Abstract:
A method of etching a device in one embodiment includes providing a silicon carbide substrate, forming a silicon nitride layer on a surface of the silicon carbide substrate, forming a silicon carbide layer on a surface of the silicon nitride layer, forming a silicon dioxide layer on a surface of the silicon carbide layer, forming a photoresist mask on a surface of the silicon dioxide layer, and etching the silicon dioxide layer through the photoresist mask.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to fabrication processes for semiconductor devices. 
       BACKGROUND 
       [0002]    Silicon carbide (SiC) has a large energy band gap and high breakdown field. As such, SiC is an attractive material for electronic devices operating at high temperatures and high power. SiC also exhibits mechanical properties and chemical inertness which are useful in micro-electromechanical systems (MEMS) as well as nano-electromechanical systems (NEMS) for applications in harsh environments. SiC based devices are therefore particularly attractive for use as high-temperature sensors and actuators. 
         [0003]    Additionally, SiC has a high acoustic velocity and extremely stable surfaces. Thus, SiC is a promising structural material for fabricating ultra-high frequency micromechanical signal processing systems. The highly stable physicochemical properties of SiC also improve the performance of high-frequency resonators as the surface-to-volume ratio increases when the resonator frequency scales into the GHz ranges. 
         [0004]    One of the challenges in fabricating SiC devices is related to the selective etching of SiC films or SiC bulk materials. Unlike silicon (Si), SiC is not etched significantly by most acids and bases at temperatures less than about 600° C. Most wet etching processes, however, are not easily effected at temperatures greater than about 600° C. Non-standard techniques such as laser-assisted photo-electrochemical etching have been developed, but such techniques require special equipment and exhibit poor lateral dimension control. 
         [0005]    Traditional fabrication processes incorporating photoresist etch masks are also problematic. Primary etch gasses that are used in SiC etching include chlorine (Cl 2 ) and hydrogen bromide (HBr). The photoresist material, however, exhibits poor selectivity compared to SiC when exposed to traditional etch gases. 
         [0006]    What is needed is a method of manufacturing a device incorporating a masking material which exhibits increased selectivity compared with traditional masking materials. What is further needed is a method of manufacturing a device incorporating a masking material which exhibits increased selectivity when exposed to traditional SiC etching gases. 
       SUMMARY 
       [0007]    In accordance with one embodiment of the present invention, there is provided a method of etching a device that includes providing a silicon carbide substrate, forming a silicon nitride layer on a surface of the silicon carbide substrate, forming a silicon carbide layer on a surface of the silicon nitride layer, forming a silicon dioxide layer on a surface of the silicon carbide layer, forming a photoresist mask on a surface of the silicon dioxide layer, and etching the silicon dioxide layer through the photoresist mask. 
         [0008]    In accordance with another embodiment of the present invention, there is provided a method of etching a semiconductor device including providing a substrate, forming an etch stop layer on a surface of the substrate, forming a silicon carbide layer on a surface of the etch stop layer, forming a hard mask layer on a surface of the silicon carbide layer, forming a photoresist mask on the hard mask layer, and etching the silicon carbide layer through the hard mask layer and the photoresist mask. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  shows a flow chart of an SiC etching portion of a process for manufacturing a device in accordance with principles of the present invention; 
           [0010]      FIG. 2  shows a cross-sectional view of a substrate, which in this embodiment is a SiC substrate, which may be used in a device in accordance with principles of the present invention; 
           [0011]      FIG. 3  shows a device including the substrate of  FIG. 2  with an etch stop layer, which may include Si 3 N 4 , formed on the upper surface of the substrate; 
           [0012]      FIG. 4  shows the device of  FIG. 3  with a SiC layer formed on the upper surface of the etch stop layer of  FIG. 3 ; 
           [0013]      FIG. 5  shows the device of  FIG. 4  with a hard mask layer, which in this embodiment includes SiO 2 , formed on the SiC layer of  FIG. 4 ; 
           [0014]      FIG. 6  shows the device of  FIG. 5  with a photoresist mask formed on the upper surface of the hard mask layer of  FIG. 5 ; 
           [0015]      FIG. 7  shows the device of  FIG. 6  with the hard mask layer etched beneath the openings of the photoresist mask to expose portions of the upper surface of the SiC layer in accordance with principles of the present invention; 
           [0016]      FIG. 8  shows the device of  FIG. 7  with the SiC layer etched beneath the openings of the photoresist mask to expose portions of the upper surface of the etch stop layer in accordance with principles of the present invention; 
           [0017]      FIG. 9  shows the device of  FIG. 8  with the etch stop layer etched beneath the openings of the photoresist mask to expose portions of the upper surface of the substrate in accordance with principles of the present invention; 
           [0018]      FIG. 10  shows the device of  FIG. 9  with the remainder of the photoresist mask removed to expose the remainder of the upper surface of the hard mask layer in accordance with principles of the present invention; and 
           [0019]      FIG. 11  shows the device of  FIG. 10  with the remainder of the upper surface of the hard mask layer removed to expose the remainder of the upper surface of the SiC layer in accordance with principles of the present invention. 
