Modern photorestists are made of a novolac resin with a photo active compound. The photo active compount when exposed to UV light forms an organic acid which is soluble is a weak alkali developer (usually tri-methyle ammonium hydroxide). The thickness of resist is spun in at between 0.6 and 1.2um for the high resolution layers and 1.2-2.2um for layers that block implants.
The resolution of the developed image depends on the resist thickness, the focus of the camera, the partial coherence of the UV light, the modulation transfer function of the image (slope of light from dark to clear) and a similar chemical MTF for the develop process.