Abstract:
Semiconductor devices required forming a stress control film to handle different stresses on each side when optimizing the stress on the respective P channel and N channel sections. A unique feature of the semiconductor device of this invention is that P and N channel stress are respectively optimized by making use of a stress control film jointly for the P and N channels that conveys stress in different directions by utilizing the film thickness.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a semiconductor device and manufacturing technology for that device, and relates in particular to a technology effective for applications to semiconductor devices including N-channel conductive type MISFET (Hereafter also called N channel or Nch.) and P-channel conductive type MISFET (Hereafter also called P channel or Pch.) on the same substrate and manufacturing technology for those devices. 
         [0003]    2. Description of Related Art 
         [0004]    Every year the performance demanded from transistors becomes ever higher due to tough demands in recent years for more performance from equipment containing semiconductor devices. One type of tough demand on transistor performance is the transistor current drive. 
         [0005]    One technology for enhancing the current drive performance in transistors is a technology that utilizes the stress in the silicon-nitride (SiN) interlayer film to change the stress in the channel sections and boost the transistor current drive performance. 
         [0006]    In Nch (N channels) the stress on the channel section is along the direction of the tensile force so that better current drive performance can be expected there. Conversely, in Pch (P channels) the stress on channel section is along the direction of compression so that better current drive performance can be expected there. The channel section is also called a current path. 
         [0007]    WO2002/043151 and JP-A-2005-057301 disclose technology for regulating the stress according to the transistor polarity. 
         [0008]    First of all in WO2002/043151, two types of stress control films are formed in different directions on the respective P and N channels, and function to regulate the stress on the respective P and N channels. 
         [0009]    The film thicknesses of the respective stress control films also control the amount of stress on the respective P and N channels. 
       SUMMARY OF THE INVENTION 
       [0010]    However, the above example of the related art requires respectively different stress control films for the P and N channels. Namely, after forming either a compression or a tensile stress control film on both the P and N channels, the process for removing one stress control film and leaving a stress control film on only either the P channel or N channel must be repeated two times, once for the P channel and once for the N channel. In other words, the number of processes is increased. 
         [0011]    The semiconductor device of this invention is characterized in respectively optimizing the channel stress on the P channel and N channel by utilizing stress control films possessing different stress along the direction of the film thickness. 
         [0012]    This stress control film more preferably controls the stress state of the P and N channel sections prior to forming that stress control film to the reverse of the stress state. 
         [0013]    This stress control film further sets the direction of stress along the film thickness according to the stress on the channels of the transistor. 
         [0014]    In the present invention as described above, the stress on the respective P and N channel sections can be controlled with good accuracy in a simple manufacturing flow by forming a stress control film jointly on the P and N channels in only one layer and then etching away this stress control film only on either the P or the N channel side. 
         [0015]    The stress on the channel sections can in addition be controlled within a wider range by forming the stress control film according to the channel section stress state from compression to tensile, or from tensile to compression in the direction of film thickness. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a drawing showing the cross section of the transistor of the first embodiment of this invention; 
           [0017]      FIG. 2  is a drawing showing a portion of the manufacturing process for the transistor of the first embodiment of this invention; 
           [0018]      FIG. 3  is a drawing showing a portion of the manufacturing process for the transistor of the first embodiment of this invention; 
           [0019]      FIG. 4  is a drawing showing a portion of the manufacturing process for the transistor of the first embodiment of this invention; 
           [0020]      FIG. 5  is a drawing showing a portion of the manufacturing process for the transistor of the second embodiment of this invention; 
           [0021]      FIG. 6  is a drawing showing a portion of the manufacturing process for the transistor of the second embodiment of this invention; 
           [0022]      FIG. 7  is a drawing showing a portion of the manufacturing process for the transistor of the second embodiment of this invention; 
           [0023]      FIG. 8  is a drawing showing a portion of the manufacturing process for the transistor of the second embodiment of this invention; 
           [0024]      FIG. 9  is a drawing showing a portion of the manufacturing process for the transistor of the second embodiment of this invention; 
           [0025]      FIG. 10  is a drawing showing a portion of the manufacturing process for the transistor of the second embodiment of this invention; and 
           [0026]      FIG. 11  is a drawing showing a portion of the manufacturing process for the transistor of the second embodiment of this invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    The above and other objects, features and effects of this invention will be further clarified in the following description of the embodiments of the present invention while referring to the drawings. 
