Patent Application
20130157466
One material that is commonly used in the formation of semiconductor devices is silicon nitride. In some applications, a silicon nitride layer is used as a sacrificial layer that is wholly or partially etched away at some point after it is deposited. Because the silicon nitride material is etched away, it is desirable in these applications for the material to have a controlled, high wet etch rate. Furthermore, because subsequent semiconductor processing operations will often expose the material to high temperatures, it is desirable for the silicon nitride material to exhibit good thermal stability. A material is more thermally stable if it does not out-gas or produce significant uncontrolled changes in internal stress when exposed to post-deposition high temperature processing operations. Further, when the silicon nitride material is used in a stack with layers of other materials (e.g., silicon oxide layers), it may be desirable for the silicon nitride material to have properties that are tunable such that the resulting stack is thermally stable and may be properly and rapidly etched. To this end, it may be desirable for the silicon nitride material to exhibit certain properties (e.g., internal stress levels) that counteract the properties of other layers in the stack. As such, there exists a need for a method and apparatus for depositing silicon nitride in a manner that allows the internal stress and/or etch rate of the silicon nitride to be tuned to particular values.
In one aspect of the embodiments herein, a method is disclosed for forming a silicon nitride film on a substrate in a plasma-enhanced chemical vapor deposition apparatus, including flowing a silicon-containing reactant, a nitrogen-containing reactant and a boron-containing reactant through the chemical vapor deposition apparatus, where the ratio of the flow rates of the silicon- to nitrogen-containing reactant is about 0.02 or less; generating or maintaining a plasma in the apparatus; and depositing the silicon nitride film on the substrate.
The silicon-containing reactant may be silane, disilane, trisilane or alkyl silane in certain cases. The nitrogen-containing reactant may be ammonia, hydrazine or nitrogen in certain cases. In some embodiments, the boron-containing reactant may be diborane or trimethyl borate. The flowing operation may include flowing diborane at a rate of about 4-15 sccm. In some cases, the silicon-containing reactant is silane and the boron-containing reactant is diborane, and the flowing operation is conducted such that the ratio of the flow rates of silane to diborane is about 3 to 20 (i.e., a ratio of about 0.15). In certain implementations, the ratio of the flow rates of the silane to diborane is between about 0.02-0.35, for example between about 0.1-0.2. Some embodiments employ an inert carrier gas to aid in flowing one or more of the reactants. For example, the diborane may be flowed into the apparatus in an inert gas carrier. In certain cases, the inert gas is nitrogen. In other cases, the inert gas may be hydrogen or argon.
Some embodiments employ a low frequency and high frequency power to generate and maintain the plasma, with a low frequency power provided at about 0-300 Watts per 300 mm wafer. In some cases, the low frequency power is provided at or below about 100 Watts per 300 mm wafer, for example at or below about 75 Watts per 300 mm wafer. The high frequency power may be provided in certain cases between about 100-750 Watts per 300 mm wafer, for example between about 100-500 Watts per 300 mm wafer. In some of the embodiments herein, the pressure in the apparatus is maintained between about 0.5-8 Torr while depositing the silicon nitride film on the substrate, for example between about 1-6 Torr. During the depositing operation in many implementations, the silicon nitride film is deposited to a thickness of between about 10-100 nm.
In some implementations, the deposited silicon nitride film etches at a rate of at least about 20 Ångstroms/minute when exposed to aqueous hydrofluoric acid provided in a volume ratio of 100 units water to 1 unit standard 50% hydrofluoric acid at 20° C. Some embodiments also include selecting an amount of internal stress for the silicon nitride film and selecting process parameters for depositing the silicon nitride film with the selected amount of internal stress. In some cases, the depositing is conducted under conditions that produce the silicon nitride film with a tensile internal stress. The tensile stress may be between about 400-600 MPa in certain implementations. The deposited silicon nitride film may include between about 1-15 atomic percent boron in some embodiments. In certain implementations, the silicon nitride film has an average roughness of less than about 6 Ångstroms as measured on the substrate. In some cases the silicon nitride film is smoother, having an average roughness of less than about 4.5 Ångstroms as measured on the substrate. The embodiments herein may further include heating the substrate with deposited silicon nitride film to a temperature of at least about 400° C. In certain implementations the substrate with the deposited film is heated to a temperature between about 400-650° C., for example between about 450-600° C.
The embodiments herein may also include forming a stack with alternating layers of an oxide and the deposited silicon nitride. In some implementations the stack contains at least about 10 layers of the silicon nitride film. Further, in some cases the stack contains at least about 50 layers of the silicon nitride film. After a stack is formed, the stack may be wet etched to form a fishbone shaped structure having recesses. The fishbone shaped structure may have “bones” of silicon oxide material and recesses where the silicon nitride material has been etched away. In certain embodiments, the fishbone shaped structure may be used to form a vertical memory device. For example, the recesses formed by etching the silicon nitride film may be filled with material that is used to form a capacitor. In some cases the recesses are filled with tungsten. Generally, the capacitor will be at least partially inside the recesses formed by wet etching the silicon nitride.
In another aspect of the disclosed embodiments, a method is provided for forming a film stack including a silicon nitride film and a second film having a different composition from the silicon nitride film on a substrate, including depositing the silicon nitride film on the substrate by plasma-enhanced chemical vapor deposition while flowing a silicon-containing reactant, a nitrogen-containing reactant, and a boron-containing reactant through the plasma-enhanced chemical vapor deposition apparatus, where the silicon nitride film has a thickness of between about 10-100 nm; depositing the second film on the silicon nitride film, where the second film has a thickness of between about 10-100 nm; and repeating the two depositing operations at least twice to form the film stack. In some implementations, the depositing silicon nitride film operation is conducted such that the ratio of flow rates of the silicon- to nitrogen-containing reactants is about 0.02 or less. In certain embodiments, the second film is a silicon oxide film. The silicon oxide film, in some cases, is formed by a thermal process. The depositing steps may be repeated various times to form the film stack, for example, these steps may be repeated at least 10 times, or in some cases at least 50 times to form the film stack. Furthermore, the silicon nitride may be wet etched from the stack to form a fishbone shaped structure having recesses. As noted above, the fishbone shaped structure may be used to form a vertical memory device. For example, some embodiments include forming capacitors at least partially inside the recesses formed by wet etching silicon nitride.
In some implementations, the method of forming the stack may also include applying photoresist to the substrate; exposing the photoresist to light; patterning the resist with a pattern and transferring the pattern to the substrate; and selectively removing the photoresist from the substrate.
In another aspect of the disclosed embodiments, a plasma-enhanced chemical vapor deposition apparatus configured to deposit a film stack on a substrate is provided. The apparatus includes a process station; a first reactant feed for supplying a silicon-containing reactant to the process station; a second reactant feed for supplying a co-reactant to the process station; a plasma source; and a controller configured to control the apparatus to maintain a plasma and process gas flow conditions, the controller having instructions for depositing a silicon nitride film on the substrate by plasma-enhanced chemical vapor deposition while flowing the silicon-containing reactant, a nitrogen-containing reactant, and a boron-containing reactant through the plasma-enhanced chemical vapor deposition apparatus containing the substrate, where the silicon nitride film has a thickness of between about 10-100 nm, further instructions for depositing the second film on the silicon nitride film, where the second film has a thickness of between about 10-100 nm. In some embodiments, the controller also has instructions for repeating the depositing operations at least twice to form the film stack. In certain implementations, the controller has instructions to repeat the depositing operations more than twice, for example ten times or fifty times, to form the stack. The plasma source may be a capacitively-coupled plasma source in certain embodiments.
In some implementations, the controller instructions for depositing the silicon oxide film may include instructions for providing a ratio of flow rates of the silicon- to nitrogen-containing reactants at about 0.02 or less. In some implementations the second film is a silicon oxide film. The controller instructions may further include instructions for forming the silicon oxide film by a thermal process. In certain embodiments, the boron-containing reactant is diborane, and the controller is configured to flow the diborane into the process station at a rate of between about 4-15 sccm. In certain cases where the boron-containing reactant is diborane and the silicon-containing reactant is silane, the controller may be configured to flow the silane and diborane at a flow rate ratio of about 3 to 20 silane to diborane (i.e., a ratio of about 0.15). In certain implementations, the controller is configured to maintain the ratio of the flow rates of the silane to diborane between about 0.02-0.35, for example between about 0.1-0.2. In some embodiments, the controller also has instructions for generating and maintaining a plasma using the plasma source. For example, the instructions may include instructions for generating low frequency and high frequency power, with the low frequency power provided at or below about 150 Watts per 300 mm wafer. As a further example, the instructions may include instructions for generating high frequency power at about 100-750 Watts per 300 mm wafer. In some implementations, the controller may further have instructions for maintaining a pressure of between about 0.5-8 Torr in the process station while depositing the silicon nitride film on the substrate.
In an additional aspect of the disclosed embodiments, a system is provided including the apparatus described above (including a process station; a first reactant feed for supplying a silicon-containing reactant to the process station; a second reactant feed for supplying a co-reactant to the process station; a plasma source; and a controller configured to control the apparatus to maintain a plasma and process gas flow conditions, the controller having instructions for depositing a silicon nitride film on the substrate by plasma-enhanced chemical vapor deposition while flowing the silicon-containing reactant, a nitrogen-containing reactant, and a boron-containing reactant through the plasma-enhanced chemical vapor deposition apparatus containing the substrate, where the silicon nitride film has a thickness of between about 10-100 nm, further instructions for depositing the second film on the silicon nitride film, where the second film has a thickness of between about 10-100 nm) and a stepper tool.
These and other features of the disclosure will be described in more detail below with reference to the drawings.
Various embodiments presented herein are made with reference to a plasma enhanced chemical vapor deposition (PECVD) process that employs a silicon-containing reactant, a nitrogen-containing reactant and a boron-containing reactant. In some embodiments, silane and ammonia are used as reactant process gases. Nitrogen, hydrogen or a noble gas may be used as a carrier. For context, some embodiments are described with reference to a “baseline process”. In such a baseline process, silane and ammonia are delivered to a four station reactor (e.g., a Vector® Extreme or Vector® Express reactor from Lam Research, Inc. of Fremont, Calif.) where they are reacted to produce silicon nitride films on 300 mm wafers. It should be understood that the disclosed embodiments are not limited to 300 mm wafers. Wafers of other sizes such as 200 mm wafers, 450 mm wafers, etc. may be used as substrates. In some cases, as will be understood by those of skill in the art, process conditions will have to be scaled from those stated for 300 mm wafers when wafers of other sizes are used.
