Plasma processing method

Abstract

Provided is a method, for semiconductor device fabrication using plasma etching equipment, to control gas exchange at HAR (High Aspect-Ratio) structures and prevent aspect-ratio (AR) dependent effects, such as excessive wall etching and damage, by applying a pressure gradient and reducing plasma density during a plasma process. A gas exchange step is applied between an etching and passivation step, during which the gas pressure is reduced depending on the other steps' pressures and on the sample AR, and during which the plasma power lowered and at least temporarily extinguished. This method enables fast gas exchange and fast etchant radical removal between etching and passivation steps at HAR structures, compensating for the slower gas conduction due to AR. This prevents excessive wall etching and improves protective step-coverage at HAR structures.

Description

PLASMA PROCESSING METHOD

[0001] The present invention relates to a plasma processing method.

[0002] The semiconductor device manufacturing industry is continuously increasing device density to advance their capabilities. Current technology is reaching the limits of two-dimensional scaling, as physical limits make miniaturization increasingly impractical. Thus, monolithic verticalization, which increases device density by integrating multiple device layers in a 3D structure on a single chip, instead of shrinking structures in a single layer, is an emerging industry trend. Manufacturing such monolithic 3D devices requires fabrication of structures with depths that are large compared to their smallest lateral dimension, also called Critical Dimension (CD). As a result, they possess High Aspect-Ratios (HAR). An example of current semiconductor devices utilizing monolithic 3D integration, with HAR structures whose Aspect-Ratio (AR) well exceeds 50, is 3D-NAND. Expected future technologies include 3D-DRAM memory-devices and C-FET logic-devices.

[0003] To manufacture the fine structures of modern semiconductor devices plasma etching is usually used due to its high reactivity and controllability. Fabrication of HAR structures is typically characterized by relatively long processing times, since a large depth must be etched with relatively low etching-rates (ER), since etching species and by-product flow is constrained by the relatively small aperture of the HAR structure. Thus, the structure walls above the etching front are exposed to plasma radical etchants for a long duration, which often leads to wall damage and unwanted radical etching during HAR structure processing.

[0004] To avoid undesirable wall etching, passivation process steps are often used in addition to etching process steps to reinforce the walls. Such passivation may, for example, be coating, to change the chemical structure of the wall to make it resistant to radical etching, or deposition, to cover the wall with a protective layer.

[0005] In the case of HAR structure fabrication, it may be necessary to repeat etching and passivation steps cyclically to obtain the required etching amount, while ensuring wall protection, as was described in PTL 1. When cycling etching and passivation step process gases in the processing chamber, chamber pressure requires a certain to stabilize at the beginning of each new process step. During the time until the prescribed chamber pressure is reached, at the beginning of cyclic etching or passivation steps, the etching or passivation process is less effective. To address this problem, a method was presented in PTL 2, whereby gas supply of the step that is ending is stopped before the prescribed step time, and gas of the step to follow is inserted early and at a higher flow rate than is prescribed for that next step, in order to decrease the time necessary to reach a stable chamber pressure when cycling process steps.

[0006] WO1994014187A1Japanese Patent No.4512533

[0007] Clausing, P. "Ueber die Stroemung sehr verduennter Gase." Annalen der Physik, 404(8): 961-989 (1932).Fick, A., "Ueber Diffusion." Annalen der Physik, 170(1): 59-86 (1855).Coburn, J. W., Winters, H. F. "Conductance considerations in the reactive ion etching of high aspect ratio features." Applied Physics Letters 55(26): 2730-2732 (1989).

[0008] HAR structures restrict gas flow, since, in general, the probability of neutral particles passing through a structure is proportional to its width and inversely proportional to its depth. Under typical conditions, gas exchange from within a structure is faster if AR is low and becomes slower if AR is high. Thus, the gas chemistry inside HAR structures is increasingly decoupled from that in the plasma processing chamber.

[0009] This becomes a critical problem when plasma chemistry is changed between etching and passivation steps for wall protection. If an etching step is followed by a passivation step, etchants from the etching step remain longer inside the HAR structure and cause more wall etching at HAR. Furthermore, the higher amount of remaining etching gas hinders the entry of protective gas species supplied during the passivating step, causing weaker wall protection due to a short step-coverage. As a result, more unwanted wall etching and wall damage by radicals occurs at HAR.

[0010] This gas exchange constriction at higher AR structures creates an AR-dependency of the plasma process. It creates different results between different AR structures etched at the same time, and different results at the same structure at different times during the process, as AR increases with etching depth.

[0011] Since this problem occurs due to the increasing decoupling of HAR structures from the processing chamber, the method of PLT 1 or PLT 2 does not solve it. The method of PLT 2 increases the speed of reaching a stable chamber gas pressure after a process step change. Thereby, it accelerates gas exchange in the process chamber, but it may not accelerate gas transfer between the chamber and remnant gas inside HAR structures.Solution to the Problem

[0012] To accelerate gas exchange to HAR structures, and to counter-act the effects of slow gas exchange at such structures described above, a typical plasma processing method according to the invention involves applying a gas exchange step after the etching and before the passivation process steps, which has a shorter duration than either of those steps, during which the gas pressure is reduced to a value that depends on the other steps’ pressures and on the sample structure AR, and during which the plasma source power is reduced and pulsed with plasma-off times exceeding 1 ms.

[0013] By reducing the gas pressure during the gas exchange step a pressure gradient is created between the HAR structure and the process chamber, which accelerates gas transfer out of the structure after the etching step, and into the structure during the passivation step. The required pressure gradient, to compensate for the gas transfer speed reduction, increases with AR, thus the gas exchange step pressure must be adjusted according to a method that takes AR into account.

[0014] Furthermore, reducing plasma source power and applying plasma source pulsing with plasma-off times exceeding 1 ms to ensure radical extinction, significantly lowers the plasma density and deactivates etching radicals that may remain from the previous etching step. The plasma may be pulsed and not completely turned-off during the gas exchange step, to enhance plasma stability during the following passivation step. If the plasma is turned off during the gas exchange step, the plasma must be newly ignited during the passivation step, thus the stability of the plasma at the beginning of the passivation step is reduced. This may have effects such as less passivation, different passivation step-coverage, or reduced passivation uniformity across a wafer. By pulsing the plasma with adequate plasma-off phase duration during the gas exchange step, the radical concentration can be significantly reduced during that step, without extinguishing the plasma and thus minimizing the impact on plasma stability during the next passivation step.

[0015] This method enables fast gas exchange and fast etchant radical removal between etching and passivation steps at HAR structures, which improves wall protection and reduces AR-dependent etch results, such as excessive wall etching, damage and low deposition step-coverage at structures with higher aspect-ratios.

[0016] Problems, configurations, and effects other than those described above will be clarified by descriptions of the following embodiment.

[0017] Fig.1 is a diagram showing the configuration of a microwave plasma etching apparatus applied to the invention.Fig.2 includes diagram (a) showing a high aspect-ratio (HAR) structure and diagram (b) showing a low aspect-ratio structure. Both consist of a SiO2etching mask 201 and a Si layer to be etched 202.Fig.3A is a diagram showing several structures with different width CD 301, forming different aspect-ratios. Detailed views of the lowest and highest aspect-ratio structures show excessive side-wall etching 303, such as bowing and wall damage 304 at the latter, but not at the former structure.Fig.3B shows a single structure during etching, whereby its depth 302 and thus aspect-ratio increases, progressively. Detailed views comparing the initial low and later high aspect-ratio state of the structure similarly show excessive side-wall etching and wall damage only at the latter one.Fig.4 is a graph showing the gas pressure ranges of the etching, passivation and gas exchange steps during a plasma process applied to the first embodiment.Fig.5 is a graph showing results with slow (empty circles) and with fast gas exchange (filled circles) at certain structure aspect-ratios and gas exchange step pressures, as well as an experimentally derived rule (dashed line) to adjust the gas exchange step pressure to obtain fast gas exchange at a certain aspect-ratio according to the first embodiment.

[0018] Hereafter, an embodiment of the invention will be described with reference to the drawings. It should be noted that the embodiments described herein are not intended to limit the invention according to the claims.

[0019] In the present embodiment of the invention, which is a technique of controlling the gas exchange and radical supply at HAR structures, the chamber pressure is adjusted according to the aspect-ratio and the plasma power source is pulsed during a gas exchange step.

[0020] Due to the lower gas exchange rate at HAR structures, rapid changes in chamber pressure can create pressure differentials between the HAR structures and the chamber. The present embodiment utilizes a low-pressure gas exchange step to create pressure differentials, which quickly evacuate etching gas from HAR structures. Moreover, when pressure rapidly increases after the gas exchange step, inverse pressure differentials quickly insert gas from the passivation step into the HAR structures.

[0021] Reducing the plasma source power and turning it off for at least 1 ms during the gas exchange step rapidly reduces etching radicals in the chamber, thus preventing a supply of radicals to the HAR structures and minimizing etching by such radicals during the gas exchange step.

[0022] As a result, effects of slow gas exchange at HAR, such as AR-dependent wall etching by radicals, low deposition step-coverage, and resultant wall damage can be reduced and prevented.

[0023] Fig.1 shows a schematic cross-sectional diagram of an electron resonance (ECR) microwave plasma etching apparatus (hereinafter, also referred to as a “plasma processing apparatus”) according to an embodiment of the invention. In the microwave plasma etching apparatus, a shower plate 102 (for example, made of quartz) for supplying an etching gas into a vacuum container 101 and a dielectric window 103 (for example, made of quartz) are installed in the upper portion of the vacuum container 101. This upper portion and the connected vacuum container 101 are sealed to form a plasma processing chamber 104. A gas supply device 105 for flowing etching gas is connected to the shower plate 102.

[0024] Further, a vacuum exhaust device 106 connects via an exhaust on-off valve 116 and an exhaust rate variable valve 117 to the vacuum container 101. The inside of the processing chamber 104 is depressurized by opening the exhaust on-off valve 116 and driving the vacuum exhaust device 106, and is brought into a vacuum state in which the pressure is reduced from atmospheric pressure. The pressure in the processing chamber 104 is adjusted to a desired pressure by using the exhaust rate variable valve 117.

[0025] The etching gas is supplied from the gas supply device 105 into the processing chamber 104 via the shower plate 102, and is exhausted by the vacuum exhaust device 106 via the exhaust rate variable valve 117.

[0026] A sample mounting electrode 110, which is a sample stage, is provided at a lower portion of the vacuum container 101 so as to face the shower plate 102. To supply a first radio frequency power for generating plasma to the processing chamber 104, waveguide 107 for transmitting an electromagnetic wave is provided above the dielectric window 103. The electromagnetic wave to be transmitted to the waveguide 107 is oscillated from an electromagnetic wave generating power supply 108, which is a microwave power supply, via a matching unit 118. A pulse generating unit 120 is attached to the electromagnetic wave generating power supply 108, whereby microwaves can be pulse-modulated at any set frequency. A frequency of the electromagnetic wave is not particularly limited, and in the present embodiment, a microwave of 2.45 GHz is used.

[0027] A magnetic field generating coil 109 is provided outside processing chamber 104, the electromagnetic wave oscillated from the electromagnetic wave generating power supply 108, by interaction with the magnetic field generated by the magnetic field generating coil 109, generates high density plasma in the processing chamber 104, and an etching process is performed on a wafer 111 which is a sample disposed on the sample mounting electrode 110, which is the sample stage.

