Patent Publication Number: US-11658035-B2

Title: Substrate processing method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of and priority to U.S. Provisional Application No. 63/046,511, filed on Jun. 30, 2020 in the United States Patent and Trademark Office, the disclosure of which is incorporated herein in its entirety by reference. 
    
    
     BACKGROUND 
     1. Field 
     One or more embodiments relate to a substrate processing method, and more particularly, to a substrate processing method capable of improving etch selectivity without increasing the power. 
     2. Description of the Related Art 
     Recently, the necessity of performing a selective deposition process on a patterned three-dimensional (3D) structure has increased. For example, in manufacturing a 3D NAND flash device, a process of selectively depositing only an upper portion of a stepwise structure has been used. In order to implement such selective deposition, it is necessary to increase the etch selectivity of thin films deposited on the top and side of a pattern structure. 
     For example, plasma may be applied to increase the etch selectivity of the thin films deposited on the top and side of the pattern structure. Due to the straightness and ion bombardment effect of radicals generated by plasma application, thin films on the top and bottom of the pattern structure in a direction perpendicular to a traveling direction of the radicals may be densified. On the other hand, the thin film on the side of the pattern structure in a direction parallel to the traveling direction of the radicals may be less dense than the thin films on the top and bottom of the pattern structure. Therefore, the thin film on the side of the pattern structure is removed by wet etching, and the thin films on the top and bottom of the pattern structure may remain. 
     There is a limit to densification of thin films by radicals and improvement of etching selectivity. For example, even when certain RF power is applied, the desired etch selectivity of the thin films deposited on the top and side of the pattern structure may not be achieved. Therefore, higher RF power may be applied to overcome this, in which case damage may occur inside a reactor. Components inside the reactor, such as a shower head, may be destroyed or damaged by, for example, high ion bombardment or a plasma arc. 
     SUMMARY 
     One or more embodiments include a method of selectively depositing a thin film on an area of a structure having a step without performing a separate photolithography process, and more particularly, a method capable of improving etch selectivity without increasing the power to selectively deposit a thin film on a pattern structure (e.g., a stepwise structure) without a photolithography process. 
     Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments of the disclosure. 
     According to one or more embodiments, a substrate processing method includes supplying a first gas onto a structure, supplying a second gas to form a first thin film on the structure, forming a second material layer by supplying the first gas on the first thin film, removing a portion of the second material layer to expose a portion of the first thin film, removing the exposed portion of the first thin film, and removing the second material layer. 
     According to an example of the substrate processing method, first plasma may be applied during the supplying of the second gas, and second plasma may be applied during the forming of the second material layer. 
     According to another example of the substrate processing method, during the supplying of the first gas, a first material layer may be formed on the structure, and the second gas may be changed to have reactivity with the first material layer by applying the first plasma. 
     According to another example of the substrate processing method, the first gas may be dissociated by the application of the second plasma to form the second material layer. 
     According to another example of the substrate processing method, the removing of a portion of the second material layer and the removing of the exposed portion of the first thin film may be performed by isotropic etching. 
     According to another example of the substrate processing method, the removing of a portion of the second material layer and the removing of the exposed portion of the first thin film may be performed using an identical etchant. 
     According to another example of the substrate processing method, the second plasma may include directional plasma, and properties of the second material layer may be partially changed by the second plasma. 
     According to another example of the substrate processing method, during the isotropic etching, the remaining portion of the second material layer functions as a mask, so that a portion of the first thin film under the second material layer remains and the remaining portion of the first thin film may be removed. 
     According to another example of the substrate processing method, a frequency of first power supplied during the application of the first plasma may be greater than a frequency of second power supplied during the application of the second plasma. 
     According to another example of the substrate processing method, the first gas may include a silicon source including a carbon element, and the second material layer may include a silicon element and a carbon element. 
     According to another example of the substrate processing method, the first thin film may include at least one of silicon oxide or silicon nitride, and the second material layer may further include oxygen or nitrogen. 
     According to another example of the substrate processing method, the second material layer may have etch selectivity with respect to the first thin film. 
     According to another example of the substrate processing method, the second material layer may include a carbon element, and a WER for hydrogen fluoride (HF) of the first thin film may be greater than a WER for hydrogen fluoride of the second material layer. 
     According to another example of the substrate processing method, for a certain etchant, a first portion of the second material layer has a first WER, and a second portion of the second material layer has a second WER greater than the first WER, and the first thin film may have a third WER greater than the second WER. 
     According to another example of the substrate processing method, the substrate processing method may further include trimming the first thin film. 
     According to another example of the substrate processing method, the trimming of the first thin film may include removing an overhang of the first thin film. 
