ETCHING METHOD AND ETCHING APPARATUS

An etching method of an oxygen-containing silicon film embedded in each recess of a substrate, which includes a plurality of recesses having different opening sizes, by supplying an etching gas to the substrate, the etching method including: adsorbing an organic amine compound gas on the oxygen-containing silicon film by supplying the organic amine compound gas to the substrate; desorbing an excess of the organic amine compound gas from the substrate; and selectively etching the oxygen-containing silicon film with respect to each recess by supplying the etching gas containing a halogen to the substrate on which the organic amine compound has been adsorbed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application Nos. 2020-144867 and 2021-101853, filed on Aug. 28, 2020 and Jun. 18, 2021, respectively, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to an etching method and an etching apparatus.

BACKGROUND

In manufacturing a semiconductor device, etching is performed on an oxygen-containing silicon film such as a silicon oxide (SiOx) film formed on a semiconductor wafer (hereinafter, referred to as a “wafer”), which is a substrate. For example, Patent Document 1 describes etching a SiOxfilm by supplying hydrogen fluoride (HF) gas and organic amine compound gas.

PRIOR ART DOCUMENT cl Patent Document

SUMMARY

An etching method of the present disclosure is etching an oxygen-containing silicon film embedded in each recess of a substrate, which includes a plurality of recesses having different opening sizes, by supplying an etching gas to the substrate. The etching method includes: adsorbing an organic amine compound gas on the oxygen-containing silicon film by supplying the organic amine compound to the substrate; desorbing an excess of the organic amine compound gas to be desorbed from the substrate; and selectively etching the oxygen-containing silicon film with respect to each recess by supplying the etching gas containing a halogen to the substrate on which the organic amine compound has been adsorbed.

Another etching method of the present disclosure is etching an oxygen-containing silicon film by supplying an etching gas to a substrate. The etching method includes: adsorbing an organic amine compound gas on the oxygen-containing silicon film by supplying the organic amine compound gas to the substrate; desorbing an excess of the organic amine compound gas to be desorbed from the substrate by supplying an inert gas to the substrate; and etching the oxygen-containing silicon film by supplying the etching gas containing a halogen to the substrate on which the organic amine compound has been adsorbed.

DETAILED DESCRIPTION

FIG. 1illustrates an etching apparatus1according to an embodiment of the etching apparatus of the present disclosure. The etching apparatus1is configured to be capable of performing first to third etching methods to be described later. The outline of the first to third etching methods will be described first. With respect to a SiOxfilm, which is an oxygen-containing Si (silicon) film formed on the surface of a wafer W, etching is performed using hydrogen fluoride (HF) gas, which is an etching gas, and trimethylamine (TMA) gas, which is an organic amine compound gas.

More specifically, as will be shown later in the evaluation tests, TMA gas has a high adsorption property with respect to an SiOxfilm and reacts with HF gas to enhance the etching property of the HF gas with respect to the SiOxfilm. Using these properties, in the first to third etching methods, a SiOxfilm is selectively etched with respect to a film other than the SiOxfilm formed on the surface of a wafer W. No plasma is used for etching.

The etching apparatus1includes a processing container11, a stage12, a shower head13, an exhaust mechanism14, and a piping system15. The inside of the processing container11is exhausted by the above-mentioned exhaust mechanism14including, for example, a vacuum pump, an exhaust pipe, a valve interposed in the exhaust pipe, and the like so as to obtain a vacuum atmosphere having a desired pressure. In addition, the stage12provided in the processing container11is provided with a heater, and a wafer W placed on the stage12is heated to a desired temperature by the heater. The processing container11is provided with a wafer W transport port that is openable/closable, and the stage12is provided with pins each of which is movable up and down. A wafer W is transported between a transport mechanism of the wafer W that has entered the processing container11via the transport port and a position above the stage12. However, illustration of the transport port and pins is omitted.

The shower head13, which is an organic amine compound gas supplier and an etching gas supplier, is installed on the ceiling in the processing container11so as to face the stage12, and supplies a gas to the entire surface of the wafer W placed on the stage12. The piping system15is configured to be capable of supplying the above-mentioned HF gas and TMA gas to the wafer W through the shower head13. Next, the configuration of the piping system15will be described. The piping system15includes pipes21A and21B, the downstream sides of which are each connected to the shower head13. The upstream side of the pipe21A is connected to a HF gas supply source23A via a gas supply device22A, and the upstream side of the pipe21B is connected to a TMA gas supply source23B via a gas supply device22B.

