Patent Application
20180174927
The present application is a non-provisional patent application claiming priority to European Patent Application No. 16205939.8, filed Dec. 21, 2016, the contents of which are hereby incorporated by reference.
The present disclosure relates to contacts in semiconductor devices and in particular to decreasing the contact resistance of contacts to source and/or drain regions therein.
As scaling of semiconductor devices continues, also the available area for making contacts, such as contacts to the source and/or drain regions, decreases. However, decreasing contact sizes results in an unwanted increase of the contact resistance. Thus, it would be beneficial to keep the contact resistance low, while still scaling down the contact size. One attempt to achieve this is to form a wrapped around contact, such as described in US 2011/0147840 A1.
However, it may be beneficial to further decrease the contact resistance to source or drain contacts.
Some embodiments disclosed herein may provide methods for controlling the contact resistance to source or drain contacts. Some embodiments may decrease the contact resistance to the source or drain region. Some embodiments may be compatible with the formation of wrap around contacts.
In a first aspect, the present disclosure relates to a method for making a contact to a source or drain region of a semiconductor device. The method may include providing the semiconductor device having at least one source or drain region, the source or drain region having an exposed area. The method may further include partially etching the source or drain region such that the exposed area is increased. The method may further include providing a contact covering at least the etched part of the source or drain region. The contact contacts the source or drain region on at least 3 sides of the source or drain region.
In a second aspect, the present disclosure relates to a semiconductor structure. The semiconductor structure may include at least one source or drain region, comprising a recess or a separation formed by sides separated by an intervening space. The semiconductor structure may further include a contact covering at least the recess or the sides of the separation and contacting the source or drain region on at least 3 sides of the source or drain region.
In a third aspect, the present disclosure relates to a semiconductor device comprising the semiconductor structure according to the second aspect or embodiments thereof.
Some aspects of the disclosure are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out in the claims.
Although there has been constant improvement, change and evolution of devices in this field, the present concepts are believed to represent substantial new and novel improvements, including departures from prior practices, resulting in the provision of more efficient, stable and reliable devices of this nature.
The above and other characteristics, features and advantages of the present disclosure will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the disclosure. This description is given for the sake of example only, without limiting the scope of the disclosure. The reference figures quoted below refer to the attached drawings.
The above, as well as additional, features will be better understood through the following illustrative and non-limiting detailed description of example embodiments, with reference to the appended drawings.
In the different figures, the same reference signs refer to the same or analogous elements.
All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary to elucidate example embodiments, wherein other parts may be omitted or merely suggested.
Example embodiments will now be described more fully hereinafter with reference to the accompanying drawings. That which is encompassed by the claims may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example. Furthermore, like numbers refer to the same or similar elements or components throughout.
The present disclosure will be described with respect to particular embodiments and with reference to certain drawings but the disclosure is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice.
Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments described herein are capable of operation in other sequences than described or illustrated herein.
Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments described herein are capable of operation in other orientations than described or illustrated herein.
It is to be noticed that the term “comprising”, used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression “a device comprising means A and B” should not be limited to devices consisting only of components A and B. It means that with respect to the present disclosure, the only relevant components of the device are A and B.
Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.
Similarly it should be appreciated that in the description of example embodiments, various features are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claims require more features than are expressly recited in each claim. Rather, as the following claims reflect, aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment.
Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the disclosure, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.
Furthermore, some of the embodiments are described herein as a method or combination of elements of a method that can be implemented by a processor of a computer system or by other means of carrying out the function. Thus, a processor with the necessary instructions for carrying out such a method or element of a method forms a means for carrying out the method or element of a method. Furthermore, an element described herein of an apparatus embodiment is an example of a means for carrying out the function performed by the element for the purpose of carrying out the disclosure.
In the description provided herein, numerous specific details are set forth. However, it is understood that some embodiments may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.
As used herein, a side of a structure is a continuous outer surface of the structure, wherein e.g. a corner constitutes a discontinuity. As such, a curved surface making a smooth rounded bend for example is considered to be a single side of the structure, while a V-shaped groove is considered to comprise two sides.
As used herein, when a first material is said to be etched or recessed selectively with respect to a second material, this means that the first material is etched or recessed faster than the second material. The etching or recessing process may etch or recess the first material at least twice faster, up to at least 10 times faster, than the second material. In some embodiments, the second material may be substantially not etched or recessed by the etching or recessing process.
