Abstract:
The present application discloses a method for manufacturing a semiconductor structure, comprising the steps of: a) providing a p-type field effect transistor; b) forming a tensile-stressed layer on the p-type field effect transistor; c) removing a portion of the tensile-stressed layer, so that the remaining portion of the tensile-stressed layer generates compressive stress in the channel of the p-type field effect transistor; and d) performing annealing, so as to achieve the object of memorizing compressive stress in a channel of a transistor and improving the performance of the transistor. The method according to the present invention memorizes the compressive stress in the channel of the transistor by a stress memorization technique, increases mobility of holes, and improves overall performance of the semiconductor structure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Section 371 National Stage Application of International Application No. PCT/CN2011/071309, filed on Feb. 25, 2011, which claims priority to CN 201010501712.3, filed on Sep. 30, 2010, the entire contents of which are incorporated herein by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention generally relates to a method for manufacturing a semiconductor structure, and more particularly, to a method for manufacturing a high-performance semiconductor structure by a stress memory technique. 
     2. Description of Related Art 
     It is well known that performance of a field effect transistor (FET) may be improved when stress is applied thereto. In such a case that stress is applied to a field effect transistor, tensile stress may increase mobility of electrons, and thus driving current of an nFET, while compressive stress may increase mobility of holes, and thus driving current of a pFET. 
     One approach for providing such stress is referred to as Stress Memorization Technique (SMT), which comprises forming a material having intrinsic stress, such as silicon nitride, at various locations of a semiconductor structure, for example, above a channel region; performing annealing so that the stress is memorized at the respective locations, such as a gate region or an extension region; and removing the material having the stress. Thus, the stress remains and increases mobility of electrons or holes, which in turn enhances overall performance of the semiconductor structure. 
     One of the problems with the SMT is that it may only be applied to nFETs. In particular, annealing should be performed so as to memorize the stress in the semiconductor structure, typically at a high temperature. However, those materials used for applying the stress to the field effect transistor, such as nitride, may only provide tensile stress at the high temperature. Consequently, the application of SMT may be limited to nFETs. 
     In view of the above problem, there is a need for SMT which may be used in pFETs. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide SMT for a pFET, which may be used to apply compressive stress to a channel of the pFET with conventional stress-inducing materials, and which may memorize the compressive stress from the stress-inducing layer above the pFET into the channel, increase mobility of holes, and improve overall performance of the semiconductor structure. Moreover, the method according to the present invention is easily implemented and has better industrial application. 
     The present invention provides a method for manufacturing a semiconductor structure, comprising: 
     a) providing a p-type field effect transistor; 
     b) forming a tensile-stressed layer on the p-type field effect transistor; 
     c) removing a portion of the tensile-stressed layer, so that the remaining portion of the tensile-stressed layer generates compressive stress in the channel of the p-type field effect transistor; and 
     d) performing annealing. 
     Preferably, the tensile-stressed layer comprises at least one selected from the group consisting of Si3N4, SiO2, SiOF, SiCOH, SiCO, SiCON, SiON, PSG and BPSG. 
     Preferably, in step b), the tensile-stressed layer is formed by a deposition process. 
     Preferably, in step b), the portion of the tensile-stressed layer is removed by selective etching 
     Preferably, between the step a) and the step b), an etching stop layer is formed by a deposition process. More preferably, the material of the etching stop layer is different for that of the tensile-inducing layer. More preferably, the etching stop layer comprises SiO2. 
     Preferably, the step c) comprises forming a photoresist layer having a predetermined pattern by lithography; and etching the tensile-stressed layer with the photoresist layer having the predetermined pattern as a mask. More preferably, after the step c), the distance in the direction of the gate length between the edge of the remaining portion of the tensile-stressed layer and the external side of the gate is in the range of 0.02-0.2 μm. 
     Preferably, the p-type field effect transistor comprises a dummy gate having a dummy gate conductor and a gate dielectric. More preferably, after the step d), the method further comprises a step e) of: removing the dummy gate conductor to form an opening; and forming a gate in the opening. More preferably, in step e), the dummy gate conductor is removed by an etching process so as to expose the gate dielectric below the dummy gate conductor. Alternatively, in step e), the dummy gate conductor and the gate dielectric are removed by an etching process so as to expose a substrate below the gate dielectric. 
     In the method for manufacturing a semiconductor structure according to the present invention, the compressive stress may be memorized in a channel of a transistor by combining a lithography process, an etching process and a stress memorization technique, so as to increase mobility of holes and improve overall performance of the semiconductor structure. Moreover, the method according to the present invention is easily implemented and has better industrial application. 
     These and other features, aspects and advantages of the present invention will be apparent by reading the following description and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an initial structure according to one embodiment of the present method. 
         FIGS. 2-7  show the semiconductor structure at intermediate stages of the process flow according to one embodiment of the present method. 
         FIG. 8  shows a semiconductor structure manufactured according to one embodiment of the present method. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
     The present invention will be described below with preferred embodiments in connection with attached drawings. However, it should be understood that the descriptions here are only illustrative and are not intended to limit the protection scope. Also, the following description omits details of known structures and techniques so that concepts of the invention are not obscured unnecessarily. 
     Top views, cross-sectional views and perspective views of various structures of the semiconductor structure according to the embodiments of the present invention are shown in attached drawings. However, these figures are not drawn to scale, and some details may be exaggerated and other details may be omitted for simplicity. Shapes, relative sizes and positions of various regions/layers shown in the figures are only illustrative. Variations may exist due to manufacturing tolerance and technical limitations. Moreover, those skilled in the art may design regions/layers having different shapes, relative sizes and positions as required. 
     According to one embodiment of the present invention, there provides a method for manufacturing a high-performance semiconductor structure with a stress memorization technique, which may memorize compressive stress in the channel of a transistor, and in turn increase mobility of holes and improve overall performance of the semiconductor structure. 
       FIG. 1  shows an initial structure according to one embodiment of the present method. 
     The initial structure is a p-type field effect transistor (pFET)  100 . In the pFET  100  shown in  FIG. 1 , a substrate  10  is subjected to initial processing steps, such as formation of conventional shallow trench isolations (STIs)  12 , well implantation, formation of a gate dielectric layer  14 , formation of a gate conductor  16 , and formation of a first sidewall spacer  18 . 
       FIGS. 2-7  show the semiconductor structure at intermediate stages of the process flow according to one embodiment of the present method. 
     According to one embodiment of the present method, an extension implantation is preferably performed to the initial structure of the pFET  100 , as shown in  FIG. 2 . Optionally, a halo implantation may be further performed. 
     The gate conductor  16  and the first sidewall spacer  18  are used as a mask, and the extension implantation may be performed in a direction indicated by arrow  202  to form extension regions  20  in the exposed portions of the substrate  10  at both sides of the gate conductor  16  and the first sidewall spacer  18 . For the pFET in the illustrated embodiment of the present invention, p-type dopants such as boron (B or BF2) and indium (In) or any combination thereof may be used in the extension implantation. The extension region  20  has the effect of reducing the peak value of the electric field, and thus suppresses short channel effects. 
     Optionally, the gate conductor  16  and the first sidewall spacer  18  may be used as a mask again, and halo implatation may be performed in a direction indicated by arrow  204  at a predetermined tilt angle to form halo regions  21  at the portion of the substrate  10  below the gate dielectric  14 . For the pFET in the illustrated embodiment of the present invention, n-type dopants such as arsenic (As), phosphor (P) or their combination may be used in the halo implantation. Here, the halo regions  21  may be used mainly for blocking diffusion into the channel region during the subsequent step of forming source/drain regions  24  (as will be shown in  FIG. 3 ), which in turn suppresses the short channel effect. 
     Referring to  FIG. 3 , a second sidewall spacer  22  is formed at both sides of the gate conductor  16  and the first sidewall spacer  18 , and source/drain regions are also formed. 
     The second sidewall spacer  22  may be formed, for example, by forming a material of the second sidewall spacer on the whole surface of the semiconductor structure by a conventional deposition process such as Physical Vapor Deposition (PVD), Chemical Vapor Deposition (CVD), Atomic Layer Deposition (ALD), sputtering, and the like, and performing anisotropic etching, preferably Reactive Ion Etching (RIE), to formed the second sidewall spacer  22 , as shown in  FIG. 3 . The material of the second sidewall spacer  22  may be the same as or different from that of the first sidewall spacer. Preferably, the second sidewall spacer  22  comprises Si3N4. In the subsequent step, the second sidewall spacer  22  will be used as a mask and/or an etching stop layer. 
