Patent Abstract:
A method for pseudo-planarization of an electromechanical device and for forming a durable metal contact on the electromechanical device and devices formed by the method are presented. The method comprises acts of depositing various layers forming a semiconductor device. Two principal aspects of the method include the formation of a planarized dielectric/conductor layer on a substrate and the formation of an electrode in an armature of a microelectromechanical switch, with the electrode formed such that it interlocks a structural layer of the armature to ensure it remains fixed to the armature over a large number of cycles.

Full Description:
PRIORITY CLAIM 
   This application claims the benefit of priority to provisional application No. 60/541,201, filed in the United States on Feb. 2, 2004, and titled “A FABRICATION METHOD FOR MAKING A PLANAR CANTILEVER, LOW SURFACE LEAKAGE, REPRODUCIBLE AND RELIABLE METAL DIMPLE CONTACT MICRO-RELAY MEMS SWITCH.” 

   BACKGROUND OF THE INVENTION 
   (1) Technical Field 
   The present invention relates to a fabrication technique for a micro-electro-mechanical system (MEMS) micro relay switch to increase the reliability, yield, and performance of its contacts. Specifically, the invention relates to a planarization process for the cantilever beam, surface passivation of the substrate, and a unique design of the metal dimple for making a reproducible and reliable contact. 
   (2) Discussion 
   Today, there are two types of MEMS switches for RF and microwave applications. One type is the capacitance membrane switch known as the shunt switch, and the other is the metal contact switch known as the series switch. Besides the two types of switches mentioned above, designs can vary depending on the methods with which the switches are actuated. Generally, switch designs are based on either electrostatic, thermal, piezoelectric, or magnetic actuation methods. 
   The metal contact series switch is a true mechanical switch in the sense that it toggles up (open) and down (close). One difference among the metal contact switch designs is in their armature structure. For example, switches from Sandia National Labs and Teravita Technologies use an all metal armature. MEMS switches from Rockwell use an armature composed of a metal layer on top of an insulator and switches from HRL Laboratories, LLC use an insulating armature having a metal electrode that is sandwiched between two insulating layers. Because of the difference in armature designs, metal contacts in these devices are all fabricated differently; however, in each of these designs the metal contacts are all integrated with part of the armature. The performance of these switches is mainly determined by the metal contact and the armature design. One important issue, occurring when the metal contact is part of the armature, relates to the fabrication process, wherein performance may be sacrificed if the contact is not well controlled. 
   U.S. Pat. No. 6,046,659 issued Apr. 4, 2000 to Loo et al. (herein after referred to as the “Loo Patent”) discloses two types of micro-electro-mechanical system (MEMS) switches, an I-switch and a T-switch. In the “Loo Patent”, both the I and T-MEMS switches utilize an armature design, where one end of an armature is affixed to an anchor electrode and the other end of the armature rests above a contact electrode. 
     FIG. 1A  depicts a top view of a T-switch  100  as disclosed in the prior art. A cross-section of the switch shown in  FIG. 1A  is shown in  FIGS. 1B and 1C . In  FIG. 1B  the switch is in an open position, while in  FIG. 1C , the switch is in a closed position. In this aspect, a radio-frequency (RF) input transmission line  118  and a RF-output transmission line  120  are disposed on the substrate  114 , shown in  FIG. 1B. A  conducting transmission line  128  is disposed across one end of an armature  116 , allowing for connection between the RF-input transmission line  118  and the RF-output transmission line  120  when the switch is in the closed position. One skilled in the art will appreciate that the cross-section only shows the contact of the armature  116  with the RF-output transmission line  120 , since the contact of the armature  116  with the RF-input transmission line  118  is directly behind the RF-output transmission line  120  when looking at the cross-section of the switch. Thus, for ease of explanation,  FIGS. 1B and 1C  will be discussed emphasizing the RF-output transmission line  120 ; however, the same explanation also holds for contacting of the RF-input transmission line  118 . Further, one skilled in the art will appreciate that the RF-input and RF-output transmission lines are labeled as such for convenience purposes only and are interchangeable. 
   When the switch is in an open position, the transmission line  128  sits above (a small distance from) the RF-input transmission line  118  and the RF-output transmission line  120 . Thus, the transmission line  128  is electrically isolated from both the RF-input transmission line  118  and the RF-output transmission line  120 . Furthermore, because the RF-input transmission line  118  is not connected with the RF-output transmission line  120 , the RF signals are blocked and they cannot conduct from the RF-input transmission line  118  to the RF-output transmission line  120 . 
   When the switch is in closed position, the conducting transmission line  128  is in electrical contact with both the RF-output transmission line  120 , and the RF-input transmission line  118 . Consequently, the three transmission lines  120 ,  128 , and  118  are connected in series to form a single transmission line in order to conduct RF signals. The “Loo Patent” also provides switches that have conducting dimples  124  and  124 ′ attached with the transmission line  128  which define metal contact areas to improve contact characteristics. 
     FIG. 1B  is a side view of a prior art micro-electro-mechanical system (MEMS) switch  100  of  FIG. 1A  in an open position. A conducting dimple  124  protrudes from the armature  116  toward the RF-output transmission line  120 . The transmission line  128  (shown in  FIG. 1A ) is deposited on the armature  116  and electrically connects the dimple  124  associated with the RF-output transmission line  120  to another dimple  124 ′ associated with the RF-input transmission line  118 . 
