Substrate processing method

Abstract

A substrate processing method according to the present application is a method of processing a substrate in which films including a first silicon oxide film, a silicon nitride film, and a second silicon oxide film are stacked from the outermost side, and includes a first etching step of etching the first silicon oxide film and a second etching step of etching the silicon nitride film and the second silicon oxide film. In the first etching step, a residual layer of the first silicon oxide film is left, and in the second etching step, the residual layer of the first silicon oxide film, the silicon nitride film, and the second silicon oxide film are etched uniformly. The present application has an effect of etching the silicon nitride film and the silicon oxide film of an etching target region uniformly and, on the other hand, protecting the films of a non-etching target region.

Description

Substrate processing method Technical Field

[0001] This invention relates to a substrate processing method. More specifically, it relates to a substrate processing method that allows for the uniform etching of both the silicon nitride and silicon oxide films in areas to be etched when silicon nitride and silicon oxide films are stacked on a substrate using a dry etching method. Background Technology

[0002] With the miniaturization of semiconductor devices, they are becoming increasingly highly integrated. Since silicon nitride (SiN) films are used as dielectric or insulating films with chemically stable properties, they are widely used not only in the basic device discrete processes of memory devices but also in contact or capping processes, serving as sidewall materials in the manufacturing processes of dynamic random access memory (DRAM) and flash memory.

[0003] On the other hand, in the manufacture of semiconductor devices, there are cases where multiple layers of silicon oxide films and silicon nitride films are stacked on a substrate. In this case, multiple etching processes are required to etch the silicon oxide films and silicon nitride films.

[0004] Figures 1a to 1d schematically illustrate conventional substrate processing methods, including etching processes for silicon oxide films and etching processes for silicon nitride films.

[0005] Referring to Figures 1a to 1d, a conventional substrate processing method performs the following process to etch the silicon oxide films 110, 130 and silicon nitride film 120 in the etchable area of ​​a substrate 101 (Figure 1a) on which the lower silicon oxide film 110, silicon nitride film 120 and upper silicon oxide film 130 are stacked.

[0006] First, as the first etching process, the upper silicon oxide film 130 in the target area is etched using a dry etching method (Fig. 1b). A silicon nitride film 140 and its lower film are formed in the non-etchable area. Next, as the second etching process, the silicon nitride film 120 is etched using a wet etching method (Fig. 1c). Then, as the third etching process, the lower silicon oxide film 110 is etched using a dry etching method (third etching process) (Fig. 1d).

[0007] However, conventional substrate processing methods require separate etching processes: a first etching process for the upper silicon oxide film (Fig. 1b), a second etching process for the silicon nitride film (Fig. 1c), and a third etching process for the lower silicon oxide film (Fig. 1d). Furthermore, dry etching is used for both the upper and lower silicon oxide films, while wet etching is primarily used for the silicon nitride film. This results in the inability to perform multiple etching processes within the same chamber. This is a major reason for the increased etching time and higher process costs.

[0008] To address this problem, an etching solution capable of uniformly etching silicon oxide and silicon nitride films has been developed (e.g., Patent Document 1).

[0009] Figures 2a and 2b show examples of etching silicon oxide and silicon nitride films using a single etching process.

[0010] Referring to Figures 2a and 2b, a method for etching a silicon oxide film and a silicon nitride film in a single process is to use an etching solution capable of etching both silicon oxide and silicon nitride films to uniformly etch the silicon oxide film 110, 130 and silicon nitride film 120 in a substrate 101 (Figure 2a) on which the lower silicon oxide film 110, silicon nitride film 120 and upper silicon oxide film 130 are stacked.

[0011] However, wet etching suffers from problems such as the etchant penetrating into the device pattern due to surface tension, or the etching not being able to proceed smoothly to the bottom layer of the film. This problem becomes more severe as the number of layers in semiconductor devices increases and the patterns become finer.

[0012] [Existing technical documents]

[0013] [Patent Literature]

[0014] [Patent Document 1] Patent Registration Gazette No. 10-0823461 (Published on April 21, 2008) Summary of the Invention

[0015] [The problem the invention aims to solve]

[0016] The problem to be solved by the present invention is to provide a substrate processing method that can uniformly etch silicon nitride film and silicon oxide film when silicon nitride film and silicon oxide film are stacked on a substrate.

[0017] In addition, the problem to be solved by the present invention is to provide a substrate processing method that can uniformly etch both the silicon nitride film and the silicon oxide film in the etchable area, and on the other hand, protect the film in the non-etchable area.

