Hydrogen plasma enhanced crystallization of hydrogenated amorphous silicon films

Abstract

We report that a room temperature hydrogen plasma exposure in a parallel plate diode type reactive ion etcher can reduce the time required for the subsequent thermal crystallization of amorphous silicon time by a factor of five. Exposure to hydrogen plasma reduces the incubation time, while the rate of crystallization itself is not greatly affected. This plasma enhanced crystallization can be spatially controlled by masking with patterned oxide, so that both amorphous and polycrystalline areas can be realized simultaneously at desired locations on a single substrate. The enhancement of crystallization rate is probably due to the creation of seed nuclei at the surface. The films have been characterized by UV reflectance, x-ray diffraction, plan view transmission electron microscopy, Fourier transform infrared absorption, secondary ion mass spectroscopy, and four-point probe measurement of electrical conductivity.

Relative importance of hydrogen atom flux and ion bombardment to the growth of μc-Si:H thin films

“…In fact, the role of the plasma is to ensure the conditions of the initial growth of an amorphous film with low energy requirements for crystallization. This aspect is further supported by a recent study of the thermal annealing of untreated and hydrogen treated a-Si:H thin films [19]. The energy barrier for crystallization was much lower for the plasma treated films compared to the un-treated ones.…”

“…The energy transferred by the H atoms to the surface is quite higher compared to the one transferred by ions even in the case of the ion -surface charge exchange process because of the much higher H atoms flux. The decrease of % SiH 4 fraction leads to an enhancement of the energy transferred by both H atoms and ions but the most important feature is that, even in the case of 1% SiH 4 , this energy is rather low (<0.22 eV), much lower than the total activation energy that is required for the phase transformation of stable a-Si:H films with low H-content (<5 wt%) calculated from thermal annealing of a-Si:H ($3.7 eV) [19].…”

Integration of amorphous and polycrystalline silicon thin-film transistors through selective crystallization of amorphous silicon

“…[4][5][6] Exposing a-Si:H to a room-temperature hydrogen plasma before a 600°C anneal reduces the time taken to crystallize the amorphous film to 4 h from ϳ20 h by creating silicon crystal nuclei, which acts as seeds for grain growth during subsequent annealing. 4,7 The principle of areaselective crystallization is to protect selected areas of the a-Si:H precursor film from the plasma exposure by masking, 4,7-9 so that subsequent 600°C anneal converts only the seeded areas to polycrystalline silicon. A 120 nm thick SiN x mask film was deposited by PECVD and patterned by wet etching.…”

Hybrid-phase growth in microcrystalline silicon thin films deposited by plasma enhanced chemical vapor deposition at low temperatures

“…5͑b͒. As has been pointed out, 14,15 some acceleration mechanisms for the solid-phase crystallization at such a low substrate temperature of 180°C must be required because solidphase crystallization by furnace annealing, 21,22 which is the most commonly used in crystallization of a-Si, is usually carried out at a temperature of 600°C and long time of the order of 20-60 h. 21 We have proposed the following mechanisms as the candidates of the acceleration mechanisms: plasma-assisted, 23 impurity-induced, [24][25][26][27] and stress-induced crystallization. 28 Unfortunately, we have not concluded the accelerations mechanisms yet, however, we have obtained some phenomena related to the above mechanisms employing the thickness evolution of I ͑220͒ / I ͑111͒ as described below.…”