XeF2 dry etching system and process

Abstract

Provided is an XeF2 dry-etching system capable of dramatically shortening the required duration for an XeF2 dry-etching process. This XeF2 dry-etching system is equipped with: a starting material vessel for storing XeF2; a variable capacity tank which is connected to the starting material vessel and is capable of storing the XeF2 supplied from the starting material vessel in a volume which can increase and decrease; an etching chamber which is connected to the variable capacity tank and subjects a substrate to dry etching using the XeF2 supplied from the variable capacity tank; a vacuum pump which is connected to the etching chamber and is capable of subjecting the etching chamber and the variable capacity tank to vacuum drawing; a first valve provided between the starting material vessel and the variable capacity tank; a second valve provided between the variable capacity tank and the etching chamber; and a third valve provided between the etching chamber and the vacuum pump.

Description

[Technical Field]

[0001] The present invention relates to a XeF2 dry etching system and process.

[0002] Miniaturization in semiconductor manufacturing processes continues to advance year by year, resulting in various improvements at each step. In particular, in photolithography, extreme ultraviolet (EUV) light with a wavelength of 13.5 nm has begun to replace the 193 nm wavelength used in conventional ArF exposure. As a result, the wavelength has suddenly decreased to less than one-tenth of its current size, and its optical properties have completely changed, necessitating the development of numerous new technologies. In particular, the development of a pellicle, a film to prevent particle adhesion to masks (reticles), is highly anticipated. This is because there are currently no pellicles with high transmittance for EUV light. The intensity of EUV light passing through a pellicle is significantly reduced, resulting in longer exposure times and reduced throughput. Furthermore, pellicles absorb EUV light, causing them to heat up and deteriorate rapidly. To address this issue, various pellicle films have been proposed. Patent Document 1 (Japanese Patent No. 6858817) discloses a pellicle membrane having a core layer including a material that is substantially transparent to EUV radiation, such as (poly)Si, and a cap layer including a material that absorbs IR radiation.

[0003] Various methods for manufacturing pellicle films have been proposed. Non-Patent Document 1 (Dario L. Goldfarb, "Fabrication of a full-size EUV pellicle based on silicon nitride," Volume 31, Issue 12, PHOTOMASK, SPIE, 2015) discloses a method for manufacturing a free-standing SiNx film as a pellicle film. The basic method is as follows: First, a SiNx film to serve as the pellicle film is formed on both sides of a Si substrate (Step A). ​​Next, a reactive ion etching (RIE) mask for etching the formed SiNx film is formed on only one side (Step B). Part of the SiNx is removed by RIE to expose the Si substrate (Step C). Both sides of the Si substrate are coated with amorphous Si, and then the Si substrate is diced to form an outer shape (Step D). Finally, the Si substrate is wet-etched using the SiNx film as a mask to form a free-standing SiNx film (Step E). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6858817 [Non-patent literature]

[0005] [Non-Patent Document 1] Dario L. Goldfarb, "Fabrication of a full size EUV pellicle based on silicon nitride", Volume 31, Issue 12, PHOTOMASK, SPIE, 2015 Summary of the Invention

[0006] When attempting to fabricate an EUV-transmitting film as a pellicle film using a conventional manufacturing method such as that disclosed in Non-Patent Document 1, one possible approach is to form an EUV-transmitting film on a Si substrate, and then remove the unnecessary portions of the Si substrate by wet etching to form a freestanding film. However, in the final step of wet etching the Si substrate, the pellicle film may be damaged by the flow of the etching solution used, or when the pellicle film is pulled out of the solution after etching, the pellicle film may be damaged by the surface tension at the interface between the etching solution on the pellicle film surface and the atmosphere. As such, handling pellicle films is extremely difficult, resulting in a problem of low yield.

[0007] Therefore, attempts have been made to avoid the problems associated with handling liquids by changing the etching method for Si substrates from wet etching to dry etching. In this case, the type of dry etching gas and etching conditions are set according to the material of the pellicle film. For example, the inventors have partially removed the Si substrate using dry etching with XeF2 gas, which does not require substrate heating or plasma, to create a free-standing EUV-transmitting film or pellicle film.

[0008] Dry etching using XeF2 gas requires repeated evacuation of the etching chamber and supply of XeF2. Specifically, when XeF2 is introduced into the etching chamber, it reacts with Si to form SiF4, which is consumed and reduced. Because XeF2 is supplied as a gas, the molar amount of XeF2 per volume is much smaller than that of a solid Si substrate. Therefore, even etching a portion of a Si substrate requires repeated supply of XeF2, which requires alternating between evacuation of the chamber and supply of XeF2 gas. Figure 3 shows the basic configuration of a conventional XeF2 dry etching system 110. This system 110 comprises a source container 112, a subtank 114, an etching chamber 116, and a vacuum pump 118. The source container 112 contains the solid XeF2 source material. The subtank 114 temporarily stores sublimated XeF2 gas. The etching chamber 116 is a device that uses XeF2 gas to etch a Si substrate S mounted on a substrate holder 116a. A vacuum pump 118 evacuates the etching chamber 116 and the sub-tank 114. XeF2, an etching raw material, has a high vapor pressure, so it can easily sublimate to obtain XeF2 gas when a low vacuum is created. XeF2 is a solid in the raw material stage, which is advantageous in that the volume of the raw material container can be made smaller than that of a gaseous raw material.

