EUV (Extreme Ultraviolet) Lithography has been delayed caused by several technical problems such as
EUV mask, source power and etc. So ArF immersion lithography has been continued with adopting new
technology. Especially, the wafer lithography tends to increase rapidly NTD(Negative Tone Develop) process
for overcoming high resolution such as small hole type patterns. For wafer NTD process, the pattern shape in
mask has changed from hole pattern to dot pattern. Also the local CD uniformity of aerial image is getting
more important. In this paper, we studied local CD uniformity with analyzing aerial images of high
transmittance HT-PSM (attenuated phase-shift mask) and conventional 6% HT-PSM from AIMS (Aerial Image
Measurement System) tool. Additionally, several cell sizes were analyzed to find an optimum target cell size
which has good wafer performance and AIMS aerial image. And we analyzed NILS(Normalized Image Log
Slope) factor which represent wafer photolithographic performance. Furthermore, we analyzed not only AIMS
NILS simulation, but also wafer lithographic performance.
The Critical Dimension Uniformity (CDU) specification on photo-mask is getting increasingly tighter which each
successive node. The ITRS roadmap for optical masks indicates that, the CDU (3 sigma) for dense lines for binary or
attenuated phase shift mask is 3.4nm for 45nm half-pitch (45HP) node and will go down to 2.4nm for 32HP node. The
current variability in mask shop processes results in CDU variation across the photo-mask of ~2-3nm.
Hence, we are entering in a phase where the mask CDU specification is approaching the limit of the capability of the
current POR (process on record). Hence, mask shops have started exploring more active mechanisms to improve or
compensate for the CDU of the masks. A typical application is in feeding back the CDU data to adjust the mask writer
dose and compensate for non-uniformity in the CDs, resulting in improved quality of subsequent masks. Another option
is to feed the CD uniformity information forward into the wafer FAB and adjust the scanner dose to correct for reticle
non-uniformity. For these purposes mask makers prefer a dense measurement of CDs across the reticle in a short time.
Mask makers are currently using the CD-SEM tool for data collection. While the resolution of SEM data ensures its
position as the industry standard, an output map of CDU from a reticle inspection tool has the advantage of denser
sampling over larger areas on the mask. High NA reticle inspection systems scan the entire reticle at high throughput,
and are ideally suited for collecting CDU data on a dense grid.
In this paper, we describe the basic theory of a new, reticle inspection-based CDU tool, and results on advanced
memory masks. We discuss possible applications of CDU maps for optimizing the mask manufacturing and wafer
As the design rule of the semiconductor circuit shrinks, the specification for photomask becomes tighter. So, more
precise control of CD MTT (Critical Dimension Mean to Target) is required. We investigated the CD MTT control of the
attenuated PSM (Phase Shift Mask) by additional Cr dry etch. In conventional process, it is difficult to control CD MTT
precisely because about 5 factors - Blank Mask, E-beam writing, Resist develop, Cr dry etch, MoSiN dry etch - affect
CD MTT error. We designed the new process to control CD MTT precisely. The basic concept of the new process is to
reduce the number of factors which affect the CD MTT error. To correct CD MTT error in the new process, we
measured CD before MoSiN dry etch, and then additional corrective Cr dry etch and MoSiN dry etch was performed. So,
the factors affecting CD MTT error are reduced to 2 steps, which is additional corrective Cr dry etch and MoSiN dry
etch. The reliability of CD measurement before MoSiN dry etch was evaluated. The generable side-effect of the
additional corrective Cr dry etch was analyzed. The relationship between 'CD shift' and 'additional corrective Cr dry
etch time' was found for various patterns. As a result, accurate CD MTT control and significant decrease of CD MTT
error for attenuated PSM is achieved.
In this study, the method for achieving precise CD MTT (critical dimension mean to target) in manufacturing attenuated PSM (phase shift mask) was investigated. As the specification for photomask becomes tighter, more precise control of CD is required. There are several causes to result in CD MTT error. In general mask patterning processes which are from blank material to dry etch, it is difficult to detect CD MTT error before final CD measurement and correct it. It is necessary to apply new process to mask production to correct CD error and control CD MTT precisely. Reducing number of factors which can have an effect on CD and introducing reliable method to correct CD error are important to achieve accurate CD MTT. For the correction of CD error, the reliability of CD in each measurement step such as resist CD or Cr CD before and after resist removal and effect on items related with CD like CD uniformity, isolated-dense CD difference, etc should be considered and evaluated. In this method to correct CD MTT error, Cr CD after removing resist was measured before MoSiN dry etch and additional corrective Cr dry etch using Cr CD information was applied to cancel CD error and then MoSiN dry etch was followed. In this case, factors affecting final CD are additional corrective Cr etch and MoSiN etch. The relationship between CD shift and corrective Cr etch time for masks with various pattern densities was found and necessary corrective Cr etch time was applied to CD correction process. The CD MTT error is canceled by additional corrective Cr dry etch step. As a result, accurate CD control and significant decrease of CD MTT error for attenuated PSM is achieved through the use of this CD correction method.
ZEP is a field-proven stable E-Beam resist for photo-mask manufacturing. The spin-spray develop method has been widely used for ZEP resist processing. Recently, we have successfully adopted the spin-stream develop process for ZEP resist by using modified TEL MARK-8 wafer process track. This paper presents a comparison result of CD uniformity between the conventional spin-spray method and new spin-stream method on 6-inch production halftone phase shift masks. In this process, we apply low temperature(18 deg. C) develop solution in room temperature ambient. The spin-stream process with low temperature solution is found to be a suitable recipe for high-end phase shift mask manufacturing with under 10 nm CD uniformity (3sigma) in 120mm X 120mm area. Moreover, the modified MARK-8 track can provide both of a FEP and a ZEP process module in one unit, and this advantage reduces the cost of ownership for a high-end mask manufacturing facility.
We have developed a new method to make cell projection aperture with high degree of accuracy which provides stable and accurate pattern fidelity on wafer and could be adaptable to mask process. As an electron beam mask, deep and vertical silicon pattern is made by MERIE poly etcher. Trench pattern profile can be optimized by etching chemistry. And to obtain fine pattern with cell projection exposure, various techniques are used such as pattern fracturing, modified cell aperture layout and shot shift. As a feasibility of cell projection EB exposure, 0.2μm feature were defined with VSB (variable shaped beam) and CPB (cell projection beam) on wafer and evaluated.