Etching method and etching apparatus

Abstract

The silicon germanium film is etched to achieve good etching control. [Solution] The etching method of the present disclosure includes an etching step of supplying a first etching gas containing fluorine atoms and a second etching gas which is a compound of germanium and fluorine to a substrate and etching a silicon germanium film provided on the substrate.

Description

Technical Field

[0004] , , , , , , , , ,

[0005]

[0001] The present disclosure relates to an etching method and an etching apparatus.

Background Art

[0002] When manufacturing a semiconductor device, it may be necessary to selectively etch one of a Si film and a SiGe film formed on the surface of a semiconductor wafer (hereinafter referred to as a wafer) which is a substrate. In Patent Document 1, when selectively etching a SiGe film in a structure in which Si films and SiGe films are alternately and repeatedly stacked, in addition to ClF3 gas which is an etching gas, by supplying HF gas, it is shown that the Si film is hydrogen-terminated to suppress etching. In Patent Document 2, when selectively etching a Si film in the above-described structure, it is described that GeF4 gas is used as an etching gas.

Prior Art Documents

Patent Documents

[0003] <a

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present disclosure provides a technique for etching a silicon germanium film so as to obtain good etching controllability.

Means for Solving the Problems

[0005] The etching method of the present disclosure includes an etching step of supplying a first etching gas containing fluorine atoms and a second etching gas which is a compound of germanium and fluorine to a substrate and etching a silicon germanium film provided on the substrate. ;

Effects of the Invention

[0006] This disclosure enables etching of a silicon germanium film in a manner that provides good etching controllability. [Brief explanation of the drawing]

[0007] [Figure 1] This is a longitudinal cross-sectional side view of a wafer etched by an etching method according to one embodiment of the present disclosure. [Figure 2] This is a longitudinal cross-sectional side view of a wafer etched using the comparative example process. [Figure 3] This is a longitudinal cross-sectional side view of a wafer etched using the comparative example process. [Figure 4] This is a longitudinal cross-sectional side view of a wafer etched using the comparative example process. [Figure 5] This is a longitudinal cross-sectional side view of a wafer etched using the comparative example process. [Figure 6] This is a longitudinal cross-sectional side view of a wafer in the process of etching according to the embodiment. [Figure 7] This is a longitudinal cross-sectional side view of a wafer in the process of etching according to the embodiment. [Figure 8] This is a longitudinal cross-sectional side view of the wafer after etching by the process of the embodiment. [Figure 9] This is a chart showing the timing of gas supply in the process of the above embodiment. [Figure 10] This is a longitudinal cross-sectional side view of the etching apparatus. [Figure 11] This chart shows the timing of other gas supply examples. [Figure 12] This chart shows the timing of other gas supply examples. [Figure 13] This is a graph showing the results of the evaluation test. [Modes for carrying out the invention]

[0008] An embodiment of the substrate processing method of this disclosure will be described. Figure 1 is a longitudinal cross-sectional side view of the surface of a wafer W, which is a substrate, showing the state before the etching treatment according to this embodiment. A lower layer film 11 is formed on the wafer W. On the lower layer film 11, a SiGe (silicon germanium) film 12 and a Si (silicon) film 13 are alternately and repeatedly stacked. By forming such a repeating structure, each of the SiGe film 12 and Si film 13 is formed in multiple layers in the thickness direction of the wafer W. Hereafter, this thickness direction of the wafer W will be described as the longitudinal direction. The Si film 13 is formed, for example, by epitaxial growth. In the example shown in Figure 1, the thickness of the SiGe film 12 is greater than that of the Si film 13, but conversely, the Si film 13 may be larger than the SiGe film 12. The germanium content in the SiGe film 12 is, for example, 20 atomic percent or less.

[0009] A mask film 14 is stacked on top of the uppermost Si film 13 in the repeating structure described above. The mask film 14 is made of, for example, a silicon nitride film or a silicon oxide film, and prevents etching of the Si film 13 from above. A recess 15 extending in the vertical direction is formed so as to open into the mask film 14, and the lower end of the recess 15 reaches the lower layer film 11. Therefore, the bottom surface of the recess 15 is formed by the lower layer film 11. In the following description, the recess 15 may be referred to as a vertical recess 15 to distinguish it from the horizontal recess 16 described later. With the formation of the vertical recess 15 in this way, the SiGe film 12 and the Si film 13 are exposed on the surface of the wafer W.

[0010] In this embodiment, etching gas is supplied to the wafer W and introduced into the vertical recesses 15, with the objective of selectively etching the SiGe film 12 from the side, compared to the Si film 13. That is, the SiGe film 12 is etched in a direction intersecting the thickness direction of the wafer W. Plasma is not formed during etching. This etching is performed so that a portion of the SiGe film 12 remains. In other words, etching is performed so that recesses 16 (not shown in Figure 1) are formed laterally. When etching the SiGe film 12 in this way, it is required to etch the SiGe film 12 in each stage with high uniformity and to make the depth L of the lateral recesses 16 the same in each stage.