The downstream side of the pipe25A is connected to the downstream side of the gas supply device22A in the pipe21A, and the upstream side of the pipe25A is connected to the supply source27of an inert gas (e.g., nitrogen (N2) gas) via a gas supply device26A. The downstream side of a pipe25B is connected to the downstream side of the gas supply device22B in the pipe21B, and the upstream side of the pipe25B is connected to the N2gas supply source27via a gas supply device26B. The gas supply devices22A,22B,26A, and26B are provided with respective flow rate control devices, such as valves and mass flow controllers, so that the supply/the stop of supply and the flow rates of respective gases supplied from the gas supply sources to the downstream side can be controlled.

The N2gas is used as a carrier gas for TMA gas, a carrier gas for HF gas, and a purge gas for purging the inside of the processing container11. For example, N2gas is constantly supplied to the pipes21A and21B during the processing of the wafer W. As a result, when TMA gas or HF gas is supplied into the processing container11, the N2gas is used as a carrier gas for the TMA gas or HF gas, and when neither HF gas nor TMA gas is supplied, the N2gas is used as a purge gas. In addition, other inert gases such as argon (Ar) gas may be used as a carrier gas and a purge gas instead of N2gas. In addition, the shower head13configured to supply the purge gas as described above, the heater of the above-mentioned stage12, and the exhaust mechanism14constitute a desorption mechanism for causing excess TMA gas on the wafer W to be desorbed in each etching method to be described later.

The etching apparatus1includes a controller10, and the controller10includes a program. An instruction (each step) is incorporated in the program so that wafer W processing described later is performed. This program is stored in a computer storage medium (e.g., a compact disk, a hard disk, a magneto-optical disk, or a DVD) and installed in the controller10. The controller10outputs a control signal to each part of the etching apparatus1according to the program, and controls the operation of each part. Specifically, the temperature of the wafer W by the heater of the stage12, the supply/the stop of supply of respective gases to the shower head13by the gas supply devices22A,22B,26A, and26B, the pressure in the processing container11by the exhaust mechanism14, and the like are controlled.

FIG. 2illustrates an example of the surface of a wafer W to be processed by the etching apparatus1. The first to third etching methods to be described later will be described with reference to a case where this wafer W is processed. A silicon nitride (SiN) film31is formed on the surface of the wafer W. The recesses32and33are formed in the SiN film31as patterns having widths different from each other.FIG. 2illustrates a vertical cross section of the recesses32and33, which are grooves, perpendicular to the extension direction thereof. That is, each of the recesses32and33extends in the front and rear direction of the paper surface.

The width of the recess32is larger than the width of the recesses33. Therefore, the size of the opening of the recess32(=width L1) is larger than the size of the opening of the recess33(=width L2). The width L1is, for example, 100 nm or more, and the width L2is, for example, 100 nm or less. When the width L2is within such a relatively small range, it is considered that blockage due to TMA, which will be described later, is likely to occur. The SiOxfilm34is embedded in the recesses32and33, and the SiOxfilms34and the SiN film31are exposed on the surface of the wafer W.

Subsequently, the first etching method according to an embodiment of the etching method of the present disclosure will be described with reference toFIG. 3, which is a flowchart illustrating a processing procedure, andFIG. 4, which is a timing chart illustrating the supply/the stop of supply of HF gas and TMA gas to the inside of the processing container11. In addition, schematic views illustrating the surface states of the wafer W inFIGS. 5A to 10will also be referred to as appropriate. In these schematic views, TMA gas is indicated as41, and HF gas is indicated as42.

First, the wafer W described with reference toFIG. 2is placed on the stage21and heated to a preset temperature, and the inside of the processing container11is exhausted so as to have a preset pressure. The TMA gas41is supplied into the processing container11in the state in which the temperature of the wafer W and the pressure in the processing container11are controlled in this way (time t1, step S1). Since the TMA gas41has a high adsorption property to the SiOxfilms34and a low adsorption property to the SiN film31, the TMA gas41is selectively adsorbed on the surfaces of the SiOxfilms34embedded in the recesses32and33, respectively (FIGS. 5A and 5B). Thereafter, the supply of the TMA gas41into the processing container11is stopped (time t2, step S2), and the inside of the processing container11is purged using the purge gas.

A part of the TMA gas41adsorbed on the wafer W is desorbed from the wafer W due to the supply of heat energy from the heated wafer W, and the actions of the exhaust and the purge gas within the processing container11, and on the surface of the SiOxfilm34in each of the recesses32and33, a TMA thin layer43is formed (FIG. 6A). The thin layer43is, for example, about one TMA molecular layer. That is, the thin layer43is a monomolecular layer or a layer in which several molecules are overlapped.

