High frequency reactive ion etching of silylated photoresist

Abstract

The effects of high frequency operation on the reactive ion etching (RIE) of silylated photoresist are investigated. Using a simple parallel plate discharge model, the frequency scalings of dc bias, ion density, and sheath width are predicted to be ω−1.5, ω2, and ω−1.125, respectively. Measurements on the RIE system reveal dependencies of ω−1.48, ω1.85, and ω−1.00, respectively, in the 13.5–100 MHz range. The high frequency discharge is applied to the etching of silylated Plasmask 200G photoresist as part of the DESIRE (diffusion enhanced silylated resist) process flow. Increasing the drive frequency is shown to increase the unsilylated:silylated etch selectivity and reduce the postetch grass residues. Statistical design of experiments (SDE) is also employed to fully characterize the resist etch process. An L934 table is designed with plasma power, pressure, oxygen flow, and frequency as the controlled factors. Measured responses are etch rate, etch uniformity, selectivity, dc bias, residue size, residue density, linewidth, and etch profile angle. Main effects plots are tabulated from the design matrix revealing which factors have the greatest effect on each of the responses. Through the use of SDE, a significant reduction in postetch residues is observed for the high frequency RIE etch of Plasmask 200G resist.

The frequency dependence of the discharge properties in a capacitively coupled oxygen discharge

“…Similarly, Curtins et al [7] and Oda [4] report a significantly increased deposition rate with increased driving frequency, with a maximum at 70 MHz and 150 MHz, respectively, when depositing a-Si:H films from silane. Increasing the driving frequency has also been shown to increase the etch selectivity and reduce the post-etch grass residues while etching silylated photoresist while the etch rate decreased [11].…”

“…Oxygen discharges are widely used in plasma materials processing including oxidation of silicon [23,24], ashing of photoresist [11,25,26], and surface modification of polymer films [27,28]. The oxygen discharge is weakly electronegative and the electronegativity depends on process parameters such as pressure and power [29].…”

On electron heating in a low pressure capacitively coupled oxygen discharge

“…Oxygen discharges are widely used in plasma materials processing including oxidation of silicon [12,13], ashing of photoresist [14,15], and surface modification of polymer films [16]. The properties of the oxygen discharge depend heavily on the accumulation of the singlet metastable oxygen molecules, which are known to play a significant role in the oxygen discharge [17,18].…”

Standing wave and skin effects in large-area, high-frequency capacitive discharges

“…Large-area plasma processing systems capacitively driven at frequencies higher than the conventional industrial frequency of 13.56 MHz, and dual frequency capacitive reactors with one high-and one low-frequency drive, have attracted much recent interest from researchers and semiconductor equipment manufacturers for silicon wafer and flat panel display processing [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. Large-area plasma sources are required as semiconductor manufacturers increase wafer sizes from 200 to 300 mm, and also for processing large (1 m × 1 m) glass panels for active matrix LCD flat panel computer and TV screens.…”