Project ID: 08CERN/2022

Duration: 1.01.2022- 30.09.2024

Project title: Acceptor removal process in irradiated p-type Silicon sensors - defect investigations and parametrization /ARP

Project objectives:

The proposed project is embedded as part of the RD50 efforts, in the subgroup Defect and Material Characterization. The director of the present project is the leader of the NIMP team involved in the CERN-RD50 collaboration and the convener of this research line within the RD50 collaboration. The specific project proposed here is embedded as part of the RD50 efforts, in the subgroup Defect and Material Characterization. The general objective of the project is to understand the acceptor removal process in irradiated p-type silicon, parametrize it for various content of B, C and O impurities and irradiation fluences, finding this way proper defect engineering solutions to maximize the radiation hardness of different types of sensors (single pads, pixel and strips, LGAD and HVCMOS). Common for all these new sensors is the loss of initial Boron doping concentration caused by irradiation, an effect known as the acceptor removal process (ARP). During the present project the necessary defect investigation studies will be performed in order to understand the B removal in irradiated p-type silicon and provide the input defect parameters and generation rates needed for a reliable parametrization of ARP in PAD, LGAD and HVCMOS devices developed within RD50 collaboration. Previous studies revealed that several major obstacles that were preventing the achievement of enough knowledge for parametrizing the ARP and find applicable solutions to minimize this process in the devices of interest: (i) The bistability of B_iO_i defect, measurable in only one of the two configurations – the B_iO_i^A(0/+), along with the long time needed for stabilizing the defect structural configuration. (ii) Impossibility of investigating the ARP in the LGADs gain layer only, after high fluences, and determine the defects depth profile caused by B and C implantations in the p⁺ gain layer. (iii) Impossibility of performing defect investigations in the junction between the p-substrate and deep n-well (DNWELL) layers of the HVCMOS structures fabricated so far by any of the spectroscopic techniques due to the small capacitances of the structures and small breakdown voltage. In addition, preliminary studies revealed that most often the amount of Boron in the samples is not equal with the doping extracted from CV measurements, the producers of the Si wafers achieving the required doping by using Phosphorus for compensation. This has tremendous influence on any attempt of parametrizing the ARP. The present project aims to overpass these issues by employing comprehensive studies for establishing: the impurity content in the wafers and in the implanted layers (by LA-ICPMS and SIMS investigations), the defect generation rates in the bulk and implanted layers of the structures of interest as well as the time constants for stabilizing the devices (by DLTS, TSC, CV/IV), all the parameters the ARP depends on for a reliable description of this process in PAD, LGAD and HVCMOS structures (by modelling with reliable inputs delivered by defect and impurities investigations). The ultimate goal of the project is to succeed parametrize the ARP effect for different operation scenarios and provide defect engineering optimization solutions for minimizing this detrimental effect.

Stages/Activities (Year)

I. Study of irradiated PAD and LGAD devices (2022)

I.1 LA-ICPMS studies (determination of impurity content in Si sensors)

I.2 CV/IV and defect investigations

I.3 Numerical modelling of the variation in time of IV/CV (Neff) and of the DLTS/TSC signals from B_iO_i^A(0/+)

I.4 Develop computing models for describing the temperature dependent measured signals in highly irradiated devices

II. Further studies including G-type PAD diodes and passive HVCMOS structures (2023)

II.1 LA-ICPMS studies on as processed and as irradiated new devices

II.2 Continue the CV/IV and defect investigations, including HVCMOS test samples and not irradiated G-type diodes with different C implantations

II.3 Modelling the defect kinetics in the investigated structures

III. Parametrization of ARP in irradiated PAD, G-PAD, LGAD and HVCMOS structures (2024)

III.1 LA-ICPMS studies on irradiated and annealed G-type PAD diodes and passive HVCMOS structures

III.2 CV/IV and defect investigations on G-type PAD with different C implantations, after irradiation, annealing studies

III.3 Develop ARP model describing all the experimental results