Phosphorus Atomic Layer Doping in Ge using RPCVD Yuji Yamamoto a , Rainer Kurps a , Christian Mai a , Ioan Costina a , Junichi Murota b and Bernd Tillack a,c a IHP, Im Technologiepark 25, 15236 Frankfurt (Oder), Germany Tel.: +49-335-56-25-156 Fax: +49-335-56-25-661 E-mail: yamamoto@ihp-microelectronics.com b Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan c Technische Universität Berlin, HFT4, Einsteinufer 25, 10587, Berlin, Germany Future nanoscaling and nanotechnology is requiring atomic-order control of process technology for device fabrication. The concept of atomically controlled processing has been demonstrated for atomic layer doping (ALD) of Si, SiGe and Ge [1, 2]. The basic idea of ALD is the separation of surface adsorption of dopant gases from the layer growth. In previous study, B-ALD in Ge (100) using single wafer reduced pressure chemical vapor deposition (RPCVD) is examined and self-limitation behavior of B 2 H 6 adsorption at 100 o C is demonstrated [3]. On the other hand, P-ALD in Ge (100) by MBE is reported in ref. [4]. In this work we investigated P-ALD in Ge (100) using RPCVD and discuss adsorption behavior and electrical activity of incorporated P. To fabricate Ge (100) surface, epitaxial Ge is deposited on Si (100) substrate at 300 o C by N 2 - GeH 4 gas mixture. In the case of samples for electrical measurement, 5 µm thick Ge buffer is deposited to realize low surface roughness and low threading dislocation density Ge material using process condition described in ref. [5]. After the Ge layer is deposited, the surface is exposed to PH 3 with N 2 carrier gas. The exposure temperature is varied between 100-300 o C. In order to investigate the effect of hydrogen- termination of the Ge surface, some wafers are cooled down in H 2 environment after the Ge layer deposition. After the exposure step the temperature is changed back to 300 o C in N 2 and the Ge layer growth is continued with N 2 -GeH 4 gas mixture. P dose and profile are measured by SIMS. Active P dose is determined by Hall measurement at 10 K. Figure 1 shows depth profile of P spikes in Ge. PH 3 is exposed at 100 o C on hydrogen-free Ge surface. With increasing PH 3 exposure time, amount of P is increased and saturation behavior is observed, indicating that the PH 3 adsorption is self-limited. The steepness of first P spike near the surface is ~3 nm/dec., indicating very low segregation. Slightly smeared P spikes are observed in deeper part of Ge. This broadening is caused by surface roughness increase due to sputtering during SIMS measurement. In order to discuss impact of hydrogen-termination on Ge surface, P dose as function of PH 3 exposure temperature is shown in Fig. 2. During the cooling, N 2 or H 2 is chosen as carrier gas. In the case of the sample cooled down in H 2 , very few P is adsorbed on the Ge surface at 100 o C. With increasing PH 3 exposure temperature adsorbed P dose is increased. On the other hand, in the case of the sample cooled down in N 2 , ~8×10 13 cm -2 of P is adsorbed even at 100 o C. In this case, temperature dependence of P dose is small. At 300 o C, no clear difference between N 2 and H 2 cooling is observed. These results indicate that the P adsorption is suppressed by hydrogen-termination of the Ge surface in the case of cooling down in H 2 . The hydrogen desorption from the Ge surface starts from ~200 o C resolving the surface passivation [6]. In Fig. 3, P dose as function of PH 3 exposure time at various PH 3 partial pressures is shown. The PH 3 exposure is performed at 300 o C on hydrogen-free Ge surface. For all PH 3 partial pressure used, P dose is increasing with increasing PH 3 exposure time and saturated at ~1.5×10 14 cm -2 , which value is close to a quarter of monolayer of Ge (100). The saturation value does not depend on PH 3 partial pressure. The incorporated P dose Q r on the hydrogen-free Ge surface can be described by Langmuir type kinetic.  ௥ ൌ  ௧ ቂ1 െ ݔ݌ ቄെ ௥ ቀ ܭ ௉ுଷ ሺ1 ൅ ܭ ௉ுଷ ሻ ൗ ቁቅቃ (1) Where N t is saturation value of incorporated P dose, k r and K are reaction rate and thermal equilibrium constants of PH 3 adsorbed on the Ge surface, respectively. Good agreement to Langmuir type adsorption model is obtained with N t =1.55×10 14 cm -2 (a quarter of monolayer), k r =77 s -1 and K=3.0×10 -2 Pa -1 . 978-1-4577-1865-6/12/$26.00 ©2012 IEEE