Patent Application
20090318061
The present disclosure is directed to mechanical and/or chemical mechanical planarization of microelectronic workpieces.
Mechanical and chemical-mechanical planarizing processes (collectively “CMP”) remove material from the surface of workpieces. These workpieces can include wafers or other microelectronic substrates in the production of microelectronic devices and other products. One goal of CMP processing is to consistently and accurately produce a uniformly planar surface on the workpiece to enable precise fabrication of circuits and photo-patterns. During the construction of transistors, contacts, interconnects and other microelectronic features, many workpieces develop large “step heights” that create highly topographic surfaces. Such highly topographical surfaces can impair the accuracy of subsequent photolithographic procedures and other processes that are necessary for forming sub-micron features. For example, it is difficult to accurately focus photo patterns within tight tolerances on topographic surfaces because sub-micron photolithographic equipment generally has a very limited depth of field. Thus, CMP processes are often used to transform a topographical surface into a highly uniform, planar surface at various stages of manufacturing microelectronic devices on a substrate.
To create a planar surface on a workpiece, a CMP system typically includes a workpiece carrier that presses the workpiece against a rotating planarizing pad. A slurry, such as an abrasive slurry, is also typically used to facilitate the planarization and material removal from the surface of the workpiece. During the planarizing process, however, many different factors can affect the planarization or material removal rate. Such factors include, for example, variances in the distribution and size of abrasive particles in the slurry, topographical areas with different densities of features across the workpiece, the velocity of the relative movement between the workpiece and the planarizing pad, the pressure with which the workpiece is pressed against the planarizing pad, the condition of the planarizing pad, etc.
Various embodiments of planarizing systems and methods of using a planarizing pad to planarize, polish, or otherwise remove material from a surface of a microelectronic workpiece are described below. Certain details are set forth in the following description to provide a thorough understanding of various embodiments of the disclosure. Other details describing well-known structures and components often associated with CMP systems and processes are not set forth below, however, to avoid unnecessarily obscuring the description of the various embodiments of the disclosure. The term “surface” can encompass planar and nonplanar surfaces, either with or without patterned and nonpatterned features of a microelectronic workpiece. Such a workpiece can include one or more conductive and/or nonconductive layers (e.g., metallic, semiconductive, and/or dielectric materials) that are situated upon or within one another. These conductive and/or nonconductive layers can also contain a myriad of electrical elements, mechanical elements, and/or systems of such elements in the conductive and/or nonconductive layers (e.g., an integrated circuit, a memory, a processor, a microelectromechanical system (MEMS), etc.). Other embodiments of planarizing systems or methods of workpiece planarization in addition to or in lieu of the embodiments described in this section may have several additional features or may not include many of the features shown and described below with reference to
The planarizing pad 140 also includes an optically transmissive pad window 142 extending therethrough. In the illustrated embodiment and as described in detail below, the pad window 142 has an annular or other suitable ring-like shape that corresponds, at least in part, to the shape of the platen window 122. The pad 140 is carried on the platen 120 such that the pad window 142 is at least generally aligned with the platen window 122. In one embodiment, the pad window 142 can be an insert embedded in the planarizing medium 141 and/or adhered to the planarizing medium 141 with an adhesive. The insert can extend completely through the body of the planarizing medium 141 from the planarizing surface 146 to a backside surface 147. Suitable materials for the optically transmissive window include polyester (e.g., optically transmissive Mylar®), polycarbonate (e.g., Lexan®), fluoropolymers (e.g., Teflon®), glass, and/or other optically transmissive materials that are suitable for contacting a surface of a workpiece 110 during a planarizing process. In other embodiments, the pad window 142 can be integrally formed in the pad 140. For example, the pad 140 can be formed from a polymeric material and the pad window 142 can be a segment of the pad 140 that is cured at a different rate than the remainder of the pad 140 to achieve the optically transmissive properties of the pad window 142. Moreover, in certain embodiments, the planarizing pad 140 can include more than one pad window 142. For example, in one embodiment the planarizing pad 140 can include several spaced-apart pad windows 142 arranged at least generally concentrically with respect to the rotational axis of the planarizing pad 140. In embodiments including multiple pad windows 142, the platen 120 can also include multiple platen windows 122 generally aligned with the corresponding pad windows 142.
