Stress and Microstructure in Electrodeposited Copper Nanofilms by Substrate Curvature and In-situ Electrochemical AFM Measurements

Abstract

Both AFM imaging and stress measurements were carried out in-situ during potentiostatic electrodeposition of copper on gold in 0.05 mol dm-3 CuSO4 in 0.1 mol dm-3 H2SO4. In the absence of additives, compressive stress generally developed initially and films subsequently underwent a compressive-to-tensile (C-T) transition. The nucleation density measured by AFM increased from 2.7x107 cm-2 at -75 mV to 2.5x109 cm-2 at -300 mV. Very little coalescence of nuclei was observed at -75 mV but the rate of coalescence increased rapidly with increasing negative potential. The time for the C-T transition correspondingly decreased rapidly until, at -75 mV, none was observed. This is consistent with models that attribute the C-T transition to increasing tensile stress due to coalescence of nuclei. With a combination of Cl-, PEG and MPSA, compressive stress generally developed initially and was greater than in additive-free electrolyte. At less negative potentials, the stress continued to evolve in the compressive direction, even though the rate of coalescence of nuclei was rapid. At intermediate potentials (-90 mV to -150 mV), classical C-T-C behavior was observed; at more negative potentials the stress continued to evolve in the tensile direction. This enhancement of a compressive component of stress is attributed to incorporation of additive-derived impurities.

Vacancy-Induced Plastic Deformation in Electrodeposited Copper Films

“…Principle of the model.-From consideration of various possible mechanisms for the observed surface morphology change, [1][2][3][4][5][6][7][8][9] it has become apparent that excess vacancies trapped in the deposit must be the key element for initiating such a sudden morphology change. In formulating the present theoretical calculation, therefore, we assumed that thin films prepared at low temperatures contain a high concentration of excess vacancies ͑as high as 1 atom %͒, and the annihilation of these vacancies at the grain boundaries ͑GBs͒ generates a biaxial tensile stress in the film.…”

“…During this event, smaller particles appear on top of the existing smooth rounded features on the surface of the deposit typically after 0.5-2 h of room-temperature aging. [1][2][3][4][5][6][7][8][9] The metallurgical phenomenon characteristic of such an event, occurring after a short period of time at low temperatures, is generally a recovery process, which involves the activity of point defects, primarily vacancies. Thin films often contain a high concentration of excess vacancies 10 and thus the early stages of thin-film relaxation is probably dominated by a recovery process.…”

“…A recent in situ atomic force microscope ͑AFM͒ study revealed that, during room-temperature aging, the surface of freshly electrodeposited polycrystalline copper films can undergo a spontaneous morphology change ͑SMC͒. [1][2][3][4][5][6][7][8][9] Typically, this takes place within a period of 30 min to 2 h after the deposition and occurs suddenly in many cases. We investigated why such a sudden morphology change occurs within a short period of time after the deposition and concluded that this particular film behavior appears to be stress-related.…”

An Isothermal Annealing Study of Spontaneous Morphology Change in Electrodeposited Copper Metallization

“…Thus, the study of the deposition and properties of copper metallization films is of major importance to the semiconductor industry. In particular, understanding and controlling the microstructure of electrodeposited copper [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] metallization is increasingly important.…”

“…4,[23][24][25][26][27][28][29][30][31][32][33] The effects of additives to the plating bath on the electrodeposition and properties of copper metallization have been studied extensively. 15,18,19 Scanning probe microscopy, including atomic force microscopy ͑AFM͒ and scanning tunneling microscopy ͑STM͒, has proved to be a useful tool to study copper electrodeposition; [4][5][6][7][8][11][12][13][14][15][16][17][18][19][20][32][33][34][35][36][37][38][39][40][41][42][43] mechanistic studies, the effect of additives, and the influence of the substrate on microstructure have been reported. The influence of various additives on the roomtemperature recrystallization of electrodeposited copper has been investigated by Stafford et al 22 using X-ray diffraction and resistance measurements.…”