Impact of Leveler Molecular Weight and Concentration on Damascene Copper Electroplating

Transcription

1 Impact of Leveler Molecular Weight and Concentration on Damascene Copper Electroplating J. Zhou and J. Reid Novellus Systems Inc SW Leveton Drive, Tualatin, OR The impact of leveler molecular weight and concentration on bottom-up fill rate, leveling activity, electrolyte polarization, and copper properties of films formed during damascene copper electroplating has been studied. A model leveler, polyvinylpyrrolidone (PVP), at molecular weights ranging from 3,500 to 1,300,000 and at concentrations from 1 to 20 mg/l was found to be effective in reducing excessive plated thickness over superfilling features, while resulting in little loss of bottom-up fill performance. Intermediate PVP molecular weights were most effective in reducing overplating, while the higher molecular weights enhanced fill performance. This behavior is explained in terms of leveler diffusion into features as a function of molecular weight, and leveler impact on electrolyte polarization. Incorporation of sulfur, carbon, and chloride in the plated films increased with increasing PVP concentration and molecular weight. This suggests leveling is accomplished by removal of adsorbed accelerator from the film surface during plating by codeposition with leveler. Introduction The literature covering copper sulfate electroplating baths, and damascene copper plating in particular, has described the function of disodium bis(3-sulfopropyl)disulfide (SPS) accelerator and polyalkylene glycol suppressor additives extensively. These additives allow void-free copper deposition in the sub-micron trench and via structures comprising integrated circuit interconnects. Numerous experimental and theoretical modeling studies demonstrated that the bottom-up feature filling in these systems is achieved by preferential adsorption of accelerating species near the feature base and/or greater adsorption of suppressing species on the wafer surface (1-6). Bottom-up fill is usually initiated as the more strongly adsorbing, non-codeposited accelerator species accumulate near the feature base. Accumulation results as surface area within the features decreases during initial conformal deposition. In smaller features, fill may also be enhanced by a suppressor diffusion gradient between the bulk solution and the base of the feature, leading to reduced suppressor adsorption and higher current at the feature base. In all cases, the surface of the electroplated copper which emerges from a feature following bottom-up fill is enriched in accelerator species, and will continue to grow at a

2 rapid rate relative to the adjacent field (7). This results in excessive topography across a die. For example, the plated thickness above superfilled features often exceeds the adjacent field thickness by a factor of two, or about 1.0 micron in the case of a typical 1.0 micron nominal field thickness. The excess Cu thickness over patterns increases the difficulty of the copper removal from the wafer surface during the subsequent chemical mechanical planarization process. As a result, reducing the thickness of plating above dense features and improving within-die topography is an important goal of damascene electroplating (8). To achieve this improved topography, nearly all damascene copper baths contain species known as levelers. A leveling agent normally has a nitrogen functional group and is added to the bath at a relatively low concentrations in the range of 1-20mg/L. Traditional leveling in applications, such as printed wiring board processing, involve the diffusion or migration of strongly current suppressing species to corners or edges of macroscopic objects which otherwise plate more rapidly than desired due to electric field and solution mass transfer effects. In the case of damascene plating, the function of a leveler is to stop the excessive growth rate of copper over a filled feature while not otherwise perturbing the process. Rather than the steady state behavior of levelers in other applications, the damascene leveler must be designed to act rapidly and specifically to reduce growth on accelerator enriched surfaces which emerge into a position of increased mass transfer. As a result, the polarization behavior, adsorption rates, and mass transfer characteristics of levelers for damascene applications may be significantly different than levelers for traditional applications. Unlike accelerator and suppressor additives, a wide variety of mostly proprietary leveling agents exist for copper plating (9). Structures can vary from small tetra-alkyl ammonium ions to complex polymers. With respect to damascene plating, two types of levelers have been briefly discussed in the literature. The impact of relatively low molecular weight species such as Janus Green (10, 11) on film planarity was found to be mass transfer dependent on a scale much larger than that of damascene features. The impact of very high molecular weight species such as polyacrylamide on damascene fill was interpreted in terms of very restricted diffusion or steric hindrance (12). In the commercial practice of damascene plating, it is normally observed that the proprietary leveler additives used to reduce the excessive growth over features following superfilling can diffuse into the features and disrupt bottom-up fill given adequate time and high concentration. Many newer commercial levelers, however, appear to selectively suppress the rapid growth over features following rapid bottom-up fill when used at sufficiently low concentrations and over short time scales. The mechanism of this apparent selectivity with respect to activity within the damascene features is not fully understood. In this work, we have studied the impact of the model leveler PVP (see Figure 1) at concentrations up to 20 mg/l, and at molecular weights from 3500 to 1,300,000, on damascene bottom-up fill rate and leveling behavior. The impact of this leveler on plating bath polarization behavior, and on the anneal behavior, purity, microvoid formation, and grain structure properties of the copper deposit was also characterized. The leveler