     FIG. 1C  depicts the MEMS switch  100  of  FIG. 1A  in a closed state. When a voltage is applied between a suspended armature bias electrode  130  and a substrate bias electrode  122 , an electrostatic attractive force will pull the suspended armature bias electrode  130  as well as the attached armature  116  toward the substrate bias electrode  122 , and the (metal) contact dimple  124  will touch the RF-output transmission line  120 . The contact dimple  124  associated with the RF-input transmission line  118  will also come into contact with the RF-input transmission line  118 , thus through the transmission line  128  (shown in  FIG. 1A ) the RF-input transmission line  118  is electrically connected with the RF-output transmission line  120  when the switch is in a closed position. Note that in the  FIG. 1A , the armature  116  is anchored to the substrate  114  by an anchor  132  and that bias input signal pads  134  and  136  are provided for supplying power necessary for closing the switch  100 . 
     FIG. 2A  depicts a top view of an I-switch  200  as disclosed in the prior art.  FIG. 2B  depicts a direct current (DC) cross-section of the switch  200  while,  FIG. 2C  depicts a RF cross-section of the switch  200 . In  FIG. 2B , a DC signal is passed from the DC contact  220  through an anchor point  222  and into a DC cantilever structure  224 . A substrate bias electrode  226  is positioned on the substrate  114 . As a DC bias is applied to the DC contact  220  and the substrate bias electrode  226 , the DC cantilever structure  224  is pulled toward the substrate  114 , causing the RF cantilever structure  215  (shown in FIG.  2 C), shown in  FIG. 2A , to also be deflected toward the substrate  114 .  FIGS. 2D and 2E  depict the switch  200  in the closed position from the same perspectives as shown in  FIGS. 2B and 2C , respectively. 
     FIG. 2C  depicts the RF cross-section of switch  200 . The RF-input transmission line  210  passes through anchor point  214  and into the RF cantilever structure  215 . The metal dimple  216  protrudes from the RF cantilever structure  215 . For ease of explanation the RF cantilever structure  215  and the DC cantilever structure  224  are described herein as two separate structures; however, one skilled in the art will appreciate that these two structures are typically made of one piece of material. The metal dimple  216  provides an electrical contact between the RF-input transmission line  210  and the RF-output transmission line  212 . As discussed above, when a DC bias is applied to the DC contact  210  and the substrate bias electrode  226  (shown in FIG.  2 B), the RF cantilever structure  215  is deflected toward the substrate  114 . The deflection of the RF cantilever structure  215  toward the substrate  114  provides an electrical path between the RF-input transmission line  210  and the RF-output transmission line  212 .  FIGS. 2D and 2E  depict the switch  200  in the closed position from the same perspectives as shown in  FIGS. 2B and 2C , respectively. Note that in  FIG. 2A  the path shown in  FIGS. 2B and 2D  is depicted between  200   b  and  200   b ′ in and that the path shown in  FIGS. 2C and 2E  is depicted between  200   c  and  200   c′.    
   The process of forming the dimple on the armature requires carefully controlled etching times. The dimple is typically formed by first depositing an armature on top of a sacrificial layer. Then a hole is etched through the armature into the sacrificial layer immediately above the RF-input and/or output transmission line. The dimple is then deposited to fill the etched hole. In this case, the height of the dimple depends on the depth of the etching through the hole into the sacrificial layer. This etching process is monitored by time. The time required to obtain the proper etch depth is mainly determined from trial and error etching experiments. Because the etching is a time-controlled process, the etch depth may vary from run to run and from batch to batch depending upon the etching equipment parameters. Thus, the quality of the contact will vary from run to run. For example, if the dimple is made too shallow, the contact will be less optimal. In the worst case, if the dimple is made too deep, a joint between the dimple and the input transmission line may form, ruining the switch. Therefore, there is a need for a switch and a method of producing a switch that may be manufactured consistently to make large volume manufacturing runs economically feasible. 
   SUMMARY 
   The present invention teaches several aspects. In a first aspect, a method for pseudo-planarization of an electromechanical device and for forming a durable metal contact on the electromechanical device is taught. The method comprises acts including:
         depositing a dielectric layer having a thickness and an area on a substrate having a substrate area;   depositing a first photoresist film on the dielectric layer, patterned to leave electrode regions exposed;   etching through at least a portion of the thickness of a portion of the area of the dielectric layer at the electrode regions to form electrode spaces in the dielectric layer;   depositing a first conducting layer on the first photoresist film and dielectric layer such that a portion of the first conducting layer is formed in the electrode spaces in the dielectric layer;   removing the first photoresist film, thereby removing a portion of the first conducting layer residing on the first photoresist film;   depositing a sacrificial layer on the dielectric layer and the first conducting layer, the sacrificial layer having a thickness;   etching through the sacrificial layer to an electrode region in order to expose a portion of the first conducting layer at an electrode region to form an anchor site;   depositing an insulating first structure layer on the sacrificial layer and the anchor site, the insulating first structure layer having an area;   etching through the insulating first structure layer across at least a portion of the anchor site so that a portion of the first conducting layer is exposed, and etching through the insulating first structure layer and through a portion of the thickness of the sacrificial layer at a top electrode site so that a top electrode space is defined through the insulating first structure layer, and into the sacrificial layer, proximate an electrode region;   depositing a second photoresist film on the insulating first structure layer, the second photoresist deposited in a pattern to form separation regions for electrically separating desired areas of the electromechanical device and for separating desired devices;   depositing a conducting second structure layer on the insulating first structure layer, the exposed portion of the first conducting layer, and in the top electrode space, the conducting second structure layer having an area;   removing the second photoresist film to eliminate unwanted portions of the conducting second structure layer in order to electrically separate desired areas of the electromechanical device and for separating desired devices;   depositing a insulating third structure layer on the electromechanical device, across the substrate area, the insulating third structure layer having an area; and   depositing a third photoresist film on the electromechanical device, across the substrate area, with the third photoresist film patterned to define desired device shapes by selective exposure; and   selectively etching through exposed portions of the insulating first structure layer and the insulating third structure layer to isolate an electromechanical device having a desired shape.       

