The present invention relates generally to the fabrication of semiconductor devices, and more particularly to process control systems and methods for the fabrication of semiconductor devices.
Generally, semiconductor devices are used in a variety of electronic applications, such as computers, cellular phones, personal computing devices, and many other applications. Semiconductor devices are manufactured by depositing many different types of material layers over a semiconductor workpiece or wafer, and patterning the various material layers using lithography. The material layers typically comprise thin films of conductive, semiconductive, and insulating materials that are patterned and etched to form integrated circuits (ICs). There may be a plurality of transistors, memory devices, switches, conductive lines, diodes, capacitors, logic circuits, and other electronic components formed on a single die or chip, for example.
Optical photolithography involves projecting or transmitting light through a pattern made of optically opaque or translucent areas and optically clear or transparent areas on a mask or reticle onto a layer of photosensitive material disposed over a wafer. For many years in the semiconductor industry, optical lithography techniques such as contact printing, proximity printing, and projection printing have been used to pattern material layers of integrated circuits. Lens projection systems and transmission lithography masks are used for patterning, wherein light is passed through the lithography mask to impinge upon a semiconductor wafer or workpiece.
There is a trend in the semiconductor industry towards scaling down the size of intergrated circuits, in order to meet the demands of increased performance and smaller device size. As features of semiconductor devices become smaller, it becomes more difficult to pattern the various material layers because of diffraction and other effects that occur during the lithography process.
In particular, lithography techniques used to pattern the various material layers become challenging as device features shrink. The position of the die on the semiconductor wafer and other parameters can affect and alter the dimensions of the features of some die on the wafer, so that the features formed do not meet the target dimensions, for example, which reduces the yield. In some applications, for example, it is important that features have substantially the same dimensions across a semiconductor wafer for every die on the workpiece, for example.
Thus, what are needed in the art are improved process control methods and systems for the fabrication of semiconductor devices.
These and other problems are generally solved or circumvented, and technical advantages are generally achieved, by preferred embodiments of the present invention, which provide novel process control systems and methods for the manufacture of semiconductor devices. Embodiments of the present invention provide methods of forming features that have substantially the same dimensions for each die across a semiconductor workpiece.
In accordance with a preferred embodiment of the present invention, a process control method includes affecting a first semiconductor device using a first process, measuring an effect of the first process on the first semiconductor device, and affecting the first semiconductor device using at least one second process. The method includes measuring an effect of the at least one second process on the first semiconductor device, and feeding forward and feeding back the measured effect of the first process and the measured effect of the at least one second process on the first semiconductor device. The first process, the at least one second process, or both the first process and the at least one second process are altered based on the fed forward and fed back measured effects of the first process and the at least one second process. A second semiconductor device is affected using the altered first process and/or the altered at least one second process. The second semiconductor device has fewer wafer-to-wafer and die-to-die variations in critical dimensions of features than the first semiconductor device.
The foregoing has outlined rather broadly the features and technical advantages of embodiments of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of embodiments of the invention will be described hereinafter, which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.
For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the preferred embodiments and are not necessarily drawn to scale.
The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that embodiments of the present invention provide many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.
The present invention will be described with respect to preferred embodiments in a specific context, namely, process control systems and methods for patterning material layers of semiconductor devices by subtractive etch processes. Embodiments of the invention may also be applied, however, to other applications where material layers are patterned, such as damascene processes, wherein an insulating material is patterned, and a conductive material is deposited to fill the patterns in the insulating material, for example. Embodiments of the present invention may also be applied to deposition processes, chemical-mechanical polishing (CMP) processes, polishing processes, implantation processes, heating processes, reduction processes, cleaning processes, growth processes, treatment processes, or other processes used in the fabrication of semiconductor devices, as examples.
In the manufacturing of integrated microelectronic circuits, it is desirable to pattern certain features independently of the environment they are in on the workpiece, e.g., regardless of the region of the workpiece the features or die are located in. For example, generally, features with a predetermined target dimension should be manufactured as closely as possible to the target dimension, regardless of what the other surrounding features are, regardless of their position on the semiconductor wafer, and regardless of density of the features, as examples. However, achieving a target dimension for all die across a semiconductor wafer may be problematic and difficult to achieve.
Then the etch process 106 is performed, wherein the patterned layer of photoresist is used as a mask while the underlying material layer is etched away, e.g., using a reactive ion etch (RIE) etch process or other etch process. The layer of photoresist is then removed or stripped from the semiconductor wafer, and measurements are made of features formed in the material layer by measurement system 108. This second CD measurement is compared to the predetermined target dimension for CD, and the second measurement information is fed back to the etch process or tool 106, as shown at 112, so that adjustments may be made in the etch process 106 for the processing of subsequent semiconductor wafers to be processed.
A problem with the process control system 100 shown in
CMT2=(chip-chip)2+(wafer-wafer)2+(lot-lot)2 Equation1:
It is desirable in many semiconductor applications for certain features of all die across a surface of a semiconductor workpiece 122 to be the same size, e.g., the target CD, for the semiconductor devices to function correctly. For example, if the features 124 formed in the material layer comprise gates of transistors, the size of the features 124 affects the resistance, which affects the performance of the transistors. Typically, a particular gate length is desired in the manufacture of transistors. If the features or gates 124 are too small or large, devices (such as die 134d and 134e in
In some applications, e.g., for semiconductor devices having larger minimum feature sizes or CD, the process control system 100 shown in
However, the process control system 100 shown in
Furthermore, chip-to-chip variations are not addressed using the process control system 100 shown in
Thus, what are needed in the art are improved process control systems and methods for semiconductor device manufacturing, wherein chip-to-chip variations in CD may be accommodated for and eliminated, as well as wafer-to-wafer and lot-to-lot variations.
The first process 202 is performed on a semiconductor device. The information from the first CD measurement 204 after the first process 202 (e.g., shown at 203) is fed back to the first process 202, as shown at feedback loop 262. The first process 202 is preferably adjusted based on the measurement information. The information from the first CD measurement 204 is preferably also fed forward to the second process 206, as shown at feed-forward loop 270, and also to a comparator 260, as shown at feed-forward loop 272.
After the first CD measurement 204 (shown at 205), then the second process 206 is performed on the semiconductor device. After the second process 206 (shown at 207), then a second CD measurement 208 is taken. The information from the second CD measurement 208 is fed back to the second process 206, as shown at 266b. The information from the second CD measurement 208 is also fed forward to the comparator 260, as shown at 266a. The information from the first CD measurement 204 and the second CD measurement 208 are compared by the comparator 260, and the information is fed back to the first process 202, as shown at feedback loop 264.
The information from the plurality of feed-forward loops 270, 272, 266a and the plurality of feedback loops 262, 264, 266b is used to adjust parameters of the first process 202 and the second process 206. For example, if the first process 202 comprises a photolithography process, the information from feedback loops 262 and 264 is used to adjust the photolithography process to reduce CD variations from chip-to-chip, wafer-to-wafer, and lot-to-lot.
In one embodiment, for example, the first process 202, which may comprise a lithography process, may be changed for some die but not for other die on the semiconductor device in response to the information from feedback loops 262 and 264, for example. The lithography system 202 may comprise a stepper that is adapted to expose one or more die at a time, for example. The exposure dose or focus may be altered for die at different positions on a semiconductor wafer surface, to achieve the same target CD for all die across a semiconductor surface, for example.
Next, an embodiment of the present invention will be described, wherein the first process 202 comprises a lithography process, and wherein the second process 206 comprises an etch process, with reference to
A material layer 224 is deposited or formed over the workpiece 222 (e.g., in a previous deposition process, not shown). The material layer 224 may comprise an insulating material, a semiconductive material, a conductive material, or multiple layers or combinations thereof, as examples. In a preferred embodiment, the material layer 224 comprises a semiconductive material such as polysilicon, as an example. The material layer 224 may comprise a single layer of material or multiple layers of materials, for example. The material layer 224 may comprise a thickness of about 500 nm or less, although alternatively, the material layer 224 may comprise other dimensions, e.g., about 500 nm or greater, for example.