     According to one or more embodiments, a substrate processing method includes supplying a silicon-containing source gas onto a structure to form a first silicon-containing material layer adsorbed on the structure, forming a first thin film on the structure by supplying a reaction gas reactive with the silicon-containing source gas, supplying the silicon-containing source gas on the first thin film and applying directional plasma to form a second silicon-containing material layer adsorbed on the first thin film, wherein the second silicon-containing material layer is partially densified or weakened by the directional plasma, exposing a portion of the first thin film by performing isotropic etching on the second silicon-containing material layer, removing the exposed portion of the first thin film, and performing anisotropic etching to remove the second silicon-containing material layer. 
     According to one or more embodiments, a substrate processing method includes forming a first thin film on a structure, forming a material layer having wet etch resistance greater than that of the first thin film on the first thin film, removing a portion of the material layer using wet etching to expose a portion of the first thin film, and removing the exposed portion of the first thin film. 
     According to an example of the substrate processing method, the forming of the material layer may include forming a material layer adsorbed on the first thin film by supplying a first gas. 
     According to another example of the substrate processing method, during the forming of the first thin film, the first gas used in the forming of the material layer may be used. In addition, during the forming of the material layer, the first gas used in the forming of the first thin film may be used. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of certain embodiments of the disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
         FIGS.  1  to  7    are flowcharts of a substrate processing method according to embodiments of the inventive concept; 
         FIG.  8    is a flowchart of a substrate processing method according to embodiments of the inventive concept; 
         FIG.  9    is a flowchart of a substrate processing method according to embodiments of the inventive concept; 
         FIG.  10    is a process flowchart of a substrate processing method according to embodiments of the inventive concept; 
         FIG.  11    is a schematic view of a process in which the process of  FIG.  10    is performed; and 
         FIG.  12    is a view showing an embodiment of the first and second steps of  FIGS.  10  and  11   ; and 
         FIG.  13    is a detailed view of a process of the fifth step of  FIGS.  10  and  11   . 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, the present embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the embodiments are merely described below, by referring to the figures, to explain aspects of the present description. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. 
     Hereinafter, one or more embodiments will be described more fully with reference to the accompanying drawings. 
     In this regard, the present embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Rather, these embodiments are provided so that the present disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to one of ordinary skill in the art. 
     The terminology used herein is for the purpose of describing particular embodiments and is not intended to limit the disclosure. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes”, “comprises” and/or “including”, “comprising” used herein specify the presence of stated features, integers, steps, processes, members, components, and/or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, processes, members, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various members, components, regions, layers, and/or sections, these members, components, regions, layers, and/or sections should not be limited by these terms. These terms do not denote any order, quantity, or importance, but rather are only used to distinguish one component, region, layer, and/or section from another component, region, layer, and/or section. Thus, a first member, component, region, layer, or section discussed below could be termed a second member, component, region, layer, or section without departing from the teachings of embodiments. 
     In the disclosure, “gas” may include evaporated solids and/or liquids and may include a single gas or a mixture of gases. In the disclosure, a process gas introduced into a reaction chamber through a shower head may include a precursor gas and an additive gas. The precursor gas and the additive gas may typically be introduced as a mixed gas or may be separately introduced into a reaction space. The precursor gas may be introduced together with a carrier gas such as an inert gas. The additive gas may include a dilution gas such as a reaction gas and an inert gas. The reaction gas and the dilution gas may be mixedly or separately introduced into the reaction space. The precursor may include two or more precursors, and the reaction gas may include two or more reaction gases. The precursor may be a gas that is chemisorbed onto a substrate and typically contains metalloid or metal elements constituting a main structure of a matrix of a dielectric film, and the reaction gas for deposition may be a gas that is reactive with the precursor chemisorbed onto the substrate when excited to fix an atomic layer or a monolayer on the substrate. The term “chemisorption” may refer to chemical saturation adsorption. A gas other than the process gas, that is, a gas introduced without passing through the shower head, may be used to seal the reaction space, and it may include a seal gas such as an inert gas. In some embodiments, the term “film” may refer to a layer that extends continuously in a direction perpendicular to a thickness direction without substantially having pinholes to cover an entire target or a relevant surface, or may refer to a layer that simply covers a target or a relevant surface. In some embodiments, the term “layer” may refer to a structure, or a synonym of a film, or a non-film structure having any thickness formed on a surface. The film or layer may include a discrete single film or layer or multiple films or layers having some characteristics, and the boundary between adjacent films or layers may be clear or unclear and may be set based on physical, chemical, and/or some other characteristics, formation processes or sequences, and/or functions or purposes of the adjacent films or layers. 
     In the disclosure, the expression “containing an Si—N bond” may be referred to as characterized by an Si—N bond or Si—N bonds having a main skeleton substantially constituted by the Si—N bond or Si—N bonds and/or having a substituent substantially constituted by the Si—N bond or Si—N bonds. A silicon nitride layer may be a dielectric layer containing a Si—N bond, and may include a silicon nitride layer (SiN) and a silicon oxynitride layer (SiON). 
