Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2000-12-21
2004-02-24
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C430S330000
Reexamination Certificate
active
06696205
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to electron projection lithography (EPL), and more particular, to an apparatus and method for forming a mask blank having a single transition metal-based scattering layer with a final stress state substantially close to a desired final stress for use in lithographic mask formation in EPL systems.
2. Description of Related Art
In modern semiconductor development, semiconductors having decreased feature sizes are increasingly desired, particularly those having feature sizes of 100 nm or smaller. As conventional optical lithographic systems are limited to feature sizes of about 250 nm, one area of focus in developing such modem semiconductors has been to provide lithographic masks with continually decreasing feature sizes while still maintaining the speed, performance, and reliability of the resultant semiconductor.
Utilization of lithographic sources with shorter wavelengths such as x-rays and electron beams provide the potential to meet such feature size requirements of 100 nm or smaller. In x-ray and electron beam lithography (EPL) systems, masks such as membrane masks are required to meet the smaller feature size requirements. The use of membrane masks for x-ray and EPL systems are well known in the art. Typically, the masks are fabricated by depositing a thick absorber layer to a thickness ranging from 300 nm to 1000 nm, or a thin scattering layer for EPL systems to a thickness ranging from 30 nm to 50 nm over a substrate having a thin membrane layer on a surface thereof. The thin membrane layer typically comprises a highly doped silicon, silicon nitride, silicon carbide, diamond or materials as known and used in the art deposited to a thickness of 2-3 microns for use in x-ray lithography and to a thickness of 100-200 nm thick for use in EPL. The x-rays or electron beams pass through the thin membrane layer without significant diffraction or absorption loss.
Electron-beam projection lithography (EPL) systems are well known in the art of semiconductor formation such as SCALPEL and PREVAIL, for example. As illustrated in the prior art EPL mask of
FIGS. 1A-B
, a mask blank
10
may be provided for forming the mask over the substrate. As illustrated in
FIG. 1A
, the mask blank
10
may comprise a thin membrane layer
14
, followed by an etch stop layer
16
and an overlying scattering layer
18
, provided over a substrate surface
12
. As will be recognized, the overlying scattering layer may be a multi-film scattering layer or a single film scattering layer.
As illustrated in
FIG. 1B
, once the absorber or scattering layer has been deposited over the membrane layer on the substrate, a membrane pattern is typically etched through the substrate from the backside using the membrane material as an etch stop, whereby the absorber or scattering layer is then patterned and etched to complete the mask. The absorption or scattering of incident energy by the patterned layer on top of the membrane then gives rise to the image on an underlying substrate coated with photoresist for subsequent device fabrication.
Typically, the scattering layer of the thin mask blanks used in EPL systems are formed over a membrane layer on the substrate by a multi-deposition process of first sputter depositing the etch stop layer over the membrane layer followed by deposition of a scattering layer thereover the etch stop layer. Typically, the etch stop layer comprises a thin chromium film while the scattering layer comprises a tungsten film. In depositing the etch stop and scattering layers of conventional mask blanks used in EPL systems, the multi-layer deposition processes generally require separate targets and separate deposition chambers or tools for the etch stop and scattering layers, whereby the substrate may be required to be moved from one chamber to the next. In depositing the etch stop and scattering layers, the as-deposited stress of the etch stop layer is typically tensile, i.e. positive, while the as-deposited stress of the scattering layer is typically compressive, i.e. negative, resulting in a combined film stack stress of the mask blank being either tensile or compressive. However, in order to obtain sufficient and reliable subsequent pattern placement on the finished mask, it is necessary that the mask blank for use in EPL systems have a combined film stack stress as close to zero as possible for subsequent mask finishing procedures.
In recognizing the above problem, prior art is aimed at controlling both stresses and thicknesses of both the etch stop and scattering layers of the mask blank during deposition procedures to produce a resultant combined film stack having a zero stress state for subsequent pattern placement on the finished mask blank to form a mask for use in EPL systems. However, conventional processes of forming EPL mask blanks also create scattering layer stacks with vertical regions of sharply different stresses, resulting in a final film stack stress of the mask blank varying significantly from substrate to substrate within a single lot of substrates, wherein some stacks possess unacceptable tensile or compressive stresses. As a result of some stacks possessing unacceptable tensile or compressive stresses, subsequent mask finishing procedures result in a final mask having reduced yield requiring additional fabrication steps as well as increased manufacturing times and costs to correct or produce an efficient mask for use in EPL systems.
In controlling the stress of the thick absorber films, prior art is further directed to controlling the stresses in thick absorber layers, such as those thick absorber films for use in x-ray mask, by re-annealing an absorber layer on a single substrate in a two-part annealing process. For example, a two step annealing process for developing and controlling stress in thick absorber films, such as those having thicknesses ranging from 300 nm to 1000 nm, may be used whereby a substrate having a thick absorbing layer is annealed in a first anneal step, the stress of the absorbing layer measured, and subsequently further annealing the same substrate to obtain a near zero stress state of the thick x-ray absorbing scattering layer.
As modern semiconductors continue to decrease in size, and therewith the thin scattering layers of mask blanks for use in EPL systems, a need continues to exist in the art to provide improved methods of making such thin scattering layers for use in the modern, smaller mask blanks for use in EPL systems, whereby the thin scattering layers have as-deposited internal stress states substantially near zero, or alternatively slightly tensile.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide an improved apparatus and method of forming a thin scattering layer for use in an improved mask blank for EPL systems whereby the improved thin scattering layer has a final stress state as near as possible to a desired stress, or stress range, such as stress states substantially close to zero, or alternatively slightly tensile.
It is another object of the present invention to provide an apparatus and method for eliminating the need for a multiple deposition and/or multi-layer deposition process for forming mask blanks for use in EPL systems.
Yet another object of the present invention is to provide a method of forming and a thin scattering layer having a high scattering cross section evident in high atomic number or highly dense materials.
It is another object of the present invention to provide an apparatus and method of forming a thin scattering layer having desirable etch characteristics.
Another object of the present invention is to provide a method of forming and a thin scattering layer having increased control of the final stress states of the thin scattering layer.
Still another object of the present invention is to provide a method of forming and a thin scattering layer whereby stress control is maintained from substrate to substrate in a single lot.
It is ano
Brooks Cameron J.
Racette Kenneth C.
DeLio & Peterson LLC
International Business Machines - Corporation
Kotulak Richard M.
Mohamedulla Saleha R.
Reynolds Kelly M.
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