The achievement of a depth of focus required for stable process conditions is one of the biggest challenges in
modern optical photolithography. There are several ways of improving the depth of focus. For line/space
layers, for instance, application of RET (Resolution Enhancement Technology) using scattering bars, phaseshift
masks or optimized illumination systems have shown good results. For contact and via layers the depth
of focus is limited and critical, due to the structure size of the holes, alternating pattern density and wafer
topology. A well known method of improving the depth of focus for contact and via layers is called focus
latitude enhancement exposure (FLEX) [1-3]. With FLEX, several focal planes are being exposed, i.e. each
during a separate exposure step. The main drawback is low throughput, as the total processing time rises
which each additional exposure.
In this paper, we investigate Nikon's CDP (continuous depth of focus expansion procedure) [4]. The CDP
option is applicable to modern scanning exposure tools [4-5]. A schematic view of the procedure is shown in
Fig. 1. The CDP value or CDP amplitude defines the tilt of the wafer and thus the range of focus in the resist,
as the focus plane migrates through the resist during the exposure. The main advantage of CDP, compared
to FLEX, is higher throughput, since focal planes are defined within a single exposure. A non-CDP exposure
may result in varying aerial images within resist thickness, therefore leading to decreased image contrast
within out-of-focus planes. As shown in Fig. 1 the averaged aerial images of a CDP exposure induce better
image contrast throughout the resist layer and therefore increase the focus window.
We present results for a rule based optical proximity (RB-OPC) and a model based optical proximity correction
(MB-OPC) for 0.13 μm SiGe:C BiCMOS technology. The technology provides integrated high performance
heterojunction bipolar transistors (HBTs) with cut-off frequencies up to 300 GHz. This requires an optical proximity
correction of critical layers with an excellent mask quality. This paper provides results of the MB-OPC and RB-OPC
using the Mentor Calibre software in comparison to uncorrected structures (NO-OPC). We show RB- and MB-OPC
methods for the shallow trench and gate layer, and the RB-OPC for the emitter window-, contact- and metal layers.
We will discuss the impact of the RB- and MB-OPC rules on the process margin and yield in the 0.13 μm SiGe:C
BiCMOS technology, based on CD-SEM data obtained from the evaluation of the RB- and MB-OPC corrected
SRAM cells.
The application of Double Exposure Lithography (DEL) would enlarge the capability of 248 nm exposure technique to
smaller pitch. We will use the DEL for the integration of critical layers for dedicated applications requiring resolution
enhancement into 0.13 μm BiCMOS technology. In this paper we present the overlay precision and the focus difference
of 1st and 2nd exposure as critical parameters of the DEL for k1 ≤ 0.3 lithography (100 nm half pitch) with binary masks
(BIM). The realization of excellent overlay (OVL) accuracy is a main key of double exposure and double patterning
techniques. We show the DEL requires primarily a good mask registration, when the wafer stays in the scanner for both
exposures without alignment between 1st and 2nd exposure. The exposure tool overlay error is more a practical limit for
double patterning lithography (DPL). Hence we prefer the DEL for the resolution enhancement, especially if we use the
KrF high NA lithography tool for 130 nm generation.
Experimental and simulated results show that the critical dimension uniformity (CDU) depends strongly on the overlay
precision. The DEL results show CDU is not only affected by the OVL but also by an optical proximity effect of 1st and
2nd exposure and the mask registration.
The CD uniformity of DEL demands a low focus difference between 1st and 2nd exposure and therefore requires a good
focus repeatability of the exposure tool. The Depth of Focus (DOF) of 490 nm at stable CD of lines was achieved for
DEL. If we change the focus of one of the exposures the CD-focus performance of spaces was reduced with
simultaneous line position changing. CDU vs. focus difference between 1st and 2nd exposure demands a focus
repeatability <100 nm for the exposure tool.
Summary, the results show DEL has the potential to be a practical lithography enhancement method for device
fabrication using high NA KrF tool generation.
In this paper we investigate the process margin for the 100nm half - pitch double exposure KrF lithography using binary
masks for different illumination settings.
The application of Double Exposure Lithography (DEL) would enlarge the capability of 248 nm exposure technique to
smaller pitch e.g. for the integration of dedicated layers into 0.13 μm BiCMOS with critical dimension (CD)
requirements exceeding the standard 248 nm lithography specification. The DEL was carried out with a KrF Scanner
(Nikon S207D, NALens = 0.82) for a critical dimension (CD) of 100nm half pitch. The chemical amplified positive resists
SL4800 or UV2000 (Rohm & Haas) with a thickness of 325nm were coated on a 70 nm AR10L (Rohm & Haas) bottom
anti-reflective coating (BARC). With a single exposure and using binary masks it is not possible to resolve 100nm lines
with a pitch of 200 nm, due to the refraction and the resolution limit.
First we investigated the effect of focus variation. It is shown that the focus difference of 1st and 2nd exposure is one
critical parameter of the DEL. This requires a good focus repeatability of the scanner. The depth of focus (DOF) of
360 nm with the coherence parameter σ = 0.4 was achieved for DEL with SL4800 resist. The influence of the better
resist resolution of UV2000 on the process window will be shown (DOF = 460 nm). If we change the focus of one of the
exposures the CD and DOF performance of spaces is reduced with simultaneous line position changing.
Second we investigated the effect of different illumination shapes and settings. The results for conventional illumination
with different values for σ and annular illumination with σinner = 0.57 and σouter = 0.85 will be shown.
In summary, the results show that DEL has the potential to be a practical lithography enhancement method for device
fabrication using high NA KrF tool generation.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.