Abstract:
A method for reducing/eliminating plasma damage in semiconductor wafer ( 100 ) processing is introduced. The method is applicable to most semiconductor processes that involves the use of plasma, and does not affect process results other than reducing antenna damage. After exposing the wafer ( 100 ) to plasma excited gases ( 108 ), a cooling/idle step is added to allow the plasma to discharge prior to removing the wafer ( 100 ) from the process chamber ( 104 ).

Description:
FIELD OF THE INVENTION  
         [0001]    The invention is generally related to the field of semiconductor plasma processing and more specifically to eliminating antenna damage that can occur during semiconductor plasma processing.  
         BACKGROUND OF THE INVENTION  
         [0002]    Antenna damage is a quite common phenomena in semiconductor processes that involve a plasma. Examples of such processes include plasma enhanced chemical-vapor-deposition (PECVD), plasma etch, and high-density-plasma (HDP) processes. Antenna damages occurs when the charge collected in the antenna (e.g., a metal layer) stresses the oxide of a device. More specifically, in a MOSFET structure, the charge collected on the antenna stresses the gate oxide of the MOSFET, thereby inducing stress-related degradation of the MOSFET. This stress-related degradation may include: shortening the lifetime of the device, increasing the gate leakage of the device, or shifting the threshold voltage of the device.  
           [0003]    Engineering solutions were often needed to reduce/eliminate antenna damage. Generally, the solutions involve changing critical process parameters that are used during the manufacturing process. For example, some solutions involved reducing certain plasma power or the transition of plasma power during different process steps. These solutions are useful, but the changes normally affect the process results. Sometimes the result is undesirable and additional adjustments are then required to ensure an acceptable end result. Therefore, a method for reducing or eliminating plasma damage without upsetting critical process parameters is desired. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]    In the drawings:  
         [0005]    [0005]FIG. 1 is a cross-sectional diagram of a semiconductor body undergoing plasma treatment according to an embodiment of the invention;  
         [0006]    [0006]FIG. 2 is a graph of diode leakage induced by antenna damage for various wafer splits;  
         [0007]    [0007]FIG. 3 is a graph of diode leakage induced by antenna damage for various wafer splits including clamp and no clamp versions.  
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0008]    The inventors have discovered that, in many cases, antenna damage actually occurs after processing while the wafers are being moved out of the chamber. This is due to the fact that the process chamber is still full of residue charges from the plasma. Therefore, in the plasma process according to the invention, a wait step is added to allow the charges to dissipate before moving the wafers out of the chamber. The wafers may also be cooled down to increase resistance to antenna damage.  
         [0009]    An embodiment of the invention will now be described in conjunction with a PSG (phosphorus doped silicate glass) deposition process at a pre-metal dielectric (PMD) level. It will be apparent to those of ordinary skill in the art that the benefits of the invention may be applied to semiconductor plasma processes in general. Examples include, but are not limited to, PECVD processes, plasma etch processes, and HDP processes.  
         [0010]    Referring to FIG. 1, a semiconductor wafer  100  is processed through the formation of transistor  102 . The wafer  100  is then transferred to a process chamber  104 , for example a HDP chamber. The PMD  106  is deposited within the process chamber using a standard recipe that uses plasma excited reactant gas mixture  108 . For example, the following recipe may be used: high frequency RF power=3250W, low frequency RF power=3750W, PH 3 =64 sccm, SiH 4 =76 sccm, O 2 =235 sccm.  
         [0011]    After deposition, a cooling/idle step is added before moving the wafers. The duration of the cooling/idle is determined by the time it takes the plasma charges to discharge. For example, the duration may be in the range of 10-60 seconds. By allowing the plasma charges to be discharged, antenna damage is reduced or even eliminated.  
         [0012]    After the cooling/idle step, the wafer 100 is removed from the chamber  104  and processing continues as normal. The cooling/idle step is independent of the main process parameters and therefore does not affect the other process results (e.g., deposition rate, film properties, etc.).  
         [0013]    Test 1:Test wafers were split into four major groups to evaluate antenna damage. Group  1  consisted of a baseline PSG deposition using SACVD (sub-atmospheric chemical vapor deposition), a non-plasma process. Group  2  consisted of an HDP-PSG process in which wafers were removed from the process chamber immediately after PSG deposition. Group  3  consisted of an HDP-PSG process in which wafers were clamped after deposition for 30 seconds and then removed from the chamber. Clamping helped to cool the wafers to ˜300° C. Group 4 used a vendor best known process in which the wafers were removed from the chamber immediately after deposition. Within groups  2  and  3 , additional splits were made to examine the effect of plasma power (high frequency-HF vs. low frequency-LF) and the effect of having a thin undoped oxide liner before PSG deposition. See Table I for wafer splits.  
         [0014]    The results of test 1 are shown in FIG. 2. FIG. 2 shows that antenna damage level in groups  3  (wafer  11 - 14 ,  19 - 22 , clamped) is compatible to group  1  (wafers  1 - 6 , SACVD, non-plasma process). Group  2  (no clamp, wafers 7- 10   15 - 18 ) and group  4  (vendor BKM, wafers  23 - 24 ) showed substantial diode leakage induced by antenna damage. This showed the effectiveness of clamping to reduce antenna damage.  
                                                           TABLE I                           Wafer split table used in test 1.            Group   Sub-Group   Wafer   Description   Clamp                    1   1   1-6   SACVD PSG   N/A       2   2    7   Low LF, Low HF, no liner   No       2   3    8   Low LF, high HF, no liner   No       2   4    9   Low LF, low HF, with liner   No       2   5   10   Low LF, High HF, with liner   No       2   10   15   High LF, Low HF, no liner   No       2   11   16   High LF, high HF, no liner   No       2   12   17   High LF, low HF, with liner   No       2   13   18   High LF, High HF, with liner   No       3   6   11   Low LF, Low HF, no liner   Yes       3   7   12   Low LF, high HF, no liner   Yes       3   8   13   Low LF, low HF, with liner   Yes       3   9   14   Low LF, High HF, with liner   Yes       3   14   19   High LF, Low HF, no liner   Yes       3   15   20   High LF, high HF, no liner   Yes       3   16   21   High LF, low HF, with liner   Yes       3   17   22   High LF, High HF, with liner   Yes       4   18   23-24   Vendor BKM   No                  
 
