Patent Publication Number: US-10759654-B2

Title: Rough anti-stiction layer for MEMS device

Description:
REFERENCE TO RELATED APPLICATIONS 
     This Application is a Divisional of U.S. application Ser. No. 15/885,016, filed on Jan. 31, 2018, which is a Continuation of U.S. application Ser. No. 15/006,301, filed on Jan. 26, 2016 (now U.S. Pat. No. 9,884,755, issued on Feb. 6, 2018). The contents of the above-referenced patent applications are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     Microelectromechanical systems (MEMS) devices, such as accelerometers, pressure sensors and gyroscopes, have found widespread use in many modern day electronic devices. For example, MEMS accelerometers are commonly found in automobiles (e.g., in airbag deployment systems), tablet computers or in smart phones. For many applications, MEMS devices are electrically connected to application-specific integrated circuits (ASICs) to form complete MEMS systems. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIG. 1A  illustrates a cross-sectional view of some embodiments of a microelectromechanical systems (MEMS) package with a rough metal anti-stiction layer. 
         FIG. 1B  illustrates a cross-sectional view of some embodiments of an enlarged portion of the MEMS package of  FIG. 1A . 
         FIG. 1C  illustrates a perspective view of some embodiments of a portion of the MEMS package of  FIG. 1A . 
         FIG. 2  illustrates a cross-sectional view of some other embodiments of a MEMS package with a rough metal anti-stiction layer. 
         FIGS. 3-11  illustrate a series of cross-sectional views of some embodiments of a method for manufacturing a MEMS package with a rough metal anti-stiction layer at various stages of manufacture. 
         FIG. 12  illustrates a flow diagram of some embodiments of a method for manufacturing a MEMS package with a rough metal anti-stiction layer. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure provides many different embodiments, or examples, for implementing different features of this disclosure. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
     Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. 
     Some microelectromechanical systems (MEMS) devices, such as accelerometers and gyroscopes, comprise a moveable mass and a neighboring fixed electrode plate arranged within a cavity. The moveable mass is moveable or flexible with respect to the fixed electrode plate in response to external stimuli, such as acceleration, pressure, or gravity. A distance variation between the moveable mass and the fixed electrode plate is detected through the capacitive coupling of the moveable mass and the fixed electrode plate and transmitted to a measurement circuit for further processing. 
     Due to the moveable or flexible parts, MEMS devices have several production challenges that are not encountered with CMOS circuits. One significant challenge with MEMS devices is surface stiction. Surface stiction refers to the tendency of a moveable or flexible MEMS part to come into contact with a neighboring surface and “stick” to the neighboring surface. This “stiction” can occur at the end of manufacturing, such that the moveable or flexible part is not quite released from the neighboring surface, or can occur during normal operation when the component suddenly becomes “stuck” to the neighboring surface. As feature sizes shrink for successive generations of technology, surface stiction is becoming an increasingly important consideration in MEMS devices. Surface stiction can arise due to any one of several different effects, such as capillary force, molecular van der Waals force or electrostatic forces between neighboring surfaces. The extent to which these effects cause stiction can vary based on many different factors such as temperature of the surfaces, contact area between the surfaces, contact potential difference between the surfaces, whether the surfaces are hydrophilic or hydrophobic, and so on. Approaches have been used to attempt to limit surface stiction, for example, performing surface treatment or coating to the moveable mass or cavity surfaces to change hydrophilic properties of the surfaces. However, these approaches are difficult to integrate with various manufacturing processes and introduce contamination. 
     The present application is related to a MEMS package with a rough metal anti-stiction layer to improve stiction characteristics, and associated methods of forming such a MEMS package. The MEMS package comprises a MEMS IC bonded to a CMOS IC. An anti-stiction layer is disposed on the CMOS IC under a moveable mass of the MEMS IC. The anti-stiction layer has a rough top surface made up of a series of peaks and valleys. These peaks and valleys, which limit the overall contact area to points where the peaks of the anti-stiction layer meet a lower surface of the moveable mass, help improve stiction characteristics. Therefore, stiction can be avoided at the end of the manufacturing process and/or during normal operation of the MEMS package, and reliability is accordingly improved. The concept will be illustrated herein with regards to some example MEMs devices, but it will be appreciated that the concept is applicable to suitable MEMS device employing moveable parts, including actuators, valves, switches, microphones, pressure sensors, accelerators, and/or gyroscopes, for example. 
