Patent Description:
In a vertical field effect transistor, a vertical channel region is formed in the body region. Laterally aside, the gate region is arranged, comprising a gate interlayer dielectric and a gate electrode. In the channel region, a channel electrically connecting the source and the drain region is or can be formed, which can be controlled by applying a voltage to the gate electrode. To avoid a floating body region, it is electrically contacted. The body region can for instance be shorted to the source region to eliminate an intrinsic parasitic npn transistor, in particular in a power device.

From <CIT> and <CIT>, vertical power devices are known, which have a highly doped body contact region embedded laterally between vertical isolation layers.

From <CIT>, a vertical FET with body contacts made of metal and extending down into the semiconductor body is known.

It is an object of the present application to provide a vertical transistor device with improved characteristics, as well as a method of manufacturing such a device.

This object is achieved by the device of claim <NUM>, and moreover it is achieved by the method of claim <NUM>. The device comprises a body contact region formed by doping of the same conductivity type like the body region, but with a higher concentration. The body region is electrically contacted via the body contact region, wherein a diffusion barrier layer is arranged in between these regions. This can limit an outdiffusion of the high dose implant, allowing for example a comparably precise positioning of the body contact region with respect to the body region, e. close to the channel region. This can be advantageous in terms of the device characteristics, see in detail below.

Furthermore, the device comprises a conductive region formed of a conductive material, for instance a metal material filler, e. a tungsten plug. Via a contact area of the conductive region, an electrical contact to the body contact region is formed. This contact area is arranged vertically above an upper end of the channel region. In simple words, the conductive region is arranged above the body contact region and does not extend down into the body region. Vice versa, the body contact region arranged below the conductive region can have a certain vertical extension, e. at least the height of the vertical channel region. This can for example be advantageous in terms of a contact formation between the conductive region and the body contact region, namely allow for a reliable contact while avoiding a leakage, see in detail below.

Further embodiments and features are provided in this description and in the dependent claims. Therein, the individual features shall be disclosed independently of a specific claim category, the disclosure relates to apparatus and device aspects, but also to method and use aspects. If for instance a device manufactured in a specific way is described, this is also a disclosure of a respective manufacturing process, and vice versa. In general words, an idea of this application is to provide a semiconductor device, in particular a field effect transistor, with a body contact region having a higher doping concentration than the body region, the body contact region being defined by a diffusion barrier structure comprising one or a plurality of diffusion barrier layers.

The source and the drain region of the device are of a first conductivity type, the body region and the body contact region are of a second conductivity type opposite to the first conductivity type. As a power device, the transistor can comprise a drift region vertically between the body and the drain region, wherein the drift region is of the first conductivity type like the drain region but has a lower doping than the latter. In the illustrated embodiments, the first conductivity type is n-type and the second conductivity type is p-type. The dopant concentration in the body contact region can be significantly larger than in the body region, for instance by at least one order of magnitude, typical values being for instance <NUM>-<NUM> orders of magnitude. The doping concentration in the body contact region can for example be at least 1E19 cm<NUM>, in particular at least 5E19 cm<NUM> or 1E20 cm<NUM>, with possible upper limits of for example 1E21 cm<NUM> or 5E20 cm<NUM>.

As discussed above, the conductive region can for instance be a metal material filler. Such a filler can be deposited into a contact hole etched into an interlayer dielectric covering the body contact region, see below. Over its vertical extension, the conductive region can be formed of the same continuous material (bulk material), e. as a tungsten plug. The bulk material of the conductive region forms the contact area, namely at a lower end of the conductive region. In particular, a lower end of a tungsten plug can form the contact area. The contact area forms the electrical contact towards the body contact region, it does not necessarily rest directly adjacent on the body contact region. To assure a low ohmic contact, for instance a silicide layer can be arranged in between. Nevertheless, a vertical distance between the contact area and the body contact region will remain rather small, possible upper limits being for instance not more than <NUM>, <NUM>, <NUM> or <NUM> (lower limits are for instance at least <NUM> or <NUM>).