In the baseline process, silane is delivered at a flow rate of about 200 sccm (100% silane), ammonia is delivered at about 1140 sccm, and the nitrogen at about 9000 sccm. The pressure employed in the baseline process is about 2 Torr. Low frequency & high frequency RF power is provided to generate the plasma. The low frequency radio frequency (LF RF) power is provided at 400 kHz and about 0 to 150 Watts (about 0-40 W per 300 mm wafer). The high frequency radio frequency (HF RF) power is provided at 13.56 MHz and about 800 Watts (about 200 W per 300 mm wafer).
The baseline process is used to produce silicon nitride films. Unless otherwise clear from context, the term silicon nitride is intended to cover stoichiometric and non-stoichiometric solid compositions of primarily silicon and nitrogen. Silicon nitride films may have various morphologies, including varying degrees of crystallinity, roughness, etc. The general term silicon nitride also encompasses compositions that include elements other silicon and nitrogen. Frequently, some hydrogen is present in the composition. In various embodiments described herein, boron is added. Thus, unless otherwise specified, the term silicon nitride includes the silicon boronitrides described herein.
Disclosed improvements on the baseline process include (a) adding a boron containing precursor to the process gases, (b) lowering the concentration of silane in the process gas, and (c) a combination of (a) and (b). In certain embodiments, an improvement includes controlling the low frequency RF power between about 0-300 Watts per 300 mm wafer, or between about 0-100 Watts per 300 mm wafer. Processes falling within the scope of these improvements do not require the exact baseline conditions described above. For example, they may be practiced within a range of silane to ammonia flow ratios (e.g., about 0.007 to 0.2), and/or within a range of RF frequencies and powers (e.g., about 100 to 750 Watts per 300 mm wafer HFRF power at 13.56 MHz and about 0 to 300 Watts per 300 mm wafer LFRF power in a frequency range between 370 to 430 KHz), and/or within a range of pressures (e.g., about 0.5 to 6.0 Torr). The above ranges are provided for a 4-station PECVD chamber equipped for depositing films on 300 mm silicon wafers. The flow rates and powers may have to be scaled as appropriate for reactors of other sizes.
In various applications, a silicon nitride layer deposited as described herein is used as a sacrificial layer. In such applications, the silicon nitride layer may be partially or wholly removed by a wet etching process. Thus, the wet-etch rate of the deposited silicon nitride layer may be important for some applications. Examples of wet etchants include hydrofluoric acid (including buffered versions of the acid) and phosphoric acid.
For various applications, the silicon nitride layer should have good thermal stability. That is, it should not out-gas or produce significant uncontrolled changes in internal stress when exposed to post-deposition high temperature processing. The following description addresses certain experiments in which the wet-etch rate and/or the thermal stability of silicon nitride films are reported.
Additionally, various experiments are described in which the deposited silicon nitride films are subjected to a high temperature “anneal.” This anneal is intended to generally represent the high temperature processing that a silicon nitride layer would normally experience after it is deposited during fabrication of other components of a memory or logic device, for example. In many of the experiments described herein, a 750° C. anneal temperature is applied to the film for two hours. In practice, it is expected that post deposition processing may sometimes exceed this temperature, sometimes reaching 800° C. or even 850° C.
Generally, the disclosed embodiments employ plasma assisted deposition processes for forming a silicon nitride-containing film that includes some fraction of boron. The film is deposited in a process station that is configured to receive a process gas containing a silicon-containing reactant, a nitrogen-containing reactant, and a boron-containing reactant. The process gas containing these reactants may be mixed in the process station or premixed upstream before entering the process station. A plasma is generated and maintained and interacts with the process gas to facilitate deposition of the silicon nitride film on a substrate. A carrier gas may be used together with the silicon, nitrogen, and boron-containing reactant gases. In certain embodiments, the carrier gas is nitrogen, hydrogen, a noble gas such as argon, or a combination of these.
In certain embodiments, a relatively low fractional amount of the silicon-containing reactant is used. In some embodiments, the ratio of flow rates of the silicon-containing reactant to the nitrogen-containing reactant is about 0.02 or less.
In certain embodiments, the silicon-containing reactant is silane (SiH4). In other embodiments, the silicon-containing reactant is a variant of silane such as disilane, trisilane, or an alkyl silane such as a mono, di-, tri-, or tetra substituted silane. The alkyl substitutions may include one, two, three, four, five, or six carbon atoms. Generally, the silicon-containing reactant is a gas at room temperature, however, in certain embodiments it may be delivered via a volatilizing carrier gas.
In certain implementations, the nitrogen-containing reactant is ammonia. However, other types of nitrogen-containing reactants may be employed. Examples include hydrazine, nitrous oxide, and elemental nitrogen in the presence of a strong plasma.
In various embodiments, the boron-containing reactant is diborane. Diborane is a liquid at room temperature. Therefore, it is typically delivered to the process station in a carrier gas such as argon, nitrogen or hydrogen. In some embodiments, it is provided at a molar concentration of about 5% diborane in argon. Other sources of boron may be used in some embodiments. These include, for example, alkyl substituted boranes such as trimethyl borane (TMB).
In various embodiments, the ratio of the silicon-containing reactant to the nitrogen-containing reactant is maintained at a relatively low level during deposition of the silicon nitride film. As mentioned, in some embodiments, the volumetric ratio of the silicon-containing reactant to the nitrogen-containing reactant is about 0.02 or less. In other embodiments, the ratio is even smaller, e.g., about 0.01 or less.
