You need to understand why YOU think achieving six sigma certification is going to benefit you.
Furthermore, which companies do you have in mind that would benefit from someone who has six sigma certification?
Ultimately, achieving a qual in Six Sigma does NOT equate to someone competent in using it in industry. An employer would look at experience first, then certification/qualifications. If you want to pursue this avenue, get into a company that uses Six Sigma and who are willing to train you.