Mask-induced polarization

As microlithography moves to smaller critical dimensions, structures on reticles reach feature sizes comparable to the operating wavelength. Furthermore, with increasing NA the angle of incidence of light illuminating the mask steadily increases. In particular for immersion lithography this will have severe consequences on the printing behavior of reticles. Polarization effects arise which have an impact on, among other things, the contrast of the printed image. Angular effects have to be considered when aggressive off-axis illumination schemes are used. Whereas numerous articles have been published on those effects and the underlying theory seems to be understood, there is a strong need for experimental verification of properties of real masks at the actinic wavelength. This paper presents measurements of polarization effects on different mask blank types produced at Schott Lithotec including chrome and alternative absorber binary mask blanks, as well as phase shift mask blanks. Thickness and optical dispersion of all layers were determined using grazing incidence x-ray reflectometry (GIXR) and variable angle spectroscopic ellipsometry (VASE). The set of mask blanks was patterned using a special design developed at the Advanced Mask Technology Center (AMTC) to allow measurements at different line width and pitch sizes. VUV Ellipsometry was then used to measure the properties of the structured materials, in particular the intensities in the 0 th and 1 st diffraction order for both polarization directions and varying angle of incidence. The degree of polarization of respective mask types is evaluated for dense lines with varying pitches and duty cycles. The results obtained experimentally are compared with simulations based on rigorous coupled wave analysis (RCWA).

Section: Fundamentals Of Mask Polarizationmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Investigation of polarization effects on new mask materials

Bubke

Teuber

Hoellein

et al. 2005

“…The substrate is matched to a complex photoresist index of n=1.7-0.018i to minimize standing wave effects and concentrate the analysis on imaging effects. Two reticle types are used: 1) a simple binary reticle using Cr on quartz, where the Cr index is n Cr =0.84-1.65i, and the quartz is n quartz =1.56; and 2) a 10% attenuated mask given by an effective medium approximation 13 to MoO 3 -SiO 2 (MoSi) where n MoSi =1.5891-0.2117i with a thickness of 164.7nm. All simulations used vector imaging with a calibrated 193nm photoresist process.…”

Section: Interaction Of the Reticle And Polarization Angle Changesmentioning

confidence: 99%

Challenges with hyper-NA (NA>1.0) polarized light lithography for sub lambda/4 resolution

Flagello¹,

Hansen²,

Geh³

et al. 2005

The use of immersion technology will extend the lifetime of 193nm and 157nm lithography by enabling numerical apertures (NA) much greater than 1.0. This paper explores the effects that will occur when the high NA systems are augmented with polarization.. Specifically we show that there are strong interactions between the polarization induced by the reticle and polarization in the optics. This has a direct impact on the across-field specification of the polarization of the optical system as it causes a large variation in the imaging impact in photoresist. The impact of lens and reticle birefringence on the imaging is also analyzed. We show that reticle birefringence should not be a major concern when the birefringence is maintained to 2nm/cm -4nm/cm levels. The lens can be modeled by a Jones matrix approach, where multiple pupils must be defined for each polarization state. We show the impact of the optical components by using a rigorous photoresist simulation on the process window of sub-50nm features using NA>1.3. The simulator uses a full Maxwell equation solver for the mask, polarized illumination, a Jones matrix approach for the pupil, and a photoresist simulation with calibrated model. The photoresist process is also shown to interact with polarization. Different photoresist will show varying degrees of sensitivity to polarization variation.

“…Hence, plane unpolarized wave falls onto the mask under normal or inclined angle of incidence that belongs to the diffraction plane (dashed contour). Silica (n=1.56+0i) was chosen as a constant substrate material, Cr (n=0.86+1.65i) based absorber was chosen as diffractive layer for binary mask, Si-Si 3 N 4 (n=2.43+0.44i) and MoO 3 -SiO 2 (n=1.59+0.21i) was used for 9% attPSM [3] and SiSi 3 N 4 -Ta (2.44+0.55i) for 6% attPSM. Cr thickness was chosen to be 100, 70 and 50nm.…”

Section: Partial Polarization Effect At Reticle Levelmentioning

confidence: 99%

“…This approach is valid for relatively large dimensions, when diffractive layer thickness (W), as shown on Figure 1, is sufficiently thin or in other words aspect ratios remains low. However, if the feature size becomes smaller while the diffractive layer thickness remains the same, the layout spectrum depends on aspect ratio, material properties and polarization state of incoming light [3]. In general, smaller features on the mask induce stronger polarization changes.…”

Section: Introductionmentioning

confidence: 99%

Influence of mask induced polarization effects on a pattern printability

Aksenov

Dirksen

Wei

et al. 2005

Through ArF immersion lithography a road towards increased optical resolution at the 193nm wavelength has been opened. According to recently proposed roadmaps, ArF immersion lithography will be used for 65nm and 45nm technology nodes. Consequently, keeping the same 4x optical demagnification factor, the dimensions on mask scale down to wavelength values when entering these nodes. Moreover CD control becomes tighter and approaches values of 2-3nm. At such conditions, topography on mask, its type and materials cannot be ignored anymore while evaluating image formation either for design analysis or OPC adjustments. The objective of this paper is to analyze the influence of mask topography on imaging. The mask topography influences polarization state and diffraction efficiencies, which are determine further image formation. Therefore these parameters and their dependence on mask type, materials and pitches are of the major concern during the analyses. We analyze the process latitude and CD variations through pitch. The complete rigorous analysis shows improved process windows with the increase of feature aspect ratio and at the same time a large through pitch CD deviation compared to the conventional Kirchhoff diffraction model.