Patent Application
20070042510
Semiconductor wafers, flat panel displays, and other similar semiconductor structures typically have numerous material layers deposited thereon during device fabrication. Semiconductor processing typically includes a multi-step sequence of photographic and chemical processing steps during which electronic circuits are gradually created on a substrate. During these steps, numerous layers are deposited sequentially and/or etched to form the device. The layers are patterned to form the desired connections or features.
In a typical process, a light-sensitive material, such as photoresist, is first deposited on a layer to be patterned, such as a dielectric or conductive layer. Light is then selectively directed onto the photoresist film through a photomask, or reticle, to form desired photoresist patterns on the base material. The photoresist is then developed to transfer the pattern of the mask to the photoresist layer. Next, portions of the photoresist are removed to expose corresponding underlying portions of the previous layer. Additional processing steps, such as the deposition of another layer, implantation, or etching, can be performed using the pattern defined by the photoresist.
Each step in a semiconductor manufacturing process requires the setting of various operational parameters for the process tool. During manufacturing, it can be difficult to assess the progress of the process being performed. In particular, it is difficult to determine when an etching, deposition, or diffusion process has reached its endpoint. One method is to cease the process step and remove the wafer from the process tool in order to inspect the state of the wafer. However, the delay and possible damage caused to the wafer by this removal and inspection process is undesirable.
Accordingly, there is a need for an improved method of providing in situ monitoring and process control for semiconductor process tools.
Systems and methods are provided for monitoring a semiconductor processing step on a wafer. The changing optical properties of the wafer are monitored during processing to determine the progress of the processing step.
In accordance with embodiments of the present invention, a method of monitoring a semiconductor manufacturing process is provided, comprising: performing a semiconductor manufacturing process step on a wafer; directing light having a known wavelength at the wafer; monitoring a predetermined spectral range of light transmitted through a selected region of the wafer to detect an optical characteristic of the selected region; and based on the detected optical characteristic of the selected region, adjusting a process condition of the semiconductor manufacturing process step.
In accordance with other embodiments of the present invention, a semiconductor manufacturing system is provided, comprising: a process chamber for performing a semiconductor manufacturing process step on a wafer; a light source for directing light having a known wavelength at the wafer; an imaging device for detecting light transmitted from the light source through a selected region of the wafer; an image processor for analyzing an image signal from the imaging device corresponding to a predetermined spectral range of light to detect an optical characteristic of the selected region; and a controller for adjusting a process condition of the semiconductor manufacturing process step based on the detected optical characteristic of the selected region.
In accordance with other embodiments of the present invention, a method of monitoring a semiconductor manufacturing process is provided, comprising: performing a semiconductor manufacturing process step on a wafer; directing light having a known wavelength at a bottom side of the wafer; monitoring a predetermined spectral range of light transmitted through a selected region of the wafer to detect a transmissivity of the selected region; and based on the detected change in the transmissivity of the selected region, adjusting a process condition of the semiconductor manufacturing process step.
Other features and aspects of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the features in accordance with embodiments of the invention. The summary is not intended to limit the scope of the invention, which is defined solely by the claims attached hereto.
In the following description, reference is made to the accompanying drawings which illustrate several embodiments of the present invention. It is understood that other embodiments may be utilized and mechanical, compositional, structural, electrical, and operational changes may be made without departing from the spirit and scope of the present disclosure. The following detailed description is not to be taken in a limiting sense, and the scope of the embodiments of the present invention is defined only by the claims of the issued patent.
Some portions of the detailed description which follows are presented in terms of procedures, steps, logic blocks, processing, and other symbolic representations of operations on data bits that can be performed on computer memory. Each step may be performed by hardware, software, firmware, or combinations thereof.
In the illustrated embodiment, the system 100 includes a process chamber 110 having a housing 112 with an upper window 114 and a lower window 115. A plate or stage 116 is provided for supporting a substrate 120 within the chamber 110. Depending on the type of process tool, one or more inlet and outlet ports may be provided in the housing, including one or more exhaust ports 118, for expelling gases or vapor from the chamber 110, and one or more intake ports 119 for providing process gases to the interior of the chamber 110. A controller 150 is provided for controlling the operation of the process chamber 110. The types of operational parameters controlled by the controller 150 may vary depending on the application, but may include chamber temperature, light source, RF power, microwave power, gas flow, pressure, processing time, and the like.
In accordance with embodiments of the present invention, the system 100 includes a light source 122, an imaging device 130, and an image processor 132 for providing in situ process monitoring and control. This monitoring method utilizes the optical characteristics of different materials forming the various layers of a semiconductor device.
In particular, different materials have different optical properties based on the energy bandgap of the material. The bandgap is the energy difference between the top of the valence band and the bottom of the conduction band in insulators and semiconductors. The bandgap is the property that determines at which wavelength the material emits light or absorbs it. The material is transparent to electromagnetic energy having a wavelength below the emission wavelength of the material, and is opaque to energy having a wavelength above the emission wavelength.
For example, silicon is transparent to electromagnetic energy in the infrared (IR) portion of the spectrum but is opaque to photons in the visible portion of the spectrum. A compound semiconductor such as a III-V compound, gallium arsenide (GaAs), also forms a lattice with covalent bonding, also making GaAs transparent to infrared light, which is unable to break the electron bonds, and opaque to visible light, which can break bonds. Similarly, aluminum oxide (Al2O3) is transparent from around 180 nm in the ultraviolet (UV) spectral range to around 6 μm in the IR spectral range. Si3N4 and SiC are transparent to X-rays of particular wavelengths. The exact transmittance properties of a material are a function of the material's thickness and purity. Germanium also has a broad transparency band (up to 12 μm), but becomes opaque at elevated temperatures, depending on the thickness of the layer. Other examples of materials exhibiting transparency to certain wavelengths of light including gallium nitride (GaN), silica (SiO2), silicon nitride (SiN), quartz, silicon oxynitride (SiON), zinc selenide, zinc sulfide, spinel (MgAl2O4), and aluminum oxynitride (AlON).
