Patent Description:
Evolution of the semiconductor manufacturing industry is placing ever greater demands on yield management and, in particular, on metrology and inspection systems. Critical dimensions are shrinking while wafer size is increasing. Economics is driving the industry to decrease the time for achieving high-yield, high-value production. Thus, minimizing the total time from detecting a yield problem to fixing it determines the return-on-investment for the semiconductor manufacturer.

Fabricating semiconductor devices, such as logic and memory devices, typically includes processing a semiconductor wafer using a large number of semiconductor fabrication processes to form various features and multiple levels of the semiconductor devices. For example, lithography is a semiconductor fabrication process that involves transferring a pattern from a reticle to a photoresist arranged on a semiconductor wafer. Additional examples of semiconductor fabrication processes include, but are not limited to, chemical-mechanical polishing (CMP), etch, deposition, and ion implantation. Multiple semiconductor devices may be fabricated in an arrangement on a single semiconductor wafer and then separated into individual semiconductor devices.

Repeater defects are a concern to semiconductor manufacturers. Repeater defects are those defects that appear on a wafer with some regular periodicity and that show some fixed relationship to the die layout on a reticle or stepping pattern on a wafer. The repeater defects are often programmed defects. Reticle defects are a common cause of repeater defects. Reticle defects that can cause repeater defects include, for example, extra chrome pattern on a mask plate, missing chrome on a mask plate, particulates on the mask plate or on the reticle, and damage to the pellicle.

An array mode algorithm and single die inspection have been used with laser-scanning inspection systems to perform repeater defect detection. Both techniques use information from a single die image in each inspection channel of the laser-scanning inspection system. As a result, sensitivity is limited by signal and noise within a single die image. Using statistics from a single die image is prone to nuisances.

<CIT> discloses systems and methods for detecting defects on a wafer.

<CIT> describes systems and methods for detecting defects on a wafer.

Therefore, an improved technique to detect repeater defects is needed.

In a first embodiment, a method as recited in claim <NUM> is provided.

In a second embodiment, a non-transitory computer readable medium as recited in claim <NUM> is provided.

In a third embodiment, a system as recited in claim <NUM> is provided.

Although claimed subject matter will be described in terms of certain embodiments, other embodiments, including embodiments that do not provide all of the benefits and features set forth herein, are also within the scope of this disclosure. Various structural, logical, process step, and electronic changes may be made without departing from the scope of the disclosure. Accordingly, the scope of the disclosure is defined only by reference to the appended claims.

Embodiments disclosed herein improve the sensitivity of a laser-scanning inspection system to repeater defects on a wafer. Incorporation of spatial correlation on multiple die images using, for example, a laser-scanning inspection system can improve inspection. Die fusion as disclosed herein shows particular usefulness during repeater defect inspection, such as with laser-scanning tools. Repeater defects are often programmed defects, detection of which is important to semiconductor manufacturers. Die fusion increases the sensitivity of laser-scanning inspection system to repeater defects and other programmed defects.

<FIG> is a flowchart of a method <NUM>. The method <NUM> can improve the sensitivity of a laser-scanning inspection system, broad-band plasma system, or other inspection system to repeater defects on dies of a wafer. Die fusion combines information from multiple dies within an inspection channel instead of relying on single die image as in existing methods. Image pixel information from multiple dies within a processing unit (job) in, for example, a laser-scanning inspection system is fused to exploit spatial correlation of defect signal on multiple die images. By virtue of the fusion operation, signal to noise ratio (SNR) of repeating defects increases, whereas SNR of non-repeating defects decreases.

At <NUM>, a plurality of die images are statistically fused to form a die-fused image using a controller. Each of the die images is of a different die. The die images may all be from a single wafer, though images of dies having a similar structure from different wafers also can be used. Statistically fusing the die images can include fusing signals or a SNR ratio. In an instance, pixel intensities from die images can directly be fused together. In another instance, pixel intensities can be first pre-processed using the statistics of an image background and then the preprocessed pixels from die images are fused.

The number of die images varies. Ten, die images are fused. Dies that are relatively far apart (e.g., more than five dies apart) can be quite different in terms of process variation and, consequently, fusing them may introduce mixing of unwanted process variation. Inspection systems may have limitations on how many die images can be acquired and used at the same time. For example, only three dies can be processed at a time on certain inspection systems.

Die images can be provided by any inspection system. For example, the die images can be formed using at least one of laser inspection (e.g., with a laser-scanning inspection system) and broad band plasma inspection.

The plurality of die images are provided by multiple inspection channels. The die-fused image can be formed by fusing images from a single inspection channel or from multiple inspection channels. In another instance, images of different dies using two different inspection channels are fused.

The die images used in image fusion are typically already registered. Incorrect registration may lead to errors during image fusion, so die images can be registered if necessary.

Some examples of image fusion that can be used include high pass filtering technique, intensity-hue-saturation (HIS) transform based image fusion, principal component analysis (PCA) based image fusion, wavelet transform image fusion, or pair-wise spatial frequency matching.

At <NUM>, a presence of a repeater defect in the die-fused image is detected using the controller. The detecting can use statistical image processing. For example, after die images are fused in any above mentioned approaches, a thresholding can be applied to fused image pixels to detect repeater defects. A set of constraints on fused pixel values and/or relative strengths of pixels values among die images also can be used to make the detection more robust.

To assist in the detection of repeater defects, a background can be subtracted using the controller and/or background noise can be scaled using the controller.

A threshold for fused image pixels can be set before or during detection of repeater defects. This threshold may be provided by a user.

<FIG> illustrates an example of image fusion which does not form part of the present invention. Three die images are disclosed. Repeater defects are generally spatially correlated in images of multiple dies inside a processing unit in a wafer inspection system, such as a laser-scanning inspection system. Die image <NUM>, <NUM>, and <NUM> each illustrate a repeater defect in the center (identified with an arrow). The defects can be consecutively placed on the wafer, but need not be consecutive. Repeater defects are difficult to detect due to the noise in each of the images. Therefore, it is possible that one of the repeater defects can be missed during defect detection. Besides a potential impact to yield caused by missing a repeater defect, it is possible that a repeater defect may not be correctly identified because the defect pattern across multiple dies may not be evident during defect detection.

Information from multiple die images <NUM>-<NUM> in the processing unit is statistically fused to form a die-fused image <NUM>. Statistical image processing then is used on the die-fused image <NUM> to detect defects and abnormalities. By virtue of fusion, a signal from the repeater defects will be amplified whereas signal from non-repeating nuisances will be diminished in the die-fused image. In one example, repeater defect signals improved from <NUM>% to <NUM>% relative to previous techniques. This maximizes all available image information about the repeater image and exploits the spatial correlation of the repeater defect signal on multiple dies.

Laser-scanning inspection systems and other inspection systems may have more than one imaging/inspection channel. Die fusion can be extended to fuse information in multiple die images from more than one inspection/imaging channels. <FIG> illustrates an exemplary image fusion using multiple inspection channels. Each inspection channel produces a die-fused image. The two die-fused images are then fused to form a die-channel fusion image.

Die images <NUM>-<NUM> come from a first inspection channel. These die images <NUM>-<NUM> are statistically fused to form a die-fused image <NUM>. This may be, for example, a bright field inspection channel.

Die images <NUM>-<NUM> come from a second inspection channel. These die images <NUM>-<NUM> are statistically fused to form a die-fused image <NUM>. This may be, for example, a dark field inspection channel.

While bright field and dark field inspection channels are used in this example, the first and second inspection channels also can be two bright field inspection channels or two dark field inspection channels from a laser-scanning inspection system.

Not part of the present invention. The die-fused image <NUM> and die-fused image <NUM> can be statistically fused to form the die-channel fusion image <NUM>.

In the example of <FIG>, the raw images have a SNR of <NUM>. The die-fused image <NUM> has a SNR of <NUM>. The die-channel fusion image has a SNR or <NUM>.

While the three images are illustrated as being fused together, this is not the case in the present invention in which ten images are fused.

<FIG> illustrates an exemplary wafer with resulting repeater defects identified. As seen in <FIG>, the repeater defects are on multiple dies across the wafer. Embodiments disclosed herein using multiple die images will improve the sensitivity of laser-scanning wafer inspection system or other inspection systems with respect to repeater defects while reducing the nuisance (non-repeating) signals.

The example of <FIG> shows <NUM> repeater defects on the wafer, which was part of a total defect count of <NUM>,<NUM>. Each repeater defect is illustrated as a dot on the wafer. A previous repeater defect analysis algorithm found <NUM> repeater defects as part of a total defect count of <NUM>,<NUM>. Thus, improved sensitivity at lower nuisance counts is provided using die fusion.

<FIG> is a block diagram of an embodiment of a system <NUM>. The system <NUM> includes a chuck <NUM> configured to hold a wafer <NUM> or other workpiece. The chuck <NUM> may be configured to move or rotate in one, two, or three axes. The chuck <NUM> also may be configured to spin, such as around the Z-axis.

The system <NUM> also includes a measurement system <NUM> configured to measure a surface of the wafer <NUM>. The measurement system <NUM> produces a beam of light, a beam of electrons, broad band plasma, or may use other techniques to measure a surface of the wafer <NUM>. In one example, the measurement system <NUM> includes a laser and the system <NUM> is a laser-scanning system. In another example, the system <NUM> is a broad-band plasma inspection tool. The measurement system <NUM> provide images of dies on the wafer <NUM> or can provide information used to form images of dies on the wafer <NUM>. The measurement system <NUM> includes at least two inspection channels, such as bright field and dark field inspection channels, two bright field inspection channels, or two dark field inspection channels.

The system <NUM> communicates with a controller <NUM>. For example, the controller <NUM> communicates with the measurement system <NUM> or other components of the system <NUM>. The controller <NUM> includes a processor <NUM>, an electronic data storage unit <NUM> in electronic communication with the processor <NUM>, and a communication port <NUM> in electronic communication with the processor <NUM>. It is to be appreciated that the controller <NUM> may be implemented in practice by any combination of hardware, software, and firmware. Also, its functions as described herein may be performed by one unit, or divided up among different components, each of which may be implemented in turn by any combination of hardware, software and firmware. Program code or instructions for the controller <NUM> to implement various methods and functions may be stored in controller readable storage media, such as a memory in the electronic data storage unit <NUM>, within the controller <NUM>, external to the controller <NUM>, or combinations thereof.

The controller <NUM> includes one or more processors <NUM> and one or more electronic data storage units <NUM>. Each processor <NUM> is in electronic communication with one or more of the electronic data storage units <NUM>. In an embodiment, the one or more processors <NUM> are communicatively coupled. In this regard, the one or more processors <NUM> receive readings received at the measurement system <NUM> and store the reading in the electronic data storage unit <NUM> of the controller <NUM>. The controller <NUM> may be part of the system itself or may be separate from the system (e.g., a standalone control unit or in a centralized quality control unit).

The controller <NUM> may be coupled to the components of the system <NUM> in any suitable manner (e.g., via one or more transmission media, which may include wired and/or wireless transmission media) such that the controller <NUM> can receive the output generated by the system <NUM>, such as output from the measurement system <NUM>. The controller <NUM> may be configured to perform a number of functions using the output. For instance, the controller <NUM> may be configured to perform an inspection of the wafer <NUM>. In another example, the controller <NUM> may be configured to send the output to an electronic data storage unit <NUM> or another storage medium without reviewing the output. The controller <NUM> may be further configured as described herein.

The controller <NUM>, other system(s), or other subsystem(s) described herein may take various forms, including a personal computer system, image computer, mainframe computer system, workstation, network appliance, internet appliance, or other device. In general, the term "controller" may be broadly defined to encompass any device having one or more processors that executes instructions from a memory medium. The subsystem(s) or system(s) may also include any suitable processor known in the art, such as a parallel processor. In addition, the subsystem(s) or system(s) may include a platform with high speed processing and software, either as a standalone or a networked tool.

If the system includes more than one subsystem, then the different subsystems may be coupled to each other such that images, data, information, instructions, etc. can be sent between the subsystems. For example, one subsystem may be coupled to additional subsystem(s) by any suitable transmission media, which may include any suitable wired and/or wireless transmission media known in the art. Two or more of such subsystems may also be effectively coupled by a shared computer-readable storage medium (not shown).

The system <NUM> may be part of a defect review system, an inspection system, a metrology system, or some other type of system. Thus, the embodiments disclosed herein describe some configurations that can be tailored in a number of manners for systems having different capabilities that are more or less suitable for different applications.

The controller <NUM> may be in electronic communication with the measurement system <NUM> or other components of the system <NUM>. The controller <NUM> may be configured according to any of the embodiments described herein. The controller <NUM> also may be configured to perform other functions or additional steps using the output of the measurement system <NUM> or using images or data from other sources.

