Low-temperature solid-phase crystallization of amorphous silicon thin films deposited by rf magnetron sputtering with substrate bias

Abstract

The crystallization properties of amorphous silicon ͑a-Si͒ thin film deposited by rf magnetron sputter deposition with substrate bias have been thoroughly characterized. The crystallization kinetics for films deposited with substrate bias is enhanced relative to unbiased a-Si by films. The enhanced crystallization for substrate biased a-Si films are attributed to ion enhanced nucleation of crystallites during sputter deposition which subsequently grow during the postdeposition anneal. Conversely films sputter deposited without substrate bias have more intrinsic defects and residual oxygen which enhance nucleation and retard growth, respectively, and lead to a large number of small crystallites.

Crystallization of as-deposited amorphous silicon films on glass prepared by magnetron sputtering with different substrate biases and temperatures

“…1(a), although the substrate bias during deposition significantly influenced the RTA crystallization, only the film deposited with a substrate bias of 100 W (100 V) showed Si characteristic peaks at 2y¼28.51, 47.51, and 56.31, corresponding to (1 1 1), (2 2 0), and (3 1 1), respectively; in contrast, the films deposited with no substrate bias, a low substrate bias of 50 W (60 V), or a high substrate bias of 150 W (125 V) showed no characteristic peaks. Enhanced crystallization of substrate-biased a-Si film is in accordance with the previous result [18]; how a particular substrate bias value was required in our experiment will be discussed below. The effects of different substrate temperatures, as shown in Fig.…”

“…Biasing the substrate is known to induce Ar ions bombardment of the film surface [14][15][16][17][18], which possibly enhances crystallization by inducing nuclei for Si crystallites [18] and by reducing oxygen incorporation in the film. Oxygen and other impurities, such as carbon and fluorine, are known to retard the Si crystallization process [9,10].…”

“…Among these conditions, substrate bias [14][15][16][17][18] and substrate temperature [19][20][21] are thought to be the predominant parameters, both of which are capable of influencing the behavior of Si ad-atoms on the film surface through ion bombardment or heating, which cause various a-Si film networks. Jun et al [17] found that substrate bias made a-Si films dense with few defects and, moreover, enhanced crystallization during the subsequent furnace annealing and the grain size in the resulting polycrystalline Si film [18]; however, these studies did not investigate how the a-Si films crystallization was influenced by different substrate biases. Substrate temperature has been reported to have an effect on the electrical properties and microstructures of a-Si films [19,20]; however, its effect on the subsequent crystallization process has not been reported.…”

Low-temperature growth of polycrystalline Ge thin film on glass by in situ deposition and ex situ solid-phase crystallization for photovoltaic applications

“…On the other hand, the as-deposited films at low T s , at which adatom diffusion is negligible, would be underdense [25], especially germanium is one of the materials with diamond cubic structure which has very low diffusivity at a given homologous temperature [24]. For the ex situ crystallization, the smaller grain size of the SPC samples could be attributed to an abundance of nucleating sites based on the large number of defects such as dislocations, vacancies, and stacking faults within the films [26,27]. Another possible reason resulting in such smaller grain size is the incorporated impurities [26] such as residual oxygen.…”

“…Another possible reason resulting in such smaller grain size is the incorporated impurities [26] such as residual oxygen. Oxygen, known to retard silicon SPC process [27], is also very likely to affect germanium SPC process.…”