A method for forming a microstructure is disclosed in which, after a polymer substance has been applied to a first substrate, the first substrate is micromachined to remove at least one portion of the first substrate. A second substrate is then adhered to the first substrate via the polymer substance. One application of such a method is in the fabrication of three-dimensional microfluidics. The polymer substance may, for example, be benzocyclobutene (BCB), and the first substrate may, for example, be a silicon wafer or a photo-etchable glass.