Substrate processing method

Abstract

The substrate processing method according to the present application is a method for processing a substrate including an ONO stack of an alternating stack of a silicon oxide layer and a silicon nitride layer, including the steps of: (a) performing a first dry etching on the silicon nitride layer of the ONO stack; (b) generating oxygen radicals, and processing the silicon oxide layer of the ONO stack with the oxygen radicals; and (c) performing a second dry etching on the silicon nitride layer of the ONO stack.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for processing a substrate including an oxide-nitride-oxide (ONO) stack of an alternating stack of a silicon oxide layer and a silicon nitride layer. More specifically, it relates to a method for selectively dry-etching a nitride layer in an ONO stack. BACKGROUND

[0002] In manufacturing semiconductor elements, there are cases where an ONO stack of an alternating stack of a silicon oxide layer and a silicon nitride layer is formed on a substrate. In order to selectively etch a silicon nitride layer in an ONO stack, an etchant having a higher etching selectivity than a silicon oxide layer should be applied.

[0003] In a dry etching process, in order to selectively etch a silicon nitride layer, carbon tetrafluoride (CF4), nitrogen trifluoride (NF3), or the like is mainly used as an etching gas. On the other hand, a hydrogen-containing etching gas such as monofluoromethane (CH3F) or difluoromethane (CH2F2) is not so much used in dry etching of a silicon nitride layer, because a thick polymer film formed of hydrogen radicals is generated when the etching gas is plasma-ized. Such a thick polymer film lowers the etching rate of a silicon nitride film.

[0004] On the other hand, recently, the number of layers of an ONO stack has been increased to 200 to 300 layers. In this case, there are problems that a silicon nitride layer adjacent to a surface (i.e., a nitride layer at the upper end of the ONO stack) is rapidly etched, and, on the contrary, the etching efficiency of a silicon nitride layer adjacent to a substrate (i.e., a nitride layer at the lower end of the ONO stack) is lowered. In addition, during selective etching of a silicon nitride layer, there are problems that a part of a silicon oxide layer is lost or the thickness of the silicon oxide layer is thinned, or the like, and the silicon oxide layer is damaged. SUMMARY

[0005] [Problems to be Solved by the Invention]

[0006] The present application aims to provide a substrate processing method which can reduce or suppress damage to a silicon oxide layer when a silicon nitride layer is selectively etched in an ONO stack.

[0007] In addition, the present application aims to provide a substrate processing method which can adjust the etching profile of an ONO stack.

[0008] [Technical Means for Solving the Problems]

[0009] A substrate processing method according to an embodiment of the present application for solving the problem is a method of processing a substrate including an ONO stack of an oxide layer and a nitride layer alternately stacked, characterized by comprising the steps of: (a) performing a first dry etching on the nitride layer of the ONO stack; (b) generating oxygen radicals and processing the oxide layer of the ONO stack using the oxygen radicals; and (c) performing a second dry etching on the nitride layer of the ONO stack.

[0010] As described above, in the substrate processing method according to the present application, the oxygen radical processing step is included between the first dry etching step and the second dry etching step. That is, in the present application, after the first etching step, the second etching step is not performed immediately, but after the first etching step, the substrate is processed by using the oxygen radicals and the oxide layer of the ONO stack is passivated, so that damage to the oxide layer of the ONO stack can be reduced or suppressed.

[0011] The oxygen radicals can be generated from a source selected from O2, O3, N2O, NO, N2O2, and H2O.

[0012] The step (b) can use oxygen radicals generated in a remote plasma system.

[0013] In the steps (a) and (c), a plurality of gases are plasma-processed to etch the nitride layer, and the plurality of gases can include a first gas containing fluorine other than nitrogen trifluoride (NF3) and a second gas containing hydrogen.

[0014] An atomic ratio (F:H) of fluorine to hydrogen included in the plurality of gases can be 15:1 or more and less than 22.5:1. As another example, the atomic ratio (F:H) of fluorine to hydrogen included in the plurality of gases can be 22.5:1 or more and 35:1 or less.

[0015] In order to achieve plasma processing of the plurality of gases, high-frequency power having a radio frequency (RF) frequency of 15 MHz or more and less than 60 MHz can be used.

