The present invention relates generally to deposition and/or etching of layers of material on a partially fabricated integrated circuit. More specifically, it relates to deposition of diffusion barrier layers.
Generally, the industry of semiconductor manufacturing involves highly complex techniques for fabricating integrating circuits from semiconductor materials that are layered and patterned onto a substrate, such as silicon, by various process systems. For example, a first process system deposits a layer of material, while another process system etches a pattern in such deposited material.
Miniaturization of integrated circuit (IC) devices demands superior electrical properties from both dielectric and conductive materials used in the manufacturing of an integrated circuit. Traditionally used materials, such as aluminum as a conductor and silicon dioxide as an insulator no longer provide adequate electrical characteristics at the modern level of miniaturization. Therefore, the manufacturers of IC devices are now employing new dielectric materials with lower dielectric constant than silicon dioxide and are increasingly turning to copper as a conductor, due to its low resistivity. The low-k dielectric materials used in the IC device processing include carbon doped silicon dioxide, hydrogenated silicon oxycarbides (SiCOH), fluorine doped silicon dioxide, and organic-containing low-k dielectrics. These materials, due to their low dielectric constants, provide low parasitic capacitance and minimize the “crosstalk” between the interconnects in an integrated circuit. At the same time, they are often porous foam-like materials and are generally more easily damaged during the processing steps than silicon dioxide. The impact of high-energy ions during such processing steps as PVD (physical vapor deposition) often results in undesired effects in a highly porous dielectric.
The barrier material 106 is removed from the bottom surface 112 of the via 114 along with any underlying oxidized copper so as to form a better connection to the conductive line 116 in a subsequent process step. Since the barrier material was deposited uniformly in the trench and the via, cleaning all of the barrier material from the via also results in etching into the dielectric material underneath the trench's barrier layer.
Accordingly, it would be beneficial to provide improved apparatus and methods for facilitating etching of via features without damaging the dielectric material within trench features or other features of a semiconductor wafer.
Embodiments of the present invention include apparatus and methods for achieving etch and/or deposition selectivity in vias and trenches of a semiconductor wafer. That is, deposition coverage in the bottom of each via of a semiconductor wafer differs from the coverage in the bottom of each trench of such wafer. The selectivity may be configured so as to result in punch through in each via without damaging the dielectric material at the bottom of each trench or the like. In this configuration, the coverage amount deposited in each trench is greater than the coverage amount deposited in each via.
In one embodiment, an apparatus for depositing material on a semiconductor wafer having recessed features, including a plurality of vias and trenches, is disclosed. This apparatus includes generally a process chamber having a target for depositing material onto the semiconductor wafer and a wafer support for holding the wafer in position during deposition of the material. The apparatus further includes a controller configured to sputter material from the target onto the semiconductor wafer under conditions that coat the recessed features and thereby form the layer of material. The wafer is positioned with respect to the target so that a first coverage amount of material deposited in each trench is greater than a second coverage amount of material deposited in each via. In one aspect, the target is three dimensional. In a specific implementation, the target is single piece target and in another implementation is a multiple piece target. In one embodiment, the material is sputtered in each trench substantially simultaneously as in each via.
In another embodiment, the invention pertains to a method for depositing material on a semiconductor wafer having recessed features, including a plurality of vias and trenches. A first coverage amount of material is deposited in each via to coat a bottom of such each via while a second coverage amount of material is deposited in each trench to coat a bottom of such each trench. The depositing of the first and second coverage amounts are selectively controlled such that a ratio of the second coverage amount over the first coverage amount is greater than about 1.5. In a specific embodiment, the first coverage amount of material is deposited in substantially only a direction that is substantially normal to a surface of the wafer and the second coverage amount of material is deposited in a plurality of directions in relation to the wafer surface, including a normal direction and a substantially non-normal angle.