[0009] Figure 4 shows an etching process using the conventional XeF2 dry etching system 110 of Figure 3. First, a Si substrate S to be etched is mounted on the substrate holder 116a in the etching chamber 116, and the etching chamber 116 and the sub-tank 114 are evacuated using a vacuum pump 118 (Figure 4(i)). When the valve 120b between the etching chamber 116 and the sub-tank 114 is closed and the valve 120a between the sub-tank 114 and the source container 112 is opened, the XeF2 gas sublimes into the sub-tank 114 because of the low vacuum inside the sub-tank 114 (Figure 4(ii)). When the pressure of the XeF2 gas in the sub-tank 114 reaches a predetermined pressure, the valve 120a between the source container 112 and the sub-tank 114 is closed, and the valve 120b between the sub-tank 114 and the etching chamber 116 is opened (Figure 4(iii)). The XeF2 gas in the subtank 114 flows into the etching chamber 116, and etching of the Si substrate S begins. During this Si etching, XeF2 reacts with Si to produce SiF4 and Xe. As the reaction progresses and the XeF2 in the etching chamber 116 decreases, the etching rate slows down, and eventually, when the XeF2 is gone, etching stops. At an appropriate time, the SiF4 and Xe produced in the etching chamber 116 are evacuated by the vacuum pump 118 (Figure 4(iv)). The valve 120a between the subtank 114 and the source container 112 is opened again, and the XeF2 is sublimated into the subtank 114 (Figure 4(ii)). In this way, by repeating the steps (cycle) shown in Figures 4(ii) to 4(iv), the Si substrate S is etched to the desired state (typically, until a portion of the EUV-transmitting film becomes a free-standing film).

[0010] Consider the amount of XeF2 gas used in the etching process. Assuming that the volumes of the subtank 114 and the etching chamber 116 are the same, transitioning from FIG. 4(ii) to FIG. 4(iii) results in only half of the XeF2 gas stored in the subtank 114 entering the etching chamber 116 and being used for etching. Once the pressures in the subtank 114 and the etching chamber 116 reach equilibrium, the narrow pipe 122 connecting them prevents the transfer of XeF2 gas, even if valve 120b is left open. Therefore, only half of the XeF2 gas sublimated into the subtank 114 is used for etching. The larger the volume of the etching chamber 116 is compared to the volume of the subtank 114, the greater the amount of XeF2 gas flowing into the etching chamber 116. However, because the XeF2 concentration in the etching chamber 116 is low and the XeF2 gas diffusion within the etching chamber 116 is small, an increase in the etching rate cannot be expected. Therefore, it is possible to consider sublimating as much XeF2 gas as possible into the subtank 114, but as the pressure inside the subtank 114 increases, the rate of pressure increase slows down and it takes time, so this does not lead to a significant reduction in the overall etching process time.

[0011] The inventors have now discovered that the time required for the XeF2 dry etching process can be significantly reduced by adopting a variable capacity tank as a sub-tank for temporarily storing XeF2 gas, which is placed between the etching chamber and the source container.

[0012] Therefore, an object of the present invention is to provide a XeF2 dry etching system and process that can significantly reduce the time required for the XeF2 dry etching process.

[0013] According to the present invention, the following aspects are provided. [Aspect 1] a source vessel containing XeF2; a variable capacity tank connected to the source container and capable of storing an increased or decreased volume of XeF supplied from the source container; an etching chamber connected to the variable volume tank and configured to dry etch a substrate using XeF supplied from the variable volume tank; a vacuum pump connected to the etching chamber and capable of evacuating the etching chamber and the variable volume tank; a first valve provided between the raw material container and the variable volume tank; a second valve provided between the variable volume tank and the etching chamber; a third valve provided between the etching chamber and the vacuum pump; XeF2 dry etching system equipped with [Aspect 2] a pressure sensor provided in each of the variable volume tank and the etching chamber; a control unit that controls the volume of the variable volume tank and / or the opening and closing of the first valve, the second valve, and the third valve based on information from the pressure sensor; 2. The XeF 2 dry etching system of embodiment 1, further comprising: [Aspect 3] A XeF2 dry etching process using the XeF2 dry etching system according to embodiment 1 or 2, (a) operating the vacuum pump to evacuate the etching chamber and the variable volume tank, thereby sublimating the XeF2 in the source container and supplying XeF2 gas into the variable volume tank; (b) reducing the volume of the variable volume tank to supply the XeF2 gas from the variable volume tank to the evacuated etching chamber, and dry etching a substrate placed in the etching chamber with the XeF2; (c) increasing the volume of the volume variable tank, thereby sublimating the XeF2 in the source container, and supplying XeF2 gas into the volume variable tank; (d) after step (b) and before, during, or after step (c), operating the vacuum pump to evacuate the etching chamber; (e) repeating steps (b), (c) and (d) as necessary; XeF2 dry etching process including: [Aspect 4] The step (a) (a1) closing the first valve and opening the second valve and the third valve, evacuating the etching chamber and the variable volume tank to reduce the pressure inside the variable volume tank, and then (a2) sublimating XeF2 in the source container to supply XeF2 gas into the volume-variable tank while the first valve is open and the second valve is closed. 4. The XeF 2 dry etching process of embodiment 3, wherein the XeF 2 dry etching process is performed by [Aspect 5] The step (b) (b1) while the first valve and the third valve are closed and the second valve is open, XeF2 gas in the variable volume tank is supplied to the etching chamber, which has been evacuated, and during and / or after that, (b2) supplying XeF2 gas to the etching chamber by decreasing the volume of the volume-variable tank while closing the first valve and the third valve and opening the second valve. 5. The XeF2 dry etching process of embodiment 3 or 4, wherein the etching is carried out by [Aspect 6] the step (c) is performed by increasing the volume of the variable volume tank while the first valve is open and the second valve and the third valve are closed, the dry etching is continued in the etching chamber during the step (c), and 6. The XeF2 dry etching process according to any one of aspects 3 to 5, wherein the evacuation in the step (d) is carried out after the step (c). [Aspect 7] step (c) is performed by increasing the volume of the variable volume tank while opening the first valve and closing the second valve; and 6. The XeF2 dry etching process according to any one of aspects 3 to 5, wherein the evacuation in the step (d) is carried out before or during the step (c). [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a conceptual diagram showing an example of the basic configuration of a XeF2 dry etching system according to the present invention. [Figure 2A] 1 is a first half of a process flow diagram of an example of a XeF2 dry etching process according to the present invention. [Figure 2B] 2B is a second half of a process flow diagram of an example of a XeF2 dry etching process according to the present invention, following FIG. 2A. [Figure 3] FIG. 1 is a conceptual diagram showing an example of the basic configuration of a conventional XeF2 dry etching system. [Figure 4] 1 is a process flow diagram illustrating an example of a conventional XeF2 dry etching process. DETAILED DESCRIPTION OF THE INVENTION

[0015] XeF 2 Dry Etching Systems and Processes FIG. 1 shows an XeF2 dry etching system 10 according to one embodiment of the present invention. The system 10 includes a source container 12, a variable volume tank 14, an etching chamber 16, a vacuum pump 18, and valves 20a, 20b, and 20c. The source container 12 is a container for storing XeF2. The variable volume tank 14 is a sub-tank that can store an increased or decreased volume of XeF2 supplied from the source container 12 and is connected to the source container 12. The etching chamber 16 is a device that performs dry etching on a substrate S using the XeF2 supplied from the variable volume tank 14 and is connected to the variable volume tank 14. The vacuum pump 18 is connected to the etching chamber 16 and is capable of evacuating the etching chamber 16 and the variable volume tank 14. A first valve 20a is provided between the source container 12 and the variable volume tank 14. A second valve 20b is provided between the variable volume tank 14 and the etching chamber 16. A third valve 20c is provided between the etching chamber 16 and the vacuum pump 18. In the illustrated example, the source container 12, the variable volume tank 14, the etching chamber 16, and the vacuum pump 18 are connected by a pipe 22, and the valves 20a, 20b, or 20c are disposed in the above-mentioned positions on the pipe 22. By employing the variable volume tank 14 as a sub-tank for temporarily storing XeF2 gas between the etching chamber 16 and the source container 12 in this manner, the time required for the XeF2 dry etching process can be significantly reduced.

[0016] As mentioned above, in a process using the conventional XeF dry etching system 110 shown in Figures 3 and 4, the XeF concentration in the etching chamber 116 is low and the XeF gas diffusion within the etching chamber 116 is also small, so an increase in the etching rate cannot be expected. Therefore, while it is possible to sublimate as much XeF gas as possible into the subtank 114, as the pressure in the subtank 114 increases, the rate of pressure increase slows and the process takes time, resulting in a problem that does not lead to a significant reduction in the overall etching process time. In contrast, the present invention employs a variable-volume tank 14 instead of the conventional fixed-volume subtank 114. After a predetermined amount of XeF gas accumulates in the variable-volume tank 14, the volume of the variable-volume tank 14 is reduced when the second valve 20b is opened to allow the XeF gas to flow into the etching chamber 16. In this way, the XeF gas can be forced from the variable-volume tank 14 into the etching chamber 16. That is, XeF2 gas that would have remained in the fixed-volume sub-tank 114 in a conventional process can now be introduced into the etching chamber 16. Therefore, even when introducing the same amount of XeF2 gas into the etching chamber 16 as in the conventional system 110, the amount of XeF2 gas required in the sub-tank can be reduced, thereby shortening the XeF2 sublimation time. Furthermore, due to the pressurization effect caused by the reduced volume of the variable-volume tank 14, a larger amount of XeF2 gas can be supplied from the variable-volume tank 14 to the etching chamber 16. This increases the amount of Si etched per etching step (i.e., per cycle), and also reduces the number of cycles required to complete the final etching. In this way, the etching time and, in turn, the time required for the XeF2 dry etching process can be significantly reduced.

[0017] Each component of the XeF2 dry etching system 10 is described below.

[0018] The source container 12 is not particularly limited as long as it is a container such as a bottle that can contain XeF2. However, it is preferable that at least the inner wall of the source container 12 is made of a material that does not react with XeF2. Preferred examples of materials that make up the inner wall of the source container 12 include aluminum and stainless steel.

[0019] The volume-adjustable tank 14 is a tank that can accommodate an increased or decreased volume of XeF2 supplied from the source container 12. Therefore, the volume-adjustable tank 14 has a mechanism for increasing or decreasing the volume. Such a volume-adjustable mechanism is not particularly limited and may be any mechanism, including a piston mechanism or a bellows mechanism. In this regard, the volume-adjustable tank 14 shown in FIGS. 1 and 2 has a piston mechanism. Specifically, the volume-adjustable tank 14 includes a tank body 14a and a piston portion 14b that is movably inserted into the tank body 14a (in the vertical direction in the illustrated example). The piston portion 14b is configured to form an internal space between the tank body 14a and the piston portion 14b, which allows XeF2 to sublimate and accumulate. In this case, the volume of the internal space can be reduced by moving the piston portion 14b toward the tank body 14a (upward in the illustrated example), and the volume of the internal space can be increased by moving the piston portion 14b away from the tank body 14a (downward in the illustrated example). Preferably, a sensor 24 is provided within the variable volume tank 14 so that the pressure and temperature within the variable volume tank 14 can be monitored.

[0020] The etching chamber 16 is an apparatus for dry etching the substrate S using XeF supplied from the variable capacity tank 14. Various XeF dry etching apparatuses are commercially available, and a known dry etching chamber can be used. The etching chamber 16 preferably includes a substrate holder 16a for mounting the substrate S. In addition, the etching chamber 16 is preferably provided with a sensor 24 so that the pressure and temperature within the etching chamber 16 can be monitored.

[0021] The vacuum pump 18 is not particularly limited and may be any known vacuum pump as long as it is capable of evacuating the etching chamber 16 and the variable volume tank 14 to a desired vacuum level. Examples of the vacuum pump 18 include a rotary vacuum pump, an oil diffusion pump, and a diaphragm pump, with a diaphragm pump being preferred.

[0022] The first valve 20a, the second valve 20b, and the third valve 20c are not particularly limited, and known valves may be used.

[0023] It is preferable that a pressure sensor 24 is provided in each of the variable volume tank 14 and the etching chamber 16. The pressure sensor 24 may also function as a temperature sensor.

[0024] The system 10 preferably includes a control unit 26 that controls the volume of the variable volume tank 14 and / or the opening and closing of the valves 20a, 20b, and 20c. The control unit 26 is preferably connected to a pressure sensor 24 in the etching chamber 16 and a pressure sensor 24 in the variable volume tank 14, and is configured to control the volume of the variable volume tank 14 and / or the opening and closing of the valves 20a, 20b, and 20c based on information from these pressure sensors 24. For example, the control unit 26 is configured to open or close the valves 20a, 20b, and / or 20c when the pressure in the variable volume tank 14 or the pressure in the etching chamber 16 reaches a predetermined value. The control unit 26 may also be configured to control the increase or decrease in the volume of the variable volume tank 14 (e.g., by moving the piston 14b up or down) at a predetermined timing based on information such as pressure from the sensors 24. However, the opening and closing of the valves 20a, 20b, and 20c and the increase or decrease in the volume of the variable volume tank 14 may also be controlled manually without relying on the control unit 26.

[0025] 2A and 2B show a XeF dry etching process using a XeF dry etching system 10. This process includes the steps of (a) initial evacuation and sublimation of XeF, (b) introduction of XeF and etching, (c) sublimation of XeF, (d) evacuation, and (e) repetition of steps (b) through (d). Each of these steps is described below.

[0026] (a) Initial evacuation and sublimation of XeF2 2A(a1) and (a2), the vacuum pump 18 is operated to evacuate the etching chamber 16 and the variable volume tank 14, thereby sublimating the XeF2 in the source container 12 and supplying XeF2 gas into the variable volume tank 14 (step (a)). This evacuation is preferably carried out until the pressure in the etching chamber 16 and the variable volume tank 14 reaches 1.0 Pa or less, more preferably 0.5 Pa or less, and even more preferably 0.3 Pa or less.

[0027] This step (a) is preferably performed in the following two steps: As shown in Fig. 2A(a1), with the first valve 20a closed and the second valve 20b and the third valve 20c open, the etching chamber 16 and the variable volume tank 14 are evacuated to reduce the pressure inside the variable volume tank 14 (step (a1)). Thereafter, as shown in Fig. 2A(a2), with the first valve 20a open and the second valve 20b closed, the XeF2 in the source container 12 is sublimated to supply XeF2 gas into the variable volume tank 14 (step (a2)).

[0028] (b) XeF2 introduction and etching As shown in Figures 2A(b1) and 2B(b2), the XeF2 gas in the variable volume tank 14 is supplied to the evacuated etching chamber 16 by reducing the volume of the variable volume tank 14, and the substrate S placed in the etching chamber 16 is dry-etched with XeF2 (step (b)). This allows a larger amount of XeF2 gas to be supplied from the variable volume tank 14 to the etching chamber 16, including XeF2 gas that would have remained in the fixed-volume sub-tank 114 in conventional processes. This improves etching efficiency and significantly reduces the etching time and the time required for the XeF2 dry etching process. The substrate S is not particularly limited as long as it can be dry-etched with XeF2, but is preferably a Si substrate (especially a Si substrate with an EUV-transmitting film or pellicle film formed thereon). In the latter case, the EUV-transmitting film or pellicle film can be made into a freestanding film by etching away unnecessary portions of the Si substrate. XeF2 dry etching may be performed under known conditions and is not particularly limited.

[0029] This step (b) is preferably performed in two steps as follows: As shown in Fig. 2A(b1), with the first valve 20a and the third valve 20c closed and the second valve 20b open, XeF2 gas in the volumetric tank 14 is supplied to the evacuated etching chamber 16 (step (b1)). Then, as shown in Fig. 2B(b2), during and / or after step (b1), with the first valve 20a and the third valve 20c closed and the second valve 20b open, the volume of the volumetric tank 14 is reduced to supply XeF2 gas to the etching chamber 16 (step (b2)).

[0030] (c) Sublimation of XeF2 2B(c), the capacity of the capacity variable tank 14 is increased, thereby sublimating XeF in the source container 12 and supplying XeF gas into the capacity variable tank 14 (step (c)). That is, because the capacity of the capacity variable tank 14 was reduced in step (b), a sufficient amount of XeF cannot be sublimated at the current capacity. However, by increasing the capacity of the capacity variable tank 14, a sufficient amount of XeF (preferably the same amount as the amount of XeF sublimated in step (a)) can be sublimated, and a sufficient amount of XeF gas can be temporarily stored in the capacity variable tank 14 in preparation for the subsequent repeat step (e). This step (c) is preferably performed by increasing the capacity of the capacity variable tank 14 while opening the first valve 20a and closing the second valve 20b (or the second valve 20b and the third valve 20c).

[0031] (d) Vacuuming After step (b) and before, during, or after step (c), the vacuum pump 18 is operated to evacuate the etching chamber (step (d)). This evacuation is preferably carried out until the pressure inside the etching chamber 16 reaches 1.0 Pa or less, more preferably 0.5 Pa or less, and even more preferably 0.3 Pa or less.

[0032] The evacuation in step (d) is preferably performed after step (c). In this case, dry etching can be continued in the etching chamber 16 during step (c), thereby further shortening the time for the entire etching process. However, the evacuation in step (d) may be performed before or during step (c).

[0033] (e) Repeat steps (b) to (d). Steps (b), (c), and (d) are repeated as necessary. That is, the cycle of steps (b) → (c) → (d) (or steps (b1) → (b2) → (c) → (d)) is repeated a desired number of times to gradually etch the substrate S with XeF. Etching can be stopped when there are no more portions to be etched away. [Example]

[0034] The present invention is further illustrated by the following examples.

