Abstract:
Provided is a method for manufacturing a fin structure. The method may include forming an initial fin on a substrate, forming a dielectric layer on the substrate to cover the initial fin, planarizing the dielectric layer by sputtering, and further etching the dielectric layer back to expose a portion of the initial fin, wherein the exposed portion serves as a fin.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a U.S. national phase application of PCT Application No. PCT/CN2012/086657, filed on Dec. 14, 2012, entitled “METHOD FOR MANUFACTURING FIN STRUCTURE,” which claims priority to Chinese Application No. 201210505449.4, filed on Nov. 30, 2012. Both the PCT Application and the Chinese Application are incorporated herein by reference in their entireties. 
     TECHNICAL FIELD 
     The present disclosure relates to the semiconductor field, and more specifically, to a method for manufacturing a fin structure. 
     BACKGROUND 
     A planarization process such as Chemical Mechanical Polishing (CMP) is generally used in semiconductor processes to obtain a relatively planar surface. However, in a case where a material layer is planarized by CMP, it is difficult to control a surface flatness of the material layer after CMP to be in a range of, e.g., several nanometers, if a relatively thick portion thereof is needed to be ground. 
     SUMMARY 
     The present disclosure aims to provide, among others, method for manufacturing a fin structure. 
     According to an aspect of the present disclosure, there is provided a method for manufacturing a fin structure, comprising: forming an initial fin on a substrate; forming a dielectric layer on the substrate to cover the initial fin; planarizing the dielectric layer by sputtering; and further etching the dielectric layer back to expose a portion of the initial fin, wherein the exposed portion serves as a fin. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features, and advantages of the present disclosure will become more apparent from following descriptions on embodiments thereof with reference to attached drawings, in which: 
         FIGS. 1-13  are schematic views illustrating a flow of manufacturing a fin structure in accordance with an embodiment of the present disclosure; and 
         FIGS. 14 and 15  are schematic views illustrating some steps in a flow of manufacturing a fin structure in accordance with another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, descriptions are given with reference to embodiments shown in the attached drawings. However, it is to be understood that these descriptions are illustrative and not intended to limit the present disclosure. Further, in the following, known structures and technologies are not described to avoid obscuring the present disclosure unnecessarily. 
     In the drawings, various structures according to the embodiments are schematically shown. However, they are not drawn to scale, and some features may be enlarged while some features may be omitted for sake of clarity. Moreover, shapes and relative sizes and positions of regions and layers shown in the drawings are also illustrative, and deviations may occur due to manufacture tolerances and technique limitations in practice. Those skilled in the art can also devise regions/layers of other different shapes, sizes, and relative positions as desired. 
     In the context of the present disclosure, when a layer/element is recited as being “on” a further layer/element, the layer/element can be disposed directly on the further layer/element, or otherwise there may be an intervening layer/element interposed therebetween. Further, if a layer/element is “on” a further layer/element in an orientation, then the layer/element can be “under” the further layer/element when the orientation is turned. 
     According to embodiments of the present disclosure, a material layer may be planarized by sputtering of, e.g., Ar or N plasma. Due to such planarization by sputtering, instead of conventional planarization by CMP, it is possible to achieve a relatively flat surface of the material layer. The material layer may comprise a variety of material layers used in semiconductor manufacture processes, for example, including but not limited to, an insulator material layer, a semiconductor material layer and a conductor material layer. 
     In an embodiment, the concept of the present disclosure is applicable to Fin Field Effect Transistors (FinFETs). 
     In general, a FinFET may be manufactured as follows. For example, an initial fin may be formed on a substrate. Subsequently, a dielectric layer may be deposited on the substrate to cover the initial fin. This dielectric layer may be planarized by, for example, Chemical Mechanical Polishing (CMP). Next, the dielectric layer may be etched back to form an isolation layer, and a portion of the initial fin is thus exposed. The exposed portion of the initial fin may then serve as a fin for a final device. However, it is difficult for the CMP process to control the surface flatness within several nanometers, and therefore the start-point surface, from which the etching-back process is started, is not flat enough, resulting in variations in height of fins, if multiple, across the wafer. 
     According to an embodiment of the present disclosure, after the dielectric layer is deposited, the dielectric layer maybe planarized by plasma sputtering. In this way, the CMP may not be used at all or the CMP may be used at a less dose as compared with the conventional technology. Therefore, the consistency of the start-point surface of the etching-back process on the dielectric layer can be improved. 
     The technology of the present disclosure can be implemented in various ways, some of which are exemplified in the following. 
     As shown in  FIG. 1 , a substrate  1000  is provided. The substrate  1000  may comprise various forms of substrates, e.g., including but not limited to, a bulk semiconductor substrate such as a bulk Si substrate, a Semiconductor-on-Insulator (SOI) substrate, a SiGe substrate, or the like. In the following descriptions, the bulk Si substrate is described by way of example. 
     The substrate  1000  may be patterned to form initial fins thereon. For example, this may be done as follows. Specifically, patterned photoresist  1002  may be formed on the substrate  1000  according to the design. The photoresist  1002  is typically patterned into a series of parallel, equally spaced lines. Subsequently, as shown in  FIG. 2 , the substrate  1000  may be etched by, e.g., Reactive Ion Etching (RIE), with the patterned photoresist as a mask, in order to form the initial fins  1004 . Then, the photoresist  1002  may be removed. 
     It should be noted that the shape of trenches (between the fins) formed by etching is not necessarily a regular rectangle as shown in  FIG. 2 , but may be tapered from top down. Further, positions and the number of the initial fins formed are not limited to the example as shown in  FIG. 2 . 
     Furthermore, the initial fins are not limited to being formed by directly patterning the substrate. For example, the initial fins may be formed by epitaxially growing another semiconductor layer on the substrate and then patterning the other semiconductor layer. If there is sufficient etching selectivity between the other semiconductor layer and the substrate, the patterning of the initial fins may be stopped at the substrate, so as to implement a more precise control on a height of the initial fins. 
     Therefore, in the context of the present disclosure, the expression “forming an initial fin on a substrate” may comprise forming the fin on the substrate in any suitable manner. 
     An isolation layer may be formed on the substrate after the initial fins are formed by the above process. 
     Specifically, as shown in  FIG. 3 , a dielectric layer  1006  may be formed on the substrate by e.g. deposition, so as to cover the formed initial fins  1004 . For example, the dielectric layer  1006  may comprise oxide such as silicon oxide. 
     Subsequently, as shown in  FIG. 4 , the dielectric layer  1006  may be subjected to sputtering so as to be planarized. For example, plasma such as Ar or N plasma may be used for sputtering. Here, sputtering parameters, such as sputtering power and atmospheric pressure, may be controlled according to a cutting rate of the dielectric layer  1006  by the plasma sputtering, so as to determine a time period for the plasma sputtering. Thus, the plasma sputtering can be performed for a certain time period so as to sufficiently smooth the surface of the dielectric layer  1006 . On the other hand, in the example as shown in  FIG. 4 , the plasma sputtering may be stopped before reaching the top surface of the initial fins  1004 , so as to avoid excessive damage to the initial fins  1004 . 
     Although  FIG. 4  shows microscopic fluctuations, the top surface of the dielectric layer  1006  actually has a sufficient flatness, with fluctuations thereof controlled within, for example, several nanometers. 
     According to another embodiment of the present disclosure, the dielectric layer  1006  may be subjected to some CMP after planarization by sputtering, if necessary. 
     After the surface of the dielectric layer  1006  is sufficiently smoothed by the plasma sputtering, the dielectric layer  1006  may be etched back by e.g. RIE to expose a portion of the respective initial fins  1004 , as shown in  FIG. 5 . The exposed portion may be subsequently used as a fin for a final device. The isolation layer may be constituted by the remaining dielectric layer  1006 . Since the surface of the dielectric layer  1006  becomes smooth by sputtering before the etching-back, the surface of the isolation layer  1006  may keep substantially consistent across the substrate after the etching-back. 
     According to an example of the present disclosure, a punch-through stopper (referring to  1008  as shown in  FIG. 7 ) may be formed by implantation in order to improve device performances, as shown by arrows in  FIG. 6 . For example, p-type impurities such as B, BF 2  or In may be implanted for an n-type device; and n-type impurities such as As or P may be implanted for a p-type device. The ion implantation may be carried out in a direction substantially perpendicular to the surface of the substrate. Parameters for the ion implantation may be controlled, so that the punch-through stopper may be formed in a portion of the initial fin which is located below the surface of the isolation layer  1006  and may have a desired doping concentration. It should be noted that a part of dopants (ions or elements) may be scattered from the exposed portions of the initial fins due to a form factor of the initial fins. Thus, it is beneficial to form an abrupt doping distribution in a depth direction. Annealing may be performed to activate the implanted impurities. Such a punch-through stopper may facilitate to reduce leakage between source and drain. 
     Next, a gate stack across the fin may be formed on the isolation layer  1006 . For example, this may be done as follows. Specifically, as shown in  FIG. 7  ( FIG. 7( b )  shows a cross-sectional view taken along line BB′ in  FIG. 7( a ) ), a gate dielectric layer  1010  may be formed by e.g. deposition. For example, the gate dielectric layer  1010  may comprise oxide with a thickness of about 0.8-1.5 nm. In the example as shown in  FIG. 7 , the gate dielectric layer  1010  is shown in a “II” shape. However, the gate dielectric layer  1010  may also include a portion extending on the top surface of the isolation layer  1006 . 
     Then, a gate conductor layer  1012  may be formed by e.g. deposition. For example, the gate conductor layer  1012  may comprise polysilicon. The gate conductor layer  1012  may fill the gaps between the fins, and then planarized by, for example, CMP. Next, the gate conductor layer  1012  may be patterned in order to form the gate stack. In the example of  FIG. 7 , the gate conductor layer  1012  is patterned into a bar intersecting the fins. According to another embodiment, the gate dielectric layer  1010  may be further patterned with the patterned gate conductor layer  1012  as a mask. 
     After the gate conductor is patterned, halo implantation and extension implantation may be performed with the gate conductor as a mask, for example. 
     Next, as shown in  FIG. 8  ( FIG. 8( b )  shows a cross-sectional view along line BB′ in  FIG. 8( a ) , and  FIG. 8( c )  shows a cross-sectional view along line CC′ in  FIG. 8( a ) ), a spacer  1014  may be formed on side walls of the gate conductor layer  1012 . For example, nitride such as silicon nitride with a thickness of about 5-20 nm may be formed by deposition, and then subjected to RIE to form the spacer  1014 . There are various methods to form the spacer, and detailed descriptions thereof are omitted here. When the trenches between the fins are tapered from top down (which is a common situation due to characteristics of etching), the spacer  1014  may have substantially no portion formed on side walls of the fins. 
     After the spacer is formed, source/drain (S/D) implantation may be performed with the gate conductor and the spacer as a mask. Subsequently, annealing may be performed to activate the implanted ions, so as to form source/drain regions, resulting in FinFETs. 
     In the embodiment as illustrated above, the gate stack is directly formed after the fins are formed. However, the present disclosure is not limited to this. For example, the present disclosure is also applicable to the gate last process. Further, the strained source/drain technique may also be incorporated. 
     According to another embodiment of the present disclosure, the gate dielectric layer  1010  and the gate conductor layer  1012  formed in  FIG. 7  may be a sacrificial gate dielectric layer and a sacrificial gate conductor layer, respectively. Next, the spacer  1014  may be formed in the way as described above in conjunction with  FIG. 8 . 
     Then, as shown in  FIG. 9  ( FIG. 9( b )  shows a cross-sectional view along line BB′ of  FIG. 9( a ) , and  FIG. 9( c )  shows a cross-sectional view along line CC′ of  FIG. 9( a ) ), exposed portions of the sacrificial gate dielectric layer  1010  may be selectively removed (by e.g. RIE). In a case where both the sacrificial gate dielectric layer  1010  and the isolation layer  1006  comprise oxide, the RIE of the sacrificial gate dielectric layer  1010  may have substantially no impact on the isolation layer  1006  because the sacrificial gate dielectric layer  1010  is relatively thin. This operation is not required any more if the sacrificial gate dielectric layer has been further patterned with the sacrificial gate conductor as a mask in the process of forming the sacrificial gate stack as described above. 
     Next, portions of the initial fin  1004  which are exposed due to the removal of the sacrificial dielectric layer  1010  may be selectively removed (by e.g. RIE). The etching of those portions of the initial fin  1004  may be carried out until the punch-through stopper  1008  is exposed. Due to the presence of the sacrificial gate stack (the sacrificial gate dielectric layer, the sacrificial gate conductor and the spacer), a portion of the initial fin  1004  may be left under the sacrificial gate stack. 