   In a further aspect, the method further comprises an act of removing the sacrificial layer to release an actuating portion from a base portion, where the actuating portion includes portions of the insulating first structure layer, the conducting second structure layer, and the insulating third structure layer, and the base portion includes the substrate, the dielectric layer, and the electrode regions. 
   In a still further aspect, the method further comprises an act of forming holes through portions of the actuating portion. This, along with removal of the sacrificial layer, assists in ensuring proper movement characteristics for the switch. 
   In another aspect, the above acts may be made to fabricate a switch according to the method. 
   In a further aspect, a method for pseudo-planarization of an electromechanical device is taught, including acts of:
         depositing a dielectric layer having a thickness and an area on a substrate having a substrate area;   depositing a first photoresist film on the dielectric layer, patterned to leave electrode regions exposed;   etching through at least a portion of the thickness of a portion of the area of the dielectric layer at the electrode regions to form electrode spaces in the dielectric layer;   depositing a first conducting layer on the first photoresist film and dielectric layer such that a portion of the first conducting layer is formed in the electrode spaces in the dielectric layer;   removing the first photoresist film, thereby removing a portion of the first conducting layer residing on the first photoresist film;   depositing a sacrificial layer on the dielectric layer and the first conducting layer, the sacrificial layer having a thickness;   etching through the sacrificial layer to form a dimple portion of a top electrode space proximate an electrode region;   etching through the sacrificial layer to an electrode region in order to expose a portion of the first conducting layer at an electrode region to form an anchor site;   depositing a dimple metal layer in the dimple portion to form a dimple portion;   depositing an insulating first structure layer on the sacrificial layer and the anchor site, the insulating first structure layer having an area;   etching through the insulating first structure layer across at least a portion of the anchor site so that a portion of the first conducting layer is exposed, and etching through the insulating first structure layer at the top electrode space so that the top electrode space is defined through the insulating first structure layer to the dimple portion;   depositing a second photoresist film on the insulating first structure layer, the second photoresist deposited in a pattern to form separation regions for electrically separating desired areas of the electromechanical device and for separating desired devices;   depositing a conducting second structure layer on the insulating first structure layer, the exposed portion of the first conducting layer, and in the top electrode space, the conducting second structure layer having an area;   removing the second photoresist film to eliminate unwanted portions of the conducting second structure layer in order to electrically separate desired areas of the electromechanical device and for separating desired devices;   depositing a insulating third structure layer on the electromechanical device, across the substrate area, the insulating third structure layer having an area; and   depositing a third photoresist film on the electromechanical device, across the substrate area, with the third photoresist film patterned to define desired device shapes by selective exposure;   selectively etching through exposed portions of the insulating first structure layer and the insulating third structure layer to isolate an electromechanical device having a desired shape.       

   As with the first aspect, this method may be further supplemented by an act of removing the sacrificial layer to release an actuating portion from a base portion, where the actuating portion includes portions of the insulating first structure layer, the conducting second structure layer, and the insulating third structure layer, and the base portion includes the substrate, the dielectric layer, and the electrode regions. 
   In a further aspect, the method includes an act of forming holes through portions of the actuating portion. 
   In another aspect, the immediately previous acts may be made to fabricate a switch according to the method. 
   In yet another aspect, a method for forming an electromechanical device having a durable metal contact is taught, including acts of:
         providing a substrate having a substrate area and having a dielectric layer with a plurality of conductors formed therein as a first conducting layer;   depositing a sacrificial layer on the dielectric layer and the first conducting layer, the sacrificial layer having a thickness;   removing a portion of the sacrificial layer to form a dimple portion of a top electrode space proximate an electrode region;   depositing a dimple metal layer in the dimple portion to form a dimple;   depositing an insulating first structure layer on the sacrificial layer, the insulating first structure layer having an area;   removing a portion of the insulating first structure layer at the top electrode space so that the top electrode space is defined through the insulating first structure layer to the dimple portion, where the dimple metal layer acts as to stop the removing process;   depositing a first photoresist film on the insulating first structure layer, the first photoresist deposited in a pattern to form separation regions for electrically separating desired areas of the electromechanical device and for separating desired devices;   depositing a conducting second structure layer on the insulating first structure layer, on exposed portions of the first conducting layer, and in the top electrode space, the conducting second structure layer having an area;   removing the second photoresist film to eliminate unwanted portions of the conducting second structure layer in order to electrically separate desired areas of the electromechanical device and for separating desired devices;   depositing a insulating third structure layer on the electromechanical device, across the substrate area, the insulating third structure layer having an area; and   depositing a second photoresist film on the electromechanical device, across the substrate area, with the second photoresist film patterned to define desired device shapes by selective exposure; and   selectively etching through exposed portions of the insulating first structure layer and the insulating third structure layer to isolate an electromechanical device having a desired shape.       

   As with the first aspect, this method may be further supplemented by an act of removing the sacrificial layer to release an actuating portion from a base portion, where the actuating portion includes portions of the insulating first structure layer, the conducting second structure layer, and the insulating third structure layer, and the base portion includes the substrate, the dielectric layer, and the electrode regions. 
   In a further aspect, the method includes an act of forming holes through portions of the actuating portion. 
   In another aspect, the immediately previous acts may be made to fabricate a switch according to the method. 
   In still another aspect, a head electrode region of a beam for an electromechanical device is taught. The head region includes a first insulating layer having electrode region edges; and a head electrode, where the head electrode comprises a locking portion, with the locking portion surrounding the electrode region edges of the first insulating layer such that the head electrode is held fixed relative to the first insulating layer. 
   In a further aspect of the head electrode region, the head electrode has a top region residing above the first insulating layer and a contact region residing below the first insulator, the head electrode region further comprising a second insulating layer formed to cover at least a portion of the top region of the head electrode. 
   In a yet further aspect, a planarized substrate structure for an electromechanical device is taught, including a substrate layer; a dielectric layer formed on the substrate layer, the dielectric layer formed with conductor spaces therein, the dielectric layer further including a dielectric top surface; and a conducting layer formed as a set of conductors in the conductor spaces of the dielectric layer, the conducting layer having a conducting layer top surface, and where the dielectric top surface and the conducting layer top surface are formed in a substantially coplanar fashion to provide a planarized substrate structure. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objects, features and advantages of the present invention will be apparent from the following detailed descriptions of the preferred aspect of the invention in conjunction with reference to the following drawings, where: 
       FIG. 1A  is a top view of a prior art T-MEMS switch; 
       FIG. 1B  is a side-view of the prior art T-MEMS switch presented in  FIG. 1A , in an open position; 
       FIG. 1C  is a side-view of the prior art T-MEMS switch presented in  FIG. 1A , in a closed position; 
       FIG. 2A  is a top view of a prior art I-MEMS switch; 
       FIG. 2B  is a side-view of the DC cross-section of the prior art I-MEMS switch presented in  FIG. 2A , in an open position; 
       FIG. 2C  is a side-view of the RF cross-section of the prior art I-MEMS switch presented in  FIG. 2A , in an open position; 
       FIG. 2D  is a side-view of the DC cross-section of the prior art I-MEMS switch presented in  FIG. 2A , in a closed position; 
       FIG. 2E  is a side-view of the RF cross-section of the prior art I-MEMS switch presented in  FIG. 2A , in a closed position; 
       FIG. 3A  is a top view of a T-MEMS switch in accordance with the present invention; 
       FIG. 3B  is a side-view of the T-MEMS switch presented in  FIG. 3A , in an open position; 
       FIG. 3C  is a cross-section of the T-MEMS presented in  FIG. 3A , in the open position, where the cross section is taken along a line through electrodes  340  and  338 ; 
       FIG. 3D  is a zoomed-in view of the metal platform of the T-MEMS switch, presented in  FIG. 3A ; 
       FIG. 3E  is a side-view of the T-MEMS presented in  FIG. 3A , in a closed position; 
       FIG. 3F  is a cross-section of the T-MEMS switch presented in  FIG. 3A , in the closed position, where the cross section is taken along a line through electrodes  340  and  338 ; 
       FIG. 4A  is a side view of a DC cross-section of an I-MEMS switch in an open position in accordance with the present invention; 
       FIG. 4B  is a side view of a RF cross-section of the I-MEMS switch presented in  FIG. 4A , in an open position; 
       FIG. 4C  is a side view of the DC cross-section of the I-MEMS switch presented in  FIG. 4A , in a closed position; 
       FIG. 4D  is a side view of the RF cross-section of the I-MEMS switch presented in  FIG. 4A , in a closed position; 
       FIG. 5A  depicts a side view of a cross-section of a doubly supported cantilever beam MEMS switch in an open position in accordance with the present invention; 
       FIG. 5B  depicts a side view of a cross-section of a doubly supported cantilever beam MEMS switch presented in  FIG. 5A , in a closed position; 
       FIGS. 6A through 6M  are side-views of a T-MEMS switch of the present invention, showing the switch at various stages of production; 
       FIG. 7  is a table presenting various non-limiting examples of materials, deposition processes (where applicable), removal processes (where applicable), etch processes (where applicable), and thickness ranges for the various layers that make up a MEMS switch according to the present invention; 
       FIG. 8  is an illustrative diagram of a computer program product aspect of the present invention; and 
       FIG. 9  is a block diagram of a data processing system used in conjunction with the present invention. 
   

   DETAILED DESCRIPTION 
   The present invention relates to fabrication techniques for increasing the reliability and performance of contacts in micro-electro-mechanical system (MEMS) switches. Specifically, the invention relates to the fabrication of a planar cantilever beam, lower surface leakage, a more reliable metal contact dimple design and a high yield process. The following description, taken in conjunction with the referenced drawings, is presented to enable one of ordinary skill in the art to make and use the invention and to incorporate it in the context of particular applications. Various modifications, as well as a variety of uses in different applications, will be readily apparent to those skilled in the art, and the general principles defined herein, may be applied to a wide range of aspects. Thus, the present invention is not intended to be limited to the aspects presented, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. Furthermore, it should be noted that unless explicitly stated otherwise, the figures included herein are illustrated diagrammatically and without any specific scale, as they are provided as qualitative illustrations of the concept of the present invention. 
   In order to provide a working frame of reference, first a glossary of terms used in the description and claims is given as a central resource for the reader. Next, a discussion of various physical aspects of the present invention is provided. Finally, a discussion is provided to give an understanding of the specific details. 
   (1) Glossary 
   Before describing the specific details of the present invention, a centralized location is provided in which various terms used herein and in the claims are defined. The glossary provided is intended to provide the reader with a general understanding for the intended meaning of the terms, but is not intended to convey the entire scope of each term. Rather, the glossary is intended to supplement the rest of the specification in more accurately explaining the terms used. 
   Actuation portion: A part of a switch that moves to connect or disconnect an electrical path. Some examples include an armature and a cantilever. 
   Cantilever: A beam that sits above the substrate. It is affixed at the metal contact electrode at one end, and suspended freely above the RF electrodes at the opposite end. 