When a preset time elapses from time t2,the HF gas42is supplied into the processing container11(time t3, step S3). The HF gas42is activated by reacting with the TMA gas41forming the thin layer43on the SiOxfilm, the HF gas42thus activated reacts with the SiOxfilms34, and the resulting reaction product sublimates. That is, the SiOxfilms34are etched (FIGS. 6B and 7A). Since the thickness of the thin layer43described above is extremely small, the etching amount (the etched film thickness) of each SiOxfilm34due to the above reaction is small. That is, the SiOxfilms34embedded in the recesses32and the SiOxfilm34embedded in the recess33are both etched little by little, and the etching amounts are the same. Then, as shown in the evaluation tests to be described later, the etching property of the HF gas42on the SiN film31is low. Therefore, among the SiN film31and the SiOxfilms34, the SiOxfilms34are selectively etched.

When a preset time elapses from time t3, the supply of the HF gas42into the processing container11is stopped (time t4, step S4), and the HF gas42remaining in the container11is purged by the purge gas supplied into the processing container11. Then, after a lapse of a preset time from the time t4, the TMA gas41is supplied into the processing container11(time t5) and is selectively adsorbed on the surfaces of the SiOxfilm34etched from time t3to time t4described above (FIGS. 7B and 8A), after which the supply of the TMA gas41into the processing container11is stopped (time t6). That is, the above-described steps S1and S2are executed again.

After the supply of the TMA gas41at time t6is stopped, the inside of the processing container11is purged by the purge gas, and a part of the TMA gas41adsorbed on the SiOxfilms34is desorbed by the purge gas, the exhaust, and the supply of heat from the wafer W as in the period from time t2to time t3. Then, a TMA thin layer43is formed again on the surface of each SiOxfilm34(FIG. 8B), and then the HF gas42is supplied into the processing container11(time t7). That is, step S3is executed again, and each SiOxfilm34is etched (FIGS. 9A and 9B). Even during this re-etching, since the TMA gas41is adsorbed on the surface of each SiOxfilm34and a thin layer43is formed on the surface of each SiOxfilm34, each of the SiOxfilms34in the recesses32and33is selectively etched with high uniformity such that the film thickness is reduced. Thereafter, the supply of the HF gas42into the processing container11is stopped (time t8). That is, step S4is executed again.

For example, even thereafter, a cycle including steps S1to S4is repeated, an adsorption step causing TMA gas41to be selectively adsorbed on the SiOxfilms34, a desorption step for causing excess TMA gas41to be desorbed from the SiOxfilms34, and an etching step for etching the SiOxfilms34by HF gas42is repeated in order. As a result, selective etching of the SiOxfilms34proceeds in each in-plane portion of the wafer W with high uniformity and little by little. Then, when the above cycle is repeated a preset number of times, the processing on the wafer W is completed, and the wafer W is carried out from the processing container11. Since the etching proceeded on the processed wafer W as described above, the uniformity in the etching amount of the SiOxfilms34in the recesses32and33is high, and a SiOxfilm34having a desired thickness remains in each of the recesses32and33(FIG. 10).

It has been described that the TMA gas is desorbed from the wafer W while the supply of the TMA gas and the HF gas is stopped. However, as described above, since the heat supply from the wafer W and the exhaust within the processing container11contribute to the desorption, such desorption also occurs, for example, when the TMA gas is supplied to the wafer W. That is, the step of desorption of the TMA gas from the wafer W is not limited to being performed at a time different from the time at which the TMA gas adsorption step is performed, and may be performed in parallel with the adsorption step.

In addition, the thin layer43at the time of supplying the HF gas is not limited to the above-mentioned monomolecular layer or a structure in which several molecules are stacked, and may be formed as a thicker layer, the thickness of which is optional. Since it is possible to change the adsorbed amount of the TMA gas by controlling the processing conditions such as the amount of TMA gas supplied to the wafer W and the temperature of the wafer W, it is possible to adjust the thickness of the thin layer43by changing the processing conditions.

In the above-described processing example, it has been described that the cycle including steps S1to S4is repeated twice or more, but the number of repetitions of this cycle may be two. In addition, the number of cycles may be one, that is, the steps S1to S4may be performed only once without repeating.

Regarding the second etching method, with reference toFIG. 11, which is a timing chart illustrating the supply/the stop of supply of TMA gas41and HF gas42into the processing container11, andFIGS. 12A to 13B, which illustrate the surface states of a wafer W, the difference from the first etching method will be mainly described. The wafer W described with reference toFIG. 2is placed on the stage21and heated to a preset temperature, and the inside of the processing container11is exhausted so as to have a preset pressure. In that state, TMA gas41and HF gas42are supplied into the processing container11(FIG. 12A, time t11).

The TMA gas41is adsorbed on the surface of each of the SiOxfilms34in the recesses32and33. Since both the TMA gas41and the HF gas42are supplied together, the HF gas42rapidly reacts with the TMA gas41adsorbed in this way, and the surfaces of the SiOxfilms34are etched. Then, the TMA gas41is newly adsorbed on the surfaces of the etched SiOxfilms34and reacts with the HF gas42, so that the surfaces of the SiOxfilms34are further etched (FIG. 12B). Then, when a preset time elapses from the start of the supply of the TMA gas41and the HF gas42, the supply of the TMA gas41is stopped, while the supply of the HF gas42into the processing container11is continued. (FIG. 13A, time t12).