[0016] A substrate processing method according to another embodiment of the present invention for solving the aforementioned problem is a method for processing an ONO stack comprising alternating layers of silicon oxide and silicon nitride, characterized by comprising the following steps: (a) performing m (m is a natural number greater than 2) dry etching on the ONO stacked silicon nitride layer; and (b) performing n (n is a natural number greater than 2) dry etching on the ONO stacked silicon nitride layer, wherein steps (a) and (b) include one or more oxygen free radical treatment steps, wherein the oxygen free radical treatment steps are performed by treating the ONO stacked silicon oxide layer with oxygen free radicals between dry etching steps.

[0017] The oxygen free radicals can be selected from O2, O3, N2O, NO, N2O2, and H2O.

[0018] The oxygen radical treatment step can utilize oxygen radicals generated in a remote plasma system.

[0019] After performing step (a), the substrate can be unloaded from the process chamber and the process chamber can be cleaned.

[0020] The cleaning can be performed using oxygen free radicals.

[0021] The oxygen radicals applied during the cleaning process can be generated under higher RF power conditions compared to the oxygen radicals applied in steps (a) and (b).

[0022] The dry etching in each of steps (a) and (b) involves plasma etching with a variety of gases to etch the silicon nitride layer, and the variety of gases may include a first gas containing fluorine other than nitrogen trifluoride (NF3) and a second gas containing hydrogen.

[0023] The atomic ratio (F:H) of fluorine to hydrogen contained in the various gases may be 15:1 or more and less than 22.5:1. As another example, the atomic ratio (F:H) of fluorine to hydrogen contained in the various gases may be 22.5:1 or more and less than 35:1.

[0024] To achieve plasmaization of the aforementioned gases, high-frequency power with an RF frequency of 15MHz or higher and less than 60MHz can be utilized.

[0025] [The effects of the invention]

[0026] In the substrate processing method according to the present invention, an oxygen free radical treatment step is included between the primary dry etching step and the secondary dry etching step. That is, in the present invention, the secondary etching step is not performed immediately after the primary etching step, but rather the substrate is treated with oxygen free radicals after the primary etching step, thereby achieving a passivation effect on the oxide layer. Therefore, during subsequent dry etching of the nitride layer, oxide layer damage can be reduced or suppressed. This is because the surface of the silicon layer becomes thermodynamically stable due to the application of oxygen free radicals.

[0027] Furthermore, in the substrate processing method according to the present invention, after a portion of the overall etching cycle, and after unloading the substrate from the process chamber, the interior of the process chamber can be cleaned. The process chamber is cleaned using oxygen free radicals, thereby removing fluorine deposited on the walls of the process chamber.

[0028] Furthermore, in the substrate processing method according to the present invention, the etching profile of the ONO stack can be controlled by controlling the atomic ratio of fluorine to hydrogen contained in the various gases used to selectively etch the nitride layer of the ONO stack. Attached Figure Description

[0029] Figure 1 The results of etching the silicon nitride layer without oxygen radical treatment are shown.

[0030] Figure 2 and Figure 3 The results show the effects of oxygen radical treatment and silicon nitride layer etching during the etching process.

[0031] Figure 4 The etching depths of the uppermost silicon nitride layer, the middle silicon nitride layer, and the lowermost silicon nitride layer relative to the etching depth of the uppermost silicon nitride layer are shown relative to the oxygen free radical treatment time and power.

[0032] Figure 5 The relative etching rates of the topmost and bottommost silicon nitride layers of the ONO stack are shown based on the atomic ratio of fluorine to hydrogen contained in the etching gas.

[0033] [Explanation of Symbols]

[0034] N: Silicon nitride layer

[0035] O: Silicon oxide layer

[0036] Sub: Silicon substrate Detailed Implementation

[0037] The advantages and features of the invention, as well as the methods for achieving them, will become clear from 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 forms that differ from each other.

[0038] 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.

[0039] The substrate processing method according to the present invention is performed in a process chamber in which a substrate is mounted on a pedestal. An oxide-nitride-oxide (ONO) stack of alternating silicon oxide and silicon nitride layers is formed on the substrate. For example, the ONO stack may have a structure with silicon oxide and silicon nitride layers stacked several times, dozens of times, or even 200 to 300 layers. Figures 1 to 3 As shown, the ONO stack can be exemplarily formed by nine layers of silicon oxide and eight layers of silicon nitride.