     In the disclosure, the expression “same material” should be interpreted as meaning that main components (constituents) are the same. For example, when a first layer and a second layer are both silicon nitride layers and are formed of the same material, the first layer may be selected from the group consisting of Si2N, SiN, Si3N4, and Si2N3 and the second layer may also be selected from the above group but a particular film quality thereof may be different from that of the first layer. 
     Additionally, in the disclosure, according as an operable range may be determined based on a regular job, any two variables may constitute an operable range of the variable and any indicated range may include or exclude end points. Additionally, the values of any indicated variables may refer to exact values or approximate values (regardless of whether they are indicated as “about”), may include equivalents, and may refer to an average value, a median value, a representative value, a majority value, or the like. 
     In the disclosure where conditions and/or structures are not specified, those of ordinary skill in the art may easily provide these conditions and/or structures as a matter of customary experiment in the light of the disclosure. In all described embodiments, any component used in an embodiment may be replaced with any equivalent component thereof, including those explicitly, necessarily, or essentially described herein, for intended purposes, and in addition, the disclosure may be similarly applied to devices and methods. 
     Hereinafter, embodiments of the disclosure will be described with reference to the accompanying drawings. In the drawings, variations from the illustrated shapes may be expected as a result of, for example, manufacturing techniques and/or tolerances. Thus, the embodiments of the disclosure should not be construed as being limited to the particular shapes of regions illustrated herein but may include deviations in shapes that result, for example, from manufacturing processes. 
       FIGS.  1  to  7    are flowcharts of a substrate processing method according to embodiments of the inventive concept. 
     Referring to  FIG.  1   , a stepwise structure  10  is provided. The stepwise structure  10  may be on a substrate (not shown). The stepwise structure  10  may include one layer or a plurality of layers. For example, the stepwise structure  10  may be formed by reactive ion etching and/or resist sliming with respect to a stacked structure including a plurality of layers. 
     Upon forming the stepwise structure  10 , the stepwise structure  10  has an upper surface U, a lower surface L, and a side surface S connecting the upper surface U to the lower surface L. For example, the stepwise structure  10  may include at least one step, and the at least one step may have the upper surface U, the lower surface L, the side surface S connecting the upper surface U to the lower surface L. 
     Although the stepwise structure  10  is illustrated in the present embodiment and the substrate processing method is described based on this, the inventive concept is not limited thereto. For example, the substrate processing method according to embodiments of the inventive concept may be utilized for selective deposition of any type of a three-dimensional (3D) structure. For example, selective deposition of a pattern structure including a plurality of overhangs may be achieved. 
     When the stepwise structure  10  is provided, at least one thin film is formed on the stepwise structure  10 . The thin film may be formed through any kind of deposition process (e.g., deposition processes such as sputtering, chemical vapor deposition (CVD), physical vapor deposition (PVD), and atomic layer deposition (ALD)). For example, a first material layer  20  is formed by supplying a first gas on a structure ( FIG.  1   ), and a second gas is supplied to form a first thin film  30  on the structure ( FIG.  2   ). The first material layer  20  and the second gas may react to form the first thin film  30 . 
     For example, the first thin film  30  may be a silicon oxide film, a silicon nitride film, or a silicon oxynitride film. The first gas used to form the first thin film  30  may include a silicon-containing source gas. Thus, a silicon-containing source gas may be supplied onto the structure to form a silicon-containing material layer chemisorbed onto the structure. 
     For example, the first gas may be an aminosilane-based silicon-containing source gas containing a methyl group (—C n H 2n+1 ) or an ethyl group (—C n H 2n+2 ). That is, the first gas may include a silicon source containing a carbon element. Accordingly, a material layer formed by the first gas may include a silicon element and a carbon element. As will be described later below, the material layer including the carbon element may have good etch selectivity to silicon oxide or silicon nitride. 
     In some embodiments, in order to form the first thin film  30 , an ALD process may be used. For example, a basic cycle of source supply, source purge, reactant supply, and reactant purge may be repeated several times to form the first thin film  30  having a desired thickness. In this case, the first gas is supplied during the source supply to form the first material layer  20 , and the second gas is supplied during the reactant supply to form the first thin film  30 . 
     In an alternative embodiment, energy may be applied to promote reaction of the first material layer  20  and the second gas. For example, during supplying of the second gas, the first plasma may be applied. By applying energy such as the first plasma, the second gas may be changed (e.g., excited) to be reactive with the first material layer  20 . Therefore, the second gas and the first material layer  20  may react to form the first thin film  30 . 
     Referring to  FIG.  3   , a second material layer  40  is formed by supplying a first gas on the first thin film  30 . The supplying of the first gas on the first thin film  30  may be repeated a plurality of times. For example, a cycle including supplying a first gas and purging the first gas may be performed a plurality of times. By repeating this cycle, the second material layer  40  of a desired thickness may be formed. 
     The second material layer  40  may have different chemical properties from those of the first thin film  30 . In more detail, the second material layer  40  may have higher wet etch resistance than that of the first thin film  30 . Accordingly, when wet etching of the first thin film  30  and the second material layer  40  is performed, the amount of the first thin film  30  removed may be greater than the amount of the second material layer  40  removed. Thus, during the etching process for the first thin film  30 , the second material layer  40  may function as an etch mask. 