[0018] [Technical means to solve the problem]

[0019] The substrate processing method according to a first embodiment of the present invention for solving the aforementioned problem is a method for processing a substrate comprising a first silicon oxide film, a silicon nitride film, and a second silicon oxide film stacked from the outermost side, comprising: a first etching step for etching the first silicon oxide film; and a second etching step for etching the silicon nitride film and the second silicon oxide film, wherein in the first etching step, a residual layer of the first silicon oxide film is retained, and in the second etching step, the residual layer of the first silicon oxide film, the silicon nitride film, and the second silicon oxide film are etched uniformly.

[0020] The first etching step and the second etching step can be performed in the same chamber.

[0021] Preferably, the first etching step is performed until the thickness of the residual layer of the first silicon oxide film is less than the maximum thickness that can be removed when the first silicon oxide film is etched once under the same conditions as those applied to the second etching step.

[0022] The second etching step can be performed using a dry etching method, which involves plasma-entraining a mixture of hydrogen fluoride (HF) and ammonia (NH3) or a mixture of nitrogen trifluoride (NF3) and ammonia (NH3) or hydrogen (H2) and using it as the etching gas.

[0023] The second etching step can be repeated multiple times, consisting of a unit cycle of etching and heating.

[0024] After the second etching step, a final heating step may be included to bring the substrate temperature to 200°C or higher, preferably 200°C to 250°C.

[0025] The substrate processing method according to a second embodiment of the present invention for solving the aforementioned problem is a method for processing a substrate in which films comprising a first silicon oxide film, a first silicon nitride film, and a second silicon oxide film are sequentially stacked from the outermost side in a first region to be etched, and one or more films comprising a second silicon nitride film are stacked from the outermost side in a second region not to be etched. The method includes: a first etching step of etching the first silicon oxide film in the first region; and a second etching step of etching the first silicon nitride film and the second silicon oxide film in the first region at a temperature higher than that of the first etching step. In the first etching step, a residual layer of the first silicon oxide film in the first region is retained. In the second etching step, the residual layer of the first silicon oxide film, the first silicon nitride film, and the second silicon oxide film in the first region are etched uniformly, and the second silicon nitride film in the second region functions as an etching stopper.

[0026] The substrate processing method according to a third embodiment of the present invention for solving the aforementioned problem is a method for processing a substrate in which films comprising a first silicon oxide film, a first silicon nitride film, and a second silicon oxide film are sequentially stacked from the outermost side in a first region to be etched, and films comprising a third silicon oxide film and a second silicon nitride film are stacked from the outermost side in a second region not to be etched. The method includes: a first etching step for etching the first silicon oxide film in the first region and the third silicon oxide film in the second region; and a second etching step for etching the first silicon nitride film and the second silicon oxide film in the first region at a temperature higher than that of the first etching step. In the first etching step, a residual layer of the first silicon oxide film in the first region is retained, and the second silicon nitride film in the second region is exposed. In the second etching step, the residual layer of the first silicon oxide film, the first silicon nitride film, and the second silicon oxide film in the first region are etched uniformly, and the second silicon nitride film in the second region functions as an etching stop.

[0027] The first etching step and the second etching step can be performed in the same chamber.

[0028] Preferably, the first etching step is performed until the thickness of the residual layer of the first silicon oxide film is less than the maximum thickness that can be removed when the first silicon oxide film is etched once under the same conditions as those applied to the second etching step.

[0029] The second etching step can be performed using a dry etching method, which involves plasma-entraining a mixture of hydrogen fluoride (HF) and ammonia (NH3) or a mixture of nitrogen trifluoride (NF3) and ammonia (NH3) or hydrogen (H2) and using it as the etching gas.

[0030] The second etching step can be performed at a temperature above 60°C.

[0031] The second etching step can be repeated multiple times, consisting of a unit cycle of etching and heating.

[0032] Following the second etching step, a final heating step may be included to bring the substrate temperature to above 200°C.

[0033] The substrate processing method according to a fourth embodiment of the present invention for solving the aforementioned problem is a method for processing a substrate in which films comprising a first silicon nitride film and a silicon oxide film are sequentially stacked from the outermost side in a first region to be etched, and one or more films comprising a second silicon nitride film are stacked from the outermost side in a second region not to be etched, including:

[0034] The sacrificial silicon oxide film formation step involves forming a sacrificial silicon oxide film on a first silicon nitride film in the first region; and

[0035] The etching step involves etching the first silicon nitride film and the silicon oxide film in the first region.

