**1. Introduction**

Synchrotron X-ray lithography (XRL) uses a hard X-ray source to fabricate nano/microstructures of various shapes [1,2]. Synchrotron XRL has been used to create high aspect ratio structures with good sidewall roughness; synchrotron X-rays are highly collimated, pass through thick polymers and other plastic materials, and exhibit high flux and intensity, the pattern accuracy of XRL is very high. Synchrotron XRL was first developed to fabricate uranium-separation nozzles, and several other applications have been found since. For example, synchrotron XRL has been used to fabricate high-density magnetic dot arrays [3], a vertical stepper [4], and micromechanical components [5].

Ultraviolet (UV) light is employed in conventional photolithography. The photomask pattern is copied to photoresist (PR) with various ratios, and a two-dimensional (2D) microstructure is formed on a flat substrate. Various techniques are used to create three-dimensional (3D) features on 2D substrates. Micro stereo lithography [6], 3D printing [7], oblique lithography [8], PR reflow [9], backside exposure lithography [10], grayscale lithography [11], nanoimprint lithography [12,13], nanosphere lithography [14], colloidal lithography [15], block copolymer lithography [16], and e-beam lithography [17] all allow extensive shaping. However, it is complicated to fabricate the desired structures using these techniques.

In 2011, Jongho et al. prepared copper microstructures on curved substrates via optical soft lithography and metal electroplating [18]. The microstructures had high aspect ratios, throughput was good, cost was low, and reproducibility was high.

Microcontact printing using cylindrical polydimethylsiloxane (PDMS) stamps has since been reported [19]. However, it was not possible to create various angles on a single substrate by flattening the curved substrates bearing the microstructures.

Here, we develop a method by which to fabricate tilted microstructures of various angles and shapes on a single substrate using synchrotron XRL. Synchrotron X-rays are highly collimated; they pass through polymers (because of their short wavelength). Such a unique feature of hard X-rays allows the fabrication of microstructures on curved substrates. The fabrication technique on curved substrates could be applied to the fabrication of precision optical elements [20] and the micromachining of ultraprecise molds on curved or cylindrical structures.
