Patent Application
20190221440
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2018-005792, filed on Jan. 17, 2018, the entire contents of which are incorporated herein by reference.
The present disclosure relates to a technique of etching a silicon-containing film using an iodine heptafluoride gas.
In a manufacturing process of a semiconductor device, a process of removing a silicon-containing film such as a polysilicon film or the like formed on a surface of the semiconductor wafer (hereinafter, referred to as a “wafer”) is often carried out. In some related arts, an iodine heptafluoride (IF7) gas having high etching selectivity to a polysilicon film is used when etching the polysilicon film. In some related arts, for the purpose of adjusting etching performance, a gas obtained by adding an oxidizing gas or an inert gas to the IF7 gas is used as an etching gas for etching a silicon layer.
When dry etching of a silicon-containing film is performed using an etching gas such as the IF7 gas or the like, it is difficult to perform the etching with high in-plane uniformity of the wafer. For example, there is a case where a process is performed so as to form a recess as a pattern by etching a silicon-containing film buried in the wafer surface. In such a case, when uniformity of etching is low, a phenomenon called “footing” in which a relatively large amount of silicon-containing film remains at a bottom portion near a sidewall of the recess may occur. That is to say, orthogonality between a side surface and a bottom surface of the recess becomes low in a longitudinal sectional view, and thus it is difficult to form a recess having a good shape with high orthogonality.
Therefore, a process of removing a lower portion of the silicon-containing film by wet etching after removing an upper portion of the silicon-containing film by anisotropic etching using plasma, for example, is often carried out. However, there is a concern that plasma etching as mentioned above may cause damage to a surface of a wafer, and it takes a long time to perform multiple processes including the plasma etching and the wet etching. Therefore, there is a demand to remove the silicon-containing film by dry etching without using plasma.
However, the techniques as described above cannot solve such a problem.
Some embodiments of the present disclosure provide a technique capable of etching a silicon-containing film with high in-plane uniformity of a substrate.
According to one embodiment of the present disclosure, there is provided an etching method including etching a silicon-containing film formed on a surface of a substrate by supplying an iodine heptafluoride gas and a basic gas to the substrate.
According to one embodiment of the present disclosure, there is provided an etching apparatus including: a process container; a mounting part installed in the process container and configured to mount a substrate having a silicon-containing film formed on a surface of the substrate; and a gas supply part configured to supply an iodine heptafluoride gas and a basic gas to the process container so as to etch the silicon-containing film.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the present disclosure, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the present disclosure.
Reference will now be made in detail to various embodiments, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. However, it will be apparent to one of ordinary skill in the art that the present disclosure may be practiced without these specific details. In other instances, well-known methods, procedures, systems, and components have not been described with reference to detail so as not to unnecessarily obscure aspects of the various embodiments.
Before describing a process of the present disclosure, a process according to a comparative example will be described with reference to
Since etching selectivity of the IF7 gas to the silicon-containing film is relatively high, an etching rate is relatively high. Thus, the polysilicon film 13 is rapidly etched downward (
Next, an outline of a process according to an embodiment of the present disclosure and a reaction presumed to occur during the process will be described with reference to
3IF7+aNH3=3IF5+bHF+cNH4F+N2 Formula (1)
(where a=2 to 5, b=8-a (=0 to 6), and c=a-2 (=0 to 3))
Then, the NH4F adhered to the surface of the wafer W reacts with the impurities 14 and the impurities 14 are etched. Furthermore, since the IF7 gas is supplied in a state where the NH4F is adhered to the wafer W, the etching rate of the polysilicon film 13 is suppressed from becoming excessively high. Therefore, the etching process is performed so that the impurities 14 exposed to the surface of the wafer W are removed by etching and the polysilicon film 13 in a region where the impurities 14 do not exist is prevented from being rapidly etched (
Subsequently, a substrate processing apparatus 2 including an etching module 4 for performing an etching process using the IF7 gas and the NH3 gas as an additive gas will be described with reference to the plan view of
The loading/unloading part 21 includes a normal pressure transfer chamber 23 kept under a normal pressure atmosphere and a carrier loading stage 25 installed at a side portion of the normal pressure transfer chamber 23. A first substrate transfer mechanism 22 is installed in the normal pressure transfer chamber 23. Carriers 24 accommodating wafers W are loaded on the carrier loading stage 25. In
A second substrate transfer mechanism 32 having, for example, an articulated arm structure, is installed in each of the load lock chambers 31. The second substrate transfer mechanism 32 transfers the wafer W among the load lock chambers 31, the heat treatment modules 30, and the etching modules 4. The interior of process containers constituting the heat treatment modules 30 and the etching modules 4 is kept under a vacuum atmosphere. The interior of the load lock chambers 31 is switched between the normal pressure atmosphere and the vacuum atmosphere so that the wafer W can be transferred between the process containers kept under the vacuum atmosphere and the normal pressure transfer chamber 23.