[0036] In the etching step, the sacrificial silicon oxide film, the first silicon nitride film, and the silicon oxide film in the first region are etched uniformly, and the second silicon nitride film in the second region acts as an etching stop.

[0037] The sacrificial silicon oxide film formation step can be performed in such a way that the thickness of the sacrificial silicon oxide film is less than the maximum thickness that can be removed when the sacrificial silicon oxide film is etched once under the same conditions as those applied to the etching step.

[0038] The etching step can be performed using a dry etching method, which involves plasma-entraining a mixture of hydrogen fluoride (HF) and ammonia (NH3) or a mixture of nitrogen trifluoride (NF3) and ammonia (NH3) or hydrogen (H2) and using it as the etching gas.

[0039] The etching step can be performed at a temperature above 60°C.

[0040] The etching step can be repeated multiple times, consisting of a unit cycle of etching and heating.

[0041] Following the etching step, a final heating step may be included to bring the substrate temperature to above 200°C.

[0042] [The effects of the invention]

[0043] According to the substrate processing method of the present invention, when silicon nitride film and silicon oxide film are stacked on a substrate, the silicon nitride film and silicon oxide film can be uniformly etched in the same chamber using a dry etching method.

[0044] Furthermore, the substrate processing method according to the present invention utilizes the phenomenon that when the silicon nitride film is exposed, the silicon nitride film functions as an etching stop at high temperature, thereby achieving the effect of uniformly etching both the silicon nitride film and the silicon oxide film in the etching target area, while protecting the film in the non-etching target area.

[0045] The effects of the present invention are not limited to those mentioned above. Another effect not mentioned will be clearly understood by those skilled in the art through the following detailed description. Attached Figure Description

[0046] Figures 1a to 1d schematically illustrate conventional substrate processing methods, including etching processes for silicon oxide films and etching processes for silicon nitride films.

[0047] Figures 2a and 2b show examples of etching silicon oxide and silicon nitride films using a single etching process.

[0048] Figures 3a to 3c schematically illustrate a substrate processing method according to an embodiment of the present invention.

[0049] Figure 4 shows an example of an etching method that can be applied to the second etching step.

[0050] Figures 5a to 5c schematically illustrate a substrate processing method according to an embodiment of the present invention.

[0051] Figures 6a to 6c schematically illustrate a substrate processing method according to an embodiment of the present invention.

[0052] Figure 7 shows the results of dry etching tests performed on silicon nitride films using hydrogen fluoride (HF) and ammonia (NH3). Detailed Implementation

[0053] The advantages and features of the present invention, as well as the methods for achieving them, will become apparent with reference to the accompanying drawings and the embodiments described in the following detailed description. However, the invention is not limited to the embodiments disclosed below, but is implemented in various ways, though these embodiments are provided only to complete the disclosure of the invention and to fully inform those skilled in the art of the scope of the invention, which is defined only by the scope of the claims. Throughout the specification, the same reference numerals refer to the same constituent elements. For clarity of description, the sizes and relative sizes of layers and regions in the figures may be exaggerated.

[0054] The phrase "above" or "on top of" another element includes not only being directly above another element or layer, but also having other layers or elements interposed in between. Conversely, the phrase "directly above" or "right above" an element indicates that no other elements or layers are interposed in between. Furthermore, it should be understood that when a constituent element is described as being "connected," "joined," or "linked" to another constituent element, although the constituent elements may be directly connected or linked to each other, other constituent elements may also be "interposed" between the constituent elements, or the constituent elements may be "connected," "joined," or "linked" through other constituent elements.

[0055] Terms such as "below," "lower part," "above," and "upper part," used as spatial relative terms, can be used to readily describe the relationship between one element or component and another, as shown in the figure. Spatial relative terms should be understood to include, in addition to the directions shown in the figure, terms indicating that elements are in different directions during use or operation. For example, when the elements shown in the figure are flipped, an element described as "below" another element may be placed "above" another element. Therefore, the illustrative term "below" can include both the lower and upper directions.

[0056] The terminology used in this specification is for illustrative purposes and is therefore not intended to limit the invention. In this specification, the singular form includes the plural form unless specifically stated in the context. The use of "comprising" and / or "including" in this specification to refer to constituent elements, steps, actions, and / or components does not exclude the presence or addition of one or more other constituent elements, steps, actions, and / or components.

[0057] Hereinafter, a substrate processing method according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings, as shown below.

[0058] The etching reaction of silicon nitride is performed as shown in the following process.

