Plasma treatment method

Abstract

The present invention is a plasma processing method that provides a method that can build a self-limited process with excellent mass producibility in a cycle etching method that repeats an adsorption step for forming a reaction layer on the surface of a wafer to be etched and a desorption step for removing the formed reaction layer using a noble gas in a metastable state, characterized by having the adsorption step for forming the reaction layer on the film to be etched using plasma generated using reactive gas, and the desorption step for removing the reaction layer using the noble gas in a metastable state generated using plasma, the adsorption step and the desorption step being repeated, and the pressure in the adsorption step being higher than the pressure in the desorption step.

Description

[Technical Field]

[0001] The present invention relates to a highly accurate plasma processing method that is excellent in mass productivity. [Background technology]

[0002] In semiconductor devices, the demand for lower power consumption and increased memory capacity is driving further miniaturization and the trend toward three-dimensional device structures. In the manufacture of three-dimensional devices, because the structures are three-dimensional and complex, "isotropic etching," which allows etching in the lateral direction as well as the conventional "vertical etching," is now widely used.

[0003] Conventionally, wet processing using chemicals has been considered for isotropic etching. However, with the progress of miniaturization, the problem of pattern collapse due to the surface tension of the chemicals has become apparent. Therefore, studies are underway to replace the conventional wet processing with dry processing that does not use chemicals.

[0004] A known technique for performing isotropic etching with high precision using dry processing is a cycle etching method that repeats an adsorption step in which a reactive layer is formed on the surface of a wafer to be etched and a desorption step in which the formed reactive layer is removed. Patent Document 1 (Patent Document 1) reports a cycle etching method that includes an adsorption step in which a reactive gas is supplied into a processing chamber to form a reactive layer on the surface of the wafer to be etched, and a desorption step in which the etchant gas is exhausted and replaced with a rare gas, and the rare gas is then converted into plasma to generate a metastable rare gas, and the wafer to be etched is then irradiated with the generated metastable rare gas to remove the reactive layer. Patent Document 2 (Patent Document 2) also discloses a method that uses two different beam sources, a molecular beam source formed in plasma and a rare gas metastable excited species beam source, to perform an adsorption step in which a reactive layer is formed by irradiating the molecular beam source with reactive gas or radicals, and a desorption step in which the reactive layer is removed by irradiating the rare gas with a high-energy metastable excited species beam source. [Prior art documents]

Patent Document

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In order to use such a cycle etching method for high-precision isotropic etching required for a three-dimensional device structure, in the adsorption step and the desorption step, it is required to selectively process only the target film in a self-limiting process. That is, in the adsorption step, a process in which the thickness of the reaction layer formed on the target material to be etched saturates at a constant thickness, and in the desorption step, only the reaction layer formed on the target material to be etched volatilizes, and the etching of the material to be etched under the reaction layer and other materials for which a selectivity is desired does not proceed.

[0007] In addition, in order to apply it to mass production of semiconductors, it is necessary to construct a cycle etching method with excellent mass productivity. That is, it is required that an etching amount of several nm to several tens of nm, which is the target, can be realized in a short-time process, that the generation of foreign substances in the chamber is suppressed, and a stable etching amount can be obtained regardless of the number of cycles or the number of wafers processed.

[0008] However, when the process of supplying the reactive gas described in Patent Document 1 and Patent Document 2 is used in the adsorption step, the thickness of the reaction layer formed on the surface is very thin, and it is difficult to obtain a sufficient etching amount per cycle.

[0009] The cycle etching of the adsorption step using CHF3 / O2 gas as the reactive gas and the desorption step supplying metastable Ar gas was repeated 50 cycles to attempt etching of the SiN film. However, the change in the etching amount after 50 cycles was less than 0.1 nm (less than 0.02 nm / cycle) below the measurement limit, and a sufficient etching amount at the level of several nm / cycle suitable for mass production could not be confirmed.

[0010] As a method for increasing the thickness of the reaction layer, a method of supplying radicals rich in reactivity can be mentioned. In particular, a method of generating and supplying radicals by plasmaizing the reactive gas is widely known.

[0011] However, in the method using two beam sources for forming the reaction layer and supplying the metastable noble gas as described in Patent Document 2, when radicals are supplied using a carbon-containing gas such as CHF3 gas used for cycle etching of the SiN film to form the reaction layer, that is, a gas that generates deposits, the deposits gradually adhere inside the molecular beam source, and the problem is that the etching amount fluctuates due to an increase in the number of cycles or the number of wafers processed. Also, the conditions for establishing a self-limiting process for realizing high-precision etching required in three-dimensional device manufacturing have not been clarified.

[0012] The present invention solves the above-described problems of the prior art and provides a method capable of constructing a self-limiting process with excellent mass productivity in a cycle etching method that repeats an adsorption step of forming a reaction layer on the surface of the wafer to be etched and a desorption step of removing the formed reaction layer using a metastable noble gas.

Means for Solving the Problems

[0013] In order to solve the above problems, the present invention provides a plasma processing method comprising an adsorption step in which a reactive layer is formed on a film to be etched by plasma generated using a reactive gas, and a desorption step in which the reactive layer is removed by using a metastable rare gas generated by the plasma, wherein the adsorption step and the desorption step are repeated, and the pressure in the adsorption step is higher than the pressure in the desorption step.

[0014] In addition, in order to solve the above-mentioned problems, the present invention provides a plasma processing method comprising an adsorption step in which a reactive layer is formed on a film to be etched by plasma generated using a reactive gas, and a desorption step in which the reactive layer is removed by using a metastable rare gas generated by the plasma, wherein the adsorption step and the desorption step are repeated, and the high frequency power for generating the plasma in the adsorption step is smaller than the high frequency power for generating the plasma in the desorption step.

[0015] Furthermore, in order to solve the above-mentioned problems, the present invention provides a plasma processing method characterized in that the adsorption process and the desorption process are performed using plasma generated in a first space above the same separation plate, and the reactive gas and the rare gas are replaced while maintaining the generation of plasma in the adsorption process and the desorption process. [Effects of the Invention]

[0016] According to the present invention, highly reactive radicals can be irradiated onto a wafer to be etched, and the surface reaction caused by the radicals can be promoted, thereby increasing the thickness of the reaction layer to a level of several nm / cycle, which is suitable for mass production.

[0017] Furthermore, if the reactive gas is excessively dissociated in the plasma, etching will proceed continuously due to the excessively dissociated reactive gas, making it impossible to realize a self-limited process. However, by making the pressure in the adsorption step higher than that in the desorption step, or by making the effective high-frequency power for generating plasma in the adsorption step lower than the effective high-frequency power for generating plasma in the desorption step, it becomes possible to form a reaction layer in which excessive dissociation of the reactive gas is suppressed, and a self-limited cycle etch process can be realized.

[0018] Furthermore, by performing the adsorption and desorption processes using plasma generated in the same first space, deposits that adhere to the inner wall of the first space during the adsorption process can be removed in the desorption process, realizing a stable process with excellent mass productivity that suppresses the adhesion of deposits per cycle.In addition, by replacing the reactive gas with a rare gas while maintaining plasma generation between the adsorption and desorption processes, it is possible to omit the process of evacuating the reactive gas that filled the vacuum chamber once after the adsorption process, introducing a rare gas again to replace it, and then generating plasma, thereby realizing a short-time process with excellent mass productivity that reduces the process time per cycle. [Brief explanation of the drawings]

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

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Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0020] The present invention relates to a plasma treatment method for performing an etching process in a dry etching apparatus provided with a vacuum chamber in which a processing gas is supplied to the inside under reduced pressure, a separation plate that divides the vacuum chamber into an upper first space and a lower second space, and a wafer stage on which a wafer to be processed is placed on the upper surface and installed in the second space. The method includes an adsorption step of forming a reaction layer on the wafer to be etched by plasmaizing a reactive gas in the upper first space, and a desorption step of removing the reaction layer by plasmaizing an inert gas in the upper first space, and performing the steps in order. The pressure in the vacuum chamber in the adsorption step is higher than the pressure in the vacuum chamber in the desorption step.

[0021] The present invention also relates to a plasma processing method for performing an etching process in a dry etching apparatus including a vacuum chamber in which a processing gas is supplied to a depressurized inside, a separation plate that divides the vacuum chamber into an upper first space and a lower second space, and a wafer stage disposed in the second space on which a wafer to be processed is placed on an upper surface. The method includes an adsorption step of forming a reaction layer on a wafer to be etched by plasmaizing a reactive gas in the upper first space, and a desorption step of removing the reaction layer by plasmaizing an inert gas in the upper first space, and the effective high-frequency power for generating plasma in the adsorption step is lower than the effective high-frequency power for generating plasma in the desorption step.

[0022] Furthermore, the present invention relates to a plasma processing method for performing an etching process in a dry etching apparatus including a vacuum chamber in which a processing gas is supplied to a depressurized inside, a separation plate that divides the vacuum chamber into an upper first space and a lower second space, and a wafer stage disposed in the second space on which a wafer to be processed is placed on an upper surface. The method includes an adsorption step of forming a reaction layer on a wafer to be etched by plasmaizing a reactive gas in the upper first space, and a desorption step of removing the reaction layer by plasmaizing an inert gas in the upper first space, and the adsorption step and the desorption step are repeatedly and continuously performed while maintaining plasma generation between the desorption step and the adsorption step or between the adsorption step and the desorption step, and a reactive gas and an inert gas are replaced while maintaining plasma generation.

[0023] In the plasma processing method, a deposition reactive gas containing carbon, boron, or the like is used as the reactive gas, and Ar gas is used as the inert gas.

[0024] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Embodiment

[0025] A first embodiment for carrying out the present invention will be described with reference to FIGS. 1, 2, and 3. Fig. 1 shows a typical apparatus structure for realizing this embodiment, which uses electron cyclotron resonance as the plasma source, Fig. 2 is a flowchart for cycle etching using this embodiment, and Fig. 3 is a time sequence diagram for step 208 in Fig. 2. Note that this embodiment describes a plasma source using electron cyclotron resonance, but this method is not limited to plasma sources using electron cyclotron resonance, and is applicable.

[0026] 1, a separation plate 1002 is installed inside a vacuum vessel 1001, and the separation plate 1002 separates the inside of the vacuum vessel into an upper first space 1003 and a lower second space 1004. The second space 1004 is equipped with a wafer stage 1006 for placing a wafer 1005 to be etched, and the wafer 1005 to be etched can be processed by irradiating it with plasma or radicals generated in the plasma.

[0027] To generate plasma, high frequency power 1007 is introduced into the vacuum vessel 1001 from above the device via a waveguide 1008 and a cavity resonator 1009. Here, microwaves with a frequency of 300 MHz to 300 GHz are used as the high frequency power 1007 to generate plasma.

[0028] Furthermore, a process gas 1010 is introduced into the vacuum chamber by a predetermined method and is exhausted from 1011 at the bottom of the vacuum chamber. At this time, the flow rate and exhaust speed of the process gas 1010 are appropriately monitored, and by controlling the flow rate and exhaust speed of the process gas in accordance with the monitored values, it is possible to maintain the inside of the vacuum chamber at any desired pressure.

[0029] The process gas introduced into the vacuum chamber generates and maintains plasma at a position where electron cyclotron resonance occurs due to the high frequency power 1007 and the static magnetic field generated by the static magnetic field coil 1012. In this device configuration, the generation position of the plasma that causes electron cyclotron resonance can be changed by changing the coil current value of the static magnetic field coil 1012, and when the generation position is set within the first space 1003, neutral radicals formed in the plasma are preferentially supplied to the wafer to be etched.

[0030] On the other hand, when the generation position is set in the second space 1004, the plasma is directly irradiated onto the wafer to be etched, making it possible to perform processing using the ions and radicals in the plasma. In other words, the separation plate 1002 can separate the plasma generation chamber into an upper plasma generation chamber formed by the first space 1003 and a lower plasma generation chamber formed by the second space 1004.

[0031] The wafer stage 1006 has a temperature control function, and can be controlled to any temperature. The wafer stage 1006 also has the function of fixing the wafer to be etched on the wafer stage, and the function of supplying a thermally conductive gas between the wafer to be etched 1005 and the wafer stage 1006, maintaining a pressure between the two at, for example, 0.1 kPa to 10 kPa. This thermally conductive gas improves the thermal conductivity between the wafer stage and the wafer to be etched, allowing the temperature of the wafer to be etched to be efficiently controlled even inside a vacuum chamber.

[0032] To fix the wafer to be etched to the wafer stage, a mechanical chuck that mechanically holds down the edge of the wafer to be etched can be used, but when the wafer is fixed, wear of the holding mechanism and the wafer can cause foreign particles to be generated, which can be an issue during mass production. Therefore, as shown in Figure 1, it is desirable to install a first electrode 1013 and a second electrode 1014 to which a DC voltage is applied inside the wafer stage 1006, and apply opposite positive and negative voltages to each electrode to generate Johnsen-Rahbek force or Coulomb force to electrically fix the wafer.

[0033] 1, a high-frequency power supply with a frequency of, for example, 10 kHz to 100 MHz may be connected to the wafer stage in order to actively attract ions formed in the plasma to the wafer to be etched. In this way, when plasma is generated in the second space 1004, high-frequency power can be supplied from the high-frequency power supply to the wafer stage, thereby realizing reactive ion etching using the ions and radicals in the plasma.

[0034] In Figure 1, separation plate 1002 is installed to supply only radicals to the wafer to be etched. The separation plate may be constructed using a metal material such as aluminum, titanium, or stainless steel, and electrically connected to a ground or a DC or AC power supply to electrically block positively charged ions and negatively charged electrons generated in the plasma, thereby supplying only radicals generated in the plasma to the wafer. However, in this case, the surface of the metal material is exposed to the plasma, causing the metal material to scatter, and metal contamination can deteriorate the electrical properties of the processed wafer, posing a problem during mass production.

[0035] One possible method for suppressing metal contamination is to coat the conductive material with a Si-containing oxide film, a Y-containing oxide film, or an Al-containing oxide film, and use a structure that prevents the metal from coming into direct contact with the plasma. However, coating increases production costs, and if part of the coating film disappears due to long-term processing, metal contamination may occur.

[0036] Therefore, it is desirable that the structure of the separator 1002 be made only of a dielectric material such as a Si-containing oxide film, a Y-containing oxide film, or an Al-containing oxide film. In particular, quartz, which is a Si-containing oxide film, does not contain metals such as Y or Al inside, and is therefore a desirable dielectric material for suppressing metal contamination.

[0037] In this case, the separation plate has no effect of electrically shielding the ions and electrons formed in the plasma. However, as shown in FIG. 4, by providing holes in the outer peripheral portion of the separation plate 1002 and generating a divergent magnetic field 4001 with the static magnetic field coil 1012, radicals can be preferentially supplied to the wafer 1005 to be etched. That is, ions with positive charges and electrons with negative charges passing through the holes in the outer peripheral portion are confined by the divergent magnetic field and diffuse in the direction of the chamber wall 4002. Therefore, only electrically neutral radicals that are not confined by the divergent magnetic field can reach the wafer 1005 to be etched installed at the center of the chamber.

[0038] Note that in FIG. 1, only one separation plate is used, but a structure combining a plurality of separation plates may also be used. However, among the plurality of separation plates, it is desirable that one of them has holes provided in the outer peripheral portion of the separation plate, that is, outside half of the radius of the separation plate. Also, it is sufficient that there is a gap between the outside of the separation plate and the chamber wall, and the structure and area of the holes are not particularly limited.

[0039] Next, with reference to the flowchart of FIG. 2 using the apparatus of FIG. 1, a detailed example of the cycle etching method including a step of forming a reaction layer by radicals generated from a reactive gas and a step of removing the reaction layer using metastable rare gas generated using a rare gas will be described.

[0040] This example describes a discharge method using electron cyclotron resonance with a high-frequency power of 2.45 GHz for generating the plasma in FIG. 1. However, the plasma source is not particularly limited as long as it is a device in which a separation plate is installed in a vacuum chamber and plasma can be generated in the first space above the separation plate. That is, other plasma sources using inductively coupled or capacitively coupled high-frequency power may be used.

[0041] First, as shown in S201 of FIG. 2, the wafer to be etched 1005 is carried onto the wafer stage 1006. When carrying in the wafer, for example, the wafer to be etched 1005 placed on the transfer arm from a transfer chamber held in a vacuum is carried onto the wafer stage 1006, and the wafer to be etched is lifted from the transfer arm by the pusher pins by raising three or more pusher pins (not shown in the following figure) provided in the wafer stage.

[0042] After that, the transfer arm is retracted into the transfer chamber, and the pusher pins holding the wafer to be etched are lowered into the wafer stage, so that the wafer to be etched can be placed on the wafer stage.

[0043] In this method, in order to suppress the generation of foreign matter due to wear between the back surface of the wafer and the pusher pins, it is desirable to select the optimal operating speed, tip shape, and material of the pusher pins.

[0044] Next, as shown in S202 of FIG. 2, by applying DC voltages of opposite polarities (positive and negative) to the first electrode 1013 and the second electrode 1014 installed in the wafer stage, a Johnson-Rahbek force or a Coulomb force is generated to electrically fix the wafer to be etched 1005 on the wafer stage 1006. It is desirable to apply the same voltage for the positive and negative voltages, but either a positive voltage or a negative voltage may be applied to the first electrode 1013.

[0045] As a result, until the electrical fixation is released, the wafer to be etched is fixed on the wafer stage, and the generation of foreign matter due to wear between the wafer to be etched and the wafer stage can be suppressed by the movement of the wafer to be etched due to pressure fluctuations during the process.

[0046] Next, as shown in S203 of FIG. 2, a heat conductive gas is introduced between the wafer to be etched and the wafer stage. By this heat conductive gas, the heat conductivity between the wafer stage and the wafer to be etched is improved, and even inside the vacuum chamber, by using the temperature control function provided in the wafer stage, the wafer to be etched can be efficiently temperature-controlled at the set temperature.

[0047] It is desirable to use He, which has good heat conductivity and is stable, as the heat conductive gas, but other gases such as Ar or N2 may be used as an alternative. Also, it is desirable to maintain the pressure between the wafer to be etched and the wafer stage at 0.1 kPa to 10 kPa, and it is desirable that the wafer to be etched is electrically fixed firmly by the DC voltage applied to the first electrode 1013 and the second electrode 1014 so that the wafer to be etched does not move due to this pressure.

[0048] Next, as shown in S204 of FIG. 2, a reactive gas at a predetermined flow rate is introduced, high-frequency power 1007 is supplied from the waveguide 1008, and the coil current value of the static magnetic field coil 1012 is set so as to cause electron cyclotron resonance in the upper first space 1003. Thereby, plasma is generated in the upper first space 1003. In this step, it is desirable to control the exhaust speed of the gas from 1011 so that the inside of the vacuum chamber 1001 is maintained at the set pressure.

[0049] Also, by generating a divergent magnetic field with the static magnetic field coil 1012, radicals formed in the plasma using the reactive gas preferentially reach the wafer to be etched. Therefore, an adsorption step of forming a reaction layer with the desired film thickness on the wafer to be etched by the radicals can be realized.

[0050] In addition, when only the reactive gas is introduced without generating plasma, the thickness of the formed reaction layer is very thin, and it is difficult to obtain a sufficient etching amount per cycle.

[0051] Also, when plasma is generated in the lower second space 1004 and the plasma is directly irradiated onto the wafer to be etched, a self-bias is generated between the plasma and the wafer to be etched. Therefore, the ions generated in the plasma are accelerated by the self-bias and are incident perpendicularly to the wafer to be etched.

[0052] As a result, the reaction layer is thickly formed in the vertical direction, and isotropic etching that etches the vertical and horizontal directions uniformly cannot be achieved. Therefore, it is desirable to form the reaction layer by a process mainly composed of radicals generated by a reactive gas. Specifically, it is desirable to construct a process in which a reaction layer is formed by irradiating radicals that are 10 times or more the irradiation amount of the ions irradiated onto the wafer to be etched.

[0053] Also, when radicals are formed using a reactive gas, if excessive dissociation progresses in the plasma, the etching of the material to be etched continuously proceeds due to the excessively dissociated reactive gas, and a self-limited process cannot be established.

[0054] In order to suppress excessive dissociation, it is desirable to set the pressure inside the vacuum chamber in the present adsorption step to be higher than the pressure inside the vacuum chamber in the desorption step. Specifically, it is desirable to select an arbitrary pressure so that the pressure inside the vacuum chamber in the adsorption step ranges from 1.0 Pa or more and 500 Pa or less, the pressure inside the vacuum chamber in the desorption step ranges from 0.05 Pa or more and 50 Pa or less, and the pressure inside the vacuum chamber in the adsorption step is higher than the pressure inside the vacuum chamber in the desorption step.

[0055] More specifically, it is desirable to select an arbitrary pressure so that the pressure inside the vacuum chamber in the adsorption step ranges from 5.0 Pa or more and 50 Pa or less, the pressure inside the vacuum chamber in the desorption step ranges from 0.1 Pa or more and 10 Pa or less, and the pressure inside the vacuum chamber in the adsorption step is higher than the pressure inside the vacuum chamber in the desorption step.

[0056] In addition, in order to suppress excessive dissociation of plasma using a reactive gas, it is also effective to set the effective high-frequency power for generating plasma lower than the effective high-frequency power for generating plasma in the desorption process.

[0057] Here, effective RF power means the total amount of power input per unit time. For example, when using pulse discharge in which the RF power is repeatedly turned on and off in a cycle of 0.0001 to 0.01 seconds, the effective RF power is calculated by multiplying the RF power by the duty ratio, which is the ratio of the RF power ON time per cycle.

[0058] In other words, when a high-frequency power of 1000 W is input and the duty ratio is set to 20%, the effective high-frequency power is 200 W. Therefore, when the same high-frequency power is set for the adsorption process and the desorption process, by setting the duty ratio in the adsorption process lower than that in the desorption process, it is possible to achieve a process in which the effective high-frequency power in the adsorption process is lower than the effective high-frequency power in the desorption process.

[0059] 2, the introduction of reactive gas into the vacuum chamber is stopped, and a rare gas is introduced at a predetermined flow rate. Then, high-frequency power is supplied from 1007, and the coil current value of static magnetic field coil 1012 is set so as to cause electron cyclotron resonance in upper first space 1003. As a result, plasma is generated in upper first space 1003.

[0060] In this step, it is desirable to control the exhaust speed of the gas from 1011 so that the inside of the vacuum vessel 1001 is maintained at a set pressure.

[0061] Furthermore, by generating a diverging magnetic field with the static magnetic field coil 1012, radicals formed in the plasma using rare gas, especially rare gas in a metastable state with a long life, reach the wafer to be etched preferentially.

[0062] The metastable rare gas is highly reactive and can easily desorb the reaction layer when it collides with the reaction layer generated in the step of S204. It is desirable to use He, Ne, Ar, or Xe gas as the rare gas for generating the metastable state. In particular, Ar gas is low-cost and suitable for mass production among rare gases, and has a long metastable state lifetime. Therefore, it is desirable to generate plasma using Ar gas.

[0063] In addition, when plasma is generated in the second space 1004 below and the plasma is directly irradiated onto the wafer to be etched, a self-bias is generated between the plasma and the wafer to be etched, and the Ar ions generated in the plasma are accelerated by the self-bias and incident perpendicularly to the wafer to be etched.

[0064] Therefore, the film for which a selectivity is desired (the film that is not desired to be etched) is also processed in the same way, resulting in a poor selectivity. Therefore, it is desirable to desorb the reaction layer by a process mainly using the metastable rare gas. Specifically, it is desirable that the reaction layer is desorbed by irradiating the metastable rare gas in an amount 10 times or more the irradiation amount of the ions irradiated onto the wafer to be etched.

[0065] In addition, although the introduction of the reactive gas is stopped between the step of S204 and the step of S205, and a rare gas with a predetermined flow rate is introduced, if the target etching amount can be achieved in the adsorption step of forming the reaction layer and the desorption step of S205 for removing the reaction layer, after the step of S204 is completed, it is desirable to change the gas species and the high-frequency power introduced into the vacuum chamber while generating and maintaining the plasma to execute the step of S205.

[0066] Thereby, the step of evacuating the reactive gas that once filled the vacuum chamber after the adsorption step, introducing the rare gas again for replacement, and then generating plasma can be omitted, and a short-time process with excellent mass productivity that reduces the process time per cycle can be realized.

[0067] In addition, deposits may be formed on the inner wall of the first space 1003 by the plasma formed by the reactive gas in the adsorption step of S204. However, by performing the desorption step of S205 that generates plasma using a noble gas in the same first space 1003 as the adsorption step of S204, the deposits can be removed. This is because inside the first space 1003, the ions formed in the plasma collide with the inner wall of the first space 1003 due to self-bias, and the deposits can be removed by sputtering reaction.

[0068] In the process of accumulating deposits inside the first space 1003, with the increase in the number of cycles or the number of wafers processed, the amount of deposits increases and the state of the plasma changes. Therefore, the process variation is large, and a stable process suitable for mass production cannot be realized.

[0069] However, by performing the adsorption step of S204 and the desorption step of S205 using the plasma generated in the same first space 1003, it is possible to remove the deposits adhering to the inner wall of the first space 1003 in the adsorption step in the desorption step, and a stable process rich in mass productivity with suppressed deposition of deposits per cycle can be realized.

[0070] In this step, it is only necessary for the metastable noble gas to reach the wafer. For example, a mixed gas of two or more noble gases such as a mixture of He and Ar may be plasmaized to generate a metastable noble gas.

[0071] In addition, in order to suppress the etching of other materials for which a selectivity is desired, a mixed gas obtained by mixing a reactive gas such as an oxygen or nitrogen mixed gas such as O2, CO2, or N2 with a noble gas is plasmaized to generate a mixture in which radicals generated from the reactive gas are mixed with the metastable noble gas, which may be used in the desorption step of S205. However, in order to actively use the metastable state of the noble gas, it is desirable that the content of the noble gas in the mixed gas be 50% or more.

[0072] Next, as shown in S206 of FIG. 2, the introduction of the noble gas into the vacuum chamber is stopped.

[0073] Next, step S204 of forming a reactive layer by radicals generated by a reactive gas and step S205 of removing the reactive layer by a metastable rare gas generated by using a rare gas are repeated a predetermined number of times, N, as shown in S207 of Fig. 2. Note that if the target etching is achieved in the first step S205, cycle etching may not be performed and N may be set to 1.

[0074] When repeating N times, the introduction of the rare gas is stopped in step S206, and the process returns to step S204 to introduce the reactive gas at a predetermined flow rate. However, if the predetermined process can be realized through the desorption step S205 and the adsorption step S204, it is desirable to change the type of gas and high-frequency power introduced into the vacuum chamber and execute step S204 after step S205 is completed, while generating and maintaining the plasma.

[0075] This makes it possible to omit the step of exhausting the rare gas that filled the vacuum chamber after the desorption step of S205, then replacing it with a reactive gas and generating plasma to perform step S204, thereby achieving a short process that is excellent for mass productivity by reducing the process time per cycle.

[0076] The time sequence diagram in Figure 3 shows a typical example of the changes in (a) the reactive gas flow rate setting, (b) the rare gas flow rate setting, (c) the pressure setting in the vacuum chamber, and (d) the effective high-frequency power setting for generating plasma when step S207 in Figure 2 is repeated N=3 times.

[0077] This time sequence shows a sequence in which an adsorption process A (S204) in which a reactive layer is formed by radicals generated by reactive gas 311 and a desorption process B (S205) in which the reactive layer is removed by using a metastable rare gas generated by using rare gas 321 are repeated three times.

[0078] As described above, in order to suppress over-dissociation in the adsorption step A (S204) and construct a self-limiting process, it is desirable to make the pressure 331 inside the vacuum chamber in the adsorption step A (S204) higher than the pressure 332 inside the vacuum chamber in the desorption step B (S205). Or, in order to suppress over-dissociation in the adsorption step A and construct a self-limiting process, it is desirable to make the set value 341 of the effective high-frequency power for generating plasma in the adsorption step A lower than the set value 342 of the effective high-frequency power for generating plasma in the desorption step B.

[0079] In FIG. 3, the pressure 331 inside the vacuum chamber in the adsorption step A (corresponding to S204) is set higher than the pressure 332 inside the vacuum chamber in the desorption step B (corresponding to S205), and the set value 341 of the effective high-frequency power for generating plasma in the adsorption step A is made lower than the set value 342 of the effective high-frequency power for generating plasma in the desorption step B. However, if a self-limiting process can be constructed, only one of them needs to be satisfied.

[0080] Furthermore, by performing the adsorption step and the desorption step using the plasma generated in the same first space, it is possible to remove the deposits adhering to the inner wall of the first space in the adsorption step during the desorption step, and a stable process rich in productivity with suppressed deposition of deposits per cycle can be realized.

[0081] In addition, by setting the effective high-frequency power for generating and maintaining plasma between the adsorption step and the desorption step to a value greater than 0, it is possible to replace the reactive gas and the rare gas while generating and maintaining the plasma, and a short-time process with excellent productivity with reduced process time per cycle can be realized.

[0082] Next, as shown in S208 of FIG. 2, plasma is generated in the lower second space 1004, and after stopping the introduction of the heat conduction gas between the wafer to be etched and the wafer stage, the electrical fixation between the wafer to be etched 1005 and the wafer stage 1006 is released. Here, if the first electrode 1013 and the second electrode 1014 have the same area and the applied voltage is turned off at the same timing, in principle, the electrical fixation can be released even without plasma.

[0083] However, due to mechanical errors, the areas of the two may be slightly different, or a slight deviation may occur in the timing of turning off the applied voltage, resulting in charge accumulation on the wafer to be etched and the wafer stage. In this case, the electrical fixation is not completely released, and in rare cases, the wafer may be damaged when the wafer is unloaded, which becomes an issue during mass production.

[0084] Therefore, it is desirable to generate plasma in the second space 1004 directly above the wafer to be etched and form an electrical path with electrons and ions in the plasma to discharge the charge accumulated on the wafer to be etched and the wafer stage. That is, it is desirable to turn off the DC voltage applied to the first electrode 1013 and the second electrode 1014 while plasma is generated in the second space 1004. With such a configuration, damage to the wafer when the wafer is unloaded can be suppressed, and a process suitable for mass production can be realized.

[0085] In addition, when turning off the DC voltage applied to the first electrode 1013 and the second electrode 1014, in order to more easily remove the accumulated charge, the voltage values applied to both can be changed, or the pusher pins can be moved up and down while plasma is generated in the second space.

[0086] Furthermore, it is desirable to select a gas that does not significantly affect the shape of the wafer to be etched, such as a noble gas, when generating plasma in this process. Also, by skipping the S206 step while leaving the state after the immediately preceding S205 step, plasma may be generated in the second space using the noble gas used in the immediately preceding S205 step. By doing so, the process of exhausting the noble gas once filled in the vacuum chamber and introducing the noble gas again can be omitted, and the process time can be shortened.

[0087] Furthermore, if the etching shape changes significantly by generating plasma in the second space 1004, the DC voltages applied to the first electrode 1013 and the second electrode 1014 may be turned off without generating plasma in the second space. However, in this case, in order to suppress wafer breakage, it is necessary to particularly consider the lifting and lowering speed of the pusher pins and select materials for the pusher pins and the wafer stage that are less likely to accumulate electric charges.

[0088] Next, as shown in S209 of FIG. 2, the plasma is extinguished and all the gases introduced into the vacuum chamber are stopped. Then, as shown in S210 of FIG. 2, the wafer to be etched 1005 is unloaded from above the wafer stage 1006.

[0089] When unloading the wafer, for example, by raising three or more pusher pins (not shown) provided in the wafer stage 1006, the wafer to be etched 1005 is lifted and loaded from the transfer chamber into the transfer arm. At this time, in order to suppress contact between the wafer to be etched 1005 and the transfer arm, the wafer to be etched 1005 needs to be lifted to a higher position than the loaded transfer arm. Then, by lowering the pusher pins into the wafer stage, the wafer to be etched can be held by the transfer arm. Then, by retracting the transfer arm into the transfer chamber, the wafer to be etched can be unloaded from the vacuum chamber 1001.

[0090] In this method, in order to suppress the generation of foreign matter due to wear between the back surface of the wafer and the pusher pin, it is desirable to select the optimal operating speed, tip shape, and material of the pusher pin.

[0091] In the sequence of FIG. 2, the temperature of the wafer stage 1006 has not been changed since the step of S202, but if necessary, it may be set to another temperature in the adsorption step of S204 and the desorption step of S205. However, since the process time increases due to the change in the temperature of the wafer stage 1006, it is desirable not to change the temperature of the wafer stage 1006 after the step of S202. Specifically, it is desirable to set an arbitrary temperature within the range of -50°C to +150°C for the temperature of the wafer stage 1006 and maintain it in the adsorption step and the desorption step.

[0092] Here, in the sequence diagram shown in FIG. 2, the wafer to be etched 1005 is described only in the process of isotropic etching, but it is also possible to perform anisotropic etching before and after isotropically etching the target film formed on the wafer to be etched 1005. In this case, it is desirable to generate plasma in the second space 1004 below the separation plate 1002 and perform anisotropic etching using the ions and radicals generated in the plasma.

[0093] Also, although not described in the sequence diagram of FIG. 2, when continuously processing different wafers to be etched, it is also possible to insert a cleaning sequence using plasma periodically between the wafer to be etched processed first and the wafer to be etched processed next. In this cleaning sequence, it is desirable to use a sequence for removing reaction products from the etched material adhering to the inner wall of the vacuum chamber during etching and a sequence for depositing deposits to keep the inner wall of the vacuum chamber in a certain state.

[0094] It is desirable to generate plasma in the second space below the separation plate where reaction products from the etched wafer are likely to adhere during the cleaning sequence. However, since reaction products from the etched wafer may also adhere to the first space above the separation plate, it is desirable to perform a cleaning sequence in which plasma is generated in the first and second spaces in order.

[0095] When performing this cleaning sequence, a cleaning wafer may be placed on the wafer stage. However, since the cost of the cleaning wafer is high, it is desirable to perform the cleaning sequence without placing the cleaning wafer on the wafer stage.

Example

[0096] Next, a second example using the present invention will be described. This example is the result of examining a cycle etch process for isotropically processing SiN using CHF3 / O2 gas as the reactive gas, Ar gas as the inert gas, and SiN as the material to be etched. In this example, the results of using a carbon-containing gas with deposition properties as the reactive gas are described, but the same process can be realized for other deposition gases, such as boron-containing gases and Si-containing gases.

[0097] Figure 5 is a graph showing the change 501 in the etching amount of the SiN film per cycle with respect to the process time of the desorption step of S205 when the cycle etch of S204 to S206 is repeated N = 6 times according to the sequence of Figure 2.

[0098] In this experiment, the pressure in the vacuum chamber during the adsorption step of S204 is set higher than the pressure in the vacuum chamber during the desorption step of S205, and the effective high-frequency power during the desorption step of S205 is set lower than that during the adsorption step of S204. Specifically, the pressure in the vacuum chamber 1001 is set to 8.0 Pa during the adsorption step of S204 and 0.2 Pa during the desorption step of S205.

[0099] In addition, the effective high-frequency power in the adsorption process of S204 was reduced to 40 W, and the desorption process of S205 was set to 600 W. In the adsorption process of S204, pulsed discharge was used to reduce the effective high-frequency power.

[0100] From the graph in Fig. 5, it can be seen that even if the process time of the desorption process of S205 is increased to 120 seconds or more, the etching amount does not increase, indicating that a self-limiting process with an etching amount saturated at 2.7 nm / cycle has been constructed. Note that the etching amount per cycle can be adjusted to any value depending on the process conditions, i.e., the temperature and pressure of the wafer stage and the gas flow rate ratio of CHF3 and O2.

[0101] Fig. 6 is a graph showing the change 601 in the etching amount of the SiN film per cycle with respect to the process time of the desorption process of S205 when, in the same process as Fig. 5, only the pressure in the adsorption process of S204 is changed to 0.2 Pa, the same as in the desorption process of S205.

[0102] From the graph in Fig. 6, it can be seen that the etching amount per cycle increases in proportion to the processing time, indicating that a self-limiting process has not been constructed. Also, when the processing pressure was further reduced, a self-limiting process could not be constructed.

[0103] This is because when the pressure in the vacuum chamber is lower than that in the desorption process of S205, the reactive gas dissociates excessively and F radicals are generated. These F radicals promote the etching of the SiN film, the material to be etched, and the etching proceeds continuously.

[0104] Similarly, as a method for promoting the dissociation of F radicals, there is a method of increasing the effective high-frequency power. When the effective high-frequency power in the adsorption process of S204 is increased to 600 W or more, the same as in the desorption process of S205, a self-limiting process could not be constructed.

[0105] This indicates that a self-limited process can be constructed when the pressure in the adsorption step S204 is higher than that in the desorption step S205, or when the effective high-frequency power in the adsorption step S204 is lower than that in the desorption step S205.

[0106] FIG. 7 shows a change 701 in the SiN etching amount per cycle depending on the ratio of the pressure in the desorption step S205 to the pressure in the adsorption step S204, when the pressure in the desorption step S205 is changed.

[0107] This figure shows that the etching amount per cycle decreases as the pressure ratio between the S205 desorption step and the S204 adsorption step increases, and when the pressure ratio becomes 1, the etching amount is less than 1 nm / cycle, which is necessary for mass production. This shows that by increasing the pressure in the S204 adsorption step compared to the S205 desorption step, it is possible to achieve an etching amount of 1 nm or more / cycle, in other words, the nm-level cycle etching required for mass production.

[0108] Similarly, we evaluated the change in the amount of etching per cycle depending on the ratio of the effective high-frequency power in the desorption process S205 to the effective high-frequency power in the adsorption process S204. As a result, we found that the amount of etching per cycle increased as the effective high-frequency power ratio increased, and that when the effective high-frequency power ratio became 1, it was not possible to achieve a value of less than 1 nm / cycle, i.e., the nm-level cycle etching required for mass production.

[0109] This indicates that etching with a high throughput can be achieved by setting the effective high frequency power in the adsorption step S204 lower than the effective high frequency power in the desorption step S205.

[0110] From the above results, it was found that, in order to construct a self-limited process and to achieve the nm-level cycle etching required for mass production, it is effective to set the pressure in the adsorption step higher than that in the desorption step, or to set the effective high-frequency power in the adsorption step lower than that in the desorption step.

[0111] In some processes where the etching amount of the target film is small, an etching amount of 1 nm / cycle or less may be required. Even in this case, a self-limited process can be constructed. Therefore, it is desirable to construct a process that satisfies the target etching amount by adjusting the temperature, pressure, and gas type from among process conditions that satisfy either of the following conditions: the pressure in the adsorption step S204 is higher than that in the desorption step S205; or the effective high-frequency power in the adsorption step S204 is lower than that in the desorption step S205.

[0112] Figure 8 shows the results of evaluating the thickness of the deposits on the inner wall of the first space 1003 after generating CHF3 / O2 plasma in the first space 1003 above the separation plate 1002 and performing the adsorption process, and after generating CHF3 / O2 plasma and Ar plasma in the first space 1003 above the separation plate 1002 and performing the adsorption process S204 and the desorption process S205.

[0113] As shown in 801 of Figure 8, if only the adsorption step S204 is performed using plasma generated in the first space 1003, deposits will adhere to the inner wall of the vacuum vessel 1001. However, as shown in 802 of Figure 8, by performing the desorption step S205 in which plasma using a rare gas is generated in the same first space 1003 as the adsorption step S204, the deposits can be removed.

[0114] This is because ions formed in the plasma inside the first space 1003 collide with the inner wall of the first space 1003 due to self-bias, and deposits can be removed by a sputtering reaction. In a process in which deposits accumulate inside the first space 1003, the amount of deposits increases and the plasma state changes as the number of cycles or the number of processed wafers increases. This results in large process fluctuations, making it impossible to achieve a stable process suitable for mass production.

[0115] However, by performing the adsorption step of S204 and the desorption step of S205 using the plasma generated in the same first space 1003, it is possible to remove the deposits adhering to the inner wall of the first space in the adsorption step of S204 in the desorption step of S205, and a stable process rich in productivity with suppressed deposition of deposits per cycle can be realized.

[0116] In addition, in this embodiment, although the results of using a carbon-containing gas as the reactive gas used in the adsorption step of S204 are described, the same process can be realized for other deposition gases, such as boron-containing gases and Si-containing gases.

[0117] Also, in this embodiment, quartz, which is an oxide film, is used for the separation plate 1002 and the inner wall of the first space 1003. Thereby, oxygen in the oxide film, which is the inner wall material of the first space 1003, reacts with the carbon-based deposition film, and by promoting the sputtering reaction in the desorption step of S205, the removal efficiency of the deposition film can be improved. Therefore, it is desirable that an oxide film is formed on a part of the surface in contact with the plasma in the first space. Specifically, it is desirable that the oxide film covers 50% or more of the surface area of the first space 1003.

[0118] FIG. 9 shows the results of comparing the amount of SiN etching per cycle 903 when the generation of plasma is interrupted between the adsorption step of S204 and the desorption step of S205 901 and when the plasma is continuously generated between the adsorption step of S204 and the desorption step of S205 902.

[0119] In addition, when the generation of plasma in 901 is interrupted, after the adsorption step of S204, the reactive gas once filled in the vacuum chamber is exhausted, a rare gas is introduced for replacement, and then plasma is generated. Also, after the desorption step of S205, the rare gas once filled in the vacuum chamber is exhausted, and the process of introducing and replacing the reactive gas again and then generating plasma is repeated.

[0120] On the one hand, when the plasma of 902 was generated and maintained, while maintaining the generation and maintenance of the plasma, the introduction of the reactive gas was stopped and the introduction of the rare gas was started. Also, while maintaining the generation and maintenance of the plasma, the process of stopping the introduction of the rare gas and starting the introduction of the reactive gas was repeated.

[0121] As can be seen from FIG. 9, it can be seen that the etching amount 903 of SiN per cycle does not change significantly between the two. From this, by replacing the reactive gas and the rare gas while maintaining the generation and maintenance of the plasma between the adsorption step of S204 and the desorption step of S205, the reactive gas that once filled the vacuum chamber after the adsorption step of S204 is exhausted, and after introducing and replacing the rare gas again, the step of generating the plasma can be omitted, and it can be seen that a short-time process with excellent mass productivity that reduces the process time per cycle can be realized.

[0122] As described above, according to this embodiment, by plasmaizing the reactive gas in the first space 1003 above the separation plate 1002, highly reactive radicals can be irradiated onto the wafer to be etched, and by promoting the surface reaction by the radicals, the thickness of the reaction layer can be increased to the level of several nm / cycle suitable for mass production.