These ratios are appropriate for silane and ammonia as the silicon-containing and nitrogen-containing reactants, respectively. In cases where one of the reactants contains proportionately more silicon and/or nitrogen (on a molar basis) than a silane-ammonia mixture, these ratios may need to be adjusted to account for the different elemental amounts of silicon and/or nitrogen in the process gases. An example is the case of a process gas containing trisilane and ammonia.
The ratio of boron-containing reactant to silicon-containing reactant is typically relatively small. In certain embodiments, it is about 0.02 to about 0.1. This represents the volumetric ratio or flow rate ratio between the actual amount of boron-containing reactant and silicon-containing reactant. So, in the case of a 5% diborane process gas, the ratio is determined by considering only the diborane and not the carrier gas in which the diborane is provided. Further, the above ratios are appropriate for diborane and silane. The use of other silicon-containing and/or boron-containing reactants may require that these ratios be adjusted to account for the number of boron or silicon atoms in a molecule of each reactant.
The deposition conditions in the process station during formation of a silicon nitride film may be further characterized by the temperature, pressure, and plasma conditions. In certain embodiments, the pressure in the station during deposition is between about 0.5 and 8 Torr, or between about 1 and 6 Torr. In certain embodiments, the temperature of the substrate on which the silicon nitride film is formed is between about 400 and 650° C. or between about 450 and 600° C. The RF power delivered to the process station during deposition may include a high frequency component and/or a low frequency component. If present, the high frequency component is provided at about 13.56 MHz. The high frequency component may be provided at a power of about 100 to 750 Watts per 300 mm wafer or between about 100 and 500 Watts per 300 mm wafer. If present, the low frequency component may be provided at a frequency of between about 100 and 1000 kHz or between about 370 and 430 kHz. If present, the low frequency component may be provided a power of between about 0 and 300 Watts for a 300 mm wafer or between about 0 and 100 Watts per 300 mm wafer or between about 0 and 75 Watts per 300 mm wafer.
The silicon nitride films formed as disclosed herein typically possess various characteristics that make them suitable for certain applications in the semiconductor device industry. For example, the films are typically no thicker than about 1000 nanometers. In certain embodiments, the films typically have a thickness of between about 10 and 100 nanometers or between about 30 and 50 nanometers. Additionally, the films are relatively smooth. For example, an arithmetically averaged film roughness (Ra), as measured by atomic force microscopy, is at most about 6.0 Ångstroms for a 1000 Ångstrom thick layer or at most about 4.5 Ångstroms for a 1000 Ångstrom thick layer.
The composition of the silicon nitride deposited film includes silicon, nitrogen, and boron. The film may contain between about 0 and 15 atomic percent boron or between about 0 and 5 atomic percent boron. The film may contain between about 30 and 50 atomic percent silicon. The film may contain between about 25 and 50 atomic percent nitrogen. In certain embodiments, the film contains hydrogen as well as silicon, nitrogen, and boron. If present, hydrogen may constitute a relatively low fraction of the film material, e.g., less than about 18 atomic percent or less than about 15 atomic percent.
The film as-deposited will have an internal stress. As described below, this internal stress can be indicated by the amount of bow in a wafer having the film deposited thereon. Of course, the internal stress can also be represented by the numerical value of tensile or compressive stress in megapascal (MPa). In certain embodiments, the boron-containing silicon nitride films disclosed herein have a tensile internal stress. In certain embodiments, that internal stress is between about 400 and 600 MPa.
Three separate measures of in internal stress were employed in the experimental section below. One of these is a bow shift ratio, which is a comparison of the bow shift in the film under consideration to the bow shift in a silicon nitride film produced by the baseline process. For the bow shift measurement described herein the films all had an as-deposited thickness of 1,000 Å. Deposition of silicon nitride films typically produces some curvature, or bow, in the wafer on which it is deposited. The bow is measured as the z-direction difference between the center and perimeter of the wafer. After annealing, this bow typically shifts to some degree (to produce a wafer with greater or lesser curvature than observed after the initial silicon nitride deposition). The change in bow after annealing is the bow shift, and it is typically reported in units of micrometers. The bow shift of a new silicon nitride film is measured and compared to the bow shift of an equal thickness of silicon nitride using the baseline process. The ratio of these two bow shifts may be used to characterize the films.
Another measure of internal stress of the deposited films involves comparing the stress of the deposited films to a “neutral” internal stress of a true stoichiometric silicon nitride film. This measure is relevant because it is assumed that after a certain amount of thermal processing, the as-deposited silicon nitride film transitions to a true stoichiometric silicon nitride film. This can be observed by heating non-stoichiometric unit layer silicon nitride films for long periods of time. Ultimately, a particular minimum internal stress will be attained, presumably corresponding to the stress associated with the stoichiometric silicon nitride. For silicon nitride the neutral stress has been determined to be approximately 700 MPa tensile.
Yet another parameter related to internal stress in silicon nitride films is the “tunability” of stress with respect to one or more process variables. Some silicon nitride and silicon boronitride films produced in accordance with the disclosed processes can have their stress adjusted to between approximately 1000 MPa tensile and approximately 1000 MPa compressive. The independent variables that drive this tunability are most notably the low frequency RF power, the ammonia concentration in the process gas, and the pressure in the PECVD reactor. Certain experiments presented in the Experimental section show that the internal stress is very sensitive to changes in the low-frequency RF power.
