| Photolithography refers to the process of transferring the pattern on the mask to the substrate using the principle of photochemical reaction,which is an indispensable process in the chip manufacturing process.Photoresist is one of the most critical photolithographic materials.As a kind of strategic material,photoresist is basically monopolized by foreign enterprises,which greatly restricts the development of semiconductor industry in China.The main components of photoresist include film forming resin,photosensitizer,solvent and other additives,among which film forming resin is the most basic component,which plays the role of skeleton and directly determines the performance of photoresist.Photosensitive polyimide(PSPI)takes polyimide as film forming resin and makes it photosensitive by adding or grafting photosensitizer to realize self-patterning.Polyimide material has excellent thermal stability,chemical stability and dielectric properties.It is an ideal dielectric insulating material in semiconductor field.In recent years,polyimide material has been widely used in multi-chip packaging,new display,MEMS,integrated circuit and other fields.Photosensitive polybenzoxazole(PSPBO),as another kind of high heat resistant polymer material,is also widely studied and used in semiconductor industry.At the same time,because of its special structure,it has certain advantages compared with PSPI in some performance,so it is called as a substitute for PSPI in semiconductor industry.Unfortunately,most of the products in both PSPI and PSPBO are imported.Although the government has invested a lot of manpower and money,the process of localization is still slow.In this paper,two positive photolithographic material systems,PSPI and PSPBO,were designed and synthesized respectively.The two polymeric resins were synthesized by using 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane(6FAP),an aromatic fluorine-containing monomer,as raw material and polymerized with another aromatic monomer.On the one hand,the aromatic main chain structure greatly improves the heat resistance and chemical stability of the polymer.On the other hand,the introduction of F atom greatly improves the transparency and dielectric properties of polymer.In this paper,the precursors of two kinds of polymers,polyamide acid(PAA)and polyo-hydroxyamide(PHA),were used as film forming resins,and the alkaline resistance of the two precursors was greatly improved by grafting protective groups or end-sealing methods.Then,the photosensitization of the two precursors was given by means of additional photosensitizer,and the positive photolithographic materials of PSPI and PSPBO were designed and synthesized.After photolithographic patterning,high resolution photolithographic patterns were obtained.High performance thin film materials were obtained by heating and curing,and the properties of the two thin films were compared.This paper has a certain reference significance for the localization of photosensitive polymers.Specific research contents are as follows:(1)Synthesis,lithography patterning and curing of PSPI positive lithography materialThe precursor PAA of polyimide(PI)was synthesized from 6FAP and 3,3’,4,4’-diphenyltetracarboxylic anhydride(BPDA)at room temperature.The influence of water and reaction temperature on polymerization was investigated by comparing the size and distribution of molecular weight.Then,through ring-opening esterification reaction,glycidyl methacrylate(GMA)was grafted to the carboxyl group of PAA,and the carboxyl group was protected,which greatly improved its alkali resistance,and modified PAA(PAA-GMA)was obtained.PAA-GMA with different amounts of graft was synthesized by changing the amount of GMA added.By comparing the graft rate and graft success rate,25 mol%was selected as the best graft ratio.PAA-GMA and photosensitizer PAC320 were mixed in cyclopentanone solvent in a certain proportion,and the photoresist solution was obtained after full stirring.By exploring the relationship between photosensitizer content,developer concentration and dissolution contrast,the optimal photosensitizer content and developer concentration were determined.By optimizing the process conditions of spin coating,baking,exposure,development,etc.,the best process conditions of patterning are obtained:The photoresist solution was coated on the silicon wafer at a rotational speed of 1200 r/min,and baked at 90℃ for 5 min to obtain 800 nm thick PSPI thin film.The film was exposed under 365 nm LED UV lamp for 30 s,and developed in Tetramethylammonium hydroxide(TMAH)developer with a mass fraction of 0.113%for 60 s,and the resolution of 4 μm was obtained.Finally,the film was solidified at 300℃ for 1 h in N2 atmosphere to obtain a high heat resistance and low dielectric pattern PSPI film.(2)Synthesis,lithography patterning and curing of PSPBO positive lithography materialThe precursor PHA of polybenzoxazole(PBO)was synthesized from 6FAP and 4,4-chloroformyl phenyl ether(DEDC)at low temperature,and was sealed with maleic anhydride(MA)to control the polymerization degree and improve the alkali resistance.PHA and photosensitizer PAC320 were mixed in propylene glycol methyl ether acetate(PMA)solvent in a certain proportion,and the photoresist solution was obtained after full stirring.By exploring the relationship between baking temperature,baking time and dissolution contrast,the optimal baking temperature and baking time were determined.By optimizing the process conditions of spin coating,baking,exposure,development,etc.,the best process conditions of patterning are obtained:The photoresist solution was coated on the silicon wafer at a rotational speed of 1200 r/min,and the film was baked at 90℃ for 5 min to obtain a PSPBO film with a thickness of 1000 nm.The film was exposed under a 365 nm LED UV lamp for 20 s and developed in TMAH developer with a mass fraction of 0.476%for 60 s.The resulting pattern has a resolution of 4 μm.Finally,the film was cured at 350℃ for 1 h in N2 atmosphere,and the patterned PSPBO film with high heat resistance and low dielectric was obtained.Compared with PSPI thin film,the obtained PSPBO thin film has higher thermal stability and better dielectric properties. |
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