Patent Application
20150136732
1. Field of the Disclosure
Embodiments of the present disclosure generally relate to a thin film deposition method and an apparatus for depositing thin films.
2. Description of the Related Art
In the manufacture of microscale and nanoscale devices, thin films are deposited by a variety of means, such as physical vapor deposition (PVD), chemical vapor deposition (CVD), and atomic layer deposition (ALD). In general, standard thin film deposition techniques will have difficulty filling (or conformally coating) features on a target substrate when the features have high aspect ratios—that is, such features as narrow, deep trenches and small diameter, deep holes.
Standard deposition techniques have problems with so called “overhang” that become apparent when faced with high aspect ratio features at the microscale and nanoscale sizes found in, for example, integrated circuit devices. “Overhang” results when the upper surfaces of a feature in the substrate accumulate deposited material at a faster rate than the lower or bottom surfaces of the feature.
Overhang can result from a variety of causes, such as, there may be a localized depletion of reactive components at the lower surfaces that is caused by the relatively slow diffusion rate of reactive components through narrow openings in a CVD process. Overhang may also result from simple geometry effects such as, for example, volatized molecules in a PVD process will be more likely to impact the upper surfaces of a feature before reaching the lower surfaces because the upper surfaces are between the PVD source and the lower surfaces. But whatever the specific causes, severe overhang may result in a failure to completely fill a feature (or in malformed conformal coatings) if the deposited material in the overhang extends from adjacent sidewalls to close the opening or otherwise significantly shield the lower surfaces from the deposition process.
The severity of overhang during deposition may be somewhat mitigated by optimization of process conditions or tool parameters, such as adjusting chemical precursor pressures or improving linearity of the impinging ions being deposited, and, in general, the amount of overhang is a function of deposited film thickness. But it may not always be possible to simply reduce the deposited film thickness and still achieve desired film properties (e.g., insulating properties) or film quality characteristics (e.g., a lack of “pinholes”). Thus, there is a need in the art to deposit material in high aspect ratio features at the microscale and nanoscale without defects caused by overhang.
The present disclosure describes a method of forming a film that includes depositing a film on substrate having a feature with a first surface at a first level and a second surface at a second level, which is not the same as the first level, then removing a portion of the deposited film by exposing the substrate to an ion flux from a linear ion source having a tailored ion angular spread of less than or equal to 90 degrees and greater than or equal to 15 degrees. The ion angular spread is measured from a line approximately normal to the substrate.
In certain embodiments, the feature in the substrate can include an opening at the first level and a bottom surface at the second level. The distance between the first and second levels can be greater than or equal to a width of the opening. The feature can be, for example, a trench, a contact hole, a via, a multilevel feature (e.g., dual damascene structure), or any patterned feature on the wafer on which a film may be deposited.
In some embodiments, the ion flux may be scanned or rastered across the substrate. In other embodiments, the entirety (or substantially all) of the substrate may be exposed to the ion flux simultaneously. The ion flux may be or may include argon ions.
The process used to deposit the film on the substrate can be, for example, a physical vapor deposition process, a chemical vapor deposition, process, or an atomic layer deposition process. Combinations of these methods may be used to form the film and/or various techniques such as plasma enhancement or radio frequency (RF) assistance can be incorporated in the deposition process.
A thin film deposition apparatus including a substrate support for supporting a substrate and a linear ion source having an ion angular spread that can be tailored to be less than or equal to 90 degrees and greater than or equal to 15 degrees is also described. The ion source of the apparatus provides a flux of ions towards (or directed towards) the substrate on the substrate support. The flux of ions removes at least a portion of the film deposited on the substrate.
The substrate support can be configured to rotate the substrate. In some embodiments, the flux of ions may be scanned across the substrate such that only a portion of the substrate is exposed to the flux of ions at any one time.