The reason for changing the TMA gas41and the HF gas42such that the HF gas42is applied alone as described above will be described. In the description,FIGS. 14A and 14B, which are schematic views illustrating the states considered to occur in the recesses33of the SiN film31, will also be referred to.FIG. 14Aillustrates the state immediately before the supply of the TMA gas41is stopped, andFIG. 14Billustrates the state after the supply of the TMA gas41is stopped.

Until the supply of the TMA gas41is stopped, the etching of the SiOxfilms34proceeds in the recesses32and33in the SiN film31, as described above. Thus, the heights of the surfaces of the SiOxfilms34decrease, and the depths of the grooves having the surfaces of the SiOxfilms34as the bottom surfaces increase. Regarding the grooves, the bottom surfaces of which are the SiOxfilms34, the groove formed in the recess32will be referred to as a “groove32A”, and the groove formed in the recess33will be referred to as a “groove33A”.

When the depths of the grooves32A and33A increase in this way, the TMA gas41and the HF gas42are likely to flow into the groove32A since the opening width of the groove32A is wide. Therefore, the etching of the SiOxfilm34continues. Meanwhile, since the opening width of the groove33A is narrow, it is difficult for the TMA gas41and the HF gas42to flow into the groove33A. However, since the TMA gas41has a high adsorption property to the SiOxfilm34as described above, the TMA gas41that has once entered the groove33A is easily adsorbed on the surface of the SiOxfilm34and stays there as illustrated inFIG. 14A, and the molecules of the TMA gas41are further adsorbed and deposited on the molecules of the adsorbed TMA gas41.

As a result, the amount of TMA molecules deposited on the SiOxfilm34of the groove33A increases, and the groove33A is closed. As a result, the supply of the HF gas42to the surface of the SiOxfilm34is hindered. That is, the HF gas42reacts with the TMA gas41adsorbed on the surface of the SiOxfilm34, and is not able to etch the SiOxfilm34. Therefore, the etching of the SiOxfilm34is stopped or the etching rate is lowered in the recesses33.

Therefore, as described above, at time t12, the supply of only the TMA gas41among the TMA gas41and the HF gas42is stopped. After the supply of the TMA gas41is stopped, the TMA gas41is gradually desorbed from the surface of the SiOxfilm34in the groove33A by the exhaust within the processing container11, the application of heat energy from the wafer W, and the purging action of the HF gas42. Meanwhile, the HF gas42, which is being continuously supplied, is able to enter the groove33A and react with the TMA gas41directly adsorbed on the surface of the SiOxfilm34due to the occurrence of the above-mentioned desorption. That is, the etching of the SiOxfilm34is restarted in the recesses33. In this way, after the supply of the TMA gas41is stopped, the etching of the SiOxfilm34proceeds by the remaining TMA gas41and the newly supplied HF gas42in the recesses33.

In the case where the TMA gas41is adsorbed and remains on the surface of the SiOxfilm34even in the groove32A when the supply of the TMA gas41is stopped at time t12, the SiOxfilm34in the groove32A is etched by the HF gas supplied after time t12and the corresponding TMA gas41. When a preset time elapses from time t12, the supply of the HF gas42into the processing container11is stopped (time t13), and the etching process is completed (FIG. 13B).

As described above, according to the second etching method, first, the adsorption step and the etching step are performed in parallel by the TMA gas41, and after time t12at which the supply of the TMA gas is stopped, the desorption step and the etching step are performed in parallel by the excess TMA gas41. As a result, it is possible to prevent the etching of the SiOxfilm34from stopping due to excessive retention of the TMA gas41in the recesses33having a relatively narrow opening width. Therefore, since it is possible to etch the SiOxfilms34in the recesses33more deeply, it is possible to form the SiOxfilms at a desired film thickness.

In the second etching method described above,FIG. 13Billustrates that at the end of etching, the etching amounts of the SiOxfilm34are different between the recess32and the recesses33, but the etching amounts may be made to be equal to each other. In this third etching method, for example, similarly to the second etching method, the wafer W described with reference toFIG. 2is processed by supplying each of the TMA gas41and the HF gas42into the processing container11according to the timing chart described with reference toFIG. 11.

