Patent Application
20130293858
The semiconductor integrated circuit (IC) industry has experienced rapid growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. However, these advances have increased the complexity of processing and manufacturing ICs and, for these advances to be realized, similar developments in IC processing and manufacturing are needed. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component that can be created using a fabrication process) has decreased.
As semiconductor fabrication technology progresses from one generation to the next, it has become increasingly more difficult for conventional lithography processes to achieve good resolution for the shrinking IC patterns. For example, minimum pitch and line end spacing may become performance bottlenecks for conventional lithography processes.
Therefore, although existing lithography processes have been generally adequate for their intended purposes, they have not been entirely satisfactory in all respects.
Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.
It is understood that the following disclosure provides many different embodiments, or examples, for implementing different features of various embodiments. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.
As semiconductor feature sizes continue to shrink, it has become increasingly more difficult for lithography processes to achieve the necessary resolution. For example, referring to
As the scaling down process continues, conventional lithography processes may not be able to achieve satisfactory resolution for the patterns 110. For example, the minimum pitch 120 and/or the line end spacing 130 may not be satisfactorily imaged for conventional lithography processes. For example, some conventional lithography processes may yield an acceptable minimum pitch, but may fail to produce an acceptable line end spacing. Some other conventional lithography processes may yield an acceptable line end spacing, but may fail to produce an acceptable minimum pitch.
According to the various aspects of the present disclosure, a method and apparatus for performing an improved lithography process is disclosed. The improved lithography process of the present disclosure is capable of achieving both good minimum pitch performance and good line end spacing performance.
The photomask 200 also includes a plurality of patterns (or features) 210 disposed on or in the substrate 205. In some embodiments, the patterns 210 correspond to semiconductor device components of an Integrated Circuit (IC). In other words, the patterns 210 may be used in a lithography process to define images of semiconductor device components on a wafer. The patterns 210 may correspond to gate lines or metal lines, for example. In some embodiments, the patterns 210 include trenches or openings formed in the substrate 205. As an example, a fragmentary cross-sectional view of the photomask 200 is taken from point A to point A′ and shown in
Still referring to
According to various aspects of the present disclosure, each pattern 210 is shifted from adjacent patterns by different amounts in different directions, but a magnitude of an amount of phase shift between adjacent patterns is approximately the same in any given direction. For instance, each pattern is phase shifted from its adjacent features in the X-direction by a first amount, and each pattern is phase shifted from its adjacent features in the Y-direction by a second amount that is different from the first amount.
Using the embodiment shown in
Referring to
It is understood that the trench depths 230A-230D may be exaggerated in
The photomask 200 having the alternating phase shifts is advantageous in enhancing the resolution of a lithography process. In more detail, the spatial frequency is reduced, so that the +1st order beam and the −1st order beam that previously may not have been able to pass through a lens may now be capable of doing so. As discussed above, the amount of phase shift between adjacent patterns 210 in the X-direction is π (180 degree phase shift). Therefore, as long as the illumination is highly coherent—which means the poles on the aperture are sufficiently small—then the line end spacing issue discussed above with reference to
Meanwhile, the patterns 210 are also phase shifted in the Y-direction (albeit with a different amount than in the X-direction). Since every pattern 210 has a different phase than its adjacent patterns in the Y-direction, there are no phase-shift conflict issues, which may occur when two adjacent patterns share the same phase. However, as the amount of phase shift between adjacent patterns 210 in the Y-direction is smaller (π/2 or 90 degrees), it alone may or may not enhance the resolution enough to overcome the minimum pitch issue discussed above with reference to
According to various aspects of the present disclosure, an off-axis illumination (OAI) technique is also implemented to effectively increase the phase shift in the Y-direction, as discussed in more detail below.
The aperture 300 contains an opaque material. The aperture 300 also includes two poles 330 and 331. The poles 330-331 are openings formed in the opaque material so as to allow light to pass. The poles 330-331 are located on the Y-axis. The poles 330-331 may also take any one of a plurality of suitable shapes, not necessarily the shapes illustrated in
The dislocation of the poles 330-331 from the center of the aperture 300 allows for off-axis illumination. For example, light beams may be projected toward the photomask 200 at an angle, since the light beams will have to pass through the aperture 300 first. This is illustrated in
A light beam 420 passes through one of the poles 330-331 and is projected toward the photomask 200. Since the poles 330-331 are “off-axis,” the light beam 420 comes at the photomask 200 at an angle with respect to the axis Z. Thus, the lithography system employs a tilted illumination source. Such “tilted” illumination effectively contributes additional phase shift in the direction in which the poles 330-331 are aligned, which is the Y-direction in the embodiment illustrated.
