Patent Application
20200111669
The present invention generally relates to a method of depositing an oxide film on an underlying layer by plasma-enhanced atomic layer deposition (PEALD) without substantially damaging the underlying layer.
Depositing a SiO2 film by PEALD is a method which can be conducted at a low temperature of e.g., 100° C. or lower and thus enables effective deposition of a conformal film on an organic film susceptible to heat by taking advantage of the low temperature deposition. This method is applied to patterning processes such as those by spacer-defined double patterning (SDDP) or spacer-defined quadruple patterning (SDQP) (more generally referred to as “SDxP”). However, conventional PEALD for depositing a SiO2 film uses a plasma of a mixed gas of Ar and O2, in which a photoresist is exposed to the plasma in the beginning of deposition until the photoresist is covered by a SiO2 film, thereby causing the photoresist to be etched and making it difficult to control the patterning size in a desired range. Considering recent trends of scale miniaturization of devices and complication of a fabrication process, the above problem can no longer be ignored in processes of next generation devices. Accordingly, there is a demand for processes which enable depositing an insulation film on an underlying photoresist while suppressing etching of the photoresist as much as possible. The present inventors have conducted research to improve patterning accuracy in semiconductor fabrication.
Any discussion of problems and solutions in relation to the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion was known at the time the invention was made.
Some embodiments of the present invention provide a method of suppressing a size reduction of patterns formed with an organic material (e.g., a photoresist) while depositing an insulation film thereon by reducing adverse effect (e.g., etching the organic material) by the deposition process. Conventionally, Ar has been used as a carrier gas for feeding a precursor to a reaction chamber, and a plasma of a mixture of Ar and O2 has been used for depositing an insulation film. Some embodiments are characterized in that N2 is used in place of Ar (wherein all Ar gas is replaced by N2 gas). A N2 plasma does not promote etching of a photoresist as compared with an Ar plasma, and a N2/O2 plasma (“/” indicates “+”) does not promote etching of a photoresist as compared with an Ar/O2 plasma (“/” indicates “+”), and thus, by taking advantage of the above characteristics, an insulation film (or a protective film) can be deposited on a photoresist while substantially suppressing a size reduction of photoresist patterns by using a N2 plasma or a N2/O2 plasma.
N2 may be used as a carrier gas for depositing a nitride film; however, in typical embodiments, N2 is used as a carrier gas for depositing an oxide film. In general, since a surface reaction for depositing a SiN film requires more energy than that for other films, the surface is exposed to a N2 plasma for a relatively long period of time to form a SiN film, whereas since an O2 plasma (or more specifically oxygen radicals) has high reactivity, a SiO2 film can be deposited by exposing a surface to the O2 plasma for a relatively short period of time. Accordingly, by adding O2 to N2 to generate simultaneously a N2 plasma and an O2 plasma (a N2/O2 plasma) and controlling a duration of exposure to the plasma for a relatively short, an oxide film can be formed even using N2 (i.e., the exposure to the N2/O2 plasma is controlled in a manner that the duration is long enough to cause oxidization to form an oxide film but is short enough not to cause nitridation to form a nitride film).
Some embodiments provide a method of forming an oxide film in a process of forming an insulation film by PEALD for SDxP patterning, while suppressing a shrinkage of an underlying carbon material layer, which method is characterized by at least one of the following:
A) N2 is used as a carrier gas for feeding a precursor to a reaction chamber, and a dry gas consists of N2, so that no other inert gas such as Ar and He is used as a plasma-forming gas.
B) As an oxidizing gas, O2, N2O, NO, NO2, CO, and/or CO2 are/is used singly or in any combination of two or more.
C) The duration of applying RF power is 1.0 second or less, preferably as short as about 0.2 seconds.
D) RF power is as low as 100 W or less (for a 300-mm wafer when using electrodes for conductively coupled plasma, CCP, or 0.14 W/cm2 or less as power density).
In some embodiments, the insulation film is constituted by SiO, TiO, ZrO, or other metal oxides wherein a precursor can be selected according to the target film.
In some embodiments, the underlying layer on which the oxide film is deposited is a photoresist or carbon hard mask, typically constituted by an organic material.