The gate region comprises a gate electrode and a gate dielectric, in particular gate oxide, for instance silicon oxide. The gate electrode is the electrical conductive part of the gate region, it is capacitively coupled to the channel region via the gate dielectric. The gate electrode may for instance be made of metal or polycrystalline silicon. The gate region can be arranged in a gate trench etched into the silicon material (the gate dielectric can be formed at the sidewall of the trench, the gate electrode can be deposited into the trench, filling it at least partly). Optionally, a field plate can be provided in the gate trench below the gate electrode (split gate), isolated therefrom by an interlayer dielectric.

Alternatively or in addition to such a split gate, the device can comprise field electrode regions which extend vertically into the drift region and are formed in field electrode trenches (separate from the gate trenches). Seen in a sectional view, the field electrode and the gate trenches can alternate in a horizontal direction. The field electrode trenches can be strip-like structures extending parallelly to the gate trenches. Alternatively, the field electrode trenches can be needle trenches, the field electrode regions having a specular or columnar shape. In this case, the gate trenches can form a crisscross or check pattern seen in a top view, the needle trenches being arranged in the spaces between.

The "vertical" direction lies perpendicular to a surface of a layer of the device, for instance a surface of a silicon substrate and/or a surface of an epitaxial layer (deposited on the substrate) and/or a surface of an interlayer dielectric, on which a frontside metallization is deposited, and/or a surface of the frontside metallization itself. The horizontal/lateral directions lie perpendicular to the vertical direction, the device/chip area is for instance taken laterally/horizontally. "Upper" and "lower" refer to the vertical direction, a vertical trench extends for instance in the vertical direction from an upper surface down into the silicon material. "Lying vertically above/below" means lying on a higher/lower level with respect to the vertical direction (in general, it shall not imply an alignment in the vertical direction).

At the frontside of the device, above the source/drain/channel region, a frontside metallization can be provided, for instance a combined source/body contact. The drain contact can be provided at the backside of the device. Alternatively, the drain connection can be routed from the bottom of the drift region to the frontside of the device by vertical conduction, for instance via an n+-sinker. In this case, a separate frontside metal contact will be provided. As a power device, the transistor can for instance have a breakdown voltage of at least <NUM> V, <NUM> V, <NUM> V or <NUM> V, with possible upper limits of for instance not more than <NUM> V, <NUM> V, <NUM> V, <NUM> V or <NUM> V.

In an embodiment, the contact area of the conductive region, which forms the electrical contact towards the body contact region, is arranged at an upper end of the source region. In this case, the conductive region can be formed above the body/source region without any etching into the body contact region material (e. epitaxially grown silicon, see below) deposited after the formation of the diffusion barrier layer. Even though the diffusion barrier layer and body contact region formation may involve a body contact trench etch beforehand, this can be better or easier in terms of a position control compared to a rather narrow trench etched into the body contact region later on. A vertical distance between the contact area and the upper end of the source region can for instance be not more than <NUM> or <NUM> (they can also lie exactly on the same height).

In an embodiment, the contact area of the conductive region lies as a whole in a horizontal plane. In other words, the contact area is flat and extends horizontally. The horizontal plane lies vertically above the upper end of the channel region, in particular at an upper end of the source region. In general however, the contact area could also extend over a step resulting for instance from the deposition of the body contact region material.

According to the invention, the body contact region is arranged laterally aside the body region with the vertical channel region. Consequently, the diffusion barrier layer arranged in between the body region and the body contact region extends vertically (seen in a vertical cross-section). According to the invention, the diffusion barrier structure comprises a horizontal diffusion barrier layer, see in detail below. By arranging the body contact region laterally aside the body/channel region, the high dose implant can be brought close to the channel, which can be advantageous in terms of a shielding from the high potential of the drain. Vice versa, the defined lateral positioning achieved by the diffusion barrier layer can help maintaining a minimum distance to prevent the channel from being pinched off, which could for instance result in a strong dependence of the threshold voltage.

At least a lower part of the body contact region lies aside the channel region, depending on the height of the body contact region an upper part thereof can extend further upward. In an embodiment, the diffusion barrier layer and the body contact region, namely at least the lower part thereof, extend vertically over the whole height of the channel region. In other words, the body contact region electrically contacts the body region over the whole height of the channel region (with the diffusion barrier layer in between).

