Surface modification of polyimide to improve its adhesion to deposited copper layer - Polyimides and Other High Temperature Polymers - page 319

Figure 4. SEM micrographs of modified polyimide surfaces. (a, c) after irradiation at normal inci-
dence (b, d) after inclined irradiation under symmetric angles of incidence (all holes shown have a
diameter of 2 µm).
The SEM-micrographs in Fig. 5 illustrate the superposition of microholes onto
well-defined “surface-depth reliefs”. On the left, a surface which was irradiated
with a low ion dose and etched for a short time is shown. Here the ion tracks are
well separated from each other and their superposition is negligible.
In the middle, a medium ion dose which resulted in a considerable superposi-
tion of the microholes after etching was used. On the right, a surface which was
irradiated with a high ion dose and more intensively etched is shown. This leads
to a strong superposition of the microholes and a significant overetching of the
surface (formation of an Alpine-like profile).
The criterion low, medium or high ion dose is determined by the relation of the
size and number of the pores. Single pores stand for a low ion dose, pores which