[0035] Example 1 A source material container 12, a variable volume tank 14, an etching chamber 16, and a vacuum pump 18, each having the specifications shown below, are connected by piping 22 equipped with valves 20a, 20b, or 20c to form a XeF2 dry etching system 10 as shown in FIG. 1. Source container 12: A container containing solid XeF2 Variable Capacity Tank 14: A piston-type variable capacity tank whose volume can be adjusted within the range of 20 to 120 mL. Etching chamber 16: 100 mL volume etching chamber Vacuum pump 18: diaphragm pump

[0036] At this time, by placing the volume-variable tank 14 and the etching chamber 16 close to each other, the volume of the piping 22 connecting them can be reduced and the effect of pressure changes can be made negligible.

[0037] Here, the pressure change in the etching chamber 16 or the variable volume tank 14 is calculated as follows: That is, the pressure P2 in the etching chamber 16 after changing the volume of the variable volume tank 14 (which is equal to the pressure in the variable volume tank 14 when the valve 20b is open) is calculated by the following formula: P2=P1×V1 / V2 (In the formula, P1 is the pressure inside the etching chamber 16 before the volume of the variable volume tank 14 is changed, V1 is the total volume of the etching chamber 16 and the variable volume tank 14 before the volume of the variable volume tank 14 is changed, and V2 is the total volume of the etching chamber 16 and the variable volume tank 14 after the volume of the variable volume tank 14 is changed.) Therefore, when the volume of the variable volume tank 14 is reduced from 120 mL to 20 mL, the pressure P2 inside the etching chamber 16 is calculated by the following formula: P2=P1×(100+120) / (100+20)=1.83P1 In this way, since the pressure inside the etching chamber 16 increases by 1.83 times, the amount of XeF2 (number of moles) inside the etching chamber 16 also increases by 1.83 times.

[0038] Using the XeF2 dry etching system 10, XeF2 etching is performed on a Si substrate S mounted on a substrate holder 16a in an etching chamber 16. Each step of this process will be explained in order, with reference to the pressure changes described above.

[0039] 2A(a1), with the first valve 20a closed and the second valve 20b and the third valve 20c open, the etching chamber 16 and the variable-volume tank 14 are evacuated by the vacuum pump 18 (step (a1)). In this step, the control unit 26 of the system 10 is set so that the process proceeds to the next step (a2) when the pressure sensor 24 attached inside the etching chamber 16 detects a pressure of 1.0 Pa or less, as shown in FIG.

[0040] 2A(a2), with the first valve 20a and the third valve 20c open and the second valve 20b closed, XeF2 gas is supplied from the source container 12 into the volumetric tank 14 until the pressure in the volumetric tank 14 reaches the set pressure (step (a2)). In this step, the control unit 26 of the system 10 is set to close the first valve 20a between the source container 12 and the volumetric tank 14 when the pressure sensor 24 attached to the volumetric tank 14 detects a pressure exceeding 267 Pa, as shown in FIG.

[0041] As shown in Figure 2A (b1), the second valve 20b between the etching chamber 16 and the variable volume tank 14 is opened to allow XeF2 gas to flow from the variable volume tank 14 into the etching chamber 16 (step (b1)). At this time, the pressure inside the etching chamber 16 and the variable volume tank 14 becomes 146 Pa, which is the total volume of the etching chamber 16 and the variable volume tank 14. In the conventional system 110 shown in Figures 3 and 4, the volume of the sub-tank 114 is not variable, so etching proceeds in the state of step (b1) (corresponding to step (iii) in Figure 4), but in the present invention, the following steps are subsequently performed.

[0042] 2B(b2), the piston portion 14b is raised to reduce the volume of the variable volume tank 14 from 120 mL to 20 mL, thereby allowing a larger amount of XeF2 gas in the variable volume tank 14 to flow into the etching chamber 16 (step (b2)). In this way, the etching efficiency using the XeF2 gas can be improved.

[0043] 2B(c), the third valve 20c between the etching chamber 16 and the volumetric tank 14 is closed, and the first valve 20a between the volumetric tank 14 and the source container 12 is opened, while the piston 14b is lowered to increase the volume of the volumetric tank 14 (step (c)). In this step, etching in the etching chamber 16 and the supply of XeF2 gas to the volumetric tank 14 are carried out simultaneously. When most of the XeF2 gas that has flowed into the etching chamber 16 has been consumed by etching, the process proceeds to the next step.

[0044] As shown in FIG. 2B(d), the etching chamber 16 is evacuated by the vacuum pump 18 to exhaust SiF4 produced by the etching reaction in the etching chamber 16 (step (d)).

[0045] Then, as shown at the end of Figure 2B, the cycle of steps (b1) to (d) is repeated a desired number of times, such as step (b1) → step (b2) → step (c) → step (d) → step (b1) → ..., gradually etching the Si substrate with XeF2. Etching is stopped when there is no Si remaining to be etched away.