[0040] The method for processing a substrate with an ONO stack according to the present invention is characterized by including a primary etching step and a secondary etching step, and including an oxygen free radical application step between the primary etching step and the secondary etching step. That is, in the present invention, the secondary etching is not performed immediately after the primary etching, but rather an oxygen free radical treatment step is performed after the primary etching, and then the secondary etching is performed.

[0041] More specifically, the substrate processing method according to the present invention includes the following steps: performing m (m is a natural number greater than 2) dry etching on an ONO stacked silicon nitride layer; and performing n (n is a natural number greater than 2) dry etching on the ONO stacked silicon nitride layer, wherein an oxygen free radical treatment step is included between any dry etching included in the m dry etching and a subsequent dry etching, and / or between any dry etching included in the n dry etching and a subsequent dry etching, and / or between the last dry etching in the m dry etching and the first dry etching in the n dry etching.

[0042] As mentioned above, oxygen radical treatment can passivate the oxide layer before subsequent etching, thus reducing damage to the oxide layer during subsequent etching. This is believed to be because the surface of the ONO-stacked silicon layer becomes thermodynamically stable due to oxygen radical treatment.

[0043] Oxygen radicals can typically be generated from an O2 source. As another example, oxygen radicals can be generated from other sources containing oxygen atoms, such as those selected from O3, N2O, NO, N2O2, and H2O.

[0044] Oxygen radical treatment can utilize oxygen radicals generated by plasma-generating a source containing oxygen atoms within the etching process chamber. Preferably, oxygen radicals can be generated using oxygen radicals generated in a remote plasma system. Utilizing oxygen radicals generated in a remote plasma system offers the advantage that oxygen radicals can be generated even without altering plasma generation conditions such as RF power within the etching process chamber.

[0045] Conditions for generating oxygen radicals from oxygen within a process chamber or a remote plasma system can be achieved using RF frequencies of 15 MHz to 50 MHz, RF power of 500 W to 2500 W, and RF conditions in capacitively coupled plasma (CCP) mode. Additionally, oxygen (O2) gas at 1000 sccm to 3000 sccm can be used as the reactant gas, and argon gas at 50 sccm to 1000 sccm can be used concurrently.

[0046] The oxygen free radical treatment time can be from 10 seconds to 120 seconds. In addition, when performing oxygen free radical treatment, process pressures of 0.3 Torr to 10 Torr and substrate surface temperatures of 0 to 50°C can be proposed, but are not limited to these, and various known process conditions can be used.

[0047] The first etching step, the second etching step, and the oxygen free radical treatment step can be performed in-situ. A substrate with alternating layers of silicon oxide and silicon nitride is loaded into the process chamber, and the substrate is unloaded from the process chamber after cyclic etching of the nitride film (e.g., 60 times) so that etching can proceed to the desired horizontal and / or vertical depth.

[0048] Here, the cyclic etching includes an oxygen radical treatment step in between. An oxygen radical treatment step may be included between all etching steps. Alternatively, an oxygen radical treatment may be performed every few etching steps. For example, it can be performed as follows: Etching 1 - Oxygen radical treatment - Etching 2 - Oxygen radical treatment - Etching 3 - Oxygen radical treatment - Etching 4 - ... Another example is the sequence: Etching 1, Etching 2, Etching 3 - Oxygen radical treatment - Etching 4, Etching 5, Etching 6 - Oxygen radical treatment - Etching 7, Etching 8, Etching 9...

[0049] As another example, the first etching step and the second etching step, along with the oxygen radical treatment step, can be performed ex-situ. This may include steps such as unloading the substrate from the process chamber and cleaning the process chamber after the first etching. The second etching can be performed in the same process chamber as the first etching or in a separate process chamber.

[0050] In the non-in-situ method, after loading the first substrate into the process chamber and etching the nitride layer to a fixed depth, the process includes oxygen radical treatment during cyclic etching (e.g., 20 times). The substrate is then unloaded from the process chamber and transferred in a standby state (to a load-locked process chamber or load pot) and exposed to the atmosphere. During this period, the process chamber is cleaned using oxygen radicals to remove fluorine deposits on the chamber walls. Subsequently, instead of reloading the first substrate into the process chamber, it is preferable to cyclically etch the second substrate until a fixed depth is achieved, and then sequentially process the desired number of substrates (e.g., 25 wafers) for the desired number of cycles (e.g., 3 * 20 = 60 cycles).