         [0015]    Test 2: To determine if the reduction in antenna damage mentioned previously was due to clamping (which cools down the wafer to ˜300° C.), or simply due to the waiting that concurred during clamping, another test (test 2) was performed. Wafers were again split into four major groups. Group  1  consisted of a baseline PSG deposition using SACVD. Group  2  consisted of HDP-PSG processes in which wafers were clamped after deposition for different duration of time (10-40 second). Group  3  consisted of HDP-PSG processes in which wafers were left in the process chamber after deposition for different duration of time (30-90 second) without clamping. Group  4  used a vendor best known process in which the wafers were removed from the chamber immediately after deposition. See table II for split details.  
                                                           TABLE II                           Wafer split table in test 2.            Group   Sub-Group   Wafer   Description   Clamp                    1   1   1-6   SACVD PSG   N/A       2   2   7-8   30s clamp   Yes       2   3    9-10   40s clamp   Yes       2   4   11-12   30s clamp   Yes       2   5   13-14   20s clamp   Yes       2   6   15-16   10s clamp   Yes       3   7   17-18   30s wait   No       3   8   19-20   60s wait   No       3   9   21-22   90s wait   No       4   10   23-24   Vendor BKM   No                  
 
         [0016]    The results of test 2 are shown in FIG. 3. FIG. 3 shows that the antenna damage level in groups  3  (unclamped with 30-90 seconds waiting post process, wafers  17 - 22 ) is compatible to group  1  (SACVD, no plasma in deposition, wafers  1 - 6 ) and group  2  (clamp post process, wafer  7 - 16 ). Again, group  4  (vendor BKM, no clamp and no waiting, wafer  23 - 24 ) showed substantial diode leakage induced by antenna damage. This result demonstrated that a simple waiting period (without clamping) is also effective in reduce antenna damage.  
         [0017]    While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments.