Occurrence of Sharp Hydrogen Effusion Peaks of Hydrogenated Amorphous Silicon Film and Its Connection to Void Structures

Sahar Jafari,Dominik Lausch,Sylke Meyer,Jonathan Linke,Barbara Terheiden,Michael Wendt

doi:10.1002/pssb.202000097

Abstract

The amount of hydrogen released from plasma‐enhanced chemical vapor (PECVD) deposited hydrogenated amorphous silicon (a‐Si:H) layers is determined by gas effusion measurements. A sharp peak (SP) is observed in the effusion spectra of samples with substrate temperature T S ≥ 200 °C. Light microscopic images indicate the formation of bubbles after deposition for all samples and film deterioration after effusion measurement in correlation with the presence of the hydrogen SPs. Change in substrate temperature varies with the microstructure of the film, the hydrogen concentration, and the density. A low T S leads to a porous structure with large number of interface bubbles, and therefore no hydrogen‐induced SP appears during hydrogen effusion. Whereas high T S causes a compact a‐Si:H film in which the hydrogen effusion is limited by the longer diffusion, while the number of interface bubbles decreases. The storage of near substrate hydrogen in the bubbles in compact material leads to a local explosion by increase in excessive pressure. The difference between the low temperature peak and the position of the SP in the effusion spectra indicates the time required to fill the interface bubbles with hydrogen, which decreases with increasing film density, suggesting that the volume of the interface bubble decreases.

Highlights

Introduction of Groups1 and 2the hydrogen effusion spectra can be classified into two groups
The normalized partial pressure of hydrogen effusion as a function of the annealing temperature Ta is shown in Figure 2 for the amorphous silicon (a-Si):H films
As the substrate temperature TS is a set temperature of the table heater, it is assumed that the temperature at the substrate surface is lower during deposition and it can explain the unexpected lower annealing temperature (LT) peak at Ta of 371 C in sample A6

Summary

Introduction

Introduction of Groups1 and 2As shown in Figure 2, the hydrogen effusion spectra can be classified into two groups. The hydrogen effusion spectra can be classified into two groups. Group 1 includes samples A1 and A2, in which the spectrum contains two main effusion peaks, one at LT of about 360 C and one at higher temperature (HT) of about 530 C. In group 2, including A3–A6, the HT peaks become the main component of the spectra with a rather small LT peak. The significant change in the spectra in group 2 was the appearance of a SP on the rising edge of the HT peak. To ensure that these SPs were not caused by an artifact introduced by the measurement equipment, the experiments were repeated three times for each sample.

Results

Discussion

Conclusion