Abstract:
A method of forming a silicon dioxide layer in a process chamber is disclosed. The process comprises: flowing silane into the process chamber; flowing N 2 O into the process chamber; generating a RF signal at a first predetermined power at a first frequency; and generating a RF signal at a second predetermined power at a second frequency.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to semiconductor manufacturing processes, and more particularly, to a method for forming a silicon dioxide layer using silane in a plasma enhanced chemical vapor deposition (PECVD) process. 
     BACKGROUND OF THE INVENTION 
     Interlayer (ILD) and intermetal (IMD) dielectric layers are commonly used to isolate conducting structures, such as metal layers, from subsequently deposited conducting layers. The interlayer and intermetal dielectric layers are typically formed using some type of silicate glass, whether it be borophosphosilicate glass (BPSG), tetraethylorthosilicate (TEOS), spin-on-glass (SOG), or chemical vapor deposition (CVD) silicon oxide. These oxides are also used in a variety of other semiconductor applications, such as passivation layers, as diffusion and implantation masks, and as capping layers. Thus, the efficient formation of oxides is an important part of the semiconductor manufacturing process. 
     One of the more popular and useful types of oxide is silicon dioxide that is deposited using a plasma enhanced CVD process (PECVD). For example, the silicon dioxide may be deposited using a PECVD apparatus, such as the Centura machine manufactured by Applied Materials. The PECVD process is dependent upon many factors, including temperature, pressure, gas composition, gas flow rate, RF power density, frequency, and duty cycle. 
     By varying the parameters upon which the PECVD oxide is formed, the “quality” of the oxide can be varied. In particular, the refractive index (n) of the oxide is often used as an indicator of quality. Thermal oxide has a refractive index of 1.46. A value of n greater than 1.46 indicates a silicon rich film, while smaller values indicate a low density, porous film. Nevertheless, for the so-called “bulk oxide” layer of an intermetal dielectric, a value of n of about 1.46 is adequate and indeed preferred. The requirement of the refractive index in many IMD applications is 1.46±0.015 for the reason of (1) electrical performance, and (2) process integrity. This is because most photolithography processes (that will inevitably be performed after deposition of the bulk oxide layer) are optimized for an index of refraction of about 1.46. Thus, while for some applications, a high index of refraction is preferred, for bulk oxide applications, an index of refraction in the 1.46 range is preferred. 
     Another measure of the quality of a silicon dioxide film is its resistance to compressive strength. Typically, conventional CVD oxides can withstand a stress level of 1E+09 dynes/cm 2 . It is preferable that the oxide have a high resistance to stress to prevent cracking. Furthermore, because PECVD oxide is used in many applications, in addition to the quality of the oxide, the process and speed by which it is formed is of great concern to reduce manufacturing cost. Semiconductor processes are constantly being examined for ways to increase throughput. Thus, the present invention provides a method for forming a high quality PECVD oxide having greater throughput and efficiency over conventional PECVD processes. 
     SUMMARY OF THE INVENTION 
     A method of forming a silicon dioxide layer in a silane based plasma enhanced chemical vapor deposition process is disclosed. The process comprises: flowing silane into said process chamber; flowing N 2 O into said process chamber; generating a RF signal at a first predetermined power at a first frequency; and generating a RF signal at a second predetermined power at a second frequency. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawing, wherein: 
     FIG. 1 is a schematic diagram of a PECVD process chamber used to implement the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The throughput of an oxide deposition process is governed by three components: (1) robot transfer time (about 10%), (2) process deposition time (about 45%), and (3) chamber cleaning process time (about 45%). Portions (1) and (3) are generally fixed. Therefore, one way to increase throughput is by decreasing the process deposition time. In other words, the deposition rate of the silicon dioxide should be increased to increase throughput. The present invention discloses a method for increasing the deposition rate of silane based silicon dioxide. Indeed, as will be seen below, the deposition rate of the oxide compared to the prior art is increased by about 90%. This corresponds to an increase of 20% in the overall throughput rate of the process. 
     A conventional silane based PECVD process deposits silicon dioxide film using a single frequency plasma power, typically a high frequency 13.56 MHz RF generator. The present invention modifies this process by using a dual frequency plasma power. In other words, not only is high frequency power applied, but also low frequency plasma power is applied through a low frequency RF generator. 
     FIG. 1 shows a schematic diagram of a PECVD process chamber adapted for implementing the method of the present invention. The process chamber  101  includes a high frequency RF generator  109  and a low frequency RF generator  111 . Preferably, the high frequency RF generator  109  generates RF power at a frequency of greater than 10 MHz and more preferably 13.56 MHz. Preferably, the low frequency RF generator  11  generates RF power at a frequency of less than 1 MHz and more preferably 350 KHz. 
     The process chamber  101  includes a silane gas line  103  and a N 2 O line  105  that inputs into a gas mixing chamber  107  of the PECVD apparatus. Although not shown, from the gas mixing chamber  107 , the silane and N 2 O gases are routed to a “showerhead style” nozzle on the top of the process chamber  101 . Also, along the sides and bottom of the process chamber  101  are various RF power delivery devices  113  that take the input from the high frequency RF generator  109  and the low frequency RF generator  111  and applies it to the plasma in the process chamber  101 . Finally, a wafer support  115  is provided for holding a wafer  117  in the proper position. 
     In accordance with the present invention, in order to deposit a high quality silicon dioxide layer on a wafer, the wafer  117  is placed on the wafer support  115  and silane and N 2 O gas are flowed into the process chamber  101 . The high frequency RF generator  109  and the low frequency RF generator  111  are activated to generate a plasma in the process chamber  101 . This causes the deposition of silicon dioxide onto the wafer  117 . 
     Specifically, the following process parameters are preferred for forming the silicon dioxide in accordance with the present invention: 
     
       
         
               
               
               
               
               
             
           
               
                   
               
             
             
               
                   
                 Power - High 
                 Power - Low 
                   
                   
               
               
                   
                 Frequency 
                 Frequency 
                 SiH 4  (sccm) 
                 N 2 O (sccm) 
               
               
                   
               
               
                 Preferred 
                 435 watts 
                 250 watts 
                 200-230 
                 1800-2100 
               
               
                 Embodiment 
               
               
                   
               
             
          
         
       
     
     The process is performed preferably at a temperature of 400° C. and a pressure of about 2.5 Torr. More preferably, the flow rate of SiH 4  is 210 sccm and the flow rate of N 2 O is 2000 sccm. 
     Under the above flow rate, pressure, dual frequency plasma power, and temperature conditions, it has been found that the deposition rate of silicon dioxide is significantly increased. In fact, the following results have been experimentally found for the method of the present invention, a conventional single frequency approach, and a prior art dual frequency approach: 
     
       
         
               
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                 Dep. 
                   
                   
                   
                   
                 CMP 
               
               
                   
                 Rate 
                   
                   
                   
                 Through- 
                 Rate 
               
               
                   
                 (Ang/ 
                   
                 Index of 
                   
                 put 
                 (Ang/ 
               
               
                 Recipe 
                 min) 
                 U% 
                 Refrac. 
                 Stress 
                 (WPH) 
                 min) 
               
               
                   
               
             
             
               
                 Preferred 
                 17741 
                 0.66 
                 1.47 
                  195E + 09 
                 50 
                 3350 
               
               
                 Embodiment 
               
               
                 Single 
                  9127 
                 0.87 
                  1.473 
                  8.3E + 08 
                 41 
                 3610 
               
               
                 Frequency 
               
               
                 CVD Oxide 
               
               
                 Dual 
                 20567 
                 0.47 
                 1.50 
                 1.28E + 09 
               
               
                 Frequency 
               
               
                 PECVD 
               
               
                 Oxide 
               
               
                   
               
             
          
         
       
     
     Note that as compared to prior art methods, the present invention produces a bulk oxide layer that: (1) has an index of refraction preferred for bulk oxides, (2) is highly resistant to stress, and (3) can be deposited at a high rate. It is the combination of all three of these attributes that make the method of the present invention advantageous over the prior art. Additionally, the parameter U% is a measure of the uniformity of the deposition process. In this case, the uniformity of the present invention is 0.66%, which is well within normal process requirements. 
     While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.