What quality metrics scrum team can use to improve the product quality?
No metrics will improve product quality, only observing a satisfactory Definition of Done will achieve that. The best measurements are usually taken as closely as possible to the time and place of work being carried out.
A metric, by itself, will not improve quality. A team may be able to use metrics to understand the quality of the product as well as the processes used to build the product. I'm having trouble thinking of a quality metric that wouldn't be useful to a team just because they were using Scrum. The hardest to use would be phase-based process quality metrics, since there are often no clear-cut definitions of phases in Scrum.
Whenever thinking about metrics, I find it best to start with a problem. Based on the problem, there may be data that is necessary to determine if there is a problem and how significant it is. The best metrics to demonstrate the existence of a problem arise from the problem itself.