Therefore, in this third etching method, the TMA gas41and the HF gas42are started to be supplied to the wafer W at time t11(FIG. 12A). Then, after the etching proceeds in each of the SiOxfilms34in the recesses32and33by the TMA gas41and the HF gas42as described above, the TMA gas41stays on the SiOxfilms34in the recesses33having a narrow opening width so that TMA molecules are deposited and etching stops. Meanwhile, since both the TMA gas41and the HF gas42easily enter the recess32due to the wide opening width of the recess32, the etching of the SiOxfilm34proceeds. As a result, as illustrated inFIG. 12B, the etching amount in the recess32is larger than the etching amount in the recesses33.

Thereafter, the supply of TMA gas41is stopped at time t12. When the supply of the TMA gas41is stopped, the TMA gas41is consumed because the etching has been continuously performed up to that point in the recess32. Thus, the amount of the TMA gas41adsorbed on the SiOxfilm34is relatively small. Therefore, after the supply of the TMA gas41is stopped, the etching amount of the SiOxfilm34in the recess32is zero to a very small amount.

Meanwhile, as described in the description of the second etching method, a large amount of TMA gas41is adsorbed on the SiOxfilms34in the recesses33at time t12. Then, after time t12, the etching of the SiOxfilms34is restarted since the desorption of the TMA gas41proceeds. However, even if the desorption proceeds to some extent, since a large amount of TMA gas41has been originally adsorbed on the SiOxfilms34, the etching amount after time t12becomes relatively large. As a result, when the supply of the HF gas42is stopped at time t13, the etching amounts of the SiOxfilm34become equal to each other between the recess32and the recesses33, as illustrated inFIG. 15.

As described above, according to the third etching method, the etching amounts of the SiOxfilms34are made to be equal to each other between the recesses32and33having different opening widths using the difference in the adsorption amount of the TMA gas41between the recesses32and33when the supply of the TMA gas is stopped. The amount of TMA gas41adsorbed on the SiOxfilms34of the recesses32and33when the supply of TMA gas41is stopped may be controlled by appropriately setting various processing conditions, such as the flow rate of TMA gas41and the temperature of the wafer W. However, although this third etching method has been described assuming that the etching amounts of the SiOxfilms34are made to be equal to each other between the recesses32and33, various processing conditions may be set such that a desired difference occurs in the etching amounts.

Meanwhile, in the second and third etching methods, it has been described that, before time t12at which the supply of HF gas alone is started, a difference is caused in the adsorption amount of the TMA gas41between the recess32and the recesses33by supplying the TMA gas41and the HF gas42at the same time. However, even if the TMA gas41and the HF gas42are sequentially supplied as in the first etching method, a relatively large amount of the TMA gas41is adsorbed in the recesses33depending on the processing conditions, such as the flow rate of the TMA gas41, and thus a difference is caused between the recesses32and33. That is, in the second etching method and the third etching method described above, the TMA gas41and the HF gas42may be sequentially supplied before time t12. Therefore, the present disclosure is not limited to supplying these gases at the same time. However, supplying these gases at the same time is desirable because it is possible to shorten the etching time.

Exemplary processing conditions for performing the first to third etching methods described above will be presented. The pressure in the processing container11is 0.13332 Pa to 13332 Pa. The flow rate of the HF gas supplied into the processing container11is 0.1 sccm to 2000 sccm, the flow rate of the TMA gas supplied into the processing container11is 0.1 sccm to 1000 sccm, and the flow rate of the N2gas supplied into the processing container11is 0.1 sccm to 2000 sccm. The temperature of the wafer W is −50 degrees C. to 200 degrees C. By processing the wafer W at such a temperature, it is possible to perform the adsorption of the gas of an organic amine compound such as TMA and the etching of SiOx(that is, sublimation of the reaction product). That is, the first to third etching methods described above are preferable because it is not necessary to change the temperature of the wafer W during the processes described in the first to third etching methods.

It has been described that the film for forming the recesses32and33in which the SiOxfilms34are embedded is composed of SiN. However, the film is not limited to being composed of SiN, and may be composed of other silicon-containing materials. The film may be composed of, for example, Si, silicon carbide (SiC), SiOC, SiCN, and SiOCN. Even in that case, it is possible to selectively etch the SiOxfilms34since the TMA gas is selectively adsorbed on the SiOxfilms34. In addition, as the oxygen-containing silicon film that is selectively etched with respect to the recesses32and33, in addition to the SiOxfilm, a SiOCN film to be described later, tetraethyl orthosilicate (TEOS) illustrated in the evaluation tests to be described, and the like may be used. Therefore, the oxygen-containing silicon film is not limited to the SiOxfilm. In addition, containing oxygen does not mean that the oxygen is contained as an impurity, but means that oxygen is contained as a main component constituting the film.