In an embodiment, the diffusion barrier layer is arranged at a lateral distance of not more than <NUM> from the channel region, further possible upper limits being not more than <NUM>, <NUM> or even only <NUM>. Possible lower limits of the lateral distance are for instance at least <NUM>, <NUM> or <NUM>. The channel region can for instance have a vertical height of <NUM> at maximum, further possible upper limits being for instance not more than <NUM>, <NUM>, <NUM> or <NUM>. Possible lower limits of the vertical channel height are for instance at least <NUM> or <NUM>.

As mentioned already, the diffusion barrier layer can belong to a diffusion barrier structure defining the body contact region also in other directions. Assuming that the diffusion barrier layer between the body and the body contact region extends vertically, namely is arranged laterally aside the body region, the diffusion barrier structure can comprise an additional barrier layer extending horizontally and defining the body contact region vertically downwards. In particular, this horizontal diffusion barrier layer can be formed directly on an upper surface of the drift region. In other words, the body region does not extend below the body contact region, the latter rests on the drift region (with the horizontal barrier layer in between). The horizontal barrier layer can prevent an outdiffusion of the highly concentrated dopant into the structure below.

Seen in a vertical cross-section, the cell with the body/source regions can generally have a symmetrical design (the sectional plane can lie perpendicular to a lateral length extension of the body contact trench). Therein, a second body region comprising a second channel region can be arranged laterally opposite to the first body region with the first channel region. The second body region can be contacted by the same body contact region, with a layer of the diffusion barrier structure arranged in between. Consequently, the body contact region can be defined in a first horizontal direction by the first vertical barrier layer towards the first body region, and it can also be defined in a second horizontal direction opposite to the first horizontal direction by a second vertical barrier layer. In addition, it can be defined vertically downwards by the horizontal barrier layer, so that the body contact region is contained in a trough formed by the barrier layers. Therein, even though the barrier layers are referred-to individually in the discussion of their position and orientation, they can be deposited in the same process step (they can be formed simultaneously at the bottom and sidewalls of the body contact trench, see below).

According to the invention the layers of the diffusion barrier structure comprise alternating sublayers of silicon and oxygen-doped silicon. The oxygen-doped silicon sublayers can respectively have a thickness in the atomic range (e. one or several atoms thick) or in the nanometer range to ensure sufficient crystal information for growing the silicon. The oxygen concentration in the oxygen-doped silicon sublayers can be comparably low, for instance below 5E14 cm<NUM>. The alternating sublayers can for example be formed by silicon epitaxy with an absorption of oxygen at different steps.

The application also relates to a method for manufacturing a semiconductor transistor device, comprising the steps:.

Therein, the doping of the body contact region can be a doping of a silicon region formed before, e.g. a doping of epitaxial silicon deposited before without any doping at all (see below). Alternatively or in addition, the silicon material can also be doped in situ during the deposition, in particular during the epitaxial growth. For instance, a body contact trench etched before can be refilled with a high doping concentration during the overgrowth already, e. a high concentration of boron.

Prior to the forming of the diffusion barrier layer in step i), a body contact trench is etched into a silicon region. In the ready-made device, the body and source region are arranged in this silicon region. When the body contact trench is etched, the body and source implants can be in place already. Alternatively, the body and/or source implantation can be performed after the body contact trench etch, as explained in detail below. Independently of these details, layers of the diffusion barrier structure are deposited or formed after the body contact trench etch. They are formed at a sidewall of the trench, in particular at each of its sidewalls lying horizontally opposite to each other. In the same process step, a horizontal barrier layer is formed at the bottom of the trench.

After the formation of the diffusion barrier structure in the body contact trench, the trench can be filled up by epitaxially grown silicon. A mask used for defining the body contact trench etch can remain in place during the formation of the diffusion barrier structure and it can also stay in place thereafter when the trench is filled with silicon again. The mask used for the body contact trench etch can comprise a photoresist and a hard mask below, formed of an interlayer dielectric material. In particular, a gate interlayer dielectric material deposited before for forming the gate region in the gate trench can be used as a hard mask for the body contact trench etch. This can reduce the overall number of process steps. Alternatively, a separate hard mask could be deposited for the body contact trench etch.