In
Subsequently, the etching module 4 will be described with reference to
The gas shower head 5, which is a gas supply part, is configured as a horizontal plate-like body. Flat diffusion spaces 51 and 52 are respectively formed in an upper portion and a lower portion of the gas shower head 5. These diffusion spaces 51 and 52 are partitioned from each other. A plurality of respective gas discharge holes 54 and 55 which are partitioned from each other are opened to a lower surface of the gas shower head 5. The gas discharge holes 54 are in communication with the diffusion space 51 and the gas discharge holes 55 are in communication with the diffusion space 52.
A downstream end of a gas flow path 56 is connected to an upper portion of the diffusion space 51. An upstream side of the gas flow path 56 is branched to form gas flow paths 57 and 58. Upstream sides of the gas flow paths 57 and 58 are respectively connected to an IF7 gas supply source 61 and an argon (Ar) gas supply source 62. A downstream end of a gas flow path 63 partitioned with respect to the gas flow path 56 is connected to an upper portion of the diffusion space 52. An upstream side of the gas flow path 63 is branched to form gas flow paths 64 and 65. Upstream sides of the gas flow paths 64 and 65 are respectively connected to an NH3 gas supply source 66 and an Ar gas supply source 67. Flow rate adjustment parts 68 configured by valves and mass flow controllers are respectively interposed in the gas flow paths 57, 58, 64, and 65. The flow rate adjustment parts 68 perform supply and stop of gases with respect to downstream sides of the flow paths 57, 58, 64, and 65 and adjustment of flow rates of the gases to the downstream sides of the flow paths 57, 58, 64, and 65. The Ar gas is a dilution gas for diluting the IF7 gas and the NH3 gas in the process container 41. By configuring the etching module 4 as described above, the IF7 gas and the NH3 gas supplied from the gas supply sources 61 and 66 are not mixed with each other until the IF7 gas and the NH3 gas are discharged from the gas shower head 5. The IF7 gas and the NH3 gas are mixed with each other in the process container 41 after being discharged from the gas shower head 5.
As illustrated in
Processing of the wafer W in the substrate processing apparatus 2 will be described. Here, processing the wafer W illustrated in
The carrier 24 storing the wafer W described with reference to
Subsequently, the IF7 gas, the NH3 gas, and the Ar gas are supplied from the gas shower head 5 to the process container 41. As described with reference to
Even if the polysilicon film 13 contains the impurities 14 made of silicon oxide described with reference to
Thereafter, after a lapse of a predetermined period of time from starting the supply of the IF7 gas, the NH3 gas, and the Ar gas, the supply of these respective gases from the gas shower head 5 is stopped, and the etching process is completed.
According to the substrate processing apparatus 2 including the etching module 4, it is possible to etch the polysilicon film 13 with high in-plane uniformity of the wafer W, and to suppress the surface of the polysilicon film 13 remaining after the etching process from being roughened. In addition, according to the aforementioned process, since it is not necessary to use plasma, each film on the surface of the wafer W is not damaged by plasma. Thus, there is also an advantage that reliability of a semiconductor device formed from the wafer W can be improved. However, cases where the etching process is performed using plasma are also included in the scope of the present disclosure. Although the substrate processing apparatus 2 has been described above with reference to an example of processing the wafer W illustrated in
In each process example as described above, only the upper portion of the polysilicon film 13 is etched. However, the entirety of the polysilicon film 13 formed on the surface of the wafer W may be etched. In that case, since uniformity in etching rate of the polysilicon film 13 in the plane of the wafer W is high, it is possible to reduce the time required for etching. More specifically, when variation in etching rate in the plane of the wafer W is large, there is a possibility that, even though one region in the plane of the wafer W has been completely etched, another region having a low etching rate has not yet been completely etched. Therefore, in order to etch all regions in the plane of the polysilicon film 13, an etching time period is set such that the etching process continues to be performed even after one region has been etched. That is to say, the etching time is set such that the one region is subjected to overetching. However, when the uniformity in etching rate is high, a time period of overetching can be shortened or eliminated. Thus, it is possible to reduce the time required for etching as described above.
