Abstract:
An exemplary embodiment relates to a method of using amorphous carbon in replacement gate integration processes. The method can include depositing an amorphous carbon layer above a substrate, patterning the amorphous carbon layer, depositing a dielectric layer over the patterned amorphous carbon layer, removing a portion of the deposited dielectric layer to expose a top of the patterned amorphous carbon layer, removing the patterned amorphous carbon layer leaving an aperture in the dielectric layer, and forming a metal gate in the aperture of the dielectric layer.

Description:
FIELD OF THE INVENTION 
     The present disclosure relates generally to integrated circuits and methods of manufacturing integrated circuits. More particularly, the present disclosure relates to a method of using amorphous carbon film as a sacrificial layer in replacement gate integration processes. 
     BACKGROUND OF THE INVENTION 
     Deep-submicron complementary metal oxide semiconductor (CMOS) is conventionally the primary technology for ultra-large scale integrated (ULSI) circuits. Over the last two decades, reduction in the size of CMOS transistors has been a principal focus of the microelectronics industry. 
     Transistors, such as, MOSFETs, are often built on the top surface of a bulk substrate. The substrate is doped to form source and drain regions, and a conductive layer is provided between the source and drain regions. The conductive layer operates as a gate for the transistor; the gate controls current in a channel between the source and the drain regions. 
     Ultra-large-scale integrated (ULSI) circuits generally include a multitude of transistors, such as, more than one million transistors and even several million transistors that cooperate to perform various functions for an electronic component. The transistors are generally complementary metal oxide semiconductor field effect transistors (CMOSFETs) which include a gate conductor disposed between a source region and a drain region. The gate conductor is provided over a thin gate oxide material. Generally, the gate conductor can be a metal, a polysilicon, or polysilicon/germanium (Si x Ge (1−x) ) material that controls charge carriers in a channel region between the drain and the source to turn the transistor on and off. Conventional processes typically utilize polysilicon based gate conductors because metal gate conductors are difficult to etch, are less compatible with front-end processing, and have relatively low melting points. The transistors can be N-channel MOSFETs or P-channel MOSFETs. 
     Conventional polysilicon-based gate conductors must be doped and annealed to achieve a suitable conductivity. Generally, the annealing process can adversely affect the formation of source/drain extensions, and pocket regions. For example, the high thermal budget can cause transient enhanced diffusion (TED). Further, the high thermal budget can preclude the use of high-K gate dielectric materials. 
     Replacement gate processes have been proposed in which a sacrificial gate material is removed after source/drain formation. The sacrificial gate material (e.g., polysilicon) is then replaced with a metal material that does not require the doping and annealing steps of a polysilicon-based gate conductors. However, such processes can damage the substrate when removing the sacrificial gate material. Further, such processes have not been utilized with amorphous carbon lithographic processes which can achieve smaller critical dimensions. 
     Generally, it is desirous to manufacture smaller transistors to increase the component density on an integrated circuit. It is also desirous to reduce the size of integrated circuit structures, such as vias, conductive lines, capacitors, resistors, isolation structures, contacts, interconnects, etc. For example, manufacturing a transistor having a reduced gate length (a reduced width of the gate conductor) can have significant benefits. Gate conductors with reduced widths can be formed more closely together, thereby increasing the transistor density on the IC. Further, gate conductors with reduced widths allow smaller transistors to be designed, thereby increasing speed and reducing power requirements for the transistors. 
     Thus, there is a need to form metal gates using an improved method. Further, there is a need to use amorphous carbon as a sacrificial layer in replacement gate integration processes. Even further, there is a need to avoid the difficulties of etching a metal gate directly while using a process capable of achieving small critical dimensions (CDs). 
     SUMMARY OF THE INVENTION 
     An exemplary embodiment relates to a method of using amorphous carbon in replacement gate integration processes. The method can include depositing an amorphous carbon layer above a substrate, patterning the amorphous carbon layer, depositing a dielectric layer over the patterned amorphous carbon layer, removing a portion of the deposited dielectric layer to expose a top of the patterned amorphous carbon layer, removing the patterned amorphous carbon layer leaving an aperture in the dielectric layer, and forming a metal gate in the aperture of the dielectric layer. 
     Another exemplary embodiment relates to a method of forming a metal gate using a sacrificial amorphous carbon structure. The method can include patterning an amorphous carbon layer to form a sacrificial amorphous carbon structure, forming a material layer over the sacrificial amorphous carbon structure, polishing the material layer to expose the sacrificial amorphous carbon structure, removing the sacrificial amorphous carbon structure, and forming a metal gate structure where the sacrificial amorphous carbon structure was located before removal. 
