Dear Ms. Wong,
Thank you for posting your request on History Hub!
Certificates of citizenship were issued by the Federal courts until October 1991 when the Immigration and Naturalization Service (INS) took over responsibility for naturalization proceedings. All INS records are now overseen by the US Citizenship and Immigration Services (USCIS). USCIS maintains duplicate copies of court records (including the certificate of citizenship) created since September 27, 1906.
We hope this is helpful. Best of luck with your research!