Abstract:
A transistor structure having source/drain regions arranged in a horizontal plane along an x axis has a recess structure, which separates the two source/drain regions from one another and increases the effective channel length L eff  of the transistor structure. A vertical gate electrode with respect to the horizontal plane extends along the x axis and in this case encloses an active zone of the transistor structure from two sides or completely. The effective channel width W eff  is dependent on the depth to which the gate electrode is formed. A memory cell having a selection transistor in accordance with the transistor structure has both a low leakage current and a good switching behavior. By a suitable integration concept, the transistor structure is integrated into a memory cell array of a DRAM having hole trench capacitors or stacked capacitors.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority under 35 U.S.C. §119 to German Application No. DE 103 61 695.0, filed on Dec. 30, 2003, and titled “Transistor Structure with a Curved Channel Memory Cell and Memory Cell Array for DRAMs, and Methods for Fabricating a DRAM,” the entire contents of which are hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention relates to a transistor structure having two source/drain regions, which are formed in a semiconductor substrate, are arranged in a horizontal plane along an x axis with respect to a substrate surface of the semiconductor substrate and are spaced apart from one another by a recess structure, a surface contour of an active zone being predefined by a contour of an auxiliary area composed of the cross sections of the source/drain regions and also the recess structure in the horizontal plane and a sidewall of the active zone being predefined by vertical projection lines of the surface contour into the semiconductor substrate, and the formation of a conductive channel between the two source/drain regions being controllable by a potential at a gate electrode.  
       BACKGROUND  
       [0003]     Memory cells of dynamic random access memories (DRAMs) are usually provided with a respective storage capacitor for storing electrical charge and a selection transistor for addressing the storage capacitor. In this case, a lower limit results for a channel length of the selection transistor, below which lower limit the insulation properties of the selection transistor are inadequate in the turned-off, non-addressed state of the memory cell. The lower limit for an effective channel length L eff  limits the scalability of conventional planar transistor cells (PTCs) with a selection transistor oriented horizontally with respect to a substrate surface of a semiconductor substrate.  
         [0004]     The functionality of a memory cell is furthermore determined by the resistance of the selection transistor in the turned-on state given addressing of the memory cell. With advancing miniaturization of the structures, an effective channel width W eff  of the selection transistor is being increasingly reduced and the charging/discharging current I on  of the memory cell is disadvantageously limited.  
         [0005]     Therefore, fin field-effect transistors (FinFETs) are known, as are described for example in “Fabrication of Body-Tied FinFETs (omega MOSFETs) using Bulk Si Wafers,” Park et al.; in “2003 Symposium on VLSI Technology Digest of Technical Papers.” Between two source/drain regions of a transistor cell that are arranged in planar fashion, a semiconductor substrate is etched back by a recess step and a fin formed by the semiconductor substrate is shaped between the two source/drain regions in the process. A gate electrode structure envelops the fin from at least two sides. The effective channel length L eff  is determined by the length of the fin in accordance with a minimum feature size F governed by the production technology. The effective channel width W eff  is determined from the height of the fin, or the depth to which the recess step is carried out.  
         [0006]     The effective channel length L eff  is linked to the minimum feature size F and limits the scaling potential of the finFET with regard to the leakage current or the insulator properties in the off state. The switching threshold of the finFET depends greatly on production parameters. The fabrication of a fin field-effect transistor as selection transistor of a memory cell with a hole trench capacitor proves to be complex.  
         [0007]     Arrangements with vertical transistor cells (VTCs) are known for memory cells with a hole trench capacitor. The source/drain regions of the selection transistor are essentially arranged vertically one above the other in the semiconductor substrate. A channel controlled by a gate electrode of the selection transistor is formed perpendicular to the cell array plane or substrate surface of the semiconductor substrate. The minimum channel width W eff  results in accordance with the minimum feature size F. The channel length L eff  is dependent on the depth at which the lower source/drain region or a lower edge of the gate electrode is formed.  
         [0008]     Disadvantages of the vertical transistor cell are the difficult integration in memory cells having stacked capacitors, the increase in the aspect ratio of a hole trench for forming the memory cell in the case of integration in memory cells having hole trench capacitors, the restricted switch-on/switch-off current I on  and also the parasitic action of the gate electrode of a selection transistor on adjacent memory cells.  
         [0009]     A vertical memory cell with a vertical transistor structure in which the gate electrode completely encloses a body region arranged between the two source/drain regions is described in “Fully Depleted Surrounding Gate Transistor (SGT) for 70 nm DRAM and Beyond”; Goebel et al. A fin is formed by etching back a semiconductor substrate. A first source/drain region is formed by outdiffusion from an adjacent structure in the base region of the fin. A second source/drain region is provided at the upper edge of the fin. The gate electrode is arranged along the four sidewalls of the fin. The effective channel length L eff  results from the depth of etching back for the fin. The effective channel width W eff  corresponds to the contour of the fin, at least one side length resulting in a manner dependent on the minimum feature size F. The total effective channel width correspondingly amounts to 2F to 3F. Like the vertical transistor cell, the transistor cell with a surrounding gate electrode, too, can only be integrated in a complex manner in memory cells having stacked capacitors. The high aspect ratios established in the course of processing and the resultant restrictions in the processing and with regard to the storage capacitor are furthermore disadvantageous.  
         [0010]     A field-effect transistor with a curved channel is described in “The Breakthrough in Data Retention time of DRAM using Recess-Channel-Array Transistor (RCAT) for 88 nm Feature Size and Beyond”; Kim et al.; in “2003 Symposium on VLSI Technology Digest of Technical Papers.” The two source/drain regions of the field-effect transistor are arranged in a horizontal plane. The gate electrode is arranged in a recess trench introduced into the semiconductor substrate between the two source/drain regions of the transistor. The effective channel length L eff  results from the distance between the two source/drain regions and also the depth to which the recess trench provided between the two source/drain regions is introduced into the semiconductor substrate. The effective channel width W eff  corresponds to the minimum feature size F.  
         [0011]     The continuing restriction of the effective channel width disadvantageously limits the switch-on/switch-off current.  
         [0012]     In the case of integration of recess channel FETs in memory cells with a high packing density, the alignment of the gate electrodes with respect to the recess trenches proves to be complex, for instance if both are respectively patterned in the course of a photolithographic method. In contrast to finFET or SGT transistor cells, the active zone is not shielded from the adjacent memory cells by the gate electrode. A parasitic punchthrough of the potential of a gate electrode to the adjacent transistor cells occurs.  
         [0013]     An arrangement for memory cells having hole trench capacitors and selection transistors having a gate electrode grooved into the semiconductor substrate (grooved gate) is described in U.S. Pat. No. 5,945,707 (Bronner et al.) and is explained below with reference to  FIG. 1 .  