     A gas supplied during the forming of the second material layer  40  and a gas supplied during the forming of the first thin film  30  may be the same. That is, while forming the second material layer  40 , a first gas including a silicon source containing a carbon element may be supplied. Therefore, the second material layer  40  may include silicon elements and carbon elements. 
     The carbon element included in the second material layer  40  may reduce a wet etch rate (WER) for hydrogen fluoride (HF). Therefore, when the first thin film  30  and the second material layer  40  are wet-etched using HF, a WER for HF of the first thin film  30  containing no carbon element may be greater than a WER for HF of the second material layer  40  containing the carbon element. 
     The second material layer  40  may be a material layer adsorbed on the first thin film  30 . For example, the first gas used to form the second material layer  40  may include a source gas used in an ALD process. In this case, the second material layer  40  may be formed by chemically adsorbing the first gas on the first thin film  30 . 
     In some embodiments, the second material layer  40  formed on the first thin film  30  may include at least a portion of components of the first thin film  30 . For example, when the first thin film  30  includes silicon oxide, the second material layer  40  may include an oxygen element. In another example, when the first thin film  30  includes silicon nitride, the second material layer  40  may include a nitrogen element. 
     In some embodiments, second plasma may be applied while supplying the first gas to form the second material layer  40 . In a conventional ALD process, plasma is not applied while supplying the source gas. On the other hand, it is noted that according to embodiments of the inventive concept, plasma is applied while supplying the source gas. The first gas may be dissociated by the application of the second plasma, and thus the formation of the second material layer  40  may be promoted. 
     In some embodiments, the application of the second plasma may be performed after the supplying of the first gas. In other words, the application of the second plasma may be included in one cycle to form the second material layer  40 . Hereinafter, it is assumed that the supplying of the first gas and the applying of the second plasma included in the forming of the second material layer  40  are sequentially performed. 
       FIG.  4    shows the applying of the second plasma. The second plasma may partially change properties of the second material layer  40 . For example, the second plasma may have directionality. As an example, the second plasma may be applied to face upper and lower surfaces of the second material layer  40 , and thus properties of an upper surface portion  40 U and a lower surface portion  40 L of the second material layer  40  may be changed by application of the directional second plasma. 
     In some embodiments, process conditions of applying first plasma to form the first thin film  30  may be different from process conditions of applying second plasma. For example, a frequency of first power supplied during the application of the first plasma may be greater than a frequency of second power supplied during the application of the second plasma. By applying second plasma at a relatively low frequency, linearity (i.e., directionality) of ions may be improved. 
     In an example, application of directional second plasma may densify portions of a second material layer located on upper and lower surfaces of the stepwise structure  10 . In another example, the application of the directional second plasma may weaken the portions of the second material layer located on the upper and lower surfaces of the stepwise structure  10 . This change in properties may be achieved by adjusting parameters (e.g., the amount of power) during a plasma process. Hereinafter, it will be described on the premise that the upper and lower surface portions  40 U and  40 L of the second material layer  40  are densified due to application of plasma. 
     Referring to  FIG.  5   , a portion of the second material layer  40  is removed to expose a portion of the first thin film  30 . A first isotropic etching process, such as wet etching, may be used to remove the second material layer  40 . When the upper and lower surface portions  40 U and  40 L of the second material layer  40  are densified due to application of directional second plasma, during first isotropic etch, a side portion  40 S (of  FIG.  4   ) of the second material layer  40  are removed, while the upper and lower surface portions  40 U and  40 L of the second material layer  40  may remain. Therefore, after the first isotropic etching, a side surface portion  30 S of the stepwise structure  10  of the first thin film  30  is exposed, while upper and lower surface portions  30 U and  30 L of the stepwise structure  10  of the first thin film  30  may be covered with the second material layer  40 . 
     Thereafter, referring to  FIG.  6   , an exposed portion of the first thin film  30  is removed. For example, a second isotropic etching may be performed on a structure after the first isotropic etching. During the second isotropic etching, the remaining portions  40 U and  40 L of the second material layer  40  may act as an etch mask. Therefore, the portions  30 U and  30 L of the first thin film under the second material layer  40  remains without being etched, while the remaining portion (i.e., exposed portion  30 S) of the first thin film  30  may be removed to expose a surface of the stepwise structure  10 . 
     In some embodiments, removing of the portion  40 S of the second material layer  40  and the removing of the exposed portion  30 S of the first thin film  30  may be performed simultaneously. For example, in other words, the removing of the portion  40 S of the second material layer  40  and the removing of the exposed portion  30 S of the first thin film  30  may be performed by a single etching process. That is, the first isotropic etching and the second isotropic etching may be the same etching process. 
     For example, for a certain etchant, densified portions (the upper and lower surface portions  40 U and  40 L of the stepwise structure  10 ) of the second material layer  40  may have a first WER, a non-densified portion (the side portion  40 S of the stepwise structure  10 ) of the second material layer  40  may have a second WER greater than the first WER, and the first thin film  30  may have a third WER greater than the second WER. 
     In this case, isotropic etching of the first thin film  30  and the second material layer  40  may be performed using the certain etchant. First, the second material layer  40  is exposed to the etchant, so that the upper and lower surface portions  40 U and  40 L of the second material layer  40  with the lowest value of the first WER may remain, and the side portion  40 S of the second material layer  40  with the relatively high value of the second WER may be removed. 