Additional embodiments include a deposition apparatus comprising a vacuum chamber and a substrate support therein. A substrate placed on the substrate support can include a feature having a first surface at a first level and a second surface substantially parallel to the first surface at a second level that is not the same as the first level. This deposition apparatus may further include a deposition system connected to or within the vacuum chamber. The deposition system can be configured to deposit a film on the substrate's first and second surfaces. The deposition system may be, for example, a physical vapor deposition system, a chemical vapor deposition system, and/or atomic layer deposition system. A linear ion source that can have a tailored ion angular spread of less than or equal to 90 degrees and greater than or equal to 15 degrees is included in the deposition apparatus. The linear ion source can be configured to provide a flux of ions towards the substrate on the substrate holder and thereby remove at least a portion of the film deposited on the first surface.
A more particular description of the disclosure, briefly summarized above, may be had by reference to example embodiments, some of which are illustrated in the appended drawings. It should be noted, however, that the appended drawings illustrate only typical embodiments and are, therefore, not to be considered limiting of the scope of this disclosure, as other embodiments of the present disclosure may be equally effective. Additionally, the drawings are not intended to be to scale or to represent relative size ratios between depicted elements, components, portions, or parts. Depicted elements may be re-shaped, re-oriented, re-sized, and/or rearranged without necessarily departing from the scope of the presented disclosure.
Rather than simply tuning processing conditions and tool parameters in attempt to mitigate overhang, it is possible to substantially reduce overhang in features formed in a substrate by preferentially removing material deposited on upper surfaces of a high aspect ratio feature as compared to material deposited on lower surfaces of the high aspect ratio feature. Material removal methods may include, for example, ion bombardment processes.
Here, feature 10 is a nanoscale feature having a high aspect ratio. As used herein, “nanoscale” means less than or equal to 1000 nm (1 micron). “High aspect ratio feature” means that the ratio of the maximum depth of the feature to the minimum width of the feature is greater than or equal to one (1.0). For example, a trench having a width of 500 nm and a depth of 1000 nm would have an aspect ratio of 2.0 and thus, would be a high aspect ratio feature. Similarly, a contact hole having a diameter of 22 nm and a depth of 22 nm would have an aspect ratio of 1.0 and thus would also be an example of a high aspect ratio feature. A feature having a width/diameter of 25 nm and a depth of 100 nm would have an aspect ratio of 4.0 and thus would also be a high aspect ratio feature. A feature having a width/diameter of 22 nm and a depth of approximately 200 nm would have an aspect ratio of approximately 9.1 and thus would also be a high aspect ratio feature.
It should be noted, that many features formed on a substrate may appear more geometrically sophisticated than a feature with a single opening size and depth, but may be considered to be the incorporation of multiple features each with one opening size and depth. For example, a dual damascene feature may be considered to comprise a trench with a via at the trench bottom. Thus, a dual damascene structure having a trench width of 50 nm, a trench length of 200 nm, and depth (to trench bottom) of 100 nm and further including a via in the trench bottom surface that is an ellipse with a minor axis dimension of 50 nm, a major axis dimension of 70 nm, and depth of 60 nm would have an aspect ratio that is 3.2 (that is, (100 nm+60 nm)/50 nm=3.2).
The first surface 30 and second surface 40 of feature 10 are substantially parallel to each other, though either or both surfaces may also include surface roughness, be non-flat, have localized tilt, or faceting such that projections or extensions of these surfaces could result in intersection of the projected/extended surfaces. In this context, “substantially parallel” means the actual (not a projection or conceptual extension) first surface 30 and second surface 40 do not intersect to form a corner.
Feature 10 also has a sidewall 50 that extends between the first surface 30 and the second surface 40. Sidewall 50 is not required to be, though it may be, perpendicular to either the first surface 30 or the second surface 40. In general, overhang may be a greater problem the closer sidewall 50 is to perpendicular. Sidewall 50 may also form an undercut feature wherein an opening formed in the first surface 30 is narrower than second surface 40—that is, sidewall 50 may angle in towards the middle of feature 10.
Feature 10 when viewed from above (and in a direction normal to the first and second surfaces) may appear as a rectangular or other polygonal shape if feature 10 is a trench or trench-like structure. Feature 10 may appear as a square, a circle, or an ellipsis from above when feature 10 is a contact hole or a via. In general, the specific shape of the feature is not important, though the method is particularly useful for depositing films on substrates including high-aspect ratio features. High aspect ratio features have relatively narrow widths as compared to feature depths. Feature 10 may be comprised of various portions and only certain portions may have a high aspect ratio and the various portions need not have the same aspect ratio. In general, problems related to overhang become more noticeable at sub-micron dimensions (i.e., nanoscale dimensions), but these problems may be present at larger feature dimensions as well.
As a film 60 is deposited on substrate 20 with the intention of filling or coating feature 10, a first portion 61 of the film 60 forms on the first (upper) surface 30 and a second (lower) portion 62 of film 60 forms on the second (lower) surface 40. Film 60 may, for example, comprise a metal such as copper, titanium, or tantalum or any other material capable of being deposited on a substrate.
As discussed, a variety of factors related to deposition techniques or specific process parameters can cause the deposition rate of the first portion 61 of the film 60 to be greater than the deposition rate of the second portion 62. Particularly important in this context is the aspect ratio of feature 10.
At the nanoscale dimensions often found in semiconductor devices, there will be difficulty getting film precursors (whether reactive compounds or impinging ions or molecules) to the lower portions of a high aspect ratio feature. For example, as depicted in
Overhang may also result because vapor-phase diffusion of reactive precursors into the narrow opening of a high aspect ratio feature is relatively slow such that the concentration of precursors at the upper and lower surfaces may be different during the deposition process. This may result in incomplete feature filling or malformed conformal coatings.
In a reactive deposition process, the concentration of precursors at the upper surface 30 may be (or substantially approach) the bulk concentration of precursors in a deposition chamber, while the concentration at the lower surface 40 may be substantially lower than the bulk concentration due the restricted movement of precursor molecules through the very small opening in the upper surface 30. If the opening in the upper surface 30 is less than the mean free path (λ) of the precursor molecules, a Knudsen-type diffusion process may be operative during deposition which may result in different concentrations (resulting from a generally preferential sorting for smaller molecules through such a narrow opening) for precursor molecules at the lower surface. Furthermore, reactive molecules may be depleted by reactions with the upper materials before they reach the lower surface.
For these and other reasons, film 60 will tend to form an overhang portion 63 as it is deposited on the substrate 20. As the overhang portion 63 extends into the opening between the sidewalls 50, the sidewalls may be further shielded from impinging ions in an RF-assisted process or impinging molecules in a sputter process. Overhang portion 63 may prevent the filling of feature 10 with the deposition material and result in the formation of unintended voids in feature 10 (see
If a conformal film deposition is desired, overhang portion 63 may cause gaps or thickness variations in the film deposited on the surfaces of feature 10 because, in general, if the surfaces of feature 10 are exposed to different processing conditions (e.g., different molecule incidence rates, different precursor concentrations, etc.), a perfectly conformal film will not form in on these surfaces.
Feature 70, depicted in
Feature 80, depicted in
In an embodiment of the present disclosure, a method of forming a thin film includes first depositing a thin film on a substrate. After this first deposition, a portion of the deposited film is removed by exposure to an ion flux from a linear ion source having an ion angular spread that can be tailored to be between 90 degrees and 15 degrees. The impinging ions provide a physical etching process which removes portions of the film exposed to the ion bombardment. Due to effects similar to those which produce overhang during a deposition process, the ion flux, which includes ions not incident perpendicularly to the substrate, provides a differential etch rate for material deposited on upper surfaces of feature 10 as compared to material deposited on the lower surfaces of feature 10.
In box 500, a substrate 20 is place on a support substrate in a thin film deposition apparatus. The substrate 20 has a feature 10 formed therein. Feature 10 has a first surface 30 and a second surface 40. First surface 30 and second surface 40 are arranged at different levels in substrate 20, but are substantially parallel to each other. As depicted in
In box, a film 60 is deposited on substrate 20. The film 60 can be deposited using, for example, physical vapor deposition methods and in this instance is intended to completely fill feature 10. But as is common in the art, film 60, as initially formed, has an overhang portion 63. An upper portion 61 of film 60 forms on first surface 30 and a lower portion 62 of film 60 forms on second surface 40. Lower portion 62 may also form on all or parts of sidewalls 50.
Film 60 can be, for example, a metal such as copper that is electrically conductive and feature 20 may form part of wiring pattern for an integrated circuit device. In other embodiments, film 60 can be intended to be a conformal coating which is not intended to completely fill feature 20, but would ideally form a coating of approximately constant thickness on surfaces 30 and 40 (and sidewalls 50). A conformal film 60 could be used as, for example, a barrier layer to prevent electromigration from metal layers into dielectric layers.
In box 520, the substrate 20 is exposed to an ion flux supplied by a linear ion source having an angular spread of less than or equal to 90 degrees and greater than or equal to 15 degrees. In box 520, the ions can be, for example, argon ions or other ions of other atoms which are generally chemically inert, or substantially so, under the present processing conditions.
The breadth of the ion angular spread (as may be described by an ion angular distribution function) provides a differential removal rate for film deposited on the upper surfaces (e.g., first surfaces 30) of the substrate and film deposited on the lower surfaces (e.g., second surfaces 40) of the features in the substrate. That is, ions which are not incident to substrate in a perpendicular manner will generally not reach the lower surfaces (e.g., surfaces covered with film portion 62) of a high aspect ratio feature due to geometry effects, while ions that are incident to the substrate 20 in a perpendicular (or nearly so) manner may reach the lower surfaces of the high aspect ratio feature.
As a simple approximation, the removal rate of film 60 can be considered a direct function of the number of ions hitting the film per unit time (which may be referred to as an ion flux). Thus, the removal rate of a material (film portion 62) on the lower surface of the high aspect ratio feature will be less than removal rate of material on the upper surfaces of the substrate because the material at the upper surface (e.g., film portion 61 and overhang portion 63) will be subjected to ions impinging in a perpendicular (or nearly so) manner plus the ions incident on the substrate at other angles and the lower surfaces of the high aspect ratio feature will only be subjected to those ions incident on substrate at a perpendicular (or nearly so) angle and not those at other angles.
As the material on the upper and lower surfaces are substantially the same material, physical etch rates will be different due to the exposure to what is effectively different ion flux rates. The material etch rates may also be angularly dependent—that is ions impinging on the surfaces at different angles may be more or less effective in removing the material. In general, the angular distribution of the ion flux at the upper and lower surfaces will be different in that the percentage of ions hitting the respective surfaces at various angles will be different, but this effect may not be significant when the overall rate of ions hitting the respective surfaces is significantly different. Thus, for example film portion 61 and overhang portion 63 may be removed by the ion bombardment process more quickly than film portion 62. Therefore, while overhang portion 63 may be substantially removed at least some of film portion 62 can remain.
The effect of the process associated with box 520, described above, is depicted in
In box 530, an optional second deposition process is performed to generate a filled feature 10. The second deposition process may be the same type process as the first deposition process used to generate initial film 660 or may be a different process type or a variant of the first deposition process. The same or different material as used to form film 660 may be deposited in this process. Box 520 may be repeated after box 530 if desired.
In general, the deposition and removal processes may be repeated to fill the feature in stages, but in many applications it may be sufficient to partially fill the feature rather than completely fill the feature. In other applications, the partial removal or paring of the overhang portion may be sufficient to generate a conformal or quasi-conformal coating necessary for subsequent processing. In any event, the deposition (box 530) and removal processes (box 520) may be performed once or any other number of times necessary to achieve the desired result.
Additionally, the removal process in box 520 may be conducted in a single stage or several stages. That is, the ion flux may be continuous or pulsed. Alternatively, in some embodiments only portions of substrate 600a are exposed to an ion flux at any given time because the size (beam diameter) of the ion source is less than the full size of substrate 600a. Thus, portions of substrate 600a may be exposed to multiple passes of the ion flux as the ion flux is scanned and re-scanned across the substrate 600a.