         [0014]     In accordance with  FIG. 1 , storage capacitors  6  are formed as hole trench capacitors  8  in a semiconductor substrate  1  below a substrate surface  10 . A hole trench capacitor  8  comprises a storage electrode  61  arranged in the interior of a hole trench and a counterelectrode  63  formed as a doped zone in a section of the semiconductor substrate  1  that surrounds a lower section of the storage electrode  61 . A capacitor dielectric  62  is provided between the storage electrode  61  and the counterelectrode  63 . In an upper section of the hole trench capacitor  6 , the storage electrode  61  is insulated from the semiconductor substrate  1  by a collar insulator structure  81 .  
         [0015]     An active zone  11  with two selection transistors  9 ,  9 ′ is formed by the semiconductor substrate  1  between in each case two adjacent capacitor structures  6 . The source/drain regions  12 ,  13  of the selection transistors  9 ,  9 ′ are in each case doped sections of the active zone  11 . A respective first source/drain region  12  adjoins the storage electrode  61  of a storage capacitor  6  in the region of a contact window  82 . The second source/drain region  13  is connected via a bit contact  31  to a-data line  33  arranged above the substrate surface  10 . The gate electrode  2  comprises a highly conductive section  2   a.  The gate electrodes of selection transistors that are adjacent in the direction perpendicular to the cross-sectional plane are connected to one another and form addressing lines. The addressing lines are enclosed by a gate stack insulator structure  95  and insulated from the data line  33  formed thereabove by an interlayer dielectric  41 .  
         [0016]     Between the two source/drain regions  12 ,  13  of the selection transistors  9 ,  9 ′, a recess trench  18  is introduced in each case from the substrate surface  10 . The recess trench  18  is filled with the material of the gate electrode  2 . A channel region  15  of the selection transistor  9 ,  9 ′ extends in the semiconductor substrate  1  along the sidewalls and the bottom of the recess trench  18 . A gate dielectric  16  is provided between the gate electrode  2  and the semiconductor substrate  1 . The recess trench  18  lengthens the effective channel length L eff  with regard to a cell current  96  compared with a conventional planar transistor structure.  
         [0017]     The patterning of the addressing lines is carried out in a manner aligned with the recess trenches  18  introduced beforehand and the patterning of the recess trenches  18  is carried out in a manner aligned with the hole trenches of the hole trench capacitors  8 . The effective channel width W eff  is disadvantageously predefined, in the direction perpendicular to the cross-sectional plane, by the distance with respect to the memory cells that are adjacent in this direction.  
       SUMMARY  
       [0018]     The invention provides a transistor structure which has an improved switch-on and switch-off behavior given the same area requirement in relation to a comparable conventional transistor structure. The invention further encompasses a memory cell with an improved switch-on and switch-off behavior and also a memory cell array and methods for fabricating a DRAM.  
         [0019]     A transistor structure with a curved channel has two source/drain regions, which are formed in a semiconductor substrate, are arranged in a horizontal plane with respect to a substrate surface of the semiconductor substrate along an x axis, and are spaced apart from one another by a recess structure. A surface contour of an active zone of the transistor structure is predefined by the outer contours of the source/drain regions and also the recess structure in the horizontal plane. Vertical projection lines of the surface contour into the semiconductor substrate define an active zone of the transistor structure that is delimited by the vertical projection lines. A sidewall of the active zone is predefined by the vertical projection lines of the surface contour.  
         [0020]     According to the invention, the gate electrode is provided along the sidewall of the active zone. The gate electrode has at least one section that extends in the x axis between the two source/drain regions and in the vertical direction from the lower edges of the source/drain regions to beyond a lower edge of the recess structure.  
         [0021]     In contrast to conventional transistor structures with a curved channel, in the case of the transistor structure according to the invention, the effective channel width is determined largely independently of the known feature size F and results from the depth to which the gate electrodes are formed at the sidewalls of the active zone of the transistor structure.  
         [0022]     The gate electrode advantageously has a second section situated symmetrically opposite to the first section at the recess structure. The active zone is protected against interfering influences (cross-gating effects) and the effective channel width is doubled.  
         [0023]     In a particularly preferred manner, the active zone of the transistor structure, along the sidewall, is completely surrounded by the gate electrode. The active zone is largely shielded against influences of adjacent transistor structures and a maximum effective channel width is obtained.  
         [0024]     A high packing density of transistor structures according to the invention can advantageously be obtained by providing the active zone with two sidewall sections parallel to the x axis. The active zones of a plurality of transistor structures can then be arranged next to one another in rows in a simple manner.  
         [0025]     The active zone is preferably formed in a fin of the semiconductor substrate that is provided between two parallel gate electrode trenches. A gate dielectric is provided between the active zone and the gate electrode. The gate electrode is arranged in the gate electrode trenches in a manner spaced apart from the active zone by the gate dielectric.  
         [0026]     The invention&#39;s transistor structure with a curved channel (curved double gate/surrounded gate FET, CFET) leads to a memory cell according to the invention having a storage capacitor for storing electrical charge and a selection transistor connected in series with the storage capacitor by a source/drain path and having a curved channel. The selection transistor has a first source/drain region connected to a storage electrode of the storage capacitor. A second source/drain region of the selection transistor is connected to a data line for transferring electrical charge to be stored or stored electrically charge. A gate electrode of the selection transistor is connected to an addressing line for the control of the memory cell. An effective channel length L eff  of the selection transistor is determined by the depth of a recess structure introduced between the two source/drain regions.  
         [0027]     The gate electrode of the selection transistor is formed in accordance with the above-described transistor structure according to the invention and an effective channel width W eff  of the selection transistor is thereby increased. The increased effective channel width W eff  improves the switching behavior of the memory cell. As a result of the lower resistance in the turned-on state of the selection transistor, a faster access to the memory cell is possible with a reduced power loss. The punchthrough from the gate electrode arranged at least on two sides to the active zone or substrate situated in between is improved. The shielding effect against cross-gating effects is increased.  
         [0028]     The memory cells according to the invention can advantageously be ordered to form a novel memory cell array. The memory cell array then has a plurality of memory cells arranged in cell rows and cell columns. Each memory cell comprises a storage capacitor for storing electrical charge and a selection transistor with a curved channel that is connected in series with the storage capacitor by a source/drain path. A first source/drain region of the selection transistor is connected to a storage electrode of the storage capacitor. A second source/drain region of the selection transistor is connected to a data line for transferring electrical charge to be stored and also electrical charge that has formerly been installed. A gate electrode of the selection transistor is connected to an addressing line for the control of the memory cell. An effective channel length L eff  of the selection transistor is determined by the depth of a recess structure fitted between the two source/drain regions.  
         [0029]     The gate electrodes of the selection transistors are in each case formed in accordance with the gate electrode of the transistor structure according to the invention, so that an effective channel width W eff  of the selection transistors is in each case increased. The gate electrodes of selection transistors of memory cells that are respectively arranged in a cell row are connected to one another and form the addressing lines for the control of the memory cells.  
