Measurement implementation with host based data-feed-forward on current XPS toolset
Publication Date: 2013-Oct-11
The IP.com Prior Art Database
Disclosed is a calculation that expands the application space of X-Ray Photoelectron Spectroscopy (XPS) to the measurement of any film that is less than ~8nm thick, which satisfies the need of most Front End of Line (FEOL) processes. The method uses DFF to measure thickness beyond limitation pose by using substrate Si signal (from SOI or bulk Si) as reference and uses a test pad as reference to measure thickness to reduce tool-drift fluctuation.
Page 01 of 3
Measurement implementation with host based data -feed-forward on current XPS toolset
The current X-Ray Photoelectron Spectroscopy (XPS) inline metrology tool provides thickness measurement based on photoelectron attenuation through overlayers. Si photoelectron from the Si bulk wafer or Semiconductor on Insulator (SOI) is being used as a reference signal in current method. This poses a limitation on the application space of the inline XPS measurement, which is that it cannot be used to measure films or film stack that is thicker than 80A-100A, due to the fully attenuation of Si with thick overlayer. In addition, when the total thickness of the films on top of Si is greater than 80A, the accuracy of the measurement is highly compromised.
XPS measurement is sensitive to surface of film composition and is currently used for inline composition and film thickness control. Due to its limitation in sampling depth, it can only be used to measure thin films. For more complicated film stacks, optical measurements can be used for thickness; however, it is model driven and cannot provide accurate composition information for a wide range of films.
The novel method uses the elemental signal from previous steps using XPS measurement for measurement in later steps to determine thickness of the added layer. By measuring the attenuation of the signal from previous step, the thickness of the added layer can be measured; meanwhile, composition of the added layer can be achieved as well.
The method uses Data Feed Forward (DFF) to measure thickness beyond limitation pose by using substrate Si signal (from SOI or bulk Si) as reference and uses a test pad as reference to measure thickness to reduce tool-drift fluctuation.
With this new method, the approach migrated away from using Si as the reference. By measuring attenuation of the photoelectron signal from the previous layers before deposition of the current layer as a reference, thickness of the deposited film (current layer) can be more accurately measured. This method can be carried out in two ways.
The first approach is to measure the same wafer before and after the deposition. The pre measurement signal can be used as a reference, and compared with the post measureme...