[0059] Si3N4(s)+16HF(g)→2(NH4)2SiF6(s)+SiF4(g)

[0060] (NH4)2SiF6(s)→NH4HF2(s)+SiF4(g)+NH3(g)

[0061] The etching reactions of silicon oxide and silicon nitride differ in whether or not H2O is generated. In the case of silicon oxide, H2O is generated and etching is accelerated, while in the case of silicon nitride, etching occurs substantially slowly due to the absence of oxygen (O).

[0062] In the case of pure silicon nitride, it cannot be successfully etched by HF. However, particularly when oxygen (O) is present on the silicon nitride surface, it has been confirmed that HF ​​can be used to etch both the surface of silicon nitride containing oxygen and the interior of silicon nitride that is substantially free of oxygen. Furthermore, it has been confirmed that if the surface of silicon nitride containing oxygen is etched and then undergoes a desalting process, a pure silicon nitride surface is formed, and subsequent etching using HF cannot successfully etch the silicon nitride.

[0063] Figures 3a to 3c schematically illustrate a substrate processing method according to an embodiment of the present invention.

[0064] Referring to Figures 3a to 3c, the substrate processing method according to an embodiment of the present invention includes a first etching step (Figure 3b) and a second etching step (Figure 3c).

[0065] In this embodiment, as shown in the example in FIG3a, the substrate to be processed is a substrate 201 consisting of a first silicon oxide film 230, a silicon nitride film 220, and a second silicon oxide film 210 stacked from the outermost layer. On the substrate, in addition to the films 210, 220, and 230, films that are not to be etched, such as a second silicon nitride film 240, may be further stacked.

[0066] In this invention, "stacked" refers not only to stacking in the vertical direction but also to stacking in the horizontal direction. Therefore, "outermost" can refer not only to the uppermost part in the vertical direction but also to the outermost part in the horizontal direction.

[0067] Additionally, additional films such as oxide films, nitride films, and metal films may be stacked between the substrate 201 and the second silicon oxide film 210. In FIG3a, since only the second silicon oxide film 210 is shown, the following description will mainly focus on the case where the first silicon oxide film 230, silicon nitride film 220, and second silicon oxide film 210 are etched. However, if silicon nitride films and silicon oxide films are further stacked under the second silicon oxide film 210, they can also be etched.

[0068] Furthermore, in Figure 3a, region A is the area to be etched, and region B is the area not to be etched. Regions A and B can be adjacent to each other, or they can be separated from each other. In the case where regions A and B are separated from each other, for example, a silicon oxide film in region A and a silicon oxide film in region B can be formed from the same layer or from different layers.

[0069] Referring to Figure 3b, the first silicon oxide film is etched in the first etching step.

[0070] Prior to the first etching step, a pre-etching step may be included, for example, using ammonia and a carrier gas without hydrogen fluoride gas.

[0071] The first etching step can be performed using a dry etching method that plasma-entrains a mixed gas, such as hydrogen fluoride (HF) and ammonia (NH3), and uses it as the etching gas. For high-speed cycling, the first etching step can be performed at a temperature above 60°C.

[0072] The first etching step is preferably composed of one cycle in terms of process efficiency, but it is not limited to this. If the silicon nitride film 220 under the first silicon oxide film 230 is not exposed, one cycle or n cycles (n≥2) can be performed.

[0073] Next, referring to FIG3c, the silicon nitride film 220 and the second silicon oxide film 210 are etched in the second etching step. The second etching step can be performed using a dry etching method, which involves plasma-enhancing a mixed gas containing hydrogen fluoride gas (HF) and ammonia gas (NH3) or a mixed gas containing nitrogen trifluoride gas (NF3) and ammonia gas (NH3) or hydrogen gas (H2) and using it as the etching gas.

[0074] The first and second etching steps can be performed using process pressures of several hundred millitors (mTorr) to several Torr, but are not limited to this.

[0075] On the other hand, the same etching gas can be used in both the first and second etching steps. For example, in both the first and second etching steps, a mixture of HF and NH3 with a flow ratio of 1:1 to 3:1, preferably 1:1 to 2:1, and more preferably 1.3:1 to 1.7:1 can be used.

[0076] On the other hand, the overall flow rate or process pressure applied to the first etching step and the second etching step may differ. For example, the first etching step may be performed at a process pressure of approximately 1.2 Torr, and the second etching step may be performed at a process pressure of approximately 0.8 Torr. In addition, the flow rate of the etching gas applied to the second etching step may be approximately 30% higher than that in the first etching step.

[0077] On the other hand, in this invention, as can be observed in FIG3b, a residual layer 235 of the first silicon oxide film is retained in the first etching step, and the residual layer 235 of the first silicon oxide film, the silicon nitride film 220, and the second silicon oxide film 210 are uniformly etched in the second etching step. At this time, it can be observed that the term "residual layer of the first silicon oxide film" corresponds to the "lower portion of the first silicon oxide film that is not etched", and the silicon nitride film below it is not exposed.

[0078] The inventors of this invention, through long-term research, have discovered that when performing dry etching using etching gases (such as hydrogen fluoride and ammonia) capable of etching both silicon oxide and silicon nitride films, if a thin silicon oxide film of about tens of angstroms is exposed, the silicon nitride film and the other silicon oxide film beneath it can be etched. Conversely, if a thick silicon oxide film is exposed, it has been confirmed that the etching rate of the silicon oxide film is slow, resulting in insufficient etching of the silicon nitride film and the other silicon oxide film beneath it.

[0079] Furthermore, the inventors have learned that when the silicon nitride film is exposed, the silicon nitride film functions as an etching stopper at high temperatures, where almost no etching occurs.

[0080] Returning to Figures 3b and 3c, in the substrate processing method according to the present invention, by retaining the residual layer 235 of the first silicon oxide film in the first etching step, the residual layer 235 of the first silicon oxide film, the silicon nitride film 220 and the second silicon oxide film 210 can be etched uniformly in the second etching step.

[0081] As described above, in the present invention, both the first etching step and the second etching step can be performed using a dry etching method, and both steps can be performed in the same chamber using the same etching gas. This provides the advantage of reducing etching time and cost compared to changing the chamber.

[0082] On the other hand, a first etching step can be performed until the thickness of the residual layer 235 of the first silicon oxide film is less than the maximum thickness that can be removed when the first silicon oxide film 230 is etched once under the same conditions as those applied to the second etching step. The maximum thickness that can be removed when the first silicon oxide film 230 is etched once can vary depending on the etching gas, temperature, pressure, etc., applied to the second etching step. Therefore, although the thickness of the residual layer 235 of the first silicon oxide film is not limited, it can generally be [missing information]. Below, left and right.

[0083] If the residual layer 235 of the first silicon oxide film is not retained, the silicon nitride film 220 will be exposed, thus preventing successful etching in the secondary etching step.

[0084] On the other hand, since the etching of the silicon oxide film is accompanied by a self-limiting reaction, etching cannot continue after reaching a certain thickness due to reaction byproducts. If the thickness of the residual layer 235 of the first silicon oxide film is too thick, the residual layer 235 of the first silicon oxide film cannot be completely etched in the second etching step, resulting in insufficient or uneven etching of the underlying silicon nitride film or the second silicon oxide film. Furthermore, over-etching of the residual layer of the first silicon oxide film may lead to undesirable uneven etching of the film.

[0085] The second etching step can be performed at the same temperature as the first etching step or at a higher temperature, preferably at a temperature above 60°C. There is no particular limitation on the upper limit temperature of the second etching step, but it can be below 110°C for etching stability. When the silicon nitride film is exposed, the exposed silicon nitride film acts as an etching stop at temperatures above 60°C, thereby suppressing the etching of the exposed silicon nitride film and the film beneath it. Therefore, in the second etching step, a separate mask may not be required for the portion where the silicon nitride film is exposed (e.g., the second silicon nitride film 240 disposed in a non-etchable area).

[0086] Figure 4 shows an example of an etching method that can be applied to the second etching step.

[0087] As shown in the example in Figure 4, the second etching step can be repeated multiple times in a unit cycle consisting of etching 410 and heating 420. A purge of the chamber may be performed between etching and heating (before or after heating). Heating refers to injecting gas after etching to remove reaction byproducts and turning on the lamp to raise the substrate temperature. Heating 420 may involve turning on the lamp to raise the substrate temperature to above 60°C, for example, turning on the lamp for approximately 30 seconds to raise the substrate temperature to approximately 120°C to 200°C. During etching 410, the temperature gradually decreases, reaching below 60°C. Therefore, by repeating the unit cycle consisting of etching 410 and heating n times (n≥2), the second etching step can be performed at a sufficiently high temperature, such as above 60°C, thereby sufficiently etching the residual layer 235 of the first silicon oxide film, the silicon nitride film 220, and the second silicon oxide film 210.