An example in which trimethylamine (TMA) gas is used as the organic amine compound gas has been illustrated, but the gas is not limited to the TMA gas, and a known organic amine compound gas may be used. Specifically, for example, gases of organic amine compounds, such as monomethylamine, dimethylamine, dimethylethylamine, diethylmethylamine, monoethylamine, diethylamine, triethylamine, mononormalpropylamine, dinormalpropylamine, monopropylamine, monoisopropylamine, diisopropylamine, monobutylamine, dibutylamine, mono(tert-butyl)amine, di(tert-butyl)amine, pyrrolidine, piperidine, piperazine, pyridine, and pyrazine, may be used.

In addition, as another specific example of the organic amine compound, compounds obtained by substituting some or all of the C—H bonds of the above-mentioned components with C—F bonds (e.g., trifluoromethylamine, 1,1,1-trifluorodimethylamine, perfluorodimethylamine, 2,2,2-trifluoroethylamine, perfluoroethylamine, bis(2,2,2-trifluoroethyl)amine, perfluorodiethylamine, and 3-fluoropyridine) may be used. These organic amine compounds are preferable in that they have a conjugated acid pKa of 3.2 or more of HF, are capable of forming a salt with HF, have a constant vapor pressure in a temperature range of 20 to 100 degrees C., and are not decomposed in this temperature range to be capable of being supplied as a gas.

In addition, as the etching gas, a halogen-containing gas may be used, and a gas of a compound, such as HCl, HBr, HI, or SF4, may be used, in addition to HF containing fluorine as halogen. Although it has been described inFIG. 2that the recesses in the SiN film in which SiOxis embedded are grooves, the recesses may be holes. That is, this technique is also applicable even when a plurality of holes having different opening diameters (=opening sizes) are provided in the SiN film and the SiOxfilm embedded in each hole is selectively etched.

It should be noted that the embodiments disclosed herein are exemplary in all respects and are not restrictive. The above-described embodiments may be omitted, replaced, modified, and/or combined in various forms without departing from the scope and spirit of the appended claims.

Next, evaluation tests conducted in connection with this technique will be described.

Evaluation Test 1

As Evaluation Test 1, the adsorption energy for each of a SiN film and a SiOxfilm for TMA in the range of −50 degrees C. to 200 degrees C. was measured by simulation. The lower the adsorption energy, the more stable the TMA molecules is, that is, the easier TMA molecules are to be adsorbed.

FIG. 16is a graph showing the results of Evaluation Test 1. In the graph, the horizontal axis represents temperature (unit: ° C.) and the vertical axis represents adsorption energy (unit: eV). As shown in this graph, when the adsorption energy for the SiOxfilm and the adsorption energy for the SiN film at the same temperature are compared, the adsorption energy for the SiOxfilm is lower.

As shown in the graph, the value of the adsorption energy of each of the SiN film and the SiOxfilm increases as the temperature rises, but the adsorption energy of the SiOxfilm had a value slightly higher than 0 eV even at 200 degrees C. That is, it can be seen that TMA has a high adsorption property to SiOxin the temperature range in Evaluation Test 1 (−50 degrees C. to 200 degrees C.). Therefore, from the results of Evaluation Test 1, it was confirmed that TMA is selectively adsorbed on the SiOxfilm among the SiN film and the SiOxfilm in the range of −50 degrees C. to 200 degrees C. It is considered that these results were obtained due to the formation of hydrogen bonds between the nitrogen atoms of the TMA and the hydrogen atoms (existing by bonding with the oxygen atoms) in the SiOxfilm, and occurrence of dipole interaction between polarized TMA and polarized SiOx. It is considered that organic amines other than TMA are also selectively adsorbed on the SiOxfilm for the same reason.

Evaluation Test 2

As Evaluation Test 2, an etching process was performed by supplying TMA gas and HF gas to each of the SiOxfilm and SiN film formed on a substrate. This etching process was performed on a plurality of substrates, and the combination of the pressure in the processing container11and the supply time of each gas was changed for each process. Then, the etching amount of each film was measured for the processed substrates, and the etching amount of the SiOxfilm/the etching amount of the SiN film was calculated as an etching selectivity.

The SiOxfilm was formed through a heating process of Si in an oxygen-containing atmosphere, and the SiN film was formed through ALD. The pressure in the processing container11was set to 2.1 Torr (280 Pa), 3 Torr (400 Pa), or 4 Torr (533.2 Pa), and the supply time for each gas was 5 sec, 10 sec, or 30 sec. Then, each etching process was performed by setting the temperature of each wafer W to 140 degrees C.