3 activity is interpreted in terms of diffusion and polarization behavior and the chemical activity of the leveler species. Experimental Electrolyte solutions used in this study contain cupric ion, sulfuric acid, and chloride ion along with commercially available SPS type accelerator and suppressor. The accelerator and suppressor were used at concentrations previously determined for optimum bottom-up fill and overall damascene plating performance in the base electrolyte. The PVP levelers of five molecular weights (3,500, 10,000, 29,000, 55,000, and 1,300,000 g/mol) were purchased from Sigma-Aldrich. Samples to evaluate bottom-up fill, leveling, and film properties were plated on a 200mm Sabre system. Samples for measuring partial fill rate, overplating height, infeature grain size evolution and microvoid formation were die-size coupons that were taped at mid-radius of 200 mm wafers using conductive adhesive copper tape. Coupons and full wafers were seeded with 100nm PVD copper on a 25 nm PVD Ta barrier layer. A total of 29 Coulombs (35 nm nominal plated thickness) of Cu was deposited to measure fill rates inside 0.15, 0.20, and 0.30µm wide, 1.1 µm deep trenches. Analysis of fill was by cleave and SEM imaging. The leveling effect of PVP's was characterized by measuring the thickness of plating over 0.13 line/0.13 µm space trench arrays compared to plated thickness on adjacent unpatterned areas following deposition of 0.7 µm films. The overplating heights were measured using a Veeco Dektak 300-Si profilometer. Infeature grain size evolution was monitored inside µm, µm, µm, and µm trench arrays at room temperature and after anneal at 400 C for 120s using the in-line anneal module of a Sabre system. Figure 2 shows the FIB/SEM image plane for in-feature grain structure and microvoid studies. The microvoid formation inside and on top of trenches of the annealed samples was characterized by the average counts of microvoid per unit volume of plated copper. For 0.2 µm wide trenches, the counting area was the center of two adjacent trenches. For 2.0 µm wide trenches, the counting areas were at 1/3 and 2/3 of the trench width within the same trench. Whole wafers with 1.0 µm deposits were used to measure room temperature anneal rates and deposit purity. The room temperature anneal rates were characterized by the changes in sheet resistance, as measured using a KLA-Tencor RS75. Deposit purity was measured by SIMS through a commercial vendor. Electrochemical behavior of electrolytes was measured in a beaker using a 4 mm diameter Pt RDE working electrode, a Cu sheet counter electrode, and a saturated Hg/HgSO 4 reference electrode. Electrochemical data were collected using a PAR EG&G Model 283 potentiostat. The potential was scanned between 400 and 800 mv vs. Hg/HgSO 4 at 2 mv/s and 300 RPM during cyclic voltammetry measurements. Before the galvanostatic measurements in the solution of interest, a thin layer of Cu (0.1 µm) was first deposited onto Pt RDE in the electrolyte without organic additives. The Cu coated Pt RDE was then rinsed in DI water and transferred into the testing electrolyte. The effect of PVP addition on galvanostatic deposition from accelerator-suppressor

4 solutions was measured by injections of small PVP volumes into well-stirred acceleratorsuppressor solutions. The accelerator-suppressor solutions were galvanostatically controlled at a given current for various times prior to PVP injection. Results and Discussions Effect of PVP MW and concentrations on bottom-up fill rates and overplating heights Figure 3 shows SEM images of cleaved 0.15, 0.20, and 0.30 µm 1.1 µm trenches after 35nm copper deposition in solutions containing accelerator and suppressor only, and upon addition of 5 and 20 mg/l PVP at MW of 3,500 and 1,300,000. In all cases the 0.15 and 0.2 micron features are already fully filled or nearly filled, while fill is partially complete in the 0.3 micron features. The addition of PVP 3,500 into the acceleratorsuppressor only solution degraded bottom-up fill in all three trench sizes, especially at 20 mg/l where the rate of filling is reduced by about 30%. The detrimental effect of the relatively small molecule leveler on superfilling is likely caused by diffusion of leveler into trenches during filling. Addition of PVP MW 1,300,000 did not degrade fill even at 20 mg/l solution concentration, and appears to have slightly increased the degree of filling following the 35 nm nominal Cu deposition. This implies that the diffusion of these large molecules into features was limited such that PVP mass transfer to the wafer surface selectively resulted in additional current suppression in this area. Figure 4 shows the results of partial fill evaluations using additional PVP molecular weights at 5 and 20 mg/l concentration. The partial fill rate of accelerator-suppressor only solution is used as the baseline and defined as unity. PVP at molecular weights of 3,500, 10,000, and 29,000 decreased the efficiency of bottom-up fill as solution concentration was increased to 20 mg/l. This behavior suggests that all of these molecular weights diffuse sufficiently into the features to disrupt the bottom-up fill process. Such behavior is typical for most commercial levelers. At 55,000 molecular weight, the fill rate is enhanced at 5 mg/l PVP concentration but degrades as concentration is increased to 20 mg/l. Taken together with the overall set of PVP effect on fill, this likely reflects reduced diffusion into the feature at this PVP molecular weight. The 1,300,000 molecular weight leveler enhances the fill rate at all solution concentrations suggesting limited diffusion into the features. The conformation of PVP in solution is not known. However, the spherical diameter of a 1,300,000 molecular weight molecule is about 13nm. Although 13 nm is still much smaller than the µm feature sizes, steric hindrance of polymer movement into the features could contribute to the fill results using these very high molecular weights if the polymer conformation is not spherical. Figure 5 shows SEM images of overplating height over µm trenches separated by 0.13µm spaces plated using accelerator and suppressor only and plated following addition of PVP. The overplating height decreased from over 1000 nm in the accelerator-suppressor only case down to about 30nm upon addition of 10 mg/l PVP 29,000. All features were completely filled in both cases indicating the bottom-up fill

5 process was not strongly disrupted despite the excellent leveling. Figure 6 shows overplating height over the trench array of Figure 5 at various PVP molecular weights and concentrations. All PVP levelers effectively reduced overplating height at concentrations as low as 1 mg/l, and become increasingly effective in leveling with increasing concentration. PVP at intermediate molecular weight (10-55K) showed the best leveling performance at a given concentration. For example, overplating was fully eliminated upon addition of 10 mg/l PVP 29,000 and 55,000. Considering the partial fill data shown above, this suggests that most effective leveling requires a slight sacrifice in bottom-up fill rate. It is interesting to note that the lowest PVP molecular weights which led to the greatest reduction in fill rate did not lead to the best leveling performance. This may suggest the low molecular weight PVP has a weaker adsorption and inhibition effect than the higher molecular weights, similar to polyalkylene glycol behavior (13). The very high molecular weight PVP which enhanced fill performance was apparently not capable of adsorbing quickly or uniformly enough on the surfaces emerging from trenches to stop some overplating formation as effectively as the intermediate molecular weights. Effect of PVP MW and concentrations on electrolyte polarization behavior Figure 7 shows the cyclic voltammetry of the accelerator-suppressor only electrolyte and with various PVP concentrations and molecular weights added to this solution. The addition of as little as 1 mg/l PVP to accelerator-suppressor only solutions polarizes the electrolyte at higher applied potentials, but has little effect at lower applied potentials. At 20 mg/l the degree of polarization roughly corresponds to leveling capability. However the impact of PVP on current at a given applied potential even in the most polarized case is only about 30%. This qualitatively seems to be a much smaller impact than the impact of the levelers on emerging accelerator rich surface following filling. The greater polarization effect of PVP noted at higher potentials might suggest specific activity toward 3-mercapto-1-propanesulfonic acid (MPS) or other species generated during plating by electrochemical reaction of the initial SPS accelerator and present on the emerging features. The hysteresis between forward and reverse scan is reduced upon addition of PVP leveler into accelerator-suppressor only electrolyte, also suggesting deactivation of accelerators which may be generated at the higher potentials. An intersection of the forward and reverse scans of three-additive electrolytes is observed at a potential which is independent of the potential scan range for a given PVP molecular weight and concentration (data not shown here). Similar effects noted in the literature (9) are interpreted as indication that the adsorption of leveler has some kinetic constraint at concentration and molecular weight ranges under study. Figure 8 shows the galvanostatic polarization behavior of SPS accelerator-suppressor only solution and electrolytes with 10 mg/l PVP at various molecular weights using a 30 ma/cm 2 current density. At this current density, the 100 mv increase in polarization observed using the higher molecular weights of PVP is in good agreement with the degree of polarization required to diminish plating over superfilling features. Also the higher degree of polarization is achieved within the first few seconds of plating as required to stop excessive thickness over bumps. This result, taken with those from

6 Figure 7, suggests the specific affinity of leveler toward accelerator species formed at higher current densities. Figure 9 shows the galvanostatic response at 30 ma/cm 2 of electrolytes upon injection of 10 mg/l PVP at various molecular weights after 300s plating in SPS acceleratorsuppressor and MPS-suppressor solutions. The long plating time was chosen to generate accelerator coverage on the copper surface similar to that present on superfilling features In all accelerator-suppressor solutions, the polarization increases sharply in the first few seconds of plating as current is suppressed by the suppressor-cl - film. Depolarization next takes place of over the first one to two minutes of plating as accelerators or accelerator by-products accumulate on the plated surface (13). At the same concentration, MPS depolarizes the surface more quickly than SPS accelerator, as expected based on its known strong accelerating capability. Following injection of PVP to the accelerator containing solutions after 300s plating, the solution quickly becomes slightly more polarized, especially using higher molecular weight PVP levelers. This small increase in polarization takes place over the same time scale of several seconds which is necessary to stop overplating above superfilling features. A similar degree of polarization takes place upon addition of PVP to both MPS and SPS containing solutions. Because the transient polarization data were collected on a planar surface, the increase of surface area which normally dilutes accumulated accelerator concentration upon completion of fill did not take place. Also, enhanced diffusion of leveler to a protruding surface which could be beneficial for leveling activity over actual emerging features did not take place in this test. These effects may combine to reduce alter the effect of the leveler impact in this RDE testing compared to the effect in actual damascene applications. Considerable further polarization following PVP addition takes place over relatively long periods of time, suggesting marginal capability to neutralize some accelerating species accumulated under the conditions of this test. Such long transition time is a very slow process compared to the actual effect of levelers on filling features, possibly due to difference is the accelerating species or the degree of accelerator surface coverage. Similar results were noted upon addition of PVP following 20 and 120 seconds of plating. Effect of PVP on film purity, anneal rate, grain growth, and microvoid formation Figure 10 shows the C, S, and Cl concentration in 1µm deposits plated in SPSsuppressor only electrolyte, and in electrolytes with 5 mg/l PVP MW3,500, MW55,000, MW1,300,000 and 20 mg/l PVP MW1,300,000. Upon addition of PVP to the SPSsuppressor electrolyte, dramatically more C, S, and Cl were incorporated into the film. The impurity concentrations following PVP addition are typical for films deposited using commercially available three-additive systems. Since no S is present in the PVP molecule we interpret the co-deposition of S as evidence that PVP leveling is achieved by causing co-deposition of accelerator, which would otherwise remain active on the plated surface. At a given PVP concentration, the least amount of impurities was incorporated in the film plated using 3,500 molecular weight PVP. Minimal difference in impurity

7 concentration was observed in deposits plated using 5 mg/l PVP molecular weights 55,000 and 1,300,000. The concentration increase from 5 to 20 mg/l PVP 1,300,000, however, doubles all three impurities concentration. In general, the higher impurity films correlate to increased leveling activity and stronger polarization, supporting the contention that leveling activity is achieved through a leveler-accelerator chemical interaction followed by co-deposition of both species. Figure 11 shows relative sheet resistance of 1µm films plated in SPS-suppressor solution and in electrolytes at 5, 10, and 20 mg/l PVP at 3,500, 55,000, and 1,300,000 molecular weights as a function of time during room temperature anneal. The change in sheet resistance is frequently used to monitor grain growth during copper anneal.. Figure 12 summarizes the normalized t 90 as a function of PVP concentration at various MW. The t 90 of accelerator-suppressor electrolyte is assigned as t 90,0, the baseline for normalization Without PVP, film anneal took place in about 200 hours at room temperature, as evidenced by the 17% decrease in film resistance. As the concentration of PVP in the electrolyte was increased from 5 to 20 ppm, film anneal rates decreased, as generally expected when the level of impurities in the plated films increases (14). Anneal rate decreases more sharply at higher PVP molecular weight, even when comparing films with similar impurity concentrations. This could be partially explained in terms of more efficient S incorporation due to SPS co-deposition using higher PVP molecular weights, however, this effect does not correlated well with leveling activity. The data is more consistent with a direct impact of the larger PVP molecules on the grain re-arrangement behavior of the plated films. During room temperature annealing, the grain size increase likely takes place concurrent with impurity movement to the grain boundaries (15). The anneal rate is impacted by the pinning of grain boundaries by various impurities (14) which diffuse to these positions. Under some conditions, the impurity level in the film is sufficiently high to pin grain boundaries and the sheet resistance of films almost remained unchanged. This data suggests that pinning of grain boundaries is more readily achieved by large molecules. Figure 13 shows a top-down view of grains in 1µm films immediately after plating and 24 days anneal at room temperature. The films were plated in SPS-suppressor only electrolyte and in electrolytes with 5 and 20 mg/l PVP MW3,500 and 29,000. Asdeposited films have very fine grain structures regardless of PVP concentrations and molecular weights as is typical of all commercial damascene plating systems. The films plated without PVP and following 5 mg/l PVP3500 and PVP29000 addition have recrystallized to form large grains after 24 days. The observed change in grain size is in good agreement with changes in sheet resistance at 5 mg/l PVP shown in Figure 12. At 20 mg/l PVP concentration, the film plated using 3,500 molecular weight has mixed small and large grains after 24 days self-annealing, while the film plated using 29,000 molecular weight shows no grain growth. Grain growth in the field copper based on SEM observation appears to correlate well to the measured sheet resistance changes and does not reveal additional unique behavior related to incorporation of specific PVP molecular weights.

