Abstract:
A method comprises measuring an RF voltage and ion current at a wafer during a plasma-enhanced deposition process, determining a sputter rate in response to the RF voltage and ion current measurements, detecting an abnormal condition in response to one of the RF voltage and ion current measurements, and sputter rate, and taking a corrective action in response to detecting an abnormal condition.

Description:
BACKGROUND  
       [0001]     Deposition processes are widely used in semiconductor fabrication to form various device features such as shallow trench isolation (STI), inter-layer dielectrics (ILD), and inter-metal dielectrics (IMD). In particular, high density plasma (HDP) enhanced chemical vapor deposition (CVD) uses a reactive chemical gas along with physical ion generation by using a radio frequency (RF) generated plasma to enhance film deposition. Because deposition is a function of sputtering, it is desirable to monitor the sputter rate in order to determine whether the deposition process is progressing normally. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0002]     Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.  
         [0003]      FIG. 1  is a schematic diagram of an embodiment of apparatus for controlling and monitoring deposition processes;  
         [0004]      FIG. 2  is a schematic diagram of a circuit model of the plasma sheath near an RF-biased electrode in the plasma chamber; and  
         [0005]      FIG. 3  is a simplified flowchart of an embodiment of a process of monitoring the deposition process.  
     
    
     DETAILED DESCRIPTION  
       [0006]      FIG. 1  is a schematic diagram of an embodiment of apparatus  10  for controlling and monitoring deposition processes. A wafer  11  is mounted on an electrostatic chuck  12  and placed inside a deposition chamber  13 . Deposition chamber  13  may include a dielectric dome  14 . Ion plasma  15  is generated in the chamber  13  by radio frequency (RF) fields supplied by top and side RF coils  16 . Each coil  16  has its own RF power supply  19  as well as an RF matching network  17 . The RF power supply  19  may comprise a controller operable to modulate the power output of the RF power supply  19 . The RF matching network  17  is used to deliver the right amount of power to the coils  16  for plasma generation. The chuck is also RF-biased by an RF power supply  21  and an RF matching network  22 . The RF power supply  20  may comprise a controller operable to modulate the power output of the RF power supply  20 . A voltage/current (V/I) probe  24  is coupled between the chuck  12  and the RF matching network  22 . An out put of the V/I probe  24  is further coupled to a microprocessor  25  or another suitable controller.  
         [0007]     The V/I probe  24  is operable to measure, in-situ, the ion current and RF voltage on the wafer  11  during deposition. Using a plasma sheath model described in Edelberg et al.,  Modeling of the Sheath and the Energy Distribution of Ions Bombarding RF - Biased Substrates in High Density Plasma Reactors and Comparison to Experimental Measurements , Vol. 86, No. 9, Journal of Applied Physics, Nov. 1, 1999, the measured data may be used to estimate the ion current on the wafer  11 . Edleberg et al. describes a circuit-equivalent  30  of this plasma sheath model, which is shown in  FIG. 2 . The plasma  15  is separated from the wafer  11  by a plasma sheath or envelope represented schematically as a capacitor  32 , a current source  33 , and a diode  34  coupled in parallel. The current though the diode  34 , I e , represents the variation of the electron current as a function of the sheath potential drop. The current source  33 , I i , represents the current due to ions that enter the sheath from the plasma-sheath boundary at the Bohm velocity. The current across the capacitor  32 , I d , is the capacitive displacement current across the sheath. A capacitor  36  coupled between the devices representing the sheath and the RF power supply  20  represents the capacitance encountered between the wafer  11  and chuck  12  and the power supply  20 .  
         [0008]      FIG. 3  is a simplified flowchart of an embodiment of a process  40  of performing real-time monitoring and controlling of the deposition process. In block  42 , a deposition process using a control wafer is monitored and RF voltage and ion current measurements are obtained by the V/I probe  24  during the deposition process. Using these voltage and current measurements, and a sputter rate obtained after the deposition process by measuring the deposited film characteristics such as its thickness, constants B and C in the following equation may be calculated: 
 Sputter Rate= B*I   ION *( V   RF   −C ),  (1)  
 where I ION  is the ion current measurement, and V RF  is the RF voltage measurement. Therefore, constants B and C for the particular equipment, equipment setup, deposition parameters, and other properties are computed in block  44 . A modification of these properties may require that steps  42  and  44  be repeated for the new conditions. The ion current and RF voltage may be measured during the control wafer run to establish a range of expected values for these measurements. 
 
         [0009]     Thereafter during each wafer production run, the RF voltage and ion current measurements are obtained in real-time during deposition, as shown in block  46 . In block  48 , these measurements may be provided to an algorithm executing in microprocessor  25  to compute the sputter rate using Equation (1). The current and voltage measurements may be obtained one or more times during each deposition of a device feature on the wafer. Alternatively, the current and voltage measurements and the computation of the sputter rate may be performed for selected runs, such as every other wafer, every five wafers, etc. or even randomly performed. Equation (1) may also be expressed as: 
 
Sputter Rate= F*I   ION *(Sqrt( V   RF )−Sqrt( G )),  (2) 
 
 where F and G are constants that may be similarly obtained using the steps described above for obtaining B and C. 
 
         [0010]     An abnormal condition during the deposition process may be detected by one or more of the measured ion current, RF voltage, and computed sputter rate deviating from the expected values in block  50 . Upon detecting an abnormal condition as exemplified by the ion current, RF voltage or sputter rate, corrective action(s) may be performed in block  52 . Such corrective action(s) may include reducing or increasing the power output of the power supplies  19  or  20 , or halting the deposition runs, for example. The determination of what corrective action to perform upon detecting the abnormal conditions may be made by a human operator or a computer algorithm.  
         [0011]     Although embodiments of the present disclosure have been described in detail, those skilled in the art should understand that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure. Accordingly, all such changes, substitutions and alterations are intended to be included within the scope of the present disclosure as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures.