Deposition of Copper Particles and Films by the Displacement of Two Immiscible Supercritical Phases and Subsequent Reaction

Abstract

Copper (Cu) particles and films were produced by forming Cu(II) compound (Cu(hfac) 2 • H 2 O) films on substrates using a displacement from two immiscible supercritical phases (DISP) technique followed by reducing the copper(II) compound films in hydrogen at 200 °C. Various surfaces including native oxide of silicon (SiO x ), titanium nitride (TiN), tungsten (W), and low-k dielectric materials such as Coral, JSR5109, and Silox were used as substrates. The nucleation and growth behavior of the Cu DISP process was evaluated over a range of reduction times (from 5 to 60 min) and copper(II) compound concentrations (0.5-3 wt %). At short reduction periods (5-15 min) or low Cu(II) compound concentrations (∼ 0.5 wt %), Cu particles ranging from 60 to 95 nm in diameter were produced. In contrast, at long reduction periods (45-60 min) and high concentrations (∼3 wt %), continuous Cu films with 220-450 nm in thickness were deposited on the substrates. A morphology transition from particle to film was observed at medium reduction period (∼30 min) or medium concentration range (∼1 wt %). High affinity of TiN to Cu nucleation and film formation leads to more dense and smooth films than Cu films deposited under similar conditions on SiO x . However, nucleation of Cu DISP is not very sensitive to the surface conditions of the substrates compared with Cu CVD (chemical vapor deposition). Chemical composition analysis of the Cu film on TiN and SiO x by X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) revealed that highly pure Cu films were obtained from Cu DISP.

Deposition of palladium catalyzed copper films by the displacement of two immiscible supercritical phases and subsequent reaction

“…As discussed in a previous paper, the larger the electron density, the rougher surface of the TiN substrate, and the metallic properties of TiN are responsible for more active initial nucleation of Cu on TiN. 22 When 0.5 mol% of Pd(hfac) 2 was codeposited with the Cu(hfac) 2 $H 2 O and the film was reduced, the number of smaller size Cu particles on SiO x and the surface coverage increased when compared with the 0 mol% Pd sample on SiO x (Fig. 1b).…”

“…The details of the deposition apparatus and deposition procedure were described in the previous paper. 22 The dependence of film thickness, number density of nucleation, and film morphology on various Pd(hfac) 2 concentrations ranging from 0-5 mol% at a fixed Cu(hfac) 2 $H 2 O concentration of 3 wt% and on various Cu(hfac) 2 $H 2 O concentration ranging 0.1-3 wt% at a fixed Pd(hfac) 2 concentration of 5 mol% was investigated. The organometallic compounds were deposited on SiO x and TiN at a pressure of 124 bar, a withdrawal velocity of 0.0035 cm s À1 , and 40 C. The reduction of deposited films was performed at a H 2 pressure of 41 bar, and a substrate heating stage temperature of 200 C for 5 min.…”

“…Cu CVD nucleation is extremely sensitive to surface properties of a substrate. It is extremely difficult to form Cu nuclei and dense Cu films on nonmetallic substrates such as SiO x and air-exposed TiN [28][29][30] (which is covered with thin titanium oxide layers, as confirmed by X-ray photoelectron spectroscopy 22 ) using Cu CVD. The absence of an adsorption step and relatively high concentration of the organocopper molecules on the surface of the substrates are responsible for the relative insensitivity of the Pd catalyzed Cu DISP.…”

“…Recently, we have developed a new supercritical fluid-based deposition technique-deposition from Displacement of two Immiscible Supercritical Phases (DISPs) and subsequent reaction. [22][23][24] Supercritical carbon dioxide (scCO 2 ) and supercritical helium (scHe) are transiently immiscible at mild conditions (<6500 psi and <60 C), thus creating an interfacial boundary between the scCO 2 phase and the scHe phase. When a scCO 2 solution phase containing an organometallic compound is displaced with a scHe phase, the organometallic compound is precipitated and deposited on a substrate at the interfacial boundary.…”

“…Subsequent hydrogen reduction of the deposited organometallic compound films resulted in metallic films. It was demonstrated that highly pure and dense copper (Cu) films can be produced on a native oxide of silicon (SiO x ) and titanium nitride substrate (TiN) by depositing Cu(II) hexafluoroacetylacetonate hydrate (Cu(hfac) 2 $H 2 O) from DISP followed by hydrogen reduction at a temperature of 200 C. 22 However, Cu films were produced only at long reduction periods of 45-60 min by a 'CVD-like' mechanism. During a short reduction period of 5 min, Cu particles in the range of 60-95 nm in diameter were produced on SiO x and TiN.…”