Research Progress of DUV Photoresists (I)——The Main Film Forming Polymer Part

Research Progress of DUV Photoresists (I) Macromolecules Formed as Films Yang Linglu, Zhang Gailian, Yu Shangxian (Department of Chemistry, Beijing Normal University, Beijing 100875, China) A detailed description of solvent blocking was given. It is pointed out that by improving the structure and composition of the photopolymer, a resist with excellent properties can be obtained.

1 With the continuous development of large-scale integrated circuits (LSI) and dynamic random-access memory, it is required that the dimension of the line width of the lithography image be changed from micrometer to nanometer scale. Due to the influence of the wavelength of the light source in the lithography imaging on the resolution, the wavelength of the light source has evolved from the original g-ine (436 nm), i-line (365 nm) to DUV light, which has been commonly used today, such as the KrF dimer. Resonant radiation from a laser (248 nm) and a low-voltage Hg lamp (254 nm) where KrF dimer laser dominates; and shorter-wavelength light of great interest, such as the ArF dimer laser (193 nm) F2 laser (157nm) and so on. The reduction of the wavelength of the light source used can not only increase the resolution, but also reduce the diffraction caused by the mask and improve the imaging properties.

With a resolution of 1 to 0.25 linewidths, light sources with emission wavelengths in the DUV zone are attractive. However, DUV photolithography still has two issues with resolution and depth of focus. People try to obtain better resolution by increasing the Na value of the light source, but the depth of focus is lost. In essence, continuous improvement and improvement of existing resist systems and the development of new resist systems are fundamental solutions to the problem. We have conducted research on patents in the past decade and after 1998, and summarized the system, hoping to help future work.

2 Resist Compositions DUV photoresists consist mainly of a host film-forming polymer (sometimes called a matrix polymer), an acid generator, a solvent blocker, a cross-linking agent, and additives. This article first introduces one of the main components of the resist system as the main film-forming resin.

2.1 The matrix film forming polymer polymethacrylate and its copolymer system is the earliest DUV photoresist, but the first people used non-chemical resists, the sensitivity of this type of resist is very Low, no great practical value. In order to increase the sensitivity, a chemical review web type resist system was later developed. Currently, DUV photoresists for (poly)methacrylate systems are still being developed.

The film-forming resins of poly(meth)acrylates and their copolymers systems that are positively developed are mainly methacrylic esters and methacrylonitrile, methacrylic anhydride, poly(p-hydroxystyrene), (3-(t Homopolymers or di-, tri-, or poly-polymers of monomers such as butoxycarbonyl) vinyl caprolactam, N-phenyl dimethyl acrylimide, etc. Among them, methacrylate may be tert-butyl ester, Alkyl esters, 2-phenylisopropyl esters, 1.4-dioxospiro-4-oxa-2-methyl vinegar, sulfamyl esters, tris(trimethylsilyl)silylethyl ether, oligosiloxanes Alkyl esters, γ-butyl propyl esters, etc. When DUV light is irradiated, the acid generator produces acid, and a deprotection reaction occurs, making the polarity of the exposed polymer and its solubility in the alkali solution significantly greater. , thereby increasing the imaging contrast of the system.

For example, the polyketaryl group with ketal groups studied by Jin-Baek Kim et al. Under the action of acid, the following reaction occurs: Cyclopentone produced in the reaction acts as a plasticizer and enhances the mobility of the acid.

Although the methacrylate has a good image in the DUV region, due to poor C-C single bond resistance in the main chain, to improve the corrosion resistance, Yasuynki Takado et al. introduced the ring structure into the polymer, polymerization The reaction is as follows: This cyclized polymer obtained by intramolecular cyclization has a relatively high Tg value and good thermal stability.

In order to give the resist system better stability over time after exposure, Jin-Baek Kim et al. introduced a basic group (caprolactam) into the polymer side chain. The introduction of such basic groups not only improves the stability of the image to the alkaline contaminants in the air, but also reduces the diffusion of acid in the exposed areas, increases the contrast of the system, and improves the resolution of the resist system.

Negative polymethacrylate systems are relatively few, in which film-forming resins mainly include: polycyclopropene ethyl methacrylate and methacrylic acid, methacrylate copolymers and poly 4-hydroxyethyl acrylate. When DUV light is irradiated, the acid-producing source produces acid, and the cross-linking occurs between the catalytic resin and the cross-linking agent or the resin itself to form a cross-linked structure, and the solubility in the developing solution becomes smaller, and a negative image appears during development. For example, Nobukazu Miyagawa et al. studied the dimerization cross-linking of polymers with cyclopropene groups. The mechanism is as follows: Due to the double bonds in cyclopropene, there is a large absorption below 250 nm. Upon irradiation with DUV light, cyclopropene dimerizes to form a tricycloalkane and is bleached to increase the transparency of the polymer, and light energy gradually reaches the bottom of the resist film, forming a latent image. This dimerization finally forms a benzene ring with good dry etching resistance.

