Abstract:
In accordance with the teachings of one embodiment of the present disclosure, a method for manufacturing a semiconductor device includes forming a support structure outwardly from a substrate. The support structure has a first thickness and a first outer sidewall surface that is not parallel with the substrate. The first outer sidewall surface has a first minimum refractive index. A first anti-reflective layer is formed outwardly from the support structure and outwardly from the substrate. A second anti-reflective layer is formed outwardly from the first anti-reflective layer. The first and second anti-reflective layers each includes respective compounds of at least two elements selected from the group consisting of: silicon; nitrogen; and oxygen.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates in general to semiconductor devices, and more particularly to manufacturing optical microelectromechanical systems (MEMS) with thin-film anti-reflective layers. 
       BACKGROUND 
       [0002]    Semiconductor devices may be designed to interact with electromagnetic radiation that is incident upon a particular area of the device. One such semiconductor device is a spatial light modulator (SLM), which serves to redirect the path of incoming radiation by action of one or more accepted principles of optics, such as reflection, refraction, or diffraction. Unfortunately, in many of these devices, some incident radiation may not be redirected in the desired manner due to physical gaps, unwanted diffraction, scattering effects, or other phenomena. Such radiation may be deemed “stray radiation,” which may degrade the performance of the overall system if a mechanism of absorbing the radiation is not present. Conventional methods of reducing stray radiation are limited for a variety of reasons. 
       SUMMARY 
       [0003]    In accordance with the teachings of one embodiment of the present disclosure, a method for manufacturing a semiconductor device includes forming a support structure outwardly from a substrate. The support structure has a first thickness and a first outer sidewall surface that is not parallel with the substrate. The first outer sidewall surface has a first minimum refractive index. A first anti-reflective layer is formed outwardly from the support structure and outwardly from the substrate. A second anti-reflective layer is formed outwardly from the first anti-reflective layer. The first and second anti-reflective layers each includes respective compounds of at least two elements selected from the group consisting of: silicon; nitrogen; and oxygen. 
         [0004]    Technical advantages of certain embodiments of the present disclosure include mitigation or elimination of stray radiation associated with reflective sidewalls and other surfaces of conventional processing through the use of one or more anti-reflective layers. In some embodiments, the relative thinness of the anti-reflective layer(s) may facilitate minimal process perturbations or changes for subsequent levels of DMD processing. Various embodiments may encase reflective sidewalls within one or more anti-reflective layers. In addition, various embodiments may mitigate or even eliminate the effect of stray radiation from metal lines within inwardly disposed substrates by providing an anti-reflective “blanket” over the surface of an interposing dielectric. In addition to potential optical advantages, the anti-reflective layer(s) of various embodiments may mitigate undesired effects of at least the following: corrosion, residue formation, delamination of the anti-reflective layers, and electrical shorts. 
         [0005]    Other technical advantages of the present disclosure will be readily apparent to one skilled in the art from the following figures, descriptions, and claims. Moreover, while specific advantages have been enumerated above, various embodiments may include all, some, or none of the enumerated advantages. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: 
           [0007]      FIG. 1  is a perspective view of a portion of a deformable micromirror device (DMD) in accordance with one embodiment of the present disclosure; and 
           [0008]      FIG. 2A  shows a cross-sectional view of a portion of the DMD of  FIG. 1  after the formation of a dielectric layer outwardly from a substrate, and after the formation of support structures disposed outwardly from the dielectric layer; 
           [0009]      FIG. 2B  shows a cross-sectional view of a portion of the DMD of  FIG. 2A  after the formation of a first anti-reflective layer outwardly from the support structures and the dielectric layer; and 
           [0010]      FIG. 2C  shows a cross-sectional view of a portion of the DMD of  FIG. 2B  after the formation of a second anti-reflective layer outwardly from the first anti-reflective layer. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    The teachings of some embodiments of the present disclosure provide a semiconductor device having thin anti-reflective layer(s) operable to absorb radiation that may otherwise reflect off surfaces disposed inwardly from the anti-reflective layer(s). Such anti-reflective layers may be utilized in any of a variety of semiconductor devices, such as a spatial light modulator, a variable diffraction grating, a liquid crystal light valve, or other semiconductor device, to reduce the effects of “stray radiation” on the performance of the device. An example of one such device is a deformable micromirror device, a subset of which includes digital micromirror devices; however, the teachings of the present disclosure may apply to any of a variety of semiconductor devices. A portion of a digital micromirror device is illustrated in  FIG. 1 . 
