Silicon‐hydrogen bonding structures at a hydrogenated amorphous silicon (a‐Si:H)/silicon nitride (SiN) interface have been investigated using Fourier transform infrared attenuated total reflection (FTIR‐ATR). Depositing a SiN overlayer markedly decreased the higher hydrides, which consist of SiHn (n=2,3) bonds, on the a‐Si:H surface. The low density of higher hydrides at the resulting SiN‐on‐a‐Si:H interface may be due to plasma‐enhanced extraction or a transfer of the growing surface. By contrast, at an a‐Si:H‐on‐SiN interface, the higher hydrides density is about 8.1×1014 cm-2. We believe this large amount of hydrogen at the a‐Si:H‐on‐SiN interface relaxes strained bonds at the interface. In both the SiN‐on‐a‐Si:H interface and the a‐Si:H‐on‐SiN interface, hydrogen is implanted in the underlayer during the deposition of the overlayer. Our results indicate the structure of underlayer near the interface is strongly affected by the deposition of the overlayer.