       First Embodiment 
       [0028]      FIG. 1  through  FIG. 4  are drawings showing the semiconductor device of the first embodiment of this invention. 
         [0029]      FIG. 1  shows the cross section along the adjoining P and N channel directions in the present embodiment. In this embodiment, the case is described where the stress on the P and N channels sections is achieved by a compressive force. The arrows in the figure show the direction of stress from an inward compressive force and an outward tensile force. 
         [0030]    Examining the stress control film  5  as shown in  FIG. 1  clearly shows that the N channel region is a thin film thickness compared to the P channel region. The stress directions are different on the respective N and P channels. 
         [0031]    The manufacturing flow in  FIG. 1  is described next utilizing  FIG. 2  through  FIG. 4  in order to provide a more detailed description. A P channel is first of all formed on the right and an N channel on the left, enclosing the device isolation  1  on the semiconductor substrate  10 . An N diffusion region  4  and a P diffusion region  41  are respectively formed to serve as the drain and source. Moreover, a gate  6  is formed by way of a gate insulation film  2  on the respective N and P channels. A sidewall insulation film  6  is also formed on the side wall of that gate. In this embodiment, the channel section for both the N channel and P channel are the stress compression directions as also shown in the figure by the arrows. 
         [0032]    As next shown in  FIG. 3 , the stress control film  5  later serving as the etch-back stopper on the transistor, is jointly formed on the N and P channels. This stress control film  5  is formed (to change) from a tensile to a compression stress in the direction of the film thickness as shown by the arrows in the upper and lower two stages in the figure. 
         [0033]    The upper and lower two stages in the figure are here described next. In the case shown by the concept diagram of this figure, the stress control film has maximum tensile stress at the bottom layer along that film thickness, and maximum compression stress at the highest layer. In other words, the stress on the stress control film gradually changes from a tensile force to a compression force along the direction of that film thickness. 
         [0034]    In the stress control film of this embodiment, the reason that the tensile stress is at the bottom layer is due to the compression stress on the channel sections. 
         [0035]    The film forming conditions for the above described change from a tensile to a compression stress are briefly described here. When for example forming an SiN film by the plasma CVD method, conditions are set in the initial film forming period that generate compression within the reaction chamber, and RF (high frequency) power to generate a tensile stress. Then, as the film forming progresses, the above conditions transition to conditions for generating a compression stress. Moreover, the SiN film can also be easily formed by reversing the above conditions from a compression to a tensile stress. In the present embodiment, the example described the case where SiN was the stress control film but the present invention is not limited to SiN, and any film functioning as an etching stopper and capable of controlling stress on the channel sections may be utilized. 
         [0036]    The stress distribution in this embodiment is next briefly described while referring to the graphs in  FIG. 5  through  FIG. 8 . In the initial film forming stage, a tensile force is generated in the stress control film, and a compression stress finally generated as already described. The graphs in  FIG. 5  and  FIG. 7  show plots of stress along the stress control film thickness on the horizontal axis, and show other stress values along the vertical axis. 
         [0037]    The stress on the stress control film consecutively changes in stages in  FIG. 5 , and changes continuously in  FIG. 7 . 
         [0038]      FIG. 6  and  FIG. 8  are graphs showing a plot of the total stress on the other points along the vertical axis versus the stress along the film thickness in the horizontal axis respectively in  FIG. 5  and  FIG. 7 . In a detailed description of  FIG. 6 , the tensile stress increases from point A, and finally reaches a peak at point B. The film is then formed in the compression direction so the stress shifts toward the compression direction, and finally achieves the neutral state at point C. 