     Because the isotropic etching is continuously performed using the etchant, the upper and lower surface portions  40 U and  40 L of the second material layer  40  with the lowest value of the first WER and the upper and lower surface portions  30 U and  30 L of the first thin film  30  under the upper and lower surface portions  40 U and  40 L remain, while the exposed portion of the first thin film  30  with the highest value of the third WER, that is, the side surface portion  30 S of the stepwise structure  10  may be removed. 
     In an alternative embodiment, the first isotropic etching and the second isotropic etching may be different etching processes. For example, removing the portion  40 S of the second material layer  40  using the first isotropic etching and removing the exposed portion  30 S of the first thin film  30  using the second isotropic etch may be performed using different types of etchant. As another example, the first isotropic etching and the second isotropic etching are performed using the same type of etchant, but at least some of process parameters may be different. 
     Referring to  FIG.  7   , the second material layer  40  remaining after isotropic etching is removed. Anisotropic etching processes, such as dry etching, may be used to remove the remaining second material layer  40 . The first thin film  30  partially formed on upper and lower surfaces of the stepwise structure  10  may be exposed by removing the second material layer  40 . 
     As shown in  FIG.  7   , the exposed first thin film  30  may include an overhang  50 . The overhang  50  may have a shape protruding from the side surface S of the stepwise structure  10 . In order to eliminate this protruding shape, trimming of the first thin film  30  may be performed. In some embodiments, a sputtering process may be performed during the trimming of the first thin film  30 . In another embodiment, any further processing (e.g., annealing) of the first thin film  30  may be performed during the trimming of the first thin film  30 . 
       FIG.  8    is a flowchart of a substrate processing method according to embodiments of the inventive concept. The substrate processing method according to the embodiments may be a variation of the substrate processing method according to the above-described embodiments. Hereinafter, repeated descriptions of the embodiments will not be given herein. 
     Referring to  FIG.  8   , in operation  810 , a silicon-containing source gas is supplied onto a structure (e.g., a stepwise structure). A first silicon-containing material layer may be formed by adsorbing the silicon-containing source gas onto the structure. In operation  820 , after the first silicon-containing material layer is formed, a residual source gas is purged. 
     Thereafter, in operation  830 , a reaction gas reactive with the silicon-containing source gas is supplied. Because the first silicon-containing material layer adsorbed on the structure reacts with the reaction gas, a first thin film may be formed on the structure. In operation  840 , after the first thin film is formed, a residual reaction gas is purged. 
     In operation  850 , when the first thin film is formed, a silicon-containing source gas is supplied on the first thin film to form a second silicon-containing material layer adsorbed on the first thin film. Directional plasma may be applied while supplying the silicon-containing source gas, and the second silicon-containing material layer may be partially densified or weakened by the directional plasma. 
     Thereafter, in operation  860 , first isotropic etching is performed on the second silicon-containing material layer to partially remove the second silicon-containing material layer. The first thin film may be partially exposed by the first isotropic etching. Because properties of the second silicon-containing material layer are partially changed by the directional plasma, patterning of the second silicon-containing material layer may be achieved only by isotropic etching without a separate lithography process, and the first thin film may be partially exposed. 
     Thereafter, in operation  870 , the exposed portion of the first thin film is removed. For example, isotropic etching may be performed on the exposed portion of the first thin film by using second isotropic etching. Because the second silicon-containing material layer exists on an unexposed portion of the first thin film, the unexposed portion of the first thin film may remain after the second isotropic etching. Therefore, patterning of the first thin film may be achieved only by isotropic etching without a separate lithography process. 
     Thereafter, in operation  880 , the second silicon-containing material layer is removed. For example, the second silicon-containing material layer may be removed using anisotropic etching. 
     According to embodiments of the inventive concept as described above, because a relatively thin material layer adsorbed (e.g., chemically adsorbed) with a source gas is formed on a thin film to be patterned (i.e., the first thin film) and selective densification/weakening is performed on the material layer without using direct selective densification/weakening of the thin film to be patterned, a thin film may be selectively deposited on a pattern structure (e.g., a stepwise structure) without a photolithography process and without increasing power. 
       FIG.  9    is a flowchart of a substrate processing method according to embodiments of the inventive concept. The substrate processing method according to the embodiments may be a variation of the substrate processing method according to the above-described embodiments. Hereinafter, repeated descriptions of the embodiments will not be given herein. 
     Referring to  FIG.  9   , in operation  910 , a first thin film is formed on the structure. The first thin film may be formed through any kind of deposition process (e.g., deposition processes such as sputtering, CVD, PVD, and ALD), and a first gas may be used during the deposition process. In an example, the first gas may include components of the first thin film. In a further example, the first gas may include an elemental component that is resistant to an etchant used in a subsequent etching process. 
     Thereafter, in operation  920 , a material layer having wet etch resistance greater than that of the first thin film is formed on the first thin film. For example, a material layer having a lower WER than that of the first thin film may be formed. The forming of the material layer may include forming a material layer adsorbed on the first thin film by supplying the first gas. In other words, during the forming of the material layer, the first gas used in the forming of the first thin film may be used. 