[0011] Before describing the etching process of this embodiment in detail, a comparative example will be discussed. Generally, gases containing fluorine atoms, such as ClF3 (chlorine trifluoride) gas and F2 (fluorine) gas, are known as etching gases for SiGe films. Let's assume that ClF3 gas is used as the etching gas when etching the SiGe film 12 on the wafer W shown in Figure 1. In that case, tests conducted by the applicant on a substrate having the same configuration as the wafer W shown in Figure 1 have confirmed that the SiGe film 12 in each layer is etched, as shown in Figure 2. As shown in the figure, there is relatively large variation in the amount of etching of the SiGe film 12 in each layer. More specifically, the depth L is large for the recesses 16 located on the upper side, and the depth L decreases as you move towards the lower layers. Although not shown in the figure, when ClF3 gas is used, the amount of etching of the Si film 13 is relatively large. That is, the etching selectivity for the SiGe film 12 is low.

[0012] The reason why the depth of the upper recess 16 is larger is thought to be that the ClF3 gas is highly reactive, resulting in a short incubation time, and that because it reacts with the SiGe film 12 and Si film 13 on the upper side of the vertical recess 15, it is more difficult to supply ClF3 gas to the lower side of the vertical recess 15 compared to the upper side. The incubation time is the time required from the start of supplying etching gas to the etching target until etching begins.

[0013] On the other hand, when etching the SiGe film 12 of the wafer W in FIG. 1, assume that F2 gas is used instead of ClF3 gas as the etching gas. Note that GeF4 gas described later is not supplied. When only F2 gas is used as the etching gas in this way, it has been confirmed that etching of the Si film 13 is suppressed and the etching selectivity for the SiGe film 12 is high.

[0014] However, when using F2 gas, since the reactivity with respect to the SiGe film 12 is low, the etching time becomes long in order to obtain a relatively large etching amount. Also, when using F2 gas, as shown in FIG. 3, it has been confirmed that the variation in the etching amount in each stage of the SiGe film 12 is relatively large. Regarding this variation in detail, the recess 16 located on the lower side of the vertical recess 15 has a large depth L, and etching is performed such that the depth L of the recess 16 decreases as it goes toward the upper part of the vertical recess 15.

[0015] Also, as shown in the evaluation test described later, when using F2 gas, it has been confirmed that the process stability is low. Specifically, the low process stability means that when processing a plurality of substrates in sequence under the same processing conditions, there is a large variation in the depth L of the recess 16 between substrates, and when the processing conditions other than the etching time (supply time of the etching gas) are the same as shown in FIGS. 4 and 5, the depth L does not increase according to the length of the etching time.

[0016] The reason why the depth L of the lower recess 16 increases and the stability of the process is low when using F2 gas is presumed to be due to the relatively low reactivity of F2 gas with the SiGe film 12, the relatively long incubation time, and the influence of the reaction products produced by the reaction between F2 gas and the SiGe film 12. These reaction products include SiF4, GeF4, and GeF2, of which at least GeF4 (germanium tetrafluoride) has relatively high etching properties against the SiGe film 12 in the presence of F2 gas. Therefore, etching of the SiGe film 12 is suppressed when the concentration of GeF4 produced in the film is low, and the etching rate (amount of etching per unit time) of the SiGe film 12 increases as the concentration of GeF4 increases. This reaction product, GeF4, is in a gaseous state at the temperature at which etching of the SiGe film 12 by F2 gas occurs.

[0017] Unlike ClF3 gas, F2 gas is supplied sufficiently to both the upper and lower sides of the vertical recess 15 due to its low reactivity with the SiGe film 12. Furthermore, in the lower side of the vertical recess 15, GeF4 gas generated during etching is less likely to be released outside the recess 15 and tends to accumulate compared to the upper side. Therefore, the concentration of GeF4 in the environment in contact with the SiGe film 12 tends to be higher in the lower side of the vertical recess 15 compared to the upper side, causing etching of the SiGe film 12 to start and proceed rapidly from the moment F2 gas is supplied. In other words, it is presumed that the shorter incubation time in the lower side of the vertical recess 15 compared to the upper side resulted in a difference in the amount of etching (= depth L) between the recesses 16. In addition, because the incubation time is relatively long when using F2 gas, the timing of GeF4 generation between substrates is relatively large, which is thought to have resulted in the low stability of the above-mentioned process.

[0018] Therefore, when etching the SiGe film 12, it is required to obtain good etching controllability. Obtaining this good etching controllability includes some or all of the following: suppressing variations in the etching amount of each recess 16, obtaining a relatively large etching amount in a relatively short time, and increasing the stability of the process.