In some embodiments, the size and location of the poles 330-331 on the aperture 300 are configured in a manner such that the off-axis illumination contributes an additional π/2 or 90 degrees of phase shift in the Y-direction to the patterns on the photomask 200. As discussed above, the phase shift in the Y-direction between adjacent patterns on the photomask 200 is π/2 or 90 degrees. The additional π/2 or 90 degrees of phase shift allows the total amount of phase shift between adjacent patterns in the Y-direction on the photomask 200 to be π or 180 degrees, which is desired. The π or 180 degrees of phase shift reduces the spatial frequency, which allows both the +1st order beam and the −1st order beam to be collected (in the Y-direction) by the lens 410, which enhances resolution in the Y-direction. As such, the combination of the off-axis illumination technique and the alternating phase shift (π/2 or 90 degrees) in the Y-direction results is utilized to resolve the minimum pitch issue discussed above with reference to
Therefore, the present disclosure involves an off-axis illumination phase shift mask (OPSM or OAIPSM) lithography technique. The OPSM lithography technique combines off-axis illumination and phase shifted masks to effectively resolve both the line end spacing and the minimum pitch issues.
It is understood that the aperture 300 discussed above is merely one of many embodiments of a suitable aperture that can be used in the off-axis illumination lithography system 400.
In the aperture 300A, two groups of poles are implemented. A first group of poles 460-463 is implemented along the Y-axis. The poles 460-463 are aligned along the Y-axis and are spaced apart from the center of the aperture 300A with distances less than the radius of the aperture 300A. A second group of poles 470-473 is implemented near various corner regions of the aperture 300A. The aperture 300A having multiple poles may improve the performance of the OPSM lithography of the present disclosure. Similarly, other suitable apertures having different number, size, location and arrangements of poles may be used to perform the OPSM lithography discussed above.
Each pattern 510 is also phase shifted from adjacent patterns by different amounts in the X and Y directions. In some embodiments, the phase shift between adjacent patterns 510 in the X-direction is π or 180 degrees, whereas the phase shift between adjacent patterns 510 in the Y-direction is π/2 or 90 degrees. Once again, an off-axis illumination method (utilizing the aperture 300 of
Each patterns 610 is also phase shifted from adjacent patterns by different amounts in the X and Y directions. In some embodiments, the phase shift between adjacent patterns 610 in the X-direction is π or 180 degrees, whereas the phase shift between adjacent patterns 610 in the Y-direction is π/2 or 90 degrees. Once again, an off-axis illumination method (utilizing the aperture 300 of
The method 700 includes a block 710, in which a patternable layer is formed over a wafer. The wafer may include a semiconductor substrate or a portion thereof, for example a silicon substrate that is doped with a P-type dopant such as boron. In other embodiments, the semiconductor substrate may be a silicon substrate doped with an N-type dopant such as arsenic or phosphorous. The substrate may also alternatively be made of some other suitable elementary semiconductor material, such as diamond or germanium; a suitable compound semiconductor, such as silicon carbide, indium arsenide, or indium phosphide; or a suitable alloy semiconductor, such as silicon germanium carbide, gallium arsenic phosphide, or gallium indium phosphide. Further, in some embodiments, the substrate could include an epitaxial layer (epi layer), may be strained for performance enhancement, and may include a silicon-on-insulator (SOI) structure. In various embodiments, the patternable layer may include a photoresist film.
The method 700 includes a block 720, in which an exposure process is performed to the patternable layer. The exposure process is performed at least in part using a phase shifted photomask. The phase shifted mask contains a plurality of patterns that are each phase shifted from adjacent patterns by different amounts in different directions. For example, the phase shifted mask may be the photomask 200 of
The method 700 includes a block 730, in which the patternable layer is patterned. The patterning of the patternable layer may include a post-exposure baking process, a developing process, a rinsing process, etc, so that the patterns of the photomask are transferred to the patternable layer (with different scales).
It is understood that other processes may be performed before, during, or after the blocks 710-730 to complete the lithography process of the method 700. However, for the sake of simplicity, these additional processes are not discussed herein.
