the above-mentioned purpose and other related purposes, the present application provides a composition for improving the undercut of a photoresist pattern and a photoetch process. The technical solution is as follows:

[0005] In a first aspect, the embodiments of the present application provide a composition for improving the undercut of a photoresist pattern, which comprises 80wt%-95wt% of a photoresist resin, 1wt%-5wt% of a photoacid generator, 0.1wt%-5wt% of an alkaline additive, and the balance of a solvent, wherein the molecular weight of the alkaline additive is 200Da-5000Da, and the decomposition temperature is higher than 150℃.

[0006] Preferably, the content of the alkaline additive is 0.5wt%-2wt%.

[0007] Preferably, the alkaline additive is selected from at least one of an organic amine compound, a quaternary ammonium salt, or a nitrogen-containing heterocyclic polymer.

[0008] Preferably, the organic amine compound is triethanolamine, tetramethylammonium hydroxide, or polyethyleneimine.

[0009] Preferably, the photoresist resin is an acrylate or a phenolic resin.

[0010] Preferably, the photoacid generator includes a triphenylsulfonium salt, and the solvent includes propylene glycol methyl ether acetate or cyclohexanone.

[0011] In another aspect, the embodiments of the present application provide a photoetching process for improving the undercut of the bottom of a photoresist pattern, which comprises the steps of coating the above-mentioned composition, pre-baking, exposing, post-baking and developing. During the developing process, the basic additive migrates to the bottom of the photoresist resin, neutralizes the excess acid to form a pH buffer layer to inhibit the undercut.

[0012] Preferably, the developing solution used in the developing step is a 2.38% aqueous solution of tetramethylammonium hydroxide, and the developing time is 20-60 seconds.

[0013] As mentioned above, the composition and photoetching process for improving the undercut of the bottom of a photoresist pattern provided by the present application have the following beneficial effects: the basic additive migrates to the bottom of the photoresist during the developing stage, neutralizes the excess H + reacts to form a pH buffer layer to inhibit the excessive dissolution of the bottom of the photoresist resin by the developing solution, solves the problem of the undercut of the bottom of the photoresist caused by the uneven acid diffusion during the developing process, and maintains the resolution and developing efficiency. DETAILED DESCRIPTION

[0014] The embodiments of the present application will be described in detail below with specific reference being made to certain embodiments. As would be obvious to one of ordinary skill in the art, other advantages and benefits of the present application can be readily ascertained by one of ordinary skill in the art from the disclosure. The present application may, however, be embodied in different forms or carried out in different ways without departing from the spirit of the present application. The disclosure of each of the embodiments is intended to be illustrative and not restrictive, and all changes that come within the spirit of the present application are therefore intended to be embraced well within the scope of the present application.

[0015] The technical solutions in the present application will be described below in detail with reference to the schemes. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by one of ordinary skill in the art without creative work fall within the scope of the present application.

[0016] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship and are only used to facilitate the description of the present application and simplify the description, and therefore cannot be understood as indicating or implying that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second", "third" are only for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0017] In the description of the present application, it should be noted that unless specifically defined and limited otherwise, the terms "mounting", "connected", "connection" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integrally connected; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through intermediate medium, or it can be the internal communication of two elements, it can be wireless connection, or wired connection. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0018] In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as there is no conflict between them.

[0019] For the problem of undercut of photoresist pattern existing in the existing photoetching process, the existing solutions and defects include:

[0020] (1) Optimize the development parameters, reduce the concentration of the developer or shorten the development time, but it may sacrifice the development rate or cause the top residue;

[0021] (2) Add surfactant to improve the wettability of the developer, but the control of acid diffusion is limited;

[0022] (3) Multi-layer photoresist structure, increase the bottom anti-reflective layer, but the process is complex and the cost is high.

[0023] In order to solve the above problems, the present application provides a composition for improving the undercut of photoresist pattern, which comprises 80wt%-95wt% of photoresist resin, 1wt%-5wt% of photoacid generator, 0.1wt%-5wt% of alkaline additive and the balance of solvent, wherein the molecular weight of the alkaline additive is 200Da-5000Da, and the decomposition temperature is higher than 150℃.