In some embodiments, the material layer 224 may comprise a semiconductive material that will be subtractively etched to form gates of transistors, for example. In this embodiment, preferably, a gate dielectric material (not shown) is formed over the workpiece 222 before the gate material 224 is deposited, for example. Alternatively, in other embodiments, the material layer 224 may comprise an insulating material that is patterned and later filled with a conductive material, e.g., in a damascene process.
After the material layer 224 is deposited, an optional anti-reflective coating (ARC) (not shown) may be deposited over the material layer 224. The ARC may comprise a thickness of about 200 nm or less, and more preferably comprises a thickness of about 90 nm in one embodiment, as an example, although alternatively, the ARC may also comprise other dimensions.
A layer of photosensitive material 226 is formed over the ARC, or over the material layer 224, if an ARC is not used, as shown in
The workpiece 222 is placed on a support, not shown. The workpiece 222 may be placed on a steppable stage of a lithography system, for example.
A lithography mask 216 is provided, as shown in
The lithography mask 216 is then used to pattern the layer of photosensitive material 226 on the semiconductor device 220 using light 218 or energy. The light 218 may be directed at the semiconductor device 220 using a lens system 214, for example. The layer of photosensitive material 226 is developed, and exposed regions or unexposed region (depending on if the layer of photosensitive material 226 comprises a positive or negative photoresist, for example) of the layer of photosensitive material 226 are removed, as shown in
The layer of photosensitive material 226 may alternatively be patterned using a projection lithography system 214 or other type of lithography system, such as an immersion lithography system, for example. The opaque material of the mask 216 comprises the pattern that will be transferred to the material layer 224 of the semiconductor device 220. For example, the lithography mask 216 may be patterned with a pattern for features having the critical dimension.
The semiconductor device 220 is placed in the chamber 232, and the layer of photosensitive material 226 is then used as a mask while the material layer 224 is patterned (e.g., exposed portions of the material 224 not protected by the layer of photosensitive material 226 are removed using an etch process), transferring the pattern of the layer of photosensitive material 226 to the material layer 224, as shown in
The layer of photosensitive material 226 is then stripped or removed, and the ARC is removed, as shown in
Note that the material layer 224 may include a hard mask disposed over a layer of material to be patterned, not shown. The hard mask may comprise an insulating material, such as SiO2, SixNy, combinations thereof, or other materials, for example. In some embodiments, for example, the layer of photosensitive material 226 may be patterned using the lithography mask, and then the layer of photosensitive material 226 is used to pattern the hard mask. The layer of photosensitive material 226 may then be removed, and the hard mask is used to pattern the material layer, for example. Or, alternatively, both the layer of photosensitive material 226 and the hard mask may be used to pattern the material layer 224, for example. The hard mask may be left remaining, or it may be removed, for example.
Referring again to
Next, the novel plurality of feed-forward loops 270, 272, 266a and the plurality of feedback loops 262, 264, 266b of the process control system 200 will be described further, in an embodiment wherein the first process 202 comprises a lithography process 202 performed in a lithography system and the second process 206 comprises an etch process 206 performed in an etch system. The feedback loop 262 provides correction of across-wafer 220 systematic variations due to the lithography process 202 of the lithography system, by changing the individual dose and/or focus for each image field of the lithography system or semiconductor device, according to the feedback loop 262 information. The feed-forward loop 270 provides correction of incoming wafer-to-wafer variations in the lithography system or lithography process 202 of the lithography system by tuning the etch process 206 parameters of the etch system. The feedback loop 264 provides correction of RIE chamber drift, an etch tool, and/or an etch process 206 from the etch system-related systematic variations in across-wafer CDs of the semiconductor device by changing the lithography process 202 conditions of the lithography system. The feedback loop 266b provides etch tool drift and CD distribution feedback to tune the etch process 206 of the etch system, e.g., by using multi-zone chuck temperatures or dual injection gases. Note that the feedback loop 262 from the first measurement process 204 to the lithography process 202 may also include an average dose feedback that does not indicate or quantify die-to-die and wafer-to-wafer variations, for example.