Furthermore, the conditions of the removal process in box 520 need not remain constant and may be varied. Such variations in process conditions may be continuous or in a step-wise manner. For example, in some embodiments, substrate 600a may be rotated during the process of box 520 and the speed of rotation can be varied. In other embodiments, the ion angular spread may be narrowed or widen during the process of box 520, for example, at an initial process phase of box 520, the ion angular spread may be relatively narrow then widened at a later phase of box 520. It is also possible for the process in box 520 to include one or more pauses in ion flux exposure, for example, to control the temperature increase experienced by the substrate.
After the desired film or coating has been achieved, additional processing such as chemical mechanical polishing, electroplating, deposition of interlayer films, photolithographic pattern, or other processing which might be necessary to form a completed device may be conducted in optional box 540.
In an embodiment of the present disclosure, deposition and removal may be performed in the same apparatus, though in other embodiments the deposition and removal may be performed in different apparatuses or in a series of different apparatuses such that a first deposition occurs in a first tool, a first removal occurs in a second tool, a second deposition occurs in a third tool, and so forth. The deposition and removal may also be performed in different chambers of the same apparatus, such as a multi-chamber tool depicted in
A substrate support 710 is located inside chamber 700. The substrate support 710 is configured to support a substrate such as substrate 600a or substrate 20 during material deposition and removal. Substrate support 710 may be configured to rotate the substrate thereon and/or translate the substrate in horizontal plane. Substrate support 710 may also be capable of translating the substrate in a vertical direction. Substrates can be securely held on substrate support 710 with vacuum suction, electrostatic force, gravity, chemical adhesives, magnetic attraction, clips, clamps, pins, notches, support rings or similar means known in the art. Substrate support 710 may incorporate various components for heating and cooling the substrate.
A linear ion source 720 is provided inside or connected to a sub-chamber 730 such that a flux of ions having an ion angular spread of less than or equal to 90 degrees and greater than or equal to 15 degrees can be provided in a direction towards the substrate. The ion angular spread from the linear ion source 720 can be controlled (tailored) to be less than or equal to 90 degrees and greater than or equal to 15 degrees. The projected shape (that is, the shape of the flux area at the substrate) of the ion flux from linear ion source 720 can be any shape or size. In some embodiments, the ion angular spread is preferably between 90 degrees and 60 degrees (inclusive). In some embodiments, the ions can be supplied with relatively low energy and achieve acceptable etching results.
While chamber 700 can incorporate components for providing an electrical bias to the substrate on substrate support 710, in general, it is preferable that an alternating electrical current bias not be applied to the substrate during the ion flux processing used to remove the portions of deposited films that form overhanging film portions. High biasing may generate plasma sheaths across the substrate and inhibit removal. Large negative bias on the substrate may serve effectively to narrow the ion angle distribution by drawing wide-angle ions toward the substrate. A narrowing of the ion angular spread may be disadvantageous as it is the angular spread which provides the differential removal rates for different portions of the deposited film.
As further depicted in
Deposition system 740 and linear ion source 720 may be provided in different sub-chambers of chamber 700, as depicted in
As mentioned, in some embodiments, removal of deposited films may be performed while the substrate is rotated relative to linear ion source. The substrate may be rotated at a constant rate and constant direction or either both the rate and direction can be varied. Alternatively the linear ion source or portions thereof can be rotated relative to the substrate to promote uniformity of ion exposure (dosing). The projected shape of the ion flux can be any shape achievable, e.g., circular, elliptical, polygonal, etc.
In other embodiments, the removal processing may be performed while the substrate is moved (translated) relative to the linear ion source. That is, the substrate may be moved along a conveyor belt mechanism or the like while the ion source remains at a fixed point. In other embodiments, the linear ion source or portions thereof can be translated relative to the substrate. That is, portions of the substrate can be scanned through the ion flux or the ion flux can be rastered across portions of the substrate.
This application claims priority to U.S. Provisional Patent Application Ser. No. 61/907,109, filed on Nov. 21, 2013, which herein is incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61907109 | Nov 2013 | US |