[0024] As an example, the photoresist resin is preferably acrylate (for ArF) or phenolic resin (for i-line); the photoacid generator includes triphenyl sulfonium salt (TPS-PAG); the solvent includes propylene glycol methyl ether acetate (PGMEA), cyclohexanone, etc.; the alkaline additive is selected from at least one of organic amine compound, quaternary ammonium salt or nitrogen-containing heterocyclic polymer, wherein the organic amine compound is triethanolamine, tetramethylammonium hydroxide (TMAH) or polyethyleneimine (PEI); the content of the alkaline additive is preferably 0.5wt%-2wt%.

[0025] The alkaline additive in the composition plays a role through the following mechanisms:

[0026] (1) Acid neutralization reaction: the alkaline additive migrates to the bottom of the photoresist resin during the development stage, and reacts with the excess H +neutralization reaction (e.g. R3N+H + → R3NH + ), reducing local acid concentration;

[0027] (2) pH buffer layer formation: the ion pair generated from the neutralization reaction forms a dynamic equilibrium at the bottom of the resist, inhibiting over-solubilization of the resist bottom by the developer;

[0028] (3) Selective action: the migration of the basic additive allows it to be enriched mainly in the bottom region, without affecting the top development rate. The distribution of the basic additive in the lithographic cross-section after development was confirmed by TOF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry) analysis, confirming its enrichment in the bottom region.

[0029] The basic additive satisfies the following properties:

[0030] Basic strength: pKb 7-12, avoiding reaction with photo-acid generator before baking;

[0031] Thermal stability: decomposition temperature > 150°C, compatible with pre-baking (100-120°C) and post-baking (PEB) (90-130°C) processes;

[0032] Solubility: compatible with resist resin and solvent, no phase separation.

[0033] The application also provides a lithographic process for improving the undercut of the bottom of a resist pattern, comprising the steps of coating the above-mentioned composition, pre-baking, exposure, post-baking and development. During the development process, the basic additive migrates to the bottom of the resist resin, neutralizes the excess acid to form a pH buffer layer to inhibit the undercut.

[0034] As an example, the developer used in the development step is 2.38% aqueous solution of tetramethylammonium hydroxide, and the development time is 20-60 seconds.

[0035] Example 1

[0036] Materials and Equipment

[0037] Resist resin: acrylate copolymer (for ArF, JSR ARX2925).

[0038] Photo-acid generator: triphenylsulfonium triflate (TPS-PAG).

[0039] Basic additive: triethanolamine (Sigma-Aldrich, purity 99%).

[0040] Solvent: PGMEA.

[0041] Developer: 2.38% aqueous solution of TMAH.

[0042] Equipment: Spin coater (SUSS MicroTec GYRSET), ArF scanner (ASML XT:1900Gi), SEM (Hitachi CG4000).

[0043] Composition Configuration

[0044] Acrylic ester copolymer: 85 wt%; TPS-PAG: 3 wt%; Triethanolamine: 1.2 wt%; PGMEA: balance (10.8 wt%).

[0045] Stir for 24 hours (25°C) until completely dissolved, then filter (using a 0.1 μm PTFE filter membrane).

[0046] Lithographic Process Steps

[0047] Photoresist coating: Spin-coat photoresist onto an 8-inch silicon wafer at 1500 rpm to a thickness of 1.5 μm.

[0048] Pre-baking: Bake on a hot plate at 100℃ for 90 seconds.

[0049] Exposure: ArF scanner (NA=0.85, σ=0.7), dose 20 mJ / cm² 2 The pattern has a linewidth / spacing of 100nm.

[0050] Post-baking (PEB): Bake on a hot plate at 110℃ for 60 seconds.

[0051] Development: Immerse in 2.38% TMAH developer for 30 seconds, rinse with deionized water and dry with nitrogen.

[0052] Results Analysis

[0053] Incision depth: 40±5nm as measured by SEM cross-section.

[0054] Linewidth uniformity: 3σ value is 8nm.

[0055] Resolution: 100nm linewidth, clear pattern, no top residue.

[0056] Comparative Example 1

[0057] The difference from Example 1 is that the composition does not contain alkaline additives, the incision depth is 120±15nm, and the linewidth uniformity is 3σ value of 15nm.

[0058] Comparative Example 2

[0059] The difference from Example 1 is that the content of the basic additive (triethanolamine) in the composition is 6 wt%, the developing rate is decreased by 20%, and slight residue appears on the top, so the content of the basic additive in the composition needs to be controlled in the range of 0.1-5 wt%.

[0060] Example 2

[0061] Materials and Equipment

[0062] Photoresist resin: acrylate copolymer (for ArF, JSR ARX2925).