[0051] While the substrate is unloaded, nitrogen plasma is typically used in the cleaning step to remove residual fluorine components on the inner wall of the process chamber. However, this invention takes into account that the residual fluorine in the process chamber is a carbon polymer residue and utilizes oxygen free radicals with high removal efficiency to remove the residual fluorine components present on the inner wall of the process chamber.

[0052] In in-situ methods, there is a problem of fluorine accumulating on the walls of the process chamber and later falling as particles. However, out-of-situ methods can solve this problem. In out-of-situ methods, in addition to the cleaning process to remove accumulated fluorine in the process chamber, the substrate temperature and the atmosphere inside the process chamber remain the same as before the process, maintaining the initial atmosphere compared to in-situ methods. Furthermore, in out-of-situ methods, the substrate reacts with oxygen in the air during unloading from the process chamber and exposure to the atmosphere, resulting in a higher passivation effect.

[0053] Ultimately, in the case of non-in-situ methods, despite the loss of throughput, many of the technical advantages described above can be observed compared to in-situ methods.

[0054] On the other hand, the conditions for generating oxygen radicals during an etching cycle while the substrate is mounted differ from the conditions for oxygen radical treatment used for cleaning the process chamber while the substrate is unloaded. During oxygen radical treatment during an etching cycle, the RF power used to generate oxygen radicals is controlled high to ensure sufficient passivation within the pattern. In contrast, during oxygen radical treatment for cleaning the process chamber, the RF power is controlled relatively low to reduce plasma damage to the process chamber components and completely remove residual fluorine, while allowing for a relatively longer radical treatment time.

[0055] In the substrate processing method according to the present invention, various gases are supplied to the process chamber in the primary etching step and the secondary etching step to selectively etch the silicon nitride layer. The primary etching step and the secondary etching step will be described in detail below.

[0056] First, in order to selectively etch the silicon nitride layer, a variety of gases are supplied to the process chamber in this invention. The various gases include a first gas containing fluorine (F) and a second gas containing hydrogen (H).

[0057] On the other hand, in this invention, it is preferable to exclude nitrogen trifluoride (NF3) from the first gas. Since nitrogen trifluoride (NF3) not only etches the silicon nitride layer but also, to a certain extent, the silicon oxide layer, it is preferable to exclude it from the various gases used for selective etching of the silicon nitride layer as much as possible.

[0058] In this invention, the first gas and the second gas are plasma-enhanced inside the process chamber, for example, inside the nozzle.

[0059] As for the process conditions for plasma etching, it is preferable to apply high-frequency power with an RF frequency of 15MHz or higher and less than 60MHz to the nozzle using the RF power supply of the etching apparatus, and more preferably an RF frequency of 15MHz to 50MHz. When the RF frequency is less than 15MHz, such as 13.56MHz, the plasmaification and decomposition efficiency of various gases is low, and therefore most of the etching free radicals are consumed in the upper silicon nitride layer. Therefore, when the RF frequency is less than 15MHz, the etching of the lower silicon nitride layer is difficult to proceed smoothly, and over-etching of the upper silicon nitride layer may cause damage such as pattern collapse; therefore, an RF frequency of 15MHz or higher is preferred. On the other hand, when the RF frequency is 60MHz or higher, such as 60MHz or 67.8MHz, the excessive ionization and decomposition efficiency makes it difficult to obtain the desired etching profile even by adjusting other process conditions.

[0060] Furthermore, the plasma mode used in this invention is more preferably CCP mode, either inductively coupled plasma (ICP) mode or capacitively coupled plasma (CCP) mode. This is because, in the case of CCP mode, due to its superior uniformity compared to ICP mode, the device can achieve a more uniform process result in the processing of large-capacity substrates.

[0061] In addition, as process conditions for plasma etching, RF power of 700W to 2500W, process pressure of 0.3 Torr to 10 Torr, and substrate surface temperature of 0 to 50°C can be proposed, but they are not limited to these, and various known process conditions can be used.

[0062] The atomic ratio (F:H) of fluorine to hydrogen contained in the various gases is preferably 15:1 to 35:1. The atomic ratio (F:H) of fluorine to hydrogen can be achieved by controlling the flow rates of the fluorine-containing gas and the hydrogen-containing gas.

