As with any concept in its early stages or realization, there are many ways of thinking about what we call "process integration" in semiconductor manufacturing. In its most simple form, we consider it to be the combining of two or more sequential processing steps, normally performed in separate systems, into a unified process flow within one fabrication tool.
David N. K. Wang,
"Process Integration: The Future of Chipmaking", Proc. SPIE 1188, Multichamber and In-Situ Processing of Electronic Materials, (15 February 1990); doi: 10.1117/12.963938; https://doi.org/10.1117/12.963938