The planarizing system 100 also includes a carrier assembly 130 having a head or workpiece holder 132 operably coupled to a drive mechanism 136. The workpiece holder 132 holds the microelectronic workpiece 110 and can press and/or move the workpiece 110 against the planarizing surface 146 of the planarizing pad 140 during processing.
The planarizing system 100 further includes a control system 150 having an optical monitor 160 and a computer 180. In the illustrated embodiment, the optical monitor 160 includes a light source 162 (e.g., a laser, LED, broad spectrum, etc.) that generates source light 164 (represented by upward pointing arrow), and a sensor 166 having a photo cell to receive reflected light 168 (represented by downward pointing arrow) from the workpiece 110. The light source 162 is configured to direct the source light 164 through the platen window 122 and the pad window 142 so that the source light 164 impinges a front surface of the microelectronic workpiece 110 during a planarizing cycle. In one embodiment, the light source 162 generates a continuous exposure of source light 164 and the sensor 166 is configured to continuously receive the reflected light 168 from the front surface of the workpiece 110. In other embodiments, however, the light source 162 can generate intermittent source light 164 (e.g., strobe, pulse, or flashing type of light, etc.) toward the workpiece 110. In the illustrated embodiment, the optical monitor 160 is retained in a generally stationary position beneath the platen 120 and planarizing pad 140. Other embodiments, however, can include a movable optical monitor or multiple optical monitors. Moreover, in certain embodiments, the optical monitor 160 can have one or more light sources that emit radiation at discrete bandwidths in the infrared spectrum, ultraviolet spectrum, visible spectrum, and/or other radiation spectrums. The terms “optical” and “light,” therefore, are not limited to the visual spectrum for the purposes of the present disclosure.
The computer 180 is coupled to the optical monitor 160 to activate the light source 162 and/or to receive a signal from the sensor 166 corresponding to characteristics (e.g., intensity, color, etc.) of the reflected light 168. The computer 180 can include a database 182 containing a plurality of sets of reference characteristics corresponding to the status of a layer of material on the workpiece 110. The computer 180 can also contain a computer-readable program 184 that causes the computer 180 to control parameters of the planarizing system 100 according to feedback from the sensor 166. For example, when the measured characteristics of the reflected light 168 correspond to a selected set of the reference characteristics in the database 182, the computer-readable program can cause the planarizing system 100 to increase or decrease the planarizing speed, pressure, time, etc.
Referring to
In this manner, the sensor 166 can continuously measure characteristics of the reflected light 168, which can vary during the planarizing cycle as the face of the workpiece 110 changes throughout the planarizing cycle. A typical workpiece 110, for example, includes several layers of materials (e.g., silicon dioxide, silicon nitride, aluminum, etc.), and each material type can have distinct reflectance properties. For example, the color properties of a surface on a workpiece are a function of the individual colors of the layers of materials on the workpiece, the transparency and refraction properties of the layers, the interfaces between the layers, the thickness of the layers, etc. As such, when the surface of the workpiece 110 changes, the characteristics of the reflected light 168 can change accordingly. As the sensor 166 continuously detects the characteristics of the reflected light 168, the computer 180 receives the corresponding data regarding the characteristics of the workpiece. The computer 180 is therefore able to continuously evaluate the surface condition of the workpiece 110 to adjust parameters of the planarizing process and/or end the planarizing process in response to the uninterrupted detection of the reflected light 168.
The continuous detection of the surface characteristics of the workpiece 110 during at least one complete rotational cycle of the planarizing pad 160 differs from the detection of a conventional CMP system, because the optical monitoring of conventional planarizing processes is limited by the platen rotation speed. In a conventional CMP system, for example, a light source is typically carried by the platen and rotates with the platen beneath a workpiece. In this type of system, a conventional planarizing pad includes a small window in the pad that is aligned with the light source that does not circumscribe a full ring within the pad. As a result, the small window exposes the workpiece to the light source during only an arc of a revolution of the platen. In this manner, the sampling frequency of the light source is limited by the rotational speed of the platen. In another type of conventional CMP system, the light source may remain stationary beneath the planarizing pad and the workpiece, and the planarizing pad includes one or more separate windows arranged in a line or a portion of an arc to expose the workpiece to the light source. Although multiple windows may increase the number of measurements, the rotational speed of the platen still limits the sampling frequency.