[0046] Table 1 shows the pressures at each step of the process of Example 1. [Table 1]

[0047] Comparative Example 1 A source container 112, a sub-tank 114, an etching chamber 116, and a vacuum pump 118, each having the specifications shown below, are connected by piping 122 equipped with valves 120a, 120b, or 120c to form a conventional XeF2 dry etching system 110 as shown in FIG. 3. Source container 112: a container containing solid XeF2 Subtank 114: Fixed-volume subtank with a capacity of 120 mL (not variable capacity) Etching chamber 116: 100 mL volume etching chamber Vacuum pump 118: Diaphragm pump

[0048] As described above, the capacity of the etching chamber 116 is 100 mL (similar to the etching chamber 16 in Example 1), and the capacity of the sub-tank 114 is 120 mL (similar to the maximum capacity of the variable capacity tank 14 in Example 1), so the XeF2 gas pressure in the etching chamber 116 and the sub-tank 114 during etching (see FIG. 4(iii)) is 146 Pa. However, since the pipe 122 connecting the etching chamber 116 and the sub-tank 114 has a small diameter, and although gas moves if there is a pressure difference, there is almost no gas movement if the pressure is the same, the gas used for etching is limited to the gas in the etching chamber 116.

[0049] A conventional XeF2 dry etching system 110 is used to perform XeF2 etching on a Si substrate S mounted on a substrate holder 116a in an etching chamber 116. Each step of this process will be described in order, with reference to the pressure changes described above.

[0050] 4(i), with the first valve 120a closed and the second valve 120b and the third valve 120c open, the etching chamber 116 and the sub-tank 114 are evacuated by the vacuum pump 118 (step (i)). In this step, as shown in FIG. 1, the control unit (not shown) of the system 110 is set so that the process proceeds to the next step (ii) when a pressure sensor (not shown) attached to the etching chamber 116 detects a pressure of 1.0 Pa or less.

[0051] 4(ii), with the first valve 120a and the third valve 120c open and the second valve 120b closed, XeF2 gas is supplied into the sub-tank 114 until the pressure inside the sub-tank 114 reaches a set pressure (step (ii)). In this step, a control unit (not shown) of the system 110 is set to close the first valve 120a between the source container 112 and the sub-tank 114 when a pressure sensor (not shown) attached inside the sub-tank 114 detects a pressure exceeding 267 Pa.

[0052] As shown in Figure 4(iii), the second valve 120b between the etching chamber 116 and the sub-tank 114 is opened to allow XeF2 gas to flow from the sub-tank 114 into the etching chamber 116 (step (iii)). At this time, the pressure inside the etching chamber 116 and the sub-tank 114 is 146 Pa, which is the total volume of the etching chamber 116 and the sub-tank 114. Etching proceeds in this state (step (iii')), and when most of the XeF2 gas that has flowed into the etching chamber 116 has been consumed by etching, the process moves on to the next step.

[0053] As shown in FIG. 4(iv), the etching chamber 116 is evacuated with a vacuum pump 118 to exhaust SiF4 produced by the etching reaction in the etching chamber 116 (step (iv)).

[0054] Then, as shown at the end of Figure 4, the cycle of steps (ii) to (iv) is repeated a desired number of times in the order of step (ii) → step (iii) → step (iii') → step (iv) → step (ii) → step (iii) → ... to gradually etch the Si substrate with XeF2. Etching is stopped when there is no Si remaining to be etched away.

[0055] Table 2 shows the pressure in each step of the process of Comparative Example 1. [Table 2]

[0056] Si etching rate The Si etching rates of the etching system 10 of Example 1 and the conventional etching system 110 of Comparative Example 1 are compared below. In both the etching systems 10 and 110, the Si substrate S is etched by repeating the cycle of XeF2 inflow, etching, and exhaust, as described above. By using the etching system 10 of the present invention, the number of cycles required to complete the etching and the time required for the cycle are reduced.

[0057] In both etching systems 10 and 110, the etching chambers 16 and 116 have the same volume of 100 mL. Considering the temperature of the XeF2 gas, the present invention may cause a slight temperature rise due to the XeF2 gas being forced into the etching chamber 16 from the variable-volume tank 14. However, such a temperature rise is negligible and has little effect, and is therefore not included in the calculation. In this case, the amount of XeF2 gas in the etching chamber 16 is simply proportional to the pressure. Therefore, the XeF2 gas pressure in the etching chamber 16 or 116 in Example 1 and Comparative Example 1 is 267 Pa in Example 1 and 146 Pa in Comparative Example 1. Thus, 1.8 times as much XeF2 is present in the etching chamber 16 in Example 1 as in Comparative Example 1. The fact that the amount of XeF2 per cycle is greater in Example 1 than in Comparative Example 1 means that the etching time per cycle is longer. However, the greater amount of XeF2 means that a greater amount of Si is etched in one cycle, and the number of cycles required to complete the final etching is reduced. Furthermore, when considering the time required to complete Si etching, the number of evacuation and XeF2 gas inflows is reduced, and including the waiting time for opening and closing the valves in sequence, etching is completed in a short time that is approximately 70% of the time required when using the conventional etching system 110. An example of the specific required time is shown below.

