Abstract:
A method of manufacturing a floating structure capable of providing increased device yield. The method includes: a) forming an insulation film, a predetermined area of which is removed, between a first substrate and a second substrate; and b) forming a floating structure in the removed predetermined area.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of Korean Patent Application No. 2005-11836 filed on Feb. 14, 2005 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a method of manufacturing a micro floating structure capable of providing improved device yield.  
         [0004]     2. Description of the Related Art  
         [0005]     A micro floating structure as mentioned above is used as an inertia weight, a spring or the like in a sensor such as an accelerometer or gyroscope. A conventional method of manufacturing such a micro floating structure is illustrated in  FIGS. 1A  to  1 E.  
         [0006]     Referring to  FIGS. 1A and 1B , according to the conventional method, first and second oxide films  12 ,  22  are formed on one surface of each of first and second substrates  10 ,  20 , respectively, and then the first and second substrates  10 ,  20  are bonded to one another such that the first and second oxide films  12 ,  22  face one another.  
         [0007]     Then, the second substrate  20  is polished to a thickness of the floating structure  30  (see  FIG. 1D ), as shown in  FIG. 1C .  
         [0008]     Next, the polished second substrate  20  is subjected to photolithographic and dry etching processes to form the floating structure  30 , as shown in  FIG. 1D .  
         [0009]     Then, if the first and second oxide films  12 ,  22  formed underneath of the floating structure  30  are removed by wet etching, the floating structure  30  is in a state in which the bottom surface thereof floats above the first substrate  10 , as shown in  FIG. 1E .  
         [0010]     During the manufacturing process described above, dry etching is performed by bombarding ion beams against the polished second substrate  20 . However, if the second oxide  22  is exposed while the etching is proceeding, ion beams are injected into the second oxide film  22  whereby the second oxide film  22  becomes charged. If so, the path of subsequent ion beams will be changed by the electrostatic force of the second oxide film  22 , and the path-changed ion beams will produce notches  32  on the bottom side of the floating structure  30 . Although the drawing shows several notches  32  on floating structure  30  formed thereby, a countlessly large number of fine notches  32  are practically formed on the bottom side of each floating structure  30 . Such notches  32  change the physical properties such as mass and spring constant of the floating structure  30 , thereby causing an error from a design value. In addition, the path-changed ion beams will produce needle-shaped by-products ablated from the notches  32  while the notches  32  are being formed. Such needle-shaped by-products can interconnect certain spaced parts in the floating structure  30 , thereby causing an electric short in the floating structure  30 .  
         [0011]     On the other hand, the first and second oxide films  12 ,  22  formed below the floating structure  30  are removed by wet etching, wherein the etchant contained in the wet etching liquid causes a capillary phenomenon (or so-called stiction phenomenon), which causes adhesion between the various parts in the floating structure  30  or between the first substrate  10  and the floating structure  30 .  
         [0012]     Notches generated in the floating structure  30 , and electric shorts caused by a needle-shaped by-product and the stiction phenomenon are main detractors of device yield in producing a floating structure  30 .  
       SUMMARY OF THE INVENTION  
       [0013]     The present invention has been made to solve the above-mentioned problems of the prior art, and an object thereof is to provide a method of manufacturing a floating structure capable of providing increased device yield.  
         [0014]     Another object of the present invention is to provide a more precise floating structure.  
         [0015]     Still another object of the present invention is to provide a floating structure, in which the above-mentioned stiction and electric short phenomena can be prevented.  
         [0016]     The above objects of the present invention have been achieved by providing a method of manufacturing a floating structure which comprises: a) forming an insulation film, a predetermined area of which is removed, between a first substrate and a second substrate; and b) forming a floating structure in an area corresponding to the removed predetermined area.  
         [0017]     According to a preferred embodiment, the step a) comprises: a1) forming the insulation film, the predetermined area of which is removed, on the first substrate; a2) bonding the second substrate to the first substrate formed with the insulation film; and a3) polishing the second substrate to a predetermined thickness. In addition, the step a1) comprises: a1-1) forming the insulation film on the first substrate; and a1-2) removing the predetermined area from the insulation film formed on the first substrate.  
         [0018]     The insulation film is preferably formed from a silicon oxide film and the step a1-1) is preferably implemented through an oxidation process. Step a1-2) is preferably implemented through a photolithographic process and an etching process, and step a2) is preferably implemented through a silicon direct bonding method. In addition, step a3) may be implemented through a lapping process and a CMP process.  
         [0019]     Moreover, the step b) may be implemented through a photolithographic process and an etching process, wherein the etching process is implemented through REE (reactive ion etching), which is a dry etching process, in particular by means of a deep RIE process. The deep RIE process is used to etch cavities having a relatively high aspect ratio, for example, by passivating the etched sidewalls with a fluoropolymer. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     The above aspects and features of the present invention will be more apparent from the description of certain embodiments of the present invention with reference to the accompanying drawings, in which:  
         [0021]      FIGS. 1A  to  1 E are process views illustrating a method of manufacturing a conventional floating structure; and  
         [0022]      FIGS. 2A  to  2 E are process views for illustrating a method of manufacturing a floating structure according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]     Hereinbelow, embodiments of the present invention are described in detail with reference to the accompanying drawings. However, the present invention should not be construed as being limited thereto.  
         [0024]     Referring to  FIG. 2E , a floating structure  130  according to an embodiment of the present invention has a floating structure  130  formed by etching a second substrate  120 , so that the floating structure  130  floats at a predetermined distance above the top side of a first substrate  110 . Although not shown in the drawing, the floating structure  130  is partially supported by the first substrate  110 , the second substrate  120  and/or an insulation film  112 . For example, the floating structure  130  may comprise a projection portion which projects over predetermined area  114 . The insulation film  112  is interposed between the first substrate  110  and the second substrate  120  to electrically isolate the first substrate  110  and the second substrate  120 . The floating structure  130  configured as described above may be used as a structure having various functions of an inertia weight, a spring, etc., in various sensors.  