In an alternative embodiment, the invention pertains to another apparatus for depositing material on a semiconductor wafer having recessed features, including a plurality of vias and trenches. The apparatus includes a process chamber having a target for sputtering the material onto the semiconductor wafer and a wafer support for holding the wafer in position during deposition of the material. The apparatus further includes a controller that is configured to perform the operations of the method embodiment that are described above.
These and other features and advantages of the present invention will be presented in more detail in the following specification of the invention and the accompanying figures which illustrate by way of example the principles of the invention.
The present invention is illustrated by way of example, and not by way of limitation.
Reference will now be made in detail to a specific embodiment of the invention. An example of this embodiment is illustrated in the accompanying drawings. While the invention will be described in conjunction with this specific embodiment, it will be understood that it is not intended to limit the invention to one embodiment. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention.
In general, particular embodiments of the present invention provide apparatus and methods for achieving etch and/or deposition selectivity in vias and trenches of a semiconductor wafer.
During a selective deposition process, a diffusion barrier layer 206, such as Ta or TaN, is deposited over the second dielectric layer 204. The selectivity results in at least two different coverage amounts for the trenches and the vias. As shown, each bottom surface of each trench has a coverage amount equal to A, while each bottom surface of each via has a coverage amount equal to B. Accordingly, a ratio of coverage for the trench and the via is defined as:
The SD ratio may be selected to be significantly greater than 1.0 for deposition of the barrier material so that A is greater than B, or rather, the amount of deposition coverage in each trench, as well as other low aspect ratio features, is greater than the amount of coverage in each via. As shown, deposition selectivity is configured to result in a barrier thickness A in the trench bottom surfaces that is significantly higher than the B thickness in the via bottoms.
While the term “deposition” includes a wide range of possible deposition and etching activities across the wafer, it is generally understood to imply that a net deposition of material occurs at the bottom of a recess being covered (e.g. a via and/or trench). Whether or not there is a net etch or deposition at other regions of the workpiece does not change the fact that deposition is taking place. Similarly, the terms “etching” and “resputtering” used with respect to a recessed feature include a wide range of both deposition and etching activities and generally imply a net etching or removal of material from the bottom of such recess (e.g., via or trench).
As shown in
The deposition and subsequent resputtering process are most often used, respectively, for deposition and resputtering of the diffusion barrier layer, but can also be employed in the deposition or etch-back of other wafer materials such as conductive metal layers; e.g., copper seed layers. That is, selective deposition of trenches and vias can be applied to any suitable material. Diffusion barrier materials commonly subjected to deposition and subsequent resputtering include but are not limited to tantalum, titanium, tungsten, ruthenium, cobalt, solid solutions of these metals and nitrogen and binary nitrides (e.g. Ta, TaNx, Ti, TiNx, W, WNx, Ru, or Co). Copper is also a commonly resputtered material.
An Ionized Physical Deposition (iPVD) process may be used for deposition and resputtering of a material. That is, a same iPVD chamber, as described further below, may be used to both deposit and remove a material with respect to a recessed feature. An important characteristic of iPVD processes is the etch rate to deposition rate ratio (E/D). It should be understood, that both etching and depositing processes are occurring simultaneously during deposition or resputter. Deposition is the result of inert gas particles bombarding the target, and sputtering target material (neutral or ionic) onto the wafer surface. Etching is the result of inert gas particles bombarding the wafer. In some embodiments of this invention, ionized metal may be used together with ionized gas for resputtering of wafer materials.
An etch and/or deposition processes can be controlled by modulating the power at the target and at the wafer pedestal. For example, to achieve low E/D ratio needed for deposition, the power at the target is increased and the bias at the wafer is decreased or turned off. This configuration causes the inert gas particles to be directed towards the target, leading to deposition of the target material on the wafer. The DC target power used for deposition step ranges from 10 to 70 kW. The bias power during deposition can range from about 0 to about 3000 W, more preferably from about 0 to about 1200 W. Conversely, if the power at the target is decreased while the power at the wafer pedestal (bias) is increased, the inert gas particles are directed to the wafer, leading to net etching of the wafer layer (resputter). Commonly employed DC target power for the resputter process is 1-8 kW, preferably 1-6 kW. The bias power for resputtering can range from about 100 to about 3000 W, preferably from about 600 to about 1500 W, and even more preferably from about 900 to about 1200 W.