An additional embodiment relates to a non-transitory computer-readable medium storing program instructions executable on a controller for performing a computer-implemented method defocus detection, as disclosed herein. In particular, as shown in <FIG>, the controller <NUM> can include a memory in the electronic data storage unit <NUM> or other electronic data storage medium with non-transitory computer-readable medium that includes program instructions executable on the controller <NUM>. The computer-implemented method includes any step(s) of any method(s) described herein. In an instance, the controller <NUM> statistically fuses a plurality of die images to form a die-fused image, wherein each of the die images is of a different die, and then detect a presence of a repeater defect in the die-fused image. The memory in the electronic data storage unit <NUM> or other electronic data storage medium may be a storage medium such as a magnetic or optical disk, a magnetic tape, or any other suitable non-transitory computer-readable medium known in the art.

The program instructions may be implemented in any of various ways, including procedure-based techniques, component-based techniques, and/or object-oriented techniques, among others. For example, the program instructions may be implemented using ActiveX controls, C++ objects, JavaBeans, Microsoft Foundation Classes (MFC), SSE (Streaming SIMD Extension), or other technologies or methodologies, as desired.

In another embodiment, the controller <NUM> may be communicatively coupled to any of the various components or sub-systems of system <NUM> in any manner known in the art. Moreover, the controller <NUM> may be configured to receive and/or acquire data or information from other systems (e.g., inspection results from an inspection system such as a review tool, a remote database including design data and the like) by a transmission medium that may include wired and/or wireless portions. In this manner, the transmission medium may serve as a data link between the controller <NUM> and other subsystems of the system <NUM> or systems external to system <NUM>.

In some embodiments, various steps, functions, and/or operations of system <NUM> and the methods disclosed herein are carried out by one or more of the following: electronic circuits, logic gates, multiplexers, programmable logic devices, ASICs, analog or digital controls/switches, microcontrollers, or computing systems. Program instructions implementing methods such as those described herein may be transmitted over or stored on carrier medium. The carrier medium may include a storage medium such as a read-only memory, a random access memory, a magnetic or optical disk, a non-volatile memory, a solid state memory, a magnetic tape and the like. A carrier medium may include a transmission medium such as a wire, cable, or wireless transmission link. For instance, the various steps described throughout the present disclosure may be carried out by a single controller <NUM> (or computer system) or, alternatively, multiple controllers <NUM> (or multiple computer systems). Moreover, different sub-systems of the system <NUM> may include one or more computing or logic systems. Therefore, the above description should not be interpreted as a limitation on the present disclosure but merely an illustration.

As used herein, the term "wafer" generally refers to substrates formed of a semiconductor or non-semiconductor material. Examples of such a semiconductor or non-semiconductor material include, but are not limited to, monocrystalline silicon, gallium nitride, gallium arsenide, indium phosphide, sapphire, and glass. Such substrates may be commonly found and/or processed in semiconductor fabrication facilities.

A wafer may include one or more layers formed upon a substrate. For example, such layers may include, but are not limited to, a photoresist, a dielectric material, a conductive material, and a semiconductive material. Many different types of such layers are known in the art, and the term wafer as used herein is intended to encompass a wafer including all types of such layers.

One or more layers formed on a wafer may be patterned or unpatterned. For example, a wafer may include a plurality of dies, each having repeatable patterned features or periodic structures. Formation and processing of such layers of material may ultimately result in completed devices. Many different types of devices may be formed on a wafer, and the term wafer as used herein is intended to encompass a wafer on which any type of device known in the art is being fabricated.

Other types of wafers also may be used. For example, the wafer may be used to manufacture LEDs, solar cells, magnetic discs, flat panels, or polished plates. Defects on other objects also may be classified using techniques and systems disclosed herein.

Claim 1:
A method (<NUM>) comprising:
statistically fusing a plurality of die images from a first inspection channel to form a first die-fused image using a controller, wherein each of the die images from the first inspection channel is of a different die (<NUM>), wherein the plurality of die images from the first inspection channel includes at least ten of the die images, and wherein each of the dies in the die images from the first inspection channel is less than five dies apart from each other of the dies in the die images from the first inspection channel;
statistically fusing a plurality of die images from a second inspection channel to form a second die-fused image using the controller, wherein each of the die images from the second inspection channel is of a different die, wherein the plurality of die images from the second inspection channel includes at least ten of the die images, wherein each of the dies in the die images from the second inspection channel is less than five dies apart from each other of the dies in the die images from the second inspection channel, and wherein a signal of a repeater defect is amplified in the first die-fused image compared to the first plurality of die images or in the second die-fused image compared to the second plurality of die images;
statistically fusing the first die-fused image and the second die-fused image to form a die-channel fusion image using the controller; and
detecting, using the controller, a presence of the repeater defect in the die-channel fusion image using statistical image processing (<NUM>).