Plating method

Abstract

Copper electroplating baths having a surface tension of ≦40 mN/m are suitable for filling vias with copper, where such copper deposits are substantially void-free and substantially free of surface defects.

Claims

1. A method of filling a via in an electronic device with copper comprising: providing an acidic copper electroplating bath comprising a source of copper ions, an acid electrolyte, a source of halide ions, an accelerator, a leveler, and a suppressor, wherein the copper electroplating bath has a dynamic surface tension of ≦40 mN/m; providing as a cathode an electronic device substrate having one or more vias to be filled with copper and having a conductive surface; contacting the electronic device substrate with the copper electroplating bath; and applying a potential for a period of time sufficient to fill the vias with a copper deposit; wherein the copper deposit is substantially void-free and substantially free of surface defects; and wherein the suppressor is a branched secondary alcohol ethoxylate.

2. The method of claim 1 wherein the electronic device is a wafer or a die.

3. The method of claim 1 wherein the copper electroplating bath has a pH of ≦2.

4. The method of claim 1 wherein the conductive surface is a seed layer.

5. The method of claim 4 wherein the seed layer is a copper seed layer.

6. The method of claim 1 wherein the suppressor further comprises propylene oxide as polymerized units.

7. The method of claim 1 wherein the copper deposit is void-free and free of swirl defects.

8. A copper electroplating bath composition comprising: a source of copper ions; an acid electrolyte; a source of halide ions; an accelerator; a leveler; and a suppressor; wherein the copper electroplating bath has a dynamic surface tension of ≦40 mN/m; wherein the copper electroplating bath is acidic; and wherein the suppressor is a branched secondary alcohol ethoxylate.

9. The composition of claim 8 wherein the suppressor is present in an amount of from 0.5 to 500 ppm.

10. A copper electroplating bath composition comprising: a source of copper ions; an acid electrolyte; a source of halide ions; an accelerator; a leveler; and a suppressor; wherein the copper electroplating bath has a surface tension of ≦40 mN/m; and wherein the suppressor is a branched secondary alcohol ethoxylate.

11. A method of filling a via in an electronic device with copper comprising: providing as a cathode an electronic device substrate having one or more vias to be filled with copper and having a conductive surface; contacting the electronic device substrate with the copper electroplating bath of claim 10; and applying a potential for a period of time sufficient to fill the vias with a copper deposit; wherein the copper deposit is substantially void-free and substantially free of surface defects.

Description

EXAMPLE 1

(1) Copper electroplating baths were prepared by first combining 63.5 g/L Cu.sup.2+ (from CuSO.sub.4.5H.sub.2O), 10 g/L H.sub.2SO.sub.4, and 80 mg/L Cl.sup.− (from 1N HCl), and then adding 4.8 mL/L of an accelerator (sodium bis(sulfopropyl)disulfide) stock solution, 3.5 mL/L of a leveler (reaction product of imiazoles with diglcidyl ether) stock solution, and an amount of an aqueous suppressor stock solution. The suppressors evaluated are shown in Table 1, where sample numbers containing a “C” are comparative.

(2) TABLE-US-00001 TABLE 1 Sample No. Suppressor Material Trade name C1 Tetrafunctional EO/PO block copolymer formed from ethylenediamine core C2 Alkyl capped EO/PO block copolymer UCON ™ 50-HB-170 (EO/PO = 1/1 w/w), M.sub.n = 750 C3 Alkyl capped EO/PO block copolymer UCON ™ 50-HB-260 (EO/PO = 1/1 w/w), M.sub.n = 970 C4 Alkyl capped EO/PO block copolymer UCON ™ 50-HB-660 (EO/PO = 1/1 w/w), M.sub.n = 1590 C5 Alkyl capped EO/PO block copolymer UCON ™ (EO/PO = 1/1 w/w), M.sub.n = 3930 50-HB-5100 1 Branched secondary alcohol ethoxylate, TERGITOL ™ having 11 moles of EO TMN-10

EXAMPLE 2

(3) The procedure of Example 1 is repeated except the suppressors listed in Table 2 are used.

(4) TABLE-US-00002 TABLE 2 Sample No. Suppressor Material Trade name 2 Branched secondary alcohol TERGITOL ™ TMN-6 ethoxylate, having 8 moles of EO 3 Alkyl capped EO/PO copolymer TERGITOL ™ XD (EO/PO = 1/1 w/w) 4 Alkyl capped EO/PO copolymer TERGITOL ™ XH (EO/PO = 1/1 w/w) 5 70:30 Blend of TERGITOL ™ TERGITOL ™ TMN-100 TMN-10 and TERGITOL ™ TMN-6 surfactants

EXAMPLE 3

(5) Swirl defect testing was performed on 4×4 cm Q-cleave D (QCD) wafer coupons. The coupons were attached to the plating head of a segment plater with conductive copper tape, which was then covered by platers tape (3M, Minneapolis, Minn.). All coupons were subjected to a 5 min. deionized water spray prior to plating. Each wafer coupon acted as the cathode and was rotated by a Pine Instruments MSRX rotator at 50 rpm and was contacted with the electroplating bath from Example 1. The temperature of the electroplating bath was 25° C. The plating waveform used to monitor surface (swirl) defects is reported in Table 3, where CD is the current density.

(6) TABLE-US-00003 TABLE 3 Cu Deposit thickness, Å CD, mA/cm.sup.2 Time, min. Hot entry 0 0.1 0 Step 1 1500 0.6 11.26 Step 2 2000 1 9.01 Step 3 2500 3 3.75 Step 4 6000 5 5.41 Total: 12000 29.43

(7) Each plated wafer coupon was evaluated for surface (swirl) defects using confocal microscope images obtained from a Leica DCM 3D microscope. Defect images were taken approximately 1 cm from each of the corners of the coupons as well as the center of each coupon. The concentration of the suppressors tested and the presence of surface (swirl) defects are reported in Table 5. In Table 5, a rating of “No” surface defects meant that no surface defects, particularly swirl defects, were observable, while a rating of “Yes” indicates the presence of swirl defects. FIG. 1A is an optical image of the copper deposit obtained from the copper electroplating bath having suppressor Sample 1 (invention). FIG. 1B is an optical image of the copper deposit obtained from the copper electroplating bath having suppressor Sample C1 (comparative). As can be seen from FIGS. 1A and 1B, the deposit obtained from the electroplating bath of the invention has no swirl defects, whereas the deposit obtained from the comparative electroplating bath (FIG. 1B) shows significant swirl defects.

EXAMPLE 4

(8) Via fill testing was performed on various test wafer coupons having 10 μm diameter×100 μm deep TSVs. The coupons were attached to the plating head of a segment plater with conductive copper tape, which was then covered by platers tape (3M, Minneapolis, Minn.). All coupons were subjected to a 5 min. deionized water spray prior to plating. Each wafer coupon acted as the cathode and was rotated by a Pine Instruments MSRX rotator at 50 rpm and was contacted with the electroplating baths from Example 1. The temperature of the electroplating bath was 25° C. The plating waveform used to monitor surface (swirl) defects is reported in Table 4, where CD is the current density. The dynamic surface tension of each of the plating baths was measured at 25° C. using a Krüss BP100 bubble pressure tensiometer at a surface age of 30 sec. The surface tension measurements are reported in Table 5.

(9) TABLE-US-00004 TABLE 4 Cu Deposit thickness, Å CD, mA/cm.sup.2 Time, min. Hot entry 0 0.1 0 Step 1 2000 0.48 18.77 Step 2 3000 0.97 13.93 Step 3 6450 2 14.53 Step 4 6050 3 9.08 Total: 17500 56.31

(10) Following copper plating to fill the TSVs, the wafer coupons were cross-sectioned and imaged by optical microscopy. The optical images were evaluated to determine the filling ability of the plating bath. A rating of “Good” meant that the TSVs were completely filled with copper which was also void-free. A rating of “Poor” meant that completely filling of the TSV was not achieved. The results are reported in Table 5. Suppressor C1 was found to produce swirl defects having a height of from 50 to 250 nm

(11) TABLE-US-00005 TABLE 5 Suppressor Surface Suppressor Concentration, Tension, TSV Sample mg/L mN/M Surface Defects Filling C1 35 52.3 Yes Good C2 1500 47 Yes — C3 13.4 — Yes Good 610 — Yes Good 1220 45.7 Yes Good C4 22 — Yes Good 150 — Slightly Reduced Good 1000 43 Slightly Reduced Good C5 4.4 — Yes Good 26.4 — Yes Good 54.4 41.6 Reduced Poor 1 62.5 37.0 No Good 100 33.4 No — 2 100 30.4 No —

(12) As can be seen from Table 5, only the copper electroplating baths of the invention were able to completely fill TSVs with a void-free copper deposit, and provide a copper deposit that was free of surface defects. The copper electroplating bath containing Suppressor C5 in an amount of 54.4 mg/L was able to reduce, but not eliminate, swirl defects, but was then unable to completely fill the TSV.

EXAMPLE 5

(13) Wafer coupons were plated according to the procedure of Example 4 using a copper electroplating bath from Example 1 containing either 75 ppm of suppressor Sample 1 (invention) or 35 ppm of suppressor Sample C1 (comparative). The plating waveform used is reported in Table 6.

(14) TABLE-US-00006 TABLE 6 Cu Deposit thickness, Å CD, mA/cm.sup.2 Time, min. Hot entry 0 0.1 0 Step 1 2000 0.60 15.02 Step 2 2000 0.90 10.01 Step 3 6350 2.4 11.92 Step 4 7150 3.2 10.06 Total: 17500 47.01

(15) Following copper plating, the wafer coupons were cross-sectioned and imaged by optical microscopy. FIG. 2A is a cross-sectional optical image of the wafer plated using the inventive copper electroplating bath (suppressor Sample 1), and FIG. 2B is is a cross-sectional optical image of the wafer plated using the comparative copper electroplating bath (suppressor Sample C1). FIG. 2A shows void-free copper filled TSVs while FIG. 2B shows copper filled TSVs having significant voids.