     In operation  930 , after the material layer is formed or during the forming of the material layer, partial densification or weakening of the material layer is performed. By applying certain energy (e.g., plasma) towards the material layer, properties of the material layer may be partially changed. In this case, a WER of the material layer may also be partially changed. 
     Thereafter, in operation  940 , the first thin film is patterned using wet etching. In more detail, wet etching is performed on a material layer having partially different WER properties, so that a portion of the material layer may be removed, and consequently, a part of a lower portion of the material layer may be exposed. Thereafter, an exposed portion of the first thin film is removed by continuous wet etching, so that the first thin film may be patterned. 
     In addition to the above-described embodiments, the disclosure discloses a method of increasing etch selectivity of upper and side portions of a material having low etch resistance deposited on a pattern structure.  FIG.  10    is a process flowchart of a substrate processing method according to the disclosure, and  FIG.  11    is a schematic view of a process in which the process of  FIG.  10    is performed. 
     First step  101 : In this step, a first thin film  2  is uniformly deposited on a surface of a pattern structure  1  to form a conformal film. The thin film deposition is performed by a PEALD method, and a precursor, a purge gas, and a reaction gas are alternately supplied to activate at least one gas by plasma. 
     Second step  201 : In this step, a second thin film  3  is deposited as a mask layer on the first thin film. The second thin film  3  is formed by dissociating a precursor molecule with plasma while supplying only a precursor and a purge gas without supplying a reaction gas. The dissociated precursor molecule is deposited on the first thin film  2 . Because the second thin film  3  has different wet etch resistance from the first thin film  2  and does not supply a reaction gas, a thin film is not formed by chemical bonding between heterogeneous elements and dissociated precursor constituent elements are densified by radicals. That is, in this step, a mask layer having different etch resistance is introduced to increase selectivity. 
     Third step  301 : In this step, the thin film is selectively removed through wet etching. In particular, in the second step, the first thin film and the second thin film on upper and lower surfaces of the second thin film (mask layer), which are densified by an ion bombardment effect and are simultaneously etch resistant, remain, and the second thin film and the first thin film on a side surface that are less dense are removed. For example, wet etching is performed using a 100:1 hydrofluoric acid (HF) solution. 
     Fourth step  401 : In this step, the second thin film on the upper and lower surfaces is removed. The removal of the second thin film is performed by dry etching. The second thin film is removed using an etching gas containing fluorine (F), such as C x F 2x . 
     Fifth step  501 : In this step, an overhang  4  remaining on an edge of the upper surface is removed. The removal of the overhang  4  proceeds with a sputtering process. For example, in order to enhance straightness of ions, low frequency Ar plasma is supplied to remove the overhang  4 . 
       FIG.  12    is a view showing an embodiment of the first and second steps of  FIGS.  10  and  11   . In the first step of  FIG.  12   , a Si source gas, an oxygen reaction gas, an Ar purge gas and plasma are sequentially supplied to a substrate to deposit a first thin film of SiO 2  on a pattern structure on the substrate. This step is repeated several times (m cycles) to uniformly form a first thin film having a thickness of 300 Å on a pattern. Thereafter, in the second step, a second thin film is deposited on the first thin film. In the second thin film, the oxygen reaction gas is not supplied, and the Si source gas, the Ar purge gas and the plasma are sequentially supplied as one cycle which is repeated several times (n cycles), and a second thin film having a thickness of 30 Å is deposited on an upper surface of the pattern. In step  2 , because there is no reaction gas, the Si source gas is deposited on the first thin film while being dissociated by an Ar radical. In an embodiment of the disclosure, a Si source containing a carbon element, for example, an aminosilane-based Si source containing a methyl group (—C n H 2n+1 ) or an ethyl group (—C n H 2n+2 ) is used. In more detail, in an embodiment of the disclosure, a diisopropylaminosilane (DIPAS) Si source is used. Therefore, the second thin film deposited on the first thin film includes Si and C components. In addition, the second thin film may include oxygen elements. For example, on locations above the first thin film contacting the second thin film, some of oxygen elements from an O 2 -terminated site or dangling bonded oxygens of the first thin film of SiO 2  may be included in the second thin film. Therefore, the second thin film may include a small amount of oxygen components. The second thin film including the carbon components and the oxygen components may be expressed as Si(O)C. 
     As described above, because the second thin film is not a film formed by chemical bonding between heterogeneous elements, the bonding force may be weaker than that of the first thin film. Therefore, the thin film is densified while supplying plasma. In addition, the second thin film is not a thin film by chemical bonding, and a thickness of the second thin film on a side of the pattern is less than a thickness of the second thin film on the upper surface of the pattern. Furthermore, the second thin film on the side of the pattern also has a small densification effect by plasma. Therefore, the second thin film on the side of the pattern has lower wet etch resistance than that of the second thin film on the upper surface of the pattern. On the other hand, because the second thin film on the upper surface of the pattern is arranged on a pattern surface in the direction perpendicular to a direction of a radical, the second thin film is densified by plasma and has strong wet etch resistance. As described above, according to embodiments of the inventive concept, a second thin film having different wet etch resistance may be selectively formed. 
     Table 1 below shows an example of process conditions of the first step described above. 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Items 
                 Conditions 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 Process temperature  
                 Room temperature to 550° C. (preferably  
               