In the process example of etching the polysilicon film 13, the IF7 gas and the NH3 gas are simultaneously supplied to the process container 41. That is to say, a period for supplying the IF7 gas and a period for supplying the NH3 gas overlap so as to coincide with each other. However, the IF7 gas and the NH3 gas may not be supplied as such. First, only the NH3 gas among the IF7 gas and the NH3 gas is supplied to the process container 41 and adsorbed to the wafer W. After the supply of the NH3 gas is stopped, only the IF7 gas among the IF7 gas and the NH3 gas is supplied to the wafer W and reacted with the NH3 gas adsorbed to the wafer W to generate NH4F. Thus, the impurities 14 are removed, and the polysilicon film 13 is etched by the IF7 gas. That is to say, the process may be performed by sequentially supplying the NH3 gas and the IF7 gas in this order. This sequential gas supply may be repeatedly performed. That is to say, after sequentially supplying the NH3 gas and the IF7 gas, the NH3 gas and the IF7 gas may be sequentially supplied again in this order. In this manner, the NH3 gas is not necessarily supplied to the wafer W as an additive gas to the IF7 gas. In addition, for example, after the simultaneous supply of the IF7 gas and the NH3 gas to the wafer W starts, the supply of the NH3 gas may be first stopped before the supply of the IF7 gas is stopped. That is to say, the overlapping of the period of supplying the IF7 gas and the period of supplying the NH3 gas is not limited to the case where these periods coincide with each other.
The silicon-containing film is a film containing silicon as a main component, and is not limited to the polysilicon film. Specifically, the silicon-containing film may include, for example, an amorphous silicon film, a single crystal silicon film, a SiGe film, a SiC film, and the like. It is considered that a basic gas may be supplied to the wafer W in addition to the IF7 gas, as long as the basic gas reacts with the IF7 gas and generates a compound containing nitrogen and fluorine like the NH4F and having an etching action on oxide. Thus, a basic gas other than the NH3 gas may be used. Specifically, the basic gas may include hydrazine (N2H4) and (CH3) methylamine (NH2), butylamine, dimethylamine, and the like, which are amine.
In the etching module 4 described above, it may be configured such that the IF7 gas and the NH3 gas are supplied to, for example, a common diffusion space in the gas shower head 5. Specifically, the gas shower head 5 may be configured such that the IF7 gas and the NH3 gas are mixed in the gas shower head 5 and this mixed gas is discharged to the wafer W. In the etching module 4 described above, for example, it may be configured such that a gas supply part having gas discharge holes concentrically opened along a circumference of the wafer W in a plan view is installed, instead of the gas shower head 5, to supply a gas to the wafer W. That is to say, the gas supply part is not limited to the gas shower head. The present disclosure is not limited to the examples described above and examples to be described with reference to evaluation tests below, and the respective examples may be appropriately changed or combined with each other.
Evaluation tests conducted according to the present disclosure will be described.
In evaluation test 1, the polysilicon film 13 was etched by simultaneously supplying an IF7 gas, an NH3 gas, and an Ar gas to the wafer W having the structure described with reference to
Furthermore, comparative tests 1-1 and 1-2, in each of which the polysilicon film 13 on the wafer W having the structure described with reference to
In evaluation test 1, flatness in the surface of the polysilicon film 13 after the etching process forming the bottom of the recess 18 was high and thus no footing was observed. Therefore, it was confirmed that the etching process was performed with high uniformity in each portion in the plane of the wafer W. The depth of the recess 18, i.e., the etching amount, was 50 nm.
In evaluation test 1, the flow rate ratio of the NH3 gas to the IF7 gas (=the NH3 gas flow rate/IF7 gas flow rate) was 0.6. The temperature of the wafer W was set to be 20 to 100 degrees C. and the internal pressure of the process container 41 was set to be 6.66 to 199.9 Pa (50 to 1,500 mTorr). Therefore, it was confirmed that, by setting the flow rate ratio, the temperature of the wafer W, and the internal pressure of the process container 41 as described above, it is possible to perform the etching process with high uniformity in the plane of the wafer W, and to obtain the high etching rate as described above. In addition, the present inventors also conducted the same test as in evaluation test 1 by setting the internal pressure of the process container 41 to be a value other than 26.6 Pa. It was confirmed that a good shape of the recess 18, similarly to the result of evaluation test 1, can be obtained when the internal pressure of the process container 41 was set to be within a range of 13.3 Pa (100 mTorr) to 133.3 Pa (1,000 mTorr). Therefore, it is desirable to set the internal pressure of the process container 41 to be 13.3 Pa to 133.3 Pa.