For purposes of summarizing aspects of the invention and the advantages achieved over the related art, certain objects and advantages of the invention are described in this disclosure. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
Further aspects, features and advantages of this invention will become apparent from the detailed description which follows.
These and other features of this invention will now be described with reference to the drawings of preferred embodiments which are intended to illustrate and not to limit the invention. The drawings are greatly simplified for illustrative purposes and are not necessarily to scale.
In this disclosure, “gas” may include vaporized solid and/or liquid and may be constituted by a single gas or a mixture of gases, depending on the context. Likewise, an article “a” or “an” refers to a species or a genus including multiple species, depending on the context. In this disclosure, a process gas introduced to a reaction chamber through a showerhead may be comprised of, consist essentially of, or consist of a silicon- and/or meal-containing precursor and an additive gas. The additive gas may include a reactant gas for oxidizing and/or nitriding the precursor, and an inert gas (e.g., noble gas and/or nitrogen gas) for exciting the precursor, when RF power is applied to the additive gas. The inert gas may be fed to a reaction chamber as a carrier gas and/or a dilution gas. The precursor and the additive gas can be introduced as a mixed gas or separately to a reaction space. The precursor can be introduced with a carrier gas such as a rare gas. A gas other than the process gas, i.e., a gas introduced without passing through the showerhead, may be used for, e.g., sealing the reaction space, which includes a seal gas such as a rare gas. In some embodiments, the term “precursor” refers generally to a compound that participates in the chemical reaction that produces another compound, and particularly to a compound that constitutes a film matrix or a main skeleton of a film, whereas the term “reactant” refers to a compound, other than precursors, that activates a precursor, modifies a precursor, or catalyzes a reaction of a precursor, wherein the reactant may provide an element (such as N, O) to a film matrix and become a part of the film matrix, when RF power is applied. The term “inert gas” refers to a gas that excites a precursor when RF power is applied, but unlike a reactant, it substantially does not become a part of a film matrix.
In some embodiments, “film” refers to a layer continuously extending in a direction perpendicular to a thickness direction substantially without pinholes to cover an entire target or concerned surface, or simply a layer covering a target or concerned surface. In some embodiments, “layer” refers to a structure having a certain thickness formed on a surface or a synonym of film or a non-film structure. A film or layer may be constituted by a discrete single film or layer having certain characteristics or multiple films or layers, and a boundary between adjacent films or layers may or may not be clear and may be established based on physical, chemical, and/or any other characteristics, formation processes or sequence, and/or functions or purposes of the adjacent films or layers. Further, in this disclosure, any two numbers of a variable can constitute a workable range of the variable as the workable range can be determined based on routine work, and any ranges indicated may include or exclude the endpoints. Additionally, any values of variables indicated (regardless of whether they are indicated with “about” or not) may refer to precise values or approximate values and include equivalents, and may refer to average, median, representative, majority, etc. in some embodiments. Further, in this disclosure, the terms “constituted by” and “having” refer independently to “typically or broadly comprising,” “comprising,” “consisting essentially of,” or “consisting of” in some embodiments. In this disclosure, any defined meanings do not necessarily exclude ordinary and customary meanings in some embodiments.
In the present disclosure where conditions and/or structures are not specified, the skilled artisan in the art can readily provide such conditions and/or structures, in view of the present disclosure, as a matter of routine experimentation.
In all of the disclosed embodiments, any element used in an embodiment can be replaced with any elements equivalent thereto, including those explicitly, necessarily, or inherently disclosed herein, for the intended purposes. Further, the present invention can equally be applied to apparatuses and methods.
The embodiments will be explained with respect to preferred embodiments. However, the present invention is not limited to the preferred embodiments.
In some embodiments, a method of depositing an oxide film on a template for patterning in semiconductor fabrication, comprises: (i) providing a template having patterned structures thereon in a reaction space; and (ii) depositing an oxide film on the template by plasma-enhanced atomic layer deposition (PEALD) using nitrogen gas as a carrier gas and also as a dilution gas, thereby entirely covering with the oxide film an exposed top surface of the template and the patterned structures. A nitrogen plasma does not cause a significant plasma damage to an underlying layer, but can be used for deposition of an oxide film by PEALD by manipulating the duration of being exposed to the nitrogen plasma, RF power to generate the nitrogen plasma, etc. so as to avoid interference with oxidization of a precursor by an oxidizing gas plasma.