     The gate conductor  16  and the second sidewall spacer  22  are used as a mask and ions are implanted in a direction indicated by arrow  206  to provide source/drain regions  24  in the exposed portions of the substrate  10  at both sides of the gate region consisting of the gate conductor  16  and the second sidewall spacer  22 . For the pFET in the illustrated embodiment of the present invention, p-type dopants such as boron (B or BF2) and indium (In) or any combination thereof may be used in the source/drain implantation. Typically, the source/drain regions  24  and the extension region  20  have dopants of the same type of conductivity, but of the same or different species and doping concentrations. 
     Referring to  FIG. 4 , an etching stop layer  26  and a tensile-stressed layer  28  are formed in sequence on the semiconductor structure shown in  FIG. 3 . Here, the respective layers may be formed, for example, by the above-mentioned deposition processes. Here, the etching stop layer  26  is made of a material different from that of the tensile-stressed layer  28 . Typically, the etching stop layer  26  comprises SiO2, and the tensile-stressed layer  28  is made of at least one selected from a group consisting of Si3N4, SiO2, SiOF, SiCOH, SiCO, SiCON, SiON, PSG and BPSG. Alternatively, the etching stop layer  26  may also be formed by a thermal oxidation process. 
     Referring to  FIGS. 5-6 , the tensile-stressed layer  28  is selectively etched. 
     Referring to  FIG. 5 , lithography is performed to provide a photoresist layer having a predetermined pattern. For example, the photoresist layer  30  is applied on the semiconductor structure shown in  FIG. 4  (for example, by spin-coating) so that the photoresist layer  30  covers the whole surface of the semiconductor structure. Then the photoresist layer  30  is patterned. Typically, the photoresist layer  30  is patterned by steps comprising exposure, development and baking for hardening the photoresist, so as to provide the photoresist layer having the predetermined pattern. 
     Referring to  FIG. 6 , a portion of the tensile-stressed layer  28  is removed with the patterned photoresist layer as a mask, for example, by selective etching such as RIE, stopping at the etching stop layer  26 , and removing the photoresist layer, so that the remaining portion of the tensile-stressed layer generates compressive stress in the channel. Here, the compressive stress concentrates on the channel region after the etching process. Specifically, the tensile-stressed layer  28  generates tensile stress (T) applied to the channel in a direction indicated by the arrow in the semiconductor structure shown in  FIG. 5 . In the semiconductor structure shown in  FIG. 6  after the etching process, the tensile-stressed layer generates compressive stress (C) in a direction indicated by the arrow. Thus, a resultant force of the intrinsic tensile stress (T) and the generated compressive stress (C) is applied to the channel. As will be known by one skilled person in the field, compressive stress is applied to the channel when the generated compressive stress (C) is larger than the intrinsic compressive stress (T). If too small a portion of the stress layer is etched away, the stress applied to the channel may be the undesired tensile stress. However, if the stress layer is excessively etched away, it may be difficult for the remaining portion of the stress layer to generate sufficiently large compressive stress. 
     In order to ensure compressive stress to be applied to the channel by the etched tensile-stressed layer  28 , the distance L between the edge of the remaining portion of the tensile-stressed layer and the external side of the gate may be preferably in the range of 0.02-0.2 μm. 
     Referring to  FIG. 7 , annealing is performed so that the stress from the tensile-stressed layer  28  is memorized in the semiconductor structure, and the dopants in the extension regions  20  and source/drain regions  24  (and halo regions  21  if exist) are activated, and the defects on the surface and in the semiconductor material are removed. In one embodiment of the present invention, rapid thermal annealing (RTA) is performed, for example, at about 1000° C. for about 0-1 second. 
     In the method for manufacturing a semiconductor structure according to the present invention, the compressive stress is memorized in the channel by depositing and etching a tensile-stressed layer and then performing annealing, which achieves an excellent stress memorization effect. 