The results of Evaluation Test 2 are shown inFIG. 17. InFIG. 17, the bar graph represents etching amounts of SiOxfilms, and the line graph represents etching selectivities. In each etching process, the etching amounts of SiN films were extremely small (less than 1 nm), and thus are not shown in the graph. As is clear from the graphs, the etching amounts and the etching selectivities of the SiOxfilms were relatively large values regardless of the combination of the supply time of each gas and the pressure in the processing container11. In addition, it can be seen from the graphs that the higher the pressure in the processing container11, the etching amount of the SiOxfilm tends to increase, and therefore the etching selectivity also increases. Specifically, when the pressure in the processing container11was 4 Torr and the supply time of the gas was 30 sec, the etching amount of SiOxwas 205 nm, and the etching selectivity was316. That is, the largest value was obtained for each of the etching amount and the etching selectivity.

From the results of Evaluation Test 2, it can be seen that when etching a SiOxfilm using HF gas, it is possible to selectively etch SiOxfilm with respect to the SiN film by supplying TMA gas. In addition, from the results of Evaluation Test 2, it was confirmed that it is possible to etch SiOxat a temperature at which TMA gas is adsorbed. That is, it was confirmed that it is not necessary to switch the temperature of the wafer W between when TMA is adsorbed and when the reaction product produced through the reaction of TMA, HF gas and SiOxis sublimated.

Evaluation Test 3

As Evaluation Test 3, each of an SiOxfilm and a TEOS film formed on a substrate was etched by supplying TMA gas and HF gas according to the cycle ofFIG. 3described in the first etching method described above. The number of cycles was changed for each etching process. The SiOxfilm was formed through a heating process of Si in an oxygen atmosphere, similar to the SiOxfilm in Evaluation Test 2.

The graph ofFIG. 18shows the results of Evaluation Test 3, and the horizontal axis and the vertical axis of the graph represent the number of cycles and the etching amount (unit: nm), respectively. As shown in the graph, the number of cycles and the etching amount are approximately proportional to each other for each of the SiOxfilm and the TEOS film, and the etching amount in one cycle is about 5 nm for the SiOxfilm and about 6 nm for the TEOS film. As described above, the etching amount of each of the SiOxfilm and the TEOS film in one cycle was at an atomic layer level.

As described above, from the results of Evaluation Test 3, it was confirmed that it is possible to etch an oxygen-containing silicon film at the atomic layer level by performing the cycle described in the first etching method and it is possible to control the oxygen-containing silicon film so as to obtain a desired etching amount by repeatedly performing the cycle. Therefore, as described as the first etching method, it is considered that it is possible to set the etching amount of the oxygen-containing silicon film in each in-plane portion of a wafer W to a desired value and to make the etching amount highly uniform in the plane of the wafer W.

Evaluation Test 4

On a substrate including a SiN film in which a recess as a groove was formed and a SiOxfilm was embedded in the recess, the SiOxfilm was etched. Then, the vertical cross-sectional surface of the substrate after the etching process was imaged, and the depth of a groove formed through the etching (=the etching amount of the SiOxfilm) was measured. In addition, the width of the opening of the recess is 1 nm.

In Evaluation Test 4, the above etching was performed while changing the gas supply method for each substrate. For one substrate, HF gas and TMA gas were simultaneously supplied to the wafer W as in the period from time t11to time t12in the timing chart ofFIG. 11. However, the supply of HF gas alone was not performed after time t12in this timing chart. The test conducted by supplying each gas in this way will be referred to as Evaluation Test 4-1.

For the other substrates, the gases were supplied as illustrated in the timing chart ofFIG. 11. That is, after supplying HF gas and TMA gas at the same time, the supply of HF gas alone was performed. Etching was performed under the same processing conditions as in Evaluation Test 4-1, except that the supply of HF gas alone was performed. The test conducted by supplying each gas in this way will be referred to as Evaluation Test 4-2.

FIG. 19is a schematic view illustrating images obtained from the substrates in Evaluation Tests 4-1 and 4-2. The depths of grooves formed in Evaluation Test 4-1 and Evaluation Test 4-2 were 21 nm and 36 nm, respectively. That is, the depth of the groove in Evaluation Test 4-2 was larger. It is considered that, in Evaluation Test 4-1, etching was stopped because HF gas was not supplied to the SiOxfilm after the adsorption of TMA gas proceeded and TMA molecules were excessively deposited. Meanwhile, it is considered that, in Evaluation Test 4-2, etching proceeded more than that in Evaluation Test 4-1 because, after the supply of TMA gas was stopped, the desorption of the TMA gas from the wafer W proceeded and thus HF gas was supplied to the SiOxfilm as described in the second etching method. Therefore, according to Evaluation Test 4, it was confirmed that it is possible to increase the etching amount by supplying TMA gas and HF gas and then supplying HF gas alone.