   Metal dimple portion: An area of metal that protrudes from an armature providing increased contact reliability in MEMS switches. Also referred to as a metal dimple contact.
         (2) Principal Aspects       

   The present invention has three principal aspects. The first is a MEMS switch with a planarized cantilever beam and low surface leakage current. The MEMS switch includes an actuating portion which moves from a first position to a second position, wherein in the second position the switch provides a path for an RF signal. A metal dimple is placed on a portion of the cantilever beam that contacts metal on the RF electrodes on the substrate when the MEMS switch is closed. The present invention also teaches a fabrication method (and products by the method) that provides a stable and firm metal dimple, and a controlled dimple dry etch for manufacturing the MEMS switch with high yield and better reliability performance. Additionally, the various acts in a method according to the present invention may be automated and computer-controlled, the present invention also teaches a computer program product in the form of a computer readable media containing computer-readable instructions for operating machinery to perform the various acts required to make a MEMS switch according to the present invention. These instructions may be stored on any desired computer readable media, non-limiting examples of which include optical media such as compact discs (CDs) and digital versatile discs (DVDs), magnetic media such as floppy disks and hard drives, and circuit-based media such as flash memories and field-programmable gate arrays (FPGAs). The computer program product aspect will be discussed toward the end of this description. 
     FIG. 3A  is a top view of a T-MEMS switch  300 . An armature  336  allows for an electrical connection between a first RF transmission line, i.e. an RF-input transmission line  340  and a second RF transmission line, i.e. an RF-output transmission line  338 , when the switch is in a closed position. 
     FIG. 3B  shows one side-view cross-section of the T-MEMS switch  300 . One skilled in the art will appreciate that the cross-section only shows the contact of the armature  336  with the RF-output transmission line  338 , since the contact of the RF-input transmission line  340  (shown in  FIG. 3A ) is directly behind the RF-output transmission line  338  when looking at the cross-section of the switch. One end of the armature  336  is affixed to an anchor electrode  332  on a substrate  114 . The other end of the armature  336  is positioned over the RF-line which is divided into two separate sections, the RF-input transmission line  340  and the RF-output transmission line  338 . The RF-input transmission line  340  and the RF-output transmission line  338  are separated by a gap (visible in FIG.  3 A). A substrate bias electrode  342  is attached with the substrate  114  below the armature  336 . The armature  336  sits above the substrate bias electrode  342  and is electrically isolated from the substrate bias electrode  342  by an air gap forming a parallel plate capacitor when the MEMS switch  300  is in an “open” position. An output top dimple electrode  345   a  is placed on one end of the armature  336  above the output RF transmission line  338 . Similarly, an input top dimple electrode  345   b  (visible in  FIG. 3A ) is placed on the end of the armature  336  above the input RF transmission line  340 , shown in FIG.  3 C. The output top dimple electrode  345   a  and the input top dimple electrode  345   b  are electrically connected via a transmission line  348 , shown in FIG.  3 A. In one aspect, the transmission line  348  is a metal film transmission line embedded inside the armature  336 .  FIG. 3D  shows a zoomed-in view of the input top dimple electrode  345   a  and the RF transmission line  338  for the base contact. 
   It is noteworthy that in the zoomed-in version shown in  FIG. 3D , the head electrode region  380  is formed with a locking portion  382  that surrounds electrode region edges  384  of the first semiconductor region  386 . The head electrode  388  has a top portion  390  and a bottom portion  392 , and a second insulating layer  394  may cover at least a portion of the top portion  390  of the head electrode  388 . 
     FIG. 3E  depicts the cross-section of the T-MEMS switch  300  in  FIG. 3B  in a closed state. When a voltage is applied between a suspended armature bias electrode  350  and the substrate bias electrode  342 , an electrostatic attractive force will pull the suspended armature bias electrode  350  as well as the attached armature  336  towards the substrate bias electrode  342 . Consequently, the output top dimple electrode  345   a  touches the output RF transmission line  338  and the input top electrode  345   b  (visible in  FIG. 3A ) touches the input RF transmission line  340  (shown in  FIG. 3F ) providing a good electrical contact. Thus, the output top dimple electrode  345   a , the transmission line  348  (visible in FIG.  3 A), the input top dimple electrode  345   b  (visible in  FIG. 3A ) provide an electrical path for bridging the gap between the RF-input transmission line  340  and the RF-output transmission line  338 , thereby closing the MEMS switch  300 . 
   The substrate  114  may be comprised of a variety of materials. If the MEMS switch  300  is intended to be integrated with other semiconductor devices (i.e. with low-noise high electron mobility transistor (HEMT) monolithic microwave integrated circuit (MMIC) components), it is desirable to use a semi-insulating semiconducting substance such as gallium arsenide (GaAs), indium phosphide (InP) or silicon germanium (SiGe) for the substrate  114 . This allows the circuit elements as well as the MEMS switch  300  to be fabricated on the same substrate using standard integrated circuit fabrication technology such as metal and dielectric deposition, and etching by using the photolithographic masking process. Other possible substrate materials include silicon, various ceramics, and quartz. The flexibility in the fabrication of the MEMS switch  300  allows the switch  300  to be used in a variety of circuits. This reduces the cost and complexity of circuits designed using the present MEMS switch. 