[0028] The shower plate 102, the sample mounting electrode 110, the magnetic field generating coil 109, the exhaust on-off valve 116, the exhaust rate variable valve 117, and the wafer 111 are disposed coaxially with respect to the central axis of the processing chamber 104, and therefore a flow of the etching gas, radicals and ions generated by the plasma, and reaction products generated by the etching are coaxially supplied to the wafer 111 and exhausted. This coaxial arrangement has the effect that the uniformity of an etching rate and the etching shape on a wafer plane is near axial symmetry, and that the wafer processing uniformity is improved.

[0029] The sample mounting electrode 110 is coated with a sprayed film (not shown) on an electrode surface thereof, and is connected to a DC power supply 115 via a radio frequency filter 114. Further, a radio frequency bias power supply 113 is connected to sample mounting electrode 110 via a matching circuit 112. The radio frequency bias power supply 113 is connected to the pulse generating unit 120 and can selectively supply a time modulated second radio frequency power to the sample mounting electrode 110. The frequency of the radio frequency bias is not particularly limited, and in the present embodiment, a radio frequency bias of 400 kHz is used.

[0030] A control unit 119 that controls the above-mentioned ECR microwave plasma etching apparatus, by an input unit (not shown), controls a repetition frequency or a duty ratio including an on / off timing of pulses of the electromagnetic wave generating power supply 108, the radio frequency bias power supply 113, and the pulse generating unit 120, and etching parameters such as a gas flow rate, a processing pressure, a microwave power, a radio frequency bias power, a coil current, a pulse-on time, and a pulse-off time for performing etching. Next, an embodiment using the above-mentioned microwave plasma etching apparatus according to the present embodiment will be described.First Embodiment

[0031] In this manifestation of the invention, etching and passivation (coating) process steps were applied. During the etching step, process gas with a chamber pressure of 5.0 Pa is applied that includes Cl, F, or Cl and F based etching species, and that may include Ar or He as a dilution gas. Furthermore, a plasma source power of 1300 W is applied to the plasma chamber and a certain radio-frequency bias power is applied to the sample mounting electrode, to control ion-assisted etching of the sample. The step duration was 30 s.

[0032] During the passivation step, process gas with a chamber pressure of 5.0 Pa is applied that includes oxygen passivation gas, and that may include Ar or He as a dilution gas. The step duration was 15 s.

[0033] Sample structures, which are etched by the process in this embodiment are shown in Fig.2, including a (a) high aspect-ratio (HAR) and a (b) low aspect-ratio structure, consisting of a SiO2etching mask 201 and a Si layer to be etched 202. The aspect-ratio (AR) indicates the ratio of the structure’s depth 204 and its width CD (Critical Dimension) 203.

[0034] At HAR structures, the gas exchange rate is depressed, since there is a smaller probability that electrically neutral particles pass through to reach the etching front at the bottom of the structure, compared to low AR structures. The probability of neutral particles passing through a structure depends on the chemical characteristics of the gas and surfaces, on the temperature, and on its geometry. The detailed shape usually influences the probability of passing through, however, the probability is generally inversely proportional to the highest AR feature of the structure (see NPL 1).

[0035] An AR-dependent decrease in gas exchange rate between etching and passivation steps can cause several undesirable results at higher AR structures, as illustrated in Fig.3A and 3B.

[0036] Fig.3A shows the case of several structures with different AR, created by the difference in width CD (Critical Dimension) 301, which are etched by the same plasma process. Due to slower gas exchange at HAR, radicals from the etching step remain longer in the structure after the etching step, and passivation gas from the passivation step achieves less coverage. As a result, unwanted effects, such as excessive side-wall etching 303, resulting in bowing and wall damage 304, can occur at the HAR structure, even when they do not occur at the structures with lower AR.

[0037] In Fig.3B, the case of etching a single structure is shown. As the etched depth 302 increases the AR becomes higher and the gas exchange rate decreases. Thus, while continuing etching with the same process, eventually excessive wall etching and damage can occur, due to a slower gas exchange rate between etching and passivation steps at HAR.

[0038] Since gas diffusion is generally proportional to the gas pressure difference (see NPL 2), a rapid gas pressure decrease in the processing chamber can create a pressure difference between the top and bottom of HAR structures that accelerates gas evacuation. Similarly, a rapid gas pressure increase accelerates gas supply into HAR structures.