[0088] On the other hand, after the second etching step, a final heating step 430 can be included to raise the substrate temperature to 200°C or higher (e.g., 200°C to 250°C). This is advantageous in terms of fume management. Fume refers to particulate forms of etching byproducts, such as NH4F or NH2F2, that cannot be completely volatilized due to heat and remain on the substrate. In the case of such fume, the surface of the film or the equipment may be contaminated, and the reliability of fine patterns may also be affected. Therefore, raising the substrate temperature to 200°C or higher by final heating after the second etching step can suppress the residual fume after etching. However, for equipment stability and process management, it is more preferable to raise the substrate temperature to below 250°C. If the substrate temperature exceeds 250°C, it may increase the equipment load and increase the probability of process reproducibility and abnormal etching phenomena.

[0089] Furthermore, referring to FIG3a, a second silicon nitride film 240 is stacked in region B, which is a non-etching target area. Because this second silicon nitride film 240 is exposed, during the second etching step, when the residual layer 235 of the first silicon oxide film, the first silicon nitride film 220, and the second silicon oxide film 210 in region A are uniformly etched, the second silicon nitride film 240 remains unetched. This can be seen because, as described above, the silicon nitride film acts as an etching stop at high temperatures.

[0090] Figures 5a to 5c schematically illustrate a substrate processing method according to an embodiment of the present invention.

[0091] Referring to Figures 5a to 5c, the substrate processing method shown involves processing the following substrate through a first etching step and a second etching step. In a first region (region A) that is the object of etching, films including a first silicon oxide film 230, a first silicon nitride film 220, and a second silicon oxide film 210 are stacked sequentially from the outermost layer. In a second region (region B) that is not the object of etching, films including a third silicon oxide film 230 and a second silicon nitride film 220 are stacked from the outermost layer. In Figure 5a, the first silicon oxide film and the third silicon oxide film, as well as the first silicon nitride film and the second silicon nitride film, are formed from the same layer and therefore are given the same reference numerals.

[0092] In the first etching step, as shown in the example in FIG5b, the first silicon oxide film in the first region (region A) and the third silicon oxide film in the second region (region B) are etched.

[0093] In the second etching step, the first silicon nitride film 220 and the second silicon oxide film 210 in the first region (region A) are etched at a higher temperature than in the first etching step, as shown in the example in FIG5c.

[0094] At this point, in the first etching step, as shown in the example in FIG5b, the residual layer 235 of the first silicon oxide film in the first region (region A) is retained, and the second silicon nitride film in the second region is exposed. If the thickness of the first silicon oxide film is greater than the thickness of the residual layer than the thickness of the third silicon oxide film, then after the first etching step, only the residual layer of the first silicon oxide film in the first region may be retained.

[0095] In the result of the first etching step and in the second etching step, the residual layer 235 of the first silicon oxide film, the silicon nitride film 220 and the second silicon oxide film 210 of the first region (region A) are etched uniformly, and the second silicon nitride film 220 of the second region (region B) acts as an etching stop, so that the second silicon nitride film 220 and the film below it are substantially almost not etched.

[0096] The features described in Figures 3a to 3c can also be applied as is in the case of the substrate processing method according to this embodiment.

[0097] That is, since the first etching step and the second etching step can be performed using dry etching methods, they can be performed in the same chamber. Furthermore, the first etching step can be performed until the thickness of the residual layer 235 of the first silicon oxide film is less than the maximum thickness that can be removed when the first silicon oxide film 230 is etched once under the same conditions as applied to the second etching step. Additionally, the second etching step can be performed using a dry etching method, which involves plasma-enhancing a mixture of hydrogen fluoride gas (HF) and ammonia (NH3), or a mixture of nitrogen trifluoride gas (NF3) and ammonia (NH3) or hydrogen (H2) and using it as the etching gas.

[0098] Furthermore, the second etching step can be performed at the same or higher temperature than the first etching step, and can be performed at a temperature of 60°C or higher. Additionally, the second etching step can be repeated multiple times in a unit cycle consisting of etching and heating. Furthermore, after the second etching step, a final heating step can be included to raise the substrate temperature to 200°C or higher.

[0099] Figures 6a to 6c schematically illustrate a substrate processing method according to another embodiment of the present invention.

[0100] In the case of Figures 6a to 6c, a method for processing a substrate is shown in which films including a first silicon nitride film and a silicon oxide film are stacked sequentially from the outermost side in a first region that is to be etched, and one or more films including a second silicon nitride film are stacked from the outermost side in a second region that is not to be etched.