   In the T-MEMS switch (see FIGS.  3 A- 3 F), when actuated by electrostatic attraction, the armature  336  bends towards the substrate  114 . This results in the output top dimple electrode  345   a  and the input top dimple electrode  345   b  on the armature  336  contacting the output RF transmission line  338  and input RF transmission line  340  respectively, and the armature  336  bending to allow the suspended armature bias electrode  350  to physically contact the substrate bias electrode  342 . This fully closed state is shown in FIG.  3 E. The force of the metallic contact between the output RF transmission line  338  and the output top dimple electrode  345   a  (also the input RF transmission line  340  and the input top dimple electrode  345   b ) is thus dependent on the spring constant force at the RF-output transmission line  340  and RF-input transmission line  338  when the switch is closed. Metallic switches that do not have protruded dimple contact designs have contacts that depend upon the whole armature flexibility and bias strength. It is considered that this type of metal contact T-switch is less reliable than the micro-relay switches with protruded dimple contacts such as those taught here. In addition to improving the switch reliability, the quality of the contact itself is improved by the dimple because the dimple has controllable geometric features such as size (area and height) and shape. Thus, MEMS switches without the dimples  345   a  and  345   b  are more likely to have time-varying contact characteristics, a feature that may make them difficult or impossible to use in some circuit implementations. 
   One skilled in the art will appreciate that the RF-input transmission line  340  may be permanently attached with one end of the transmission line  348  in the armature  336 . In this case, the switch  300  is open when a gap exists between the RF-output transmission line  338  and the transmission line  348 . Further, one skilled in the art will appreciate that the RF-output transmission line  338  may be permanently attached with one end of the transmission line  348  in the armature  336 . In this case the switch is open when a gap exists between the RF-input transmission line  340  and the transmission line  348 . 
     FIG. 4A  depicts a DC cross-section of an I-MEMS switch  400  in accordance with the present invention. Depicted in  FIG. 4A , a DC signal is passed from the DC contact  420  through an anchor point  422  and into the DC cantilever structure  424 . In the cross-sectional view of  FIG. 4A , a portion of a metal dimple  416  (shown in  FIG. 4B ) would be seen in the background if the RF portion of the switch  400  were shown. A substrate bias electrode  426  is positioned on the substrate  114 . As a DC bias is applied to the DC contact  420  and the substrate bias electrode  426 , the DC cantilever structure  424  is pulled toward the substrate  114 .  FIGS. 4C and 4D  depict the switch of  FIGS. 4A and 4B , respectively, in a closed position. 
     FIG. 4B  depicts the RF cross-section of switch  400 . The RF-input transmission line  410  passes through anchor point  414  and into the RF cantilever structure  415 . Upon contact, the metal dimple  416  allows electricity to passes through the RF cantilever structure  415 . The metal dimple  416  also provides an electrical contact between the RF-input transmission line  410  and the RF-output transmission line  412  when the switch is in a closed position. As discussed above, when a DC bias is applied to the DC contact  420  and the substrate bias electrode  426 , the DC cantilever structure  424  is pulled toward the substrate  114 . The deflection of the DC cantilever structure  424  toward the substrate  114  also causes the RF cantilever structure  415  to bend toward the substrate  114 , providing an electrical path between the RF-input transmission line  410  and the RF-output transmission line  412 . 
   In the I-MEMS switch (see FIGS.  4 A- 4 D), the gap between the RF-output transmission line  412  and the metal dimple  416  is smaller than the gap between the substrate bias electrode  426  and the suspended armature bias electrode in the armature  424 . When actuated by electrostatic attraction, the armature structure, comprising the DC cantilever structure  424  and the RF cantilever structure  415 , bends towards the substrate  114 . First, the metal dimple  416  on the RF cantilever structure  415  contacts the RF transmission line  416 , at which point the armature bends to allow the DC cantilever structure  424  to physically contact the substrate bias electrode  426 . This fully closed state is shown in  FIGS. 4C and 4D . The force of the metallic contact between the RF transmission line  412  and the metal dimple  416  is thus dependent on the spring constant force at the RF transmission line  412  when the switch is closed. Existing metallic switches that do not have contact dimples have contacts that depend upon the whole armature flexibility and bias strength. It is considered that this type of metal contact T-switch is less reliable than the micro-relay switches with dimple contacts such as those taught by the present invention. In addition to improving the switch reliability, the quality of the contact itself is improved by the dimple because the dimple has controllable geometric features such as size (area and height) and shape. Thus, MEMS switches without the dimple contact are more likely to have time-varying contact characteristics, a feature that may make them difficult or impossible to use in some circuit implementations. 
     FIG. 5A  depicts a cross-section of a doubly supported cantilever beam MEMS switch  500 . An RF-input transmission line  510  is included in a cantilever beam  512 . An RF-output transmission line  514  is located on a substrate  114 . The cantilever beam  512 , unlike the switches previously discussed, is attached with the substrate  114  at two ends. The cantilever beam  512  also includes a cantilever bias electrode  516 . A substrate bias electrode  518  is located on the substrate  114 . When a DC bias is applied to the cantilever bias electrode  516  and the substrate bias electrode  518 , the cantilever beam  512  moves from the open position, shown in  FIG. 5A  to a closed position, shown in FIG.  5 B. In the closed position, an electrical path is created between the RF-input transmission line  510  and the RF-output transmission line  514 . Note that rather than passing along the beam, the RF signal could also be passed from an RF-input transmission line to an RF-output transmission line by using a line with a pair of dimples. 
   As discussed above, the prior art T-MEMS switches have dimples attached with the armature. Because the formation of the dimple in the armature requires a highly sensitive, time-controlled etching process, the yield and performance of the MEMS switches will vary from lot to lot. However, with the design disclosed herein, by placing metal platforms on the input and output RF electrodes that are protruded from the substrate (instead of having a deep dimple on the armature), the yield and performance of MEMS switch fabrication is increased. A few of the potential applications of these MEMS switches are in the RF, microwave, and millimeter wave circuits, and wireless communications spaces. For example, these MEMS switches can be used in commercial satellites, antenna phase shifters for beam-steering, and multi-band and diversity antennas for wireless cell phones and wireless local area networks (WLANS). 
