Abstract:
A method for manufacturing integrated circuits having at least one silicon-germanium heterobipolar transistor is provided, wherein a dielectric applied to the surface of the wafer is planarized. The dielectric having elevations produced by the thickness of monocrystalline semiconductor regions structured below the dielectric, wherein the semiconductor regions are covered by a first stop layer, in that for the purpose of planarization, a second stop layer is applied to the dielectric. Subsequently, a planarization layer, which in the area of each elevation forms a smaller layer thickness than outside the area of each elevation, is applied to the second stop layer. Thereafter, the planarization layer is removed in the area of each elevation and the second stop layer is removed in the area of each elevation. Then, the wafer is polished chemically-mechanically in such a way that the dielectric in the area of each elevation is made thinner at least up to the first stop layer.

Description:
[0001]     This nonprovisional application claims priority under 35 U.S.C. § 119(a) on German Patent Application No. DE 102005004708, which was filed in Germany on Feb. 2, 2005, and which is herein incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a method for manufacturing integrated circuits having at least one silicon-germanium heterobipolar transistor.  
         [0004]     2. Description of the Background Art  
         [0005]     Semiconductor circuits and methods for manufacturing the same, which have heterobipolar transistors with a silicon-germanium mixed crystal in the base semiconductor region, are known from the state of the art.  
       SUMMARY OF THE INVENTION  
       [0006]     It is an object of the present invention to provide a method for manufacturing integrated circuits.  
         [0007]     According to an embodiment of the present invention, a dielectric applied to the surface of the wafer is planarized. The wafer is preferably a monocrystalline silicon wafer having, for example, a lattice orientation of &lt;100&gt;. The dielectric is, for example, silicon dioxide (SiO 2 ), the invention also includes other planarizable dielectrics. The dielectric made of silicon dioxide may also be called a field oxide in its later function.  
         [0008]     The dielectric has elevations, produced by the thickness of monocrystalline semiconductor regions structured below the dielectric. These monocrystalline semiconductor regions can be, for example, epitaxially applied collector semiconductor regions of high-frequency bipolar transistors. In addition to the monocrystalline semiconductor regions, other structural unevennesses below the dielectric may also lead to the formation of elevations. The monocrystalline semiconductor regions can be covered by a first stop layer. In this respect, a dielectric material layer, which is thinner compared with the stop layer, can be placed between the first stop layer and the monocrystalline semiconductor region.  
         [0009]     “Subsequent” is understood hereinafter to mean that these one or more “subsequent” process steps occur later in time in the overall manufacturing process. In this respect, no direct linking of the process steps is necessary, but additional process steps, such as, for example, cleaning steps, can be inserted before the process steps that follow.  
         [0010]     The nature of the invention in this respect is the combination of the process steps described hereinafter. In so doing, it is provided first that for planarization a second stop layer is applied to the dielectric and subsequently a planarization layer, which in the area of each elevation forms a smaller layer thickness than outside the area of each elevation, is applied to the second stop layer. For example, the layer thickness of the planarization layer can vary by half.  
         [0011]     Again subsequent to these process steps, the planarization layer in the area of each elevation and the second stop layer in the area of each elevation are removed. To remove the second stop layer, the layer can be etched, for example, by exposing the material of the second stop layer to an etchant, which results in a lower etching rate with respect to the second stop layer, compared with the planarization layer.  
         [0012]     Again subsequently, the wafer is polished chemically-mechanically in such a way that the dielectric in the area of each elevation is made thinner up to the first stop layer. Outside the area of each elevation, the dielectric in contrast is not or only made slightly thinner. The first stop layer and the second stop layer therefore act as polishing stops, which significantly reduces the removal of the surface material by the chemical mechanical polishing.  
         [0013]     A further embodiment of the invention provides that the planarization layer remaining outside the area of each elevation is removed before the chemical-mechanical polishing (CMP). For this purpose, the remaining planarization layer can be etched, for example, with an etchant acting selectively on the dielectric and the stop layer.  
         [0014]     The exposed first stop layer and/or the exposed second stop layer can be removed after the chemical mechanical polishing (CMP).  
         [0015]     Another embodiment of the invention provides that the planarization layer can be removed in the area of each elevation in such a way that outside the area of each elevation a residual planarization layer with such a thickness remains that etching of the second stop layer, covered by the planarization layer, does not occur or occurs only insignificantly. At least the function of the second stop layer as a polishing stop for the chemical mechanical polishing remains assured.  