[0019] In this embodiment, two etching gases are supplied to the wafer W: a first etching gas, F2 gas, and a second etching gas, GeF4 gas, which is a compound of germanium and fluorine. This exposes each SiGe film 12 to an environment with a relatively high concentration of GeF4, allowing etching to start quickly (i.e., shortening the incubation time), and then proceeding with a high etching rate. By performing etching in this manner, variations in the etching amount of each recess 16 formed after processing are suppressed, a relatively large etching amount can be obtained in a relatively short time, and the stability of the process is enhanced.

[0020] The processing of this embodiment will be explained below using the longitudinal cross-sectional side views of the wafer W shown in Figures 6 to 8 and Figure 9, which is a time chart showing the supply state of each gas to the wafer W. In this embodiment, the wafer W is processed while it is stored in a processing container where a vacuum atmosphere of a predetermined pressure is formed. During processing, the wafer W is placed on a stage and adjusted to a predetermined temperature.

[0021] First, the supply of F2 gas 21 and GeF4 gas 22 to the wafer W shown in Figure 1 is started (time t1 in the chart). The F2 gas 21 and GeF4 gas 22 enter the vertical recess 15 and are supplied to the SiGe film 12 from the side. As the F2 gas and GeF4 gas are supplied in this manner, the reaction shown in Equation 1 below proceeds. Note that the stoichiometric ratios on the left and right sides of this reaction equation are not the same. As the reaction proceeds in this manner, from the perspective of the SiGe film 12, GeF4 is supplied not only as a reaction product generated by the etching gas, as in the comparative example where only F2 gas was supplied as the etching gas, but also as an etching gas itself. F2 gas + GeF4 + SiGe → SiF4 (gas) + GeF4 (gas) + GeF2 (solid) + GeFx ... Equation 1

[0022] As shown in Figure 6, the reaction of Equation 1 proceeds on the surface layer of each SiGe film 12 facing the vertical recess 15, initiating the transformation into a reaction product layer 17. Similar to the case where only F2 gas 21 is supplied as the etching gas as described in the comparative example, reaction products containing GeF4 accumulate on the lower side of the vertical recess 15, and the SiGe film 12 on the lower side is exposed to an environment with a relatively high concentration of GeF4. On the other hand, GeF4 gas 22 is supplied into the vertical recess 15, and the concentration of GeF4 gas 22 is particularly high on the upper side near the opening of the vertical recess 15. Therefore, each SiGe film 12 is exposed to an environment with a sufficiently high concentration of GeF4. As a result, the transformation into a reaction product layer 17 proceeds uniformly and rapidly among the SiGe films 12 in each stage. Furthermore, the generated reaction product layer 17 is removed by vaporization. In this way, etching of each SiGe film 12 is initiated with a relatively short incubation time and high uniformity.

[0023] As etching progresses, the depth L of each recess 16 increases. Due to the presence of the reaction products GeF4 and GeF4 gas, this etching proceeds at a high etching rate. At time t2, after a predetermined time has elapsed from time t1, the supply of GeF4 gas to the wafer W is stopped, and the supply of F2 gas only continues. Even when only F2 gas is supplied, as explained in the comparative example, GeF4 is generated from the F2 gas and the SiGe film 12. Therefore, while the uniformity of the depth L between the recesses 16 is maintained, etching of each SiGe film 12 continues due to the action of F2 gas and GeF4 (Figure 7). Subsequently, after a predetermined time has elapsed from time t2, and recesses 16 of the desired depth L have been formed, the supply of F2 gas to the wafer W is stopped (time t3), and the etching process is completed. Figure 8 shows the wafer W after this etching is completed.

[0024] As described above, in the etching process of this embodiment, GeF4 gas is supplied to the wafer W from the start of etching with F2 gas until partway through, thereby equalizing the concentration of GeF4 in the environment on the surface of each SiGe film 12 in the depth direction of the vertical recess 15. This ensures that each SiGe film 12 is etched with high uniformity and relatively large area in a short etching time. As will be shown in the evaluation tests later, it has been confirmed that the etching process of this embodiment also improves the stability of the process. Furthermore, it has been confirmed that etching of the Si film 13 can be suppressed by the method of this embodiment.

[0025] Next, we will describe etching apparatus 3, which is an example of an etching apparatus capable of performing the etching process of this embodiment described above. Figure 10 is a longitudinal cross-sectional side view of etching apparatus 3. In the figure, 31 is the processing container described above and constitutes etching apparatus 3. In the figure, 32 is a wafer W transport port opening in the side wall of processing container 31, which is opened and closed by a gate valve 33. A stage 41 on which wafers W are placed is provided inside processing container 31, and the stage 41 is provided with lifting pins (not shown). Wafers W are transferred between the substrate transport mechanism located outside processing container 31 and the stage 41 via these lifting pins.

