Understanding the Roughening and Degradation of 193 nm Photoresist during Plasma Processing: Synergistic Roles of Vacuum Ultraviolet Radiation and Ion Bombardment

Abstract

We have identified a synergistic roughening mechanism of 193 nm photoresist, where simultaneous ion bombardment, vacuum ultraviolet (VUV) radiation, and moderate substrate heating in a well‐characterized beam system results in a similar level of surface roughness observed during conditions typical of plasma etching. VUV radiation (147 nm) results in bulk modification of the photoresist polymer, witnessed by the loss of carbon–oxygen bonds through transmission FTIR. Ion bombardment (150 eV) results in the formation of a densified surface layer on the order of a few nanometers in depth. We have shown that elevated levels of roughness are observed only during simultaneous exposure and that sequential exposure is not sufficient to produce surface roughness. In addition, through the use of transmission FTIR we have shown that an etching synergy does not exist and that etch rates are nearly independent of temperature. We propose that the observed roughness could be due to the drastically different mechanical properties of the ion‐modified near‐surface region and VUV‐modified bulk photoresist, where the difference is exaggerated at elevated temperatures. A more complete understanding of plasma‐induced surface roughness will require further study, resulting in the improvement of existing pattern transfer technologies and possibly novel new technologies as well.

Benefits of plasma treatments on critical dimension control and line width roughness transfer during gate patterning

“…Those chemical changes convey the cleavage of pending groups and the removal of lactone group caused by photoetching mechanisms and that are typically observed when 193 nm PR are exposed to wavelength below 200 nm. 14,15,19,20,[25][26][27][28] In the case of HBr or VUV cured resists, those modifications have already been performed during the cure treatment and those polymers become less sensitive to Si-ARC plasma light.…”

Changes to Charge and Defects in Dielectrics from Ion and Photon Fluences during Plasma Exposure

“…10 Vacuum ultraviolet ͑VUV͒-modified dielectric layers were typically shown to be deeper than the ion-modified layer. 11 Based on this, it is our contention that, within the dielectric, beyond the ion penetration depth, photons are responsible for the damage in this region, while on the surface, the damage is primarily caused by ions. Here, the two sources of damage generated during plasma processing will be considered to determine the effects of ion and photon fluences on the damage.…”

An atomic force microscopy-based method for line edge roughness measurement

“…The degradation can be explained be the softening of the PR bulk and the formation of a hard layer on the PR surface. [18][19][20][21][22] Despite the resist LER increase, the Si-ARC LER is decreased compared to the initial resist LER. It shows that the rough resist foot does not negatively affect the LER transfer into the Si-ARC layer.…”