In some embodiments, in step (ii), the carrier gas and the dilution gas consist essentially of nitrogen gas. If a noble gas such as Ar is used as or added to the carrier gas and/or the dilution gas, the underlying layer is likely to be damaged by sputtering effect of an Ar plasma. In some embodiments, substantially, all carrier gas and all dilution gas are constituted solely by nitrogen gas. In some embodiments, at least 95%, preferably at least 97%, by volume of the carrier gas and dilution gas are constituted by nitrogen gas. In some embodiments, substantially no noble gas is supplied to the reaction space during step (ii).
In some embodiments, the carrier gas and the dilution gas each are continuously supplied to the reaction space throughout step (ii) at a flow rate of 0.5 to 5 slm, preferably 1 to 2 slm.
In some embodiments, an oxidizing gas used in step (ii) is one or more gases selected from the group consisting of O2, N2O, NO, NO2, CO, and CO2.
In some embodiments, the oxidizing gas is continuously supplied to the reaction space throughout step (ii) at a flow rate of 10 sccm to 1000 sccm, preferably 50 sccm to 500 sccm. In some embodiments, a ratio of flow rate of oxidizing gas to flow rate of carrier/dilution gas is 2/100 to 40/100, preferably about 4/100 to about 30/100.
In some embodiments, in a PEALD cycle used in step (ii), a duration of applying RF power to the reaction space is 1.0 seconds or less, preferably 0.1 to 1.0 seconds, more preferably 0.1 to 0.5 seconds.
In some embodiments, in a PEALD cycle used in step (ii), RF power applied to the reaction space is 0.14 W/cm2 or less per area of a substrate on which the template is formed, preferably 0.014 to 0.14 W/cm2, more preferably 0.042 to 0.14 W/cm2.
In some embodiments, a precursor used in step (ii) contains silicon or a metal such as Ti, Zr, Ta, etc., so as to deposit a film constituted by SiO, TiO, ZrO, TaO, etc., i.e., the oxide film formed in step (ii) is constituted by silicon oxide or metal oxide.
In some embodiments, the patterned structures are constituted by polymer resist and/or carbon hard mask. For example, the vertical spacers can be formed using as a pre-patterned feature (mandrel) a photoresist pattern or a hard mask patterned using a photoresist. In some embodiments, the patterned structures are constituted by an organic material.
In some embodiments, the method further comprises, after step (ii): (iii) etching the oxide film-covered template to remove an unwanted portion of the oxide film and the patterned structures so as to form vertical spacers isolated from each other for use in spacer-based patterning.
In some embodiments, the spacer-based patterning is spacer-defined double patterning (SDDP), spacer-defined quadruple patterning (SDQP), spacer-defined direct patterning, or the like. The oxide film according some embodiments can be applied to various patterning processes including processes of spacer-defined multiple patterning such as those disclosed in U.S. Publication No. 2017/0316940, processes of spacer-defined double patterning such as those disclosed in U.S. Pat. No. 8,197,915, and U.S. application Ser. No. 15/489,660, filed Apr. 17, 2017, U.S. application Ser. No. 15/832,188, filed Dec. 5, 2017, and U.S. Pat. No. 8,901,016, each disclosure of which is herein incorporated by reference in its entirety.
The present invention will be explained with reference to the drawings. However, the drawings are not intended to limit thereto.