8 During bottom-up fill, the impurity incorporation in the copper deposited inside small features may be different that in the field. While it is very difficult to directly access copper purity within features, an understanding of purity related behavior such as grain growth and microvoid formation within features is important in understanding interconnect reliability behavior. In this work, the grain structure and microvoid counts inside and on top of trenches was studied using FIB/SEM micrographs to establish any correlations with impurity incorporation. Figure 14 shows the grain structure inside and above trenches for films plated using SPS-suppressor baths containing 5 and 20 mg/l PVP3,500 and PVP55,000 following anneal at 400C for two minutes. Four trench dimensions were used, µm, µm, µm, and µm. Using the relatively high temperature anneal conditions of this test, the field grain structure penetrates into the 2.0µm wide trenches regardless of the trench depth. The grain size is also independent of leveler concentration or molecular weight suggesting a fairly complete anneal in all cases. In the 0.2µm wide trenches, the grain structure has a strong dependence on trench depth, PVP MW, and concentration. In shallow (0.55µm x 0.2µm) trenches, the grain growth penetrates into trenches in films formed using both concentrations of PVP3,500 and using 5 mg/l PVP55,000. At 20 mg/l PVP55,000, however, the grain growth at the bottom of trenches was restricted by the trench size and remains similar to the as-plated state. In the 0.2µm 1.1µm trenches, the grain growth was reduced at all PVP concentrations and MW. The number of small grains appears to increase with increasing PVP MW and concentration. These results show that grain growth rate inside trenches decreases with increasing PVP concentrations and PVP molecular weight. Figure 15 shows the grain structure following 24 days room temperature anneal for films plated using 5 and 20 mg/l PVP MW10,000 and 55,000 for the four trench dimensions shown in Figure 14. At the early stage of self-annealing (24 hours), the films deposited in 20 mg/l PVP solutions have fine grains in the field and inside trenches. After 24 days, the films plated using 5 mg/l PVP concentration behave similarly to those subject to 400C anneal. Large grains penetrate into 2.0µm trenches and the grain size is independent of trench depth and PVP molecular weight. In 0.2µm trenches, small grains remain at the bottom of trenches, especially in the case of the deeper features. At 20 mg/l concentration, the grain growth even in the field is reduced using all molecular weights, and higher molecular weight PVP s result in little if any grain growth within the smaller features. Since grain growth was restricted in small features even using high molecular weight PVP we cannot conclude that a higher purity in-feature film was produced. However, because grain growth within features depends on growth in the adjacent field, it is possible that the film purity is high but grain growth remains inhibited due to behavior of the field copper. Microvoids are in the range of 0.01 to 0.03 microns in diameter are frequently found at grain boundary triple points in plated copper following anneal and grain growth. These voids have previously been shown to increase with film impurity levels and have been correlated to electromigration failure (16). Figure 16 summarizes the microvoid density above and inside trenches for 1.0 micron plated films following anneal at 400C for two

9 minutes. In general, the microvoid density inside and on top of trenches increases with increasing PVP concentration, as expected for films with higher impurity content. For the larger features, and in the field above smaller features, the number of microvoids was least using PVP3,500 and PVP10,000, when compared to higher molecular weights. This also is roughly correlated with film purity behavior. However, inside the smaller features, there was no clear dependence of microvoid density on PVP molecular weight. A decrease in microvoids within small features might have been expected if a higher purity film was formed using the higher molecular weights of PVP which do not appear to diffuse into small features, and based on fill results and microvoid dependence on film purity. The observation of microvoids suggests a strong interaction of copper within the feature with the impure field copper during anneal, or impurities in the feature not related to the PVP. Summary PVP was found to be effective in reducing overplating above superfilled features, while not strongly impacting bottom-up fill. Low molecular weight PVP degraded fill at high solution concentrations, apparently due to diffusion into features during bottom-up fill. Very high molecular weights of PVP enhanced fill at all concentrations as diffusion into submicron features was inhibited. At a given solution concentration, leveling was most efficient at intermediate PVP molecular weights which may yield a favorable combination of polymer adsorption strength and continuous surface coverage. Film purity data suggests leveling activity is achieved through accelerator removal by codeposition with leveler. Generally more impure copper films which underwent slower grain growth during anneal at a given temperature and which exhibited an increased concentration of microvoids both in the field and with features were generated using higher PVP concentrations. Acknowledgements The authors would like to thank Daniel Pullman and Brenda Purcell who performed FIB/SEM analysis used in this study. References 1. J. Reid, Jpn. J. Appl. Phys., 40, 2650 (2001). 2. P. M. Vereecken, R. A. Binstead, H. Deligianni and P. C. Andricacos, IBM. J. Res. & Dev., 49, 3 (2005). 3. T. P. Moffat, D. Wheeler, M. D. Edelstein and D. Josell, IBM. J. Res. & Dev., 49, 19 (2005). 4. K. R. Hebert, S. Adhikari and J. E. Houser, J. Electrochem. Soc., 152, C324 (2005). 5. K. Kondo, T. Matsumoto and K. Watanabe, J. Electrochem. Soc., 151, C250 (2004).