       FIG. 1A  illustrates a cross-sectional view of some embodiments of a MEMS package  100  with a rough metal anti-stiction layer. The MEMS package  100  comprises a CMOS IC  102  comprising CMOS devices disposed within a CMOS substrate  104  and a MEMS IC  112  bonded to the CMOS IC  102 . The MEMS IC  112  comprises a MEMS device layer  130  bonded the CMOS IC  102 . The MEMS device layer  130  comprises a fixed portion  132  and a moveable mass  116 . In some embodiments, the moveable mass  116  is connected to the fixed portion  132  by one or more cantilever beams or springs (not shown) and at least a portion of the moveable mass  116  can move in at least one direction with respect to the fixed portion  132 . In some embodiments, the CMOS substrate  104  and the MEMS device layer  130  may comprise monocrystalline silicon. The MEMS device layer  130  is bonded to the CMOS substrate  104 , enclosing a cavity  120  between the moveable mass  116  and the CMOS substrate  104 . The moveable mass  116  is arranged in the cavity  120 . An anti-stiction layer  110  is disposed over the CMOS substrate  104  and under the moveable mass  116 . The anti-stiction layer  110  has a rough top surface  110   s , which is configured to limit contact area to a lower surface  116   s  of the moveable mass  116  when the moveable mass  116  moves downwardly to reach the anti-stiction layer  110 . Thus stiction is limited. 
     In some embodiments, a fixed electrode plate  106  is disposed over the CMOS substrate  104  between portions of the anti-stiction layer  110 . A measurement circuit is configured to detect a distance change between the moveable mass  116  and the fixed electrode plate  106 , for example based on changes of a varying current or voltage measured between the moveable mass  116  and the fixed electrode plate  106 . Compared to the anti-stiction layer  110 , the fixed electrode plate  106  has a smooth top surface  106   s . An uppermost region of the rough top surface  110   s  is spaced apart from the lower surface  116   s  of the moveable mass  116  by a first vertical distance d 1 , and an uppermost region of the smooth top surface  106   s  is spaced apart from the lower surface  116   s  of the moveable mass  116  by a second vertical distance d 2  that is greater than the first vertical distance d 1 . In this way, the anti-stiction layer  110  prevents the moveable mass  116  from reaching and “sticking” to the fixed electrode plate  106 . In some embodiments, the smooth top surface  106   s  has a surface height from a bottom surface of the fixed electrode plate  106  that is substantially same as a mean surface height of the rough top surface  110   s . The mean surface height of the rough top surface  110   s  is a height from a mean surface  122   s  of the rough top surface  110   s  to a bottom surface of the anti-stiction layer  110 . The height of the mean surface  122   s  is calculated from the roughness profile. In some embodiments, the anti-stiction layer  110  and the fixed electrode plate  106  comprise the same metal material and have the bottom surfaces substantially aligned one another. In some other embodiments, the anti-stiction layer  110  and the fixed electrode plate  106  can alternatively be made of different materials from one another. In some embodiments, the anti-stiction layer  110  may comprise aluminum (Al), nickel (Ni) or copper (Cu). 
       FIG. 1B  illustrates a cross-sectional view of some embodiments of an enlarged portion of the MEMS package  100  of  FIG. 1A . As shown in more detail in  FIG. 1B , the rough top surface  110   s  of the anti-stiction layer  110  faces the lower surface  116   s  of the moveable mass  116  and has a series of peaks (e.g.,  124 ) and valleys (e.g.,  126 ), that reduce contact area between the moveable mass  116  and the anti-stiction layer  110 . Thus, stiction force between the moveable mass  116  and anti-stiction layer  110  is decreased and the possibility of stiction is reduced. In some embodiments, the rough top surface  110   s  of anti-stiction layer  110  has a root mean square (RMS) surface roughness in a range of from about 10 nm to about 60 nm, preferably greater than 40 nm. The RMS surface roughness is calculated as the root mean square of a surface&#39;s measured microscopic peaks and valleys, as provided by the formula below: 
                 R   q     =         1   n     ⁢       ∑     i   =   1     n     ⁢     y   i   2             ;         
wherein R q  is the RMS surface roughness of the anti-stiction layer  110 , y i  is the vertical distance from the mean surface  122  to each of n data points, which can be spaced at regular intervals on the mean surface  122 . In some embodiments, a distance d s  between the rough top surface  110   s  of the anti-stiction layer  110  and the lower surface  116   s  of the moveable mass  116  is less than 100 μm, for example, between about 10 μm and about 20 μm, such that stiction could be a consideration that may affect yield and performance of the MEMS package  100 .
 
       FIG. 1C  illustrates a perspective view of some embodiments of a portion of the MEMS package  100  of  FIG. 1A . As shown in  FIG. 1C , the anti-stiction layer  110  can have a ring shape surrounding the fixed electrode plate  106 . The anti-stiction layer  110  can also be one or a plurality of rectangular, round or other suitable shaped portions disposed alongside the fixed electrode plate  106 . During operation of the MEMS package  100 , the moveable mass  116  can move with respect to the CMOS substrate  104  commensurate with a force experienced by the MEMS package  100 . For example, if the MEMS package  100  is moved upward suddenly, the moveable mass  116  will tend to stay at rest such that the moveable mass  116  and CMOS substrate  104  will squeeze closer together during the acceleration. This temporary change in spacing due to the acceleration correspondingly provides a temporary change in a capacitance between the moveable mass  116  and the fixed electrode plate  106 . The capacitance between the fixed electrode plate  106  and moveable mass  116  can be monitored, and the acceleration experienced by the MEMS device can then be calculated based on this monitored capacitance. In some cases, the acceleration is extreme that the lower surface  116   s  of the moveable mass  116  moves very close and may even reach on the rough top surface  110   s  of the anti-stiction layer  110 . Since the peaks (see  124  in  FIG. 1B ) of the rough top surface  110   s  are closer to the moveable mass  116  than the smooth top surface  106   s , the anti-stiction layer  110  prevents the fixed electrode plate  106  from contacting the moveable mass  116 . Thereby, stiction between the fixed electrode plate  106  and the moveable mass  116  is limited. Further, compared to the rough top surface  116   s  which provides good mechanical anti-stiction properties, the smooth top surface  106   s  of the fixed electrode plate  106  provides good electrical properties for MEMS devices over different ICs in that the smoothness helps provide a consistent distance between the fixed electrode plate  106  and the lower surface of the moveable mass. 
       FIG. 2  illustrates a cross-sectional view of some other embodiments of a MEMS package  200  with a rough metal anti-stiction layer. The MEMS package  200  comprises a CMOS IC  202  including a CMOS substrate  204  and an interconnect structure  232  disposed over the CMOS substrate  204 . The interconnect structure  232  includes a plurality of metal layers disposed within a plurality of ILD layers. A MEMS IC  212  is bonded to an upper surface  232   s  of the interconnect structure  232  and, in cooperation with the CMOS IC  202 , enclosing a cavity  220  between the MEMS IC  212  and the CMOS IC  202 . A moveable mass  216  of the MEMS IC  212  is arranged within the cavity  220 . 
     In some embodiments, the MEMS IC  212  further comprises a capping substrate  214  having a recess  222  disposed directly above the moveable mass  216  and which constitutes a portion of the cavity  220  in fluid communication with a lower portion between the moveable mass  216  and the CMOS IC  202 . The cavity  220  is hermetically sealed from the ambient environment surrounding the MEMS package  200 . In other embodiments, the capping substrate  214  encloses the recess  222  in cooperation with the moveable mass  216  to form a second hermetically sealed cavity that is isolated from the cavity  220  having the same or different pressures. The moveable mass  216  can be a flexible MEMS membrane, and/or other MEMS structures, configured to deflect in proportion to external stimuli, such as pressure, acceleration, etc. 
