Hydrogen Anti-diffusion Methods for Poly-Si Quenching Resistor in Silicon Photomultipliers

[Aims] Silicon photomultipliers (SiPMs) are prime candidate of solid state photo-sensors for the next generation fusion medical image systems. SiPM is combined by the hundreds ~ thousands microcells with consisting of... [ view full abstract ]

[Aims]
Silicon photomultipliers (SiPMs) are prime candidate of solid state photo-sensors for the next generation fusion medical image systems. SiPM is combined by the hundreds ~ thousands microcells with consisting of geiger-mode avalanche photodiode (GM-APD) and poly-silicon quenching resistor. The poly-silicon resistors are affected by the non-uniform inflow of the hydrogen atoms during the semiconductor fabrication. As a result, it causes critical problems such as degradation with resistance and uniformity. In this paper, we present hydrogen anti-diffusion methods to improve stability and uniformity of resistance on the poly-silicon resistors.

[Experimental Methods]
Generally, the dangling bonds of GM-APD are reduced by the forming gas annealing (FGA, hydrogen contents about 10%) in order to improve the electrical stability.
But this method has a problem of losing the resistive site due to the hydrogen recovery of interface trap site in the resistor.
In this experiment, we applied two methods to prevent the injection of unwanted hydrogen atoms. The first method is forming the SixN1-x layer in the surface of resistor using the nitrogen ion implantation. The second method is deposition of the thin Si3N4 film on surface of the resistor.

[Results]
The figure shows uniformity and total resistance of resistors on whole dies of 8 inch wafer.
Uniformity of the resistors with nitrogen ion implantation is improved 19 ~ 53% as compared with the reference resistors of only applying FGA.
In addition, the resistors of deposited Si3N4 are confirmed that uniformity is a 61% improvement. However, resistance is decreased on nitrogen ion implanted resistors than the reference resistors. This reason is reduced physical resistive sites due to the influence of generated SixN1-x film of surface of the resistor by implanted nitrogen ions. However, Si3N4 film deposited resistors is confirmed that indicates a high resistance than the reference resistors, because it has not lost additional silicon atom.
If poly-silicon quenching resistors are applied hydrogen anti-diffusion method of depositing the Si3N4 films considering resistance and uniformity of resistor, it seems to be able to fabricate the more stable poly-silicon quenching resistors.

[Acknowledgments]
This study is supported by the Nano·Material Technology Development Program of NRF (NRF-2015M3A7B7045446).