In contrast to conventional CMP systems, embodiments of the planarizing system 100 with the continuous ring-like window 142 provide continual access for the optical monitor 160 to the workpiece 110 throughout a complete revolution of the platen 120. Uninterrupted data collection can provide for more precise adjustments to processing parameters (e.g., zone pressures, polishing speed and time, pad condition, etc.) resulting in better control of the workpiece polishing. The continuous monitoring also provides consistent planarization results because real-time adjustments can be made at anytime throughout the rotational position of the platen 120. The continuous data collection can also accurately endpoint a planarizing cycle without significantly increasing the processing time for each workpiece. For example, it is generally desirable to maximize the throughput of CMP processing by producing a planar surface on a workpiece as quickly as possible. The throughput of CMP processing is a function, at least in part, of the polishing rate of the workpiece and the ability to accurately stop CMP processing at a desired endpoint. The ability to continuously monitor the surface condition of the workpiece throughout the entire revolution of the platen 120 can therefore enhance the accuracy of determining the endpoint of a planarizing cycle.
In the first position 261a, the optical monitor 260 is positioned generally beneath the center portion of the workpiece 110, and in the second position 261b the optical monitor 260 is positioned beneath a peripheral edge portion of the workpiece 110. As the optical monitor 260 moves between positions 261, it can continuously assess the surface characteristics across an entire radial segment of the surface of the workpiece 110. For example, when the workpiece 110 is rotating in the direction indicated by the arrow 111 and the optical monitor 160 moves between the first position 161a and the second position 161b, the optical monitor 160 can assess all of the surface characteristics of the workpiece 110 ranging from the center portion to the outer periphery portion of the workpiece 110.
In the operation of the embodiment illustrated in
According to another feature of the embodiment illustrated in
The process further includes continuously exposing the surface of the workpiece to the light source through the optically transmissive portion throughout at least one complete revolution of the planarizing pad (block 540). This stage of the method can further include directing the light toward the workpiece and detecting light reflected from the workpiece through the optically transmissive planarizing pad while the workpiece is held face-down in a chuck throughout at least one complete revolution of the platen. The optical monitor can also include a sensor to detect the reflected light. In one embodiment, the optical monitor can be located in a stationary position with reference to the planarizing pad to direct the light toward the workpiece and detect the reflected light from the workpiece. In other embodiments, however, the optical monitor can oscillate between positions generally aligned with the optically transmissive portion to monitor the entire surface of the workpiece. For example, the optical monitor can move between a first position corresponding to a center portion of the workpiece and a second position corresponding to a periphery edge portion of the workpiece. In still further embodiments, multiple optical sensors can be used to continuously monitor the entire surface of the workpiece. The method can further include controlling one or more processing parameters (e.g., processing time, pressure, rotational speed, etc.) in response to the continuously detected reflected light.
The process illustrated in
From the foregoing, it will be appreciated that specific embodiments of the disclosure have been described herein for purposes of illustration, but well-known structures and functions have not been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments of the disclosure. Where the context permits, singular or plural terms may also include the plural or singular term, respectively. Moreover, unless the word “or” is expressly limited to mean only a single item exclusive from the other items in reference to a list of two or more items, then the use of “or” in such a list is to be interpreted as including (a) any single item in the list, (b) all of the items in the list, or (c) any combination of the items in the list. Additionally, the term “comprising” is inclusive and is used throughout to mean including at least the recited feature(s) such that any greater number of the same feature and/or additional types of other features are not precluded. It will also be appreciated that specific embodiments of the disclosure have been described herein for purposes of illustration, but that various modifications may be made without deviating from the inventions. For example, many of the elements of one embodiment can be combined with other embodiments in addition to, or in lieu of, the elements of the other embodiments. Furthermore, although the illustrated embodiments generally describe CMP processing in the context of rotationally planarizing the surface of a microelectronic workpiece, other non-illustrated embodiments can employ CMP processing for other purposes such as for polishing. Accordingly, the disclosure is not limited except as by the appended claims.