Due to the varying optical characteristics (in particular, light transmissivity) of different materials used in semiconductor processing, it is possible to monitor the optical characteristics of a particular region in a substrate undergoing processing in order to determine the state of the wafer during processing.
The light source 122 directs light at the bottom of the wafer 300. The light source 122 may be configured to direct a broadband spectrum of light, or may be configured to direct a particular wavelength or narrow spectral range of light at the wafer 300. A waveguide, such as an optical fiber, may be provided for precisely directing the light to a desired region of the wafer 300. In this example, the light source 122 directs light in the IR spectral range at the bottom of the substrate 302 in a region corresponding to the metal layer 304.
An imaging device 130 is provided on the opposite side of the wafer 300 to detect the light from the light source 122 transmitted through the wafer 300. The imaging device 130 may comprise, e.g., a CCD camera. A filter 132 may be provided so that only IR light is detected by the imaging device 130, and that light from other sources (such as, e.g., energized plasma within the chamber 110) will be filtered out of the signal. Because the metal layer 304 is opaque to IR light, the IR light from the light source 122 cannot pass through the wafer 300. Therefore, as long as the metal layer 304 is present in the region being monitored by the imaging device 130, the IR light from the light source 122 will not be detected.
The monitoring and detection of the IR light from the light source 122 may occur at various times during the manufacturing process. In some embodiments, the manufacturing process may temporarily cease while the imaging device 130 attempts to detect the light from the light source 122. In other embodiments, the imaging device 130 may continuously monitor the wafer for the detection of the light from the light source 122 as the manufacturing process proceeds. An alignment mechanism may be provided for ensuring that the imaging device 130 is aligned with the light source 122, and that both the imaging device 130 and the light source 122 are positioned to monitor the desired region of the wafer.
In accordance with other embodiments, the system 100 may be used for process control. For example, the controller 150 may be provided with expected optical characteristic states for various points during the manufacturing process. If the imaging device 130 does not detect the expected optical characteristic at any point during the process, the controller 150 may adjust a process condition of the chamber 110. In the example above, if the IR light has not been detected within a predetermined amount of time after initiation of the etching process, the controller 150 may adjust one or more of the operational parameters of the chamber 110 in order to increase the speed of metal removal. In other cases, if the IR light is detected earlier than expected for multiple etching processes, one or more operational parameters of the chamber 110 may be adjusted for subsequent wafers in order to decrease etching speed.
In accordance with the embodiment described above, the image processor 132 monitors the signal from the imaging device 130 for detection of an expected wavelength of light. In other embodiments, the image processor 132 may process the signal in other ways. For example, the image processor 132 may analyze the signal to determine whether an expected intensity of light (either broadband or of limited spectral range) has been detected. Thus, the image processor 132 may be able to monitor the progress of the deposition, removal, or diffusion of a particular layer, based on the changing optical characteristics of the wafer as the deposition, removal, or diffusion proceeds. The observed change in the optical characteristics can be compared to expected optical characteristics in order to provide improved process control.
In yet other embodiments, the image processor 132 may analyze the signal to determine whether an expected image has been detected.
In yet other embodiments, other types of optical characteristics may be monitored. For example, interference patterns produced by the transmission of light through various structures having different optical characteristics may be analyzed. Each layer in the semiconductor wafer may be treated as a filter for a particular type of light. Therefore, the effect of the combination and arrangement of materials on light from the light source may be analyzed in order to determine the progress of a semiconductor processing step.
While the invention has been described in terms of particular embodiments and illustrative figures, those of ordinary skill in the art will recognize that the invention is not limited to the embodiments or figures described. For example, the embodiments described above provide examples for monitoring and process control of deposition and etching processes. In other embodiments, the semiconductor manufacturing process being monitored may vary. For example, the changing optical properties of the wafer during diffusion or oxidation steps may be monitored in order to provide endpoint detection and/or process control.
In addition, in the above-described embodiments, a single imaging device and a single light source are provided. In other embodiments, the multiple imaging devices (such as a CCD array) and/or multiple light sources may be used to monitor changing optical characteristics of different locations on the processed wafer.
In the embodiment illustrated in
In various embodiments, the region of the wafer being monitored may vary in size and location. In some embodiments, the region corresponds to a very small region of the wafer, such as, e.g., a 0.1 μm spot on the surface of the wafer. In other embodiments, the region may correspond to a very large region of the wafer, such as a 15 mm spot covering an entire die on the wafer or the entire sample area (e.g., the wafer or glass plate). In this case, the transmissivity being monitored corresponds to the overall transmissivity of the entire die region, rather than the transmissivity of a single device or layer. In yet other embodiments, the region being monitored may be a test region designed to provide a predetermined optical characteristic at one or more points during the manufacturing process.
The program logic described indicates certain events occurring in a certain order. Those of ordinary skill in the art will recognize that the ordering of certain programming steps or program flow may be modified without affecting the overall operation performed by the preferred embodiment logic, and such modifications are in accordance with the various embodiments of the invention. Additionally, certain of the steps may be performed concurrently in a parallel process when possible, as well as performed sequentially as described above.
Therefore, it should be understood that the invention can be practiced with modification and alteration within the spirit and scope of the appended claims. The description is not intended to be exhaustive or to limit the invention to the precise form disclosed. It should be understood that the invention can be practiced with modification and alteration and that the invention be limited only by the claims and the equivalents thereof.