   The following is an exemplary set of operations that may be used in the manufacturing of the device disclosed herein. One skilled in the art will appreciate that the acts outlined are to indicate changes from the prior art manufacturing process, and are not intended to be a complete list of all acts used in the process. One skilled in the art will appreciate that the MEMS switches may have varying designs, such as I configurations and T configurations. However, the manufacturing acts disclosed herein are for the formation of a fabrication method for making a reliable microrelay MEMS switch on a substrate, which may be utilized in any MEMS switch configuration. The manufacturing process is described using the terminology for the I configuration as an illustration, however, those of skill in the art will realize that the acts presented are readily adaptable for other switch types. 
     FIG. 6  depicts a substrate. As shown in  FIG. 6A , a first Si 3 N 4  (dielectric) layer  600  having a thickness and an area is deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) or by Low Pressure Chemical Vapor Deposition (LPCVD) on top of a substrate having a substrate area. It is then, as shown in  FIG. 6B , followed by the depositing of a first (optional) insulating (SiO 2 ) layer  602  on top of the first Si 3 N 4  layer  600 . In one aspect, the Si 3 N 4  thickness is between 1000 angstrom to 5000 angstrom, and the SiO 2  thickness is approximately in the range from 1.0 micron to 3.0 microns. The wafer is then patterned with a first photoresist layer to cover the SiO 2  layer and open windows in areas where the DC, RF, and actuation metal electrodes will be situated. This is done by first removing the oxide in the DC, RF, and actuation metal electrode areas by wet or dry etching to form electrode spaces, and is followed by Au depositing to refill and to replace the etched oxide totally, thus depositing a first conductor layer in the electrode spaces in the first dielectric layer  600 . The unwanted Au may then be removed by a lift-off process. In one aspect, the planarized first metal layer  604  is approximately between one micron and three microns thick gold (Au) and the substrate  114  is a material such as Gallium Arsenide (GaAs), high resistivity silicon (Si) or glass/Quartz. In short, this planarized first metal layer  604  is used to form an input contact electrode, an anchor electrode, an RF-input and output lines and a substrate bias electrode on the substrate. This processing act completes the planarization of the cantilever beam, and it is also acting as a surface passivation layer to the substrate. The results of these operations are shown in FIG.  6 C. 
   Next, as shown in  FIG. 6D , a thick SiO 2  sacrificial layer  606  having a thickness is deposited over the planarized first conductor (metal) layer  604 . This sacrificial oxide layer  606  is used to provide a base for the armature, and will later be removed. In one aspect, the sacrificial oxide layer  606  is a silicon dioxide layer approximately between 2 microns to 3 microns thick. 
   Next, as shown in  FIG. 6E , a small area  608  (depicted as a square area) above the RF electrode  610  is etched into the sacrificial oxide layer  606  defining the metal dimple contact area (a top electrode space). Again, a lift-off process is performed to deposit Au inside to form the bottom dimple contact electrodes  612 . In one aspect, the small square area is approximately between 100 to 600 square microns in area, and the depth of the etched dimple contact is approximately between 0.2 to 0.5 microns. Note that this act, may be performed either before or after the act resulting in  FIG. 6F  below. It is important to note that departures from the specific order of the steps presented may be made without affecting the general nature of the invention, as will be appreciated by those skilled in the art. 
   Following, as shown in  FIG. 6F , a via  614  is etched in the sacrificial oxide layer  606  over the anchor electrode  616 , which is a portion of the planarized first metal layer  604 , thus forming an anchor site. This is then followed, as shown in  FIG. 6G , by a deposition of a low stress PECVD Nitride layer  618  over the sacrificial oxide layer  606 . The Nitride Layer  618  acts as a first structural layer having an area. In one aspect, the low stress Nitride layer  618  is approximately between one micron and two microns thick. The Nitride Layer  618  is then etched across at least a portion of the via  614  (anchor site) so that a portion of the first conductor layer  604  is exposed. 
   The next operation is illustrated in  FIG. 6H , where via holes  620  are created by removing the nitride layer  618  over the anchor electrode  616  and in the small area over the dimple contact  612 . The removal of the nitride layer  618  over the dimple contact  612  provides for a small input dimple or an input top electrode  619  attached with the armature. This operation of removal may be accomplished using dry etching, and this etching cannot be over etched because it will stop at the previously deposited dimple metal layer. This is a useful manufacturing act because the switch contact depth is well controlled by the metal layer (the metal acts as a barrier to the etching process). 
   Next, as shown in  FIG. 6I , a seed metal layer  622  is deposited over the substrate  114  for plating. The thin metal layer  622  may be gold (Au). In one aspect, the thin metal layer  622  is approximately between one hundred and five hundred angstroms thick. After the deposition of the seed metal layer  622 , a photoresist layer  624  is placed over areas of the seed metal layer  622  on which the deposition of metal is not desired. This allows for the formation of separation regions for electrically separating (isolating) desired areas of the overall device (e.g., the armature bias pad from the input top electrode) as well as separating different devices on a substrate wafer. A plated metal layer  626  is then created above the thin metal film (seed metal layer  622 ) using techniques well known in the art. This plated metal layer  626  allows for the formation of the input top electrode  628 , the transmission line, and the armature bias electrode. In one aspect, the plated metal layer  626  is approximately between one to three microns thick. 
   Then, as shown in  FIG. 6J , a gold etch photoresist layer  630  is deposited over the areas of the plated layer  626  to be protected. Next, the un-protected thin metal seed layer  622  is etched so that the un-protected thin metal seed layer  622  is removed from the areas where the photoresist layer  630  was not placed. The photoresist layer  630  is then removed. The etching may be, for example, wet etching. The result is shown in FIG.  6 K. 