     An anti-stiction layer  210  is disposed on the upper surface  232   s  of the interconnect structure  232  under the moveable mass  216 . In some embodiments, the anti-stiction layer  210  is made of metal and has a rough top surface. The MEMS package  200  may further comprise a fixed electrode plate  206  disposed on the upper surface  232   s  of the interconnect structure  232  under the moveable mass  216 , coupled to a measurement circuit configured to detect a distance change between the moveable mass  216  and the fixed electrode plate  206  through capacitive coupling of the moveable mass  216  and the fixed electrode plate  206 . In some embodiments, the fixed electrode plate  206  is made of the same metal as the anti-stiction layer  210  but has a smooth top surface. 
     In some embodiments, the MEMS package  200  further comprises a bonding structure  224  disposed between the MEMS IC  212  and the CMOS IC  202 , configured to bond the two together. In some embodiments, the bonding structure  224  can be a semiconductor-to-metal bonding structure where a first bonding pad  208  of the CMOS IC  202  comprises a metal material such as Al, Cu, Ti, Ta, Au, Ni, Sn and a second bonding pad  218  of the MEMS IC  212  comprises a semiconductor material such as Ge, Si, SiGe. In some other embodiments, the bonding structure  224  can be a eutectic bonding structure and the first bonding pad  208  and the second bonding pad  218  each including at least one of Al, Cu, Ti, Ta, Au, Ni, Sn, or another metal. As an example, the first bonding pad  208  can comprise aluminum and the second bonding pad  218  can comprise germanium. In some embodiments, the first bonding pad  208  or the second bonding pad  218  can be a conformal layer lining a protrusion portion of the CMOS IC  202  or the MEMS IC  212 . The first bonding pad  208  can be disposed on the upper surface  232   s  of the interconnect structure  232  and comprise the same metal with a substantially same thickness of anti-stiction layer  210 . In some embodiments, the upper surface  232   s  of the interconnect structure  232  is a top surface of a top ILD layer  228  surrounding a top metal layer  226  as shown in  FIG. 2 . The first bonding pad  208  and the fixed electrode plate  206  can be respectively coupled to the CMOS devices of the CMOS IC  202  through metal lines of the top metal layer  226 . In some embodiments, an additional dielectric layer  230  is disposed over the top ILD layer  228  and surrounds the first bonding pad  208 . In some embodiments, the bonding structure  224  can have a ring-like configuration as viewed from top, and the first and second bonding pads  208 ,  218  can laterally surround the cavity  220 . In some other embodiments, the first bonding pad  208 , the anti-stiction layer  210  and the fixed electrode plate  206  are disposed aligned within an uppermost metallization plane of the interconnect structure  232 . 
     In some embodiments, the CMOS substrate  204 , or the capping substrate  214  may comprise bulk semiconductor substrates including one or more of, for example, silicon, germanium, silicon carbide, a group III element, and a group V element. In other embodiments, the CMOS substrate  204  or the capping substrate  214  are semiconductor-on-insulator (SOI) substrates, such as silicon-on-insulator or polysilicon-on-insulator (POI) substrates, for example. 
     Therefore, as can be seen from the above embodiments, a rough metal anti-stiction layer can be advantageous in reducing stiction in MEMS structures. The precise surface roughness that is present for the metal anti-stiction layer can vary depending on the manufacturing processes and conditions, such as annealing temperature and time, but typically exhibit a rough surface of peaks and valleys. These peaks and valleys are often irregular, with the depths and widths of the valleys varying over a length or area of the surface, and/or the height and widths of the peaks also varying over a length or area of the surface. Aside from advantageously limiting stiction, metal anti-stiction layer is simple to incorporate into modern semiconductor manufacturing process, and is compatible with other MEMS materials (e.g. bulk silicon). It also avoids contamination problem of the other anti-stiction coatings. 
       FIGS. 3-11  illustrate a series of cross-sectional views of some embodiments of a method for manufacturing a MEMS package with a rough metal anti-stiction layer at various stages of manufacture. 
