Abstract:
A semiconductor manufacturing device comprises a holder having sealing members and supporting a semiconductor substrate so that an open space is formed above the semiconductor substrate and a sealed space is formed below the semiconductor substrate. The semiconductor substrate has a first main surface exposed to the open space and a second main surface exposed to the sealed space. When the holder is immersed in an etching solution, the first main surface of the semiconductor substrate is exposed to the etching solution and subjected to wet etching while the etching solution does not flow into the sealed space.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a semiconductor manufacturing device for performing wet etching only on one main surface of a semiconductor substrate, particularly a semiconductor manufacturing device suitable for producing a cantilever used for a probe of a scanning probe microscope. 
     In a scanning probe microscope represented by an atomic force microscope (AFM), a cantilever in which an exploring needle is formed at a free end of a beam portion is used as a scanning probe. In the configuration, because attraction or repulsion based on interatomic force appears between a surface of a sample and the exploring needle by scanning the exploring needle on the surface of the sample, a shape of the surface of the sample can be measured by detecting the interatomic force as a deflection of the cantilever. 
     FIGS. 7A to  7 D are sectional views showing a method of processing the conventional cantilever as a specimen. First as shown in FIG.  7   a , layered substrate  3  is prepared, which is layered with a SiO 2  film  30 , a silicon thin film  31  acting as a beam portion of the cantilever and an exploring needle, a SiO 2  film  32  as an intermediate layer, a silicon substrate  33  acting as a supporting table of the cantilever, and a SiO 2  film  34 . 
     Next, a beam portion  31   a  of the cantilever and an exploring needle  31   b  are formed on a surface of the SiO 2  film  34  by etching SiO 2  film  30  into a proper shape so as to become a protecting film and by etching the silicon substrate  31  as the mask of the protecting film as shown in FIG.  7 B. Moreover, SiO 2  film  34  is properly etched so as to form a protecting film  34   a , and surface &lt;100&gt; of the silicon substrate  33  is exposed. 
     Next, an end portion of layered substrate  3  is supported with a jig (etching holder)  50  sealed with an O-ring  51  for preventing inflow of liquid so that only the other main surface where said beam portion  31   a  and the exploring needle  31   b  of the layered substrate  3  is not formed is exposed by etching solution as shown in FIG.  7 C. SiO 2  film  32  exposes by etching the silicon substrate  33  as a mask of the protecting film  34  ( 34   a ) using anisotropic wet-etching. 
     For the etching solution, a potassium hydroxide (KOH) aqueous solution of 40 percentage by weight at 60 to 80° C. a tetraalkylammonium hydroxide (TMAH) aqueous solution of 20 percentage by weight at 80 to 90° C., and so on can be used. With these etching solutions, plane &lt;100&gt; of the silicon substrate  33  is etched much faster than plane &lt;111&gt; so that the protecting film  34   a  is not actually etched. Therefore, anisotropic wet-etching actually stops at plane &lt;111&gt; referenced with the end of the protecting film  34   a . At the end, the extra SiO 2  film  32  is removed as shown in FIG.  7 D. By the above-described process, a cantilever is completed which has an exploring needle  31   b  at one end of the beam portion  31   a  and the other portion thereof is supported by a cantilever-like supporting table  60 . 
     In the above-mentioned prior art, pressure increases corresponding to the depth of the etching solution at a processing plane of layered substrate  3  while pressure in the etching holder  50  is substantially at atmospheric pressure when the etching holder  50  holding the layered substrate  3  is sunk in the etching solution. Because of that, there has been problems that etching is performed unevenly and the substrate itself is broken by stress corresponding to a difference in pressure applied to both main surfaces. 
     When temperature of etching solution, gas in the etching holder  50  gradually expands thermally, and pressure applying to non-processing surface of the layered substrate  3  gradually increases. There has been a problem that stress toward reverse direction to the above-mentioned appears at the layered substrate  3  when pressure applied to the non-processing surface becomes higher than pressure applied to a processing surface corresponding to depth in the etching solution. 
