Effect of additive concentration during copper deposition using EnFACE electrolyte

Abstract

10Copper deposition from solutions using high concentration of acid, metal ions and 11 polyethylene glycol (PEG), and bis-(3-sulfopropyl) disulfide (SPS) and chloride ions (Cl -) is 12 well known. A recent maskless micropatterning technology, which has the potential to 13 replace traditional photolithographic process, called EnFACE, proposed using an acid-free, 14 low metal ion solution which is in direct contrast to those used in standard plating 15 technology. In this work copper has been deposited using standard electroplating solutions 16 and those used in the EnFACE process. In the standard electrolyte 0.63 M CuSO4 and 2.04 M 17 H2SO4 has been used, along with Gleam additives supplied by Dow Chemicals. For the Enface 18 electrolyte, copper deposition has been carried out using without any acid, and with Morphological analysis (SEM and EBSD) was done using the JEOL JSM-5300LV. 70Resistivity of the plated films were measured using the Signatone Pro4 (four point probe) 71 system in the Electronics and Electrical Engineering department Newcastle University UK. Prior to actual plating, the stainless steel coupons were cleaned with concentrated 93 HNO3, and then rinsed with water for 1 minute. The coupons were mechanically polished 94 using silicon carbide sheets, starting at grit #220 and progressing to grit #4000. One side of 95 the coupon was coated with the photoresist, and left to dry. The exposed side of the coupon 96 was swabbed with ethanol for 30 seconds and again allowed to dry. Chemicals and Electrolytes 97Electrodeposition was carried out in direct current (DC) mode. The counter and 98 working electrode was set-up in the plating cell containing different electrolytes. Table 2 99 shows the plating parameters used for the different experiments. These parameters were 100 derived from polarization experiments that yielded limiting current regarding each bath 101 type. Since the deposits become rougher as they approach the limiting current [21], the 102 current was set at a fraction of this value to ensure that dendritic copper was not plated. 103The total plating time was calculated to obtain a copper film with thickness of 25 um. 104After the allotted deposition time was reached, the coupons were removed from the 105 solution and washed with deionized water for 1 minute. The surface was dried using a lint 106 free cloth and left to dry in air. The plated copper films were then carefully peeled off from 107 the stainless steel substrate, and were prepared for subsequent characterization. Each 108 experiment was repeated three times to check for reproducibility. 109For SEM and EBSD analysis, a 2x2 cm 2 area was cut out from the central portion of 110 the copper coupon. For mechanical and resistivity testing, the whole coupon was used. The rightmost column in Table 2 gives a summary of the calculated grain size of using EnFACE electrolyte. Clearly, the progressive addition of additives created a more 171 resistive copper deposit. Furthermore, the resistivity of some of the EnFA...