Elsevier

Applied Surface Science

Volume 426, 31 December 2017, Pages 406-417
Applied Surface Science

Full Length Article
Experimental investigation of the tip based micro/nano machining

https://doi.org/10.1016/j.apsusc.2017.07.181Get rights and content

Highlights

  • An examination method has been presented to examine the horizontal place of the sample.

  • The effects of scratching parameters and sample material on the scratching process have been investigated.

  • Some complex three dimensional micro/nano structures have been fabricated with the selected scratching parameters.

Abstract

Based on the self-developed three dimensional micro/nano machining system, the effects of machining parameters and sample material on micro/nano machining are investigated. The micro/nano machining system is mainly composed of the probe system and micro/nano positioning stage. The former is applied to control the normal load and the latter is utilized to realize high precision motion in the xy plane. A sample examination method is firstly introduced to estimate whether the sample is placed horizontally. The machining parameters include scratching direction, speed, cycles, normal load and feed. According to the experimental results, the scratching depth is significantly affected by the normal load in all four defined scratching directions but is rarely influenced by the scratching speed. The increase of scratching cycle number can increase the scratching depth as well as smooth the groove wall. In addition, the scratching tests of silicon and copper attest that the harder material is easier to be removed. In the scratching with different feed amount, the machining results indicate that the machined depth increases as the feed reduces. Further, a cubic polynomial is used to fit the experimental results to predict the scratching depth. With the selected machining parameters of scratching direction d3/d4, scratching speed 5 μm/s and feed 0.06 μm, some more micro structures including stair, sinusoidal groove, Chinese character ‘田’, ‘TJU’ and Chinese panda have been fabricated on the silicon substrate.

Introduction

Nowadays, the fabrication of nanochannel and nanostructure is a hot issue in micro/nano field. There are many different methods, such as photolithography [1], LIGA [2], FIB (Focused Ion Beam) technology [3], nanoimprint [4] and tip based nanomanufacturing (TBN) [5]. Among all of these methods, every technique has its own advantages and special applications, but the tip based micro/nano machining is attracting more and more attention for the low-cost, simple operation and high accuracy. The scanning tunneling microscopy (STM), atomic force microscope (AFM) and nanoindenter are three common devices for the TBN technology, especially the application of AFM makes this technology greatly developed, and it has successfully combined the chemical and thermal effects to the traditional mechanical removal [6].

In the AFM tip based mechanical nanomanufacturing, the effects of machining parameters including applied normal load, scratching direction, scratching cycles, scratching speed and scratching feed on the machined depth and surface roughness have been investigated by many scholars in the last decades [7], [8], [9], [10], [11], [12], [13]. Recently, some researchers focus on the theoretical modeling of scratching depth. Wang studied the relationship between the initial and final nanochannel depth through both theoretically and experimentally [14], [15]. Geng modeled the scratching depth theoretically in both single and multiple scratching, and micro/nano structures were manufactured based on the proposed model [16]. Lin estimated the cutting depth based on regression equations of nanoscale contact pressure factor and specific down force energy, respectively [17].

The probe cantilever of the AFM is essentially a single flexible beam, as a result, the stiffness of the AFM cantilever in the longitudinal direction is different from that in the transverse direction, which affects the experimental results when scratching in different directions. Unfortunately, the tip-sample interface is also affected by the scratching direction due to the tip geometrical asymmetry. These factors make the investigation of scratching direction complex. Moreover, the AFM cantilever is usually very soft in the vertical direction, which makes it sensitive to the environmental changes. Finally, the low positioning precision of the AFM motion platform reduces the machining accuracy in xy plane. In order to overcome these shortcomings of the AFM, many different mechanical designs have been proposed for the micro/nano machining. Lee adopted a strain gauge measured load beam to substitute the AFM cantilever [18]. Park designed a displacement-force device to realize the micro/nano machining [19]. Jeong presented an air lubricated hydrostatic sliding mechanism based portable nano probe system [20]. Gozen constructed a nano milling system to fabricate the micro channel [21]. All these designs can realize the micro/nano structure scratching, but they also have obvious drawbacks, such as the overlarge normal load in Lee’s mechanism, the residual friction of the probe shaft in Jeong’s design, and the limitation of machining width in Gozen’s system. As to the position precision in xy plane, the piezo-actuated flexure-mechanism is a good choice to solve this problem, which has been studied by many scholars [22], [23], [24], [25].

In this paper, a self-developed three dimensional micro/nano machining system is used for the experimental investigation, which mainly includes the probe system and precise positioning stage. The cross-shaped probe suspension mechanism in the probe system effectively avoids the singal axis and low stiffness of the AFM cantilever. Before the scratching experiments, an examination method is presented to examine the horizontal place of the sample. Subsequently, the scratching parameters including scratching direction, normal load, scratching cycles, scratching speed and scratching feed are systematically investigated and analyzed. Further, the copper sample is scratched and the material removal results are compared with those of silicon samples. Finally, some more micro structures are fabricated on the silicon base with the selected scratching parameters.

Section snippets

The micro/nano machining system

All of experiments are performed in a self-developed three dimensional micro/nano machining system, which is shown in Fig. 1. The overall frame applies the gantry structure. Three manual coarse mobile platforms (WN115TM50 M, winner optical instruments, China) arranged orthogonally are used to realize the broad adjustment with the full stroke of 50 mm and minimal regulating amount of 2 μm. The probe system and the 3-DOF micro/nano positioning stage are the two core parts of the machining system,

The experimental investigation

In the experimental investigation, the silicon is firstly selected as the sample for the wide application in semiconductor industry. After micro/nano machining, the sample is cleaned using ultrasonic wash with acetone solution for ten minutes to remove the generated chips, and then the machined micro/nano grooves or structures are measured using AFM (CSPM5500, Benyuan, China).

Three dimensional micro/nano machining

Based on the above experimental results, some additional three dimensional micro/nano structures are fabricated on silicon substrate by controlling the normal force. The following machining parameters are adopted: scratching direction d3/d4, scratching speed 5 μm/s and feed 60 nm.

Fig. 16 shows the normal force used for the fabrication of a stair micro/nano structure and the corresponding experimental result. The average scratching depth in right stair is about 10 nm smaller than the left one, the

Conclusion

In the micro/nano machining, the machining parameters include scratching direction, normal load, scratching cycles, scratching speed and feed amount. According to the experimental results, the scratching depth in the d2, d3/d4 and d1 directions is successively reduced, but it is affected more obvious by the normal load. Multi scratching can also increase the scratching depth, and the groove become smoother as the number of scratching cycle number increases. The scratching depth difference is

Acknowledgements

This research is supported by National Natural Science Foundation of China (Nos. 51675371, 51675367, 51675376, 51405333, 51420105007) and EU H2020 FabSurfWAR (No. 644971).

References (30)

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