Thus, embodiments of the present invention achieve technical advantages by providing novel advanced process control schemes with multiple feed-forward and feedback loops to enable corrections for systematic variations in across-wafer CD distributions of lithography and etch processes (e.g., providing correction per image field) in order to reduce final CD variations across a wafer 220; in particular, chip-to-chip contribution to CD error budget. The complexity of the present process control scheme and frequency of corrections may depend on the frequency and amplitude of changes in CD distribution variation, for example. Embodiments of the present invention enable within-image-field corrections via utilization of exposure dose and/or exposure tilt corrections, as examples, to allow corrections for systematic final CD and CDs within individual exposure fields, for example.
Embodiments of the present invention are particularly advantageous and provide more flexibility with regard to CD adjustments via exposure focus and/or exposure tilt with relatively wider depth of focus (DOF) values when implemented in immersion lithography systems, for example. In an immersion lithography system, a fluid is disposed between the lithography mask and the semiconductor device during the lithography process, for example (not shown).
Embodiments of the present invention may be implemented in advanced process control (APC) systems and/or software, for example. Embodiments of the present invention may be implemented in hardware, software, or both hardware and software, for example.
Embodiments of the present invention may be implemented at an initial set-up of a process for a particular semiconductor device design. A single wafer or a few wafers may be processed using the process control system 200 shown in
The measurement of CD 204 and 208 may comprise sampling a predetermined number of features of each die across a semiconductor device, or alternatively may comprise testing each feature of all or some die across a semiconductor device in some applications, for example.
After the CD measurement 204 step, in some embodiments, if the CD measurement is determined to be excessively larger or smaller than the target CD dimension, the patterned layer of photosensitive material 226 (see
Some examples of embodiments of the present invention will next be described. First, an embodiment wherein there is slow drift of both across-wafer CD distribution and final CD average will be described. For several or all wafers of a first lot, first, scatterometric measurement of lithography and final CD CMT for all chips, or a selected number of chips, if information of expected across-wafer trends already known, is taken, e.g., using CD measurement processes 204 and 208, as shown in
Possible incorporations in the exemplary procedure mentioned above include a feed-forward correction (feed-forward loop 270) of average lithography CD of each wafer to an etch tool, in order to minimize wafer-to-wafer variations, and feed-forward of an average lithography CD of a “send ahead” wafer to correct across-wafer lithography CD distribution of following wafers. Note that it is possible in some embodiments that across-wafer CD variation trends of the lithography and etch processes may compensate each other, for example.
A second embodiment includes a scenario wherein there is slow drift of both across-wafer CD distribution and final CD average. For subsequent lots, first, feedback correction (e.g., feedback loop 262) is made of the lithography dose for individual die to minimize systematic across-wafer CD trends input from a previous lot, if required. Second, feedback correction (e.g., feedback loop 266b) is made to the etch tool to adjust tool parameters, such as flows in individual zones of multiple-zone gas distribution plates or temperatures in a multi-zone electrostatic chuck (ESC), in order to reduce radial non-uniformities in the etch process, for example. Third, scatterometric measurement 208 of final CD CMT is made for every wafer or for a defined number of wafers in a lot. This information may be fed forward to the next lot for adjustment of RIE trim conditions in the event that the CD average shifts. Fourth, verification is made of the stability of distribution of minimized across-wafer differences of final CD vs. target CD. If a statistically significant deviation to the previous lot (e.g., defined by a trigger criterion or trend over time) is observed, then the execution of the first step (feedback loop 262) is repeated with the next lot.
A third embodiment includes a scenario wherein there is slow drift of both across-wafer CD distribution and a final CD average and RIE process with less trim. First, correction of exposure doses of individual die to minimize systematic across-wafer variations is made, if required. Second, feedback to the lithography tool is made, if required, e.g., feedback loop 262. Third, a feed-forward is made of final CDs to the next lot for adjustment of RIE trim conditions. Fourth, a verification of stability of remaining final across-wafer CD variations is made, and fifth, the first step (correction of exposure doses) is repeated for the next lot, if needed.
In a fourth embodiment, there may be slow drift of across-wafer CD distribution and a fast drift of final CD average. In this embodiment, first, correction of exposure doses of individual die to minimize systematic across-wafer variations is made, if required (feedback loop 262). Second, lithography CD measurements (204) are made on every wafer for feed-forward correction to the etch tool, in order to minimize lithography wafer-to-wafer, if a benefit is expected (feed-forward loop 270). Third, final CD measurements are made on every wafer for feedback to the etch tool, in order to minimize impact of drifts in etch conditions, e.g., to reduce wafer-to-wafer final CD variation (feedback loop 266b). Fourth, verification of stability of remaining final across-wafer variations may be made, and fifth, the first step above made be repeated for the next lot, if needed.