     Another exemplary embodiment relates to a method of using amorphous carbon in the formation of a metal structure. The method can include forming an amorphous carbon structure having a critical dimension corresponding to a desired critical dimension for a metal structure, forming a first oxide layer adjacent a first side of the amorphous carbon structure and a second oxide layer adjacent a second side of the amorphous carbon structure, and replacing the amorphous carbon structure with a metal structure. 
    
    
     Other principle features and advantages of the invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description, and the appended claims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The exemplary embodiments of the disclosure will hereafter be described with reference to the accompanying drawings, wherein like numerals denote like elements, and: 
     FIG. 1 is a flow diagram for a process of using amorphous carbon film as a sacrificial layer in replacement gate integration processes in accordance with an exemplary embodiment; 
     FIG. 2 is a schematic cross-sectional view representation of a portion of a integrated circuit, showing a stack application operation in accordance with an exemplary embodiment; 
     FIG. 3 is a schematic cross-sectional view representation of the portion of the integrated circuit of FIG. 2, showing a photoresist application operation; 
     FIG. 4 is a schematic cross-sectional view representation of the portion of the integrated circuit of FIG. 2, showing a patterning operation; 
     FIG. 5 is a schematic cross-sectional view representation of the portion of the integrated circuit of FIG. 2, showing a patterning operation; 
     FIG. 6 is a schematic cross-sectional view representation of the portion of the integrated circuit of FIG. 2, showing a removal operation; 
     FIG. 7 is a schematic cross-sectional view representation of the portion of the integrated circuit of FIG. 2, showing a dielectric deposition operation; 
     FIG. 8 is a schematic cross-sectional view representation of the portion of the integrated circuit of FIG. 2, showing a polishing operation; 
     FIG. 9 is a schematic cross-sectional view representation of the portion of the integrated circuit of FIG. 2, showing a removal operation; 
     FIG. 10 is a schematic cross-sectional view representation of the portion of the integrated circuit of FIG. 2, showing a metal deposition operation; and 
     FIG. 11 is a schematic cross-sectional view representation of the portion of the integrated circuit of FIG. 2, showing a polishing operation. 
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     FIG. 1 illustrates a flow diagram  10  of an exemplary process of using amorphous carbon film as a sacrificial layer and replacement gate integrated processes. Flow diagram  10  illustrates by way of example some steps that may be performed. Additional steps, fewer steps, or combination of steps may be utilized in various different embodiments. 
     In an exemplary embodiment, a step  15  is performed in which an amorphous carbon layer is deposited. The amorphous carbon layer can be deposited using a chemical vapor deposition (CVD) operation or other suitable deposition technique. One exemplary amorphous carbon layer deposition operation is described below with reference to FIG.  2 . 
     In a step  25 , the amorphous carbon layer is patterned to form sacrificial gate features. The amorphous carbon layer can be patterned using a variety of different techniques. An exemplary patterning operation is described below with reference to FIGS. 4-5. 
     In a step  45 , a layer is deposited above the sacrificial gate&#39;s features. Such a deposited layer can be a dielectric layer, such as an oxide. The deposited layer can be a tetraethyl orthosilicate (TEOS) layer. The layer can be deposited using plasma enhanced chemical vapor deposition (PECBD). An exemplary layer deposition operation is described below with reference to FIG.  7 . 
     In a step  55 , the layer above the sacrificial gate features is planarized. In an exemplary embodiment, a chemical mechanical polish (CMP) operation is used to remove portions of the dielectric layer and planarize the layer with the sacrificial gate features. One exemplary planarization operation is described below with reference to FIG.  8 . 
     In a step  65 , sacrificial gate features are removed. Sacrificial gate features can be removed using an ashing operation. One exemplary removal operation is described below with reference to FIG.  9 . Ashing can involve the introduction of a O 2  plasma. 
     In a step  75 , metal gate conductors are deposited in a location where sacrificial gate features were present before removal. Formation of metal gate conductors can include deposition of a metal material layer, such as the deposition operation described below with reference to FIG.  10 . The metal material layer is then polished down to the level of the dielectric layer using a removal process, such as the removal operation described below with reference to FIG.  11 . 
     Referring to FIG. 2, a portion  100  of an integrated circuit includes an anti-reflective coating (ARC) layer  120 , an amorphous carbon layer  130 , a gate dielectric layer  122 , and a substrate  150 . ARC layer  120  can be a layer including silicon oxide nitride (SiON). While a SiON material is preferably used in ARC layer  120 , alternatively other oxides and suitable materials can be used. 