     As shown in cross-sectional view  300  of  FIG. 3 , a CMOS IC  202 , which includes an interconnect structure  232  over a CMOS substrate  204 , is provided. A plurality of CMOS devices are formed within the CMOS substrate  204 . In various embodiments, the CMOS substrate  204  may comprise any type of semiconductor body (e.g., silicon/CMOS bulk, SiGe, SOI, etc.) such as a semiconductor wafer or one or more die on a wafer, as well as any other type of semiconductor and/or epitaxial layers formed thereon and/or otherwise associated therewith. In some embodiments, the interconnect structure  232  may be formed by forming one or more dielectric layers such as inter-layer dielectrics (ILD) over a front surface of the CMOS substrate  204 . The ILD layers are subsequently etched to form via holes and/or metal trenches. The via holes and/or metal trenches are then filled with a conductive material to form a plurality of metal layers. In some embodiments, the ILD layers may be deposited by a physical vapor deposition technique (e.g., PVD, CVD, etc.). The plurality of metal layers may be formed using a deposition process and/or a plating process (e.g., electroplating, electro-less plating, etc.). In various embodiments, the plurality of metal layers may comprise tungsten, copper, or aluminum copper, for example. In some embodiments, a top metal layer  226  of the plurality of metal layers has an upper surface aligned with an upper surface of the top ILD layer  228  of the plurality of ILD layers. 
     As shown in cross-sectional view  400  of  FIG. 4 , a metal layer  402  is formed over the CMOS IC  202 . In some embodiments, the metal layer is formed directly on the upper surfaces of the top metal layer  226  and the top ILD layer  228 . In some embodiments, the metal layer is formed by a chemical vapor deposition process, such as low pressure chemical vapor deposition (LPCVD), plasma-enhanced chemical vapor deposition (PECVD) or an atmospheric pressure chemical vapor deposition (APCVD) growth process. In some embodiments, the metal layer may comprise aluminum (Al), nickel (Ni) or copper (Cu). 
     As shown in cross-sectional view  500  of  FIG. 5 , the metal layer  402  is patterned to form an anti-stiction precursor  502 , a fixed electrode plate  206  and a first bonding pad  208 . An additional dielectric layer  230  can be formed to surround the first bonding pad  208 . 
     As shown in cross-sectional view  600  of  FIG. 6 , an amorphous silicon layer  602  is formed on exposed surfaces of the interconnect structure and the patterned metal layer. In some embodiments, the amorphous silicon layer  602  is formed by a chemical vapor deposition process, such as low pressure chemical vapor deposition (LPCVD), plasma-enhanced chemical vapor deposition (PECVD) or an atmospheric pressure chemical vapor deposition (APCVD) growth process. For example, the amorphous silicon layer  602  can be formed by a PECVD process at a temperature lower than about 400° C. 
     As shown in cross-sectional view  700  of  FIG. 7 , the amorphous silicon layer  602  is patterned to leave a portion  702  on the anti-stiction precursor  502  and to remove remaining portions such as a second portion of the amorphous silicon layer  602  on the fixed electrode plate  206 . 
     As shown in cross-sectional view  800  of  FIG. 8 , an annealing process is performed to facilitate inter-diffusion between the portion  702  of the amorphous silicon layer and the anti-stiction precursor  502  such that the anti-stiction precursor  502  converts to an anti-stiction layer  210  with a rough top surface. Metal silicide micro-particles can be formed at an interface of the anti-stiction layer  210  and the portion  702  of the amorphous silicon layer through a granulation process of the anti-stiction precursor  502  at applicable temperatures. The size, density, and the composition of the micro-particles could be controlled by adjusting the annealing temperature, time, and the film thickness. As an example, the anti-stiction layer  210  can be made of aluminum and be annealed at a temperature of about 430° C. for about 1 hour. A diameter of the formed micro-particles can be in a range of about several tens of nanometers. 
     As shown in cross-sectional view  900  of  FIG. 9 , an etching process is performed to remove the portion  702  of the amorphous silicon layer and to leave a rough top surface of the anti-stiction layer  210  exposed. In some embodiments, the portion  702  of the amorphous silicon layer is removed by a selective etching process such as a Reactive Ion Etching (RIE) process, for example. 