[0063] Photoacid generator: triphenylsulfonium triflate (TPS-PAG).

[0064] Basic additive: polyethyleneimine (PEI, Mw=2000).

[0065] Solvent: PGMEA.

[0066] Developer: 2.38% TMAH aqueous solution.

[0067] Equipment: spin coater (SUS MicroTec GYRSET), ArF scanner (ASML XT:1900Gi), SEM (Hitachi CG4000).

[0068] Composition Configuration

[0069] Acrylate copolymer: 86 wt%; TPS-PAG: 3 wt%; PEI: 0.8 wt%; PGMEA: balance (10.2 wt%).

[0070] Stirring for 24 hours (25°C) until complete dissolution, filtration (0.1 μm PTFE filter membrane is used).

[0071] Lithographic Process Steps

[0072] Coating: spin coating of photoresist on silicon wafer (8 inches) at 1500 rpm, thickness 1.5 μm.

[0073] Pre-baking: hot plate 100°C for 90 seconds.

[0074] Exposure: ArF scanner (NA=0.85, σ=0.7), dose 20 mJ / cm 2 , pattern 100 nm line width / pitch.

[0075] Post-exposure baking (PEB): hot plate 110°C for 60 seconds.

[0076] Developing: 2.38% TMAH developer soak for 25 seconds, DI water rinse and nitrogen dry.

[0077] Results Analysis

[0078] Etch depth: 35 ± 4 nm by SEM cross-section measurement.

[0079] Developing rate improvement 10% (synergistic wetting effect of PEI).

[0080] Resolution: 100 nm line width pattern clear, no top residue.

[0081] The composition for improving the bottom undercut of photoresist pattern provided by the present application significantly reduces the bottom undercut depth of photoresist, while maintaining the developing rate and resolution, and is suitable for ArF (193 nm), EUV (13.5 nm) and g-line / i-line photolithography processes. It does not need to change the existing exposure or developing equipment, and can be directly integrated into the standard process, and has a wide industrial application prospect.

[0082] It should be noted that the embodiments provided in the present application are only illustrative of the basic concept of the present application, and only show the components related to the present application, not the number, shape and size of the components when actually implemented. The actual implementation of each component type, quantity and proportion can be a random change, and the component layout type can be more complex.

[0083] In summary, the composition for improving the bottom undercut of photoresist pattern and the photolithography process provided by the present application, the basic additive migrates to the bottom of the photoresist during the developing stage, and the excess H + occurs a neutralization reaction to form a pH buffer layer to inhibit the excessive dissolution of the developing solution to the bottom of the photoresist resin, solve the bottom undercut defect problem caused by uneven acid diffusion during the photoresist developing process, while maintaining the resolution and developing efficiency. Therefore, the present application effectively overcomes the various shortcomings in the prior art and has a high industrial utilization value.

[0084] The above embodiments only illustratively explain the principles and effects of the present application, and are not used to limit the present application. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical idea disclosed by the present application should be covered by the claims of the present application.

Claims

1. A composition for improving the undercut of a photoresist pattern, characterized by, The composition comprises 80wt%-95wt% of photoresist resin, 1wt%-5wt% of photoacid generator, 0.1wt%-5wt% of basic additive and the rest of solvent, wherein the molecular weight of the basic additive is 200Da-5000Da and the decomposition temperature is higher than 150℃.

2. The method of claim 1, wherein, The content of the basic additive is 0.5wt%-2wt%.

3. The method of claim 1, wherein, The basic additive is selected from at least one of organic amine compound, quaternary ammonium salt or nitrogen-containing heterocyclic polymer.

4. The method of claim 3, wherein, The organic amine compound is triethanolamine, tetramethylammonium hydroxide or polyethyleneimine.

5. The method of claim 1, wherein, The photoresist resin is acrylate or phenolic resin.

6. The method of claim 1, wherein, The photoacid generator comprises triphenylsulfonium salt and the solvent comprises propylene glycol methyl ether acetate or cyclohexanone.

7. A photolithography process for improving the undercut of photoresist pattern bottom, comprising the steps of coating the composition of any one of claims 1-6, pre-baking, exposing, post-baking and developing, wherein the basic additive migrates to the bottom of the photoresist resin during the developing process, neutralizes the excess acid to form a pH buffer layer to inhibit the undercut.

8. The method of claim 7, wherein, The developing solution used in the developing step is 2.38% aqueous tetramethylammonium hydroxide solution and the developing time is 20s-60s.