In a fifth embodiment, there may be fast drift of both across-wafer CD distribution and of final CD average. In this embodiment, first, for every lot, correction of exposure doses of individual die is made, in order to minimize systematic across-wafer variations, or at least make corrections in shorter intervals. Second, lithography CD measurements are made on every wafer for feed-forward correction to the etch tool, in order to minimize lithography wafer-to-wafer variations. Third, final CD measurements 208 are made on every wafer for feedback to the etch tool for the next wafer, in order to minimize drifts in the etch conditions, e.g., wafer-to-wafer final CD variation. Fourth, verification is made of the stability of remaining final across-wafer variations, and fifth, the first step may be repeated for the next lot, if needed.
Thus, one or more feed back loops 262, 266b, 264, and one or more feed-forward loops 270, 272, 266a may be implemented and utilized selectively in accordance with embodiments of the invention.
Advantages of embodiments of the present invention include benefits not only for minimization of wafer-to-wafer (W2W) and lot-to-lot (R2R) CD variation, but also for minimization of die-to-die (C2C) variations, as well. A higher integrated level integrated metrology module (IMM) and more universal advanced process controls for CD are achieved by embodiments of the present invention.
The novel embodiments of the present invention may be implemented in semiconductor processing in any two or more interactive processes where the systematic variation induced by such interactions or variations introduced by one process can be minimized. Embodiments of the present invention may be implemented in software that enables the feedback and feed-forward calculations described herein. The calculations may be made in the subroutines of existing tools, or in new tools implemented specifically to implement embodiments of the present invention described herein, for example.
Referring again to
For example, in some applications where a material layer 224 will be patterned to form gates of transistors, a trim etch process may be used that trims the gate lengths (typically the smallest dimension in an x or y direction of a transistor gate from a top view of a semiconductor wafer) by about 30 nm to 40 nm. The trim portion of the etch process is typically adjusted by adding more of particular gases, such as 02, to the etch process, or by adjusting the pressure, as examples. During a trim etch process having a high trim amount, the etch component tends to outweigh the deposition component, for example.
Note that only two processes 202 and 206 are shown in
Embodiments of the present invention are described herein with reference to optical lithography systems and masks, and may be implemented in lithography systems that utilize ultraviolet (UV) or extreme UV (EUV) light, as examples. The novel process control systems and methods described herein may also be used in non-optical lithography systems, x-ray lithography systems, interference lithography systems, short wavelength lithography systems, Scattering with Angular Limitation in Projection Electron-beam Lithography (SCALPEL) systems, and immersion lithography systems, or other lithography systems that utilize lithography masks or direct patterning, as examples.
The features 224 described herein may comprise transistor gates, conductive lines, vias, capacitor plates, and other features, as examples. Embodiments of the present invention may be used to pattern features 224 of memory devices, logic circuitry, and/or power circuitry, as examples, although other types of ICs may also be fabricated using the novel patterning methods and mask sets described herein.
Advantages of embodiments of the invention include providing novel methods of patterning features in a material layer, wherein the features comprise the same critical dimension across a surface of a workpiece, regardless of the region of the workpiece the features are formed in. Thus, circuits and devices on each die across a surface of a semiconductor wafer advantageously comprise substantially the same performance characteristics, such as speed, resistance, current, voltage, and other parameters, as examples. Increased process control and increased semiconductor device yields are achieved by the embodiments of the present invention described herein.
The process control systems and methods described herein produce semiconductor wafers wherein critical dimensions of die across a wafer surface are maintained within acceptable, tight tolerances. The process control systems and methods may be implemented periodically or continuously, to maintain CD control in the fabrication of semiconductor devices, for example.
Although embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. For example, it will be readily understood by those skilled in the art that many of the features, functions, processes, and materials described herein may be varied while remaining within the scope of the present invention. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.