     As shown in cross-sectional view  1000  of  FIG. 10 , a MEMS IC  212  is provided. In some embodiments, a MEMS device layer  1002  is etched back from a front side to form a protrusion  1004  at a position to be bonded to the CMOS IC. A second bonding pad  218  is formed on the protrusion  1004 . In some embodiments, the second bonding pad  218  is formed conformally covering sidewalls of the protrusion  1004 . In some embodiments, a capping substrate  214  is bonded to the MEMS device layer  1002  at a back side that is opposite to the protrusion  1004 . The capping substrate  214  can be prepared from a bulk semiconductor wafer  302  including, for example, a monocrystalline wafer, or another substrate made of germanium, silicon carbide, a group III element, and/or a group V element, for example. In some embodiments, a recess  222  can be etched to a proper depth at a location corresponding to moveable or flexible portion of the MEMS device layer. Notably, among other considerations, applicable heights of the protrusion  1004  and the recess  222  are formed with a consideration of providing sufficient space for motion and/or suitable stiction force between a moveable or flexible part of the MEMS device to be formed and a neighboring component. The MEMS device layer  1002  is patterned to form MEMS devices including a moveable mass  216 . The MEMS devices include, for example, micro-actuators or micro-sensors such as a micro-valve, a micro-switch, a microphone, a pressure sensor, an accelerator, a gyroscope or any other device having a moveable or flexible part that moves or flexes with respect to the fixed portion. 
     As shown in cross-sectional view  1100  of  FIG. 11 , the MEMS IC  212  is bonded to the CMOS IC  202 . A cavity  220  is enclosed between the moveable mass  216  and the fixed electrode plate  206 . In some embodiments, the MEMS IC  212  and the CMOS IC  202  are bonded by semiconductor-to-metal bonding where the first bonding pad  208  comprises metal materials such as Al, Cu, Ti, Ta, Au, Ni, Sn and the second bonding pad  218  comprises semiconductor materials such as Ge, Si, SiGe. In some other embodiments, the MEMS IC  212  and the CMOS IC  202  are bonded by eutectic bonding between two metal materials each including at least one of Al, Cu, Ti, Ta, Au, Ni, Sn, or another metal. The materials to be bonded are pressed against each other in an annealing process to form a eutectic phase of the materials. For example, a eutectic bonding between Ge and Al is formed at an annealing temperature in a range from 400° C. to 450° C. After the MEMS IC  212  is bonded to the CMOS IC  202 , the MEMS package is formed when the bonded CMOS IC  202  and MEMS IC  212 , which are often bonded at the wafer level, are diced into separate chips after bonding. 
       FIG. 12  illustrates a flow diagram of some embodiments of a method for manufacturing a MEMS package with a rough metal anti-stiction layer. 
     While disclosed method  1200  is illustrated and described herein as a series of acts or events, it will be appreciated that the illustrated ordering of such acts or events are not to be interpreted in a limiting sense. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. In addition, not all illustrated acts may be required to implement one or more aspects or embodiments of the description herein. Further, one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases 
     At  1202 , a CMOS IC is provided. CMOS devices are formed within a CMOS substrate and an interconnect structure including a plurality of metal layers formed within a plurality of ILD layers is formed over the CMOS substrate.  FIG. 3  illustrates a cross-sectional view corresponding to some embodiments corresponding to act  1202 . 
     At  1204 , a metal layer is formed over the CMOS IC. In some embodiments, the metal layer is formed directly on an upper surface of the interconnect structure.  FIG. 4  illustrates a cross-sectional view corresponding to some embodiments corresponding to act  1204 . 
     At  1206 , the metal layer is patterned to form an anti-stiction precursor, a fixed electrode plate, and a first bonding pad.  FIG. 5  illustrates a cross-sectional view corresponding to some embodiments corresponding to act  1206 . 
     At  1208 , an amorphous silicon layer is formed over the patterned metal layer. In some embodiments, the amorphous silicon layer can be formed by a PECVD process.  FIG. 6  illustrates a cross-sectional view corresponding to some embodiments corresponding to act  1208 . 