[0058] As shown in FIGS. 2A and 2B, the etching process of Example 1 proceeds in the order of step (a1) → step (a2) → step (b1) → step (b2) → step (c) → step (d) → step (e) (i.e., step (b1) to step (d) are repeated), whereas the etching process of Comparative Example 1 proceeds in the order of step (i) → step (ii) → step (iii) → step (iii') → step (iv) → step (v) (i.e., step (ii) to step (iv) are repeated) (as shown in FIG. 4). Steps (a1) to (b1) and steps (i) to (iii) are performed in both Example 1 and Comparative Example 1 with the variable volume tank 14 or sub-tank 114 remaining at 120 mL, so the required time is the same. Step (b2) is a step performed only in Example 1. The amount of XeF2 in the etching chamber 16 or 116 differs between step (c) and step (iii). Steps (d) and (iv) involve drawing a vacuum inside the etching chamber 16 or 116. Although the amount of XeF2 differs between Example 1 and Comparative Example 1, the vacuum is low, so the same level of vacuum is reached immediately after starting the vacuum, and there is no difference in the time required. The same applies to steps (b1) to (d) in the repeating step (e) and steps (ii) to (iv) in the repeating step (v). The time required for each step in Example 1 and Comparative Example 1 is summarized in Table 3 below.

[0059] [Table 3]

[0060] The number of cycles required to complete the targeted Si etching was 19 in Example 1 and 34 in Comparative Example 1, and the time required to complete etching was 1378 seconds in Example 1 and 1915 seconds in Comparative Example 1. Therefore, it can be seen that Example 1 can complete Si etching in about 70% of the time compared to Comparative Example 1.

Claims

1. XeF ２ a raw material container containing the A source of XeF is connected to the source container and supplied from the source container. ２ a variable capacity tank capable of storing the above in an increase or decrease capacity; A XeF ２ an etching chamber for performing dry etching on a substrate by the etching; a vacuum pump connected to the etching chamber and capable of evacuating the etching chamber and the variable volume tank; a first valve provided between the raw material container and the variable volume tank; a second valve provided between the variable volume tank and the etching chamber; a third valve provided between the etching chamber and the vacuum pump; XeF ２ Dry etching system.

2. a pressure sensor provided in each of the variable volume tank and the etching chamber; a control unit that controls the volume of the variable volume tank and / or the opening and closing of the first valve, the second valve, and the third valve based on information from the pressure sensor; The XeF of claim 1 further comprising: ２ Dry etching system.

3. The XeF according to claim 1 or 2 ２ XeF using a dry etching system ２ 1. A dry etching process comprising: (a) activating the vacuum pump to evacuate the etching chamber and the variable volume tank, thereby evacuating the XeF ２ is sublimated and XeF is placed in the variable volume tank. ２ supplying a gas; (b) XeF in the variable volume tank ２ The gas is supplied to the etching chamber, which has been evacuated, by reducing the volume of the variable volume tank, and XeF ２ performing dry etching by (c) increasing the volume of the variable volume tank, thereby increasing the XeF ２ is sublimated and XeF is placed in the variable volume tank. ２ supplying a gas; (d) after step (b) and before, during, or after step (c), operating the vacuum pump to evacuate the etching chamber; (e) repeating steps (b), (c) and (d) as necessary; Including XeF ２ Dry etching process.

4. The step (a) (a1) closing the first valve and opening the second valve and the third valve, evacuating the etching chamber and the variable volume tank to reduce the pressure inside the variable volume tank, and then (a2) With the first valve open and the second valve closed, XeF ２ is sublimated and XeF is placed in the variable volume tank. ２ Supplying gas The XeF of claim 3 is ２ Dry etching process.

5. The step (b) (b1) With the first valve and the third valve closed and the second valve open, the XeF ２ A gas is supplied to the evacuated etching chamber, during and / or after which (b2) The first valve and the third valve are closed, and the second valve is opened, and the volume of the volume-variable tank is decreased to obtain XeF ２ supplying a gas to the etching chamber; The XeF of claim 3 is ２ Dry etching process.

6. the step (c) is performed by increasing the volume of the variable volume tank while the first valve is open and the second valve and the third valve are closed, the dry etching is continued in the etching chamber during the step (c), and 4. The XeF of claim 3, wherein the evacuation in step (d) is performed after step (c). ２ Dry etching process.

7. the step (c) is carried out by increasing the volume of the variable volume tank while opening the first valve and closing the second valve; and 4. The XeF of claim 3, wherein the evacuation in step (d) is performed before or during step (c). ２ Dry etching process.

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