               
                 (° C.) 
                 50° C. to 300° C.) 
               
               
                 Process pressure (Torr) 
                 1.0 Torr to 5.0 Torr (preferably 2.0 Torr  
               
               
                   
                 to 3.0 Torr) 
               
               
                 Si precursor  
                 DIPAS (diisopropylaminosilane) 
               
               
                 Reactant  
                 O2 
               
               
                 Purge gas 
                 Ar 
               
            
           
           
               
            
               
                 First step (SiO2 layer forming step) 
               
            
           
           
               
               
               
            
               
                 Process  
                 Source supply 
                 0.05 sec to 2.0 sec (preferably 0.1 sec to 1.0 
               
               
                 time  
                 (S1) 
                 sec) 
               
               
                 (sec)  
                 Source purge 
                 0.05 sec to 2.0 sec (preferably 0.1 sec to 1.0 
               
               
                   
                 (S2)  
                 sec) 
               
               
                   
                 Plasma  
                 0.05 sec to 2.0 sec (preferably 0.1 sec to 1.0 
               
               
                   
                 application (S3)  
                 sec) 
               
               
                   
                 Purge (S4)  
                 0.05 sec to 2.0 sec (preferably 0.1 sec to 1.0 
               
               
                   
                   
                 sec) 
               
               
                 Gas flow 
                 Source carrier 
                 100 sccm to 10,000 sccm (preferably 600 
               
               
                 rate  
                 (Ar) 
                 sccm to 1,200 sccm) 
               
               
                 (sccm)  
                 Reactant (O2) 
                 50 sccm to 400 sccm (preferably 100 sccm to 
               
               
                   
                   
                 300 sccm) 
               
               
                   
                 Purge gas (Ar)  
                 1,000 sccm to 10,000 sccm (preferably 3,000 
               
               
                   
                   
                 sccm to 6,000 sccm) 
               
               
                 Plasma  
                 RF power (W)  
                 100 W to 1,000 W (preferably 200 W  
               
               
                 conditions 
                   
                 to 400 W) 
               
               
                   
                 RF frequency 
                 13 MHz to 100 MHz (preferably 27 MHz  
               
               
                   
                   
                 to 60 MHz) 
               
               
                   
               
            
           
         
       
     
     Table 2 below shows an example of the process conditions of the second step described above. 
     
       
         
           
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Item 
                 Condition 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 Process temperature (° C.) 
                 Room temperature to 550° C. (preferably  
               
               
                   
                 50° C. to 300° C.) 
               
               
                 Process pressure (Torr) 
                 1.0 Torr to 5.0 Torr (preferably 2.0 Torr to  
               
               
                   
                 3.0 Torr) 
               
               
                 Si precursor  
                 DIPAS (diisopropylaminosilane) 
               
               
                 Purge gas 
                 Ar 
               
            
           
           
               
            
               
                 Second step (mask layer forming step) 
               
            
           
           
               
               
               
            
               
                 Process  
                 Source supply  
                 0.05 sec to 2.0 sec (preferably 0.1 sec to  
               
               
                 time  
                 (S1) 
                 1.0 sec) 
               
               
                 (sec)  
                 Source purge  
                 0.05 sec to 2.0 sec (preferably 0.1 sec to  
               
               
                   
                 (S2)  
                 1.0 sec) 
               
               
                   
                 Plasma  
                 0.05 sec to 2.0 sec (preferably 0.1 sec to  
               
               
                   
                 application (S3)  
                 1.0 sec) 
               
               
                   
                 Purge (S4) 
                 0.05 sec to 2.0 sec (preferably 0.1 sec to  
               
               
                   
                   
                 1.0 sec) 
               
               
                 Gas flow 
                 Source carrier 
                 100 sccm to 10,000 sccm (preferably 600 
               
               
                 rate  
                 (Ar) 
                 sccm to 1,200 sccm) 
               
               
                 (sccm)  
                 Purge gas (Ar) 
                 1,000 sccm to 10,000 sccm (preferably  
               
               
                   
                   
                 3,000 sccm to 6,000 sccm) 
               
               
                 Plasma  
                 RF power (W)  
                 100 W to 1,000 W (preferably 200 W to  
               
               
                 conditions 
                   
                 400 W) 
               
               
                   
                 RF frequency 
                 13 MHz to 100 MHz (preferably 27 MHz  
               
               
                   
                   
                 to 60 MHz) 
               
               
                   
               
            
           
         
       
     
     The RF power applied in the first step of Table 1 and the second step of Table 2 may remain the same. That is, it is not necessary to increase the RF power in the second step in order to increase etch selectivity of thin films on the upper surface and the side of the pattern. This is because the etch selectivity may be increased by introducing two thin films having different wet etch resistances, as described later below. Therefore, the substrate processing method according to the disclosure has a technical effect that may prevent problems such as increased fatigue of a substrate processing device due to an increase in applied RF power, for example, damage to components constituting the substrate processing device and resulting reduction in uptime of the substrate processing device. 
     An RF frequency of the RF power applied in the second step of Table 2 may remain the same as in step  1 , but in another embodiment, relatively low frequency RF power may be applied in the second step. Low-frequency RF power has low ion density compared to high-frequency RF power, but has a technical effect to further increase the density of the second thin film on the upper surface of the pattern because ion straightness is improved. Preferably, an RF frequency of about 300 kHz to about 500 kHz may be applied. 
     In the case of the third step  301  of  FIG.  10   , wet etching is performed for 3 minutes in an HF solution diluted to 100:1. Table 3 below shows wet etch resistances to HF of the first SiO 2  thin film and the second Si(O)C thin film according to the disclosure. The etch resistance below is measured by depositing each thin film on a flat substrate under the conditions shown in Table 1 and Table 2 and etching the each thin film for 3 minutes in the HF solution diluted to 100:1. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                   
                 SiO2 
                 Si(O)C 
               
