Provided herein, among other things, is a method for producing a ligation product on a support. In some embodiments, the method may comprise hybridizing a first double-stranded oligonucleotides and a second double-stranded oligonucleotide to a substrate comprising surface-tethered oligonucleotides and ligating the distal ends of the first and second double-stranded oligonucleotides together, thereby producing a first ligation product that is tethered to the support at both ends.