There is considerable interest in the spatial control of plasma polymerisation such as to produce sub‐millimetre features with high fidelity, versatility and reproducibility, for example, for arrays or writable specific patterns. This study reports the design of a microcavity plasma device and a method for its fabrication, with the device comprising a single cavity of ≈400 µm diameter. The device can be fabricated within a short time and at low cost in a standard laboratory, with no need for a clean room facility. The device is capable of multiple operations in plasma polymerisation mode. XPS imaging combined with small‐spot ROI analysis showed localised thin film deposition of an acrylic acid plasma polymer with good retention of carboxylate groups from the monomer. The device can be configured with flexibility and addressed for plasma polymer writing of complex patterns.