The tunability of the internal stress can be important in certain applications making use of silicon nitride and other materials in stacks, particularly those applications where the electrical properties of the other material must be tightly controlled. In certain embodiments, the internal stress of sacrificial silicon nitride layers may be tuned to offset bowing introduced by other layers which cannot have their internal stresses tuned in the same manner. For example, for certain vertical memory applications, where alternating silicon nitride and silicon oxide layers are deposited, silicon oxide layers are not sacrificial and in fact must have highly specific electrical properties, which greatly constrains the process window for depositing them. Within this tight process window, there is little leeway to adjust parameters to modify the internal stress of the as-deposited silicon oxide layer. Therefore, it is left to the silicon nitride layers to offset any significant bowing introduced by the silicon oxide layers. This can be a significant role for the silicon nitride layers, as the vertical stacks in memory applications typically have many layers and the cumulative effect of the internal stress produced by each of the silicon oxide layers can be very great.
One application of particular interest for using silicon nitride films produced as described herein is in vertical memory stacks. These stacks may employ alternating layers of silicon oxide and silicon nitride. After deposition, the stack is etched to form columns and then the columns are subsequently wet etched to partially or fully remove the sacrificial silicon nitride while substantially preserving the silicon oxide. This produces a “fishbone” structure such as that shown in
In the examples presented in the experimental section below, various single layer silicon nitride films (sometimes referred to as “unit layer” films) were produced and then characterized in terms of their chemical composition (Fourier Transform Infrared Spectroscopy (FTIR) spectra), wet-etch rate ratio, internal stress, and other characteristics. Regarding the wet-etch ratio, this was typically measured as a ratio of the wet etch rate of the unit layer silicon nitride film to the wet-etch rate of a thermal oxide film grown at a temperature of 1100° C. Thermal oxide growth on silicon wafers can be achieved using a tube furnace with either wet or dry oxygen as the oxidizing gas. The wet etchant employed was aqueous hydrofluoric acid provided in a volume ratio of 100 units of water to 1 unit standard 50% hydrofluoric acid. In certain embodiments, the ratio of the wet-etch rate of the silicon nitride film relative to the wet etch rate of thermal silicon dioxide in dilute HF is about 0.7 or lower. In some implementations, the wet etch ratio of the silicon nitride to thermal silicon dioxide in dilute HF is between about 0.25 and 0.45. Thermal silicon dioxide is formed by exposing the flat surface of an elemental silicon substrate to oxygen and/or water vapor at a temperature of between about 800 to 1200° C. In some cases, the wet etch rate of silicon nitride in dilute HF is between below about 25 Ångstroms/min. In certain embodiments, the wet etch rate of silicon nitride in dilute HF is between about 10 and 20 Ångstroms/minute or between about 8 and 16 Ångstroms/minute. When using hot phosphoric acid as an etchant, silicon nitride etches faster than thermal silicon dioxide. In some embodiments, silicon nitride formed as described herein etches in hot phosphoric acid at a rate of between about 50 and 200 Ångstroms/minute or between about 100 and 200 Ångstroms/minute. When using hot phosphoric acid, the wet etch ratio between silicon nitride and silicon dioxide is between about 20:1 and 300:1, or between about 30:1 and 200:1, or between about 30:1 and 100:1.
The methods described herein may be performed by any suitable apparatus. A suitable apparatus includes hardware for accomplishing the process operations and a system controller having instructions for controlling process operations in accordance with the present invention. For example, in some embodiments, the hardware may include one or more process stations included in a process tool.
The system controller will typically include one or more memory devices and one or more processors configured to execute instructions for controlling process operations so that the apparatus will perform a method in accordance with the present disclosure. For example, in some embodiments, the system controller may operate various valves, temperature controllers, plasma controllers, and pressure controllers to adjust process conditions within the apparatus. In some embodiments, machine-readable media containing instructions for controlling process operations in accordance with the present disclosure may be coupled to the system controller.
For example,
In some embodiments, showerhead 3178 may be a dual-plenum or multi-plenum showerhead having a plurality of sets of gas distribution holes. For example, a first set of gas distribution holes may receive gas from a first process gas delivery line and a second set of gas distribution holes may receive gas from a second process gas delivery line, etc. Such physical isolation of process gases may provide an approach to reducing the amount of small particles generated from reaction of incompatible process gases in process gas delivery plumbing upstream of showerhead 3178.
Showerhead 3178 and holder 3180 electrically communicate with RF power supply 3188 and matching network 3190 for powering a plasma 3192. Plasma 3192 may be contained by a plasma sheath 3194 located adjacent to showerhead 3178 and holder 3180. While
In the embodiment shown in
In some embodiments, holder 3180 may be temperature controlled via heater 3184. Further, in some embodiments, pressure control for process station 3100 may be provided by butterfly valve 3196 or by any other suitable pressure control device. As shown in
It will be appreciated that control of one or more process parameters may be provided locally (e.g., RF power may be controlled by a plasma controller communicating with RF power supply 3188, process station pressure may be controlled by a valve controller communicating with butterfly valve 3196 or with gas metering valves or flow controllers included coupled with process gas delivery line 3174, etc.) or under partial or total control provided by a system controller (described in more detail below) communicating with process station 3100 without departing from the scope of the present disclosure.