     Subsequently, as shown in  FIG. 10  ( FIG. 10( b )  shows a cross-sectional view along line BB′ of  FIG. 10( a ) , and  FIG. 10( c )  shows a cross-sectional view along the line CC′ of  FIG. 10( a ) ), a semiconductor layer  1016  may be formed on exposed portions of the initial fin by e.g. epitaxy. Then, source/drain regions may be formed in the semiconductor layer  1016 . According to an embodiment of the present disclosure, the semiconductor layer  1016  may be doped in-situ while being grown. For example, n-type in-situ doping may be performed for an n-type device; while p-type in-situ doping may be performed for a p-type device. Moreover, in order to further improve the performances, the semiconductor layer  1016  may comprise a material different from that of the fin  1004  to apply strain to the fin  1004  (in which a channel of the device will be formed). For example, in a case where the fin  1004  comprises Si, the semiconductor layer  1016  may comprise Si:C (where an atomic percentage of C is e.g. about 0.2-2%) to apply tensile stress for the n-type device, or SiGe (where an atomic percentage of Ge is e.g. about 15-75%) to apply compressive stress for the p-type device. 
     In a case where the sacrificial gate conductor layer  1012  comprises polysilicon, the growth of the semiconductor layer  1016  may occur on the top surface of the sacrificial gate conductor  1012 . This is not shown in the drawings. 
     Next, as shown in  FIG. 11  ( FIG. 11( b )  shows a cross-sectional view along line BB′ of  FIG. 11( a ) ), a further dielectric layer  1018  may be formed by e.g. deposition. The dielectric layer  1018  may comprise e.g. oxide. Subsequently, the dielectric layer  1018  may be planarized by e.g. CMP. The CMP may be stopped at the spacer  1014 , so as to expose the sacrificial gate conductor  1012 . 
     Then, as shown in  FIG. 12  ( FIG. 12( b )  shows a cross-sectional view along line BB′ of  FIG. 12( a ) , and  FIG. 12( c )  shows a cross-sectional view along line CC′ of  FIG. 12( a ) ), the sacrificial gate conductor  1012  may be selectively removed by e.g. TMAH solution, so as to form a gap  1020  inside the spacer  1014 . According to another example, the sacrificial gate dielectric layer  1010  may be further removed. 
     Next, as shown in  FIG. 13  ( FIG. 13( b )  shows a cross-sectional view along line BB′ of  FIG. 13( a ) , and  FIG. 13( c )  shows a cross-sectional view along line CC′ of  FIG. 13( a ) ), a gate dielectric layer  1022  and a gate conductor layer  1024  may be formed in the gap  1020 , so as to form a final gate stack. The gate dielectric layer  1022  may comprise a high-K gate dielectric, e.g. HfO 2 , with a thickness of about 1-5 nm. The gate conductor layer  1024  may comprise a metal gate conductor. Preferably, a work function adjustment layer (not shown) may also be formed between the gate dielectric layer  1022  and the gate conductor layer  1024 . 
     According to another embodiment of the present disclosure, as shown in  FIG. 14 , initial fins  2004  are formed on a substrate  2000 . After a dielectric layer  2006  is formed on the substrate  2000  to cover the initial fins  2004 , the dielectric layer  2006  may be planarized by sputtering. In this regard, reference may be made to the above descriptions with reference to  FIGS. 1-4 , for example. Here, the difference consists in that the sputtering is performed until portions of the initial fins at a top end thereof are removed, as shown in  FIG. 15 . The sputtering parameters, such as sputtering power and atmospheric pressure, may be controlled until the sputtering reaches the top ends of the respective initial fins  2004 . In order to remove damages of the initial fins  2004  caused by the sputtering, an annealing or etching-back may be performed on the top ends of the initial fins  2004  after the sputtering. 
     The subsequent processes may be performed in the way described above with reference to  FIGS. 5-13 . 
     In the above descriptions, details of patterning and etching of the layers are not described. It is to be understood by those skilled in the art that various measures may be utilized to form the layers and regions in desired shapes. Further, to achieve the same feature, those skilled in the art can devise processes not entirely the same as those described above. 
     From the foregoing, it will be appreciated that specific embodiments of the disclosure have been described herein for purposes of illustration, but that various modifications may be made without deviating from the disclosure. In addition, many of the elements of one embodiment may be combined with other embodiments in addition to or in lieu of the elements of the other embodiments. Accordingly, the technology is not limited except as by the appended claims.