Patent Application
20060134917
The present invention relates to the formation of semiconductor devices.
During semiconductor wafer processing, features of the semiconductor device are defined in the wafer using well-known patterning and etching processes. In these processes, a photoresist (PR) material is deposited on the wafer and then is exposed to light filtered by a reticle. The reticle is generally a glass plate that is patterned with exemplary feature geometries that block light from propagating through the reticle.
After passing through the reticle, the light contacts the surface of the photoresist material. The light changes the chemical composition of the photoresist material such that a developer can remove a portion of the photoresist material. In the case of positive photoresist materials, the exposed regions are removed, and in the case of negative photoresist materials, the unexposed regions are removed. Thereafter, the wafer is etched to remove the underlying material from the areas that are no longer protected by the photoresist material, and thereby define the desired features in the wafer.
Various generations of photoresist are known. Deep ultra violet (DUV) photoresist is exposed by 248 nm light. To facilitate understanding, FIG. 1A is a schematic cross-sectional view of a layer 108 over a substrate 104, with a patterned photoresist layer 112, over an ARL (Anti-reflective layer) 110 over the layer 108 to be etched forming a stack 100. The photoresist pattern has a critical dimension (CD), which may be the width 116 of the smallest feature. Presently, for 248 nm photoresist a typical CD for the photoresist may be 230-250 nm using conventional processes. Due to optical properties dependent on wavelength, photoresist exposed by longer wavelength light has larger theoretical minimal critical dimensions.
A feature 120 may then be etched through the photoresist pattern, as shown in
In order to provide features with smaller CD, features formed using shorter wavelength light are being pursued. 193 nm photoresist is exposed by 193 nm light. Using phase shift reticles and other technology, a 90-100 nm CD photoresist pattern may be formed, using 193 nm photoresist. This would be able to provide a feature with a CD of 90-100 nm. 157 nm photoresist is exposed by 157 nm light. Using phase shift reticles and other technology sub 90 nm CD photoresist patterns may be formed. This would be able to provide a feature with a sub 90 nm CD.
The use of shorter wavelength photoresists may provide additional problems over photoresists using longer wavelengths. To obtain CD's close to the theoretical limit the lithography apparatus should be more precise, which would require more expensive lithography equipment. Presently 193 nm photoresist and 157 nm photoresist may not have selectivities as high as longer wavelength photoresists and may more easily deform under plasma etch conditions.
In the etching of conductive layers, such as in the formation of memory devices, it is desirable to increase device density without diminishing performance.
To achieve the foregoing and in accordance with the purpose of the present invention a method for forming features in an etch layer in an etch stack with an etch mask over the etch layer, wherein the etch mask has etch mask features with sidewalls, where the etch mask features have a first critical dimension, is provided. A cyclical critical dimension reduction is performed to form deposition layer features with a second critical dimension, which is less than the first critical dimension. Each cycle, comprises a depositing phase for depositing a deposition layer over the exposed surfaces, including the vertical sidewalls, of the etch mask features and an etching phase for etching back the deposition layer leaving a selective deposition on the vertical sidewalls. Features are etched into the etch layer, wherein the etch layer features have a third critical dimension, which is less than the first critical dimension.
In another embodiment of the invention a method for forming a feature in an etch layer is provided. An etch stack with an etch layer is placed into an etch chamber, wherein an etch mask with etch mask features with sidewalls is over the etch layer, where the etch mask features have a first critical dimension. For at least two cycles a cyclical critical dimension reduction is performed to form deposition layer features with a second critical dimension, which is less than the first critical dimension, within the etch chamber. Each cycle comprises a depositing phase for depositing a deposition layer over the sidewalls of the etch mask features and an etching phase for etching back the deposition layer. Features are etched into the etch layer within the etch chamber, wherein the etch layer features have a third critical dimension, which is less than the first critical dimension.
In another embodiment of the invention, an apparatus for forming a features in an etch layer is provided, where the layer is supported by a substrate and where the etch layer is covered by an etch mask with mask features with a first CD. A plasma processing chamber comprises a chamber wall forming a plasma processing chamber enclosure, a substrate support for supporting a substrate within the plasma processing chamber enclosure, a pressure regulator for regulating the pressure in the plasma processing chamber enclosure, at least one electrode for providing power to the plasma processing chamber enclosure for sustaining a plasma, a gas inlet for providing gas into the plasma processing chamber enclosure, and a gas outlet for exhausting gas from the plasma processing chamber enclosure. A gas source is in fluid connection with the gas inlet. A controller is controllably connected to the gas source and the at least one electrode and comprises at least one processor and computer readable media. The computer readable media comprises computer readable code for providing for at least five cycles a cyclical critical dimension reduction process to form deposition layer features with a second critical dimension, computer readable code for providing a flow of an etchant gas to the plasma processing chamber after completion of the at least five cycles of the cyclical critical dimension reduction process, and computer readable code for etching features in the etch layer, using the etchant gas wherein the features in the layer have a third critical dimension. The computer readable code for providing for at least five cycles a cyclical critical dimension reduction process to form deposition layer features with a second critical dimension, comprises computer readable code for providing a flow of a deposition gas to the plasma processing chamber enclosure, computer readable code for stopping the flow of the deposition gas to the plasma processing chamber enclosure, computer readable code for providing a flow of an etch phase gas to the plasma processing chamber enclosure after the flow of the first deposition gas is stopped, and computer readable code for stopping the flow of the etch phase gas to the plasma processing chamber enclosure.