         [0016]     In a further embodiment, the dielectric, the first stop layer, and the second stop layer are applied in such a way that a parallel displacement of the similarly oriented surfaces of the first stop layer and the second stop layer is smaller than a thickness of the first stop layer and/or than a thickness of the second stop layer. Therefore, the application of the dielectric can be designed to be closely tolerant to the thickness of the monocrystalline semiconductor regions.  
         [0017]     According to an another embodiment of the invention, to remove the planarization layer in the area of each elevation the planarization layer is etched. The etching occurs preferably thereby as a function of a time measurement.  
         [0018]     Furthermore, the first stop layer and/or the second stop layer can have silicon nitride (Si 3 N 4 ), which has a lower removal value in regard to the chemical-mechanical polishing than, for example, the silicon dioxide of the dielectric.  
         [0019]     To achieve the desired planarization effects by the planarization layer, advantageous embodiments of the invention provide that the planarization layer has a photoresist or a polymer. Thereby, the planarization layer can also include several individual layers of the same or different materials, which intensify the planarization action during combined use. If, for example, a photoresist is used, it can be applied advantageously by spin coating.  
         [0020]     Another aspect of the invention particularly with respect to a method for manufacturing integrated circuits having silicon-germanium heterobipolar transistors is provided as the modularization of the manufacturing process. The manufacturing process is divided into several process modules. A process module hereby, however, preferably has at least two process steps of the manufacturing process. For the division, according to the invention several or all process steps are combined into modules.  
         [0021]     Defined as process modules are: a connection module to create a buried connection region; a collector/emitter module to create a collector region, adjacent to the connection region, and/or an emitter region, adjacent to the connection region; and a base module to create a base region.  
         [0022]     A buried connection region is can be a conductive region, which is arranged relative to the wafer surface at least partially below an active semiconductor region particularly of the heterobipolar transistor. The active semiconductor region can be at least partially monocrystalline. The semiconductor region of the base is preferably directly adjacent to the collector region and/or the emitter region, which is made monocrystalline at least at the interface.  
         [0023]     The nature of this aspect of the invention thereby is the development of a technology version, which is different from the existing technology version, in that the process modules have such process interfaces relative to one another that at least one process step of a process module with maintenance of the process interface is changed independent of the process steps of the other process modules for the different technology version.  
         [0024]     The process interfaces preferably have one or more process conditions, which relate to the processes of at least two modules. For example, a high-temperature epitaxy process step in the collector/emitter module relates to both the diffusion and thereby the dopant distribution of the dopants, introduced in the connection module, and also the diffusion and thereby the dopant distribution of the dopants, introduced in the collector/emitter module, the dopant diffusing during the high-temperature epitaxy process step.  
         [0025]     Technology versions differ when the electrical properties of at least one integrated component change with the change in technology. Preferably, the heterobipolar transistor is adapted to the desired specifications with the new technology version.  
         [0026]     The creation of the preferably high-doped, metallic, and/or silicided leads for the aforementioned regions can thereby be a component of the specific process module and/or form one or more separate process modules.  
         [0027]     According to a further embodiment of the invention, at least one process module has at least two module variants. The module variants thereby are used in one and the same technology version to create different components with a reduced number of necessary process steps. Preferably, the at least two module variants are carried out in the same integrated circuit. For example, a first module variant can be designed to create a collector region and a second module variant for the at least partial parallel creation of an emitter region.  
         [0028]     Another embodiment of the invention provides that a first interface of the process interfaces is placed between the connection module and collector/emitter module in a sequence of the process steps before an epitaxial application of semiconductor material of the collector region and/or the emitter region.  
         [0029]     Further, one of the process interfaces can be placed between the collector/emitter module and base module in a sequence of the process steps after the planarization of the dielectric. This can be, for example, a second process interface to the aforementioned interface, so that the manufacturing process has at least three process modules.  
         [0030]     Another aspect of the invention is a use of the previously described manufacturing process for a semiconductor array to adapt the technology version to an application-specific boundary condition. Similarly, an aspect of the invention is the use of the method for manufacturing an integrated high-frequency circuit having at least one silicon-germanium heterobipolar transistor.  
         [0031]     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0032]     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:  
         [0033]      FIG. 1  illustrates process modules with assigned process interfaces,  
         [0034]      FIG. 2   a  illustrates a first schematic sectional view after the process steps of the manufacture of a semiconductor array,  
         [0035]      FIG. 2   b  illustrates a second schematic sectional view after the process steps of the manufacture of a semiconductor array,  
         [0036]      FIG. 2   c  illustrates a third schematic sectional view after the process steps of the manufacture of a semiconductor array,  
         [0037]      FIG. 2   d  illustrates a fourth schematic sectional view after the process steps of the manufacture of a semiconductor array  
         [0038]      FIG. 2   e  illustrates a fifth schematic sectional view after the process steps of the manufacture of a semiconductor array. 
