Device fabrication by X-ray lithography utilizing stable boron nitride mask

DETAILED DESCRIPTION Hydrogen-containing (or hydrogenated) boron nitride of the type priorly used to form mask membranes for X-ray lithography exists in practice in different compositional forms.
The particularly form of hydrogenated boron nitride that is actually deposited is a function of the specific process parameters (e.
g.
, temperature, pressure, B.
sub.
2 H.
sub.
6 /NH.
sub.
3 ratio, B.
sub.
2 H.
sub.
6 partial pressure, etc.
) selected to deposit the material.
One particular form of known boron nitride may be represented as B.
sub.
3 NH.
This is the specific composition of the amorphous boron nitride investigated and reported upon in the aforeidentified article by Johnson et al.
As indicated earlier above, three radiation-induced effects in an X-ray mask membrane made of a known material such as B.
sub.
3 NH cause both the surface and bulk properties of the membrane to be deleteriously modified.
First, the aforementioned growths on the surface of the membrane are believed to result from the availability in the material of excess free boron.
Under irradiation, surface dangling bonds of boron are created.
In turn, these bonds can react with an oxygen environment to form growths of boric oxide crystallites.
These growths can degrade optical alignment signals.
Second, dangling boron bonds interior to the surface of the membrane can create midband gap traps (or color centers) which decrease the optical transparency of the membrane.
And, third, when a B.
sub.
3 NH membrane is irradiated at sufficiently high doses and dose rates, the bonding configurations of the hydrogen therein are modified such that more of the hydrogen becomes loosely bonded.
This in turn causes the membrane to become less tensile and to relax.
Such variable stress changes in the membrane can cause large and variable distortions in the mask pattern.
These variable changes cannot be tolerated if accurate overlay alignments are to be achieved in a multi-mask fabrication process.
In accordance with the principles of applicant's invention, a mask membrane for X-ray lithography is made of a material comprising hydrogen-free boron nitride