         [0030]     Compared with conventional memory cell arrays having selection transistors with a curved channel, for instance that in U.S. Pat. No. 5,945,707, cited in the background, the introduction of recess trenches for the recess structures, on the one hand, and the formation of the gate electrodes, on the other hand, are advantageously decoupled from one another. A difficulty that results from the fact that, by way of example, a first mask for introducing the recess trenches and a second mask for patterning the gate electrodes have to be aligned relative to one another is obviated.  
         [0031]     The storage capacitors and the selection transistors of the memory cell array are advantageously arranged in the manner of a chessboard pattern, the selection transistors being assigned to first arrays that are in each case diagonally adjacent to one another and the storage capacitors being assigned in each case to second arrays that are situated in between. In a first preferred embodiment of the memory cell array according to the invention, the storage capacitors are formed as stacked capacitors above a substrate surface of the semiconductor substrate and, in a second preferred embodiment of the memory cell array according to the invention, the storage capacitors are formed as hole trench capacitors, the hole trench capacitors in each case being formed in a manner oriented to a hole trench introduced into the semiconductor substrate.  
         [0032]     If the storage capacitors are provided as stacked capacitors, then the active zones are preferably formed with a rectangular surface contour and in each case separated from one another within a cell row by narrow cell insulator trenches. Adjacent cell rows are in each case isolated from one another by wide word line trenches. The recess structures are provided parallel to the cell insulator trenches and approximately equidistantly from in each case two adjacent cell insulator trenches. The addressing lines are arranged in the word line trenches the data lines are led above the substrate surface in each case essentially over the recess structures and also over the cell insulator trenches. This advantageously results in a small area requirement of the memory cells, comparatively minor requirements being made of the alignment of required masks relative to one another.  
         [0033]     The cell insulator trenches and the word line trenches preferably emerge from the same etching step and have the same depth.  
         [0034]     Preferably, the width of the cell insulator trenches is less than and the width of the word line trenches is greater than twice the layer thickness of the gate electrodes. If the gate electrodes emerge from a spacer etching with a conformal disposition of a gate electrode material and subsequent anisotropic etching-back of the deposited gate electrode material, then the gate electrodes of selection transistors of memory cells that are adjacent in a cell row adjoin one another and form the addressing lines, while gate electrode sections that are separated from one another are produced at the sidewalls of the word line trenches.  
         [0035]     The recess structures are preferably made of silicon oxide.  
         [0036]     If the storage capacitors of the memory cells are formed as hole trench capacitors, then the active zones and the hole trench capacitors assigned to the active zones are in each case arranged within a cell row, in each case two active zones being separated from one another by a hole trench capacitor situated in between. The cell rows are isolated from one another by word line trenches, and the recess trenches are formed perpendicular to the word line trenches and also arranged approximately equidistantly from the two respectively adjacent hole trench capacitors. The addressing lines are provided in the word line trenches and the data lines are led above the substrate surface perpendicular to the word line trenches. The recess structures provided in the recess trenches are arranged offset to the data lines or respectively equidistantly from two adjacent data lines, thus resulting in a small area requirement of the memory cells of approximately 8×F 2 .  
         [0037]     For memory cells with hole trench capacitors, the recess trenches are preferably filled with silicon nitride. If the recess trenches are introduced with the aid of a silicon oxide mask, then it is possible, when using silicon nitride as filling material, for the filling material to be caused to recede selectively as far as the upper edge of the silicon oxide layer.  
         [0038]     In accordance with the method according to the invention for fabricating a DRAM having a memory cell array formed from memory cells having stacked capacitors, and a logic region having logic transistor structures for control, addressing and evaluation of the information stored in the memory cell array, firstly a protective layer is provided on a semiconductor substrate. The protective layer comprises a comparatively thick silicon nitride layer (pad nitride) and a stress compensating layer between the semiconductor substrate and the silicon nitride layer. The stress compensating layer reduces thermomechanical stresses between the silicon nitride layer and the semiconductor substrate that are attributable to different coefficients of thermal expansion of the materials.  
         [0039]     Afterward, in a photolithographic process, word line trenches and, perpendicular to the word line trenches, cell insulator trenches are introduced through the protective layer into the semiconductor substrate. In this case, the cell insulator trenches are provided such that they are narrower than the word line trenches. A gate dielectric is provided at sidewalls both of the word line trenches and of the cell insulator trenches.  
         [0040]     By conformal deposition and anisotropic etching-back, gate electrodes in the form of sidewall spacers are arranged at the sidewalls of the word line trenches and the cell insulator trenches. In the wide word line trenches, the sections of the sidewall spacers that are opposite one another in a respective one of the word line trenches remain insulated from one another, while the gate electrodes in the narrow cell insulator trenches adjoin one another and are connected to one another.  
         [0041]     The word line trenches and the cell insulator trenches are filled with a dielectric from which a word line insulator structure emerges. The protective layer is removed in the memory cell array and the uncovered sections of the semiconductor substrate are doped in order to prepare for the formation of the source/drain regions of the selection transistors in a section adjoining the substrate surface.  
         [0042]     An auxiliary layer made of a conductive semiconductor material is applied in the region of the memory cell array and caused to recede as far as the upper edge of the word line insulator structures. Through the auxiliary layer, recess trenches are introduced into the semiconductor substrate between the cell insulator trenches, source/drain regions of the selection transistors that are separated from one another by the recess trenches emerging from the doped sections of the semiconductor substrate.  
         [0043]     The recess trenches are either covered or partly or completely filled with a dielectric material. Logic transistor structures are produced in the logic region by processing the logic region. The source/drain regions in the memory cell array are in each case connected to a storage electrode of a stacked capacitor or to a data line.  
         [0044]     The method according to the invention makes it possible to fabricate DRAMs having the above-described transistor structures as selection transistors in the memory cell array. It is necessary merely to align an exposure mask for forming the recess trenches relative to a mask for forming the cell insulator trenches. Since none of the effective channel length nor the effective channel width W eff  is significantly influenced by a misalignment of the mask for the recess trenches, the method according to the invention advantageously has no critical mask processes or alignment processes for lithographic masks.  
         [0045]     A further simplification of the processing results by virtue of the word line trenches, the cell array insulator trenches and also shallow insulator trenches in each case being formed simultaneously in the logic region and being filled with a dielectric material. Afterward, the logic region including the shallow insulator structure is covered with a blocking mask and the dielectric material is etched back in the memory cell array to an extent such that it only fills a lower section of the word line trenches and of the cell insulator trenches and forms bottom insulator structures.  
         [0046]     The recess trenches are preferably introduced by a hard mask made of silicon oxide being provided on the auxiliary layer and being patterned photolithographically. The recess trenches are introduced into the semiconductor substrate in the region of the openings of the hard mask by an etching process that acts selectively with respect to silicon oxide.  