[0063] When the atomic ratio of fluorine to hydrogen (F:H) is less than 15:1, there is an excess of hydrogen, resulting in a thick polymer film formed on the surfaces of the silicon oxide and silicon nitride layers by plasma generation. Consequently, the etching rate of the silicon nitride layer may decrease significantly. Conversely, when the atomic ratio of fluorine to hydrogen (F:H) exceeds 35:1, insufficient hydrogen causes the polymer film to form too thin, resulting in a higher etching rate for the silicon oxide film, which may damage the pattern.

[0064] The first gas may be carbon tetrafluoride (CF4). The second gas may be one or more selected from difluoromethane (CH2F2), monofluoromethane (CH3F), methane (CH4), hydrogen (H2), ammonia (NH3), and trifluoromethane (CHF3). More preferably, the first gas is carbon tetrafluoride (CF4), and the second gas is difluoromethane (CH2F2). The flow rate of the first gas may be determined to be about 800 sccm or less, and the flow rate of the second gas may be determined to be 200 sccm or less, but is not limited thereto.

[0065] On the other hand, various gases may additionally include nitrogen and oxygen. Nitrogen combines to form NO and helps etch the silicon nitride layer. In addition, oxygen helps remove process byproducts. Nitrogen can be supplied into the process chamber at a flow rate of, for example, less than 2000 sccm, and oxygen can be supplied into the process chamber at a flow rate of, for example, less than 3000 sccm.

[0066] After selective etching of the silicon nitride layer, a heat treatment can be performed during the etching process to remove the condensed film formed on the surface of the silicon nitride layer. The heat treatment can be performed in a temperature range of 80°C to 300°C.

[0067] Effect of oxygen free radicals

[0068] exist Figure 1 The image shows the results of etching a silicon nitride layer without oxygen radical treatment. Figures 1 to 3 In this context, Sub refers to the silicon substrate, O refers to the silicon oxide layer, and N refers to the silicon nitride layer.

[0069] Figure 1This illustrates an example of etching with a gradually decreasing etching rate from the topmost silicon nitride layer to the bottommost silicon nitride layer. (See reference...) Figure 1 The following results can be observed: the topmost silicon nitride layer is etched rapidly, while the bottommost silicon nitride layer is etched most slowly. Furthermore, according to... Figure 1 It can be seen that the silicon oxide layer is undesirably damaged.

[0070] exist Figure 2 , Figure 3 The image shows the results of oxygen radical treatment and silicon nitride layer etching during the etching process.

[0071] Figure 2 The following example illustrates etching at a gradually increasing etch rate from the top silicon nitride layer towards the middle layer in the thickness direction, and at a gradually decreasing etch rate from the middle layer towards the bottom layer in the thickness direction. The following results can be observed: the middle silicon nitride layer is etched rapidly, while the bottom layer is etched relatively slowly, and the top layer is etched the slowest.

[0072] Figure 3 This example illustrates etching from the top silicon nitride layer to the bottom silicon nitride layer with a gradually increasing etching rate. The following result can be observed: the bottom silicon nitride layer is etched rapidly, while the top silicon nitride layer is etched most slowly.

[0073] In addition, according to Figure 2 , Figure 3 It can be seen that almost no undesirable damage to the silicon oxide layer occurs.

[0074] Figure 4 The etching depths (T), (C), and (B) of the uppermost silicon nitride layer relative to the uppermost silicon nitride layer are shown relative to the oxygen radical treatment time and power. Each etching session lasted 12 seconds, for a total of 4 etching passes (×4 12").

[0075] Reference Figure 4 As can be seen on the left, when there is a 40-second (40") oxygen radical treatment between etchings, the etching of the middle silicon nitride layer proceeds faster than that of the reference (Ref.) without oxygen radical treatment, and when there is an 80-second (80") oxygen radical treatment, the etching of the bottom silicon nitride layer proceeds faster.

[0076] Reference Figure 4 As can be seen on the right side, the etching depth of the middle and bottom parts is relatively large due to the use of oxygen free radical treatment with a power of 1700W.

[0077] In addition, the uniformity, oxide film etching selectivity, and etching rate were evaluated for cases without oxygen radical treatment and cases including 40 seconds of oxygen radical treatment in non-patterned wafers (NPW), and are shown in Table 1.