         [0025]     Now, a method of manufacturing the floating structure  130  configured as described above is described in detail.  
         [0026]     Referring to  FIG. 2A , according to a preferred embodiment, the inventive method comprises a step of cutting a monocrystalline silicon ingot to prepare the first substrate  110  and the second substrate  120  (see  FIG. 2C ). Then, an insulation film  112  is formed on the first substrate  110 . The insulation film  112  is formed on one side of the first substrate  110  is typically a silicon oxide film formed through an oxidation process. However, the insulation film  112  may be selected from various non-conductive films such as a nitride film, an epoxy film, a photoresist film, etc.  
         [0027]     Referring to  FIG. 2B , the insulation film  112  formed on the first substrate  110  is removed from a predetermined area  114 . The predetermined area  114  is a portion corresponding to the bottom side of the floating structure  130  described below. By previously removing the portion underneath of the floating structure  130 , it is possible to omit a wet etching step which was essential in a conventional method of manufacturing such a floating structure. Because the wet etching process is omitted, the stiction phenomenon, which occurs in a conventional method, can be prevented, thereby improving the yield of such a floating structure  130 . The predetermined area  114  of the insulation film  112  is removed by photolithographic and etching processes. More specifically, photoresist is coated on the insulation film  112 , and photoresist covering the predetermined area  114  to be removed from the insulation film  112  is irradiated through a mask and developed using a photolithographic process. Then, wet etching is performed to remove the exposed insulation film  112  of the predetermined area  114 , and the remaining photoresist is then removed. Dry etching is preferably employed in the etching process. Although the predetermined area  114  is removed after the insulation film  112  is provided, it is possible to deposit the insulation film  112  on the first substrate  110  using a mask having a predetermined pattern. Beyond this, it is possible to form the insulation film  112 , the predetermined area  114  of which is removed, on the first substrate  110  by using various other methods known to those of ordinary skill.  
         [0028]     Referring to  FIG. 2C , the second substrate  120  is bonded to the insulation film  112 , the predetermined area  114  of which has been removed. In this manner, the predetermined area  114  is adapted to form a cavity  114 . The second substrate  120  is bonded to the insulation film  112  of the first substrate  110  by a silicon direct bonding method. However, various bonding methods known to those of ordinary skill in the art can be employed, other than the direct bonding method.  
         [0029]     Referring to  FIG. 2D , the second substrate  120  bonded to the top side of the first substrate  110  is polished. The polishing process is employed to polish the second substrate  120  to a predetermined thickness, wherein the polishing process comprises a lapping step for polishing the second substrate  120  to a predetermined thickness and a CMNP (chemical and mechanical polishing) step for improving the flatness and facial precision of the surface of the second substrate  120  polished to the predetermined thickness.  
         [0030]     Referring to  FIG. 2E , the floating structure  130  is formed in the second substrate  120  polished to a predetermined thickness. The process for forming the floating structure  130  comprises etching the second substrate in a predetermined pattern. More specifically, the floating structure  130  can be formed by coating photoresist on a side of the second substrate  120 , and exposing and developing the photoresist in a pattern corresponding to the floating structure  130 , and then etching the second substrate  120  along the pattern formed by developing the photoresist. Once the etching of the second substrate  120  is completed, the photoresist can be removed. In the etching process, RIE (reactive ion etching), which is a type of dry etching using ion particles in a plasma state, in particular, a deep RIE process, which is appropriate for etching a trench having a high aspect ratio cross-section, is preferably employed. The deep RIE process repeats the RIE process and a coating process for coating the area etched by the RIE process a plural number of times, in which the coating process can prevent the etched area (generally, the etched side walls) from being excessively etched by subsequent etching processes. Therefore, by using the deep RIE process, it is possible to more precisely etch in a high aspect ratio while keeping a constant cross-section. Because the floating structure  130  is desirably etched to have a constant cross-sectional shape, the etching is executed more deeply than the thickness of the floating structure  130 . Therefore, a series of grooves  116  are formed in the first substrate  110  as shown in  FIG. 2E . Because the insulation film  112  in the predetermined area  114  for forming the floating structure  130  is previously removed, there is no exposure of the existing oxide film while the etching is proceeding. Therefore, the oxide film is not exposed and not charged by the etching ions. A result, the path of subsequent ion beams are not changed, and it is possible to prevent the generation of a notch. Because a notch is not generated, physical properties such as mass and spring constant of the floating structure can achieve more accurate values. In addition, it is possible to avoid the occurrence of a needle-shaped by-product resulting from the generation of a notch formed as in a conventional technique.  
         [0031]     According to the present invention, because the occurrence of a notch can be prevented, it is possible to manufacture a more precise floating structure.  
         [0032]     In addition, because a needle-shaped by-product is not generated by preventing the occurrence of a notch, it is possible to prevent the floating structure from being electrically shorted.  
         [0033]     Furthermore, because wet etching is not employed, it is possible to avoid a stiction phenomenon in fabricating the floating structure.  
         [0034]     Because the occurrence of a notch, a needle-shaped by-product and a stiction phenomenon can be prevented, it is possible to increase the yield of the floating structure.  
         [0035]     Although several embodiments of the present invention have been shown and described in order to exemplify the principle of the present invention, the present invention is not limited to the above-described specific embodiments. It will be understood that various modifications and changes can be made by one skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, such modifications, changes and equivalents thereof are within the scope of the present invention.