The present invention relates to controlling the contact area of cantilever-based micro-electromechanical devices for use in, for example, semiconductor device technology.
A significant problem impeding the progress of micro-electromechanical devices (MEMS) is the propensity for cantilever structures to “stick” to electrode(s) or electrodes to stick to one another upon contact, making it difficult to separate the surfaces. The adhesive forces behind this phenomenon are generally and collectively known as “stiction”. Stiction refers to various forces tending to make two surfaces adhere to each other. Such forces include Van der Waals forces, surface tension caused by moisture between surfaces and bonding between surfaces (e.g. through metallic diffusion).
One solution to the problem of stiction is to provide MEMS devices which are made of materials having high spring constants. When, under the effect of electromagnetic forces, the cantilever structures of these MEMS devices are bowed in order to be brought into contact with an electrode so as to, for example, close a switch, the bending of the material creates a restorative force in the device that naturally seeks to break the contact between the surface of the device and the surface of the electrode. Such a force, if sufficient in magnitude, can overcome the effects of stiction. However, devices using this approach have poor scalability in that, the smaller a cantilever structure becomes, the less resilient is becomes.
A first solution to this problem has been sought in the application of thin (often mono-layer) coatings to the contact area of the cantilever structure and/or the electrode, thereby reducing the surface contact between the two elements. However, this solution provides a serious disadvantage in that these surface coatings are non-conductive and therefore prevent the transfer of charge from one element to another. They are therefore not suitable for applications requiring charge transfer.
A second solution to this problem has been sought in what is known as “bump technology”. This method involves the step of patterning and etching a protrusion on the surface of an electrode which is to come into contact with a cantilever structure. Although this does solve the problem of controlling the contact area between the cantilever structure and the electrode, it requires an extra masking step in the fabrication process. This will add to the complexity and the cost involved in manufacturing the MEMS device.
There is therefore a clear need for a method of manufacturing a cantilever-based MEMS device where the contact area between the cantilever structure and the contact electrode can be controlled, without the need for extra masking steps and without the need to degrade the conductivity of the contact area.
In order to solve the problems associated with the prior art, the present invention provides a method of manufacturing a cantilever-based micro-electromechanical device, the method comprises the steps of:
providing a first conductive material layer on a substrate;
patterning and etching the first conductive material layer to from a plurality of electrodes;
depositing a sacrificial material layer on the electrodes and substrate, thereby defining a non-exposed surface of the sacrificial material layer, the non-exposed surface of the sacrificial material layer adjoining the plurality of electrodes and an exposed surface of the sacrificial material, the exposed surface of the sacrificial material layer being opposed to the non-exposed surface of the sacrificial material layer;
patterning and etching the sacrificial material layer such that at least a portion of at least one electrode is exposed;
sputter etching the sacrificial material layer such that the exposed surface of the sacrificial material layer comprises edges which are incongruous with the edges of the non-exposed surface of the sacrificial material layer;
depositing a second conducting material layer on the at least one exposed electrode and exposed surface of the sacrificial material layer;
patterning and etching the second conducting material layer in order to form a cantilever structure;
removing at least a portion of the sacrificial material layer such that at least a portion of the cantilever structure is suspended.
Preferably, the sacrificial material layer is an etchable material layer.
Preferably, the first and second conducting layers are formed from a group of materials selected from Nickel, Copper, Chromium, Cobalt, Zinc, Iron, Titanium, Aluminum, Tantalum, Ruthenium Platinum and Cobalt, including their alloys or compounds.
Preferably, the first and second conducting layers are made from titanium nitride or tantalum nitride.
Preferably, the sacrificial material layer is made form silicon-based materials or carbon-based materials.
Preferably, silicon based materials include silicon-nitride, amorphous silicon, silicon oxide and a spin on glass material.
Preferably, carbon based materials include amorphous carbon or polyimide
Preferably, the step of removing at least a portion of the sacrificial material layer further comprises the step of:
etching at least a portion of the sacrificial material layer using a nitrogen trifluoride or sulphur hexafluroide in an RF or microwave plasma etching process.
Preferably, the step of removing at least a portion of the sacrificial material layer further comprises the step of:
etching at least a portion of the sacrificial material layer using oxygen in a plasma etching process.
As will be appreciated by a person skilled in the art, the present invention provides several advantages over the prior art. First of all, the present invention provides a method of controlling the contact area between a cantilever structure and an electrode which does not require any extra masking steps. Moreover, the contact area of the present invention will not be adversely affected by any non-conductive thin films. Therefore, the device of the present invention can be used in applications such as radio frequency switches, micro relays and memory.
Examples of the present invention will now be described with reference to the accompanying drawings, in which:
a shows a plan view of the device having an electrode with a selective opening;
b shows an end view of the tip of device indicating the points of contact of the structural element with the electrode;
c shows an end view of the tip of device indicating where a misaligned structural element makes contact with the electrode.
With reference to
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The next step in the method is the removal of the sacrificial layer 400. This step may include using a fluorine source gas, preferably nitrogen trifluoride or sulphur hexafluoride in an etching process or an RF or microwave plasma etching process. Removing at least a portion of the sacrificial layer may include using oxygen gas in a plasma etching process.
Now, with reference to
Accordingly, the cantilever structure of the present invention will be permitted to contact the third electrode 303, allowing a transfer of charge to take place, but will not be permitted to directly adjoin or entirely cover the third electrode 303, thereby minimising (or otherwise controlling) the effects of stiction forces without the need for extra masking steps in the process.
a shows a top view of the cantilever structure 501 and the two electrodes 302 and 303. Electrode 303 has “U” shape as viewed from the top. The cantilever 501 width is wider than the spacing between the two lateral portions of the “U”.
b and 11c show a cross-section view through the end of the cantilever perpendicular to the plane of the substrate and the longitudinal direction of the cantilever 501.
Number | Date | Country | Kind |
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0523715.1 | Nov 2005 | GB | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/GB2006/004354 | 11/22/2006 | WO | 00 | 5/22/2008 |