These and other features of the present invention will be described in more detail below in the detailed description of the invention and in conjunction with the following figures.
The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:
FIGS. 1A-B are schematic cross-sectional views of a stack etched according to the prior art.
FIGS. 3A-D are schematic cross-sectional views of a stack processed according to an embodiment of the invention.
FIGS. 4A-F are schematic cross-sectional views of a stack processed according to an example of the invention.
FIGS. 6A-B illustrate a computer system, which is suitable for implementing a controller used in embodiments of the present invention.
The present invention will now be described in detail with reference to a few preferred embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present invention.
The invention provides features with small critical dimensions (CD). More specifically, the invention provides a features with CD's that are less than the CD of the patterned mask used to etch the feature.
To facilitate understanding,
A cyclical critical dimension reduction is performed to reduced the CD (step 208). The cyclical critical reduction process comprises at least two steps of depositing a layer over the sidewalls of the etch mask feature 314 (step 209) and then etching back the deposition layer (step 210).
Preferably, the reduced CD 324 of the deposition layer feature 322 is at least 10% less than the CD 316 of the mask feature (i.e. not greater than 90% of the CD 316 of the mask feature). More preferably, the reduced CD 324 of the deposition layer feature 322 is at least 20% less than the CD 316 of the mask feature (i.e. not greater than 80% of the CD 316 of the mask feature). Most preferably, the reduced CD 324 of the deposition layer feature 322 is at least 30% less than the CD 316 of the mask feature (i.e. not greater than 70% of the CD 316 of the mask feature). For example, the deposition layer feature may have a reduced CD 316 that is 99% less than the CD 316 of the mask feature. It is also desirable that the deposition layer feature 322 has substantially vertical sidewalls 328, which are highly conformal as shown. An example of a substantially vertical sidewall is a sidewall that from bottom to top makes an angle of between 88° to 90° with the bottom of the feature. Conformal sidewalls have a deposition layer that has substantially the same thickness from the top to the bottom of the feature. Non-conformal sidewalls may form a faceting or a bread-loafing formation, which provide non-substantially vertical sidewalls. Tapered sidewalls (from the faceting formation) or bread-loafing sidewalls may increase the deposition layer CD and provide a poor etching mask. Preferably, the deposition on the side wall is thicker than the deposition on the bottom of the mask feature. More preferably, no layer is deposited over the bottom of the mask feature.
In some embodiments of the invention, none of the deposition layer is on top of the etch mask. In other embodiments, part of the deposition layer is formed over the top of the etch mask.
Features are then etched into the layer to be etched 308 through the deposition layer features 322 (step 212).
Due to the nature of a vapor phase deposition method, formation of a conformal layer 320 is always difficult since deposition rate invariably favors the top portion of the profile because of the line of sight leading to formation of a bread-loaf shape of the deposition layer and in the extreme a pinch-off at the profile top. Methods used to obtain a more vertical profile, such as a thermal “re-flow” post deposition, often lead to other undesirable side-effects.
One advantage of the inventive process is that a non-vertical deposition profile can be made more vertical by the subsequent anisotropic etch step. Another advantage of the inventive process is that deposition layers may be added and etch back resulting in a thin deposition layer formed during each cycle. Such a thin later can help to prevent delamination, which can be caused by forming a single thick layer. A single thick film may also cause other problems. In addition the cyclical process provides more control parameters, which allow for more tuning parameters, to provide a better conformal deposition layer. Since the cyclic process will keep the bread-loaf at a minimum throughout the CD reduction process, the CD gains at the bottom portion of the deposition profile can keep growing.
In an example of the invention, a layer to be etched is a dielectric layer 408, which is placed over a substrate 404, as shown in
CPU 1322 is also coupled to a variety of input/output devices, such as display 1304, keyboard 1310, mouse 1312 and speakers 1330. In general, an input/output device may be any of: video displays, track balls, mice, keyboards, microphones, touch-sensitive displays, transducer card readers, magnetic or paper tape readers, tablets, styluses, voice or handwriting recognizers, biometrics readers, or other computers. CPU 1322 optionally may be coupled to another computer or telecommunications network using network interface 1340. With such a network interface, it is contemplated that the CPU might receive information from the network, or might output information to the network in the course of performing the above-described method steps. Furthermore, method embodiments of the present invention may execute solely upon CPU 1322 or may execute over a network such as the Internet in conjunction with a remote CPU that shares a portion of the processing.