[0026] A temperature control unit 42 is embedded in the stage 41, and the temperature of the wafer W placed on the stage 41 is controlled. This temperature control unit 42 is configured as a flow path that forms part of a circulation path through which a temperature-controlling fluid, such as water, flows, and the temperature of the wafer W is controlled by heat exchange with the fluid. However, the temperature control unit 42 is not limited to a flow path for such a fluid, and may be configured as, for example, a heater for resistance heating.

[0027] Furthermore, one end of an exhaust pipe 34 is open inside the processing container 31, and the other end of the exhaust pipe 34 is connected to an exhaust mechanism 36, which is composed of, for example, a vacuum pump, via a valve 35, which is a pressure changing mechanism. By adjusting the opening of the valve 35, the exhaust flow rate inside the processing container 31 is adjusted, and the pressure inside the processing container 31 is set to the desired vacuum pressure.

[0028] A showerhead 43 is provided on the upper side of the processing container 31, facing the stage 41. The downstream side of gas supply passages 51 to 54 is connected to the showerhead 43, and the upstream side of gas supply passages 51 to 54 is connected to gas supply sources 61 to 64 via flow rate adjustment units 50. Each flow rate adjustment unit 50 is equipped with a valve and a mass flow controller. The supply of each gas from gas supply sources 61 to 64 is controlled by opening and closing the valves included in the flow rate adjustment unit 50 to switch the supply to the downstream side. Therefore, each of the times t1 to t3 shown in the time chart is the timing when the opening and closing of the valves in gas supply passages 51 and 52 is switched. In addition, the flow rate supplied to the downstream side for each gas is adjusted by each flow rate adjustment unit 50. Each gas supplied to the gas passage provided in the showerhead 43 is discharged downward from a number of discharge ports provided on the lower surface of the showerhead 43.

[0029] F2 gas, GeF4 gas, N2 gas, and Ar gas are supplied from gas supply sources 61, 62, 63, and 64, respectively, and each of these gases is supplied into the processing container 31 via a showerhead 43. The supply of each of these gases can be controlled independently by each flow rate adjustment unit 50. The flow rate adjustment units 50 provided in the gas supply sources 61, 62 and the gas supply paths 51, 52 correspond to the gas supply mechanism that supplies etching gas into the processing container 31. N2 gas and Ar gas are supplied as carrier gases into the processing container 31 together with the etching gases, F2 gas and GeF4 gas. In addition, N2 gas and Ar gas are supplied after the supply of etching gas into the processing container 31 is stopped, and they also act as purge gases to purge any remaining processing gas from inside the processing container 31.

[0030] Furthermore, the etching apparatus 3 is equipped with a control unit 30, which is a computer. This control unit 30 includes a program, memory, and a CPU. The program incorporates instructions (each step) to perform the processing and transport of the wafer W as described above. This program is stored on a storage medium, such as a compact disk, hard disk, magneto-optical disk, or DVD, and installed in the control unit 30. The control unit 30 outputs control signals to each part of the etching apparatus 3 using this program, thereby controlling the operation of each part. Specifically, the operations of the etching apparatus 3 controlled in this manner include, for example, adjusting the temperature of the fluid supplied to the stage 41 (i.e., the processing temperature of the wafer W), cutting off the supply of each gas from the shower head 43, and adjusting the exhaust flow rate by the valve 35 (i.e., adjusting the pressure inside the processing container 31).

[0031] Using the etching apparatus 3 described above, etching gas is supplied into the processing container 31 as shown in the time chart in Figure 9, and the wafer W is processed as shown in Figures 6 to 8. There are no particular restrictions on the pressure inside the processing container 31 during the etching process, but for example, it is set to 1.33 Pa (10 mTorr) to 1333 Pa (10 Torr). The preferred partial pressures of F2 gas and GeF4 gas will be described later. The processing temperature of the wafer W (temperature of the wafer W during etching gas supply) should be a temperature at which each product constituting the reaction product layer 17 can be vaporized and removed, for example, -20°C to 150°C.

[0032] Incidentally, the time chart shown in Figure 11 shows a different processing example from the processing example shown in the time chart in Figure 9. In this processing example in Figure 11, the supply of GeF4 gas to wafer W is not stopped while the supply of F2 gas is being supplied to wafer W, but rather the supply of GeF4 gas to wafer W is stopped at the same time t3 when the supply of F2 gas is stopped. As shown in this example in Figure 11, the supply of GeF4 gas is not limited to being stopped in the middle of the supply of F2 gas. However, as mentioned above, even if the supply of GeF4 gas is stopped midway, etching can still proceed with the GeF4 generated from the SiGe film 12, so from the viewpoint of avoiding the supply of unnecessary gas, it is preferable to stop the supply of GeF4 gas in the middle of the supply of F2 gas (i.e., in the middle of etching).

[0033] Furthermore, as will be shown in the evaluation tests described later, the SiGe film 12 cannot be etched by supplying only GeF4 gas to the wafer W, rather than using F2 gas alone. Therefore, GeF4 gas is not used as an etching gas on its own, but is supplied together with F2 gas as an etching gas. In other words, these gases are supplied to the wafer W such that the period during which F2 gas is supplied to the wafer W and the period during which GeF4 gas is supplied to the wafer W overlap.

