Elsevier

Materials Letters

Volume 264, 1 April 2020, 127344
Materials Letters

A metal lift-off process through hyperbolic undercut of laser heat-mode lithography

https://doi.org/10.1016/j.matlet.2020.127344Get rights and content

Highlights

  • A lift-off method through hyperbolic undercut of laser heat-mode lithography was proposed.

  • A desirable undercut profile was obtained by manipulating the temperature field.

  • Different Cr structures with a minimum feature size of 0.42 μm were prepared.

  • This lift-off process can be used to fabricate submicron metal structures.

Abstract

Laser heat-mode lithography is an important method for the fabrication of micro and nanostructure. A metal lift-off method through hyperbolic undercut of laser heat-mode lithography was proposed. In this method, a desirable hyperbolic undercut profile was used to replace the inverted trapezoid undercut, and the hyperbolic undercut profile can be obtained through laser heat-mode lithography technique. Cr structures of gratings, grids and planar spiral inductor with a minimum linewidth of 0.42 μm and a height of 100 nm were obtained successfully. These indicate that the lift-off process through hyperbolic undercut of laser heat-mode lithography can be used to fabricate the submicron metal structures.

Introduction

In lithography applications, the relief patterns on the resist film needs to be transferred to metal materials to form functionalized templates or devices. Compared with other transfer methods, the metal lift-off is proved to be a low cost and high-throughput method. As it can transfer patterns to almost all metal materials, and it is even the only transfer way for some special metals [1], [2].

However, the metal lift-off process is difficult to achieve submicron for the negative photoresist, as the line lodging occurs in the process [3], [4]. The critical reason is that it is difficult to produce an appropriate undercut profile on the photoresist film. With the decrease of pattern feature size to the submicron, the inverted trapezoid undercut (as shown in Fig. 1a) in the traditional metal lift-off process is hard to support the liquid surface tension during development, resulting in the pattern collapse. As Zheng et al pointed out in Ref. [5], the essence of collapse results from the small contact area between resist and substrate. To increase the contact area between resist and substrate, we propose to use a hyperbolic undercut to replace the inverted trapezoid undercut (as shown in Fig. 1b). Besides the large contact area, the hyperbolic undercut configuration can also lead the metal deposition toward the vertical directions of resist layer.

The fabrication of hyperbolic undercut is critical in our method. Fortunately, in laser heat-mode lithography, the undercut profile on the heat-mode resist film could be adjusted through the design and optimization of temperature field profile [6], [7], [8]. In this letter, a hyperbolic undercut was fabricated through laser heat-mode lithography technique, and then the metal lift-off process was carried out. Through optimizing the design of the undercut profile, Cr structures for gratings, grids and planar spiral inductors with a characteristic size of submicron were prepared accordingly.

Section snippets

Analysis and calculation of hyperbolic undercut of laser heat-mode lithography

Fig. 1c shows the schematic of laser heat-mode lithography. When a focused Gaussian laser beam irradiates the surface of the heat-mode resist film, the light intensity decreases with the depth due to the absorption of resists. The light field distribution at a certain position in the resist film can be expressed as:Ir,z=2Pπw02exp-2r2w02exp-αz,where r and z are the radial and vertical coordinates, respectively. α is the absorption coefficient of resist, w0 is the spot radius, and P is the laser

Experimental details

Fig. 2a shows the flow chart of the lift-off process based on laser heat-mode lithography. Firstly, a 300 nm-thick amorphous heat-mode resist (AIST) film with a root-mean-squared (RMS) surface roughness of 0.3 nm was deposited on a fused silica substrate (Φ30 mm, thickness: 1 mm) by the magnetron-controlled sputtering system (JPG560) at a background pressure of approximately 6.0 × 10−4 Pa. A sputtering power of 40 W and a working pressure of 0.8 Pa in the Ar environment were used. Heat-mode

Results and discussion

The cross-section of the gratings shows obvious hyperbolic structure, as shown in Fig. 3a. The width at the surface, waist, and bottom of the grating structures is 1.5 μm, 0.8 μm, and 1.2 μm respectively. Fig. 3d shows the transferred Cr patterns using electron beam evaporation deposition method. The height of Cr structures is about 120 nm. To further investigate the process controllability of the proposed lift-off method, grid structures was prepared on the AIST resist film with a laser power

Conclusion

A metal lift-off method through hyperbolic undercut of laser heat-mode lithography was presented. Based on the design of hyperbolic undercut profile and electron beam evaporation deposition method, Cr structures of gratings, grids and planar spiral inductor with a minimum linewidth of 0.42 μm and a height of 100 nm were obtained successfully. These indicate that the lift-off method can be used to fabricate the submicron metal structures through hyperbolic undercut of laser heat-mode lithography.

CRediT authorship contribution statement

Zhengwei Wang: Investigation, Writing - original draft. Kui Zhang: Writing - review & editing. Guodong Chen: Writing - review & editing. Zhendong Zhu: Writing - review & editing. Yang Wang: Supervision. Jingsong Wei: Supervision.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was partially supported by the National Natural Science Foundation of China (Nos. 51672292 and 61627826) and Strategic High-Tech Innovation Fund of Chinese Academy of Sciences (No. GQRC-19-08).

References (11)

  • Y. Fu et al.

    Mater. Lett.

    (2012)
  • A. Finn et al.

    Microelectron. Eng.

    (2013)
  • Y. Meng et al.

    Appl. Surf. Sci.

    (2020)
  • R.D. Nagel et al.

    J. Appl. Phys.

    (2017)
  • T. Toshihiko et al.

    Jpn. J. Appl. Phys.

    (1993)
There are more references available in the full text version of this article.

Cited by (10)

  • NSbTe heat-mode resist possessing both positive and negative lithographic characteristics

    2022, Materials Letters
    Citation Excerpt :

    The complexity of the device requires the utilization of positive or negative resist. It is meaningful to enrich the procedure choice of device fabrications, generally achieved by selecting appropriate resists and developers [7,13]. For instance, GeTe acts as both positive and negative resists at tetramethyl ammonium hydroxide (TMAH) and nitric acid solutions, respectively [14].

  • CrSb<inf>2</inf>Te thin film as a dry resist and its etching mechanism for lithography application

    2021, Materials Chemistry and Physics
    Citation Excerpt :

    Wet development is usually utilized in the lithography. However, wet development readily leads to the undercut, thus influencing pattern fidelity [4]. Fortunately, dry development, as an alternative method, has been proposed to address such issue, which is based on reactive ion etching technology [5–12].

View all citing articles on Scopus
View full text