Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2000-02-09
2002-08-27
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
Reexamination Certificate
active
06440615
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of repair a scattering stencil type mask utilized in the electron-beam projection lithography systems.
2. Description of the Related Art
In manufacture of semiconductor elements such as IC and LSI, a lithography process is used to create fine circuit patterns on a semiconductor substrate. The performance of the semiconductor elements is mostly determined by the number of circuits provided in each element, which significantly dependent on the size of patterns of circuits. The recent developments in semiconductor integrated circuit production technology have been remarkable, and show a strong tendency toward miniaturization and further integration. As a method of forming an integrated circuit pattern on semiconductor substrates, a lithography method utilizing ultraviolet light is commonly used.
However, with the further miniaturization of the circuit pattern, it has been a concern that the resolution of the light is approaching its limit. Thus, the high-resolution lithography technology using a charged particle beam such as electron beam and ion beam, or X-ray is being examined. For example, since exposure technology utilizing a charged particle beam can make the beam diameter to be as small as order of nm, it is characterized by that a miniaturized pattern below 100 nm can be easily formed, and an electron beam writing technology has been known for a long time. However, in so-called direct-writing method where the writing is performed by scanning very fine electron beam, it takes a very long time to form a large-area or large-size pattern, that is, the throughput (a processing rate per unit time) is low. For that reason, a photolithography method where the light source is ultraviolet light is still being used as the lithography method of manufacturing the semiconductor integrated circuits, while the electron beam direct-writing method is used only in limited fields such as in manufacturing of reticles, or masks, for use with photolithography and trial manufacturing of devices for the purpose of experimentation.
Then, in order to solve such a problem, lithography technology EBPS (Electron Beam Projection System) is proposed, in which, instead of a direct writing by a charged particle, a predetermined reticle pattern is transferred by reduction-projection on a wafer by means of an electron optical system.
For example, Jpn. J. Appl. Phys. 34 (1995), page 6658, explains the electron beam lithography technology in terms of its development from the direct writing method using an electron beam as a projection light source, to a method of projection exposure with variable axis immersion lenses.
As a reticle used in the EBPS, it seems that a scattering stencil type thereof is desirable in light of the exposure characteristics. The scattering stencil type includes a pattern portion to be exposed which consists of voids or openings and a supporting structure, membrane. The method for forming a scattering stencil type reticle is such that an oxide film is formed on a silicon substrate and then a predetermined pattern is formed on this oxide film. The silicon substrate is then etched in accordance with this pattern.
For this scattering stencil type reticle, a pattern defect is always caused at the time of forming the reticle. Namely, there are occasions where the material is absent in the necessary electron beam scattering material pattern (clear defect), or an extra material is occurred due to an additional amount of electron beam scattering material (opaque defect). In general, it is considered that the clear pattern is caused by an error made at the time when the pattern is projected onto a membrane (at the time of the resist-pattern writing), so that the portion where the resist pattern is missing becomes itself a clear defect. On the other hand, a opaque defect is the electron beam scattering material which has remained in unwanted areas due to the fact that such foreign materials or the like, for example one that could become an etching mask, adheres to the resist pattern.
As a method which repairs a opaque defect, it is possible to undertake selective milling by irradiating a charged particle beam such as a focused ion beam so as to perform pattern correction thereof. However, there is a problem that after the milling is once performed the material adheres again to a portion of the pattern. Since this portion with adhered material might become a opaque defect depending on the size thereof, this portion will have to be pattern-corrected at a later stage. Thus an etching method is needed by which the material adhered can be suppressed as much as possible.
A gas-assist etching is suggested as a method, which solves the problem of material adhertion as described above. The gas-assist etching is a method in which the etching is performed using a focused ion beam, while material to be etched and gas which is liable to chemically react are supplied at a suitable level thereof in the vicinity of the portion to be etched. Though this etching can suppress the material adhered to a certain degree; it does not suppress it completely. Moreover, though the gas to be supplied has a low etching capacity, the gas corrodes the material to be etched. Thus it is difficult to appropriately control the shape of a cross section of a portion to be processed.
Since these defects in the reticles also occur in photomasks for use in ultraviolet light exposure, a reticle repair device is used for correcting the defects of photomasks. In this reticle repair device, the opaque defect is corrected using an ion beam etching method, by locally removing the chrome serving as a shielding material. A clear defect is corrected using the method of Focused Ion Beam (FIB)-Induced Deposition using a focused ion beam, by locally coating a carbon film. Moreover, it is considered reasonable that when a mask is used in the X-ray equi-multiple exposure method, or EUV lithography, which is in the course of being developed both opaque defect repair and clear defect repair can be accomplished by a focused ion beam.
In a scattering stencil type reticle used in electron beam reduction projection lithography with an electron beam serving as an exposure source, we are faced with the following new problems, which do not exist in the conventional reticles:
(1) Since the reduction projection lithography method using an electron beam concerns a technology forming a pattern of less than 0.1 &mgr;m, it is necessary to form an electron scattering material pattern of less than 0.4 &mgr;m on the reticle in the event that the reduction factor is one forth. On the other hand, as the electron beam scattering material requires a thickness of approximately 2 &mgr;m, the aspect ratio of the electron beam scattering material pattern is approximately 5. Since severe specification is required for the size of a portion to be processed in a reticle and a cross sectional shape thereof, the miniaturization processing for the reticle requires an advanced processing technique as the aspect ratio increases, thus its processing becomes excessively difficult to carry out.
(2) The reticle, or mask, used in reduction projection lithography using an electron beam is constituted by the electron beam scattering material alone, and is of so-called scattering stencil type. Namely, in this scattering stencil type mask, a pattern of an electron beam scattering material is not formed on the substrate which is illuminated by the electron beam, instead, the region which is illuminated by the electron beam is opened, so that the projected pattern is formed and consists of the electron beam scattering material alone. In scattering stencil reticle, incident beam is usually absorbed by the membrane or substrate but can pass through void, aperture, opening which forms a pattern. In scattering stencil reticle, incident beam is scattered by the membrane or substrate but can pass through void, aperture, opening which form pattern to be projected. In scattering membrane reticle, incident
Chapman and Cutler
Nikon Corporation
Rosasco S.
LandOfFree
Method of repairing a mask with high electron scattering and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of repairing a mask with high electron scattering and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of repairing a mask with high electron scattering and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2895354