تکرار و کنترل کیفیت بعدی از سطوح های صنعتی مقیاس نانو با استفاده از اندازه گیری کالیبراسیون AFM و SEM پردازش تصویر

Ultra-high precision manufacture of nanoscale structured polymer surfaces poses the highest challenges in terms of tooling and replication. This paper introduces new procedures for quality control of nickel stampers and polymer moulded discs for CD, DVD and HD-DVD manufacture: quantitative application of AFM to calibrate height, depth and pitch of sub-micrometer features and SEM image processing to detect replication accuracy in terms of number of replicated features. Surface replication is analyzed using a metrological approach: nano-features on nickel stampers and injection–compression moulded polycarbonate substrates are measured, measurement uncertainty calculated, replication fidelity assessed quantitatively, and dimensional tolerances at the nanometre scale verified.

In the field of media support for both data storage and entertainment, polymer-based substrates composed of thin polycarbonate discs having a sub-micro structured surface (so-called optical discs) are nowadays the established format for a variety of different uses. Since the beginning of its introduction, first at research and development level and then at the market place in 1982, the compact disc (CD) format attained a successful market position, reaching its peak of 15 billion CDs produced worldwide in 2001 [1] and [2]. The need for higher data content in both the entertainment sector (to achieve the shift from digital audio to audio/video content) and the electronic/information technology sector (increased data storage) created the motivations to enhance the capacity of the CD support and to develop the digital versatile disc (DVD) format which was introduced in 1996. Different strategies were adopted to increase the capacity of the media support, particularly related to drives and drive precision, multi-layer technology, encoding/decoding electronics (more powerful encoding methods and a redesigned logical format of the disc), and optics design. The latter dealt with the use of shorter laser wavelength and larger numerical aperture, which reduced the CD spot diameter from 780 nm to 650 nm. This has enabled to miniaturize the surface structures and therefore to increase data density [3]. The result was that a single-layer DVD has a storage capacity 7 times higher than the one of a CD and a double-layer DVD up to 14 times, equivalent to 135 min of wide-screen high quality video including multiple audio and subtitle channels. DVD production worldwide has grown since the format introduction into the market in 1998 with a peak in 2006 of about 10 billion discs and a market worth $100 billion [2] and [4]. Lately, starting from 2004, new formats appeared on the market in order to satisfy a renovated demand for increased capacity; for example, the high definition DVD (HD-DVD), capable of storing 15–30 GB on a single- and double-layer disc respectively. The drive for such increased capacity has been mainly the spreading of the High Definition Television (HD-TV) service which promoted the diffusion of high definition flat screens larger than 30 in. (in order to take advantage of the new TV format) with a market size of 7.6 million and 10.5 million units in Japan and USA respectively in 2006. As a consequence, high definition flat displays larger than 30 in. have shown the limitations of the current DVD format in terms of image quality and therefore the need for a new optical disc support, creating a technology gap to be addressed [4]. For the same reasons, also the Blue-ray Disc (BD-ROM) format, with a storage capacity of 25 GB, has been introduced. Both HD-DVD and BD-ROM present features with characteristic dimensions in the order of about 100–400 nm. In this paper, the focus will be on HD-DVD, as well as on CD and DVD.

Tolerance verification and replication quality evaluation were performed on nickel stampers and polycarbonate optical moulded discs for data storage application. Three different disc formats such as CD, DVD, and HD-DVD were investigated. A quantitative evaluation of the replication quality was performed using both scanning electron microscopy (SEM) and atomic force microscopy (AFM). The former was employed for a replication assessment study based on a stochastic feature-counting method, the latter for dimensional tolerance verification at nanometre scale and replication accuracy investigation using a metrological approach (track pitch and pit height of sub-micrometer sized features on the discs surfaces were measured and calibrated using AFM). The feature-counting approach showed to be consistent for all three substrate formats: a maximum deviation of 0.2% between the number of features on the stamper and the polymer disc was found. With regards to AFM measurements, comprehensive uncertainty budgets were created in order to calculate the measuring uncertainty and establish traceability. It has been shown that an increased feature miniaturization challenges both the replication process and the quality control technology. In fact, less favourable uncertainty to tolerance ratios (U/T) were observed on smaller features typical of HD-DVD discs when compared to DVD and CD discs showing the challenge of performing an effective quality control at nanometre dimensional scale.