Advanced DRAM manufacturing demands rigorous and tight process control using high measurement precision,
accurate, traceable and high throughput metrology solutions. Scatterometry is one of the advanced metrology techniques
which satisfies all the above mentioned requirements and it has been implemented in semiconductor manufacturing for
some time for monitoring and controlling critical dimensions and other important structural parameters. One of the
major contributions to the optical critical dimensions metrology uncertainty is the variations in optical properties
(n&k's) of film stack materials. And it is well-known that the optical properties of materials depend very much on
process conditions (such as operating conditions of deposition tools). However, in traditional scatterometry approach all
the n&k's have been used as fixed inputs in a scatterometry model which might result in significant metrology error.
This paper shows the use of the integrated scatterometry system in a real production environment. The significant
improvement in accuracy of CD data was achieved following the implementation of new floating n&k's option for the
Optical Digital Profilometry (ODPTM) system. It has been clearly shown that to achieve desired sub-nanometer accuracy
in scatterometry measurements for advanced processes we need to pay scrupulous attention to every detail of the
scatterometry modeling and measurement. Still further work is needed to better understand the impact of n&k's
variations on tool-to-tool matching.
CD-SEMs fleet matching is a widely discussed subject and various approaches and procedures to determine it were
described in the literature [1,2,4-6]. The different approaches for matching are all based on statistical treatment of CD
measurements that are performed on dedicated test structures. The test structures are a limited finite set of features, thus
the matching results should be treated as valid only for the specific defined set of test features. The credibility of the
matching should be in question for different layers and specifically production layers. Since matching is crucial for
reliable process monitoring by a fleet of CD-SEMs, the current matching approaches must be extended so that the
matching will be only tool dependent and reproducible on all layers regardless their specific material or topographic
characteristics. In our previous work [1] the new approach named "Physical Matching" was introduced and a new
matching procedure based on the direct estimation of tool physical parameters was described. This approach extends the
conventional matching methods to enable significant improvement of the matching between CD-SEM tools in
production environment.
In this work we present results of applying the physical matching method in FAB environment by using the physical
parameters of the brightness and SNR, extend it to noise frequency domain characteristics monitoring, and enhanced
collection uniformity. Improving the collection uniformity is also demonstrated and proved to be a significant factor.
The advantage of the physical matching with noise spectra analysis approach for a case study is demonstrated. This
method will enable detection of specific reasons for mismatching between the tools, based on analysis of specific
frequencies that are resulted from known mechanical/electrical noise. The proposed procedure allows tool problems
fixing before CD measurements are affected. In order to get a reliable visualization of the difference between two
systems, new automatic and manual tool finger print methods were developed. The application of the proposed approach
to vendor to vendor matching problem is considered.
Controlling a very tight CD budget in Photolithography is one of the challenges of the next technology nodes. The Post
Exposure Bake (PEB) process is known as one of the main Litho contributors to CD non-uniformity for processes using
resists with moderate or high PEB sensitivity. However, to achieve a good CD uniformity plate to plate (PtP) and within
plate (WiP) - the current temperature calibration procedures of PEB plates will not be sufficient enough to fulfil the
requirements of future technology nodes.
TEL's CD Optimizer - which is a software integrated to the Coater / Developer using a mathematical model based on
scatterometry CD data and the PEB sensitivity of the resist - allows an accurate PtP and WiP CD uniformity adjustment.
Compared to the conventional time consuming temperature calibration procedures the CD Optimizer can improve the
CD uniformity significantly - and it saves lots of productive time.
This method already has been confirmed by using bare Si wafers [1]. We will show for the first time the effect of the CD
optimization on the CD uniformity of production wafer in a high-volume 300mm DRAM FAB. We did analyse CD mass
production data obtained from Integrated Metrology (IM) scatterometry measurements before and after optimization of
the PEB plates. We can also show that it is possible to use IM mass production data for the PEB temperature
optimization directly.
KEYWORDS: Semiconducting wafers, Scatterometry, Metrology, Lithography, 3D modeling, Scatter measurement, Critical dimension metrology, Process control, Process modeling, Data processing
With critical dimensions in microelectronics devices shrinking to 70nm and below, CD metrology is becoming more and more critical, and additional measurement information will be needed, especially for sidewall profiles and profile height. Integrated scatterometry is, on the one hand, giving the needed measurement precision, and on the other hand, it enables more measurements than stand-alone metrology. Both high precision and large sampling are needed for future technology nodes. This paper shows results from several full volume DRAM applications of state-of-the-art technology nodes on 300 mm wafers. These applications include critical line/space (L/S) layers as 2D applications and contact-hole (CH) layers consisting of elliptical CH-like structures as critical 3D applications. The selected applications are significantly more challenging with respect to scatterometry model generation than the applications presented in previous papers [1, 2]. Simultaneously, they belong to the most critical lithography steps in DRAM manufacturing. In the experiments, the influences of both pre-processes and the litho cluster on Critical Dimension Uniformity (CDU) have been investigated. Possible impacts on Run-to-Run systems like Feed-back and Feed-forward loops will also be discussed. We show that using integrated scatterometry can significantly increase the productivity of lithography clusters.
In our work, Tokyo Electron's iODP103 (integrated Optical Digital Profilometry) technology is used for integrated measurements on a next-generation Lithius Clean Track on after develop inspect (ADI) 300mm wafers. We show that single tool precision and tool-to-tool matching of three integrated systems fulfill the precision requirements of the 70nm DRAM technology node. Further results from a long-term pilot test using integrated scatterometry in a full-volume DRAM production of the 110nm technology node on 300mm wafers are also discussed. The data from our experiment is collected and charted in fab monitored statistical process control (SPC) charts, and compared to the charts from the POR CD-SEM measurements. The sampling plans are optimized in such a way as to perform fully integrated measurements on all wafers per lot, without throughput loss of the litho cluster. We demonstrate that the possibility of measuring all wafers per lot directly after development, in combination with the sensitivity of the method, allows the identification of effects that could not previously be identified by CD-SEM measurements alone.
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