[0101] In this embodiment, as shown in the example of FIG6b, a sacrificial silicon oxide film 236 is formed on the first silicon nitride film 220, which is the first region (region A) to be etched. The formation of the sacrificial silicon oxide film 236 can be achieved by deposition, or by oxygen plasma treatment, natural oxide film formation, etc. The formation result of the sacrificial silicon oxide film is substantially similar to the result of a single etching operation as shown in FIG5b. That is, although the case of FIG5b is the product of a single etching operation, and the case of FIG6b is the product of deposition, etc., the results are substantially similar.

[0102] That is, in this embodiment, a silicon oxide film corresponding to the residual layer of the first silicon oxide film is formed by deposition or the like, so as shown in the example shown in FIG5c, the sacrificial silicon oxide film 236, the first silicon nitride film 220 and the silicon oxide film 210 of the first region (region A) can be etched uniformly in the etching step described below.

[0103] In the case of the second region (region B), which is not the object of etching, since no sacrificial silicon oxide film is formed and the silicon nitride film is exposed, as shown in the example in FIG5c, the exposed silicon nitride film acts as an etching stop in the high-temperature etching step, thereby preventing the silicon nitride film in the second region (region B) and the film underneath from being etched.

[0104] In the case of the substrate processing method according to this embodiment, some of the features described in FIG3a to FIG3c may also be applied as is.

[0105] The sacrificial silicon oxide film formation step can be performed using methods such as deposition, oxygen plasma, and natural oxidation. The sacrificial silicon oxide film formation step can be performed such that the thickness of the sacrificial silicon oxide film 236 is less than the maximum thickness that can be removed in a single etching operation under the same conditions as those applied to the etching step, for example... The following thicknesses.

[0106] The etching step can be performed using a dry etching method, which involves plasma-entraining a mixture of hydrogen fluoride (HF) and ammonia (NH3) or a mixture of nitrogen trifluoride (NF3) and ammonia (NH3) or hydrogen (H2) and using it as the etching gas.

[0107] Furthermore, the etching step can be performed at a temperature above 60°C. The etching step can be repeated multiple times in a single cycle consisting of etching and heating. Following the etching step, a final heating step may be included to raise the substrate temperature to above 200°C.

[0108] As described above, the substrate processing method according to the present invention allows for the simultaneous etching of silicon nitride and silicon oxide films in the same chamber using a dry etching method when silicon nitride and silicon oxide films are stacked on a substrate.

[0109] Furthermore, the substrate processing method according to the present invention can simultaneously etch both the silicon nitride film and the silicon oxide film in the etchable area while protecting the film in the non-etchable area.

[0110] The results of a dry etching test performed on a silicon nitride film using a mixture of hydrogen fluoride (HF) and ammonia (NH3) at a flow rate ratio of 1.5:1 are shown in Figure 7.

[0111] During a single etching operation, the amount of silicon nitride film etched is approximately [amount missing].

[0112] Then, a second etching is performed under the following conditions: a second etching is performed immediately after the first etching, a second etching is performed after exposure to the atmosphere after the first etching, and a second etching is performed after oxygen plasma treatment after the first etching.

[0113] i) Perform a second etching immediately after the first etching: As can be observed with reference to Figure 7, if a second etching is performed immediately after the first etching at 65°C, almost no further etching of silicon nitride is performed.

[0114] ii) Secondary etching after exposure to atmosphere following primary etching: Referring to Figure 7, it can be observed that after primary etching, when silicon nitride is exposed to atmosphere for three days, a secondary etching at 65°C results in approximately [amount missing] etched. This is due to the formation of a natural oxide film on the silicon nitride surface during exposure to the atmosphere. The natural oxide film on the silicon nitride surface corresponds to a residual layer of the first oxide film described above.

[0115] iii) Secondary etching after oxygen plasma treatment following primary etching: Referring to Figure 7, it can be observed that after primary etching, when the silicon nitride surface is treated with oxygen plasma, a secondary etching at 65°C results in approximately [amount missing] being etched. This is due to the formation of a strong oxide film on the silicon nitride surface using oxygen plasma treatment. The oxide film formed on the silicon nitride surface by the oxygen plasma process corresponds to a residual layer of the first oxide film described above.

[0116] That is, as can be seen from the results in Figure 7, when there is a natural oxide film or a strong oxide film on the surface of silicon nitride, silicon nitride can be further etched. When there is no such oxide film on the surface of silicon nitride, silicon nitride acts as an etching stop at high temperatures above 60°C, so that silicon nitride is hardly etched further.