[0034] In order to ensure that the supply periods of the gases overlap, if the F2 gas is supplied to the wafer W before the GeF4 gas, the amount of GeF4 generated from each stage of the SiGe film 12 will differ from one another, as explained in the comparative example, resulting in different etching rates between each stage of the SiGe film 12. Therefore, as shown in Figures 9 and 11, it is preferable to start supplying the F2 gas and GeF4 gas to the wafer W simultaneously.

[0035] Furthermore, the etching apparatus 3 may be configured to supply HF (hydrogen fluoride) gas into the processing container 31 in addition to the etching gas and inert gas described above. Specifically, in addition to the apparatus configuration shown in Figure 10, the etching apparatus 3 is configured to include an HF gas supply source, a gas supply path connecting the HF gas supply source and the shower head 43, and a flow rate adjustment unit 50 interposed in the gas supply path. Then, as shown in the time chart of Figure 12, HF gas is also supplied to the wafer W at times t1 to t3 while F2 gas is being supplied. As described in Patent Document 1, it is preferable that the surface of the Si film 13 is hydrogen-terminated by the HF gas, protecting it from the etching gas, thereby more reliably suppressing the etching of the Si film 13. In the example shown in Figure 12, HF gas is always supplied to the wafer W from time t1 to time t3 when F2 gas is supplied, but it is not limited to supplying HF gas in this way, and HF gas may be supplied only for a part of the period within the time t1 to time t3 when F2 gas is supplied.

[0036] The wafer W to be etched is not limited to having the structure shown in Figure 1. For example, even when a SiGe film forms the upper surface of the wafer W and the SiGe film is etched from above, the etching method of this embodiment described above can be used. Furthermore, the etching method described above is not limited to wafers W on which both a Si film and a SiGe film are formed on the surface; the etching method of this embodiment may also be used when only a SiGe film is formed on the surface of the wafer W. Even when selective etching of the Si film is not performed in this way, this embodiment is preferable because it is possible to obtain a relatively large amount of etching of the SiGe film in a short etching time and to obtain high stability in the process.

[0037] Furthermore, ClF3 gas may be supplied as the etching gas instead of F2 gas. In other words, ClF3 gas and GeF4 gas may be supplied to wafer W as etching gases. However, as mentioned in the comparative example, ClF3 gas has high etching properties for Si films, so it is preferable to use F2 gas when selectively etching the SiGe film among the Si film and SiGe film.

[0038] Up to this point, wafers have been used as an example of substrates to be processed, but the substrates processed in the processing container 31 include, in addition to wafers, substrates for manufacturing flat panel displays, substrates for manufacturing exposure masks used in photolithography, and dummy substrates processed for the purpose of testing and setting processing parameters in the substrate processing apparatus. Furthermore, the embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The above embodiments may be omitted, replaced, modified, and combined in various ways without departing from the scope and spirit of the attached claims.

[0039] [Evaluation Test] The evaluation tests conducted in connection with this embodiment will be described. • Evaluation Test 1 As Evaluation Test 1, a substrate having a film structure similar to that of wafer W described in Figure 1 was placed on the stage 41 of the etching apparatus 3, and F2 gas, N2 gas, and Ar gas were supplied into the processing container 31 to etch the SiGe film 12. Therefore, in this Evaluation Test 1, GeF4 gas was not supplied to the substrate, and the process described as a comparative example was performed. The combination of etching time and substrate processing temperature was changed for each substrate, and each substrate was processed. After processing, an SEM image was acquired, and the depth L of the recess 16 (i.e., etching amount) was measured from the image, and the average value was calculated. The substrate processing temperature was set to 20°C or 40°C, and the pressure inside the processing container 31 during etching gas supply was set to a pressure within the range described in the embodiment. Some of the multiple substrates were processed under the same processing conditions.

[0040] Tables 1 and 2 below show the results of Evaluation Test 1. Table 1 shows the test results when the substrate processing temperature was 20°C, and Table 2 shows the test results when the substrate processing temperature was 40°C. In each table, the average value of the depth L is normalized by dividing it by a predetermined positive number. Unless otherwise specified, the depth L shown in the following explanation is the same as the depth L shown in the results of Evaluation Test 1, normalized from the average value. Furthermore, for each result of a substrate processed under the same processing conditions, the results of the first processing and the results of the second processing are shown in the table, respectively. In the substrate, multiple vertical recesses 15 are formed, and the SiGe film 12 is etched from both the left and right sides. For this reason, there is a limit to the depth L of the recesses 16, and if etching exceeds this limit, the left and right recesses 16 are connected. The description of a depth L of 42.5 or more in Tables 1 and 2 indicates that the limit of the depth L is 42.5, and etching was performed to exceed this limit, resulting in the left and right recesses 16 being connected to each other. Furthermore, when presenting the results of each evaluation test other than evaluation test 1, if the depth L exceeds the limit value, the word "greater than or equal to" will be added to indicate that limit value.