     In an exemplary embodiment, ARC layer  120  has a thickness of 5-100 nm. ARC layer  120  is provided above amorphous carbon layer  130 . Amorphous carbon layer  130  has a thickness of, for example, 60 nm. ARC layer  120  and amorphous carbon layer  130  can be deposited using any of a variety of deposition techniques, such as chemical vapor deposition (CVD). Gate dielectric layer  122  can have a thickness of &lt;40 Angstroms and can include dielectric materials, such as, SiOxNy or HfSixOy, or HfxAlySizOα. In at least one exemplary embodiment, high-K gate dielectric materials are used in gate dielectric layer  122 . 
     FIG. 3 illustrates portion  100  after application of a photoresist layer  170 . Photoresist layer  170  is provided above ARC layer  120  and can have a thickness between 100 nm and 500 nm. In an exemplary embodiment, photoresist layer  170  can be provided using a spin-on process. 
     FIG. 4 illustrates portion  100  after patterning of photoresist layer  170 . Photoresist layer  170  can be patterned to form apertures  175 . In an exemplary embodiment, apertures  175  have a critical dimension (i.e., width) of 200 nm. Alternatively, aperture  175  can have critical dimensions of between 50 nm and 800 nm. 
     FIG. 5 illustrates portion  100  after etching ARC layer  120  and amorphous carbon layer  130  to extend apertures  175  to ARC layer  120  and amorphous carbon layer  130 . A variety of techniques may be used to extend aperture  175  into ARC layer  120  and amorphous carbon layer  130 . The patterning of amorphous carbon layer  130  forms sacrificial amorphous carbon structures  135 . 
     In an exemplary embodiment, an etching technique is used whereby photoresist layer  170  and ARC layer  120  are removed during the patterning of amorphous carbon layer  130 . Alternatively, photoresist layer  170  can be removed during the etching of ARC layer  120  and amorphous carbon layer  130 , and ARC layer  120  is subsequently removed. 
     FIG. 6 illustrates portion  100  after removal of ARC layer  120 . ARC layer  120  can be removed using a plasma etch or reactive ion etching or wet etch (hot phosphoric acid) process. As described above, in an alternative embodiment, ARC layer  120  can be removed during the etching of ARC layer  120  and photoresist layer  170  described with reference to FIG.  5 . Alternatively, the ARC layer can remain on the stack to be removed later during the chemical mechanical polish (CMP) process. 
     FIG. 7 illustrates portion  100  after a deposition of a dielectric film  185  over sacrificial amorphous carbon structures  135  and gate dielectric layer  122 . Dielectric layer  185  can be conformally deposited using a variety of different techniques. In an exemplary embodiment, dielectric layer  185  is deposited using a plasma enhanced chemical vapor deposition (PECVD) operation. 
     FIG. 8 illustrates portion  100  after a polishing of dielectric layer  185  to planarize dielectric layer  185  with sacrificial amorphous carbon structures  135 . Portions of dielectric layer  185  are removed such that dielectric layer  185  has a cross-sectional height approximately equivalent to the cross-sectional height of sacrificial amorphous carbon structures  135 . 
     FIG. 9 illustrates portion  100  after removal of sacrificial amorphous carbon structures  135 . Sacrificial amorphous carbon structures  135  can be removed using an ashing operation which introduces a O 2  plasma. Advantageously, use of an ashing operation provides the ability to remove the dummy gate material (amorphous carbon) using a downstream plasma process. Other materials, such as polysilicon, do not lend themselves to such low damage plasma processing and likely require the use of more energetic reactive ion etching processes. 
     FIG. 10 illustrates portion  100  after deposition of a metal layer  195 . Metal layer  195  is deposited over dielectric layer  185  and fills spaces remaining from removal of sacrificial amorphous carbon structures  135 . Metal layer  195  can contain a variety of metal materials, such as Mo, W, Ta, CoSi, NiSi and poly Si, or any similarly conductive material or alloy. 
     FIG. 11 illustrates portion  100  after a polishing operation of metal layer  195  to form metal gates  205  in spaces where previously patterned amorphous carbon layer  130  was located. 
     Advantageously, a metal gate can be formed where sacrificial amorphous carbon gate structures were. As such, a small critical dimension (CD) can be achieved while avoiding the difficulties of etching a metal gate directly. The process described with reference to FIGS. 1-11 also avoid the incapability of metal processing with front end processes. 
     While the exemplary embodiments illustrated in the FIGURES and described above are presently preferred, it should be understood that these embodiments are offered by way of example only. Other embodiments may include, for example, different material layers as well as additional or combined steps in the process. The invention is not limited to a particular embodiment, but extends to various modifications, combinations, and permutations that nevertheless fall within the scope and spirit of the appended claims.