In evaluation test 2-1, an amorphous silicon film having a film thickness of 200 nm was formed on the surface of the wafer W, and then was etched by simultaneously supplying an IF7 gas and an NH3 gas for eight seconds using an etching apparatus configured substantially similarly to the etching module 4 described with reference to
In evaluation test 2-2, a test similar to evaluation test 2-1 was conducted except that a polysilicon film, instead of the amorphous silicon film, was formed on the surface of the wafer W and then was etched. Then, the etching amount of the polysilicon film (200 nm—the thickness of the remaining polysilicon film) and surface roughness of the polysilicon film were measured. The roughness of the polysilicon film prior to the etching process is 7.46 nm.
Graphs of
The graphs of
For the etching amount, a value within a range of approximately 4 to 54 nm was obtained in evaluation test 2-1, and a value within a range of approximately 4 to 44 nm was obtained in evaluation test 2-2. For the roughness, a value within a range of approximately 2.5 to 5.5 nm was obtained in the evaluation test 2-1, and a value within the range of approximately 4.0 to 8.0 nm was obtained in the evaluation test 2-2. Therefore, in evaluation tests 2-1 and 2-2, the values of the surface roughness in the amorphous silicon film and the polysilicon film remaining after the etching process do not significantly increase compared with the roughness values prior to the etching process. Thus, it was confirmed from the result of this evaluation test 2 that, by supplying the IF7 gas and the NH3 gas under the temperature of the wafer W set to be 35 to 120 degrees C., the effect of the present disclosure, i.e., the etching process with high in-plane uniformity of the wafer W, is obtained. Further, when the temperature of the wafer W was 35 degrees C., the roughness value was 4.2 nm or less in evaluation test 2-1 and 7.2 nm or less in evaluation test 2-2. That is to say, the surface roughness was relatively suppressed from being increased from the roughness value prior to the etching process. It is considered that the roughness value does not significantly vary even if the temperature of the wafer W is slightly lower than 35 degrees C. Thus, it is estimated that when the temperature of the wafer W is, for example, 30 to 120 degrees C., the effect of increasing the etching uniformity as described above is obtained.
As illustrated in
As illustrated in
In evaluation test 2-1, comparing the case where the temperature of the wafer W was 80 degrees C. and the case where the temperature of the wafer W was 100 degrees C., when the flow rate ratio of the NH3 gas/IF7 gas was the same, the etching amount was larger in the case where the temperature of the wafer W was 80 degrees C. In addition, when the flow rate ratio of the NH3 gas/IF7 gas was 0.2 and 0.4, the roughness value was smaller in the case where the temperature of the wafer W was 80 degrees C. In evaluation test 2-2, comparing the case where the temperature of the wafer W was 80 degrees C. and the case where the temperature of the wafer W was 100 degrees C., when the flow rate ratio of the NH3 gas/IF7 gas was the same, the etching amount was larger and the roughness value was smaller in the case where the temperature of the wafer W was 80 degrees C. Among the temperatures of the wafer W set in evaluation test 2 as described above, 80 degrees C. was the most preferable value from the viewpoint of increasing the etching rate and suppressing the increase in roughness after etching. In the above, it has been described that, according to the processing conditions, differences in etching mount and roughness occurred between the wafer W having the temperature of 80 degrees C. and the wafer W having the temperature of 100 degrees C. However, as described above,
The internal pressure of the process container 41 during the etching process was set as described above. Thus, the NH4F was sublimated from the wafer W when the temperature of the wafer W was 80 degrees C. or higher. It is considered that the reason why the etching amount was relatively large when the temperature of the wafer W was 80 degrees C. or higher in evaluation tests 2-1 and 2-2 is that, even if the NH4F is adhered, the NH4F is sublimated and the etching action of the IF7 gas is not largely hindered by the NH4F. The probability that the NH3 gas and NH4F adsorb to the wafer W increases as the temperature of the wafer W decreases. Therefore, when the temperature of the wafer W is too high during the etching process, the action of the NH4F becomes weak. For such a reason, it is presumed that the case where the temperature of the wafer W was 100 degrees C. shows a preferable result than the case where the temperature of the wafer W was 120 degrees C., and the case where the temperature of the wafer W was 80 degrees C. shows a more preferable result. Even at temperatures slightly varying from 80 degrees C., it is considered that the etching rate is high and the roughness is low. Considering that it is possible to sublimate the NH4F when the temperature of the wafer W is 80 degrees C. or higher as described above, it is considered that a particularly preferable temperature range of the wafer W is 80 degrees C. or higher and lower than 100 degrees C., specifically, 80 to 90 degrees C.