[0039] In this embodiment of the invention, the chamber pressure is lowered during a gas exchange step to be lower than the pressure during the previous etching step and the following passivation process step, as shown by the graph in Fig.4. During the gas exchange step, gas that does not facilitate etching is provided, such as inert gas, or gas that is similar to the gas that will be used during the following passivation step. The chamber pressure applied during the gas exchange step is chosen to compensate the gas exchange rate reduction due to HAR via pressure gradients, and thus achieve a high gas exchange rate even at HAR structures with a short gas exchange step duration.

[0040] Increasing the gas exchange step time can also facilitate thorough gas exchange. However, accelerating gas exchange during a shorter gas exchange step is preferable, since extending it can result in more etching and wall by etchants that may remain in HAR structures. Moreover, a faster gas exchange enables shorter process time and better throughput.

[0041] To minimize the effect of etchants during the gas exchange step, the plasma power source is reduced and pulsed, with plasma-off times exceeding 1 ms. Applying a plasma-off time of at least 1 ms enables extinction of the plasma in the chamber, which significantly reduces radical concentration and prevents remaining etching radicals from being supplied to the sample. By applying a plasma pulse the plasma stability during the following passivation step can be enhanced, which is preferable for the total plasma etching process.

[0042] In this embodiment, gas exchange rates are controlled via the pressure difference between the gas exchange step and the etching and passivation steps, while step durations are not changed. Since both gas removal after etching and gas insertion during passivation should be accelerated, the pressure difference between the lowest chamber pressure, which is applied at either the deposition or at the passivation step, and the chamber pressure applied at the gas exchange step, is considered.

[0043] To avoid AR-dependent effects, the process must be adjusted to sufficiently accelerate gas exchange to the structure with the highest AR that is currently etched. This may be with respect to a HAR structure that is etched together with other structures with lower ARs, as in Fig.3A. Alternatively, it may be an adjustment during a process that etches a single structure with progressively increasing AR during etching, as shown in Fig.3B.

[0044] The graph in Fig.5 plots experimental results of the present embodiment, including results from different AR structures where the pressure exchange step was either effective (filled circles) or ineffective (empty circles) at facilitating fast gas exchange to avoid excessive wall etching, bowing or damage depending on the chamber pressure during the gas exchange step. Whether gas exchange is sufficiently fast is judged by the presence or absence of the effects of slow gas exchange at the etched structure, i.e. excessive wall etching, wall bowing or wall damage. The gas exchange step pressure is shown as a proportion of the lower pressure applied at either the previous etching step or at the following passivation step.

[0045] Fig. 5 suggests that, to obtain high gas exchange rates, lower chamber pressures during the gas exchange step are necessary at higher AR. Based on these results, a rule for the gas exchange pressure (Gas Exchange Step Pressure Rule) can be determined, which prescribes the necessary chamber pressure to effectively accelerate the gas exchange rate at a wide range of AR.

[0046] Gas flow is proportional to the pressure gradient across the structure, and, since the pressure in a HAR structure lags that of the chamber, decreasing the chamber pressure during the gas exchange step induces a pressure gradient across HAR structures. This pressure gradient accelerates gas removal during the gas exchange step, and accelerates gas insertion during the passivation step. Thus, reducing the gas exchange step pressure such that the pressure difference, as a proportion of the lower pressure that is applied at the etching step before or at the deposition step after, does not exceed a limit, the proportional reduction of the gas flow probability due to AR, enables rapid gas exchange at a wide range of AR.