After the refill of the body contact trench, the epitaxially grown silicon can project vertically above the upper ends of the sidewalls of the body contact trench, namely above the silicon region into which the trench has been etched. In case that a lithography mask was in place during the epitaxial growth, the epitaxial silicon can project even above the hard mask. By a planarization, for instance by chemical mechanical polishing (CMP), some of the epitaxial silicon can be removed thereafter.

During the planarization, the hard mask used for the body contact trench etch before can remain in place. This can for instance protect other structures of the device, like the gate region or field electrode regions. Thereafter, the hard mask can be etched back, so that for example a defined screen oxide can be deposited for a subsequent implantation (see below). In consequence, there can remain a vertical step, namely between a silicon region, which is arranged laterally between the diffusion barrier layer and the gate region, and the silicon refill of the body contact trench. The height of the step can correspond to the thickness of the hard mask used before, in particular to the thickness of the gate interlayer dielectric deposition.

In an embodiment, the body contact trench is refilled with epitaxially grown silicon deposited undoped. The body contact region is formed thereafter by implantation into this epitaxial silicon. Prior to the implantation, a screen oxide can be deposited (see above), which can suppress a channelling during the implantation.

In general, the body and the source region could be formed prior to the body contact trench etch, so that the trench would be etched into the p- and n-doped silicon material. In combination with an in situ doped refill of the body contact trench, no implantations would be required after the refill in this case.

In an alternative embodiment, the body and the source region are implanted after the body contact trench has been etched and the diffusion barrier structure has been formed. The trench can be refilled with or without an in situ doping, the body and the source region are formed after the refill. In case that the doping of the body contact region is performed after the refill (e. undoped refill), this high dose implant can in particular be performed after the body doping, and optionally also after the source doping. Having the high dose implant at the end can for instance save a thermal anneal in between.

The body implantation can be performed without a mask, for the source implantation a source mask (e. photolithography) shielding a central portion of the body contact trench from the source implant can be used, restricting the source implant to a region adjacent to the gate trench (forming a source pocket there). In particular, the so-defined source region can extend laterally across the step discussed above. The central portion shielded from the source implant can for instance have a width of around <NUM> (with photolithography only, could for example be narrowed with an additional oxide layer below the screen oxide). Alternatively to a photoresist layer, for instance an oxide plug could be formed above the central portion of the trench to avoid an implantation below the plug. If the body contact region is implanted after the refill, a body contact mask (e. photolithography) can restrict this implantation to a portion of the body contact trench, maintaining a certain lateral distance from the vertical layers of the diffusion barrier structure, such that the high dose implant is continued inside the diffusion barrier structure.

Independently of the sequence in detail, all implantations can be performed prior to the deposition of an interlayer dielectric, on which the front side metallization is placed thereafter. Prior to a deposition of the frontside metallization, a contact hole can be etched into the interlayer dielectric to contact the body contact region and the source region. A further contact hole can be etched to contact the gate electrode and, if applicable, a field electrode.

The contact hole or holes can be filled with a metal material filler, for instance tungsten. To assure a good electrical contact, a silicide layer can be formed below the metal material filler. For that purpose, a silicide formation layer is deposited prior to the metal material filler (the silicide can be formed by letting diffuse metal atoms out of this layer).

To form titanium silicide for instance, the silicide formation layer can be a titanium or titanium/titanium nitride layer, deposited for example by sputtering. In a subsequent thermal treatment, the silicide will form where the silicide formation layer is in contact with silicon (doped silicon or polysilicon). Consequently, a silicide layer will form at the upper surface of the body contact region. Therein, with a progressing silicide formation, this silicide layer will increasingly extend into the body contact region. In this respect, the arrangement of the contact area above the upper end of the channel region, which assures a sufficient height of the body contact region material below (see above), can allow for a stable process window. In terms of the electrical contact, a sufficiently thick silicide layer can be formed, while a penetration of the silicide down into the drift region is avoided.

Below, the transistor device and the manufacturing of the same are explained in further detail by means of exemplary embodiments. Therein, the individual features can also be relevant for this application in a different combination.

<FIG> shows a semiconductor transistor device <NUM> comprising a source region <NUM>, a body region <NUM>, a drain region <NUM> and a gate region <NUM>. The gate region <NUM> is arranged laterally aside the body region <NUM>, it comprises a gate electrode <NUM> and a gate dielectric <NUM>. The gate dielectric <NUM>, e. gate oxide, capacitively couples the gate electrode <NUM> to the body region <NUM>. By applying a voltage to the gate electrode <NUM>, a channel can be formed in a channel portion <NUM> of the body region <NUM>, see also <FIG>.