Evaluation Test 5

As Evaluation Test 5-1, the cycle including steps S1to S4described inFIGS. 3 and 4was performed 5 times on a substrate having a SiOxfilm formed on the surface thereof. Therefore, in one cycle, HF gas was supplied after supplying TMA gas, and in repeating the cycle, during the supply of the TMA gas and the supply of HF gas, purge gas was supplied into the processing container that stores the substrate and the processing container was exhausted. The time of one cycle was 30 seconds, and the temperature of the substrate during processing was 40 degrees C. After such etching, water was supplied to the surface of the processed substrate, and thus the components contained in the substrate were eluted into the water. Then, the fluorine content in the water was measured using an ion chromatography method.

As Evaluation Test 5-2, a substrate having a SiOxfilm formed on the surface thereof was processed with TMA gas and HF gas, and the fluorine content in the water supplied to the surface of the processed substrate was measured using an ion chromatograph method, as in Evaluation Test 5-1. Evaluation Test 5-2 may be said to be different from Evaluation Test 5-1 in that TMA gas and HF gas were simultaneously supplied to the substrate for 4 seconds. In both Evaluation Tests 5-1 and 5-2, the etching process was performed in the state in which the substrate temperature was set to a temperature within the range described above.

In Evaluation Test 5-1, the fluorine content was 3.0×1014atoms/cm2, and in Evaluation Test 5-2, the fluorine content was 5.8×1014atoms/cm2. As described above, Evaluation Test 5-1 had a smaller value for the fluorine content. Therefore, from Evaluation Test 5, it can be seen that it is possible to suppress the amount of halogen remaining on the etched substrate to a low level by etching the oxygen-containing silicon film by supplying an halogen-containing etching gas subsequent to an organic amine compound gas. It is considered that the above test results were obtained by suppressing permeation of HF gas supplied later into the substrate by forming a protective film on a SiOxfilm since the organic amine compound has a relatively high adsorptivity to the SiOxfilm, as described above.

In Evaluation Test 5, TMA gas, that is, an organic amine compound gas in which amino groups are bonded to branched alkyl groups was used as the organic amine compound gas, but it is more preferable to use an organic amine gas in which amino groups are bonded to branchless linear alkyl groups. Concerning the reason for this, it is considered that the organic amine compound is adsorbed on the oxygen-containing silicon film since the amino groups in the organic amine compound are adsorbed on the oxygen-containing silicon film. Assuming that the organic amine compound is composed of branched alkyl groups, it may be considered that the side chains of the alkyl groups interfere with the film, which prevents the amino groups in the same molecules as the alkyl groups from coming into contact with the film. In addition, assuming that a large number of molecules of the organic amine compound are adsorbed on a film, the side chains of the molecules interfere with each other. It may be considered that the number of molecules of the organic amine compound adsorbed per unit area of the film is relatively small so that the interference does not occur, and the gaps between the molecules are relatively large.

However, when the organic amine compound having linear alkyl groups is used, there are no chains of alkyl groups. Therefore, inhibition of the adsorption of amino groups to the film by side chains and interference between side chains of molecules do not occur. Therefore, it is considered that, since the molecules of the organic amine compound are more reliably and densely adsorbed on the oxygen-containing silicon film, it is possible to more reliably obtain the effect as a protective film that suppresses the permeation of halogen into the substrate.

As described above, since the amino groups are adsorbed on the film, the linear alkyl groups extend toward the opposite side of the film when viewed from the amino groups. Therefore, the linear alkyl group becomes longer as the number of carbons increases, and when viewed as the protective film, the linear alkyl group is more preferable because the linear alkyl group is thick and thus the function thereof as the protective film is enhanced. From the foregoing, as the organic amine compound gas, it is preferable to use an organic amine compound having a linear alkyl group represented by CnH2n+1, wherein n, which indicates the number of carbon atoms in CnH2n+1+1, is an integer of 4 or more. Specifically, for example, it is preferable to use butylamine, hexylamine, octylamine, decylamine, or the like.

Even if the alkyl group has a branched structure, it is considered that the permeation of halogen can be sufficiently prevented if the n (=the number of carbons) is relatively large. In addition to octylamine and decylamine having a linear alkyl group taken as specific examples, for example, decylamine having a branched alkyl group represented by the following Molecular Formula 1 is known to have a relatively high anti-corrosion property, i.e., high protective performance, with respect to a metal surface. Therefore, even when decylamine having a branched alkyl group is used as a protective film against the oxygen-containing silicon film, it is considered that the permeation can be sufficiently prevented. Therefore, for example, n is more preferably an integer of 10 or more. Each amine described above may be used in each etching method described in the embodiments. Therefore, while obtaining the effects described in each embodiment, it is possible to suppress a residual halogen, such as fluorine, in a processed wafer W so as to suppress the influence of the halogen on a post-etching process of the wafer W.

According to the present disclosure, when etching oxygen-containing silicon films embedded in a plurality of recesses having different opening widths in a substrate, it is possible to improve the controllability of the etching amount in each in-plane portion of the substrate.