Multi-focus method of enhanced three-dimensional exposure of resist

A method of forming a three-dimensional latent image with good depth and shape control in a thick resist layer applied over a workpiece surface, the method including:

• using in the thick resist layer a positive resist;
• selecting multiple focal planes at which to focus exposing energy, wherein at least one of the focal planes is in a lower half of the thick resist layer, the lower half being the half that is further from a surface to which exposing energy is applied;
• converting a relief map that represents a three-dimensional surface into point-by-point and layer-by-layer exposure doses calculated to exceed an exposure threshold of the positive resist at a plurality of controlled depths within the resist layer, taking into account a numerical aperture value to be used during patterning, producing an exposure map;
• and
• patterning the resist layer using the multiple focal planes to form a three-dimensional latent image using a pattern generator that varies effective exposure doses on a point-by-point basis using the exposure map.