An inert gas, such as argon, is introduced through a gas inlet into the hollow region of the cathode target 307 powered by a DC source to create a plasma. The pump 315 is positioned to evacuate or partially evacuate the process chamber. The control of pressure in the process chamber can be achieved by using a combination of gas flow rate adjustments and pumping speed adjustments, making use of, for example, a throttle valve or a baffle plate. Alternatively, pressure above the wafer can be controlled by varying the height of the wafer pedestal 303. An intense magnetic field is produced by electromagnets 305a-305b within the cathode target region. Additional electromagnets 305c are arranged downstream of the cathode target so that different currents can be applied to each electromagnet, thereby producing an ion and/or neutral particle flux and a controlled deposition and/or etch rate. A floating shield 309, existing in equilibrium with the floating plasma potential, is used, in conjunction with the source electromagnets to shape the plasma distribution at the target mouth. A stream of ions and/or particles is directed to the surface of the wafer, as shown by arrows on
In certain embodiments, a system controller 311 is employed to control process conditions during deposition and resputter, insert and remove wafers, etc. The controller will typically include one or more memory devices and one or more processors. The processor may include a CPU or computer, analog and/or digital input/output connections, stepper motor controller boards, etc. Alternatively, the controller may contain hardware devices, such as ASIC's, that are configured to manage the process conditions.
In certain embodiments, the controller controls all of the activities of the deposition apparatus. The system controller may execute system control software including sets of instructions for controlling the timing, mixture of gases, chamber pressure, chamber temperature, wafer temperature, RF power levels, wafer chuck or susceptor position, and other parameters of a particular process. Other computer programs stored on memory devices associated with the controller may be employed in some embodiments.
Typically there will be a user interface associated with controller 311. The user interface may include a display screen, graphical software displays of the apparatus and/or process conditions, and user input devices such as pointing devices, keyboards, touch screens, microphones, etc.
In one implementation, the computer program code for controlling the deposition and resputtering processes can be written in any conventional computer readable programming language: for example, assembly language, C, C++, Pascal, Fortran or others. Compiled object code or script is executed by the processor to perform the tasks identified in the program.
The controller parameters relate to process conditions such as, for example, wafer position, process gas composition and flow rates, temperature, pressure, plasma conditions such as RF and DC power levels and frenquency, cooling gas pressure, and chamber wall temperature. At least a portion of these parameters may be provided to the user in the form of a recipe, and may be entered utilizing the user interface.
Signals for monitoring the process may be provided by analog and/or digital input connections of the system controller. The signals for controlling the process are output on the analog and digital output connections of the deposition apparatus.
In one embodiment, the system software may be designed or configured in many different ways. For example, various chamber component subroutines or control objects may be written to control operation of the chamber components necessary to carry out the inventive deposition processes. Examples of programs or sections of programs for this purpose include substrate positioning code, process gas control code, pressure control code, heater control code, and plasma control code.
A substrate positioning program may include program code for controlling chamber components that are used to load the substrate onto a pedestal or chuck and to control the spacing between the substrate and other parts of the chamber such as a gas inlet, target, and/or separatrix, which is explained further below. A process gas control program may include code for controlling gas composition and flow rates and optionally for flowing gas into the chamber prior to deposition in order to stabilize the pressure in the chamber. A pressure control program may include code for controlling the pressure in the chamber by regulating, e.g., a throttle valve in the exhaust system of the chamber. A heater control program may include code for controlling the current to a heating unit that is used to heat the substrate. Alternatively, the heater control program may control delivery of a heat transfer gas such as helium to the wafer chuck. A plasma control program may include code for setting RF and DC power levels applied to the process electrodes at the target and the wafer chuck.
Examples of chamber sensors that may be monitored during deposition and/or resputtering include pedestal or chuck positioning sensors, mass flow controllers, pressure sensors such as manometers, and thermocouples located in pedestal or chuck. Appropriately programmed feedback and control algorithms may be used with data from these sensors to maintain desired process conditions.
As shown in this HCM configuration, the wafer is positioned a distance 317 from the target that results in the wafer receiving a mostly unidirectional stream of ions and/or neutral particles 313 for deposition. This distance is referred to as a “Directional Distance.” For instance, a typical distance is greater than 20 cm from the bottom edge of the target 307 and the wafer will cause the wafer to only receive ions and/or neutral particles that are mostly directed at a normal angle with respect to the wafer surface. The reason for this is that the ions and/or neutral particles sputtered from the sidewalls of the target at shallow or non-normal angles mostly miss the wafer when the wafer is positioned far from the target, while a significant portion of neutral particles that are sputtered from the top surface of the target at a normal angle to the wafer surface reach the wafer surface. Consequently, a mostly unidirectional stream will tend to cover the bottoms of the vias and trenches (as well as the field and other wafer features) at about the same rate and thickness as shown in
One way to minimize this TDDB effect is to prevent dielectric damage during the etching step of the barrier deposition. This may be accomplished by providing a selective deposition coverage amount for the trenches and the vias. To achieve this selectively, the wafer may be positioned closer to the target so that more shallow or oblique angled (or rather non-normal angles) neutral particles reach the trench bottom surfaces, as compared to the via bottom surfaces, during the deposition process. Any suitable configuration may be utilized so as to have oblique angled or non-normal angled neutral particles to reach the trench surfaces.
The HCM system includes a three dimensional target that is formed from a single piece of material. In this example, the single piece target is bell shaped with ions and/or neutral particles being sputtered from the interior of the bell in a deposition process. This arrangement provides a simplified design since the target is formed from a single piece, as opposed to a multiple piece target. For instance, a single piece target does not require precise positioning of multiple target pieces with respect to one another to achieve a particular deposition result.
In the example of
Although an HCM type iPVD system having a bell shaped target is illustrated in
In any of the described embodiments, the separatrix or null field position that occurs during a deposition and/or etch process may be positioned in any suitable position with respect to the target. In general, an electric field is typically formed along the sidewall of the target using the side magnets to generate positive and negative polarities along the sidewall of the target. In the examples of
In other embodiments, the separatrix may be formed at a position along higher up in the target.
The wafer may be positioned so that SD is greater than 1.2 and most preferably greater than 2.5. As a result of this wafer positioning, substantially directional material is used to cover the bottom surfaces of vias in operation 504 while highly angled (or oblique or non-normal) and directional material are used to cover the bottom surfaces of the trenches in operation 506. The operations for covering the via and trench areas with the deposited material are performed substantially simultaneously in a single deposition process. Said in another way, material for the vias is deposited substantially only in a direction that is normal to the wafer surface and material for the trenches is deposited in a plurality of directions, including a normal direction and one or more non-normal angles. This deposition process may be performed utilizing any of the deposition systems described herein. For example, a three dimensional target may be utilized in the form of an HCM (e.g.,
After barrier material is deposited, the via areas may be etched to substantially clear the previously deposited material while damage to the dielectric material underlying the trench material is minimized or eliminated in operation 508. In one embodiment, anchors are formed in the dielectric material underlying the barrier material that is etched or resputtered away from the bottom surfaces of the vias while a minimum or zero amount of barrier material remains in the bottom surfaces of the trenches.
Embodiments of the present invention provide several advantages. For example, asymmetric low angle flux is reduced.
In contrast,
Embodiments of the present invention also reduce deposition uniformity.
Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. Therefore, the described embodiments should be taken as illustrative and not restrictive, and the invention should not be limited to the details given herein but should be defined by the following claims and their full scope of equivalents.
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