[0078] [Table 1]

[0079]

[0080] Referring to Table 1, the differences in uniformity (Unif.) and etching rate (E / R) are not significant, but the difference in etching selectivity (Sel.) for oxide film (Tox) is significant, and this situation shows the effect of oxygen free radical treatment included in the etching step.

[0081] In this invention, the etching gas, as described above, contains both hydrogen and fluorine gases, and the etching profile is adjusted by regulating the atomic ratio of fluorine to hydrogen. Furthermore, in this invention, while adjusting the etching profile through oxygen free radical treatment during etching, a passivation effect on the silicon oxide layer is achieved.

[0082] Etching profile control of ONO stack

[0083] Carbon tetrafluoride (CF4) and difluoromethane (CH2F2) were used as etching gases for selectively etching the silicon nitride layer in the ONO stack, and the flow rates were controlled according to the atomic ratio of fluorine to hydrogen (F:H) in Table 2. In addition, the process conditions shown below were applied.

[0084] -RF frequency of the RF power supply: 27.12MHz

[0085] -RF power of the RF power supply: 1000W

[0086] -Plasma mode: CCP mode

[0087] -Intracavitary pressure 1 Torr

[0088] -Base surface temperature: room temperature

[0089] Table 2 shows the T / B ratio representing the etching rates of SiN, SiO2, and the etching rate of the uppermost silicon nitride layer to the lowermost silicon nitride layer, based on the atomic ratio of fluorine to hydrogen (F:H).

[0090] In Table 2, the SiN etching rate and SiO2 etching rate are values ​​obtained from the results of the unpatterned wafer process.

[0091] Furthermore, the T / B ratio indicates the etching rate of the top silicon nitride layer over the bottom silicon nitride layer. When the T / B ratio is 1, the etching rates of the bottom and top silicon nitride layers are the same. When the T / B ratio is greater than 1, the top silicon nitride layer is etched more than the bottom silicon nitride layer. Conversely, when the T / B ratio is less than 1, the bottom silicon nitride layer is etched more than the top silicon nitride layer.

[0092] [Table 2]

[0093]

[0094] Referring to Table 2, it can be seen that when the atomic ratio of fluorine to hydrogen (F:H) is less than 15:1, the etching of the bottom silicon nitride layer is almost negligible. A fluorine to hydrogen atomic ratio (F:H) of less than 15:1 refers to a relatively high hydrogen ratio compared to other examples. Due to the very high hydrogen ratio, the polymer film derived from the plasma forms a very thick layer on the surfaces of the silicon oxide and silicon nitride layers during plasma etching, thus making the silicon nitride layer appear almost unetched. Therefore, the fluorine to hydrogen atomic ratio (F:H) is preferably 15:1 or higher.

[0095] Furthermore, referring to Table 1, it can be seen that pattern collapse occurs when the atomic ratio of fluorine to hydrogen (F:H) exceeds 35:1. It was observed that due to the very low hydrogen ratio, the polymer film is formed thinly on the surfaces of the silicon oxide and silicon nitride layers, thus greatly increasing the etching amount of the silicon oxide layer, resulting in pattern collapse. Therefore, the atomic ratio of fluorine to hydrogen (F:H) is preferably 35:1 or less.

[0096] Figure 5 The relative etching rates of the topmost and bottommost silicon nitride layers of the ONO stack are shown based on the atomic ratio of fluorine to hydrogen contained in the etching gas.

[0097] Refer to Table 2 and Figure 5 With an atomic ratio of fluorine to hydrogen (F:H) of 15:1, the T / B ratio, representing the etching rate of the uppermost silicon nitride layer to the lowermost silicon nitride layer, is approximately 2.6. With an atomic ratio of fluorine to hydrogen (F:H) of 18:1, the T / B ratio is approximately 2.3. This is useful when a gradual decrease in etching rate is required towards the lowermost silicon nitride layer.

[0098] In addition, when the atomic ratio of fluorine to hydrogen (F:H) is 22.5:1, the T / B ratio is approximately 1.0, which is useful when it is necessary to make the etching rates of the topmost and bottommost silicon nitride layers substantially uniform.

[0099] In addition, when the atomic ratio of fluorine to hydrogen (F:H) is 25:1, 30:1, or 35:1, the T / B ratio is less than 1.0, which is useful when the etching rate of the silicon nitride layer needs to gradually increase towards the bottom.