In addition, embodiments of the present invention further relate to computer storage products with a computer-readable medium that have computer code thereon for performing various computer-implemented operations. The media and computer code may be those specially designed and constructed for the purposes of the present invention, or they may be of the kind well known and available to those having skill in the computer software arts. Examples of computer-readable media include, but are not limited to: magnetic media such as hard disks, floppy disks, and magnetic tape; optical media such as CD-ROMs and holographic devices; magneto-optical media such as floptical disks; and hardware devices that are specially configured to store and execute program code, such as application-specific integrated circuits (ASICs), programmable logic devices (PLDs) and ROM and RAM devices. Examples of computer code include machine code, such as produced by a compiler, and files containing higher level code that are executed by a computer using an interpreter. Computer readable media may also be computer code transmitted by a computer data signal embodied in a carrier wave and representing a sequence of instructions that are executable by a processor.
Other examples may use other devices to carry out the invention.
Next, the cyclical critical dimension reduction is performed to provide deposition layer features with reduce the CD (step 208). In this example, the deposition phase (step 209) comprises providing a deposition gas and generating a plasma from the deposition gas to form a deposition layer. In this example, the deposition gas comprises a polymer forming recipe. An example of such a polymer forming recipe is a hydrocarbon gas such as, CH4 and C2H4, and a fluorocarbon gas, such as CH3F, CH2F2, CHF3, C4F6, and C4F8. Another example of a polymer forming recipe would be a fluorocarbon chemistry and a hydrogen containing gas, such as a recipe of CF4 and H2. In a preferred embodiment, CF4 and H2 have a molar ratio (CF4:H2) in the range of 1:2 to 2:1. In this example, power is supplied at 400 watts at 2 MHz and 800 watts at 27 MHz.
The etch phase (step 210) comprises providing an etch phase gas and generating an etch phase plasma from the etch phase gas to etch away part of the deposition layer 420. The etch phase gas is different from the deposition gas. As illustrated, the deposition phase (step 209) and the etch phase (step 210) occur at different times. Preferably, the etch is an anisotropic etch. In this example the etch gas comprises a fluorocarbon chemistry, such as CF4, CHF3, and CH2F2. Other additives such as O2, N2, and H2 may be added. In this example, power is supplied at 0 watts at 2 MHz and 800 watts at 27 MHz.
In this example, the deposition phase (step 209) is repeated a second time. The same deposition recipe is used here as described above. In alternative embodiments, the deposition recipe can also be modified from the recipe in the first deposition phase.
The etch phase (step 210) is repeated a second time. The same etch recipe is used here as described above. The etch recipe can also be modified from the recipe in the first deposition phase.
The cyclical critical dimension process (step 208) can repeat these cycles as many times as possible until the desired critical dimension reduction is reached.
After the cyclical critical dimension reduction (step 208) is completed, the dielectric layer is then etched using the etch mask with the reduced CD (step 212). The etch comprises providing an etch gas and forming an etch plasma from the etch gas. In this example a different etch recipe is used for the dielectric layer etch (step 212) than the etch recipe used in the etch phase (step 210) or the recipe in the deposition phase (step 209). This is because it is desirable that the dielectric layer 408 is not etched during the cyclical critical dimension reduction (step 208). An example of an etch chemistry for etching the dielectric layer would be C4F6 with O2 or N2.
The etch mask is then removed (step 216). In this example a standard photoresist strip is used to remove the etch mask. Additional formation steps may also be performed (step 220).
Preferably, each deposition layer for each deposition phase is between 1 to 100 nm. More preferably, each deposition layer for each deposition phase is between 1 to 50 nm. Most preferably, each deposition layer for each deposition phase is between 1 to 10 nm. As a result, each deposition layer would have a thickness between the thickness of a typical bottom antireflective coating (BARC) to about a quarter of the thickness of the reduction of CD, so that the desired reduction in CD may be performed in two cycles. Preferably, the cyclical critical dimension reduction is performed in at least two cycles. More preferably, the critical dimension reduction is performed in at least five cycles.
The invention is useful for reducing CD for features that are either trenches or holes.
In different embodiments of the inventions, the etch layer may be a dielectric layer, such as a low-k dielectric layer or a metal containing layer. The etch layer may also be a hardmask layer, such as amorphous carbon or a SiN layer that serves as a hardmask for the later etching of a feature.
In other embodiments of the invention, the temperature of the wafer is kept below glass transition temperature of the photoresist materials to avoid distortion of the photoresist mask features. Preferably, the wafer temperature is kept in the range from 100 C to −100 C. More preferably, the temperature is kept in the range of 80 C to −80 C. Most preferably, the temperature is maintained in the range of 40 C to −40 C.
Since the deposited material is most likely of properties different from the photoresist materials, excessive accumulation of the deposited materials on top of the photoresist layer can cause undesirable distortion of the photoresist features. By doing the deposition and etch process in more than five cycles, it is possible to avoid excessive accumulation of the deposited material buildup during any time in the CD reduction process.
While this invention has been described in terms of several preferred embodiments, there are alterations, permutations, and various substitute equivalents, which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and apparatuses of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and various substitute equivalents as fall within the true spirit and scope of the present invention.