10 6. R. Akolkar and U. Landau, J. Electrochem. Soc., 151, C702 (2004). 7. A. C. West, S. Mayer and J. Reid, Electrochem. Solid-State Lett., 4, C50 (2001). 8. Y. H. Im, M. O. Bloomfield, S. Sen and T. S. Cale, Electrochem. Solid-State Lett., 6, C42 (2003). 9. T. P. Moffat, D. Wheeler, S.-K. Kim and D. Josell, J. Electrochem. Soc., 153, C127 (2006). 10. J. J. Kelly, C. Tian and A. C. West, J. Electrochem. Soc., 146, 2540 (1999). 11. W.-P. Dow, H.-S. Huang, M.-Y. Yen and H.-C. Huang, J. Electrochem. Soc., 152, C425 (2005). 12. J. Reid, US Patent 6,024,857, Issued Feb. 15, W.-P. Dow, M.-Y. Yen, W.-B. Lin and S.-W. Ho, J. Electrochem. Soc., 152, C769 (2005). 14. J. Sukamto and J. Reid, in Electrochemical Processing in ULSI and MEMS, H. Deligianni, S. T. Mayer, T. P. Moffat, G. R. Stafford and Editors, PV , p. 82, The Electrochemical Society Proceedings Series, Pennington, NJ (2005). 15. S. H. Brongersma, E. Kerr, I. Vervoort, A. Saerens and K. Maex, J. Mater. Res., 17, 582 (2002). 16. G. B. Alers, J. Sukamto, P. Woytowitz, X. Lu, S. Kailasam and J. Reid, in IEEE 43rd Annual International Reliability Physics Symposium Proceedings, p. 36, San Jose (2005).

11 H 3 C CH CH 2 CH 3 O N Figure 1. Chemical structure of polypvinylyrrolidone (PVP) n Image Plane Figure 2. FIB/SEM image plane for in-feature grain structure and microvoid studies Acceleratorsuppressor µm µm µm + 5 mg/l PVP (MW=3,500) + 20 mg/l PVP (MW=3,500) + 5 mg/l PVP (MW=1,300,000) + 20 mg/l PVP (MW=1,300,000) Figure 3. Cleave/SEM images of partially filled 0.15, 0.20, and 0.30 µm trenches after 35nm field Cu plating in electrolytes with accelerator-suppressor only, 5 and 20 mg/l PVP at MW of 3,500 and 1,300,000.

12 Relative partial fill rate PVP concentration (mg/l) MW3,500 MW10,000 MW29,000 MW55,000 MW1,300,000 Figure 4. Relative partial fill rate inside µm trenches after 35nm field Cu plating in solutions containing 5 and 20 mg/l PVP at MW of 35,000, 10,000, 29,000, 55,000, and 1,300,000. PVP added Figure 5. Overplating height over 0.13/0.13µm trench arrays upon 0.7µm field Cu plating without and with addition of 10 mg/l PVP MW29,000 into accelerator-suppressor electrolyte. Overplating height (A) MW=3500 MW=10K MW=29K MW=55K MW=1.3M PVP concentation (mg/l) Figure 6. Overplating height measured using a Dektak profilometer as a function of PVP MW and concentration over the trench array shown in Figure 5.

