Low Temperature Metal Induced Lateral Crystallization of Ge Using Germanide Forming Metals

Abstract

Low temperature ͑ranging from 350 to 420°C͒ metal induced lateral crystallization of Ge using germanide forming metals Ni, Co, and Pd is performed. The lateral growth lengths and crystallized Ge films' quality are optimized when annealed at 375°C, above which self-nucleation in Ge hinders the metal induced crystallization process. At 375°C, the sample with Pd as the seed metal has the largest lateral growth length, while the sample using Co as the seed layer exhibits the largest crystal grain size. The experiments suggest that the lateral growth length is associated with the diffusivity of the metal and germanide in Ge, while the crystal quality is related to the lattice mismatch between germanide and Ge.Polycrystalline germanium ͑poly-Ge͒ on insulator and low cost substrates has many potential applications in solar cell, optoelectronics, and three-dimensional integrated circuit ͑3D-IC͒. With a small bandgap of 0.67 eV at room temperature, poly-Ge can be employed in a thin-film tandem solar cell to enhance the absorption of the IR spectrum. It can also be used in optical detectors of 1.3 and 1.55 m wavelength. Vertical transistors stacking in a 3D-IC structure is expected to lessen performance degradation due to interconnects delay and power dissipation. Poly-Ge is a promising material for active layers in this 3D-IC architecture because of their high mobilities 1 and lower crystallization temperatures as compared to Si. 2 For poly-Ge to be integrated on top of existing devices or low cost substrates in optoelectronic and integrated circuit applications, it should be crystallized at low temperature, preferably below 400°C.Crystallization of deposited amorphous Ge ͑a-Ge͒ can be performed by various techniques, three of which are often discussed: laser anneal, solid-phase crystallization, and metal induced ͑lateral͒ crystallization ͑MIC/MILC͒. While laser anneal gives a high quality Ge due to local heating without damaging the underlying layers, this technique is complex and expensive. Conversely, conventional solid-phase crystallization of Ge requires a relatively long anneal time and a high temperature of around 450-550°C. 3,4 A longer incubation time is needed for a lower anneal temperature. 5 MIC/MILC is similar to solid-phase crystallization, but in this method, metals are deposited on top of or inside Ge to enhance the crystallization of Ge, with a possible reduction of the crystallization temperature to as low as 100°C. 6 MIC and MILC are the crystallization of regions inside and outside the metal coverage, respectively. Due to the lesser metal contaminant and larger grain size in the MILC region, it is preferable over MIC.The MILC of Si has been extensively studied, and the preferred metal is Ni due to the small lattice mismatch between NiSi 2 and Si. However, fewer works were done on Ge, in which the choice of seed metal is still not obvious. Metals used in the MILC process can be categorized into two groups: the first ͑Co, Ni, Pd, etc.͒ forms a germanide and the second ͑Au, Ag, Al, etc.͒ creates a eutecti...

Three-Dimensionally Orientation-Controlled Ge Rods on an Insulator Formed by Low-Temperature Ni-Induced Lateral Crystallization

“…58 The theoretical and experimental studies on the lattice alignment of NiGe and Ge revealed that NiGe{100}//Ge{110} was the best match. 47,59,60 Figure 5 shows the NiGe{100}//Ge{110} lattice matching relationship predicted from the lattice parameters. From a Ge lattice constant of 0.566 nm, the lattice mismatch in NiGe{100}//Ge{110} was estimated to be 1.2% in the baxis direction and 2.9% in the c-axis direction.…”

“…38−40 Using MILC for Si, stable TFT performance was demonstrated. 41−43 The MILC of Ge has also been investigated using various metal catalysts, such as Ni, 44−48 Co, 47,48 Pd, 47,48 Cu, 48,49 Sn, 50 and Au. 51 MILC of Ge at low temperatures (<400 °C).…”

“…Metal-induced lateral crystallization (MILC) has been identified as a method to lower the crystallization temperature of semiconductor thin films and control the grain boundary direction and crystal orientation in the channel region. − Using MILC for Si, stable TFT performance was demonstrated. − The MILC of Ge has also been investigated using various metal catalysts, such as Ni, − Co, , Pd, , Cu, , Sn, and Au . These metals successfully provide the MILC of Ge at low temperatures (<400 °C).…”

Large-Grained Polycrystalline (111) Ge Films on Insulators by Thickness-Controlled Al-Induced Crystallization

“…[4][5][6][7][8] In line with this, metal-induced crystallization (MIC) of amorphous Ge (a-Ge) films on insulators has been studied for over a decade. [9][10][11][12][13] In the MIC, catalytic metals (Ni, Au, Cu, etc.) enable the low-temperature crystallization of a-Ge in the temperature range 150-400 • C, [9][10][11][12][13] which are significantly lower than the crystallization temperatures of a-Ge without the metals.…”

“…[9][10][11][12][13] In the MIC, catalytic metals (Ni, Au, Cu, etc.) enable the low-temperature crystallization of a-Ge in the temperature range 150-400 • C, [9][10][11][12][13] which are significantly lower than the crystallization temperatures of a-Ge without the metals. 2,14,15 In particular, a nanowire-like single-crystal Ge is achieved by metal-induced lateral crystallization (MILC), which is promising for high-speed Ge transistors.…”