         [0047]     The processing of the logic region preferably comprises the following steps: firstly, the protective layer is removed in the logic region and a silicon nitride protective coating is applied. After the removal of the silicon nitride protective coating in the logic region, logic transistor structures are formed in the logic region. In this case, the region of the memory cell array remains protected against the processing in the logic region by virtue of the overlying silicon nitride protective coating.  
         [0048]     The method according to the invention for fabricating a DRAM having a memory cell array having memory cells with hole trench capacitors as storage capacitors firstly comprises the provision of a protective layer on a semiconductor substrate, in which case the protective layer may have a plurality of partial layers, as described above. Hole trench capacitors are formed in the semiconductor substrate, the hole trench capacitors in each case having a contact window (buried strap window) in the upper section. In the region of the contact window, a storage electrode of the hole trench capacitor that is arranged in the interior of a hole trench electrically conductively adjoins the adjoining semiconductor substrate. Outside the contact window, the hole trench capacitor is electrically insulated from the surrounding semiconductor substrate.  
         [0049]     The hole trench capacitors are arranged to form cell rows in the memory cell array. Through the protective layer, word line trenches running parallel to the cell rows are introduced between the cell rows.  
         [0050]     A gate dielectric is provided on sidewalls of the word line trenches and gate electrodes are arranged in the manner of sidewall spacers on the gate dielectric. The gate electrodes of selection transistors of memory cells that are adjacent in a cell row adjoin one another and form addressing lines. The word line trenches are filled with a dielectric material that forms word line insulator structures beneath the upper edge of the protective layer. The storage electrodes of the hole trench capacitors are caused to recede to below the upper edge of a substrate surface of the semiconductor substrate, thereby uncovering vertical sidewalls of the protective layer that are oriented toward the hole trench capacitors.  
         [0051]     The protective layer or the silicon nitride layer as a constituent part of the protective layer is caused to recede in an etching process having a high isotropic component. Since the vertical sidewalls of the protective layer that are oriented toward the hole trenches are uncovered, a section of the protective layer resting between two hole trench capacitors is in each case caused to recede from the sides oriented toward the hole trench capacitors. After the receding step, residual sections of the protective layer remain only over those regions of the semiconductor substrate which are provided for forming the recess trenches. Since no vertical sidewalls of the protective layer are uncovered in the logic region, the protective layer is caused to recede there only in terms of the layer thickness.  
         [0052]     An auxiliary oxide layer is applied and caused to recede as far as the upper edge of the residual sections of the protective layer. The residual sections of the protective layer are removed selectively with respect to the auxiliary oxide layer.  
         [0053]     A mask for forming the recess trenches has thus emerged from the protective layer in an advantageous and self-aligned manner and without a photolithographic process.  
         [0054]     Before the introduction of the recess trenches, the logic region is covered by a blocking mask. The recess trenches are introduced into the semiconductor substrate with the auxiliary oxide layer as a mask in the region of the memory cell array. The blocking mask over the logic region is removed. The recess trenches are covered or at least partly filled with a dielectric.  
         [0055]     The logic region is processed, logic transistor structures being formed in the logic region.  
         [0056]     The source/drain regions of the selection transistors that are not connected to a storage electrode via a contact window are in each case connected to a data line.  
         [0057]     An essential advantage of the method according to the invention resides in the self-aligned formation of a non-photolithographic mask for forming the recess trenches.  
         [0058]     In accordance with a preferred embodiment of the method according to the invention, the word line trenches and shallow insulator trenches are filled with a dielectric material in the logic region, the logic region including the shallow insulator structures is covered with a temporary blocking mask and the dielectric material is then caused to recede in the memory cell array. As a result of the dielectric material that has been caused to recede, bottom insulator structures are formed in lower sections of the word line trenches. The insulator structures are advantageously formed simultaneously in the logic region and in the memory cell array.  
         [0059]     In accordance with a preferred embodiment of the method according to the invention, source/drain regions of the selection transistors are formed by an implantation, the residual sections of the protective layer that have been caused to recede being used as an implantation mask.  
         [0060]     According to a preferred embodiment of the method according to the invention, the filling of the recess trenches firstly comprises an oxidation of the sidewalls of the recess trenches. A conformal nitride liner is deposited and caused to recede essentially anisotropically to below the upper edge of the auxiliary oxide layer.  
         [0061]     Parts of the method described can advantageously also be used for fabricating known recess channel transistor structures for memory cells. For this purpose, a protective layer is provided on a semiconductor substrate. Hole trench capacitors arranged to form cell rows are formed in the semiconductor substrate, a storage electrode of the hole trench capacitor being formed in each case by filling a hole trench with a conductive material. The storage electrodes of the hole trench capacitors are caused to recede to below the lower edge of the protective layer. The protective layer is etched back in an etching process having a high isotropically acting component, with the result that residual sections of the protective layer in each case remain in a self-aligned manner approximately centrally between in each case two hole trench capacitors that are adjacent in a cell row. The residual sections of the protective layer that have been caused to recede form a mask for implantation of source/drain regions of the selection transistors that are to be provided in the semiconductor substrate and/or a precursor mask for forming recess trenches.  
         [0062]     In order to form the recess trenches, after the protective layer has been caused to recede isotropically, an auxiliary oxide layer is applied, which is subsequently caused to recede as far as the upper edge of the residual sections of the protective layer. After the removal of the residual sections of the protective layer, a self-aligned mask for the introduction of recess trenches is produced by the auxiliary oxide layer.  
         [0063]     In contrast to the previously mentioned methods, in this case a section of a gate electrode of the respective selection transistor is provided in the recess trenches. In contrast to customary methods for fabricating conventional recess channel transistors, the critical overlay of the lithographic mask for forming the hole trenches with the mask for forming the recess trenches is obviated. According to the invention, the lithographic mask for forming the recess trenches is unnecessary; it is instead produced in a self-aligned manner with respect to the hole trenches.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0064]     The invention and its advantages are explained in more detail below with reference to figures, mutually corresponding components in each case being designated by the same reference symbols, in each case in a simplified schematic illustration that is not true to scale:  
         [0065]      FIG. 1  shows a schematic cross section through a known memory cell arrangement having selection transistors having gate electrodes grooved into the semiconductor substrate (grooved gate);  
         [0066]      FIG. 2  shows two cross sections through a transistor structure according to the invention according to a first exemplary embodiment of the invention;  
         [0067]      FIGS. 3A-3K  show a plan view of and cross sections through a memory cell array according to the invention having stacked capacitors according to a second exemplary embodiment of the invention in different phases of the method according to the invention according to a third exemplary embodiment; and  
         [0068]      FIGS. 4A-4I  show a plan view of and cross sections through a memory cell array according to the invention having hole trench capacitors according to a fourth exemplary embodiment of the invention in different phases of the method according to the invention according to a further exemplary embodiment. 
