A structure includes a transistor including a first source/drain region, a source/drain contact plug over and electrically coupling to the first source/drain region, and a via over and contacting the source/drain contact plug. The via has a bottom portion having a first length, and an upper portion having a second length. The first length is greater than the second length. Both of the first length and the second length are measured in a same direction parallel to a top surface of the source/drain contact plug.