13 -j (ma/cm 2 ) no PVP 1ppm 5ppm 20ppm PVP Potential vs. Hg/HgSO 4 (mv) -800 Figure 7. Polarization behavior of electrolytes at various MW and concentrations illustrated by cyclic voltammetry collected at 300RPM, 2mV/s on Pt RDE. -j (ma/cm 2 ) ppm PVP(1.3M) Potential vs. Hg/HgSO 4 (mv) no PVP 20ppm PVP(3.5K) 20ppm PVP(10K) -850 E vs. Hg/HgSO4 (mv) no PVP PVP3500 PVP10K PVP1.3M PVP55K PVP29K t (s) Figure 8. Galvanostatic response of SPS accelerator-suppressor only and electrolytes with 10 mg/l PVP at various molecular weights. The data were collected at 300 RPM and 30 ma/cm 2 on a Cu coated Pt RDE. E vs. Hg/HgSO4 (mv) PVP 1.3M PVP 3500 PVP 10K PVP 55K E vs. Hg/HgSO4 (mv) PVP 3500 PVP 10K PVP 55K PVP 1.3M t (s) t (s) Figure 9. Galvanostatic response of electrolytes upon injection of 10 mg/l PVP at various molecular weights after 300s plating in (1) SPS accelerator-suppressor and (2) MPS-suppressor solutions at given concentrations.

14 C (ppm) no PVP 5 ppm PVP3500 5ppm PVP55K 5ppm PVP1.3M 20ppm PVP55K S (ppm) no PVP 5 ppm PVP3500 5ppm PVP55K 5ppm PVP1.3M 20ppm PVP55K Depth (µm) Depth (µm) Cl (ppm) no PVP 5 ppm PVP3500 5ppm PVP55K 5ppm PVP1.3M 20ppm PVP55K Depth (µm) Figure 10. Effect of PVP MW and concentration on C, S, and Cl content in 1µm deposits Rs/Rs0 1 no PVP ppm 10ppm ppm 0.85 PVP Time after plating (hrs) Rs/Rs PVP55K 0ppm 5ppm 10ppm 20ppm Time after plating (hrs) Rs/Rs no PVP 5ppm ppm 20ppm 0.85 PVP 1.3M Time after plating (hrs) Figure 11. Relative sheet-resistance as a function of time at various PVP concentrations of MW 3,500, 55,000, and 1,300,000. R s0 is the sheet resistance of as-deposited films.

15 t90/t90, MW3,500 MW10,000 MW29,000 MW55,000 MW1,300, PVP concentration (mg/l) Figure 12. Relative t 90 as a function of PVP concentration at various molecular weights. The t 90 is defined as the time required for sheet-resistance to reach 90% of as-plated film value. The t 90,0 is the t 90 for the samples in accelerator-suppressor only electrolyte. As plated Acceleratorsuppressor 5 mg/l PVP MW3, mg/l PVP MW3,500 5 mg/l PVP MW29, mg/l PVP29, days postplate Figure 13. The as-deposited and 24 days post-plate grain structures of 1µm films plated in accelerator-suppressor only electrolyte and electrolytes at 5 and 20 mg/l PVP3,500 and 29, mg/l PVP3, µm µm µm µm 20 mg/l PVP3,500 5 mg/l PVP55, mg/l PVP55,000 Figure 14. Grains structure inside and on top of trenches after 2 min. anneal at 400 C at various PVP concentration and MW and trench dimensions.

16 5 mg/l PVP10, µm µm µm µm 20 mg/l PVP10,000 5 mg/l PVP55, mg/l PVP55,000 Figure 15. Grain size following 24 days self-annealing at room temperature at various PVP molecular weights, concentrations, and trench dimensions. microvoid#/µm on top of trenches inside 0.2x0.55um trenches K 29K 55K 1.3M K PVP concentration (mg/l) 29K 55K 1.3M microvoid#/µm on top of trenches inside 2.0x0.55um trenches K 29K 55K 1.3M K PVP concentration (mg/l) 29K 55K 1.3M microvoid#/µm on top of trenches inside 0.2x1.1um trenches K 29K 55K 1.3M K 29K 55K PVP concentration (mg/l) 1.3M microvoid#/µm on top of trenches inside 2.0x1.1um trenches K 29K 55K 1.3M K PVP concentration (mg/l) 29K 55K 1.3M Figure 16. Microvoid counts inside and on top of trenches as a function of PVP concentration at various PVP MW and trench dimensions