               
                   
                   
               
             
            
               
                   
                 WER (Å/min) 
                 ~120 
                 ~0.88 
               
               
                   
                   
               
            
           
         
       
     
     As can be seen from Table 3, the wet etch resistance of the second Si(O)C thin film to HF is significantly greater than that of the first SiO2 thin film. Because the carbon component (C) is known to have strong etch resistance to HF, a precursor containing a carbon component is introduced such that a second thin film may include the carbon component. As described above, the substrate processing method according to the disclosure has a technical effect that may further improve etch selectivity of upper and side surfaces of a pattern without increasing RF power by introducing two thin films with different wet etch resistances or elements with strong etch resistance. 
     Also, as described above, because the second thin film on a side surface of the pattern is less dense than the second thin film on the upper surface of the pattern, there is a technical effect of promoting etching of the first and second thin films on the side surface of the pattern more than those on the upper surface of the pattern. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 below shows etching conditions of the fourth and fifth steps of FIG. 11. 
               
            
           
           
               
               
            
               
                 Items 
                 Conditions 
               
               
                   
               
            
           
           
               
            
               
                 Fourth step (dry etching step) 
               
            
           
           
               
               
               
            
               
                 CF 4  gas 
                 Temperature 
                 Room temperature to 550° C. 
               
               
                   
                 (° C.) 
                   
               
               
                   
                 Pressure (Torr) 
                 5 Torr or less (preferably 3 Torr or less) 
               
               
                   
                 Flow rate (sccm) 
                 50 sccm to 200 sccm (preferably 100 sccm  
               
               
                   
                   
                 to 150 sccm) 
               
               
                   
                 Supply time 
                 5.0 seconds to 20.0 seconds (preferably  
               
               
                   
                 (sec)  
                 10.0 seconds to 15.0 seconds) 
               
            
           
           
               
            
               
                 Fifth step (sputtering step) 
               
            
           
           
               
               
               
            
               
                 Ar gas 
                 Temperature 
                 Room temperature to 550° C. 
               
               
                   
                 (° C.) 
                   
               
               
                   
                 Pressure (Torr) 
                 7 Torr or less (preferably 5 Torr or less) 
               
               
                   
                 Flow rate (sccm)  
                 8,000 sccm to 15,000 sccm (preferably  
               
               
                   
                   
                 10,000 sccm to 12,000 sccm) 
               
               
                   
                 Supply time 
                 5.0 seconds to 20.0 seconds (preferably  
               
               
                   
                 (sec)  
                 10.0 seconds to 15.0 seconds) 
               
               
                   
                 RF plasma 
                 400 watt, 430 kHz, 10 seconds. 
               
               
                   
               
            
           
         
       
     
       FIG.  13    is a detailed view of the process of the fifth step. Referring to  FIG.  13   , an Ar radical physically removes an overhang of a first thin film, such as a SiO 2  thin film on an upper surface of a pattern. In order to increase a sputtering effect, an Ar gas is supplied, which is heavier than other elements, and low frequency RF power is supplied to enhance straightness of a radical. After sputtering, the overhang is removed, and a portion of the first thin film on the upper surface of the pattern may be etched depending on the size and time of applied RF power (see dashed lines in  FIG.  13   ). In addition, a portion of an upper surface of the first SiO 2  thin film on the upper surface of the pattern may be etched together due to sputtering. 
     According to the disclosure, in order to improve etch selectivity of the first thin film deposited on the pattern, a second thin film having different wet etch resistance from that of the first thin film is formed on the first thin film as a mask layer. In an embodiment according to the disclosure, the second thin film has a high wet etch resistance compared to the first thin film, and has a technical effect of improving etching selectivity of upper and side portions of the pattern without increasing RF power. 
     In addition, the substrate processing method according to the disclosure has a technical effect of preventing an increase in fatigue of a substrate processing device due to high RF power application. 
     In addition, in an embodiment according to the disclosure, by selectively forming a film having strong wet etch resistance on an upper surface of the pattern compared to a side surface of the pattern, the substrate processing method has a technical effect that may further accelerate an etching rate of the film on the side surface. 
     In addition, the substrate processing method according to the disclosure has a technical effect of physically removing the overhang of the thin film on the upper surface of the pattern by realizing etching selectivities of the thin films on the upper and side surfaces of the pattern and by applying a sputtering method to the overhang of the thin film. 
     It should be understood that embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments. While one or more embodiments have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the disclosure as defined by the following claims.