High resolution electron projection

Details High resolution electron projection High resolution electron projection

1999-05-19

2003-02-04

Berman, Jack (Department: 2881)

Radiant energy

Irradiation of objects or material

Irradiation of semiconductor devices

C430S296000

Reexamination Certificate

active

06515292

ABSTRACT:

BACKGROUND
The size of a semiconductor often relies on small lines and features being formed on a semiconductor substrate such as silicon. Processes such as lithography and pattern transfer are often used to form such small features on the silicon backbones. Many of these techniques have a resolution that is limited to the wavelength of the illuminating radiation. Many techniques for forming small lines require a totally new technology for forming the mask. For example, techniques have been suggested based on x-ray or high energy electron projection. These techniques may require the construction of complex and expensive sources, and may be dependent on either high mass/thickness contrast thin-film masks or expensive multilayer x-ray reflecting masks. Presently, the technology required to produce adequate masks, such as microplating, anisotropic etching, and construction of large unstrained membranes requires enormous efforts for further reductions in feature sizes.
Photocathode electron projection lithography was first proposed in the 1970's as a way to generate large areas of sub-micron patterns. Projector systems were demonstrated and built, and were able to successfully print features in the 0.5 micron range. Typically, these systems used high power levels and low level magnetic fields—e.g., 20 keV accelerating voltages and magnetic fields of 0.1 Tesla.
In 1995, a group at AT&T Bell Laboratories reported results of a pilot study using lower energy electrons and higher magnetic fields, using gold as a photocathode. This system, however, still had certain problems, including sample heating, proximity effects, electrostatic charging and resist sensitivity.
SUMMARY
The present technique defines a new way of carrying out photocathode electron projection lithography to effect a pattern transfer which enables reducing the size of the eventual lines and features on the semiconductor device. This is carried out in a new way which avoids damage to the wafer being patterned. The system leverages off existing mask formation technology to form a system that can make sub-wavelength features.
The present system describes new materials that are used, new parameters for the process, and new techniques of operation. These features enable the technology to operate in an improved way. One such technique includes emitting a substantially monochromatic electron. Another technique uses an integer number of cyclotronic orbits, preferably 1 orbit. Yet another technique uses fields less than 5 Kev, and magnetic fields greater than 1.5 Tesla.
Unlike other proposed techniques, the masks that are proposed according to the preferred embodiment need only very thin layers of chromium to block the ultraviolet radiation source. These masks can be patterned with standard electron beam mask-making processes. As such, they can leverage off technology already in place from most e-beam mask vendors. Further reductions in feature sizes over large areas in the master masks are therefore mainly dependent on the fidelity of beam-written lithographic patterns, and do not require a complex pattern transfer processes. In modern direct electron-beam lithography systems, these dimensions can approach 30 nm.


REFERENCES:
patent: 3745358 (1973-07-01), Firtz et al.
patent: 3879613 (1975-04-01), Scott et al.
patent: 5294801 (1994-03-01), Aton et al.
patent: 5395738 (1995-03-01), Brandes et al.

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