At&t Bell Laboratories

Lucent Technologies Inc.

At+t Corp.

Robert L Kostelak, Jr

Sheila Vaidya

Joseph G Garofalo

Christophe Pierrat

John J DeMarco

William T Lynch

Taeho Kook

An attenuating phase-shifting optical lithographic mask is fabricated, in a specific embodiment of the invention, by first depositing a uniformly thick molybdenum silicide layer on a top planar surface of quartz. The molybdenum silicide layer has a thickness sufficient for acting as an attenuating (partially transparent) layer in a phase-shifting mask. A uniformly thick chromium layer is deposited on the molybdenum silicide layer. The chromium layer has a thickness sufficient for acting as an opaque layer in the phase-shifting mask. Next, the chromium layer is patterned by dry or wet etching, while the chromium is selectively masked with a patterned resist layer. Then the molybdenum silicide is patterned by dry or wet etching, using the patterned chromium layer as a protective layer, whereby a composite layer of molybdenum silicide and chromium is formed having mutually separated composite stripes. Any remaining resist is removed. Next the top and sidewall surfaces of some, but not others, of these mutually separated stripes are coated with a second patterned resist layer. Finally, the chromium layer, but not the molybdenum silicide layer, is removed from the others of the mutually separated composite stripes.

Self-aligned opaque regions for attenuating phase-shifting masks

A phase-shifting optical lithographic mask is made by a method that produces a set of phase shifting features (11) located in phase-shifting areas and a set of reinforced alignment marks (13, 33) located in alignment areas of the mask. Both of these sets are located on a single slab of quartz (10). The method involves a lift-off step that results in the self-alignment of the alignment marks with respect to the phase-shifting features. All of the phase-shifting features together with all of the alignment marks are patterned during a single step, and all of them comprise a bottom layer (11) of common material and common thickness so as to be partially transparent to optical radiation used in an optical lithographic system. Typically the bottom layer is essentially chromium oxynitride. In order to suppress optical radiation leakage from the phase-shifting features to the alignment mark areas, a reinforced alignment-mark shutter layer (12, 32) is located between the reinforced alignment marks and the phase-shifting areas, and it is made simultaneously with the reinforced alignment marks. And in order to suppress optical radiation leakage from one chip area to another chip area, both located on a single wafer, a reinforced chip shutter layer (14, 34) is also made simultaneously with the reinforced alignment marks and is located between chip areas.

Self-aligned alignment marks for phase-shifting masks

In order to print an isolated feature having a width W in a photoresist layer using an optical radiation imaging system whose lateral magnification is equal to m, a phase-shifting mask is used having a corresponding isolated feature. In one embodiment this corresponding isolated feature has a central square portion having a refractive index n.sub.1 and a thickness t.sub.1, and a peripheral (rim) square-ring phase-shifting portion having a width B, as well as a refractive index n.sub.2 and a thickness t.sub.2, such that the phase-shift .phi.=2.pi.(n.sub.2 t.sub.2 -n.sub.1 t.sub.1)/.lambda. of the central portion relative to the peripheral portion is equal to .pi. radian or odd multiple integral thereof. The width C of the central portion advantageously is selected such that mC/W is equal to at least 1.2, and preferably greater than 1.5, rather than unity. In another embodiment, the isolated feature has an opaque central portion, also of width C, and a peripheral square-ring phase-shifting portion having a width B and having a phase-shift of .pi. radian relative to a surrounding transparent wide area ('bright field')--in which case, advantageously the value of m(C+2B)/W is equal to less than 1/(1.2), and preferably less than 1/(1.5).

Phase-shifting lithographic masks with improved resolution

A phase-shifting lithographic mask is fabricated, in one embodiment, by using a resist layer that is negative tone with respect to a (patterned) electron beam and is positive tone with respect to a (flood) mid-ultraviolet beam, with the tone of the electron beam predominating over that of the mid-ultraviolet beam. The resist layer is spun on a body comprising a patterned metallic layer located on a (transparent) quartz slab. The body is subjected from below to a flood mid-ultraviolet beam and from above to a patterned electron beam whose edges are located somewhere in the midst of the patterned opaque layer but are not coincident with any edges of the patterned opaque layer. Thus, a subsequent development of the resist layer removes those regions and only those regions of the resist layer upon which the ultraviolet beam was incident--i.e., not in the shadows cast by the patterned opaque layer--in the absence of incidence of the patterned electron beam. Then, an anisotropic etching removes to a prescribed depth the portions of the (transparent) substrate not covered by the remaining (patterned) resist layer. In other embodiments, the (patterned) electron beam is replaced by a (patterned) deep ultraviolet beam. In still other embodiments the same radiation (wavelength) can be used for the patterned beam as for the flood radiation in conjunction with a resist layer whose tone can be reversed by an intermediate processing step between irradiations with the patterned and flood beams, respectively.

Fabrication of phase-shifting lithographic masks

A phase-shifting lithographic mask is made by a procedure involving only a single patterned electron, ion, or photon beam bombardment of a resist layer. The bombardment is arranged to produce three kinds of regions in the resist: no dosage, low dosage, and high dosage. These three regions in the resist are then utilized--in conjunction with an ordinary wet development step followed by either a silylation or an optical flooding technique, and thereafter by another ordinary wet development step--to pattern the resist layer and thereby to enable forming, by dry or wet etching, an underlying double layer consisting of a patterned opaque layer and a patterned transparent phase-shifting layer, the phase-shifting layer being located on, or being part of, a transparent substrate.

Single-alignment-level lithographic technique for achieving self-aligned

Phase-shifting (two-optical-level) masks are manufactured by a self-aligned technique in which after first-level trenches in the mask have been formed, second-level trenches therein are formed by patterning an electron resist overlying the mask in such a manner that the edges of the patterned resist can be located anywhere within the first-level trenches, whereby the need for precise alignment of the resist patterning for the second-level trenches is avoided.

Method of making phase-shifting lithographic masks

In order to reduce alignment errors arising in the fabrication of semiconductor integrated circuits using electron beam lithography, enhanced registration marks--(i.e., registration marks that are more easily and accurately detectable by the electron beam)--are formed at the edges of oxide layers, located at the surface of a silicon body, by means of forming metal silicide layers having edges coincident with the edges of the oxide layers. Advantageously, the enhancing of the registgration marks by forming the metal silicide is performed subsequent to any high temperature processing steps, whereby the integrity of the marks is maintained.

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Morris Plains, NJ, United States of America

Robert L Kostelak, Jr