As described above, one or more process stations may be included in a multi-station processing tool. In some embodiments of a multi-station process tool, control and/or supply of various process inputs (e.g., process gases, plasma power, heater power, etc.) may be distributed from shared sources to a plurality of process stations included in the process tool. For example, in some embodiments, a shared plasma generator may supply plasma power to two or more process stations. In another example, a shared gas distribution manifold may supply process gases to two or more process stations.
For example,
In some embodiments, inbound load lock 3302 may be connected to a remote plasma source (not shown) configured to supply a plasma to load lock. This may provide remote plasma treatments to a substrate positioned in inbound load lock 3302. Additionally or alternatively, in some embodiments, inbound load lock 3302 may include a heater (not shown) configured to heat a substrate. This may remove moisture and gases adsorbed on a substrate positioned in inbound load lock 3302. While the embodiment depicted in
The depicted processing chamber 3314 comprises four process stations, numbered from 1 to 4 in the embodiment shown in
In some embodiments, each process station may have different or multiple purposes. For example, a process station may be switchable between a tunable wet etch ratio and internal stress process mode and a conventional PECVD or CVD mode. Additionally or alternatively, in some embodiments, processing chamber 3314 may include one or more matched pairs of tunable wet etch ratio/stress and conventional PECVD stations (e.g., a pair including a tunable wet etch ratio/stress PECVD SiN station and a conventional PECVD SiO2 station). In another example, a process station may be switchable between two or more film types, so that stacks of different film types may be deposited in the same process chamber.
While the depicted processing chamber 3314 comprises four stations, it will be understood that a processing chamber according to the present disclosure may have any suitable number of stations. For example, in some embodiments, a processing chamber may have five or more stations, while in other embodiments a processing chamber may have three or fewer stations.
It will be appreciated that, in some embodiments, a low-pressure transfer chamber may be included in a multistation processing tool to facilitate transfer between a plurality of processing chambers. For example,
Turning back to
System controller 3350 may include one or more memory devices 3356, one or more mass storage devices 3354, and one or more processors 3352. Processor 3352 may include a CPU or computer, analog and/or digital input/output connections, stepper motor controller boards, etc.
In some embodiments, system controller 3350 controls all of the activities of processing tool 3300. In some embodiments, system controller 3350 executes machine-readable system control software 3358 stored in mass storage device 3354, loaded into memory device 3356, and executed on processor 3352. Alternatively, the control logic may be hard coded in the controller. Applications Specific Integrated Circuits, Programmable Logic Devices (e.g., FPGAs) and the like may be used for these purposes. In the following discussion, wherever “software” or “code” is used, functionally comparable hard coded logic may be used in its place.
System control software 3358 may include instructions for controlling the timing, mixture of gases, chamber and/or station pressure, chamber and/or station temperature, substrate temperature, target power levels, RF power levels, substrate pedestal, chuck and/or susceptor position, and other parameters of a particular process performed by processing tool 3300. System control software 3358 may be configured in any suitable way. For example, various process tool component subroutines or control objects may be written to control operation of the process tool components for performing various process tool processes. System control software 3358 may be coded in any suitable computer readable programming language.
In some embodiments, system control software 3358 may include input/output control (IOC) sequencing instructions for controlling the various parameters described above. For example, each phase of a tunable wet etch rate/stress process may include one or more instructions for execution by system controller 3350. The instructions for setting process conditions for a tunable PECVD process phase may be included in a corresponding tunable recipe phase. In some embodiments, the tunable PECVD recipe phases may be sequentially arranged, so that all instructions for—a tunable PECVD process phase are executed concurrently with that process phase.
Other computer software and/or programs stored on mass storage device 3354 and/or memory device 3356 associated with system controller 3350 may be employed in some embodiments. Examples of programs or sections of programs for this purpose include a substrate positioning program, a process gas control program, a pressure control program, a heater control program, and a plasma control program.
A substrate positioning program may include program code for process tool components that are used to load the substrate onto process station substrate holder 3318 and to control the spacing between the substrate and other parts of processing tool 3300.
A process gas control program may include code for controlling gas composition and flow rates and optionally for flowing gas into one or more process stations prior to deposition in order to stabilize the pressure in the process station. For example, the process gas control program may include code for achieving a desired wet etch rate and/or internal stress by supplying a particular amount of a boron-containing precursor such as diborane. The amount of diborane flowed is determined by the controller based on the desired wet etch rate and/or internal stress. As another example, the process gas control program may include code for achieving a desired wet etch rate and/or internal stress by supplying a particular ratio of silane-containing precursor to nitrogen-containing precursor. The ratio of these precursors is controlled by the controller to achieve the desired film property. A pressure control program may include code for controlling the pressure in the process station by regulating, for example, a throttle valve in the exhaust system of the process station, a gas flow into the process station, etc.
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 substrate.
A plasma control program may include code for setting RF power levels applied to the process electrodes in one or more process stations. In one example, a plasma control program may include code for setting the LF RF power level based on a desired internal stress level.
In some embodiments, there may be a user interface associated with system controller 3350. 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 some embodiments, parameters adjusted by system controller 3350 may relate to process conditions. Non-limiting examples include process gas composition and flow rates, temperature, pressure, plasma conditions (such as RF bias power levels), pressure, temperature, etc. These parameters may be provided to the user in the form of a recipe, which may be entered utilizing the user interface.