In (a2), ideally, the bar critical dimension (Bar CD) of the vertical spacer 36 is the same as the thickness of the oxide film 33 deposited on the sidewall of the SOH 34, and the inner spacer critical dimension (Inner Space CD) is the same as the thickness of the SOH 34. However, although the oxide film is deposited by ALD at a low temperature, since the photoresist and the SOH are constituted by a carbon-based material or organic material which is easily damaged by an oxygen plasma, when an oxygen plasma is used as a reactant for depositing the oxide film, the carbon-based material or organic material is etched by the oxygen plasma while the oxide film is depositing even at a low temperature. As a result, as illustrated in (b1), the sidewall of the SOH 34 is etched by the oxygen plasma, forming concaved sidewalls. Then, when the oxide film 33 is subjected to anisotropic etching to strip the core material to form vertical spacers 37, since the thickness of the SOH is reduced along the sidewalls, the inner space CD is reduced by the amount of the sidewall of the SOH being etched, which constitutes a CD shew as illustrated in (b2). This CD change may affect the quality of a final semiconductor product. If thermal ALD is used which does not use an oxygen plasma for depositing an oxide film, theoretically, the above problem may not occur. However, such non-plasma approach (e.g., by thermal ALD using H2O) is quite challenging and has not been fully successful. In some embodiments of the present invention, by using nitrogen gas in combination with oxygen, in place of conventional Ar in combination with oxygen, as a carrier gas (and/or a dilution gas), even when depositing an oxide film by PEALD, CD changes can be minimized.
The continuous flow of the carrier gas can be accomplished using a flow-pass system (FPS) wherein a carrier gas line is provided with a detour line having a precursor reservoir (bottle), and the main line and the detour line are switched, wherein when only a carrier gas is intended to be fed to a reaction chamber, the detour line is closed, whereas when both the carrier gas and a precursor gas are intended to be fed to the reaction chamber, the main line is closed and the carrier gas flows through the detour line and flows out from the bottle together with the precursor gas. In this way, the carrier gas can continuously flow into the reaction chamber, and can carry the precursor gas in pulses by switching the main line and the detour line.
A skilled artisan will appreciate that the apparatus includes one or more controller(s) (not shown) programmed or otherwise configured to cause the deposition and reactor cleaning processes described elsewhere herein to be conducted. The controller(s) are communicated with the various power sources, heating systems, pumps, robotics, and gas flow controllers or valves of the reactor, as will be appreciated by the skilled artisan.
In some embodiments, an oxide film can be deposited according to the sequence illustrated in
In this disclosure, any indicated RF power for a 300-mm wafer can be converted to W/cm2 (wattage per unit area of a wafer) which can apply to a wafer having a different diameter such as 200 mm or 450 mm.
In some embodiments, the oxide film is constituted by SiO2, TiO, HfO, ZrO, TaO, or AlO. In some embodiments, the precursor for PEALD is an alkylaminosilane. In some embodiments, the alkylaminosilane is selected from the group consisting of bisdiethylaminosilane (BDEAS), bisdimethylaminosilane (BDMAS), hexylethylaminosilane (HEAD), tetraethylaminosilane (TEAS), tert-butylaminosilane (TBAS), bistert-butylaminosilane (BTBAS), bisdimethylaminodimethylaminosilane (BDMADMS), heptamethylsilazane (HMDS), trimethysylyldiethlamine (TMSDEA), trimethylsyledimethylamine (TMSDMA), trimethyltoribinylcycletri silazane (TMTVCTS), tristrimethylhydroxyamine (TTMSHA), bisdimethylsaminomethylsilane (BDMAMS), and dimetyhlsilyldimethylamine (DMSDMA). The precursor can be constituted by a single precursor or a mixture of two or more precursors. In some embodiments, the oxide film has a conformality of 80% to 100% (typically about 90% or higher) wherein the “conformality” is determined by comparing film thickness deposited at some point (typically a middle point in a cross sectional view) on a sidewall or on a bottom of a recess to film thickness deposited on a flat surface just outside the recess.
The template having patterned structures on which the oxide film is deposited can be formed by any suitable methods including conventional methods. Typically, the thickness of the patterned structures is in a range of about 100 nm to about 500 nm, preferably, about 100 nm to about 200 nm, the distance between the patterned structures (the interval) is in a range of about 20 nm to about 200 nm, preferably, about 30 nm to about 100 nm, and the depth thereof is in a range of about 100 nm to about 500 nm, preferably, about 100 nm to about 200 nm, depending on the designed width of target trenches, the design of circuits, the fabrication processes, etc.
The oxide film-covered template can effectively be etched by any suitable methods to remove an unwanted portion of the oxide film and the patterned structures so as to form vertical spacers isolated from each other for use in spacer-based patterning, under conditions which a skilled artisan in the art can readily provide in view of the present disclosure, as a matter of routine experimentation.
