In our paper we make an analysis of conditions for the haze development on photomask fabricated on Mo-Si
containing substrates. We bring in focus cases of haze formation on masks with intrinsically very low contaminants level
and being exposed in very well controlled atmosphere. There are clear indications that this new type of haze formation
deviates from the generally accepted models not only with respect to the formation mechanisms but also with regard to
the chemical composition of the haze products. In our analysis we speculate that the new haze type formation is closely
related to the earlier reported CD degradation observed on Mo-Si masks. We also analyze the hypothesis that the
ingredients for the haze formation are not only airborne contaminants and/or traces on the mask surface, but are also
provided by the substrate material. Finally we present and discuss experimental data in the view of the advanced models.
Since introduction of 193nm exposure wavelength, the haze formation becomes a serious challenge especially at mask
used for big number of exposures. Several compounds present in air as low concentration contaminants are leading to
haze building. Well understood is the sulphate based haze formation, however, still causing significant losses and
demanding for re-cleaning of the mask during mask life time.
There are plenty of publications taking different approaches to reduction of the final sulphate concentration on the mask
and reduction of the use of sulphuric acid during the mask manufacturing. Beside traditional process as hot water
extraction, UV exposure, baking, IR exposure at vacuum, Ammonia solution treatment more exotic method were
published as surface treatment preventing migration of the sulphate ions on mask surface. The number of exposures till
haze crystals growth prevents further use of the mask is not solely dependent on the sulphate concentration on the freshly
manufactured mask. Additional factors as storage and use conditions are significantly influencing the period till re-clean
of the mask is needed.
In this work we try to assess above mentioned approaches and provide rough estimate of their limits.
In order to fulfil the upcoming requirements for photomasks there is a need for improving the process stability
(reproducibility) of the unit processes in photomask fabrication. In order to understand and minimize the etch
contribution to the CD stability impedance sensors integrated into the capacitively coupled radio frequency (RF) circuit
(bias circuit) have shown a big potential.
The last step towards a full characterization of the RF properties is the integration of impedance sensors in the
inductively coupled RF circuit (source). This kind of sensor measures voltage, current and phase angle for the
fundamental (13.56 MHz) and higher harmonics (up to the 5th harmonic).
In this paper we are describing the integration of the Z-Scan sensors into the source RF matchbox and its impact on the
RF and CD characteristics of the mask etcher. The central point is the correlation of impedance data to CD data. We will
also compare the responses for bias and source impedance measurements.
The Critical dimension off-target (CDO) is a key parameter for mask house customer, affecting directly the performance
of the mask. The CDO is the difference between the feature size target and the measured feature size. The change of
CD during the process is either compensated within the process or by data correction. These compensation methods are
commonly called process bias and data bias, respectively. The difference between data bias and process bias in
manufacturing results in systematic CDO error, however, this systematic error does not take into account the instability
of the process bias. This instability is a result of minor variations - instabilities of manufacturing processes and changes
in materials and/or logistics.
Using several masks the CDO of the manufacturing line can be estimated. For systematic investigation of the unit
process contribution to CDO and analysis of the factors influencing the CDO contributors, a solid understanding of each
unit process and huge number of masks is necessary. Rough identification of contributing processes and splitting of the
final CDO variation between processes can be done with approx. 50 masks with identical design, material and process.
Such amount of data allows us to identify the main contributors and estimate the effect of them by means of Analysis of
variance (ANOVA) combined with multivariate analysis.
The analysis does not provide information about the root cause of the variation within the particular unit process,
however, it provides a good estimate of the impact of the process on the stability of the manufacturing line. Additionally
this analysis can be used to identify possible interaction between processes, which cannot be investigated if only single
processes are considered.
Goal of this work is to evaluate limits for CDO budgeting models given by the precision and the number of
measurements as well as partitioning the variation within the manufacturing process. The CDO variation splits
according to the suggested model into contributions from particular processes or process groups. Last but not least the
power of this method to determine the absolute strength of each parameter will be demonstrated.
Identification of the root cause of this variation within the unit process itself is not scope of this work.
The ever-narrowing specifications for high-end masks can only be derived from the continuous improvement of all manufacturing processes. Here, the metrology is crucial prerequisite since the development relies almost entirely on measurement results. In this paper we will address this relation by showing how the limits of metrology repeatability and reproducibility define also the limits of process development. In particular, we will show that improved metrology tool performance on resist results in a deeper understanding for the dry etch process. This is very important since resist metrology is not part of the ITRS roadmap and serves "only" as a supporting engineering process. Better short-term repeatability results in the possibility to detect more variables that might influence the etch regime. As an example, results from two CD scanning electron microscopes (SEM) were compared with very different short-term repeatability. The better knowledge based on the more accurate metrology data allows then to optimize the process within a process space which was previously not detectable with the other tool. An estimate is given how much this influenced the final performance of the process. We conclude from these results, that metrology parameters not covered in standard roadmaps become increasingly important to achieve process development goals in other process areas.
Increasing demand for high end lithography mask especially phase shift masks and narrowing the specification, lead to development of etch processes with minimum critical dimension uniformity (CDU) and very low etch bias. The etch bias becomes one of the limiting parameters for the Cr etch process, due to strong cross links between etch bias and other etch characteristics like linearity and loading effect, thus contributing strongly to the CDU for masks with non uniform pattern distribution. The goal was to develop a Cr etch process with very low etch bias, keeping the other parameters at the same level and providing a wider process window for further optimization of the CDU, loading effect and linearity. In the paper we want to present a feasibility study of one specific approach to the mentioned methods and compare different ways for measurement of the CDU and etch bias. The work presented was done on the Applied Materials Tetra II Mask Etch system.