     
    
     DETAILED DESCRIPTION  
       [0069]      FIG. 2  shows on the left a cross section through a transistor structure  98  according to the invention, and a cross section perpendicular thereto in the right-hand illustration.  
         [0070]     In a semiconductor substrate  1 , a first source/drain region  12  and a second source/drain region  13  are formed along a substrate surface  10  along an x axis. The two source/drain regions  12 ,  13  are spaced apart from one another by a recess trench  18 . The recess trench  18  is introduced from the substrate surface  10  to below a lower edge of the source/drain regions  12 ,  13 . Beneath the source/drain regions  12 ,  13 , a body region  14  of the transistor structure  98  is formed by the semiconductor substrate  1 . The body region  14  is surrounded by a gate electrode  2  and is in this case spaced apart from the gate electrode  2  by a gate dielectric  16 . The gate electrode  2  extends essentially from the lower edge of the source/drain regions  12 ,  13  to beneath a lower edge of the recess trench  18 . The recess trench  18  is filled with a dielectric material or remains unfilled. The filled or only covered recess trench  18  forms a recess structure. The gate electrode  2  is provided in two partial sections in two gate electrode trenches  20   a  running parallel to the x axis.  
         [0071]     During operation of the transistor structure  98 , by a suitable potential at the gate electrode  2 , in a section of the body region that adjoins the gate dielectric  16 , a conductive channel  15  is formed between the two source/drain regions  12 ,  13 . A cell current  96  flows through the channel  15 . The length of the channel  15  is essentially determined by the depth of the recess structure  18 . The effective channel width is determined by the extent of the gate electrode  2  in the vertical direction with respect to the substrate surface  10 . The source/drain regions  12 ,  13  and also the body region  14  form an active zone  11 , which is formed in a fin  17  of the semiconductor substrate  1 , the fin  17  being bounded by the gate electrode  2  on at least two mutually opposite sides.  
         [0072]      FIG. 3A  shows a plan view of a detail from a memory cell array. In this case, the storage capacitors of the memory cells are formed as stacked capacitors. The memory cells are arranged in mutually orthogonal cell rows and cell columns and the storage capacitors are arranged within the cell rows and cell columns in each case in a manner alternating with selection transistors in a chessboard-like manner.  
         [0073]     The active zones  11  of the selection transistors are illustrated as rectangular and separated from one another within a row by narrow cell insulator trenches  64 . Word line trenches  20  are introduced between the cell rows formed by the active zones  11  and the cell insulator trenches  64 , the word line trenches having a larger width than the cell insulator trenches  64 . The source/drain regions  12 ,  13  of the active zones  11  are in each case arranged along the row axis corresponding to the x axis of  FIG. 2 . The two source/drain regions  12 ,  13  of a respective active zone  11  are separated from one another by a recess trench  18 , which has a smaller depth than the word line trenches  20  and the cell insulator trenches  64 . Respectively adjacent source/drain regions  12 ,  13  of active zones  11  arranged in a cell column are in each case assigned alternately to a data line  33  or a stacked capacitor. The position of the stacked capacitors results from the position of the respective storage electrodes  61 , which in each case rests on a node pad  36  as upper termination of a capacitor connection structure.  
         [0074]     The first source/drain regions  12  are connected to the storage electrode  61  of the respectively assigned stacked capacitor via the capacitor connection structures. The second source/drain regions  13  are connected via bit line contacts  32  to data lines  33  routed between the bit line contacts  32  and an upper edge of the capacitor connection structures or node pads  36 .  
         [0075]      FIG. 3C  to  FIG. 3K  illustrate cross sections along the line A-B-C-D in  FIG. 3A  in various phases of an exemplary embodiment of the method according to the invention.  
         [0076]     A semiconductor substrate  1  is provided and a stress equalizing layer, for instance made of silicon dioxide (pad oxide), is applied on a substrate surface  10  of the semiconductor substrate  1 . Well implantations are optionally embodied in the memory cell array at this point in time. A silicon nitride layer (pad nitride) is applied as protective layer  51  to the stress equalizing layer. Active zones  11  of selection transistors are patterned in a photolithographic process. The requisite exposure is performed twice with a head-to-head distance of less than F.  
         [0077]     The semiconductor substrate  1  is patterned in the region of a memory cell array  91  by wide word line trenches  20  and narrow cell insulator trenches  64  running perpendicular to the word line trenches  20 , fins with the active zones  11  being shaped between the word line trenches  20  and the cell insulator trenches  64  in the semiconductor substrate  1 . The sidewalls of the active zones  11  are oxidized by an oxidation process. Shallow insulator trenches are formed at the same time as the word line trenches  20  and the cell insulator trenches  64  in a logic region  92  supplementing the memory cell array  91 .  
         [0078]     The cell insulator trenches  64 , the word line trenches  20  and also the shallow insulator trenches are filled with silicon oxide. The silicon oxide is planarized and in the process caused to recede as far as the upper edge of the protective layer  51 . The logic region  92  including the shallow insulator trenches is covered by a blocking mask and the silicon oxide is etched back into the trenches  20 ,  64  in the memory cell array  91 .  
         [0079]      FIG. 3C  reveals the state of a semiconductor substrate  1  processed in the manner described after the silicon oxide has been caused to recede. The protective layer  51  rests on a substrate surface  10  of the semiconductor substrate  1 . In the logic region  92 , shallow insulator structures  23 ′ have emerged from the shallow insulator trenches.  
         [0080]     In the memory cell array  91 , word line trenches  20  and cell insulator trenches  64  having the same depth are introduced into the semiconductor substrate  1  through the protective layer  51 . Bottom insulator structures  23  formed by the silicon oxide are in each case arranged in the lower section of the word line trenches  20  and of the cell insulator trenches  64 .  
         [0081]     A gate dielectric  16  is formed on the sidewalls of the active zones  11  by oxidation of the material of the semiconductor substrate  1 . By conformal deposition of titanium nitride or doped polysilicon, sidewall spacer structures  21  are formed as sections of gate electrodes on the sidewalls of the word line trenches  20  and of the cell insulator trenches  64 .  
         [0082]     As illustrated in  FIG. 3D , in this case the sidewall spacer structures  21  are separated from one another in the wide word line trenches  20 , whereas in the narrow cell insulator trenches  64  they adjoin one another and form conductive structures or addressing lines that are contiguous along the cell row.  
         [0083]     After the formation of the sidewall spacer structures  21 , the word line trenches  20  and also the cell insulator trenches  64  are filled with a dielectric material. The dielectric material is caused to recede as far as the upper edge of the protective layer  51  by a planarization step. The dielectric material that has been caused to recede forms word line insulator structures  24  in the word line trenches  20  and the cell insulator trenches  64 .  