The embodiments of the present disclosure offer advantages, it being understood that different embodiments may offer different advantages, and not all the advantages are discussed herein, and that no particular advantage is required for all embodiments.
One of the other advantages of certain embodiments of the present disclosure is that, critical patterns that the phase shifted photomasks discussed above may be used to enhance the resolution of a lithography process. For example, by implementing photomask patterns having phase shifts of about 180 degrees in the X-direction, the line end spacing problem associated with conventional lithography processes can be avoided. Furthermore, the photomask patterns in the Y-direction are also implemented with phase shifts, thereby preventing conflict issues. In addition, the smaller phase shift in the Y-direction is compensated by using an off-axis illumination method (wherein the poles are aligned in the Y-direction), so that the overall phase shift in the Y-direction can still approach 180 degrees. In this manner, the minimum pitch issue associated with conventional lithography processes can also be resolved.
In addition, the embodiments of the present disclosure are compatible with existing process flow and do not increase fabrication costs. Other advantages may exist, but they are not discussed herein for reasons of simplicity.
One of the broader forms of the present disclosure involves a photomask. The photomask includes: a substrate; and a plurality of patterns disposed on the substrate; wherein each pattern is phase shifted from adjacent patterns by different amounts in different directions.
In some embodiments, an amount of phase shift between adjacent patterns is approximately an integer multiple of π/2.
In some embodiments, a magnitude of an amount of phase shift between adjacent patterns is approximately the same in any given direction.
In some embodiments, a magnitude of a first amount of phase shift between adjacent patterns in a first direction is substantially greater than a magnitude of a second amount of phase shift between adjacent patterns in a second direction, the second direction being different from the first direction.
In some embodiments, each pattern is spaced apart from adjacent patterns in both a first direction and a second direction, the first and second directions being perpendicular to one another.
In some embodiments, each pattern is spaced apart from first adjacent patterns in one of a first direction and a second direction but is substantially abutted to second adjacent patterns in another one of the first direction and the second direction, the first and second directions being perpendicular to one another.
In some embodiments, each pattern is abutted to adjacent patterns in both a first direction and a second direction, the first and second directions being perpendicular to one another.
In some embodiments, at least some of the patterns are defined by trenches formed in the substrate; and a phase shift between adjacent patterns is defined as a trench depth difference between adjacent trenches.
Another one of the broader forms of the present disclosure involves a lithography system. The lithography system includes: a photomask that contains a plurality of features formed in a substrate; wherein: each feature has a first phase shift with respect to a first adjacent feature in a first direction; and each feature has a second phase shift with respect to a second adjacent feature in a second direction different from the first direction.
In some embodiments, a magnitude of the first phase shift is substantially equal to π; and a magnitude of the second phase shift is substantially equal to π/2.
In some embodiments, no feature shares a phase shifted edge with its adjacent features.
In some embodiments, each feature shares at least one phase shifted edge with its adjacent features.
In some embodiments, at least some of the features each include an opening formed in the substrate; and a phase shift between adjacent features is defined as a difference between heights of the respective openings of the adjacent features.
In some embodiments, the lithography system further includes an off-axis illumination apparatus disposed over the photomask.
In some embodiments, the off-axis illumination apparatus includes an aperture containing a non-centrally located pole, and wherein a distance from the pole to a center of the aperture is substantially less than a radius of the aperture.
Yet another one of the broader forms of the present disclosure involves a method of performing a lithography process. The method includes: forming a patternable layer over a wafer; performing an exposure process to the patternable layer, wherein the exposure process is performed at least in part through a phase shifted photomask, and wherein the phase shifted photomask contains a plurality of patterns that are each phase shifted from adjacent patterns by different amounts in different directions; and thereafter patterning the patternable layer.
In some embodiments, an amount of phase shift between adjacent patterns of the photomask is approximately an integer multiple of π/2.
In some embodiments, a magnitude of an amount of phase shift between adjacent patterns of the photomask is substantially the same in any given direction.
In some embodiments, the patterns of the phase shifted mask are bordering adjacent patterns in at least one direction.
In some embodiments, the exposure process is performed at in part through an off-axis illumination source.
The foregoing has outlined features of several embodiments so that those skilled in the art may better understand the detailed description that follows. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure.