Vertically between the body region <NUM> and the drain region <NUM>, a drift region <NUM> is arranged. It is doped with the same conductivity type but a lower concentration than the drain region <NUM>. In this example, the source region <NUM>, the drift region <NUM> and the drain region <NUM> are n-type regions, and the body region <NUM> is a p-type region. To contact the body region <NUM>, a body contact region <NUM> is provided, which is formed by doping (in situ during the deposition or thereafter, see below). The body contact region <NUM> has the same conductivity type but a higher doping than the body region <NUM>, in this example a high dose boron doping. To avoid an outdiffusion of this high dose implant, it is contained in a diffusion barrier structure <NUM>, see <FIG> in detail.

The diffusion barrier structure <NUM> comprises a vertical diffusion barrier layer <NUM> arranged between the body contact region <NUM> and the body region <NUM>. It prevents an outdiffusion in the first horizontal direction <NUM>. Further it comprises a horizontal diffusion barrier layer <NUM> preventing an outdiffusion vertically downwards into the drift region <NUM> (in the vertical direction <NUM>), and it comprises a further vertical diffusion barrier layer <NUM> defining the body contact region <NUM> horizontally in the opposite direction. The sectional view of <FIG> illustrates a symmetrical setup in the active region of the device <NUM>, laterally opposite to the body region <NUM> another body region <NUM> and another source region <NUM> are formed. They are arranged at a gate region <NUM> comprising a gate electrode <NUM> and a gate dielectric <NUM>.

In <FIG>, a field electrode region <NUM> arranged in a field electrode trench <NUM> is shown in addition. The field electrode region <NUM> comprises a field electrode <NUM>, e. formed of polysilicon, and an interlayer dielectric <NUM> isolating it from the drift region <NUM>. The field electrode region <NUM> can for example allow for a field shaping, e. controlling the location of peak electric fields and preventing avalanche or hot carrier generation. The field electrode region <NUM> can also be used as an edge termination defining the active area of the device <NUM> laterally. In this case, typically, no source region <NUM> would be formed adjacent to the field electrode trench <NUM> (unlike shown in the figure). Between an edge termination field region on one lateral side of the device <NUM> and another edge termination field region on the opposite side, the active area extends, formed by instance of a plurality of symmetrical cells as shown in <FIG>. However, field electrode regions <NUM> could also be arranged inside the active area of the device <NUM>, alternating with the gate regions <NUM> in the lateral direction <NUM> (seen in a vertical cross section through the active area).

As can be seen in <FIG>, the gate region <NUM> is formed in a gate trench <NUM>. In the example shown here, a field plate region <NUM> is arranged in the gate trench <NUM> below the gate region <NUM>. The field plate region <NUM> comprises a field plate electrode <NUM>, e. made of polysilicon, and an interlayer dielectric <NUM> isolating it from the drift region <NUM> and from the gate region <NUM>. Like the field electrode region <NUM>, the field plate region <NUM> can allow for a field shaping.

Referring to <FIG> again, this figure illustrates that a lower part <NUM> of the body contact region <NUM> is arranged laterally aside the body region <NUM>. Since the body contact region <NUM> is contained in the diffusion barrier structure <NUM>, it can be brought close to the channel region <NUM>. A lateral distance <NUM> between the diffusion barrier layer <NUM> and the channel region <NUM> is only around <NUM>, which can be advantageous regarding a shielding of the high drain potential.

The body contact region <NUM> is contacted by a conductive region <NUM> made of tungsten in this case. The conductive region <NUM> has a contact area <NUM> forming the electrical contact towards the body contact region <NUM>. To assure a good electrical connection to the body contact region <NUM> and also to the source region <NUM>, a silicide layer <NUM> is arranged between the contact area <NUM> and the body contact region <NUM>, as well as between the body contact region <NUM> and the source region <NUM>. The contact area <NUM> lies vertically above an upper end <NUM> of the channel region <NUM>; it is arranged at an upper end <NUM> of the source region <NUM>. Consequently, there is sufficient body contact material below, which can allow for a stable processing, see the general description in detail. The channel region <NUM>, which extends between the upper end <NUM> and a lower end <NUM>, has a vertical height <NUM> of around <NUM>.