[0041] [Table 1]

[0042] [Table 2]

[0043] As is clear from Tables 1 and 2, when the processing temperature is the same between substrates, the depth L does not increase as the etching time increases, and the phenomenon shown in Figure 4 occurs. Furthermore, when the etching time is the same, the difference in depth L is relatively large. In addition, even when the etching time is set to a relatively long time, the depth L before normalization was generally small. Based on these results, it is desirable to obtain a relatively large etching amount with a short etching time, and to increase the stability of the process (suppressing the variation in the depth L of the recesses 16 between substrates and making the depth L increase in proportion to the length of the etching time).

[0044] • Evaluation Test 2 This section will explain Evaluation Test 2, focusing on the differences from Evaluation Test 1. In Evaluation Test 2, some of the multiple substrates were processed using F2 gas and GeF4 gas as etching gases, as described in the embodiment, while other parts were processed using only F2 gas as the etching gas, as in Evaluation Test 1. In Evaluation Tests 2-1 and 2-3, only F2 gas was used as the etching gas, while in Evaluation Tests 2-2 and 2-4, both F2 gas and GeF4 gas were used as the etching gases.

[0045] In evaluation tests 2-1 and 2-2, and in evaluation tests 2-3 and 2-4, the processing conditions are the same except for the flow rates of each gas supplied to the substrate. To describe the setting of these gas flow rates in detail, in evaluation tests 2-1 to 2-4, N2 gas and Ar gas are supplied into the processing container 31 along with the etching gas. The flow rates of each gas supplied into the processing container 31 are as follows. Evaluation Test 2-1: F2 gas = A 1 sccm, GeF4 gas = 0 sccm, Ar gas = C 1 sccm, N2 gas = D 1 sccm Evaluation Test 2-2: F2 gas = A 1 sccm, GeF4 gas = B 1 sccm, Ar gas = C 2 sccm, N2 gas = D 1 sccm Evaluation Test 2-3: F2 gas = A 1 sccm, GeF4 gas = 0 sccm, Ar gas = C 1 sccm, N2 gas = D 2 sccm Evaluation Test 2-4: F2 gas = A 1 sccm, GeF4 gas = B 1 sccm, Ar gas = C 2 sccm, N2 gas = D 2 sccm

[0046] Between evaluation tests 2-1 and 2-2, and between evaluation tests 2-3 and 2-4, the total flow rates of etching gas, N2 gas, and Ar gas supplied into the processing container 31 are set to be equal. That is, (A1+C1+D1) sccm in evaluation test 2-1 is equal to (A1+B1+C1+D1) sccm in evaluation test 2-2, and (A1+C1+D2) sccm in evaluation test 2-3 is equal to (A1+B1+C2+D2) sccm in evaluation test 2-2. Consequently, in evaluation tests 2-2 and 2-4, the flow rate of Ar gas supplied into the processing container 31 is set lower than in evaluation tests 2-1 and 2-3, respectively, by the amount of the GeF4 gas flow rate. Regarding the N2 gas flow rate, D1 sccm in evaluation tests 2-1 and 2-2 < D2 sccm in evaluation tests 2-3 and 2-4, indicating that the total gas flow rate is higher in evaluation tests 2-3 and 2-4 than in evaluation tests 2-1 and 2-2, and that the dilution rate of the etching gas by the inert gas is higher. In evaluation tests 2-2 and 2-4, the F2 gas flow rate is greater than the GeF4 gas flow rate, specifically, F2 gas flow rate A1 sccm / GeF4 gas flow rate B1 sccm = 2.

[0047] In this evaluation test 2 and the evaluation tests described later, when supplying F2 gas and GeF4 gas to the substrate, the supply of GeF4 gas was not stopped during the supply of F2 gas. As shown in Figure 11, the supply of GeF4 gas to the substrate was continued while F2 gas was being supplied to the substrate. Regarding processing conditions other than gas flow rate, in evaluation tests 2-1 to 2-4, the processing temperature of the substrate was set to 20°C. In evaluation tests 2-1 to 2-4, the pressure inside the processing container 31 was set to a value within the range described in the embodiment, with E1 Torr in evaluation tests 2-1 and 2-2, and E2 Torr (higher than E1 Torr) in evaluation tests 2-3 and 2-4. The etching time was set to 2400 seconds in evaluation tests 2-1 and 2-2, and to 1600 seconds in evaluation tests 2-3 and 2-4.

[0048] Table 3 below summarizes the results of Evaluation Test 2. As shown in the table, between Evaluation Tests 2-1 and 2-2, and between Evaluation Tests 2-3 and 2-4, the depth L was greater in Evaluation Tests 2-2 and 2-4, where GeF4 gas was supplied. Therefore, supplying GeF4 gas along with F2 gas as an etching gas yielded favorable results.