As used herein, a structure typically has a height, a width and a length. The height being the dimension perpendicular to the substrate. The width and length being the shortest and longest dimension parallel to the substrate, respectively.
In a first aspect, the present disclosure relates to a method for making a contact to a source or drain region of a semiconductor device. The method may include providing the semiconductor device having at least one source or drain region, the source or drain region having an exposed area. The method may further include partially etching the source or drain region such that the exposed area is increased. The method may further include providing a contact covering at least the etched part of the source or drain region. The contact contacts the source or drain region on at least 3 sides of the source or drain region.
The semiconductor device is typically a transistor, comprising source and drain regions, a channel region between the source and drain regions and a gate region able to control the flow of charges in the channel region. In some embodiments, the semiconductor device may be a fin field effect transistor (FinFET) or a nanowire field effect transistor (Nanowire FET); i.e. the semiconductor device may be a transistor based on a fin or on a nanowire.
The semiconductor device typically comprises a substrate. The substrate typically comprises fins. The source or drain region may be comprised in the substrate. For instance, the source or drain region may be comprised in a fin.
The substrate is typically a semiconductor substrate, such as a Si wafer, or semiconductor-on-insulator substrate (SOI) or strain relaxed buffer (SRB).
In some embodiments, the contact may be a wrapped around contact (i.e. a contact covering at least one sidewall of the source or drain region). In some embodiments, the contact may be a layer following the contour of the source or drain region (see e.g.
In some embodiments, the source or drain region may comprise a semiconductor material, such as Si, SiGex (wherein x is from 0 to 100%, e.g. SiGe50%) or Ge. In some embodiments, the source or drain region may be doped. The source or drain region may for example be doped with phosphorus or arsenic (in the case of an n-type transistor), or with boron (in the case of a p-type transistor).
In some embodiments, the source or drain region may be formed for instance by providing a substrate comprising one or more fins (each fin optionally comprising one or more nanowires extending along its length and superposed along its height) having an exposed top portion, providing spacers on the sides of the fin top portion, removing the top portion of the fin selectively with respect to the spacers, filling the space between the spacers with a doped semiconductor material such as a phosphorus-doped Si or boron-doped SiGe or with alternating layers of two different semiconductor materials such as a phosphor-doped Si and a phosphor doped SiGe or a boron-doped SiGe and a boron-doped Si.
The fins typically have one or more gate structures thereon and spacers on the sides of the gate structures. The gate structures typically comprise a gate dielectric at the interface with the fin, a metal stack on the gate dielectric, and a dielectric cap on the metal stack. The gate structure also typically has a high-k dielectric layer at the interface between the metal stack and the spacers.
In some embodiments, partially etching the source or drain region may comprise recessing part of the top side, thereby forming a recess (e.g. a concavity or a cavity) therein, or recessing part of a lateral side of the source or drain region, thereby forming a recess (e.g. a concavity or a cavity) or a separation therein. When the semiconductor device is placed on a horizontal surface, the top side of the source or drain region is typically substantially parallel to that surface. The top side of the source or drain region may for example be at an angle of −15° to 15°, or even −5° to 5°, with respect to that surface; or it may be parallel thereto. Lateral sides of the source or drain region are typically substantially perpendicular to that surface. The lateral side of the of the source or drain region may for example be at an angle of 75° to 105°, or even 85° to 95°, such as 90°, with respect to that surface.
