Dear Shirley,
Unfortunately, you would need to wait until you have your actual diploma before applying for your visa.

Immigration used to allow a verification letter from the registrar's office stating that you have completed all the requirements for your degree, however, due to numerous counterfiet documents provided by ESL teachers without real degrees, this is no longer a viable option.

Sincerely,

Park English, Recruitment Agency
Suite #402, 4th Floor Bomm Building
124-7 Itaewon-dong Yongsan-gu, Seoul
South Korea, (zip) 140-858