         [0084]     In the memory cell array  91 , the protective layer  51  is removed and the formation of source/drain regions  12 ,  13  is prepared by doping of sections of the semiconductor substrate  1  which is uncovered in the region of the memory cell array  91 , said sections adjoining the substrate surface  10 . An auxiliary layer  71  made of n-doped polysilicon is applied and caused to recede by a planarization step as far as the upper edge of the word line insulator structures  24  in a manner corresponding to the upper edge of the protective layer  51  in the logic region  92 .  
         [0085]     In accordance with  FIG. 3E , the protective layer  51  is replaced by the auxiliary layer  71  in the memory cell array  91 . A section of the semiconductor substrate  1  that adjoins the substrate surface  10  is doped in preparation for the formation of the source/drain regions  12 ,  13 .  
         [0086]     A hard mask  72  is applied to the auxiliary layer  71  in the region of the memory cell array  91  and also to the section of the protective layer  51  that remains in the logic region  92 , and is patterned by a photolithographic method for forming the recess trenches  18 .  
         [0087]     In accordance with  FIG. 3F , the hard mask  72  is opened at the locations provided for forming the recess trenches  18 .  
         [0088]     The recess trenches  18  are introduced into the semiconductor substrate  1  through the openings of the hard mask  72  and through the auxiliary layer  71  by an etching process that acts selectively with respect to silicon oxide. The mask for forming the recess trenches  18  is striplike.  
         [0089]     The sidewalls of the recess trenches  18  are oxidized. The recess trenches  18  are filled with silicon oxide, which is subsequently caused to recede as far as the upper edge of the auxiliary layer  71  by a planarization step. The protective layer  51  is removed in the logic region  92 . A silicon nitride protective coating  73  is applied over the whole area and subsequently removed again in the logic region  92 .  
         [0090]      FIG. 3G  shows the recess trenches  181  filled with silicon oxide and also the silicon nitride protective coating  73  covering the memory cell array  91 .  
         [0091]     The silicon nitride layer protective coating  73  protects the structures formed in the region of the memory cell array  91  against processing in the logic region  92 . In the course of the processing of the logic region  92 , logic transistor structures  93  having logic gate structures  53  and logic source/drain regions  54  are formed in the logic region  92  for instance in the course of a dual work function process. An interlayer dielectric  41  is applied and planarized. In a photolithographic process, openings corresponding to second source/drain regions  13  that are to be connected to a data line  33  are introduced into the interlayer dielectric  41 .  
         [0092]      FIG. 3H  shows logic transistor structures  93  having logic gate structures  53  and logic source/drain regions  54  in the logic region  92 . In the memory cell array  91 , the interlayer dielectric  41  together with the underlying silicon nitride protective coating  73  is opened above the second source/drain regions  13 .  
         [0093]     The openings in the interlayer dielectric  41  are filled with a conductive material, for instance tungsten. After a planarization step, the conductive material caused to recede into the openings forms bit contacts  32 , which adjoin the sections of the auxiliary layer  71  which are assigned to the second source/drain regions  13 .  
         [0094]     Once again a conductive material, for instance tungsten, and also silicon nitride are deposited successively. In a photolithographic method, the silicon nitride layer and the underlying layer made of the conductive material are patterned jointly, data lines  33  emerging from the layer made of the conductive material and a data line dielectric  42  covering the data lines  33  emerging from the silicon nitride layer. Vertical sidewalls of the data lines  33  are covered with silicon nitride spacer structures by conformal deposition and anisotropic etching-back. A further filling dielectric  43  (BL interdielectric fill) is provided between the data lines  33  by deposition and subsequent receding as far as the upper edge of the data line dielectric  42 .  
         [0095]     In accordance with  FIG. 3I , the second source/drain regions are in each case connected via bit line contacts  32  to data lines  33  routed above the substrate surface  10 . The data lines  33  are covered by a data line dielectric  42 . Between the data lines  33 , an intermediate data line dielectric  43  supplements the interlayer dielectric  41 . Equivalently to this, a wiring plane  32 ′ is shaped in the logic region  92 .  
         [0096]     A further silicon dioxide layer is deposited and capacitor connection structures  35  are patterned, via which the first source/drain regions  12  are to be connected to storage electrodes  61  of stacked capacitors  7  that are subsequently to be processed. In this case, sections of the conductive auxiliary layer  71  are uncovered in the region of the first source/drain regions  12  by an etching through the further silicon dioxide layer and between two data lines  33  that are in each case encapsulated by silicon nitride spacer structures. The contact holes produced in this way are filled with a conductive material, for instance tungsten. The conductive material is planarized, capacitor connection structures  35  being formed in the contact holes. Aerially extended node pads  36  rest on the capacitor connection structures  35 .  
         [0097]      FIG. 3J  shows capacitor connection structures  35  that are led as far as the upper edge of the sections of the auxiliary layer  71  that correspond to the first source/drain regions  12 .  
         [0098]     Stacked capacitors  7  are subsequently formed, the storage electrodes  61  of which in each case rest on the node pads  36  and adjoin them.  
         [0099]      FIG. 3K  illustrates storage capacitors  6  formed as stacked capacitors  7 . The stacked capacitors  7  in each case comprise a storage electrode  61 , a counterelectrode  63  and a capacitor dielectric  62  that spaces apart the two electrodes  61 ,  63  from one another. The storage electrode  61  in each case electrically conductively adjoin the respectively assigned node pad  36 .  
         [0100]     The structure and also the functioning of the memory cell are explained with reference to the two cross sections illustrated in  FIG. 3B .  
         [0101]     The left-hand illustration of  FIG. 3B  shows a cross section through a memory cell according to the invention along a row direction which is predetermined by the arrangement of the two source/drain regions  12 ,  13  and defines an x axis. The right-hand illustration shows two memory cells arranged in two adjacent cell rows perpendicular to the x axis, the two source/drain regions  12 ,  13  of two adjacent selection transistors in each case being arranged offset relative to one another.  
         [0102]     As can further be gathered from the left-hand illustration of  FIG. 3B , the active zones  11  of selection transistors that are in each case adjacent in a cell row are separated from one another by cell insulator trenches  64 . A first source/drain region  12  is in each case formed within the active zone  11 , and is connected to a storage electrode  61  of a stacked capacitor via a section of an auxiliary structure  71  and a capacitor connection structure  36 . A second source/drain region  13  is connected to a data line  33  via a further section of the auxiliary structure  71  and via an adjoining bit line contact  32 . The lower section of the cell insulator trenches  64  is filled with a bottom insulator structure  23 . Between the two source/drain regions  12 ,  13 , the semiconductor substrate  1  forms a body region  14  into which a recess trench  18  is introduced.  
         [0103]     The right-hand illustration of  FIG. 3B  reveals that the active zones  11  are enclosed along the x axis by gate electrodes in the form of sidewall spacer structures  21  which are spaced apart from the semiconductor substrate  1  and the active zones  11  by a gate dielectric  16 .  