     
    
     DETAILED DESCRIPTION  
       [0039]     According to  FIG. 1 , the manufacturing process for a semiconductor array having a silicon-germanium heterobipolar transistor is divided into several process modules: module  1   a,  module  1   b,  module  2 , module  3   a,  and module  3   b . In this respect, the module division in the exemplary embodiment of  FIG. 1  shows a first module variant module  1   a  for the first module (module  1   a /module  1   b ) and a second module variant module  1   b,  as well as the module variants module  3   a  and module  3   b  for the third module.  
         [0040]     The exemplary embodiment of  FIG. 1  shows by way of example the advantageous division into three process modules, it being possible to combine both module variant  1   a  with module  2  and module variant  3   a , module variant  1   a  with module  2  and module variant  3   b , module variant  1   b  with module  2  and module variant  3   a , and module variant  1   b  with module  2  and module variant  3   b , in order to create transistors having different electrical properties on a semiconductor chip. The first module (module  1   a , module  1   b ), the second module  2 , and the third module (module  3   a ,  3   b ) according to the exemplary embodiment of  FIG. 1  follow one after another in time t.  
         [0041]     The modules, module  1   a , module  1   b , module  2 , module  3   a , and module  3   b , each have one or several process steps, P 1  to P 3 , P 4  to P 7 , or P 8  to P 9 , respectively, of the manufacturing process, which are also identical for the different module variants. Variants of the modules can be produced, for example, by appropriate masking and thereby by a lateral offset “s” on the wafer.  
         [0042]     The modules, module  1   a , module  1   b , module  2 , module  3   a , and module  3   b , are thereby defined relative to each other by process interfaces I 12 , I 23 . In the exemplary embodiment of  FIG. 1 , the process interfaces I 12 , I 23  are arranged in time between the first module, module  1   a,  module  1   b , and the second module, module  2 , and between the second module, module  2 , and the third module, module  3   a  and module  3   b . An interface, not shown in  FIG. 1 , between the first module, module  1   a,  module  1   b , and the third module, module  3   a , module  3   b , is also possible.  
         [0043]     The invention is thereby not limited to the exemplary embodiment depicted in  FIG. 1 . It is possible to add additional modules and interfaces by suitable definition. Additional modules are indicated in  FIG. 1  by dots.  
         [0044]     For example, module  1  is a buried connection region for the electrical contacting of a collector semiconductor region or an emitter semiconductor region of the heterobipolar transistor. Module variant  1   a,  in comparison with module variant  1   b,  has a lower dopant concentration or a different dopant, so that the thermal budget defined in the subsequent modules  2  and  3  leads to different diffusion of the dopant, introduced into module  1 , into semiconductor layers arranged above during modules  2  and  3 .  
         [0045]     If this semiconductor layer is, for example, an active collector semiconductor layer, both module variants  1   a  and  1   b  accordingly produce different collector drift zones for heterobipolar transistors with different high-frequency properties. Furthermore, the module variants  3   a  and  3   b  can create, for example, different base regions.  
         [0046]     If proceeding from process steps P 1  to P 9 , assigned to the modules, a new technology generation with new heterobipolar transistors with, for example, a higher breakdown voltage stability is desired, in this case only process steps P 4  to P 7  of module  2  are changed. The other process steps, P 1  to P 3  and P 8  to P 9 , remain unchanged. The options for changing process steps P 4  to P 7  of module  2  are thereby limited by the defined interfaces I 12  and I 23 . In other words, the interface-defined boundary conditions for process steps P 4  to P 7  remain unchanged.  
         [0047]     For example, module  1  according to the process interface I 12  requires a certain thermal budget due to the following module  2 . If process steps P 4  to P 7  for the new technology version in new process steps (P 4 ′ to P 7 ′, not shown in  FIG. 1 ) are changed, maintenance of the thermal budget is absolutely necessary. If the thermal budget, for example, is too low, a thermal replacement process must be added, which is used exclusively to maintain the process interface condition.  
         [0048]     In  FIGS. 2   a  to  2   e  processes of the second module are shown, which define a structural condition of a process interface I 23 . This therefore adds the boundary condition that for process steps of the subsequent module, the geometric interface, shown schematically in  FIG. 2   d , is to be assumed.  