Matrix resins for positive systems in this class of resists include: semi-polymers of styrene and maleic acid half esters, 2-(4-vinylbenzyl)malonic acid half esters, 4-(2-hydroxyhexafluoro) Isopropyl)-copolymers of styrene and styrene, polyaacetoxystyrene, copolymers of maleimide derivatives and styrene derivatives, and the like. When DUV light is irradiated, the acid generator produces acid, which catalyzes the reaction to remove the protecting group or the main chain cleavage reaction, or changes the photosensitizer (such as diazotide) in the system from dissolving into dissolving. The solubility of the exposed area in the developer is increased to give a positive latent image.

Shintaro Yamada et al. studied the environment-friendly resist 2-(4-vinylbenzyl) malonate half-ester system, and did not use organic solvents during the entire process. Its typical structure is as follows: There are two changes in solubility throughout the process: 1 When heated before exposure, the malonate monoester decarboxylates, making it water soluble to water insoluble; 2 Acid-catalyzed off-acid production during exposure In addition to the protective group reaction, it becomes soluble in alkali water. It is because of these two changes in solubility that the entire process does not use organic solvents. The sensitivity of this system is relatively good (20mJ/cm2) but the resolution is poor (m). How to increase the resolution is a problem faced by this environment-friendly resist.

(4) A copolymer of vinylimidazole and styrene, poly(4-hydroxy-2-isopropyl)styrene, 4-butoxycarbonylcarbon-protected polystyrene, and the like. When DUV light is irradiated, the acid generator produces acid to crosslink the resin with the cross-linking agent in the system, or the electrophilic cross-linking of the resin occurs, so that the solubility of the exposed area in the developer is reduced. For example, the mechanism of the electrophilic cross-linking reaction of poly(4-hydroxy-2-isopropyl)styrene is as follows: This type of resist is also an older system and is applicable to both DUV light and EB. From the patent situation, there have been some new developments recently. Among them, matrix resins in the positive resist system include: alkali-soluble silicon polymers, a mixture of poly-p-hydroxyphenylsiloxane and p-hydroxystyrene, and a silicon compound with an acid-decomposable group, and the structure is as follows: Z - Non-aromatic hydroxy monocyclic or polycyclic and bridged cyclic hydrocarbons When DUV light is irradiated, photosensitizers (such as DNQ or a diazotide) in the system produce carboxylic acid in the exposed area, from dissolving to dissolving, making The contrast of the system increases; or under the action of acid, the easily decomposable group of acid is removed, so that the polymer can be dissolved in the developer.

The main negative resins are polyalkylsiloxanes, polyvinylsiloxanes, three-dimensional polysilazanesiloxanes, and phenyltrimethoxysilane and 2-(3,4-epoxyhexyl). ) Sol-gel reaction product of ethyltrimethoxysilane. When DUV light is irradiated, the exposed area of ​​the resin is cross-linked, or a condensation reaction is performed under the effect of an acid so that the exposed area is insoluble in the developer. The initial siloxanes were generally chain and trapezoidal structures, and later developed a more rigid three-dimensional structure. This three-dimensional siloxane resist has better resolution, high contrast, low swelling, and good resistance to dry etching.

In addition to the above-mentioned DUV photoresists, there are some other compounds. Among the positive system resins are: polyimide, poly(4-trimethylsilyl-phthalaldehyde), and the like. When the DUV light is irradiated, the acid source produces acid, and the polymer undergoes deprotection, chain scission, or degradation reaction under the action of the acid, so that the exposed area is changed from insoluble to soluble in the alkali solution to form a positive latent image. .

The resins of the negative resist system mainly include poly(trimethylsilyl) propyne, N-vinyl carbazole and fumarate copolymers with epoxy groups, maleic anhydride and 3-trimethylsilyl-1-propene, tert-butyl methacrylate, copolymers of ethylene derivatives, 4,4,7,7-tetramethyl-47-disilazane-2-octyne, and the like. When DUV light is irradiated, the acid-producing source produces acid, the resin cross-links with the cross-linking agent or the resin itself, so that the solubility of the exposed area in the developing solution is reduced; or the system contains both the heat-producing acid source and the light-producing alkalinity source. After the acid is produced from the acid source of the thermal acid in the exposed area, a reaction to remove the protective group occurs, so that the solubility of the non-exposed area increases. Since the exposed area contains both alkali generated by light and acid generated by heat, a neutralization reaction takes place and there is no effect on the properties of the resin. A negative image is developed in the developer. For example, copolymer systems of maleic anhydride and 3-trimethylsilyl-1-propene, tert-butyl methacrylate, and ethylene derivatives utilize this mechanism. This resist system avoids line edge roughness problems in positive resists.

(To be continued)