In a first type of embodiments, the recessing step may be performed in a top side of the source or drain region. In some embodiments, recessing part of the top side may be performed selectively with respect to spacers present along the sides of the source or drain region. In some embodiments, the recess may be a V-shaped groove in the top side. In some embodiments, the V-shaped groove may be defined by at least one, possibly two, planes (or facets) of Miller indices (111) of the source or drain region. Since etching rates can typically be anisotropic along different planes, a V-shape defined by (111) planes can be obtained using a suitable etching chemistry, e.g. using HCl to etch SiGe or using tetramethylammonium hydroxide (TMAH) to etch Si. Different steps along the formation of a V-shaped groove defined by (111) planes are depicted in
In a second type of embodiments, the recessing step may be performed in a lateral side of the source or drain region. In some embodiments, recessing part of a lateral side may be performed after having removed spacers present along the sides of the source or drain region. In some embodiments, the source or drain region may comprise a layer of a first material on top of a layer of a second material and forming the recess in the lateral side may comprise selectively etching at least part of the second material with respect to the first material. In some embodiments, forming the recess may comprise etching away the entire layer of second material. Depending on the dimensions of the recess that is formed, either etching away only part or etching away the entire layer of second material creates the largest increase of the exposed area. Etching away the entire layer of second material forms a separation in the source or drain region, comprising two newly formed surfaces separated by an intervening space. The newly formed surfaces count as sides of the source or drain region when counting “at least 3 sides”. Etching away only part of the layer of second material may allow for no intervening space to be filled but that the contact surface is nevertheless much improved. Such intervening spaces are not easy to fill without defects such as bubbles. In some embodiments, the source or drain region may comprise layers of the first material alternated with layers of the second material. When the source or drain region comprises a plurality of layers of the first material, alternated with layers of the second material, then a number of recesses corresponding to the number of layers of the second material may be formed in each treated lateral side of the source or drain region. A plurality of recesses allows a larger increase of the exposed area. In some embodiments, the first material may be a semiconductor material, such as Si or SiGe (e.g. SiGe50%) or Ge. In some embodiments, the second material may be a semiconductor material, such as selected from SiGe and Si, with the proviso that the second material differs from the first material. The first and second material are typically selected in such a way that the second material can be etched selectively with respect to the first material with at least one etching chemistry. For instance, in the case of Si and SiGe, Si can be removed selectively by using tetramethylammonium hydroxide (TMAH) and SiGe can be removed selectively by using an HCl vapor etching.
In some embodiments, features of the first and second type of embodiments may be combined. Recesses may for example be formed in both the top side and in one or more lateral sides of the source or drain region.
In some embodiments, the contact may cover the exposed area (obtained after partially etching the source or drain region) completely. In other embodiments, the contact may cover only part of the exposed area.
In some embodiments, both an NMOS and a PMOS device region may be present on a substrate. In these embodiments, any step of the process may be applied to either of the NMOS or PMOS device region, separately from the other of the PMOS or NMOS device region. To that end, the PMOS (or NMOS) device region may be covered by a mask layer (e.g. a SiN mask), such that only the NMOS (or PMOS) device region may be processed in a given step.
In some embodiments, providing the semiconductor device may include providing a first device region (e.g. either of an PMOS or NMOS device region) and a second device (e.g. the other of a NMOS or PMOS device region) region, each comprising fin structures optionally comprising nanowire structures, at least one gate structure over the fin structure, a spacer material covering lateral sides of the fin structures, a spacer covering the lateral sides of the gate structure, the gate structure being covered by a hardmask on a top side. Providing the semiconductor device may further include covering the first device region with a first mask layer, forming, in the second device region, second source or drain regions in the fin structures or nanowire structures, covering the second device region with a second mask layer and removing the first mask layer, forming, in the first region, first source or drain regions in the fin structures or nanowire structures, and removing the second mask layer.
In some embodiments, the gate structure may be a dummy gate structure and the method may further comprise replacing the at least one dummy gate structure by at least one gate structure, the gate structure being covered by the spacer material on lateral sides and by a gate cap on a top side.
In some embodiments, the method may further include, prior to replacing the at least one dummy gate structure, filling up a void adjacent to the spacer material with a dielectric material and, after replacing the at least one dummy gate structure, removing the dielectric material.
In some embodiments, covering the first or second device region with the first or second mask layer may comprise (i) depositing a mask layer, (ii) depositing a photoresist layer on the mask layer, (iii) making an opening in the photoresist layer, (iv) removing the mask layer beneath the opening and, (v) optionally, removing the photoresist layer.
In some embodiments, making an opening in the photoresist layer may comprise exposing an area of the photoresist layer to light and removing either the exposed or unexposed area. In some embodiments, the mask layer may be a hardmask layer (e.g. a SiN layer).
In some embodiments, removing the first or second mask layer may comprise (i) depositing a photoresist layer on the mask layer, (ii) making an opening in the photoresist layer, (iii) removing the mask layer beneath the opening and, (iv) optionally, removing the photoresist layer.
