Semiconductor device manufacturing: process – Chemical etching – Liquid phase etching
Reexamination Certificate
2001-04-23
2004-06-29
Vinh, Lan (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Liquid phase etching
C438S691000, C438S706000, C438S749000, C438S750000, C216S072000
Reexamination Certificate
active
06756317
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to making a microstructure by surface micromachining. One aspect relates to making a structurally reinforced microstructure to provide a flatter profile on one or more of its structural layers. Another aspect relates to providing a plurality of at least generally laterally extending etch release channels to facilitate the release of the microstructure from the substrate.
BACKGROUND OF THE INVENTION
There are a number of microfabrication technologies that have been utilized for making microstructures (e.g., micromechanical devices, microelectromechanical devices) by what may be characterized as micromachining, including LIGA (Lithographie, Galvonoformung, Abformung), SLIGA (sacrificial LIGA), bulk micromachining, surface micromachining, micro electrodischarge machining (EDM), laser micromachining, 3-D stereolithography, and other techniques. Bulk micromachining has been utilized for making relatively simple micromechanical structures. Bulk micromachining generally entails cutting or machining a bulk substrate using an appropriate etchant (e.g., using liquid crystal-plane selective etchants; using deep reactive ion etching techniques). Another micromachining technique that allows for the formation of significantly more complex microstructures is surface micromachining. Surface micromachining generally entails depositing alternate layers of structural material and sacrificial material using an appropriate substrate which functions as the foundation for the resulting microstructure. Various patterning operations may be executed on one or more of these layers before the next layer is deposited so as to define the desired microstructure. After the microstructure has been defined in this general manner, the various sacrificial layers are removed by exposing the microstructure and the various sacrificial layers to one or more etchants. This is commonly called “releasing” the microstructure from the substrate, typically to allow at least some degree of relative movement between the microstructure and the substrate. Although the etchant may be biased to the sacrificial material, it may have some effect on the structural material over time as well. Therefore, it is generally desirable to reduce the time required to release the microstructure to reduce the potential for damage to its structure.
Microstructures are getting a significant amount of attention in the field of optical switches. Microstructure-based optical switches include one or more mirror microstructures. Access to the sacrificial material that underlies the support layer that defines a given mirror microstructure is commonly realized by forming a plurality of small etch release holes down through the entire thickness or vertical extent of the mirror microstructure (e.g., vertically extending/disposed etch release holes). The presence of these small holes on the upper surface of the mirror microstructure has an obvious detrimental effect on its optical performance capabilities. Another factor that may have an effect on the optical performance capabilities of such a mirror microstructure is its overall flatness, which may be related to the rigidity of the mirror microstructure. “Flatness” may be defined in relation to a radius of curvature of an upper surface of the mirror microstructure. This upper surface may be generally convex or generally concave. Known surface micromachined mirror microstructures have a radius of curvature of no more than about 0.65 meters.
BRIEF SUMMARY OF THE INVENTION
The present invention is generally embodied in a method for making a microstructure by surface micromachining. In this method, at least one and more typically a plurality of at least generally laterally extending etch release channels or conduits are formed within a sacrificial material. This sacrificial material is used to fabricate the microstructure on an appropriate substrate. At least some of this sacrificial material is removed when the microstructure is released from the substrate (and thereby encompassing the situation where all of this sacrificial material is removed).
A first aspect of the present invention is embodied in a method for making a microstructure by surface micromachining that includes forming a first structural layer over a sacrificial material. “Over” includes being deposited directly on the substrate or being deposited on an intermediate layer that is disposed between the subject sacrificial layer and the substrate. “On” in contrast means that there is an interfacing relation. In any case, a plurality of hollow etch release pipes, channels, conduits, or the like extend at least generally laterally through/within this sacrificial material. Lateral or the like, as used herein, means that the etch release conduits are disposed or oriented in a direction which is at least generally parallel with the substrate. Although the etch release conduits will typically extend laterally at a constant elevation relative to the substrate, such need not necessarily be the case. Ultimately, at least some of the sacrificial material is removed at least in part by allowing an etchant to flow through any and all of these hollow etch release conduits (and thereby encompassing the situation where all of this sacrificial layer is removed).
Various refinements exist of the features noted in relation to the first aspect of the present invention. Further features may also be incorporated in the first aspect of the present invention as well. These refinements and additional features may exist individually or in any combination. In one embodiment, at least one end of at least one etch release conduit may be disposed at least generally at the same radial position as a perimeter of the first structural layer. Hereafter, “at least generally at the same radial position” in relation to any end of any etch release conduit or structure used to define the same means within 50 &mgr;m of the radial position of the perimeter of the relevant structural layer in one embodiment, more preferably within 25 &mgr;m of the radial position of the perimeter of the relevant structural layer in another embodiment, and even more preferably at the same radial position as the perimeter of the relevant structural layer. As such, the etchant does not have to etch in from the perimeter “too far” before encountering an open end of one or more etch release conduits associated with the first aspect. Reducing the time required for the etchant to reach the etch release conduits should at least to a point reduce the overall time for accomplishing the release of the microstructure from the substrate.
Various layouts of the plurality of etch release conduits in the noted lateral dimension may be utilized in relation to the first aspect. In one embodiment, each of the plurality of etch release conduits may be disposed in non-intersecting relation, in another embodiment the plurality of etch release conduits are disposed in at least substantially parallel relation, and in yet another embodiment at least some of the etch release conduits intersect. The plurality of etch release conduits may extend at least generally toward (and thereby including to) a common point, such as one that corresponds with a center of the first structural layer in the lateral dimension. All etch release conduits need not extend the same distance toward this common point, although such may be the case. Some of the plurality of etch release conduits may extend at least generally toward (and thereby including to) a first common point (e.g., one that corresponds with a center of the first structural layer in the lateral dimension), while some of the plurality of etch release conduits may extend toward a different common point. The plurality of etch release conduits may also extend in the lateral dimension in a variety of configurations. In one embodiment, the plurality of etch release conduits are at least generally axially extending, while in another embodiment the plurality of etch release conduits are non-linear (e.g., in a sinusoidal configur
Rodgers M. Steven
Sniegowski Jeffry J.
Marsh & Fischmann & Breyfogle LLP
MEMX, Inc.
Vinh Lan
LandOfFree
Method for making a microstructure by surface micromachining 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 for making a microstructure by surface micromachining, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for making a microstructure by surface micromachining will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3349174