   Next, as shown in  FIG. 6L , a low stress structure Nitride layer  632  may be deposited using PECVD to cover the substrate  114 . In one aspect, the low stress Nitride layer  632  is one to two microns thick. 
   As depicted in  FIG. 6M , portions of this Nitride layer  632  are etched to remove the unwanted nitride and drill release holes  634 , as shown in  FIG. 3A , though the armature. Release holes are shown more clearly in FIG.  3 A. The drill release holes  643  are useful for several reasons: first, they assist in the beam releasing process, second, the holes play a role during actuation by providing an exit for air caught between the beam and the substrate, and third, the drill holes reduce the mass of the beam, which helps to increase the switching speed. 
   The final act is etching off the sacrificial layer using an etching solution, such as Hydrogen Fluoride (HF). The cantilever beam is then released in a supercritical point dryer. The result is the MEMS switch similar to that shown in  FIGS. 3A  through  3 E. One skilled in the art will appreciate that the same acts can be used in the manufacture of the MEMS T-switch as shown in  FIG. 4  as well as in the manufacture of the bridge-type MEMS switch shown in FIG.  5 . 
   In one aspect, the chip size containing the MEMS switch, such as those taught herein is 800×400 microns. The metal electrode pad is on the order of 100×100 microns. The actuation pad may vary from 100-20×100-20 microns depending upon the design of the specific actuation voltage. The RF line may vary between 60-15 microns wide. The above dimensions are provided as exemplary and are not intended to be construed as limiting. Instead, one skilled in the art will appreciate that different dimensions may be used depending upon the size of the MEMS switch being designed and the application for which it is being used. Furthermore, a table is presented in  FIG. 7 , providing non-limiting examples of materials, deposition processes (where applicable), removal processes (where applicable), etch processes (where applicable), and thickness ranges for the various layers that make up a MEMS switch according to the present invention. It is important that this table be considered simply as a general guide and that it be realized that the present invention may use other materials, deposit processes, removal processes, etch processes, and thicknesses than those described and that the information provided in  FIG. 7  is intended simply to assist the reader in gaining a better general understanding of the present invention. 
   Gold is a noble material. It is also an excellent conductor. Unlike the other good conductors such as Al, Cu etc. gold is inert and will not be oxidized and corroded. Therefore, Au is an ideal dimple contact material for switches according to the present invention. However, gold is very precious and expensive. Much gold is wasted during evaporation in forming the cantilever beam that consists of the dimple contact attached to the beam at the free standing end, and the DC actuation electrode anchored to the metal base at the opposite end. This is because both the dimple contact and the actuation pad are fabricated in a single Au deposition step. 
   The invention described herein will provide a solution to forming the dimple contact and the actuation pad separately. This permits selection of materials other than Au to form the actuation bias electrode while gold is still being used as the material for the metal dimple. Furthermore, by doing so, there is an additional advantage; that is, a lighter metal such as Ta may be used for the actuation bias electrode to reduce the mass of the cantilever beam to increase the switching speed. 
   The fabrication sequence for such a process is described below: 
   Step 1. Forming the metal dimple in the sacrificial oxide by using a photolithographic lift-off process (same process as in step . . . ′); 
   Step 2. Depositing the lower nitride structure over the sacrificial oxide and the metal dimple (same . . . ); 
   Step 3. Etching a hole through the lower nitride structure into the metal dimple. (same as . . . ); 
   Step 4. Evaporating Au above the metal dimple to fill up the hole by the lift-off process or plating process. (same as . . . except no metal deposition in the actuation electrode.); 
   Step 5. Removing the nitride in the base region to form a metal anchor. (same as . . . ); 
   Step 6. Depositing a metal other than Au to form the dc actuation pad by using the lift-off or plating process. (same as step in . . . except no metal deposition for the metal dimple.); and 
   Step 7. Depositing the upper nitride to complete the beam formation. 
   As stated previously, the operations performed by the present invention may be encoded as a computer program product. The computer program product generally represents computer readable code stored on a computer readable medium such as an optical storage device, e.g., a compact disc (CD) or digital versatile disc (DVD), or a magnetic storage device such as a floppy disk or magnetic tape. Other, non-limiting examples of computer readable media include hard disks, read only memory (ROM), and flash-type memories. An illustrative diagram of a computer program product embodying the present invention is depicted in FIG.  8 . The computer program product is depicted as a magnetic disk  800  or an optical disk  802  such as a CD or DVD. However, as mentioned previously, the computer program product generally represents computer readable code stored on any desirable computer readable medium. 
   When loaded onto a semiconductor process control computer as shown in  FIG. 9 , the computer instructions from the computer program product provides the information necessary to cause the computer to perform the operations/acts described with respect to the method above, resulting in a device according to the present invention. 
   A block diagram depicting the components of a computer system that may be used in conjunction with the present invention is provided in FIG.  9 . The data processing system  900  comprises an input  902  for receiving information from at least a computer program product or from a user. Note that the input  902  may include multiple “ports.” The output  904  is connected with a processor  906  for providing information regarding operations to be performed to various semiconductor processing machines/devices. Output may also be provided to other devices or other programs, e.g. to other software modules for use therein or to display devices for display thereon. The input  902  and the output  904  are both coupled with the processor  906 , which may be a general-purpose computer processor or a specialized processor designed specifically for use with the present invention. The processor  906  is coupled with a memory  908  to permit storage of data and software to be manipulated by commands to the processor.

Technology Classification (CPC): 7