         [0104]     If a suitable potential is applied to the gate electrode or the sidewall spacer structure  21 , then a conductive channel  15  forms in the sections of the body zone  14  that are opposite to the sidewall spacer structures  21  at the gate dielectric  16 , the conductive channel connecting the two source/drain regions  12 ,  13  to one another. The effective channel length L eff  of the channel  15  results from the depth of the filled recess trench  18 . The effective channel width W eff  of the channel  15  results from the distance between the lower edge of the recess structure in the recess trench  18  and the lower edge of the sidewall spacer structures  21 .  
         [0105]     The drawings of  FIGS. 4A-4I  illustrate an exemplary embodiment of a method for forming a memory cell array having hole trench capacitors as storage capacitors.  
         [0106]      FIG. 4A  shows the structure to be processed in plan view. In this case, the selection transistors are represented by active zones  11  assigned to them. The active zones  11  are arranged with the respectively assigned hole trench capacitors  8  in cell rows which are arranged offset relative to one another, thus resulting in a chessboard-like arrangement of active zones  11  and hole trench capacitors  8 . The active zone  11  of a memory cell is delimited by in each case two hole trench capacitors  8  within a cell row, one of the two hole trench capacitors  8  that delimit the active zone  11  having a contact window in the region of which a first source/drain region  12  of the active zone  11  adjoins a storage electrode  61  in the interior of the hole trench capacitor  8 . The active zone  11  is insulated from the storage electrode of the other hole trench capacitor  8 ′ by a collar insulator structure provided in the interior of the hole trench capacitor  8 .  
         [0107]     Word line trenches  20  are introduced between the cell rows formed by the hole trench capacitors  8  and the active zones  11 , said word line trenches intersecting an upper section of the hole trench capacitors  8 . Data lines  33  are routed orthogonally with respect to the word line trenches  20 , and are connected via bit line contacts  32  to in each case a second source/drain region  13  of the selection transistors or the active zones  11 . Recess trenches  18  are introduced into the active zones  11  in each case between the bit lines  33 , which recess trenches in each case separate the first source/drain regions  12  from the second source/drain regions  13  and the depth of which recess trenches predefines an effective channel length L eff  of the selection transistors.  
         [0108]     An illustration is given below of an exemplary embodiment of the method according to the invention for fabricating a DRAM having such a memory cell array along the cross section A-B-C-D of  FIG. 4A .  
         [0109]     A protective layer  51  made of silicon nitride, under which is situated a stress equalizing layer, is applied to a semiconductor substrate  1 . Hole trenches are introduced into the semiconductor substrate  1  by a photolithographic process. Hole trench capacitors  8  are formed in a manner oriented in or at the hole trenches. In an upper section, the hole trench capacitors  8  are in each case lined by a collar insulator structure  81 , which insulates a storage electrode  61  provided in the interior of the hole trench from the active zones  11  formed in the adjoining semiconductor substrate  1 . Opposite a respective active zone  11  that is adjacent in the cell row, the collar insulator structure  81  has an opening that forms a contact window  82 . The formation of the hole trench capacitor  8  is concluded by the formation of the storage electrode  61 , for which the hole trench is finally filled with doped polysilicon that is subsequently caused to recede as far as the upper edge of the protective layer  51 .  
         [0110]     By a photolithographic process, word line trenches  20  are introduced in striplike fashion parallel to the cell rows. The cell rows are separated from one another by the word line trenches  20 . Uncovered vertical sidewalls of the active zones  11  are oxidized. The word line trenches  20  in the memory cell array  91  and shallow insulator trenches in the logic region  92 , which have emerged for instance from the same lithographic process, are filled with silicon oxide that is subsequently caused to recede as far as the upper edge of the protective layer  51 . The silicon oxide is caused to recede into the word line trenches  20  by an etching-back step that acts only in the memory cell array  91 .  
         [0111]      FIG. 4B  illustrates the silicon oxide that has been caused to recede and forms bottom insulator structures  23  in lower sections of the word line trenches  20 . In the logic region  92 , the silicon oxide is not caused to recede and forms shallow insulator structures  23 ′.  
         [0112]     In the memory cell array  91 , the active zone  11  of a selection transistor assigned to a hole trench capacitor  8 ′ is delimited by two hole trench capacitors  8 ,  8 ′. The storage electrode  61  of the hole trench capacitor  8 ′ adjoins the active zone  11  in the region of a contact window  82 . The storage electrode  61  of the second hole trench capacitor  8  that delimits the active zone  11  in the cell row is insulated from the active zone  11  of the memory cell by the collar insulator structure  81 .  
         [0113]     A gate dielectric  16  is formed on the uncovered vertical sidewalls of the active zones  11  by an oxidation process. By conformal deposition and anisotropic etching-back of a conductive material such as titanium nitride or doped polysilicon, gate electrodes are formed in the manner of sidewall spacer structures  21  on the sidewalls of the word line trenches  20 . The word line trenches  20  are subsequently filled with a dielectric material that is caused to recede as far as the upper edge of the protective layer  51  by a planarization step and forms word line insulator structures  24  in the word line trenches  20 . The upper edge of the storage electrode  61  is caused to recede to below the lower edge of the protective layer  51  by an etching step that acts selectively on polysilicon.  
         [0114]      FIG. 4C  illustrates the sidewall spacer structures  21  in the word line trenches  20 , which in each case enclose an active zone  11  on both sides. The sidewall spacer structures  21  arranged within a word line trench  20  are insulated from one another by the word line insulator structure  24 . The sidewall spacers structures  21  respectively forming the gate electrode of active zones  11  that are respectively adjacent in a cell row adjoin one another via the intervening hole trench capacitors  8 ,  8 ′ and form addressing lines.  
         [0115]     The protective layer  51  or a silicon nitride layer portion thereof is caused to recede by an etching process having an isotropically acting component. Since the vertical sidewalls of the residual sections of the protective layer  51  that are oriented toward the hole trench capacitors  8 ,  8 ′ are uncovered, the protective layer  51  is also caused to recede from the side areas oriented toward the hole trench capacitors  8 ,  8 ′. The receding process is terminated as soon as residual sections  511  of the protective layer that has been caused to recede in each case cover that section of the active zone  11  which is provided for forming the recess trenches  18 .  
         [0116]      FIG. 4D  illustrates the sections of the protective layer  511  that has been caused to recede in this way. The sections of the protective layer  511  that has been caused to recede have a smaller layer thickness than the original protective layer  51 . No etching attack has taken place via the side areas of the protective layer  51  that are covered by the word line insulator structures  24 . By contrast, the protective layer  51  has been caused to recede from the side areas oriented toward the hole trench capacitors  8  and completely covers only a central section of the active zone  11  between the two adjacent word line insulator structures  24 . The protective layer  51  has not been caused to recede from the side areas facing the word line insulator structures  24 .  
