As Jamie said A benchmark is a mark, or standard to which we compare our efforts. Maybe once it was a mark in a bench or timber board. A yard stick is a stick/timber pole which is one yard long (i.e. 91.5 cm long). Think of it as a stick to measure something - the length of a field or building. In your question you note that they are sometimes can mean the same thing, but Jamie above points out how they are different. A benchmark is a mark to which we compare ourselves/our efforts. A yardstick is the tool by which we measure something also, but in a sense of length, rather than quality. But similar too.

thank you a lot.

I would say, yes; they are similar but different. A benchmark is a standard to which people compare themselves and hope to reach; e.g. "Harvard University's teaching sets/is the benchmark for quality tertiary education." You couldn't say "Harvard University's teaching is the yardstick for quality tertiary education." A yardstick is a way of measuring something; e.g. "Academic test results are a yardstick for (judging) the quality of teaching in an institution." You couldn't say "Academic results are a benchmark for (judging) the quality of teaching in an institution."