[0100] In addition, it can be seen that when the atomic ratio of fluorine to hydrogen (F:H) increases from 22.5:1 to 30:1, the T / B ratio decreases, but when the atomic ratio of fluorine to hydrogen (F:H) increases from 30:1 to 35:1, the T / B ratio increases instead.

[0101] As described above, by using the substrate processing method according to the present invention, the following effects can be obtained: selective etching of the silicon nitride layer relative to the silicon oxide layer can be performed, and the etching profile of the silicon nitride layer formed on the substrate can also be adjusted by controlling the atomic ratio of fluorine to hydrogen contained in the etching gas.

[0102] In particular, by controlling the atomic ratio of fluorine to hydrogen (F:H) to be above 22.5:1 and below 35:1, etching can be performed uniformly from the top silicon nitride layer to the bottom silicon nitride layer in a multilayer silicon nitride layer, or the etching can be performed gradually from the top silicon nitride layer to the bottom silicon nitride layer, thereby controlling the etching profile.

[0103] On the other hand, even when the RF frequency is fixed at 50MHz, similar T / B ratio results as in Table 2 can be obtained by adjusting the atomic ratio of fluorine to hydrogen (F:H) to 15:1 to 35:1.

[0104] Conversely, when the RF frequency is fixed at 60MHz, even with variations in the process formulation using different RF powers and pressures, the thickness profile of the silicon nitride layer cannot be adjusted. This is due to the excessive ionization and decomposition efficiency during plasma etching. Therefore, this result indicates that an RF frequency less than 60MHz is more suitable for the substrate processing method according to the present invention.

[0105] 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, comprising processing an ONO stack comprising alternating layers of silicon oxide and silicon nitride, characterized in that... Includes the following steps: (a) Perform a dry etching on the ONO stacked silicon nitride layer; (b) Generate oxygen free radicals and use the oxygen free radicals to treat the silicon oxide layer of the ONO stack; as well as (c) Perform a second dry etching on the ONO stacked silicon nitride layer. The dry etching in steps (a) and (c) involves plasma etching of multiple gases to etch the silicon nitride layer, and the multiple gases include a first gas containing carbon tetrafluoride and a second gas containing hydrogen.

2. The substrate processing method according to claim 1, characterized in that, The oxygen free radicals are generated from sources selected from O2, O3, N2O, NO, N2O2, and H2O.

3. The substrate processing method according to claim 1, characterized in that, Step (b) utilizes oxygen free radicals generated in a remote plasma system.

4. A substrate processing method, comprising processing an ONO stack comprising alternating layers of silicon oxide and silicon nitride, characterized in that... Includes the following steps: (a) The ONO stacked silicon nitride layer is subjected to m dry etching cycles, where m is a natural number greater than 2; (b) Perform n dry etching operations on the ONO stacked silicon nitride layer, where n is a natural number greater than or equal to 2. Steps (a) and (b) include one or more oxygen radical treatment steps, wherein the oxygen radical treatment steps involve treating the ONO stacked silicon oxide layer with oxygen radicals between dry etching processes. The dry etching in each of steps (a) and (b) involves plasma etching with a variety of gases to etch the silicon nitride layer, and the variety of gases includes a first gas containing carbon tetrafluoride and a second gas containing hydrogen.

5. The substrate processing method according to claim 4, characterized in that, The oxygen radical treatment step utilizes oxygen radicals generated in a remote plasma system.

6. The substrate processing method according to claim 4, characterized in that, After performing step (a), the substrate is unloaded from the process chamber and the process chamber is cleaned.

7. The substrate processing method according to claim 6, characterized in that, The cleaning process utilizes oxygen free radicals.

8. The substrate processing method according to claim 7, characterized in that, The oxygen free radicals applied during the cleaning process are generated under higher radio frequency power conditions compared to the oxygen free radicals applied in steps (a) and (b).

9. The substrate processing method according to claim 4, characterized in that, The atomic ratio of fluorine to hydrogen contained in the various gases is greater than 15:1 and less than 22.5:

1.

10. The substrate processing method according to claim 4, characterized in that, The atomic ratio of fluorine to hydrogen contained in the various gases is greater than 22.5:1 and less than 35:

1.

11. The substrate processing method according to claim 4, characterized in that, To achieve plasmaization of the various gases, high-frequency power with a radio frequency of 15MHz or higher and less than 60MHz is utilized.

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