Referring to <FIG>, the processing of the device <NUM>, in particular of the body contact region <NUM> is explained in further detail. In the situation shown in <FIG>, the field electrode trench <NUM> and the gate trench <NUM> have already been etched into the drift region <NUM>. The trenches <NUM>, <NUM> have been filled again, the field electrode region <NUM> and the field plate region <NUM> have been formed, and the gate region <NUM> has been formed in the gate trench <NUM>. From this previous process step, namely from the deposition of the interlayer dielectric <NUM>, a layer <NUM> of the interlayer dielectric material remained at the surface <NUM> of the drift region <NUM>. This layer <NUM>, e. an oxide layer, is used as a hard mask <NUM> subsequently (alternatively, a short low-temperature oxide could be deposited). A thin layer or oxide could be added onto the layer <NUM> to adjust the thickness of the hard mask to the trench etch if required.

This is shown in <FIG>, where a photoresist layer <NUM> has been deposited on the layer <NUM> and structured by photolithography. After etching through the layer <NUM>, a body contact region trench <NUM> is etched into the drift region <NUM>, wherein the layer <NUM> serves as a hard mask <NUM> (the photoresist layer <NUM> could be removed prior to etching into the drift region <NUM>, the trench would be etched due to the selectivity between oxide and silicon). If the topology would be critical, the trenches <NUM>, <NUM> could be refilled with oxide, combined with a planarization, e. When the body contact region trench <NUM> has been etched, the diffusion barrier structure <NUM> is formed at the sidewalls <NUM>, <NUM> and the bottom <NUM> of the trench <NUM>.

As shown schematically in the enlarged view, the diffusion barrier structure <NUM> is formed of alternating silicon sublayers <NUM> and oxygen-doped silicon sublayers <NUM>. Between the silicon substrate forming the drift region <NUM> and the alternating sublayers <NUM>, <NUM>, a silicon buffer layer <NUM> can be arranged. Furthermore, a capping layer <NUM> of epitaxially grown silicon can be placed on the alternating sublayers <NUM>, <NUM> (prior to filling the trench completely with epitaxial silicon, see below). It can provide a high carrier mobility in this region. The silicon buffer layer <NUM> may be relatively thin, e.g. in the range of <NUM> to <NUM> thick. Both, the silicon buffer layer <NUM> and the capping layer <NUM> are optional. In addition to limiting the out-diffusion of the doping, the oxygen-doped silicon sublayers <NUM> of the barrier structure <NUM> may also improve carrier mobility within the channel region <NUM> of the device <NUM>.

The oxygen-doped silicon sublayers <NUM> of the diffusion barrier structure <NUM> may be formed by introducing oxygen partial monolayers to a silicon lattice. The oxygen atoms are interstitially placed to minimize disruption of the silicon lattice. Silicon sublayers <NUM> of silicon atoms separate adjacent oxygen partial monolayers (the oxygen-doped silicon sublayers <NUM>). The alternating sublayers <NUM>, <NUM> may be formed by silicon epitaxy with absorption of oxygen at different steps. For example, temperature and gaseous conditions can be controlled during the epitaxy process to form the oxygen-doped silicon sublayers <NUM>, namely the partial oxygen monolayers. Oxygen may be introduced/incorporated between epitaxial layers of silicon (the silicon sublayers <NUM>), e.g. by controlling the introduction of an oxygen precursor into the epitaxy chamber. The resulting diffusion barrier structure <NUM> includes the oxygen-doped silicon sublayers <NUM> that comprise mainly silicon but have a doped level or concentration level of oxygen alternating with standard epitaxial layers of silicon without oxygen, namely the silicon sublayers <NUM>.

Subsequently, the body contact trench <NUM> is filled up with epitaxially grown silicon <NUM>, see <FIG>. In the situation shown there, the photoresist layer <NUM> has been removed again, the epitaxial silicon <NUM> projects vertically. By a planarization, for instance CMP, the silicon projecting above can be removed so that the epitaxial silicon <NUM> lies flush with the upper surface <NUM> of the layer <NUM> (dotted line).