[0049] [Table 3]

[0050] • Evaluation Test 3 Evaluation Test 3 (3-1 to 3-8) was conducted in the same manner as Evaluation Test 2, except that the substrate processing temperature and etching time were different. Evaluation Tests 3-1, 3-2, 3-3, and 3-4 were conducted under the same processing conditions as Evaluation Tests 2-1, 2-2, 2-3, and 2-4, except that the substrate processing temperature was set to 35°C and the substrate processing times were set to 1200 seconds, 1200 seconds, 600 seconds, and 600 seconds, respectively. Therefore, in Evaluation Tests 3-2 and 3-4, both F2 gas and GeF4 gas were supplied to the substrate as etching gases, and in Evaluation Tests 3-3 and 3-4, the total flow rate of the supplied gas was larger and the dilution ratio of the etching gas was higher than in Evaluation Tests 3-1 and 3-2.

[0051] For evaluation tests 3-5, 3-6, 3-7, and 3-8, the processing conditions were the same as for evaluation tests 2-1, 2-2, 2-3, and 2-4, respectively, except that the substrate processing temperature was set to 50°C and the substrate processing times were 1200 seconds, 1200 seconds, 480 seconds, and 480 seconds. Therefore, in evaluation tests 3-6 and 3-8, both F2 gas and GeF4 gas were supplied to the substrate as etching gases.

[0052] [Table 4]

[0053] [Table 5]

[0054] Tables 4 and 5 above summarize the results of evaluation tests 3-1 to 3-8. Note that the depth L of recess 16 in evaluation test 3-3 was too small to be accurately measured. As is clear from Tables 4 and 5, when comparing evaluation tests 3-1 and 3-2, 3-3 and 3-4, 3-5 and 3-6, and 3-7 and 3-8, which differ in the presence or absence of GeF4 gas supply, the tests in which GeF4 gas was supplied showed a larger depth L.

[0055] Furthermore, in evaluation tests 3-4 and 3-8, where GeF4 gas was supplied and the size of the recesses 16 did not exceed the limit, the acquired images showed no significant difference in depth L between the recesses 16 in each stage, confirming that the SiGe film 12 was etched with high uniformity in each stage. Thus, in evaluation test 3, as in evaluation test 2, supplying GeF4 gas along with F2 gas as etching gas yielded favorable results.

[0056] As described above, evaluation tests 2 and 3 showed that supplying F2 gas and GeF4 gas as etching gas resulted in a larger depth L of the recess 16 compared to supplying only F2 gas as etching gas. This is presumed to be due to the shortened incubation time caused by the supply of GeF4 gas, as explained in the embodiment.

[0057] • Evaluation Test 4 For evaluation tests 4-1 to 4-4, the substrate was processed under the same conditions as in evaluation test 2-2, except that the etching time was changed. Similarly, for evaluation tests 4-5 to 4-8, the substrate was processed under the same conditions as in evaluation test 2-4, except that the etching time was changed. Therefore, in evaluation tests 4-1 to 4-8, F2 gas and GeF4 gas were supplied to the substrate as etching gases. In evaluation tests 4-1, 4-2, 4-3, and 4-4, the etching times were set to 900 seconds, 1200 seconds, 1800 seconds, and 2400 seconds, respectively. In evaluation tests 4-5, 4-6, 4-7, and 4-8, the etching times were set to 1200 seconds, 1400 seconds, 1400 seconds, and 1500 seconds, respectively. Therefore, the etching time was the same between evaluation tests 4-6 and 4-7.

[0058] [Table 6]

[0059] [Table 7]

[0060] Tables 6 and 7 above summarize the results of evaluation tests 4-1 to 4-8. Looking at the results of evaluation tests 4-1 to 4-4, where only the etching time differs, the depth L of the recess 16 increases as the etching time increases. Looking at the results of evaluation tests 4-5 to 4-8, where only the etching time differs, the depth L of the recess 16 increases as the etching time increases, and there is no significant difference in depth L between evaluation tests 4-6 and 4-7, where the etching time is the same. From the results of evaluation tests 4 above, it was confirmed that the stability of the process can be increased by supplying F2 gas and GeF4 gas to the wafer W as etching gases.

[0061] • Evaluation Test 5 As part of evaluation test 5, F2 gas, GeF4 gas, N2 gas, and Ar gas were supplied to wafer W, and etching was performed on multiple substrates as in the other evaluation tests. The state of the Si film 13 and SiGe film 12 was observed from the images acquired after etching. When etching multiple substrates in this manner, the flow rate of GeF4 gas supplied to the processing container 31 was kept constant between substrates, while the combination of the flow rates of F2 gas and N2 gas was changed. Among the multiple substrates, some were processed with the flow rate of either F2 gas or GeF4 gas set to 0 sccm. The total flow rate of gas supplied to the processing container 31 was kept constant between substrates. Therefore, in this evaluation test 5, the combination of partial pressures of F2 gas and GeF4 gas in the processing container 31 was set differently for each substrate. Processing conditions other than the gas flow rate were the same for all substrates, with the processing temperature (i.e., the temperature of the stage 41) set to 40°C and the etching time set to 300 seconds for each substrate.