According to the result when the temperature of the wafer W was 35 degrees C. or 60 degrees C. in evaluation test 2-1, the etching amount was relatively small when the flow rate of the NH3 gas was larger than the flow rate of the IF7 gas, namely when the flow rate ratio of the NH3 gas/IF7 gas was 1.2 and 1.8. However, when the flow rate of the NH3 gas was smaller than the flow rate of the IF7 gas, namely when the flow rate ratio of the NH3 gas/IF7 gas is 0.2 to 0.6, the etching amount was relatively large, except for the case where the temperature of the wafer W was 35 degrees C. and the flow rate ratio of the NH3 gas/IF7 gas was 0.6.
In evaluation test 2-2, according to the result when the temperature of the wafer W was 35 degrees C. or 60 degrees C., when the flow rate ratio of the NH3 gas/IF7 gas was 1.2 and 1.8, the etching amount was relatively small. When the flow rate ratio of NH3 gas/IF7 gas was 0.2 to 0.6, the etching amount was a relatively large, except for the case where the temperature of the wafer W was 35 degrees C. and the flow rate ratio of NH3 gas/IF7 gas was 0.6.
It is considered that the reason for these results is that the temperature at which the NH4F is sublimated from the wafer W is 80 degrees C. or higher as described above, and in the case of 35 degrees C. and 60 degrees C. at which the sublimation does not occur, an excessive amount of NH4F is adhered to the wafer W when the flow rate of the NH3 gas is relatively large, so that the etching amount by the IF7 gas is reduced. Therefore, from the result of evaluation test 2, it was confirmed that when the temperature of the wafer W is lower than 80 degrees C., it is desirable to set the flow rate ratio of NH3 gas/IF7 gas to be 0.6 or less.
In evaluation tests 2-1 and 2-2, when the temperature of the wafer W was set to be 80 degrees C. or higher, the roughness value did not significantly vary depending on the flow rate ratio of the NH3 gas/IF7 gas. However, the etching amount was larger when the flow rate ratio of NH3 gas/IF7 gas was set to 1.2 or 1.8 than when the flow rate ratio of NH3 gas/IF7 gas was set to 0.6. Therefore, it was confirmed that in the case where the temperature of the wafer W is 80 degrees C. or higher, when the flow rate ratio of the NH3 gas/IF7 gas is 1.2 to 1.8, it is possible to obtain a high etching rate and to significantly suppress roughness after the etching process from being increased. That is to say, it was confirmed that it is desirable to set the flow rate of the NH3 gas/the flow rate of the IF7 gas to be within a range of 1.2 to 1.8.
It is considered that when the temperature of the wafer W is 80 degrees C. or higher, the etching action does not vary greatly even if the flow rate ratio of the NH3 gas/IF7 gas is slightly smaller than 1.2. It is also considered that when the temperature of the wafer W is lower than 80 degrees C., the etching action does not vary greatly even if the flow rate ratio of the NH3 gas/IF7 gas is slightly larger than 0.6. Specifically, it is considered that the variation of the etching action is small, when the flow rate ratio of the NH3 gas/IF7 gas is, for example, 1 or more in the case where the temperature of the wafer W is 80 degrees C. or higher, and when the flow rate ratio of the NH3 gas/IF7 gas is, for example, 1 or less in the case where the temperature of the wafer W is lower than 80 degrees C. Therefore, it is estimated that when the temperature of the wafer W is 80 degrees C. or higher, the flow rate ratio of the NH3 gas/IF7 gas is preferably 1 to 1.8, and when the temperature of the wafer W is lower than 80 degrees C., the flow rate of the NH3 gas/IF7 gas is preferably 1 or less.
According to the present disclosure in some embodiments, it is possible to etch a silicon-containing film with high in-plane uniformity of a substrate by supplying an iodine heptafluoride gas and a basic gas to the substrate having a silicon-containing film formed on a surface of the substrate.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosures. Indeed, the embodiments described herein may be embodied in a variety of other forms. Furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the disclosures. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosures.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-005792 | Jan 2018 | JP | national |