In some embodiments, the first and second source or drain regions may each comprise different materials. In some embodiments, partially etching the source or drain region may comprise partially etching the first source or drain regions separately from the second source or drain regions. In some embodiments, partially etching the source or drain region may comprise selectively etching the first source or drain regions with respect to the second source or drain regions. In some embodiments, partially etching the source or drain region may comprise selectively etching the second source or drain regions with respect to the first source or drain regions. In some embodiments, forming the source or drain regions may comprise removing the fin or nanowire structure over a section of its length between the spacer material and filling the resulting opening with a source or drain material. In some embodiments, the method may comprise uncovering at least one lateral side of the source or drain material prior to providing a contact (900) covering at least the etched part of the source or drain region, such as after providing the semiconductor device or after partially etching the source or drain region. In some embodiments, uncovering the at least one lateral side may comprise removing the spacer material covering said at least one lateral side.
In some embodiments, a distance between centres of two gate structures may be from 30 to 50 nm, such as 42 nm. In some embodiments, an opening may be present between two opposing lateral sides (e.g. each covered by the spacer material) of two gate structures, the opening having a width of from 10 to 20 nm, such as 14 nm. In some embodiments, a width of a fin or nanowire structure may be from 5 to 15 nm, such as 10 nm.
In a second aspect, the present disclosure relates to a semiconductor structure, which may include at least one source or drain region, comprising a recess or a separation formed by sides separated by an intervening space. The semiconductor structure may also include a contact covering at least the recess or the sides of the separation and contacting the source or drain region on at least 3 sides of the source or drain region.
In any embodiments of the first or second aspect, the contact may be a wrapped around contact (i.e. a contact covering at least one sidewall of the source or drain region). In any embodiments of the first or second aspect, the contact may be layer following the contour of the source or drain region (see e.g.
In some embodiments, the recess may be a V-shaped groove in a top side of the source or drain region (see e.g.
In some embodiments, one or more recesses may be present in a lateral side of the source or drain region (see e.g.
In some embodiments, the one or more separation of the source or drain region may be present (see e.g.
In some embodiments, the different features of the second aspect and its embodiments may independently be as correspondingly described for the first aspect and its embodiments.
In a third aspect, the present disclosure relates to a semiconductor device comprising the semiconductor structure according to the second aspect or embodiments thereof.
In some embodiments, the different features of the third aspect and its embodiments may independently be as correspondingly described for the first or second aspect and their embodiments.
Reference will be made to transistors. These are devices having a first main electrode such as a drain, a second main electrode such as a source and a control electrode such as a gate for controlling the flow of electrical charges between the first and second main electrodes.
Some embodiments are applicable to similar devices that can be configured in any transistor technology, including for example, but not limited thereto, CMOS, BICMOS, Bipolar and SiGe BICMOS technology. Furthermore the findings of the present disclosure are explained with reference to PMOS and NMOS transistors as an example, but the present disclosure includes within its scope a complementary device whereby PMOS and NMOS transistors become NMOS and PMOS transistors, respectively.
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A similar procedure is performed in the PMOS device area, differing in that that the dummy gates (411) are replaced by a PMOS work function metal stack (413) and the top of the fins is replaced by a B doped SiGe50% source or drain region (720).
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The procedures described in example 2 to 4 for FinFETs may also be applied for NanowireFETs. As an example the formation of a NanowireFET with V-shaped grooves in a top side of the source or drain region is briefly described hereunder.
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It is to be understood that although some embodiments, specific constructions and configurations, as well as materials, have been discussed herein, various changes or modifications in form and detail may be made without departing from the scope and technical teachings of this disclosure. For example, any formulas given above are merely representative of procedures that may be used. Functionality may be added or deleted from the block diagrams and operations may be interchanged among functional blocks. Steps may be added or deleted to methods described within the scope of the disclosure.
While some embodiments have been illustrated and described in detail in the appended drawings and the foregoing description, such illustration and description are to be considered illustrative and not restrictive. Other variations to the disclosed embodiments can be understood and effected in practicing the claims, from a study of the drawings, the disclosure, and the appended claims. The mere fact that certain measures or features are recited in mutually different dependent claims does not indicate that a combination of these measures or features cannot be used. Any reference signs in the claims should not be construed as limiting the scope.
| Number | Date | Country | Kind |
|---|---|---|---|
| 16205939.8 | Dec 2016 | EP | regional |
