SQLServer it self does not need Java at all; I'm assuming you're asking about its
JDBC driver. It's not the DB server, but its JDBC driver that requires a particular Java version. A quick search for "sqlserver jdbc driver" finds
https://docs.microsoft.com/en-us/sql/connect/jdbc/microsoft-jdbc-driver-for-sql-server?view=sql-server-2017 from which various useful pages are linked.
Irrespective of this,
you should not be using any JRE older than Java 8 at this point - Java 6 has been obsolete and unsupported for years now.
