Patent Application
20060049036
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.
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.
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
Sputter Rate=B*IION*(VRF−C), (1)
where IION is the ion current measurement, and VRF 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.
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*IION*(Sqrt(VRF)−Sqrt(G)), (2)
where F and G are constants that may be similarly obtained using the steps described above for obtaining B and C.
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.
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.
