Patent Abstract:
A semiconductor component, in particular a micromechanical pressure sensor based on silicon, having a base layer, an at least largely self-supporting diaphragm and an overlayer situated on the diaphragm, the diaphragm and the base layer, at least from place to place, delimiting a void. Furthermore, at least from place to place, above the diaphragm a conducting region is provided in the overlayer which is electrically poorly conductive as compared to the conducting region, to which the surface of the diaphragm that faces the overlayer is able to be electrically contacted.

Full Description:
FIELD OF THE INVENTION 
   The present invention relates to a semiconductor component configured as a micromechanical pressure sensor. 
   BACKGROUND INFORMATION 
   In the case of many pressure sensor elements patterned out of silicon by the application of surface micromechanics, the reference pressure cavern is produced so as to make possible an examination of the formation of the cavern in an “open” state. However, such a procedure is not possible in the case of semiconductor components and pressure sensor elements which are described in German Patent Application Number 100 32 579.3. Rather, in that case, producing the cavern or void by thermal treatment of the semiconductor material, that is, above all of silicon, requires new concepts for checking expansion and dimensioning of the void or diaphragm above it with respect to thickness and mobility. The usual standard methods for testing such voids, such as x-ray techniques, ultrasound analysis or thermographic analysis are too costly and not usable in mass production. 
   SUMMARY 
   An object of the present invention is to make available a semiconductor component which, after being produced in the “closed” state, is able to be tested in a simple way with respect to the formation of the cavern and the mobility of the diaphragm. During the production of pressure sensors based on porous silicon, whether the cavern generated or the void generated is being formed completely and correctly, and whether there might not be remainders of porous silicon or crystalline column structures in the area of the void which would hinder the desired free mobility of the diaphragm situated above the void are monitored. 
   Because of its design, the semiconductor component according to the example embodiment of the present invention may increase the ease of examining the generated diaphragm with respect to thickness, mobility and mechanical properties, such as its modulus of elasticity. Furthermore, the dimensions of the generated cavern or the generated void may be monitored, and the still present remains of, for instance, porous silicon or crystalline column structures (support locations) may be detected inside the void. 
   The semiconductor component, in an airtight, closed state may still be checked after the end of production, so that, after this examination, no further production steps follow that are relevant to the performance reliability of the diaphragm or to the assessment of the structure of the cavern. 
   Due to the construction of the semiconductor component, the diaphragm opposite the diaphragm floor, i.e. the side of the cavern opposite the diaphragm, may be set to a different electrical potential, so that information may be obtained on the mobility of the diaphragm and the structure and development of the void by way of static and/or dynamic capacitance measurements. 
   Thus, as a response to the formation of column structures in the region of the void, an electrical short-circuit appears in connection with such capacitance measurements in the borderline case, from which one may conclude that, in the region of the void, the diaphragm is supported by a column and is thereby impeded in its mobility. 
   It is further possible to set the diaphragm into oscillation, particularly resonant oscillation, via a capacitive excitation. From the resonant frequency and the quality of resonant oscillation, one may be able to draw conclusions on the freedom of motion of the diaphragm and possibly on columns being present even in the edge regions of the void. In addition, such a determination of the resonant frequency or analysis of the quality of the resonant oscillation offers the possibility of retroactively drawing conclusions on the material properties of the diaphragm, such as its modulus of elasticity and/or its thickness. 
   Finally, by a dying-out of the diaphragm, within the framework of these resonant oscillations, up to the limit stop, the height of the generated void is also able to be checked (maximum diaphragm deflection). 
   If the diaphragm is made of porous silicon and, on its side facing away from the base layer, is completely covered with the overlayer, the enclosed void or cavern may be closed off in a gastight fashion. 
   For the electrical insulation of the diaphragm from the area of the base layer which is located on the other side of the cavern, a circumferential edge layer may be furnished laterally around the void or the cavern, which, may be made of silicon, just as the diaphragm and the base layer, but which, in contrast to these, has a different doping, so that, between the diaphragm, the circumferential edge layer and the base layer a pnp junction is implemented which acts electrically insulating. 
   If the conductor region provided above the diaphragm has at least two subsections, the first subsection covering the entire surface of the side of the diaphragm facing away from the base layer, it is possible to contact the diaphragm electrically; and, starting from the surface of the overlayer, a second subsection of the conductive layer may be provided in the overlayer, which, at least from place to place, is in contact with the first subsection in an electrically conductive manner, and which is able to be electrically contacted on or in the overlayer, via printed circuit traces running there. 
   The first subsection of the conductor area may be produced in a simple manner by a temperature treatment of the semiconductor component during the course of which an out-diffusion of the doping of the diaphragm occurs into the area of the overlayer lying above it, which makes this diffusion region a comparatively well electrically conducting one, vis-à-vis the remainder of the detection layer. 
   In a corresponding manner, the second subsection of the conducting region provided in the region of the surface of the overlayer may be produced by a doping of the surface of the overlayer which, likewise, diffuses out during the course of this or a further temperature treatment, and leads to a diffusion region which thus defines the second subsection of the conducting layer. This second subsection of the conducting region, may be electrically well conducting compared to the remaining areas of the overlayer. 
   During the course of the temperature treatment, as soon as there is contact or an electrically conductive connection between the two subsections of the conducting layer, an electrical contacting of the diaphragm, closed off from the overlayer, is possible without a problem on its upper side, even in the closed state of the semiconductor component. 
   The conducting region and a plurality of second subsections of the conducting region, circular in a top view, which are, for example, in the area of the corners of the diaphragm, may be electrically connected to several printed circuit traces positioned on the diaphragm symmetrically with respect to a top view of it, to each of the second subsections of the conducting region a printed circuit trace being assigned. An even number of printed circuit traces, for example, four, may be provided, which may run along the plane diagonals, above the diaphragm designed, for example, to be rectangular, square, round or oval. 
   Because of such a symmetrical arrangement of the printed circuit traces, the means running along in the region of the overlayer, or on the overlayer, for induction and/or detection of a warping of the diaphragm, such as piezoresistive components or also heating elements, may not be differently influenced by lead wires. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
       FIG. 1  illustrates a top view of an example embodiment of a semiconductor component according to the present invention in the form of a micromechanical pressure sensor. 
       FIG. 2  illustrates a cross sectional view along the vertical section line drawn in  FIG. 1 . 
       FIG. 3  illustrates a cross sectional view along the diagonal section line drawn in  FIG. 1 . 
       FIG. 4  illustrates a second example embodiment of a semiconductor component in the form of a micromechanical pressure sensor according to the present invention. 
       FIG. 5  illustrates a cross sectional view along the vertical section line drawn in  FIG. 4 . 
       FIG. 6  illustrates a cross sectional view along the diagonal section line drawn in  FIG. 4 . 
   

   DETAILED DESCRIPTION 
     FIG. 1  illustrates a semiconductor component in the form of a pressure sensor element  5  produced by surface micromechanical technique for the atmospheric pressure or near-atmospheric pressure range. This pressure sensor element  5  may be produced on the basis of porous silicon technology, such as is described in German Application Number 100 32 579.3 with respect to construction design and production method, and including modifications according to the present invention as described below. 
   In  FIG. 1  there is first shown in top view of pressure sensor element  5 , how, on the surface or in the area of an overlayer of n-doped silicon, for example, episilicon, first actor elements  11  and second actor elements  12 , each, for instance, in the form of piezoresistors or structured piezoresistive layers, are provided. These may be, for example, made of silicon suitably doped in a conventional manner.  FIG. 1  also shows that on the surface, or in the area of the surface of the overlayer, run printed circuit traces  10 , which, for example, are likewise made of correspondingly doped silicon. 
   In addition, it is shown in  FIG. 1  that actor elements  11 ,  12  end in an edge area region  14  which is, for example, made of n-doped silicon, particularly episilicon, while printed circuit traces  10  are guided beyond these edge area regions  14  into a diaphragm region  16 , which is formed rectangularly in top view or, for example, square. 
   Below diaphragm area region  16  and below the overlayer there is a diaphragm  22 , not visible in  FIG. 1 , which covers a cavern or a void  23 . First actor elements  11  are, in addition, for example, bent over at right angles in the vicinity of edge area region  14 , which simplifies the warping of diaphragm  22  or also the detection of the warping of diaphragm  22 . This may achieve a more uniform, desired feeding of force into diaphragm  22 , for example, in the edge region of diaphragm  22 . In  FIG. 2  it may be seen that edge area region  14  extends into the region above diaphragm  22 , for example, as far as possible. 
   Actor elements  11 ,  12  may be used for the warping as well as the detection of the warping of diaphragm  22 , for instance, by a changing external pressure. Thus, actor elements  11 ,  12  may also be designed and operated as sensing elements or as passive components, such as piezoresistive resistors. 
     FIG. 2  shows a cross sectional view of  FIG. 1  along the vertical section line drawn in, second actor elements  12  being recognizable in the region of the surface of overlayer  19 . These are each formed from a first, suitably structured conducting layer  26  which may be used for the electrical contacting and the supply or removal of electrical current, as well as from an actor layer  17  which separates conducting layer  26  from overlayer  19  and may be electrically contacted via it, which runs below first conducting layer  26 . Actor layer  17  may be, for instance, a piezoelectric or piezoresistive layer. 
     FIG. 2  also shows that overlayer  19  runs above a base layer  18  or a substrate made, for example, of p-doped silicon, a block-shaped void  23  being enclosed between base layer  18  and overlayer  19 , which is delimited from overlayer  19  by diaphragm  22 . In the edge region of cavern  23 , between base layer  18  and overlayer  19 , an edge layer  15  may also be provided, made, for example, of n-doped silicon, which runs around void  23  and is in contact with diaphragm  22  in an encircling manner. This edge layer  15  is also indicated in  FIG. 1  as being encircling, however, there it is not visible in the top view. 
   Diaphragm  22  is made, for instance, of p-doped silicon, which may be porous silicon. Its thickness may range, for example, from to 0.5 μm to 1.0 μm, at a lateral extension in each direction between 100 μm and 800 μm, depending on the pressure range. Overlayer  19  may be gastight and thereby closes off void  23  in a gastight manner from the outer atmosphere. Its thickness may range, for example, from 5 μm to 10 μm, and the height of cavern  23  may lie, for example, between 3 μm and 7 μm. This ensures that, when there is a change in the external pressure, a bending deformation of diaphragm  22  and also overlayer  19  takes place, which is of an order of magnitude of 0.5 μm/bar to 5 μm/bar, especially 1 μm/bar to 2 μm/bar. 
     FIG. 3  shows a cross sectional view through  FIG. 1 , along the diagonals, printed circuit traces  10  now being recognizable in the area of the surface of overlayer  19 , each of which is made of a second, for example, p + -doped and comparatively low-resistance conducting layer  25 , which may be used for electrical supply or electrical contacting, as well as a separating layer  27  present below it, which may be, for instance, p − -doped and of comparatively high resistance. An electrical insulation of separating layer  27  and conducting layer  25  from overlayer  19  may be ensured, in this case, by the pn junction obtained. 
   Both second conducting layer  25  and separating layer  27  may be, for example, made of silicon which may be, in each case, suitably and differently doped. In  FIG. 3 , printed circuit traces  10  extend into diaphragm area region  16 . 
   In  FIGS. 2 and 3 , above diaphragm  22 , a first conducting region  21  made of doped silicon is provided, which conducts well compared to remaining overlayer  19 . This first conducting region  21  covers the entire surface of the surface of diaphragm  22  facing away from base layer  18 . Furthermore, a second conducting region  20  made of p-doped silicon is provided, proceeding from the surface of overlayer  19  facing away from diaphragm  22 , which also conducts well, compared to remaining overlayer  19 . Second conducting region  20  and first conducting region  21  are in contact with each other, or rather pass over into each other, at least from place to place, so that thereby electrical contacting of the entire surface of diaphragm  22  may be possible, starting from the surface of overlayer  19 . According to  FIG. 2  or  3 , second conducting region  20  extends to the outer surface of semiconductor component  5  and is thus directly accessible from there, as shown in  FIG. 1  in a top view. 
   According to  FIG. 3 , printed circuit traces  10  are connected in electrically conducting fashion to second conducting region  20 , while second actor elements  12  are electrically insulated from second conducting region  20 . In addition, according to  FIGS. 2 and 3 , first conducting region  21  is electrically insulated from base layer  18 , since, in the construction, a pnp junction has formed between base layer  18 , edge layer  15  and diaphragm  22  or first conducting region  12 . 
   In the example embodiment according to  FIGS. 1 to 3 , diaphragm  22  is electrically insulated from the bottom of cavern  23  formed by base layer  18 , and at the same time, an electrical lead or an electrical contacting possibility from the surface of overlayer  19  to diaphragm  22  exists. 
   For the analysis of the mobility of the diaphragm and the extension and cavern  23 , conventional means may be provided, by the use of which a predefinable and or variably adjustable electrical voltage may be applied and/or particularly measured as a function of time between the surface of diaphragm  22  facing void  23  and the part of the surface of base layer  18  lying opposite diaphragm  22 , or by the use of which at least this surface of diaphragm  22  opposite the surface of base layer  18  may be set to a specific electrical potential, for example, one that is changeable as a function of time. 
   The means may be electrical components by the use of which, for example, a static measurement of the capacitance between the surface of diaphragm  22  facing void  23  and the part of the surface of base layer  18  lying opposite diaphragm  22  may be carried out. Furthermore, using these components, a possibly present electrical short-circuit may also be detected between the surface of diaphragm  22  facing void  23  and the part of the surface of base layer  18  delimiting void  23  and lying opposite diaphragm  22 . 
   With the aid of the named electrical components, diaphragm  22  may be set into oscillation, for example, a resonant oscillation, by capacitive excitation. At the same time, these may be used for the analysis of the oscillation produced, particularly of the measurement of the resonant frequency and/or the quality of the resonant oscillation, in order thereby to determine mechanical properties of diaphragm  22  as well as its mobility with respect to void  23 , and/or its modulus of elasticity and/or its lateral extension or thickness. Suitable components for this and their interconnection are sufficiently well known from the related art, and do not require detailed explanation here. 
   As a matter of priority, the preceding explained analysis may determine the electrical capacitance between the lower side of the diaphragm and the cavern floor, which, in the static case, may permit a statement to be made about the cavern height and possibly about shunts or short-circuits, for instance, due to remains of porous silicon or columns in cavern  23 . 
   In the case of excitation of an oscillation, such as a resonant oscillation, one also obtains from the analysis, such as with respect to frequency and quality of the oscillation, for example, under consideration of the electrical capacitance, information about the mobility of diaphragm  23 , about its maximum deflection, about reinforcement or support locations of diaphragm  22  in the region of cavern  23 , or even about mechanical properties of the diaphragm, such as its thickness or its modulus of elasticity. 
     FIGS. 4 to 6  explain an alternative example embodiment to that in  FIGS. 1 to 3 , for a semiconductor component in the form of a micromechanical pressure sensor element  5 , which differs from the first exemplary embodiment in that second conducting region  20 , as in  FIG. 2  or  3 , is developed dot-shaped or circular in top view, in the region of third conducting regions  24  positioned in the corners of diaphragm  22 . This is shown in  FIG. 6 , which shows a section along the diagonal shown in  FIG. 4 . 
   According to this example embodiment, it may not be necessary to introduce printed circuit traces  10  into the region above diaphragm  22 , and third conducting regions  24  are limited to relatively tightly defined regions within overlayer  19 , which have been produced by a suitable local doping of overlayer  19 , such as with the aid of an appropriate mask. Thus, according to  FIG. 4 , diaphragm area region  16  provided in  FIG. 1  may also remain electrically insulating, i.e., it is developed farther away from overlayer  19  of electrically insulating material or of a material such as n-doped silicon that is comparatively poorly electrically conductive, compared to conducting regions  20 ,  21 ,  24 . 
   First actor elements  11  and/or second actor elements  12  are not essential for the functioning of the explained pressure sensor, since a warping of diaphragm  22  may, for example, also be detected by a change in capacitance between diaphragm  22  and base layer  18 , due to a changing exterior pressure. 
   Furthermore, actor elements  11 ,  12  may also be developed as heating elements or heat conductors, which may effect warping of diaphragm  22 , via a heat supply and mechanical stresses induced thereby. 
   Finally, the function of a printed circuit trace  10  and an actor element  11 ,  12  may also be unified in one structural element, with the use of which, then, in each case, both electrical contacting of second conducting region  20  and of third conducting region  24 , as well as warping of diaphragm  22 , may be induced or detected.

Technology Classification (CPC): 6