     At  1210 , the amorphous silicon layer is patterned to leave a portion on the anti-stiction layer and to remove remaining portions of the anti-stiction layer.  FIG. 7  illustrates a cross-sectional view corresponding to some embodiments corresponding to act  1210 . 
     At  1212 , an annealing process is performed. The annealing process facilitates inter-diffusion between the amorphous silicon and the anti-stiction layer to form silicide micro-particles at an interface.  FIG. 8  illustrates a cross-sectional view corresponding to some embodiments corresponding to act  1212 . 
     At  1214 , the amorphous silicon layer is removed. In some embodiments, the amorphous silicon layer is removed by a RIE process. After removing the amorphous silicon layer together with the silicide micro-particles, a rough top surface of the anti-stiction layer is exposed.  FIG. 9  illustrates a cross-sectional view corresponding to some embodiments corresponding to act  1214 . 
     At  1216 , a MEMS IC is provided. In some embodiments, a MEMS device layer is prepared for following bonding process by forming a protrusion and a second bonding pad for the MEMS IC. MEMS structures are formed including forming a moveable mass. In some embodiments, a capping substrate is bonded to a back side of the MEMS device layer.  FIG. 10  illustrates a cross-sectional view corresponding to some embodiments corresponding to act  1216 . 
     At  1218 , the MEMS IC is bonded to the CMOS IC. A cavity can be enclosed between the moveable mass of the MEMS IC and the fixed electrode plate on the CMOS IC.  FIG. 11  illustrates a cross-sectional view corresponding to some embodiments corresponding to act  1218 . 
     Thus, as can be appreciated from above, the present disclosure relates to a MEMS package with a rough metal anti-stiction layer to improve stiction characteristics, and associated methods of forming such a MEMS package. The MEMS package comprises a MEMS IC bonded to a CMOS IC and an anti-stiction layer is disposed on the CMOS IC under a moveable mass of the MEMS IC. In some embodiments, the anti-stiction layer is formed by forming an amorphous silicon layer on a metal precursor followed by performing an annealing process. The annealing process facilitates inter-diffusion and formation of silicide micro-particles at an interface between the metal precursor and the amorphous silicon layer. Then the amorphous silicon is removed, together with the formed silicide micro-particles, leaving a rough surface for the metal precursor. 
     In some embodiments, the present disclosure relates to a method for manufacturing a microelectromechanical systems (MEMS) package. The method comprises providing a CMOS IC including CMOS devices arranged within a CMOS substrate. The method further comprises forming and patterning a metal layer over the CMOS substrate to form an anti-stiction layer and a fixed electrode plate and forming a rough top surface for the anti-stiction layer. The method further comprises providing a MEMS IC comprising a moveable mass arranged within a recess of a MEMS substrate and bonding the CMOS IC to the MEMS IC to enclose a cavity between the moveable mass and the fixed electrode plate and the anti-stiction layer. 
     In other embodiments, the present disclosure relates to a method for manufacturing a microelectromechanical systems (MEMS) package. The method comprises providing a CMOS IC including CMOS devices arranged within a CMOS substrate and providing a MEMS IC comprising a moveable mass arranged within a recess of a MEMS substrate. The method further comprises forming an anti-stiction layer and a fixed electrode plate at a position spaced apart from the moveable mass. The method further comprises bonding the CMOS IC to the MEMS IC to enclose a cavity between the moveable mass and the fixed electrode plate and the anti-stiction layer. 
     In yet other embodiments, the present disclosure relates to a method for manufacturing a microelectromechanical systems (MEMS) package. The method comprises providing a CMOS IC comprising CMOS devices disposed within a CMOS substrate. The method further comprises forming an anti-stiction layer over the CMOS substrate. The method further comprises bonding a MEMS device layer to the CMOS IC. The MEMS device layer comprises a fixed portion and a moveable mass connected to the fixed portion and over the anti-stiction layer. The method further comprises bonding a capping substrate to a back side of the MEMS device layer opposite to the CMOS IC so as to enclose a cavity between the capping substrate and the CMOS substrate. The moveable mass is arranged in the cavity. 
     The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.