         [0117]     A section of the semiconductor substrate  1  that adjoins the substrate surface  10  is doped by implantation, thus preparing for the formation of source/drain regions  12 ,  13 . An auxiliary oxide layer  84  is applied and is caused to recede by a planarization step as far as the upper edge of the protective layer  511  that has been caused to recede. The residual sections  511  of the protective layer that have been caused to recede are removed and, for the subsequent etching step, the logic region  93  is covered by a blocking mask  52  made of a photoresist material.  
         [0118]     The structure illustrated in  FIG. 4E  is produced. The protective layer  51  or  511  has been completely removed. Instead, a patterned auxiliary oxide layer  84  rests in the region of the memory cell array  91 . The openings of the auxiliary oxide layer  84  corresponds to the residual sections  511  of the protective layer  51  that have been caused to recede. The auxiliary layer  84  forms a mask for the subsequent etching process for forming the recess trenches  18 . The mask is self-aligned with respect to the hole trench capacitors  8 . The logic region  92  is covered by a blocking mask  52 .  
         [0119]     Recess trenches  18  are introduced into the semiconductor substrate  1  through the openings of the auxiliary oxide layer  84 .  
         [0120]     The etching process for forming the recess trenches  18  is effected selectively with respect to the silicon oxide of the auxiliary oxide layer  84  and furthermore selectively with respect to the photoresist material of the blocking mask  52 .  
         [0121]      FIG. 4F  illustrates the recess trenches  18  introduced into the semiconductor substrate  1  in the region of the active zones  11 . Within the active zone  11 , a first source/drain region  12  connected to the storage electrode  61  of the assigned hole trench capacitor  8  is separated from a second source/drain region  13  by the recess trench  18 .  
         [0122]     The blocking mask  52  is removed and the sections of the active zones  11  that are freed by the recess trenches  18  are oxidized. A conformal silicon nitride layer is deposited and the recess trenches  18  are filled in the process. The conformally deposited silicon nitride layer is caused to recede as far as the upper edge of the auxiliary oxide layer  84 .  
         [0123]     In accordance with  FIG. 4G , the recess trenches  18  are filled with a silicon nitride filling structure  182 . The deposition of the silicon nitride layer and also the process of causing it to recede are controlled such that the silicon nitride layer is completely removed in the logic region  92 .  
         [0124]     The logic region  92  is processed, logic transistor structures having logic gate structures  53  and logic source/drain regions  54  being formed. After the formation of the logic gate structures  53 , a dielectric material is applied, which insulates the logic gate structures  53  from one another and is provided as an interlayer dielectric  41  in the region of the memory cell array  91 .  
         [0125]     The structures covered by the interlayer dielectric  41  in the memory cell array  91  and also in the logic region  92  are illustrated in  FIG. 4H .  
         [0126]     By a photolithographic method, openings are provided in the interlayer dielectric  41  as far as the substrate surface  10  in the region of the second source/drain regions  13 . The openings are filled with a conductive material, for instance tungsten. After the filling material has been caused to recede as far as the upper edge of the interlayer dielectric  41 , the conductive material forms bit line contacts  32  that adjoin the semiconductor substrate  1  in the region of the second source/drain regions  13 . A layer made of a conductive material is applied and data lines  33  are patterned from the layer made of the conductive material by a photolithographic method. An intermediate data line dielectric  43  is provided between the data lines  33 .  
         [0127]     In accordance with  FIG. 4I , the method yields a DRAM having a memory cell array  91  and a logic region  92 . The memory cell array  91  comprises memory cells having in each case a selection transistor  9  and a hole trench capacitor  8 . The active zone  11  of the selection transistor  9  is formed in a fin  17  of the semiconductor substrate  1 .  
         [0128]     Within a cell row, the fin  17  is delimited by in each case two adjacent hole trench capacitors  8 . Toward adjacent cell rows, the fin  17  is delimited by word line trenches  20  running parallel. A gate dielectric  16  is formed along the sidewalls of the fins  17  oriented toward the word line trenches  20 .  
         [0129]     Furthermore, provision is made of gate electrodes that are arranged along the fins  17  in the word line trenches  20 , said gate electrodes being formed in the manner of sidewall spacer structures  21 . The sidewall spacer structures  21  are seated on bottom insulator structures  23  in the word line trenches  20 . In the upper section, the hole trench capacitors  8  are lined by a collar insulator structure  81 , which insulates a storage electrode  61  arranged in the interior of a hole trench from the semiconductor substrate  1  adjoining the upper section of the hole trench and from the structures formed there. The collar insulator structure  81  is caused to recede on the side facing the active zone  11  of the assigned selection transistor, with the result that the storage electrode  61  electrically conductively adjoins the first source/drain region  12  of the assigned selection transistor in the region of a contact window  82 .  
         [0130]     A second source/drain region  13  of the selection transistor adjoins the collar insulator structure  81  of the hole trench capacitor  8  of the adjacent memory cell. A recess trench  18  is introduced between the two source/drain regions  12 ,  13  and is filled with a silicon nitride filling  182 . The second source/drain region  13  adjoins a bit line contact  32  which rests on the substrate surface  10  and via which the second source/drain region  13  is connected to a data line  33  provided above the bit line contacts.  
         [0131]     While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof. Accordingly, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.  
         [0000]     List of Reference Symbols  
         [0000]    
       
           1  Semiconductor substrate  
           10  Substrate surface  
           11  Active zone  
           12  First source/drain region  
           13  Second source/drain region  
           14  Body region  
           15  Channel  
           16  Gate dielectric  
           17  Fin  
           18  Recess trench  
           181  Filling of recess trench  
           182  Filling of recess trench  
           2  Gate electrode  
           2   a  Highly conductive section  
           20  Word line trench  
           20   a  Gate electrode trench  
           21  Sidewall spacer structure  
           22  Addressing line  
           23  Bottom insulator structure  
           23 ′ Shallow insulator structure  
           24  Word line insulator structure  
           31  Bit contact  
           32  Bit line contact  
           33  Data line  
           33 ′ Date line  
           35  Capacitor connection structure  
           36  Node pad  
           41  Interlayer dielectric  
           42  Data line dielectric  
           43  Intermediate data line dielectric  
           44  Intermediate capacitor dielectric  
           51  Protective layer  
           511  Protective layer caused to recede  
           52  Blocking mask  
           53  Logic gate structure  
           54  Logic source/drain region  
           6  Storage capacitor  
           61  Storage electrode  
           62  Capacitor dielectric  
           63  Counterelectrode  
           64  Cell insulator trench  
           7  Stacked capacitor  
           71  Auxiliary layer  
           72  Hard mask  
           73  Silicon nitride protective coating  
           8  Hole trench capacitor  
           80  Hole trench recess  
           81  Collar insulator structure  
           82  Contact window  
           84  Auxiliary oxide layer  
           9  Selection transistor  
           91  Cell array  
           92  Logic region  
           93  Logic transistor structure  
           94  Intergate dielectric fill  
           95  Gate stack insulator structure  
           96  Cell current  
           97  Memory cell  
           98  Transistor structure