In the process steps shown in <FIG>, the layer <NUM> used as a hard mask <NUM> has been removed, resulting in a step <NUM> formed by the epitaxial silicon. As discussed in the general description in detail, the epitaxial silicon <NUM> could also be doped in situ during the growth. In the example shown here, it has been deposited undoped, and a high dose implant is introduced later on. Prior to that, the implantations for the body region <NUM> and the source region <NUM> are performed. The body implant can be introduced without a mask, <FIG> illustrates a source mask <NUM> for the subsequent source implant. Prior to the deposition and structuring of the source mask <NUM>, a screen oxide <NUM> has been deposited for the subsequent implantations. The source mask <NUM> shields a central portion <NUM> of the body contact trench <NUM> from the source implant, defining the source region <NUM> at the edge.

After removal of the source mask <NUM>, a body contact mask <NUM> for the high dose implant <NUM> is formed, see <FIG>. The mask <NUM> defines a certain lateral distance <NUM> of the high dose implant <NUM> from the diffusion barrier structure <NUM>. In a subsequent activation step, e. thermal annealing, the high dose implant <NUM> extends up to the diffusion barrier structure <NUM>.

<FIG> illustrates a process step after the body contact mask <NUM> has been removed and an interlayer dielectric <NUM> has been deposited (after a removal of the screen oxide <NUM>). On top of the interlayer dielectric <NUM>, a mask <NUM> has been formed, defining the positions of the contact holes <NUM>-<NUM> etched through the interlayer dielectric <NUM>. After a removal of the mask <NUM>, a titanium or titanium/titanium nitride layer <NUM> is deposited (see <FIG>). In the contact holes <NUM>-<NUM>, this layer serves as a silicide formation layer, the silicide formation is achieved by a subsequent thermal treatment. As shown in <FIG>, a metal material filler <NUM> can be deposited into the contact holes <NUM>-<NUM>, forming a respective electrical contact via the respective silicide layer <NUM>, <NUM>, <NUM>. In case of the body contact region <NUM>, the metal material filler <NUM> forms the conductive region <NUM> and the contact area <NUM>, which lies in a horizontal plane <NUM>.

<FIG> gives an overview of some of the process steps in a flow chart, beginning with the etching <NUM> of the body contact trench <NUM>. After forming <NUM> the diffusion barrier structure <NUM> at the bottom <NUM> and the sidewalls <NUM>, <NUM>, the body contact trench <NUM> is filled <NUM> with the epitaxially grown silicon <NUM>. Thereafter, the body region <NUM> and the source region <NUM> are formed <NUM> by implantation (see in detail above). After a doping <NUM> of the epitaxially grown silicon <NUM> for forming the body contact region <NUM>, the silicide layer <NUM> is formed <NUM>. Thereafter, the metal material filler <NUM> is deposited <NUM> and forms the conductive region <NUM>.

Claim 1:
A semiconductor transistor device (<NUM>) having
a source region (<NUM>),
a body region (<NUM>) comprising a vertical channel region (<NUM>),
a drain region (<NUM>),
a gate region (<NUM>) laterally aside the channel region (<NUM>),
a body contact region (<NUM>) formed by doping,
a diffusion barrier structure (<NUM>) comprising a vertical diffusion barrier layer (<NUM>) extending vertically, and
a conductive region (<NUM>) formed of a conductive material,
wherein the body contact region (<NUM>) electrically contacts the body region (<NUM>), the vertical diffusion barrier layer (<NUM>) being arranged in between,
and wherein the doping of the body contact region (<NUM>) is of the same conductivity type but of higher concentration than a doping of the body region (<NUM>),
and wherein the conductive region (<NUM>) has a contact area (<NUM>), which forms an electrical contact towards the body contact region (<NUM>), the contact area (<NUM>) of the conductive region (<NUM>) being arranged vertically above an upper end (<NUM>) of the channel region (<NUM>),
characterized in that the diffusion barrier structure (<NUM>) comprises additionally a horizontal diffusion barrier layer (<NUM>),
wherein the diffusion barrier layers (<NUM>, <NUM>) comprise alternating sublayers of Si and oxygen-doped Si.