     As shown in  FIG. 7 , the extension regions  20  diffuse towards the channel region below the gate dielectric  14  after annealing. 
     Referring to  FIG. 8 , the tensile-stressed layer  28  and the etching stop layer  28  are removed, for example, by wet etching or reactive ion etching (RIE), and a conventional silicidation process is performed to the semiconductor structure. 
     Optionally, a replacement gate process may be performed after removal of the tensile-stressed layer  28  and the etching stop layer  26 . Specifically, the dummy gate conductor  16  may be removed by etching so as to expose the gate dielectric  14  after removal of the tensile-stressed layer  28  and the etching stop layer  26 . Furthermore, a new gate conductor may be formed by the replacement gate process (not shown). For example, a new gate conductor layer may be formed on the whole surface of the semiconductor structure by a deposition process, followed by etching such as RIE so as to remove the portions of the new gate conductor material that cover the surfaces of the substrate and the sidewall spacer. 
     Optionally, the gate dielectric  14  may also be removed by further etching after removal of the dummy gate conductor  16  so as to expose the substrate beneath the gate dielectric  14 . Furthermore, a new gate dielectric and a new gate conductor may be formed by the replacement process. For example, a new gate dielectric and a new gate conductor layer may be formed on the whole surface of the semiconductor structure by a deposition process, followed by etching such as RIE so as to remove the portions of the new gate dielectric and the new gate conductor material that cover the surfaces of the substrate and the sidewall spacer. 
     Here, the material of the new gate dielectric comprises high-K materials. Examples of the high K material include, but not limited to, hafnium-based materials such as HfO2, HfSiO, HfSiON, HfTaO, HfTiO or HfZrO, zirconia, lanthana, titania, barium strontium titanate (BST), or lead zirconate titanate (PZT). 
     The new gate conductor material comprises, but not limited to, metals, metal alloys, metal nitrides, metal silicides, any stack or combination thereof. Here, the gate conductor layer  36  preferably comprises a stack of a work function metal layer and a gate metal layer. Examples of the work function metal layer include, but not exclusively, TiN, TiAlN, TaN, TaAlN, or their combinations. 
     As shown in  FIG. 8 , a conventional silicidation process is performed to the semiconductor structure. A metal layer (not shown) is formed on the semiconductor layer by a deposition process so that it covers the whole semiconductor device. The metal layer preferably comprises NiPt. Annealing is performed at about 250° C.-500° C. so that the deposited metal reacts with the underlying silicon to provide a silicide layer  32 . Here, the silicide layer  32  preferably comprises NiPtSi. 
     In the illustrated embodiment of the present invention, silicides are provided at the surface of the source/drain regions  24  and the gate conductor  16 , which is suitable for a gate-first process. However, in the replacement gate process, silicides may be provided or not provided at the surface of the gate conductor. In the interconnect structure to be formed, the silicide layer  32  may reduce ohmic contact of the plugs in the contact holes with the source/drain regions  24  and the gate conductor  16 . The unreacted metals are selectively removed by wet etching in which a solution of sulfuric acid is, for example, used. 
     In the method for manufacturing a semiconductor structure according to the present invention, the compressive stress may be memorized in the channel of a transistor by combining an etching process by lithography process and a stress memorization technique, so as to increase mobility of holes and improve overall performance of the semiconductor structure. Moreover, the method according to the present invention is easily implemented and has better industrial application. 
     While the present invention has been described in the above embodiment with reference to the semiconductor structure shown in  FIG. 8 , one skilled person will appreciate that various conventional variations may be made in the semiconductor structure according to the present invention. The applicant intends to encompass any of the existed structures and those developed in the future but having the same function. 
     In the above description, no details are given for those conventional operations. Nevertheless, one skilled person will understand that the layers and regions having desired shapes may be formed by various approaches well known in the field. Moreover, one skilled person may propose a process completely different from the above processes for providing the same structure. 
     While the invention has been described with reference to specific embodiments, the description is only illustrative of the invention. The description is not construed as limiting the invention. The protection scope is defined by the attached claims and their equivalents. One skilled person will readily recognize that various modifications and changes may be made to the present invention without departing from the true scope of the present invention.