[0117] Based on this result, almost no etching occurs on silicon nitride, which is not the object of etching, and the residual oxide layer can be used to uniformly etch both the silicon oxide film and the silicon nitride film, which are the objects of etching.

[0118] While the above description has focused on embodiments of the present invention, various modifications and variations can be made by those skilled in the art. Such modifications and variations are all within the scope of the present invention without departing from its scope. Therefore, the scope of the present invention should be determined based on the foregoing claims.

Claims

1. A substrate processing method for processing a substrate comprising a first silicon oxide film, a silicon nitride film, and a second silicon oxide film stacked from the outermost side, the method comprising: The first etching step involves etching the first silicon oxide film; The process includes a second etching step, in which the silicon nitride film and the second silicon oxide film are etched. In the first etching step, a residual layer of the first silicon oxide film is retained. In the second etching step, the residual layer of the first silicon oxide film, the silicon nitride film, and the second silicon oxide film are etched together. The first etching step is performed until the thickness of the residual layer of the first silicon oxide film becomes less than 100 Å.

2. A substrate processing method for processing a substrate wherein a first silicon oxide film, a first silicon nitride film, and a second silicon oxide film are sequentially stacked from the outermost side in a first region to be etched, and one or more films including a second silicon nitride film are stacked from the outermost side in a second region not to be etched, the method comprising: The first etching step involves etching the first silicon oxide film in the first region; The process includes a second etching step, in which the first silicon nitride film and the second silicon oxide film in the first region are etched at a higher temperature than that in the first etching step. In the first etching step, a residual layer of the first silicon oxide film in the first region is retained. In the second etching step, the residual layer of the first silicon oxide film, the first silicon nitride film, and the second silicon oxide film in the first region are etched together. The second silicon nitride film in the second region acts as an etching stop. The first etching step is performed until the thickness of the residual layer of the first silicon oxide film becomes less than 100 Å.

3. A substrate processing method for processing a substrate wherein, in a first region to be etched, a film comprising a first silicon oxide film, a first silicon nitride film, and a second silicon oxide film is sequentially stacked from the outermost side, and in a second region not to be etched, a film comprising a third silicon oxide film and a second silicon nitride film is stacked from the outermost side, the method comprising: The first etching step involves etching the first silicon oxide film in the first region and the third silicon oxide film in the second region. The process includes a second etching step, in which the first silicon nitride film and the second silicon oxide film in the first region are etched at a higher temperature than that in the first etching step. In the first etching step, a residual layer of the first silicon oxide film in the first region is retained, and the second silicon nitride film in the second region is exposed. In the second etching step, the residual layer of the first silicon oxide film, the first silicon nitride film, and the second silicon oxide film in the first region are etched together, and the second silicon nitride film in the second region acts as an etching stop. The first etching step is performed until the thickness of the residual layer of the first silicon oxide film becomes less than 100 Å.

4. The substrate processing method according to any one of claims 1 to 3, wherein, The first etching step and the second etching step are performed in the same chamber.

5. The substrate processing method according to any one of claims 1 to 3, wherein, The second etching step is performed using a dry etching method, which involves plasma-entraining a mixed gas containing hydrogen fluoride and ammonia, or a mixed gas containing nitrogen trifluoride and ammonia or hydrogen, and using it as the etching gas.

6. The substrate processing method according to any one of claims 1 to 3, wherein, The second etching step is repeated multiple times, consisting of a unit cycle of etching and heating.

7. The substrate processing method according to claim 6, wherein, Following the second etching step, a final heating step is included to bring the substrate temperature to 200°C to 250°C.

8. The substrate processing method according to claim 2 or 3, wherein, The second etching step is performed at a temperature above 60°C.

9. A substrate processing method for processing a substrate wherein a first silicon nitride film and a silicon oxide film are sequentially stacked from the outermost side in a first region to be etched, and one or more films including a second silicon nitride film are stacked from the outermost side in a second region not to be etched, comprising: The sacrificial film formation step involves forming a sacrificial silicon oxide film on the first silicon nitride film in the first region; The process includes an etching step in which the first silicon nitride film and the silicon oxide film in the first region are etched. In the etching step, the sacrificial silicon oxide film, the first silicon nitride film, and the silicon oxide film in the first region are etched together. The second silicon nitride film in the second region acts as an etching stop. The sacrificial silicon oxide film is formed to a thickness of less than 100 Å.

Images