     An object of the present invention is to provide a semiconductor manufacturing device substantially adjusting pressure applied to a non-processing surface to a processing surface of a semiconductor substrate in wet-etching in which the processing surface of the semiconductor substrate is exposed outside and the non-processing surface is sunk in etching solution so as to be sealed from outside preventing from inflow of the solution to solve the above-mentioned problem in the prior art. 
     SUMMARY OF THE INVENTION 
     To achieve the above-mentioned object, the present invention is characterized by providing a substrate holding member for holding the semiconductor substrate so that one main surface of the substrate exposes outside and the other main surface exposes in a space sealed to prevent inflow of liquid from outside, and a pressure control means for controlling pressure in said space so that similar pressure as pressure applied to the one main surface of said semiconductor substrate is applied to the other main surface in performing wet etching only on the one main surface of the semiconductor substrate. 
     According to the above-mentioned configuration, since similar pressure as pressure applied to one main surface is applied to the other main surface of the semiconductor substrate, stress caused by difference of pressure applying to each main surface does not appear at the semiconductor substrate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view showing a construction of main portion of an etching holder according to an embodiment of the present invention. 
     FIG. 2 is a view showing hole construction and how to use a semiconductor manufacturing device of the present invention including the etching holder. 
     FIG. 3 is a sectional view showing a second embodiment according to the present invention. 
     FIG. 4 is a sectional view showing a third embodiment according to the present invention. 
     FIG. 5 is a sectional view showing how to use of the third embodiment according to the present invention. 
     FIG. 6 is a sectional view showing a construction of and how to use a fourth embodiment according to the present invention. 
     FIGS. 7A to  7 D are sectional views showing a method of processing the conventional cantilever as a specimen. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the figures, the present invention will be described in detail. FIG. 1 is a plane view showing a construction of a main portion of an etching holder according to an embodiment of the present invention. FIG. 2 is a view showing a whole construction of and how to use of a semiconductor manufacturing device the present invention including the etching holder of FIG.  1 . 
     An etching holder  10  of the present invention comprises a ring-shaped substrate holding member  11  having an opening portion at a center thereof, a ring-shaped substrate holding member  12  having an opening portion expanding step by step toward one main surface, and screws  15  fixing mutually each of the substrate holding members  11  and  12  through an O-ring. To an opening of said substrate holding member  12 , one end of a gas passageway  13  is connected, and to the other end, pressurizing means comprised of a pressure control device  14  is connected as shown in FIG.  2 . 
     In the configuration, a semiconductor substrate  20  exposes outside at processing surface  20   a  thereof and is held by the substrate holding members  11  and  12  through the O-ring  18  so that non-processing surface  20   b  exposes in a cavity or space  16  sealed from outside preventing inflow of the solution as shown in FIG.  1 . The etching holder  10  holding the substrate holding member  20  is sunk in etching solution  40  of an etching vessel  70  as shown in FIG.  2 . 
     In the etching solution  40 , pressure A is applied to the processing surface  20   a  of the semiconductor substrate  20  corresponding to the depth of the etching solution  40 . The pressure control device  14  applies pressure in the space  16  of the etching older  10  through gas passage  13  so that the similar pressure B as said pressure A is applied to the non-processing surface  20   b  of the semiconductor substrate  20 . 
     As the pressure A applied to the processing surface  20   a  of the semiconductor substrate can be easily obtained as a function of position (depth) of the semiconductor substrate  20  in the etching solution  40  and the specific gravity of the etching solution  40 , the pressure control device can control pressure linearly in the space  16  if the specific gravity of the etching solution and depth of the substrate are always constant. 
     According to the present embodiment, as the similar pressure as pressure applied to the processing surface  20   a  is applied to the non-processing surface  20   b  of the semiconductor substrate  20 , stress caused by difference of pressure applied to each main surface at the semiconductor substrate  20  is prevented. 
     If a pressure sensor for detecting pressure applied to the processing surface  20   a  of said semiconductor substrate  20  is additionally formed so that said pressure control device  14  controls the application of pressure in the space  16  corresponding to an output signal of said pressure sensor, pressure applied to the non-processing surface  20   b  can always be controlled accurately independent of the specific gravity of the solution and depth of the substrate. 
     FIG. 3 is a plane view showing a construction of a main portion of an etching holder according to a second embodiment of the present invention. The same symbols in FIGS. 1 and 2 as said symbols show the same or similar parts. 
     The present embodiment is characterized by that an exhaust valve  80  opening and exhausting gas in a space  16  when pressure in the space  16  is over a predetermined value is formed. The threshold value of pressure at which the exhaust valve  80  opens is previously set so that difference between pressure A applied to a processing surface  20   a  of a semiconductor substrate  20  and pressure B applied to a non-processing surface  20   b  is less than value having a bad influence to the semiconductor substrate  20 . 
     According to the present embodiment, when pressure B applied to the non-processing surface  20   b  of the semiconductor substrate  20  becomes higher than pressure A applied to the processing surface being over the predetermined value by expansion of gas in the space  16  because of high temperature of the etching solution, the exhaust valve  80  opens and gas in the space  16  is exhausted so that pressure B applied to the non-processing surface  20   b  decreases. Therefore, stress does not appear at the semiconductor substrate even when temperature of the etching solution is high. 
     FIG. 4 is a plane view showing a construction of a main portion of an etching holder according to a third embodiment of the present invention. The same symbols as said symbols of FIGS. 1 and 3 show the same or similar parts. The present embodiment is characterized by that a piping  90  is formed for generating pressure corresponding to a depth of a substrate in the etching solution into said space  16 . One end of said piping  90  is connected in gas-tight to an opening  19  of said substrate holding member  12 , and the other end leads to an opening end  90   a  through a U-shaped pipe portion  90   b.    
     In the configuration, etching solution flows in the piping  90  from the opening end  90   a  when the etching holder holding the semiconductor substrate  20  similarly as said embodiment is sunk in etching solution  40  as shown in FIG.  5 . As the result, pressure corresponding to a liquid-level of the etching solution is applied to the non-processing surface  20   b  by the etching solution  40  flowing from the opening end  90   a  based on Pascal&#39;s principle. 
     Because of that, if the position of the opening end  90   a  is previously determined based on the specific gravity of the etching solution and depth of the substrate so that the liquid-level of the etching solution flowing from the opening end  90   a  becomes the same level as the processing surface  20   b  of the semiconductor substrate  20 , it is possible make pressures applied to the processing surface  20   a  and non-processing surface  20   b  of the semiconductor substrate  20  substantially equal. 
     Although it is described that the position of the opening end  90   a  is previously fixed, it is possible make pressures applied to the processing surface  20   a  and non-processing surface  20   b  of the semiconductor substrate  20  substantially the same pressure without relation to the specific gravity of the etching solution by adjusting properly a distance  90   c  corresponding to the specific gravity of the etching solution if distance  90   c  between the U-shaped pipe portion  90   b  and the opening end  90   a  can be freely adjusted. 
     FIG. 6 is a plane view showing a construction of a main portion of an etching holder according to a fourth embodiment of the present invention. The same symbols as said symbols of the previous figures show the same or similar parts. 
     The present embodiment is characterized by that a piping  95  which one end thereof is connected to an opening  19  of a substrate holding member  12  in gas-tight and the other end of which is opened outside is formed. Said piping  95  is constructed so that the other end of the piping exposes in the air outside when the etching holder sunk in the etching solution  40 . 
     According to the present embodiment, it is possible make pressures applied to the processing surface  20   a  and non-processing surface  20   b  of the semiconductor substrate  20  substantially the same pressure without relation to temperature of the etching solution  40  by holding the etching holder at a comparatively shallow position in the etching solution  40  as shown in the figure because the inside of the space  16  is always kept in atmospheric pressure even if temperature of the etching holder increases due to the etching solution  40 . 
     According to the present invention, in the wet etching process in which the semiconductor substrate is sunk in the etching solution being held so that the processing surface thereof is exposed and the non-processing surface is sealed preventing inflow of the etching solution, pressure applied to the processing surface can be matched to pressure applied to the non-processing surface. Therefore, stress does not appears so that uneven etching and breakage of the substrate is prevented.