In this disclosure, any indicated RF power for a 300-mm wafer can be converted to W/cm2 (wattage per unit area of a wafer) which can apply to a wafer having a different diameter such as 200 mm or 450 mm.
In some embodiments, alternatively, the first template/hardmask 91 is not used, and the core material 96 (which may be referred to generally as “a resist pattern”) is constituted by a photoresist material. Further, alternatively, the core material 96 is constituted by both a photoresist material and a carbon hardmask material.
It should be noted that when depositing the thin oxide layer by PEALD on the resist pattern, since PEALD generates more radicals and creates more ion bombardment than does thermal ALD or radical ALD (remote plasma), conventionally, the resist pattern surface is trimmed to a certain extent in step (c). Thus, the width of the resist pattern is reduced in step (c). The above-described phenomenon (trimming takes place while depositing) can be seen or confirmed by observing a STEM photograph of a cross section of the resist pattern or by measuring an increase of the line width in step (c) which is lower than that in the case where the same layer is deposited under the same conditions except that the layer is deposited on a chemically stable non-resist material. When step (c) is conducted as the above-discussed depositing step using a nitrogen/oxygen plasma, substantially without using other inert gas plasma such as an rare gas plasma (e.g., an Ar plasma), the trimmed quantity of the resist pattern can be substantially reduced.
These processes can be performed using any suitable apparatus including an apparatus illustrated in
In some embodiments, in the apparatus depicted in
In some embodiments, a dual chamber reactor (two sections or compartments for processing wafers disposed closely to each other) can be used, wherein a reactant gas and a noble gas can be supplied through a shared line whereas a precursor gas is supplied through unshared lines.
The present invention is further explained with reference to working examples below. However, the examples are not intended to limit the present invention. In the examples where conditions and/or structures are not specified, the skilled artisan in the art can readily provide such conditions and/or structures, in view of the present disclosure, as a matter of routine experimentation. Also, the numbers applied in the specific examples can be modified by a range of at least ±50% in some embodiments, and the numbers are approximate.
A photoresist layer (a blanket photoresist constituted by e.g., Novolacs designed for Argon Fluoride laser (ArF) lithography) was formed on a 300-mm substrate at a thickness which was considered to be an initial CD (“PR initial”) shown in
As shown in
A silicon oxide film (a blanket film) was deposited on a 300-mm substrate by PEALD in an apparatus illustrated in
As shown in
Additionally, silicon oxide films were deposited on substrates, respectively, under conditions substantially similar to those shown in Table 3 above. The deposited silicon oxide films were then subjected to wet etching using a dHF (500:1) solution (at a temperature of 25° C. for 180 seconds). As a result, both silicon oxide films (both “N2/O2 PEALD SiO” and “N2/O2 PEALD SiO”) exhibited a WERR (a wet etch rate relative to that of thermal oxide film) of about 20. Further, the film uniformity of both silicon oxide films remained low.
Silicon oxide films were deposited on substrates, respectively, in a manner similar to that in Reference Example 2 under conditions shown in Table 4 blow. Thus-obtained silicon oxide films were subjected to composition analysis based on a Fourier Transform Infrared (FTIR) spectrum.
A photoresist layer (a blanket photoresist) was formed on a 300-mm substrate in a manner similar to that in Reference Example 1, and then the substrate was loaded to an apparatus illustrated in
As shown in
A 300-mm substrate with a photoresist pattern (ArF resist) is prepared by photolithography, which has a width of 50 nm, a pitch of 70 nm, and a height of 100 nm, wherein the resist pattern has a CD of <0.5 nm. A silicon oxide film is then deposited on the substrate by PEALD in an apparatus illustrated in
Next, the SiO film is subjected to etching (anisotropic etching) to remove an unwanted portion of the SiO film and the photoresist so as to form vertical spacers isolated from each other under conditions shown in Table 6 below for use in spacer-based patterning.
As a result, the vertical spacers having substantially the same CD as that of the initial photoresist pattern are obtained.
It will be understood by those of skill in the art that numerous and various modifications can be made without departing from the spirit of the present invention. Therefore, it should be clearly understood that the forms of the present invention are illustrative only and are not intended to limit the scope of the present invention.
