Trench isolation methods for integrated circuit substrates may be simplified by eliminating the steps of forming a silicon nitride layer, etching the silicon nitride layer and removing the silicon nitride layer. In particular, a silicon nitride-free mask pattern, such as a photoresist mask pattern, may be formed on a silicon nitride-free integrated circuit substrate. The silicon nitride-free integrated circuit substrate is etched through the silicon nitride-free mask pattern to form a trench in the substrate. An insulating layer is formed in the trench and is chemical-mechanical polished to form a trench isolating layer. By eliminating the silicon nitride layer, simplified processing and improved performance may be obtained.