[0062] Images obtained after etching confirmed etching of the Si film 13 on some substrates. The graph in Figure 13 shows the relationship between the setting of the partial pressures of F2 gas and GeF4 gas in the processing container 31 and the presence or absence of etching of the Si film 13. The horizontal axis of the graph is set to the partial pressure of F2 gas in the processing container 31, and the vertical axis is set to the partial pressure of GeF4 gas in the processing container 31. As shown in the graph, the test was conducted with the partial pressure of GeF4 gas set to 100 mTorr (13.3 Pa), and the partial pressure of F2 gas was changed within the range of 0 mTorr to 200 mTorr (26.6 Pa). Note that a partial pressure of 100 mTorr of GeF4 gas means that the flow rate of GeF4 gas supplied to the processing container 31 / the total flow rate of gas supplied to the processing container 31 × the pressure inside the processing container 31 = 100 mTorr, and the partial pressures of gases other than GeF4 are calculated in the same way.

[0063] Within the partial pressure range of F2 gas described above (0mTorr to 200mTorr), when the partial pressure of F2 gas was 0mTorr (i.e., the flow rate of F2 gas was 0 sccm), the Si film 13 was not etched, but the SiGe film 12 was also not etched. Therefore, as described in the embodiment, it was shown that the SiGe film 12 could not be etched with GeF4 gas alone, and that it was necessary to supply F2 gas together with GeF4 gas in order to perform such etching.

[0064] Furthermore, as shown in the graph, with the partial pressure of F2 gas set to 200 mTorr, the partial pressure of GeF4 gas was varied within the range of 0 mTorr to 300 mTorr (39.9 Pa). Within this range, etching of the Si film 13 was not observed when the partial pressure of F2 gas was between 0 mTorr and 200 mTorr, and the SiGe film 12 was selectively etched. However, when the partial pressure of GeF4 gas was set to 300 mTorr, etching of the Si film 13 was observed.

[0065] As described above, when supplying F2 gas and GeF4 gas to wafer W, the etching selectivity for the SiGe film 12 changes depending on the relationship between the partial pressure of F2 gas and the partial pressure of GeF4 gas. Specifically, if the partial pressure of F2 gas is too low, the selectivity decreases. The results of this evaluation test 5 indicate that, in order to prevent this decrease in selectivity, it is preferable to set the partial pressure of F2 gas to be greater than, for example, 150 mTorr, and more preferably 200 mTorr or higher. Also, as shown in the graph, if the partial pressure of GeF4 gas is too high, the etching selectivity for the SiGe film 12 decreases. The results of this evaluation test 5 indicate that, in order to prevent this decrease in selectivity, it is preferable to set the partial pressure of GeF4 gas to be less than, for example, 300 mTorr, and more preferably 200 mTorr or lower. [Explanation of symbols]

[0066] W wafer 21 F2 (fluorine) gas 22 GeF4 (Germanium tetrafluoride) gas

Claims

1. An etching method comprising an etching step of supplying a first etching gas containing fluorine atoms and a second etching gas which is a compound of germanium and fluorine to a substrate, thereby etching a silicon germanium film provided on the substrate.

2. The etching method according to claim 1, wherein the second etching gas is germanium tetrafluoride gas.

3. The etching method according to claim 2, wherein the first etching gas is a fluorine gas.

4. A silicon film is formed on the substrate, and the silicon film and the silicon-germanium film are exposed on the surface of the substrate. The etching method according to claim 3, wherein the etching step is a step of selectively etching the silicon germanium film among the silicon film and the silicon germanium film.

5. The substrate is provided with a laminate comprising a plurality of silicon germanium films and a plurality of silicon films. The silicon germanium film and the silicon film are alternately stacked in the thickness direction of the substrate. The etching method according to claim 4, wherein the etching step is a step of etching the silicon germanium film in a direction intersecting the thickness direction of the substrate.

6. The etching method according to claim 3, further comprising the step of stopping the supply of the second etching gas to the substrate while the first etching gas is being supplied to the substrate.

7. The etching method according to claim 3, further comprising the step of supplying hydrogen fluoride gas to the substrate while supplying the first etching gas to the substrate.

8. A processing container for housing a substrate on which a silicon germanium film is provided, A gas supply mechanism is provided to supply both a first etching gas containing fluorine atoms and a second etching gas, which is a compound of germanium and fluorine, into the processing container in order to etch the silicon germanium film. An etching apparatus equipped with the following features.

Images