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EP-3935371-B1 - METHOD AND SYSTEM FOR MONITORING DEPOSITION PROCESS

EP3935371B1EP 3935371 B1EP3935371 B1EP 3935371B1EP-3935371-B1

Inventors

  • POIS, Heath, A.
  • WARAD, Laxmi
  • RANGARAJAN, SRINIVASAN

Dates

Publication Date
20260506
Application Date
20200312

Claims (11)

  1. A method for monitoring deposition process, comprising: providing a sample (215) having an atomic layer deposition, ALD, layer of material deposited over a second layer of a SiO 2 material (105), the second layer having a pattern of metal therein; generating an X-ray beam and directing the X-ray beam towards the sample (215) to irradiate the sample (215); intercepting part of the X-ray beam with an X-ray detector (230) to generate an X-ray flux value; collecting electrons emitted from the sample (215) and separating the electrons according to electron energies; determining electron count for each of the electron energies; determining the presence of material of the ALD layer over the pattern of metal by using the X-ray flux value to normalize the electron count of electron energies corresponding to electrons emitted from the pattern of metal, and comparing resulting normalized electron count to reference electron count.
  2. The method of claim 1, wherein comparing resulting normalized electron count to reference electron count comprises obtaining a ratio of the resulting normalized electron count to reference electron count.
  3. The method of claim 1, further comprising determining the thickness of the ALD layer over the SiO 2 material (105) by using the X-ray flux value to normalize the electron count of electron energies corresponding to electrons emitted from the SiO 2 material (105), and applying a correction factor.
  4. The method of claim 1, wherein the correction factor comprises an effective attenuation length of photoelectrons emitted from the SiO 2 material (105) and traveling through the material of the ALD layer.
  5. The method of claim 1, wherein a first thickness of the ALD layer material deposited over the second layer and a second thickness of the ALD layer material deposited over the pattern are determined by: using the electron count for each of the electron energies to generate intensity values I 1 , I 2 and I 3 , corresponding to photo electrons emitted from the ALD layer material, the SiO 2 (105), and metal, respectively; calculating modeled intensities I' 1, I' 2 and I' 3 , corresponding to photo electrons emitted from the ALD layer material, the SiO 2 (105) and metal using iterative estimated thicknesses values for the first thickness and second thickness; minimizing difference between measured ratios of intensity values I 1 , I 2 and I 3 , and ratios of the modeled intensities I' 1, I' 2 and I' 3 , to thereby obtain true values of the first thickness and second thickness.
  6. The method of claim 5, further comprising expressing each of the intensity values I 1 , I 2 and I 3 , as a function of the modeled intensities I' 1, I' 2 and I' 3 , an associated atomic sensitivity factor of each of the ALD layer material, the SiO 2 (105) and the metal, and an effective attenuation length of photoelectron emitted from each of the ALD layer material, the SiO 2 (105) and the metal, and using values obtained from the minimizing step to obtain the first thickness and the second thickness.
  7. The method of claim 5, wherein the minimizing step comprises performing a regression on the difference between measured ratios and the ratios of modeled intensities.
  8. The method of claim 5, wherein the difference between measured ratios and the ratios of modeled intensities is expressed as: [(I' 1 /I' 2 ) - (I 1 /I 2 )] and [(I' 1 /I' 3 ) - (I 1 /I 3 )].
  9. The method of claim 5, wherein performing a regression comprises performing a non-linear regression to minimize the expression: I ′ 1 / I ′ 2 − I 1 / I 2 2 / I 1 / I 2 2 + I ′ 1 / I ′ 3 − I 1 / I 3 2 / I 1 / I 3 2
  10. The method of claim 1, wherein a first thickness of the ALD layer material deposited over the second layer and a second thickness of the ALD layer material deposited over the pattern are determined by: using the electron count for each of the electron energies to generate intensity values I 1 , I 2 and I 3 , corresponding to photo electrons emitted from the ALD layer material, the SiO 2 (105) and the metal, respectively; setting expected intensity I' 1 as corresponding to a sum of a first contribution of emission from thick part of the first layer deposited over SiO 2 (105) and correlated to the first thickness and second contribution of emission from a thin part of the first layer deposited over the metal and correlated to the second thickness, wherein a material constant of the ALD layer material and an effective attenuation length of the ALD layer material is applied to each of the first contribution and the second contribution; setting expected intensity I' 2 as corresponding to photo electrons emission from the second layer and passing through the first thickness and adjusted by a material constant of the SiO 2 (105) and an effective attenuation length of emission from the SiO 2 (105); setting expected intensity I' 3 as corresponding to photo electrons emission from the pattern and passing through the second thickness and adjusted by a material constant of the metal and an effective attenuation length of emission from the metal; using the intensity values I 1 , I 2 and I 3 and the expected I' 1 , I' 2 and I' 3 to obtain the first thickness and the second thickness.
  11. The method of claim 10, comprising: iteratively calculating the expected intensities I' 1 , I' 2 and I' 3 by using different estimated values for the first thickness and the second thickness; for each iteration determining a residual value between intensity values I 1 , I 2 and I 3 and the expected I' 1 , I' 2 and I' 3 ; setting the estimated value for the first thickness and the second thickness that generates the smallest residual value as true first thickness and second thickness.