         [0012]      FIG. 1  illustrates a perspective view of a portion of a deformable micromirror device (DMD)  100 . In the illustrated embodiment, DMD  100  includes an array of hundreds of thousands of micromirrors  102  encased within a cavity at least partially defined by a substrate  118  and a transparent window (not explicitly shown). Each micromirror  102  may tilt up to plus or minus twelve degrees, for example, creating an active “on” state condition or an active “off” state condition. Each micromirror may selectively communicate at least a portion of an optical signal or light beam  102  by transitioning between its active “on” and “off” states. To permit micromirrors  102  to tilt, each micromirror  102  is attached to a respective hinge  104  mounted on a hinge post  106 , and spaced by means of an air gap over support structures  108 . In some embodiments, support structures  108  may each be considered a MEMS base that supports outwardly disposed MEMS superstructure (e.g., hinge posts  106 , which in turn support hinge  104  and micromirror  102 ). In some embodiments, thin anti-reflective layers of silicon nitride (Si 3 N 4 ), silicon dioxide (SiO 2 ), and/or silicon oxynitride (Si 2 N 2 O) may be formed outwardly from portions of the support structures  108 , including sidewalls  110 , as explained further below. 
         [0013]    Micromirrors  102  tilt in the positive or negative direction as a result of preferential electrostatic forces between a micromirror  102  and at least one of its corresponding electrodes  114 . In this example, a yoke  105  increases the electrostatic forces acting on micromirror  102  and stops micromirror  102  rotation by contacting conductive conduits  112 . Although this example includes yoke  105 , other examples may eliminate yoke  105 . In those examples, micromirrors  102  may tilt in the positive or negative direction until micromirrors  102  contact a suitable mirror stop (not explicitly shown). 
         [0014]    In this particular example, support structures  108  form an arrangement having electrically-isolated conductive conduits  112  portions and electrode  114  portions. In addition, support structures  108  are multi-layered etched-metallic structures encased within an anti-reflective layer(s) and disposed outwardly from a dielectric layer  116 , as explained further below. Dielectric layer  116  operates to isolate support structures  108  from a substrate  118 . 
         [0015]    In this particular example, substrate  118  comprises the control circuitry associated with DMD  100 . The control circuitry may include any hardware, software, firmware, or combination thereof capable of at least partially contributing to the creation of the electrostatic forces between electrodes  114  and micromirrors  102 . The control circuitry associated with substrate  118  functions to selectively transition micromirrors  102  between “on” state and “off” state based at least in part on data received from a processor (not explicitly shown). 
         [0016]    Substrate  118  and support structures  108  typically comprise one or more layers of metals and dielectrics that may be optically reflective. During operation of some embodiments, portions of substrate  118  and support structures  108 , including sidewalls  110 , may be exposed to incident radiation, referred to herein as “stray radiation,” due to the tilting of micromirrors  102  and the gaps between micromirrors  102 . In conventional DMDs, this stray radiation can result in unwanted reflections that may reduce the image quality produced by the DMD. 
         [0017]    Accordingly, the teachings of some embodiments of the disclosure recognize methods of disposing thin film anti-reflective layer(s) along the reflective surfaces of support structure  108 , including, for example, sidewalls  110 . In addition, the layer(s) may form a protective “blanket” outwardly from dielectric layer  116  between support structures  108 , thereby mitigating or eliminating stray radiation from optically reflective surfaces within substrate  118 . 
         [0018]    In some embodiments, the anti-reflective layer(s) may be more chemically stable than layers used in conventional designs. For example, layers formed from alternative materials, such as, for example, titanium nitride (TiN), may delaminate over time after exposure to various compounds enclosed within the cavity of a MEMS device. In contrast, the anti-reflective layers of some embodiments of the present disclosure may be less chemically reactive than TiN when exposed to the same compounds enclosed within a MEMS device. Anti-reflective layers that are less-reactive or even non-reactive with the various compounds enclosed within the cavity of a MEMS device, or chemically stable anti-reflective layers, may enhance structural stability, optical performance, and reliability. According to the teachings of some embodiments, examples of such chemically stable anti-reflective layers include thin films composed of any suitable combination of silicon, nitrogen, and/or oxygen (e.g., silicon nitride (Si 3 N 4 ), silicon dioxide (SiO 2 ), and/or silicon oxynitride (Si 2 N 2 O)). 
         [0019]    DMD  100  may be used as a basis for forming any of a variety of semiconductor devices, including optical MEMS devices. Some examples of such semiconductor devices include a spatial light modulator, a gain equalizer, an optical filter, or any combination of these or other optical devices. Methods for manufacturing a semiconductor device in accordance with the teachings of various embodiments of the present disclosure are illustrated in  FIGS. 2A through 2C . 
         [0020]      FIGS. 2A through 2C  illustrate one example of a method of forming a portion of the DMD  100  of  FIG. 1  that disposes thin film, chemically stable, anti-reflective layers  208  and  210  capable of mitigating or even eliminating stray reflections from inwardly disposed support structure sidewalls and metal lines. More specifically,  FIG. 2A  shows a cross-sectional view of a portion of DMD  100  after the formation of dielectric layer  116  outwardly from substrate  118 , and after the formation of support structures  108  disposed outwardly from dielectric layer  116 . 
         [0021]    Substrate  118  may comprise any suitable material used in semiconductor chip fabrication, such as silicon, poly-silicon, indium phosphide, germanium, or gallium arsenide. In various embodiments, substrate  118  can include complementary metal-oxide semiconductor (CMOS) circuitry capable of controlling DMD  100  after its formation. In one non-limiting example, the CMOS circuitry may comprise a CMOS memory circuit, such as, for example, a 5T or 6T SPAM cell. 
         [0022]    Dielectric layer  116  acts to electrically isolate support structures  108  from substrate  118 . Dielectric layer  116  may be formed from any dielectric material suitable for use in semiconductor manufacturing, such as TEOS oxide, HDP oxide, or any suitable combination of dielectrics. In addition, dielectric layer  116  may have any suitable thickness, such as approximately 10,000 angstroms, and may be formed in any suitable manner. Such suitable deposition techniques include, but are not limited to, sputtering, chemical vapor deposition, plasma-enhanced chemical vapor deposition, and spin-coating. In some cases, dielectric layer  116  can be planarized, such as by using a chemical mechanical polish (CMP) technique, to provide a relatively flat surface. 
         [0023]    Support structures  108  are each generally operable to provide a stable base and conductive conduits for respectively coupled electromechanical components, such as, for example, hinge posts  106  and electrode posts  115  of  FIG. 1 . Support structures  108  may have any suitable arrangement and include any suitable number of layers (e.g., layers  202 ,  204 , and  206 ). In addition, support structures  108  may be composed of any suitable material. For example, each layer  202 ,  204 , and  206  may be respectively formed from aluminum or an aluminum alloy, copper, silver, gold, tungsten, titanium, titanium nitride (TiN), silicon, polysilicon, carbon, chromium, and nickel and/or a combination of these or other suitable materials. Support structure  108  may have any suitable thickness, such as approximately 5,000 angstroms, and may be formed in any suitable manner, such as deposition. Such suitable deposition techniques include, but are not limited to, sputtering, chemical vapor deposition, plasma-enhanced chemical vapor deposition, and spin-coating. 
         [0024]    In this particular embodiment, plural layers  202 ,  204 , and  206  were previously deposited and collectively patterned and etched in the approximate arrangement of support structures  108  of  FIG. 1 . As shown in  FIG. 2A , support structures  108  include sidewalls  250  that are substantially perpendicular to the surface of dielectric layer  116 . In various embodiments, sidewalls  250  may be highly reflective and positioned within the pathway of potential stray radiation, as illustrated by beam  252 . As shown in  FIG. 2B , an anti-reflective layer  208  may make the use of more reflective materials possible for layer(s)  202 ,  204 , and  206  by covering exposed support structure  108  surfaces, including sidewalls  250 , with a light absorptive material. 
         [0025]      FIG. 2B  shows a cross-sectional view of a portion of the DMD  100  of  FIG. 2A  after the formation of a first anti-reflective layer  208  outwardly from support structures  108  and dielectric layer  116 . Although anti-reflective layer  208 , support structures  108 , and dielectric layer  116  are shown as being formed without interstitial layers between them, such interstitial could alternatively be formed without departing from the scope of the present disclosure. 
         [0026]    In various embodiments, anti-reflective layer  208  may be an insulator. An anti-reflective layer  208  that sufficiently resists the flow of electric current will not electrically connect support structures  108  and thus will not short electrodes  114  to conductive conduits  112 . Some examples of anti-reflective layers  208  with insulator or nonconductive properties include thin films composed of any suitable combination of silicon, nitrogen, and/or oxygen (e.g., silicon nitride (Si 3 N 4 ), silicon dioxide (SiO 2 ), and/or silicon oxynitride (Si 2 N 2 O)). In this example, anti-reflective layer  208  is formed by sputter depositing a silicon nitride layer to a thickness that is less than the total thickness of support structures  108 ; however, any suitable material, processing, or thickness may be used. 
         [0027]    In some embodiments, all or a portion of anti-reflective layer  208  may be exposed to chemical components encased within a cavity of a MEMS device (e.g., DMD  100 ) or otherwise proximately available in the atmosphere. Some chemical reactions can create residue that may inhibit, for example, the mechanical and optical performance of DMD  100 . In addition, some reactions can cause all or a portion of thin film layers to delaminate, which might cause catastrophic failure of some MEMS devices. Accordingly, some embodiments provide an anti-reflective layer  108  that is not reactive, or less reactive, to such proximately positioned chemical components. In some embodiments, anti-reflective layers  208  with such non-reactive properties include thin films composed of any suitable combination of silicon, nitrogen, and/or oxygen (e.g., silicon nitride (Si 3 N 4 ), silicon dioxide (SiO 2 ), and/or silicon oxynitride (Si 2 N 2 O)). In addition, some embodiments of the present disclosure provide a second anti-reflective layer, or a “capping” layer, as described further with reference to  FIG. 2C , which may shield all or a portion of the first anti-reflective layer  208  from exposure to an outwardly disposed atmosphere or layer. 
         [0028]      FIG. 2C  shows a cross-sectional view of a portion of DMD  100  of  FIG. 2B  after the formation of a second anti-reflective layer  210  outwardly from the first anti-reflective layer  208 . Although anti-reflective layers  208  and  210  are shown as being formed without interstitial layers between them, such interstitial could alternatively be formed without departing from the scope of the present disclosure. Various embodiments may not include second anti-reflective layer  210 . In this example, however, anti-reflective layer  210  is formed by depositing silicon dioxide to any suitable thickness; however, any suitable processes or materials may be used. 
         [0029]    In some embodiments, completely covering the first anti-reflective layer  208  by a second anti-reflective layer  210  of silicon dioxide may further enhance optical performance by mitigating stray reflections. In addition, in some embodiments, such a second anti-reflective layer  210  may further mitigate or even eliminate undesired chemical reactions by shielding all or a portion of the first anti-reflective layer  208  and all underlying layers from chemical components enclosed within a cavity of a fully fabricated DMD  100 . 
         [0030]    Thus,  FIGS. 2A through 2C  provide enhanced and cost-effective methods for manufacturing a portion of DMD  100  or any other suitable optical MEMS device in accordance with the teachings of various embodiments of the present disclosure. Subsequent semiconductor processing techniques well known in the art may than be utilized to complete DMD  100  by forming the superstructure of DMD  100  including, without limitation, hinge posts  106 , remaining electrodes  112 , hinges  104 , and micromirrors  102 . Such processing techniques may or may not also include selectively removing portions of anti-reflective layer  208  and/or capping layer  210 . 
         [0031]    The present disclosure describes various systems and methods that mitigate the detrimental optical effects of stray radiation using thin anti-reflective layer(s). In some embodiments, the relative thinness of the anti-reflective layer(s)  208  and  210  may enable minimal process or design changes for subsequent levels of DMD processing. For example, various embodiments may be implemented with minimal adjustments of the distance between micromirrors  102  and substrate  118  compared to conventional designs and processes. In various embodiments, such anti-reflective layer(s)  208  and  210  may also provide protection against corrosion and electrical shorts. 
         [0032]    Although the present disclosure has been described with several embodiments, a myriad of changes, variations, alterations, transformations, and modifications may be suggested to one skilled in the art, and it is intended that the present disclosure encompass such changes, variations, alterations, transformations, and modifications as fall within the scope of the appended claims.