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Real-time measurements of plasma photoresist modifications: The role of plasma vacuum ultraviolet radiation and ionsa)
a)No proof corrections received from author prior to publication.
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10.1116/1.3697752
/content/avs/journal/jvstb/30/3/10.1116/1.3697752
http://aip.metastore.ingenta.com/content/avs/journal/jvstb/30/3/10.1116/1.3697752

Figures

Image of FIG. 1.
FIG. 1.

Schematic of ellipsometric multilayer models for PR exposure to (a) direct plasma with the substrate at the plasma potential (VPP ≈ 25 V) and (b) direct plasma with −100 V self-bias voltage applied to the substrate accounting for ion-induced surface modifications. The resulting maximum ion energies are estimated at Eion ≤ 25 eV for the substrate at VPP and Eion ≤ 125 eV for the biased substrate.

Image of FIG. 2.
FIG. 2.

(Color online) Schematic of the experimental setup (not to scale) for measuring material modifications by plasma radiation in real-time by in situ ellipsometry (a) and for measuring plasma emission spectra and determining filter cut-off wavelength with VUV spectroscopy (b). For ellipsometric measurements an optical filter (MgF2, sapphire, or glass) was placed on top of a housing, reducing the plasma-PR interactions to plasma radiation of selected wavelength ranges. The ellipsometer laser probed the sample surface through small aperture holes on either sides of the housing. Direct plasma exposures were performed without the housing. For the spectroscopic measurements plasma emission was measured with a differentially pumped VUV spectrograph viewing a cone of light ≈20 mm above and centered with the substrate. The spectrometer was separated from the plasma system by an MgF2, sapphire, or glass window to prevent degradation of the spectrometer optics and determine cut-off wavelengths of the filter materials.

Image of FIG. 3.
FIG. 3.

(Color online) Characteristic Ar plasma emission transmitted through the glass (a), sapphire (b), and MgF2 filter (c) and H2 plasma emission transmitted through the MgF2 fitler (d). Cut-off wavelength (λc) and assignments of identified emission lines are indicated in the spectra.

Image of FIG. 4.
FIG. 4.

(Color online) Ellipsometric measurement of (a) 193 nm PR exposed to Ar plasma radiation for 4800 s using glass, sapphire, and MgF2 filters. The ellipsometric model shows trajectories for various film thicknesses (350–380 nm, solid lines) and Ñ (1.525–1.560, dashed lines). Extracted time evolutions of film thickness reduction and increase in Ñ are shown in (b) and (c), respectively. Dashed and dotted lines indicate the MgF2 exposure times, ≈2050 s and ≈300 s, which led to equivalent thickness reduction and increase in Ñ for 4800 s exposure using the sapphire and glass filter, respectively.

Image of FIG. 5.
FIG. 5.

(Color online) Ellipsometric measurement of (a) 248 nm PR exposed to Ar plasma radiation for 2400 s using glass, sapphire, and MgF2 filters. The ellipsometric model shows trajectories for various film thicknesses (392–400 nm, solid lines) and Ñ (1.560–1.566, dashed lines). Extracted time evolutions of film thickness reduction and increase in Ñ are shown in (b) and (c), respectively.

Image of FIG. 6.
FIG. 6.

(Color online) Ellipsometric measurement of 193 nm PR exposed to Ar plasma with (a) Eion ≤ 25 eV for 180 s and (b) Eion ≤ 125 eV for 60 s together with ellipsometric models. For Eion ≤ 25 eV the model shows film thicknesses between 370 and 320 nm (solid lines) and Ñ (1.525 to 1.560, dashed lines). For Eion ≤ 125 eV a thin (1.8 nm), optically dense (Ñ = 1.870–0.197i) ion crust was formed by energetic ion bombardment. Changes in film thicknesses (370–320 nm, solid lines) and Ñ (1.525–1.560, dotted lines) below the modified surface region were modeled in the same fashion as in Fig. 4(a).

Image of FIG. 7.
FIG. 7.

(Color online) Dependence of (a) ion-crust thickness for Eion ≤ 125 eV, [(b) and (d)] Ñ increase, and [(c) and (e)] film thickness reduction on exposure time of 193 nm PR exposed to the low and high Eion condition. Surface modification was a rapid, ion driven process and saturated in 3 s (dotted line). The dashed line indicates two characteristic time regimes: (I) material removal and optical densification and (II) further thickness reduction without optical densification.

Image of FIG. 8.
FIG. 8.

(Color online) Ellipsometric measurement of 248 nm PR exposed to Ar plasma with (a) Eion ≤ 25 eV and (b) Eion ≤ 125 eV for 60 s together with ellipsometric models. For Eion ≤25 eV the model shows film thicknesses between 394 and 399 nm (solid lines) and Ñ (1.560 to 1.570, dashed lines). For Eion ≤ 125 eV changes in film thicknesses (380–395 nm, solid lines) and Ñ (1.560–1.570, dotted lines) are modeled below the thin (1.8 nm), optically dense (Ñ = 2.182–0.319i) ion-crust.

Image of FIG. 9.
FIG. 9.

(Color online) Dependence of (a) ion-crust thickness for Eion ≤ 125 eV, [(b) and (d)] Ñ increase, and [(c) and (e)] film thickness reduction on exposure time of 248 nm PR exposed to the low and high Eion condition. Surface modification was a rapid, ion driven process and saturated in 5 s (dotted line). 248 nm PR did not reach saturation of the Ñ increase and both exposures remained in regime I.

Image of FIG. 10.
FIG. 10.

(Color online) Correlation of film thickness reduction and Ñ increase for exposures to plasma radiation (glass, sapphire, and MgF2 filters) and direct plasma (Eion ≤ 25 eV and Eion ≤ 125 eV) of (a) 193 nm PR and (b) 248 nm PR. For plasma radiation and Eion ≤ 25 eV exposures, Ñ and film thickness changed at the same rate and modifications were UV/VUV-dominated. For Eion ≤ 125 eV, film thickness reductions increased due to ion-driven material removal.

Image of FIG. 11.
FIG. 11.

(Color online) Schematic of bulk material modifications of 193 nm PR (a) and 248 nm PR (b) by UV/VUV radiation indicating bond scissioning (circled) and rebonding (dotted lines) in the polymer structure.

Image of FIG. 12.
FIG. 12.

(Color online) Surface roughness and morphology of 193 nm PR [(a) and (b)] and 248 nm PR [(c) and (d)] after 60 s exposure to direct Ar plasma with low Eion [(a) and (c)] and high Eion [(b) and (d)].

Tables

Generic image for table
TABLE I.

UV/VUV modification rates of PR beneath the MgF2, sapphire and glass filters normalized to the direct exposure (Eion ≤ 25 eV) in an Ar plasma for 193 nm PR and 248 nm PR.

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/content/avs/journal/jvstb/30/3/10.1116/1.3697752
2012-05-23
2014-04-23
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Real-time measurements of plasma photoresist modifications: The role of plasma vacuum ultraviolet radiation and ionsa)
http://aip.metastore.ingenta.com/content/avs/journal/jvstb/30/3/10.1116/1.3697752
10.1116/1.3697752
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