Description

RELATED APPLICATIONS This application claims priority benefit from U.S. Provisional Application No. 62/817,492, filed on March 12, 2019. BACKGROUND 1. Field This disclosure relates generally to the field of process control and monitoring in the semiconductor fabrication field. The disclosed process control technique is particularly suitable for monitoring selective deposition processes. 2. Related Art For decades the semiconductor industry relied on photolithography to generate the patterning required for the chips' circuitry. Photolithography enabled depositing each layer over the entire wafer, and then patterning the layer to form the circuitry. In addition to adding many steps and cost to the chip fabrication process, current nano-scale features make photolithography incredibly difficult and, indeed, perhaps at some point impossible. Additionally, double and multi-patterning used to define nano-scale features (requiring two or more separate lithography and etch steps to define a single layer) may lead to unacceptable edge placement errors (EPE) and overlay misalignments. An emerging technique, called Selective Deposition, deposits each layer only at the areas of the designed circuitry, thus avoiding the need for photolithography patterning. One promising example of selective deposition is the use of Atomic Layer Deposition (ALD) to repeatedly form Self-Assembly Monolayers (SAM), wherein each monolayer is deposited only at the regions of the designed circuitry. A similar technique, Molecular Layer Deposition (MLD) is used for deposition of organic materials. Generally, the top surface of the substrate has a dielectric pattern, a metal pattern, and possibly a semiconductor pattern, and the next layer to be formed may be a metal layer over the metal pattern, a dielectric layer over the dielectric pattern, or a semiconductor over the semiconductor pattern. This may require area activation or area deactivation (passivation) prior to the next layer's formation. The ALD deposition using SAM with surface passivation may be a promising technique as it both avoids the photolithography step and uses the surface's chemistry to make the alignments, thus preventing EPE and overlay errors. Regardless of which technique is used, metrology and process control tools will be required in order to implement an integrated process with acceptable yield. However, to date no suitable metrology tools have been developed for process monitoring and qualification. The conventional tools used in the labs today for investigating these processes include Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and Tunneling Electron Microscopy (TEM). These tools are too slow to be employed in a production environment, and are incapable of providing real-time monitoring of the process, so as to indicate a drift or a failure of the process in a commercial fabrication setting. X-ray photoelectron spectroscopy (XPS) has been used to analyze surface chemistry of substrates. XPS spectra are obtained by irradiating the substrate with a beam of X-rays, while simultaneously measuring the kinetic energy and number of electrons that escape from the top layers of the substrate. Similarly, X-ray fluorescence (XRF) has been widely used for elemental and chemical analysis of samples, by sampling the emission of characteristic "secondary" (or fluorescent) X-rays from a material that has been excited by bombarding with high-energy X-rays or gamma rays. Such systems are, for example, disclosed in US 2013/077742 A1. 3. Problem to be Solved In order to enable selective deposition in commercial fabrication environment, a need exists in the art for process monitoring and control. The methodology should provide fast, direct, and non-destructive measurements of the quality of the process on the wafer, to enable analysis of process quality and detection of process drift. SUMMARY The following summary of the disclosure is included in order to provide a basic understanding of some aspects and features of the invention. This summary is not an extensive overview of the invention and as such it is not intended to particularly identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented below. Disclosed embodiments enable analyzing and monitoring deposition and/or passivation processes, especially in the context of selective deposition. The embodiments also enable quantifying the quality of the process and identifying process drifts or predicting required maintenance of the deposition equipment. As such, the embodiments enable the implementation of selective deposition in a commercial fabrication environment. In the disclosed embodiments, XPS measurements are used to analyze the thickness of layers formed during selective deposition. The measurements can be implemented during diff