Signals for monitoring the process may be provided by analog and/or digital input connections of system controller 3350 from various process tool sensors. The signals for controlling the process may be output on the analog and digital output connections of processing tool 3300. Non-limiting examples of process tool sensors that may be monitored include mass flow controllers, pressure sensors (such as manometers), thermocouples, etc. Appropriately programmed feedback and control algorithms may be used with data from these sensors to maintain process conditions.
System controller 3350 may provide program instructions for implementing the above-described deposition processes. The program instructions may control a variety of process parameters, such as DC power level, RF bias power level, pressure, temperature, etc. The instructions may control the parameters to operate in-situ deposition of film stacks according to various embodiments described herein.
The various hardware and method embodiments described above may be used in conjunction with lithographic patterning tools or processes, for example, for the fabrication or manufacture of semiconductor devices, displays, LEDs, photovoltaic panels and the like. Typically, though not necessarily, such tools/processes will be used or conducted together in a common fabrication facility.
Lithographic patterning of a film typically comprises some or all of the following steps, each step enabled with a number of possible tools: (1) application of photoresist on a workpiece, e.g., a substrate having a silicon nitride film formed thereon, using a spin-on or spray-on tool; (2) curing of photoresist using a hot plate or furnace or other suitable curing tool; (3) exposing the photoresist to visible or UV or x-ray light with a tool such as a wafer stepper; (4) developing the resist so as to selectively remove resist and thereby pattern it using a tool such as a wet bench or a spray developer; (5) transferring the resist pattern into an underlying film or workpiece by using a dry or plasma-assisted etching tool; and (6) removing the resist using a tool such as an RF or microwave plasma resist stripper. In some embodiments, an ashable hard mask layer (such as an amorphous carbon layer) and another suitable hard mask (such as an antireflective layer) may be deposited prior to applying the photoresist.
It is to be understood that the configurations and/or approaches described herein are exemplary in nature, and that these specific embodiments or examples are not to be considered in a limiting sense, because numerous variations are possible. The specific routines or methods described herein may represent one or more of any number of processing strategies. As such, various acts illustrated may be performed in the sequence illustrated, in other sequences, in parallel, or in some cases omitted. Likewise, the order of the above described processes may be changed.
The electroplating apparatus/methods described hereinabove may be used in conjunction with lithographic patterning tools or processes, for example, for the fabrication or manufacture of semiconductor devices, displays, LEDs, photovoltaic panels and the like. Generally, though not necessarily, such tools/processes will be used or conducted together in a common fabrication facility. Lithographic patterning of a film generally comprises some or all of the following steps, each step enabled with a number of possible tools: (1) application of photoresist on a work piece, i.e., a substrate, using a spin-on or spray-on tool; (2) curing of photoresist using a hot plate or furnace or UV curing tool; (3) exposing the photoresist to visible, UV, or x-ray light with a tool such as a wafer stepper; (4) developing the resist so as to selectively remove resist and thereby pattern it using a tool such as a wet bench; (5) transferring the resist pattern into an underlying film or work piece by using a dry or plasma-assisted etching tool; and (6) removing the resist using a tool such as an RF or microwave plasma resist stripper.
The subject matter of the present disclosure includes all novel and nonobvious combinations and sub-combinations of the various processes, systems and configurations, and other features, functions, acts, and/or properties disclosed herein, as well as any and all equivalents thereof.
The following description explains certain aspects of
Analysis has determined that some samples of the baseline SiN film contain about 13.4 atomic percent hydrogen as determined by RBS/HFS spectroscopy. This same film was found to have a hydrogen concentration of 15.6% when measured by FTIR, using an assumed bond density of 8.9×1022/cm3. The film was smooth, with average roughness Ra of 5.0 Ångstroms as determined by Atomic Force Microscopy.
The baseline process is a plasma enhanced chemical vapor deposition (PECVD) process that employs silane and ammonia as reactant process gases. Nitrogen is used as a carrier gas. In the baseline process, these process gases are delivered to a four station reactor (e.g., a Vector® Extreme or Vector® Express reactor from Novellus Systems, Inc. of San Jose, Calif.) where they are reacted to produce silicon nitride films on 300 mm wafers. The silane is delivered at a flow rate of about 200 sccm (100% silane), the ammonia is delivered at about 1140 sccm, and the nitrogen at about 9000 sccm. The pressure employed in the process is about 2 Torr. Low-frequency & high-frequency RF power is provided to generate the plasma. It employs a low frequency radio frequency (LF RF) of 400 kHz at a power of about 0 to 150 Watts (about 0-40 W per 300 mm wafer) and a high frequency radio frequency (HF RF) of 13.56 MHz at a power of about 800 Watts (about 200 W per 300 mm wafer).
Turning now to
“Ratio Bow Shift,” “Bow Ratio,” and “Bow Shift Ratio” refer to the ratio of wafer bow shift induced by annealing a silicon nitride layer produced using the improved processes described herein to the bow shift induced by annealing a silicon nitride layer produced by the baseline process. Generally, a suitable result will be observed when the new silicon nitride layer produces a bow shift that is nominally equal to or less than the bow shift exhibited by the silicon nitride produced by the baseline process. However, in certain implementations it may be desirable to achieve a bow shift ratio above 1. As described herein, the internal stress of the silicon nitride layer (one measure of which is the bow shift) may be tuned to offset stress induced by other layers. As such, the target bow shift ratio may be variable based on the particular application.
