Chamber having process monitoring window

Details Chamber having process monitoring window Chamber having process monitoring window

2000-07-05

2004-03-30

Lund, Jeffrie R. (Department: 1763)

Adhesive bonding and miscellaneous chemical manufacture

Differential fluid etching apparatus

With measuring, sensing, detection or process control means

C156S345250, C156S345280, C156S345410, C156S345430, C156S345480, C118S713000, C118S712000, C118S7230AN, C118S7230ER, C118S7230AN

Reexamination Certificate

active

06712927

ABSTRACT:

BACKGROUND
The present invention relates to a process chamber and process monitoring window.
In integrated circuit fabrication, layers of semiconductor, dielectric, and conductor materials, such as for example, polysilicon, silicon dioxide, aluminum and copper layers are deposited on a substrate and subsequently processed, for example, by etching with an etchant plasma, to form active devices. The layers are deposited on the substrate in a process chamber by processes such as chemical vapor deposition (CVD), physical vapor deposition (PVD), thermal oxidation, ion implantation and ion diffusion. After deposition, a resist layer of photoresist or hard mask is applied on the deposited layer and patterned by photolithography. Portions of the deposited layers lying between the resist features are etched using RF or microwave energized halogen and other reactive gases to form etched features.
In these fabrication processes, it is often desirable to monitor in-situ the process being performed on the substrate by a process monitoring system. For example, in CVD and PVD processes, it is desirable to stop the deposition process after a desired thickness of a layer is deposited. In etching processes, endpoint detection methods are used to prevent overetching of layers that are being etched. Typical process monitoring methods, include for example, plasma emission analysis, ellipsometry, and interferometry. In plasma emission analysis, an emission spectra of a plasma is measured to determine a change in chemical composition that corresponds to a change in the layer being processed, as for example, taught in U.S. Pat. No. 4,328,068 which is incorporated herein by reference. In ellipsometry, a polarized light beam is reflected off a layer on the substrate and analyzed to determine a phase shift and a change in magnitude of the reflected light that occurs with changes in the thickness of the layer, as for example disclosed in U.S. Pat. Nos. 3,874,797 and 3,824,017, both of which are incorporated herein by reference. In interferometry, a non-polarized light beam is reflected off the layer and analyzed to determine a change in magnitude of the reflected light that occurs due to interference of reflected light components from the top and bottom surfaces of the layer on the substrate, as for example, described in U.S. Pat. No. 4,953,982, issued Sep. 4, 1990, which is incorporated herein by reference. These process monitoring methods require a high strength optical transmission signal through the window and also require viewing or signal sampling of relatively large surface area of the substrate.
A typical process monitoring system comprises an optical sensor system for detecting and measuring light emissions or light reflections through a window in a wall of the process chamber. The window is transparent to particular light wavelengths to allow light to be transmitted in and out of the chamber while maintaining a vacuum seal with the chamber. When monitoring a layer on a substrate, the transparent window is positioned in the chamber wall in direct line of sight of the substrate. Process monitoring windows are typically constructed from quartz which is resistant to high temperatures and are sealed to the chamber surface with O-ring seals positioned along their edges.
However, in many deposition and etching processes, a thin cloudy film of residue deposits and byproducts are deposited on the process monitoring window as substrates are being processed in the chamber. The process residues are deposited on the window at rates often in excess of 1 micron in 25 to 50 hours of process operation. The deposited film of process residue changes the properties or intensity of the light transmissions passing through the window. For example, in plasma emission analysis, the residue deposits selectively filter out particular wavelengths of light from the optical emission spectra of the plasma resulting in errors in process monitoring measurements. In ellipsometry, the residue deposits change the state of polarization of the light beam transmitted or reflected through the window causing erroneous ellipsometric measurements. As another example, in interferometry, the deposits absorb and lower the intensity of the light passing through the window resulting in a lower signal-to-noise ratio.
To avoid these problems, conventional processing monitoring windows are periodically replaced or cleaned to remove the residue deposits formed on the windows. For example, in typical etching processes, after etching a certain number of wafers, or operating cumulatively for about 10 hours, the chamber is opened to the atmosphere and cleaned in a “wet-cleaning” process, in which an operator uses an acid or solvent to scrub off and dissolve the deposits accumulated on the window and chamber walls. After cleaning, the chamber is pumped down for 2 to 3 hours to outgas volatile acid or solvent species, and a series of etching runs are performed on dummy wafers. In the competitive semiconductor industry, the downtime of the chamber during such cleaning processes can substantially reduce process throughput and increase processing costs per substrate. Also, manually performed wet cleaning processes are often hazardous, and the quality of cleaning varies from one session to another.
One approach to solving the residue deposition problem uses a recessed window positioned in a long tube that opens into the chamber. Because the process gas or plasma in the chamber has to travel through the length of the tube before reaching the recessed window, the deposition of process residues on the surface of the recessed window inside the tube is markedly reduced. However, the high aspect ratio (length/diameter) of the elongated tube makes it difficult to monitor a sufficiently large sampling area inside the chamber, and reduces the total light flux. This limits the accuracy of the process monitoring systems during processing of a batch of substrates or sometimes even for a single substrate. In addition, the elongated tube takes up a large amount of space outside the chamber, which is undesirable in tight clean room spaces, and the tube is also difficult to fit in-between other components of the process chamber.
In another solution, the process monitoring window is selectively heated to prevent deposition of process residue deposits, as described in commonly assigned U.S. Pat. No. 5,129,994, to Ebbing et al., issued on Jul. 14, 1992. However, while suitable for certain types of processes, heating does not prevent all forms of residues from condensing and depositing on the window, and in certain processes, heating can actually increase the rate of deposition of process residue on the window.
In yet another approach, photosensitive equipment is used to sample signals of the light emissions or reflections from the chamber/substrate and mathematically manipulate the sampled data to increase the signal to noise ratio of the light signal passing through a cloudy window, as for example, described in U.S. Pat. No. 5,738,756 to Liu, issued on Apr. 14, 1998. However, complex mathematical manipulations can delay process response times. In etching processes, even a small time delay can result in undesirable charging or lattice damage of the underlying layers, especially for underlying polysilicon layers. In addition, these processes are not always able to increase the signal to noise ratio by a sufficient amount to provide a discernible signal. If the signal is too small, the fabrication process may never be terminated, and if it is too large, the process may be prematurely terminated.
The process residues deposited on windows are a particular problem when monitoring etching processes in which etching of a thick overlayer has to be stopped before etching through a relatively thin underlayer. For example, the aggressive halogen containing gases etchant gases that are used to etch a relatively thick layer will often uncontrollably etch through or damage any thin underlayers, without an accurate and reliable process monitoring system. This is especially a problem when

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