         [0049]     Sectional views of a segment of a processed wafer after certain process steps are shown in  FIGS. 2   a  to  2   e . The process steps are used thereby to create a substantially planar surface without elevations, which could influence the later process steps.  
         [0050]     A portion of a monocrystalline, p-doped silicon substrate  100  is shown, on which a high-doped, buried layer  60  of the n-conductivity type is deposited epitaxially. A heterobipolar transistor is to be produced in a region of the buried layer  60  in the following process steps—not all of which are shown in  FIGS. 2   a  to  2   e . To isolate this heterobipolar transistor from other transistors or other components, trench isolations are provided, which are filled with a polycrystalline silicon  70 .  
         [0051]     A monocrystalline collector semiconductor region  50 , which has a lower dopant concentration than the buried layer  60 , is applied epitaxially to the buried layer  60 . A first stop layer  30  of silicon nitride, which may be separated from the collector semiconductor region  50  by a thin silicon dioxide layer, is applied to the semiconductor region  50 .  
         [0052]     A dielectric  10  of silicon dioxide, which has a thickness dependent on the collector semiconductor region  50 , is applied over the surface structure, which comprises the buried layer  60 , the collector semiconductor region  50 , and the first stop layer  30 . Preferably, the collector semiconductor region  50  and the dielectric  10  have the same thickness within the scope of production tolerances.  
         [0053]     The nonplanar surface, determined by the built-up height of the collector semiconductor region  50  and the first stop layer  30 , upon application of the dielectric  10  over the entire wafer surface, has the effect that in the area of the collector semiconductor region  50  an elevation  1  within the surface of dielectric  10  is formed, which can negatively affect or prevent the following process steps for creating the base (not shown).  
         [0054]     To obtain a planar surface as a starting point for the additional process steps, the following process steps, partially depicted in  FIGS. 2   a  to  2   e , are carried out one after another. In addition to the process steps described hereinafter, additional process steps, such as cleaning steps, etc., may be necessary in terms of process technology, which are omitted in this explanation for the purpose of simplification.  
         [0055]     First, a second stop layer  20  is applied over the entire wafer surface. On this stop layer  20 , a photoresist  40 , acting as a planarization layer, is spin coated onto the entire stop layer area, so that in the area of the elevations  1  the photoresist  40  has a lower thickness than outside the area of the elevations  1 .  
         [0056]     The state after the applied photoresist  40  of  FIG. 2   a  has been etched for a time is shown in  FIG. 2   b.  The etching time thereby is selected such that outside the area of the elevation  1  a residual resist layer  41  remains, which covers the second stop layer  20  in the area outside elevation  1 . Here, the remaining thickness of the residual resist layer  41  is sufficiently large, so that, as depicted in  FIG. 2   c,  the second stop layer  20  of  FIG. 2   b  is etched exclusively in the area of the elevation  1 . Accordingly, after the etching the unetched second stop layer  21  remains underneath the residual resist layer  41 .  
         [0057]     Before a chemical mechanical polishing (CMP) of the surface of the wafer, the residual resist layer  41  is removed as depicted in  FIG. 2   d . The first stop layer  30  disposed within elevation  1  and the second stop layer  21 , now covering the surface of the wafer outside elevation  1 , remain; both act as a polishing stop.  
         [0058]      FIG. 2   e  shows the state of the wafer segment after the chemical-mechanical polishing (CMP). The wafer has a planar surface. Elevation  1  of the preceding figures has been removed. A first residual stop layer  31  and a second residual stop layer  22  remain, which can be removed for subsequent processes. Furthermore, two dielectric regions  11  have formed.  
         [0059]     The obtained planar surface of the wafer is preferably a process interface condition of a second process interface I 23 , previously explained with respect to  FIG. 1 . Additional process interface conditions are, for example, the dopant concentration or the lattice defects at the boundary of the collector semiconductor region  50 .  
         [0060]     The advantages of the exemplary embodiments in  FIGS. 2   a  to  2   e  are that by the application of the second stop layer, no further structuring effort arises during the manufacturing process. Irregularities of the chemical mechanical polishing are reduced. The uniformity of the entire process sequence in the exemplary embodiment of  FIGS. 2   a  to  2   e  corresponds substantially only to the uniformity of the dielectric formation. For this reason, minor tolerances in the process result of the entire process chain can be achieved in the depicted collector module. As a result, the manufacture of smaller structures is possible in particular.  
         [0061]     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.