New metallization method of modified tannic acid photoresist pattern

Metal patterning converted from a modified tannic acid (TA-Boc-MA) photoresist and the processes are designed by protection of hydroxyl groups in tannic acid, formulation into a photoresist, exposure and pattern...


Synthesis of modified tannic acid (TA-Boc-MA)
TA-Boc-MA samples were prepared by reaction of tannic acid with t-Boc and MA in a mixture of acetone and DMF. Briefly, Di-tert-butyl decarbonate (t-Boc) (10.0 g) was dropped into acetone and DMF solution (4:1, volume ratio) of tannic acid (170 g/L, 50 mL) with stirring in N 2 atmosphere at room temperature (25 o C), followed by the addition of the DMF solution of DMAP (0.02 g/L, 10 mL) in 10 minutes and then the reaction mixture was continued for 12 h. Then, 7.0 g triethylamine and 7.3 g methylacryloyl chloride were successively dropped into the solution within 15 minutes after the resultant solution was cooled down below 5 o C. After 15 minutes of reaction, the solution was raised to room temperature naturally and the reaction was maintained for 9 h. Next, the resulting solution was dropwise added into ultrapure water to precipitate the product. The product was filtrated and washed with ultrapure water for three times. Finally, the solid powder was dried in vacuum at 40 o C for 24 h.

Blending of photoresist
The photoresists were blended by mixing TA-Boc-Ma, PAG103 and 3D, PETA with PGMEA with stirring continuously above 6 h. The detailed ratio of components was shown in Table  S1. The formation of lithographic pattern based on modified tannic acid The photoresists were filtrated through a 0.22 μm filter and then spin-coated onto silicon wafers (or Polyethylene terephthalate film, Polyimide film, flexible ITO and so on) at 1200 rpm for 30 s, followed by soft baking at 90 o C for 90 s. Subsequently, the film was first exposed for 4 minutes with a mask by 365 nm UV light (14 mw/cm 2 ), baked at 110 ℃ for 90 s, developed in an TMAH aqueous solution for 1 min and washed with ultrapure water at room temperature. After that, a second blanket exposure was applied to the patterned substrate for 1 min, followed by baking at 120 o C for 2 minutes.

Formation of Ag Pattern
Ag pattern was fabricated by a simple electroless plating process. Firstly, 1.0 g of silver nitrate was dissolved in 100 mL of water, followed by dripping ammonia water (25 wt%) to form a white precipitate and then continue to drip until the white precipitate disappears for preparing the solution of tollens' reagent. Afterwards, 1.0 g of trisodium citrate dihydrate and 1.0 g of polyvinylpyrrolidone (K30) was mixed with tollens reagent by stirring for 15 minutes, followed by adjusting the pH to about 8.5 with acetic acid. And then lithographic patterned substrate from the previous step was immersed into the solution at 60 °C for certain time and was taken out for washing with ultrapure water and drying with compressed air. At this point, the fabrication of Ag pattern had been finished. Finally, Ag pattern was annealed on a hot plate at 200 °C for 10 min.

Preparation of Ag Film
The method for preparation of Ag film was similar to the fabrication of Ag pattern. The Si substrate coated with the photoresist directly underwent the second exposure mentioned above without first exposure and other treatments were the same.

Etching of Ag film
The etching of Ag film was conducted by XPS spenctra (Thermo Scientific ESCALAB 250Xi spectrometer). Etching energy was 1 keV and etching time was 1500 s and etching rate is 40 nm/min.

Characterization
Fourier transform infrared spectrum (FTIR) test was performed on a TensorⅡFTIR spectrometer at room temperature. 1 H spectra were set down on Bruker 400 MHz Spectrometer in DMSO-d6 with TMS as a standard at room temperature. SEM imaging and elemental mapping was obtained by an SU8018 electron microscope with an Oxford energy-dispersive X-ray (EDX) analysis system. XRD patterns were obtained by a Smart Lab Se diffractometer equipped with Cu Kα radiation. XPS spectra were obtained by a Thermo Scientific ESCALAB 250Xi spectrometer. The UV-visible absorption spectra were carried out with TU-1901 double beam UV-vis spectrophotometer. Square resistance test was performed by a resistance tester with four-point probe. The measurement of flexible electronic device was performed by an electrochemical workstation.

The calculation method of graft ratio of t-Boc and MA:
The grafting molar ratios of t-Boc and MA on the phenolic group of tannic acid were calculated by the numbers of phenolic group on tannic aicd, hydrogen on the phenyl ring, methyl in the tertiary butyl and vinyl. 1 mol of tannic acid, t-Boc and MA has 20 mol hydrogen of phenyl ring, 9 mol of methyl hydrogen on tert butyl and 2 mol of hydrogen on vinyl, respectively. And 1mol of tannic acid has 25 mol of phenolic group. The calculation formulas are as follows: Figure S1 UV-vis absorption spectra of 3D, PAG103, and their mixtures (1:1, mass ratio).

Figure S2
The FTIR of photoresist before and after baking.

Figure S3
The FTIR of photoresist before and after exposure by 365 nm UV light.