[0123] Also, when the reactive gas is excessively dissociated in the plasma, continuous etching proceeds due to the excessively dissociated reactive gas and a self-limiting process cannot be realized. However, by making the pressure in the adsorption step of S204 higher than that in the desorption step of S205, or by making the effective high-frequency power for generating the plasma in the adsorption step of S204 lower than the effective high-frequency power for generating the plasma in the desorption step of S205, it becomes possible to form a reaction layer that suppresses the excessive dissociation of the reactive gas, and a self-limiting cycle etching process can be realized.

[0124] Furthermore, by performing the adsorption step S204 and the desorption step S205 using plasma generated in the same first space 1003, it is possible to remove deposits that have adhered to the inner wall of the first space during the adsorption step S204 in the desorption step, thereby realizing a stable process suitable for mass production that suppresses the adhesion of deposits per cycle.

[0125] In addition, by replacing the reactive gas with a rare gas while maintaining plasma generation between the adsorption step S204 and the desorption step S205, it is possible to omit the steps of exhausting the reactive gas that filled the vacuum chamber after the adsorption step, then introducing a rare gas again to replace it and then generating plasma, thereby achieving a short process that is excellent for mass productivity by reducing the process time per cycle.

[0126] The present invention is not limited to the above-described embodiments, but includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations. [Explanation of symbols]

[0127] 1001...vacuum vessel, 1002...separator plate, 1003...first space, 1004...second space, 1005...wafer to be etched, 1006...wafer stage, 1007...high frequency power, 1008...waveguide, 1009...cavity resonator, 1010...process gas, 1011...exhaust direction, 1012...static magnetic field coil, 1013...first electrode, 1014...second electrode, 4001...divergent magnetic field

Claims

1. An adsorption step of forming a reaction layer on an etching target film with plasma generated using a reactive gas, and a desorption step of removing the reaction layer using a metastable rare gas generated by plasma, and having repeating the adsorption step and the desorption step, shifting from the adsorption step to the desorption step while maintaining the plasma, or shifting from the desorption step to the adsorption step while maintaining the plasma, and a plasma processing method characterized in that the pressure in the adsorption step is higher than the pressure in the desorption step.

2. An adsorption step of forming a reaction layer on an etching target film with plasma generated using a reactive gas, and a desorption step of removing the reaction layer using a metastable rare gas generated by plasma, and having repeating the adsorption step and the desorption step, the temperature of the sample stage on which the sample having the etching target film is placed in the adsorption step is the same as the temperature of the sample stage in the desorption step, and a plasma processing method characterized in that the pressure in the adsorption step is higher than the pressure in the desorption step.

3. An adsorption step of forming a reaction layer on an etching target film with plasma generated using a reactive gas, and a desorption step of removing the reaction layer using a metastable rare gas generated by plasma, and having repeating the adsorption step and the desorption step, making the pressure in the adsorption step higher than the pressure in the desorption step, the plasma processing apparatus in which the adsorption step and the desorption step are performed includes a processing chamber in which a sample having the etching target film is processed and a dielectric plate is disposed above, a high-frequency power source that supplies microwave high-frequency power for generating plasma through the dielectric plate, a sample stage on which the sample is placed, and a separation plate disposed between the dielectric plate and the sample stage, and a plasma processing method characterized in that the processing chamber is cleaned using the plasma generated between the separation plate and the sample stage.

4. An adsorption step of forming a reaction layer on an etching target film with plasma generated using a reactive gas, and a desorption step of removing the reaction layer using a metastable rare gas generated by plasma, and having repeating the adsorption step and the desorption step, shifting from the adsorption step to the desorption step while maintaining the plasma, or shifting from the desorption step to the adsorption step while maintaining the plasma, A plasma processing method characterized in that the high-frequency power for generating plasma in the adsorption step is smaller than the high-frequency power for generating plasma in the desorption step.

5. An adsorption step of forming a reaction layer on an etching target film by plasma generated using a reactive gas, and a desorption step of removing the reaction layer using a metastable rare gas generated by plasma, wherein the adsorption step and the desorption step are repeated, the temperature of the sample stage on which the sample having the etching target film is placed in the adsorption step is the same as the temperature of the sample stage in the desorption step, A plasma processing method characterized in that the high-frequency power for generating plasma in the adsorption step is smaller than the high-frequency power for generating plasma in the desorption step.

6. An adsorption step of forming a reaction layer on an etching target film by plasma generated using a reactive gas, and a desorption step of removing the reaction layer using a metastable rare gas generated by plasma, wherein the adsorption step and the desorption step are repeated, the high-frequency power for generating plasma in the adsorption step is made smaller than the high-frequency power for generating plasma in the desorption step, the plasma processing apparatus in which the adsorption step and the desorption step are performed, comprises a processing chamber in which a sample having the etching target film is processed and a dielectric plate is disposed above, a high-frequency power source that supplies microwave high-frequency power for generating plasma through the dielectric plate, a sample stage on which the sample is placed, and a separation plate disposed between the dielectric plate and the sample stage, A plasma processing method characterized by cleaning the processing chamber using the plasma generated between the separation plate and the sample stage.

7. In the plasma processing method according to any one of Claims 1 to 6, the pressure in the adsorption step is a pressure within the range of 1.0 Pa to 500 Pa, and the pressure in the desorption step is a pressure within the range of 0.05 Pa to 50 Pa.

8. In the plasma processing method according to any one of Claims 1 to 6, a plasma processing method characterized by pulse-modulating the high-frequency power for generating plasma in the adsorption step.

9. In the plasma processing method according to any one of Claims 1 to 6, A plasma treatment method characterized by using a carbon element-containing gas, a boron element-containing gas, or a silicon element-containing gas as the reactive gas.

10. In the plasma treatment method according to any one of Claims 1 to 6, A plasma treatment method characterized by using Ar gas as the rare gas.

11. In the plasma treatment method according to any one of Claims 1 to 6, As the reactive gas, CHF ３ gas and O ２ A plasma processing method characterized by using gas.

12. In the plasma treatment method according to Claim 3 or Claim 6, A plasma treatment method characterized by not placing the sample on the sample stage during the cleaning.

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