URL Encoding in Google Chrome
That's standard percent URL encoding, in this case of UTF-8 encoded text. A URL cannot contain non-ASCII characters (actually, a subset thereof, different subsets for different parts of the URL). You cannot actually have "이윤희" in a URL. To embed arbitrary characters, you can percent encode them. This simply takes a single byte and encodes its hex value as %xx. The UTF-8 byte representation of "이윤희" is EC 9D B4 EC 9C A4 ED 9D AC, which is exactly what you're seeing in the URL.
The URL is always this way, it's not Chrome doing it when you copy. On the contrary, if the URL displays as www.bing.com/search?q=이윤희&..., that's Chrome being nice and displaying the URL decoded for you.
See What every web developer must know about URL encoding.
In PHP this can be replicated with rawurlencode:
echo rawurlencode('이윤희'); // (assuming UTF-8 encoded source code)