The terms “LowHSiN” and “LowH (BKM)” refer to silicon nitride produced using the baseline process. It is presumed that the silicon nitride produced by the baseline process has a relatively low content of silicon hydrogen bonding.
The parameter “WER ratio” refers to the wet-etch rate ratio between a thermal oxide film grown at a temperature of 1100° C. and a silicon nitride film under consideration. The etch rate of a film is determined by exposing it to dilute hydrofluoric acid as described above.
The parameter “AFM Ra” is a measure of the average roughness of the surface of the substrate (an arithmetic mean).
The spectra presented in
In the plot on the lower right hand side, the baseline process is shown in the lower curve, the low diborane process is represented by the intermediate curve, and the high diborane process is represented by the upper curve. The relative positions of these curves are reversed in the plot on the lower left, i.e. the plot having a peak centered near 3300 reciprocal centimeters. Notably, the FTIR shows that increasing the diborane flow results in two B—N peaks appearing at around 1200 cm−1 and 1380 cm−1. Further, higher diborane flow leads to a lower N—H peak and corresponding area.
The third column in
In
The plot presented in
FIGS. 13 and 14A-D illustrate the effect of the ammonia flow rate in the low silane process space described above.
Films deposited using processes employing diborane are characterized in
SiH4=40 sccm
NH3=1040 sccm
N2=9000 sccm
Diborane varied as noted in table on Page 11
Pressure=2.4 torr
Temperature 550° C.
HFRF=800 W (200 W per 300 mm wafer)
LFRF=adjusted between 65 and 100 W to tune stress (between 16-25 W per 300 mm wafer)
All examples and information provided in
As shown in the FTIR plots show in
In
The data in
The silicon nitride employed in the stacks has different compositions at different levels. Specifically, three different compositions of silicon nitride (including silicon boronitride) were employed in each of the stacks. These different silicon nitrides were introduced in successive silicon nitride layers in the stacks as depicted in the diagram of
Note that the bow shift ratio decreased with increasing etch rates. Both of these changes are desirable. For many applications, it is important to have not only a thermally stable film, but also a film that exhibits a high wet etch rate. Further, it may be desirable to be able to adjust the wet etch rate and/or bow shift to a desired value.
The stack considered in
Each of the three unique nitride layer compositions used to generate the stacks and micrographs shown in
In certain embodiments, the flow ratio range of silane flow to total diborane flow (where only about 5% of the total diborane flow is diborane, and the remaining 95% is a carrier gas) is about 0.15 to about 0.5 (SiH4/5% B2H6). In certain embodiments, the flow ratio range of SiH4 to NH3 is about 0.02 or less. In a specific embodiment, the flow ratio between SiH4 to NH3 is about 0.013 or less. It should be understood that variations of the process employ boron precursors other than diborane and/or silicon hydrides other than silane, and/or nitrogen-containing gases other than ammonia or elemental nitrogen.
The data presented in
With a 31 layer stack and the baseline nitride, a 62 micrometer bow shift was observed with a 750° C. anneal. With the same 31 layer stack, the bow shift essentially doubled when the anneal temperature was raised to 800° C. In contrast, the 30 layer stacks including boronitride had a much smaller bow shift (about 33 micrometers), which was essentially temperature invariant. Similar results were observed with the 61 and 91 layer stacks.
This application claims benefit of U.S. Provisional Patent Application Ser. No. 61/612,872, titled “SMOOTH SILICON—CONTAINING FILMS,” and filed on Mar. 19, 2012 and U.S. Provisional Patent Application Ser. No. 61/598,814, titled “SMOOTH SILICON—CONTAINING FILMS,” and filed on Feb. 14, 2012, both of which are incorporated herein by reference in their entireties and for all purposes. This application is also a continuation-in-part of U.S. patent application Ser. No. 12/970,853, titled “SMOOTH SILICON—CONTAINING FILMS,” filed on Dec. 16, 2010, which claims benefit of each of the following U.S. provisional patent applications: U.S. Provisional Patent Application Ser. No. 61/394,707, titled “IN-SITU PLASMA-ENHANCED CHEMICAL VAPOR DEPOSITION OF FILM STACKS,” and filed on Oct. 19, 2010; U.S. Provisional Patent Application Ser. No. 61/382,465, titled “IN-SITU PLASMA-ENHANCED CHEMICAL VAPOR DEPOSITION OF FILM STACKS,” and filed on Sep. 13, 2010; U.S. Provisional Patent Application Ser. No. 61/382,468, titled “SMOOTH SILANE-BASED FILMS,” and filed on Sep. 13, 2010; and U.S. Provisional Patent Application Ser. No. 61/317,656, titled “IN-SITU PLASMA-ENHANCED CHEMICAL VAPOR DEPOSITION OF FILM STACKS,” and filed on Mar. 25, 2010, each of which is incorporated by reference in its entirety and for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 61612872 | Mar 2012 | US | |
| 61598814 | Feb 2012 | US | |
| 61394707 | Oct 2010 | US | |
| 61382465 | Sep 2010 | US | |
| 61382468 | Sep 2010 | US | |
| 61317656 | Mar 2010 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12970853 | Dec 2010 | US |
| Child | 13766696 | US |