       
    
    
     DESCRIPTION 
       [0020]    For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the invention is thereby intended. It is further understood that the present invention includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the invention as would normally occur to one skilled in the art to which this invention pertains. 
         [0021]      FIG. 1  shows a flow chart  100  of SiC etching portion of a manufacturing process for a device in accordance with principles of the present invention. The process  100  of  FIG. 1  begins at step  102  and a substrate is provided at  104 . At step  106 , an etch stop layer is formed on the surface of the substrate followed by formation of a SiC layer on the etch stop layer at the step  108 . A hard mask is then formed on the SiC layer at step  110  and a photoresist mask is patterned on the hard mask at step  112 . 
         [0022]    Etching of the device begins with etching of the hard mask layer through the photoresist mask at the step  114 . Next, the SiC layer is etched at the step  116  through the photoresist mask and the hard mask layer. The etch stop layer is then etched at the step  118 . 
         [0023]    When the desired etching is concluded, the photoresist mask is removed at the step  120  followed by the removal of the hard mask layer at the step  122 . The process then ends at the step  124 . After the process shown in  FIG. 1  is complete, further processing of the device may be performed. 
         [0024]    One example of the process of  FIG. 1  is shown in  FIGS. 2-11 . A substrate  130  is shown if  FIG. 2 . The substrate  130  may either be a SiC substrate or a substrate having a layer of SiC formed thereon. Next,  FIG. 3  shows an etch stop layer  132  formed on the upper surface  134  of the substrate  130 . The etch stop layer  132  preferably includes silicon nitride (Si 3 N 4 ). Next, a layer  136  of SiC is formed on the upper surface  138  of the etch stop layer  132  as shown in  FIG. 4  and a hard mask layer  140  is formed on the upper surface  142  of the SiC layer  136  as shown in  FIG. 5 . The hard mask layer  140  in this embodiment includes silicon dioxide (SiO 2 ). 
         [0025]      FIG. 6  shows a photoresist mask  144  in position on the upper surface  146  of the hard mask layer  140 . The photoresist mask  144  may be patterned to include a number of openings  148 . The openings  148  may be of any desired form such as circles, rectangles, etc. Portion of the upper surface  146  of the hard mask layer  140  are exposed through the openings  148 . 
         [0026]    Etching of the device may then be performed using an etching gas which preferably includes Cl 2 , HBr or both Cl 2  and HBr. The etching gas contacts the hard mask layer  140  through the openings  148  thereby etching the material directly beneath the openings  148  and generating a via  150  through the hard mask layer  140  to expose the SiC layer  136  as shown in  FIG. 7 . 
         [0027]    Continued exposure to etching gases results in the etching of the SiC layer  136 . The hard mask layer  140  is exposed to the etching gases about the vias  150 . The SiC layer  136 , however, is more rapidly etched by the etch gases than the material used to form the hard mask layer  140 . In the embodiment of  FIGS. 2-11 , the selectivity ratio of the SiC layer to the SiO 2  hard mask layer is about 6:1. Accordingly, the predominant effect of the etch gas is to extend the via  150  through the SiC layer  136  to expose the upper surface  138  of the etch stop layer  132  as shown in  FIG. 8 . 
         [0028]    Continued exposure to etching gases results in the etching of the etch stop layer  132 . The selectivity ratio of SiC to the Si 3 N 4  used in this embodiment is about 1.4:1. Accordingly, the via  150  widens as the etch stop layer  132  is etched, particularly in the SiC layer  136 . Etching concludes when the upper surface  134  of the substrate  130  is exposed to the desired extent as shown in  FIG. 9 . 
         [0029]    At this point, the photoresist mask  144  is no longer needed. Accordingly, any remnant of the photoresist mask  144  is removed using any desired process leaving the remainder of the upper surface  146  of the hard mask layer  140  exposed as shown in  FIG. 10 . The remainder of the hard mask layer  140  is likewise removed using any desired process leaving the remainder of the upper surface  142  of the SiC layer  136  exposed as shown in  FIG. 11 . 
         [0030]    While the invention has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the invention are desired to be protected.