         [0039]      FIG. 8  is the same except for the rate of change. This graph only expresses the concept type so numerical values in  FIG. 6  are larger among the numerical values along the vertical axis shown in  FIG. 5  and  FIG. 6 . 
         [0040]    Though not plotted in  FIG. 5  through  FIG. 8 , the C point is more than likely to be exceeded. In other words, the stress control film may even be formed extremely thick during manufacture. The stress control film thicknesses shown in  FIG. 5  through  FIG. 8  may be set from point A to point C, or to point C or higher as desired according to the stress needed on the channel sections. 
         [0041]      FIG. 5  through  FIG. 8  showed examples for changing the stress on the stress control film from tensile to compression. Conversely, if changing from compression to tensile, then the respective directions for compression and tensile in the figure will be reversed. 
         [0042]    After forming this type of stress control film, a mask  11  is applied to cover just the P channel region, and the stress control film  5  on the N channel region is etched (etch back). A section of stress control film  5  with a tensile stress on the bottom layer in this way remains on the N channel region, the compression stress on the N channel section is canceled out, and is changed to a tensile stress as shown by the direction of the arrows in the figure. The channel for the P channel region is still under a compression stress. Both the N and P channels can in this way be set to the desired stress. In the figure, a stress control film directly contacts the diffusion regions  4 ,  41 ; however, a thin oxide film may in fact be present in some cases. 
         [0043]    The subsequent processes such as forming holes in the contact performed on the transistor formed in this way are omitted here. 
       Second Embodiment 
       [0044]    The second embodiment of this invention is described next while referring to  FIG. 9  through  FIG. 11 . In the case described in the first embodiment, the channel regions below the gate are subject to a compression force after forming the gate insulation film and the N and P channel gate electrodes. 
         [0045]    Here, the case is described where each channel section of the N and P channels are subject to a tensile force as shown in  FIG. 9  by the outward facing arrows. 
         [0046]    Unlike the first embodiment, a stress control film  5  later functioning as an etching stopper for the transistor is formed next while conforming to the condition that the stress transitions from a compression to a tensile force along the direction of film thickness as shown in  FIG. 10 . 
         [0047]    The reason the stress control film of this embodiment is subject to compression stress in the bottom layer is because there is a tensile stress on the channel section. 
         [0048]    A mask  11  is then applied to cover just the N channel region, and the stress control film  5  on the P channel region is etched (etch back) as shown in  FIG. 11 . A section of stress control film  5  with a compression stress on the bottom layer in this way remains on the P channel region, the tensile stress on the P channel section is canceled out, and is changed to a compression stress as shown by the direction of the arrows in the figure. The channel in the N channel region remains a tensile stress. Consequently, a tensile stress can be generated on the N channel section, and a compression stress generated on the P channel section the same as in the first embodiment. 
         [0049]    The present invention is not limited to the above described embodiments and as is apparent to those skilled in the art the embodiments maybe modified as desired. In the first and second embodiments for example, immediately after forming the stress control film, the stress control film was etched back in order to optimize the stress on the channel sections of the transistor, however the invention is not limited to this method. In other words, when the stress on the channel regions tended towards either the compression or tensile direction in the subsequent manufacturing processes, there was no need to optimize the stress on the channel sections ahead of time according to the type of stress immediately after forming the above described stress control film. The thickness of the initial stress control film for example may be set for the C point or higher in  FIG. 6 . Moreover the stress control film itself is not limited to silicon-nitride (SiN) film. 
         [0050]    Moreover, a conventional bulk type transistor was utilized here however the invention is not limited to this type of transistor, and Silicon-On-Insulator (SOI) type transistors may also be utilized. Also, if forming a stress film to control the stress on the channel sections then needless to say, a fin-shaped FET (FinFET) may also be utilized.