The HRI2020 proceedings are available from the ACM digital library.
Full papers:
https://dl.acm.org/doi/proceedings/10.1145/3319502
Companion Proceedings (alt.HRI, Demonstrations, Late-Breaking Reports, Pioneers Workshop, Student Design Competitions, Video Presentations, Workshop Summaries):
https://dl.acm.org/doi/proceedings/10.1145/3371382