Development of Photosensitive Polyimides for LCD with High Aperture Ratio. May 24, 2004

Transcription

1 Development of Photosensitive Polyimides for LCD with High Aperture Ratio May 24, 2004

2 utline Why is polymer dielectric required for TFT LCD? Requirements of the polymer dielectrics What is polyimide? Problems of the polyimides Development of colorless photosensitive polyimide Application

3 Why is Polymer Dielectric Required for TFT LCD? TRANSMISSIN F LCD CMPNENTS Item Transmittivity (%) Glass substrate 95 Aperture ratio 40~60 Polarizer 35~36 Color filter 25 Total 3.5

4 Development New LCD Devices ε

5 Dielectric Materials for TFT LCD Property Inorganic material Polymeric mterial Dielectric constant high low Processability CVD Spin coating Flexibility rigid flexible

6 ypical Polymer Dielectrics (I) : BCB of Dow Chem. B-staging Si Si ligomer FW = 375 Transmittance : No conjugation beyond styrene, No heteroatom except & Si Excellent Planarization by Low MW design Still have Processability : Not crystalline due to Si--Si linkage Reactive End-functionality : easily crosslinkable by cyclobutene group Heat Resistance : No thermal degradation component Solubility Limitation : Nonpolar aromatic solvent Curing in the absence of xygen required Extra Adhesion Promotor required

7 Typical Polymer Dielectrics (II):Photoacryl of JSR m n H Photo polymerization Transmittance : Acryl based material Alkaline Solution Developable Process window : Easy formulation control Heat Resistance : Acrylic component Relatively low Price

8 Comparison of rganic Dielectrics Type Photo-Acryl BCB (Dry-Etch) PSPI Maker JSR, etc DW LGC/KRICT Status commercialized commercialized developing Patterning K No* K Dielectric Constant Heat Resistance Transmittance at 400nm (expected) 250 > % 97% 93% Planarization Good Good Good Water absorption high Curing air N 2 atmosphere air Resoluiton < 10um - 15um low 300 High Price Low High Medium Solvent Develop Type **Dry-Etch BCB : Problems in processing condition and price Mi Hie Yi / KRICT

9 Requirement of Polymer Dielectrics chemical resistance and heat resistance photosensitivity Liquid crystal low dielectric planarization adhesion Gate bus line transmittance Data bus line planarization

10 Why is Polyimide Required for TFT LCD? Price High PI PEEK LCP PPS PA PM PBT PET PAI High PEI PES PSF PAR PC m-pp Heat resistance Super Engineering Plastics Engineering Plastics PE Crystalline PP ABS PS PMMA Amorphous Commodity Plastics

11 What is Polyimide? Structure Anhydride Imide Amine Imide.. Synthesis + H2N RNH2 R NHC HC CH CNH R NHC HC CH CNH N N R N N Insoluble and Infusible Mi Hie Yi / KRICT

12 Charateristics of Polyimide Excellent Thermal and Cyrogenic Temperature Stability : -269~400 o C Wear and friction properties Radiation and xidative Stability Excellent Electrical and Mechanical Properties (TS : 1,700 kg/cm 2 ) Inherently Flame Retardancy (LI : 37, UL 94 V-0) Good Chemical Resistance

13 Weak Point and Solutions of Polyimide (I) (I) Transmittance Color : Introduction of alicyclic dianhydride Polyimide containing alicyclic structure

14 Weak Point and Solutions of Polyimide (II) (II) Photosensitivity Why is photosensitive dielectric layer required?

15 Advantage of photosensitive polyimide 1. Coupler 2. PI precursor 3. PR coating Thermal treatment coating drying coating drying UV irradiation Developing 4. PI pattern Removment of coupler Washing/drying Removment of Drying Conventional patterning process New process using PSPI

16 Weak Point and Solutions of Polyimide (III) (III) Degree of planarization

17 Development of Novel Alkali-Developable Photosensitive Polyamic Acid (PAA)

18 Molecular Design of Photosensitive Polyamic Acid TFT, IT deposition Processability High Aperture ratio Pattern formation Hest resistance Chemical resistance Transmittance, Dielectric constant Aromatic group Crosslinking group Alicyclic group Photosensitive group Adhesion Polyimide precursor (PAA) Photosensitive low dielectric materials

19 Positive vs. Negative Type PSPI Advantage of Positive PSLD Advantage of Negative PSLD Positive Negative

20 Chemistry of Negative Type PSPI

21 Synthetic Results of the PAAs with various MW Polyamic acids a Molar ratio of Molecular weight monomers (g/mol) c (A:B:C) b M d w M e n MWD f PAA-1 3 : 2: 2 17,900 14, PAA-2 10 : 9 : 2 43,600 27, PAA-3 15 : 14 : 2 49,900 31, PAA-4 1 : 1 : 0 101,200 81,

22 Thermal Properties of the PAAs PAA-1 PAA-4 80 Weight (%) Temperature ( o C) Mi Hie Yi / KRICT

23 Effect of MW of PAAs on Transmittance at 400 nm 100 Transmittance (%) PAA-1 PAA-2 PAA-3 PAA Wavelength (nm) Mi Hie Yi / KRICT

24 Chemical Resistance of PAAs Residual thickness (%) NMP DMAc 2.38 wt% PR aq.tmah stripper MeH PAA PAA PAE

25 Chemical Resistance for PR Stripper of PAA-1 Processing condition Solubility for PR stripper 80 C, 7min 80 C, 14min 250, for 30 min 250 for 1hr 250 for 2hr Insol Insol Insol Insol Insol Insol

26 Effect of MW on Degree of Planarization 80 PAA-4 70 PAA-3 PAA-2 t 1 t 2 Pattern width(µm) Degree of Planarization = (1 t 1 /t 2 )*100 Measured by α-step 500 Degree of Planarization (%) DP Mw Pattern width DP PAA Pattern width(µm)

27 Photolithography Process of PAAs UV 90, 2 min Exposure dose : 200 mj 160, 10 min 2.38% aq. TMAH 250, 60 min N R N n Mi Hie Yi / KRICT

28 Effect of an Exposure Dose on a Normalized Film Thickness of PAA (a) (b) Exposure dose (mj/cm 2) Mi Hie Yi / KRICT Normalized film thickness (d 1 /d 0 ) Normalized film thickness (d 1 /d 0 ) CGI-124 Igacure Exposure dose (mj/cm 2 )

29 Effect of an Amount of Photoinitiator on a Normalized Film Thickness of PAA-1 Mi Hie Yi / KRICT Normalized film thickness (d 1 /d 0 ) Amount of Photoinitiator (%)

30 Typical Negative Patterns of PAA-1 (Film thickness : 2 ) Mi Hie Yi / KRICT

31 Typical Negative Patterns of PAA-1 (Film thickness : 35 ) Mi Hie Yi / KRICT 50 width 50 width 50 width 50 width 50 width 25 width

32 Typical Application of Polymer Dielectrics (I) Development of High Aperture LCD Black matrix LC IT glass Passivation layer : SiNx Column line (a) s Black matrix LC IT glass d ε rganic Passivation layer (b)

33 Typical Application of Polymer Dielectrics (II) TC Technology Conventional structure TC structure vercoat for TC Aperture Ratio ~ 65% Assembly Margin ~ 5 Total Pitch Problem Aperture Ratio ~ 72% Assembly Margin ~ 1 Free from Total Pitch Problem