[0047] In this embodiment of the invention, a rule determining the gas exchange step pressure (Gas Exchange Step Pressure Rule) is applied, which ensures rapid gas exchange at structures with different AR. This rule prescribes that the gas exchange step pressure (PΔPX) should be reduced below the pressure applied at the steps before and after, such that the pressure difference as a proportion of the lower pressure applied at the steps before or after (Pmin), does not exceed a limit (Gas Exchange Step Pressure Limit), i.e., the inverse of the sum of the neutral gas particle desorption probability (1-s), which is the complement of the sticking coefficient (s), and the product of the sticking coefficient and AR (s×AR). In this formulation of the rule, the coefficients are named based on the expected gas flow probability (see NPL 3). The pressure limit that this rule prescribes is also plotted in Fig.5 (dashed line). Sticking coefficient (s) can be experimentally derived based on data depending on various conditions. The Gas Exchange Step Pressure Rule can be written as Inequality (1), The gas flow probability is the probability of a neutral gas particle passing through the structure. The neutral gas particle desorption probability is the probability of such a particle being removed from the bottom of the structure when it is adsorbed to that surface. The sticking coefficient is the probability of a particle not being removed from that surface. Using this rule, the necessary pressure during a certain gas exchange step to prevent AR-dependent gas exchange effects can be known. For example, when etching structures with a range of aspect-ratios, as shown in Fig.3A, or when the aspect ratio of one target structure increases during the etching process, as illustrated in Fig.3B.

[0048] In this embodiment of the invention, during the gas exchange step, process gas may be applied that includes passivation species such as oxygen, and that may include Ar or He as a dilution gas, which can facilitate deposition or passivation during the passivation step. Chamber pressure is reduced below the AR-dependent limit (Gas Exchange Step Pressure Limit) according to the rule discussed above. In this embodiment, fast gas exchange was obtained at structures with AR between 10 and 90 with gas pressures between 2.0 Pa and 0.2 Pa. Here, the sticking coefficient value for the gas exchange pressure rule was determined as 0.07 based on experimental results. Furthermore, a plasma source power of 700 W is applied to the plasma chamber and the plasma power supply was pulsed with a frequency of 125 Hz and a duty cycle of 50%, thus applying a plasma-off time of 4 ms, which ensures etchant extinction. The step duration was 3 s.

[0049] As a result, in this embodiment of the invention, even at HAR structures, etching gas can be rapidly evacuated and passivation gas rapidly inserted, via a pressure gradient applied by the gas exchange step, during which etching radicals can be quickly removed, via a lower plasma source power and sufficiently long plasma-off duration, which can prevent AR-dependent effects, such as wall etching and wall damage and can increase the step-coverage during the passivation step at HAR structures.

[0050] In the first embodiment, the given plasma process conditions and samples were used, however, the gas exchange step, as shown in Fig.4, with the described method of controlling gas exchange rates and etching radicals at HAR sample structures via chamber pressure and plasma source power, can be applied to different plasma process conditions and samples as well.

[0051] In this embodiment, an SiO2layer is used as the etching mask, however, other manifestations of the invention are not limited to this material, but could also utilize a different silicon-based, or a metal or carbon-based material, instead, for example, SiN, SiON, TiN, or other titan-based metallic hard mask materials, metal-oxide, amorphous carbon, or diamond-like carbon mask materials. Furthermore, in this embodiment Si forms the etching target material, but other manifestations of the invention are not limited to this, but could use, for example, SiN, SiON, or layered materials such as Si / SiGe as etching target materials. In this embodiment, argon Ar or helium He gas is used as a diluent gas, but neon Ne, krypton Kr, xenon Xe, or other gases, which are generally used as diluent gas, may be used instead. Moreover, in this embodiment oxygen O gas is used as a passivation gas, however, other manifestations can instead use other passivation or deposition gases, such as gasses containing nitrogen N, or gasses containing Si and oxygen, or carbon C, hydrogen H and fluorine F. Although, in this embodiment, chlorine Cl and fluorine F based etching gas was used, other manifestations of the invention may employ other etchants that include fluorine F, chlorine Cl, or bromine Br gas well, such as SF6, CF4, C4F8, CHF3, BCl3, NF3, or HBr. In the above manifestation, the explanation assumed an ECR (Electron Cyclotron Resonance) etching apparatus using microwaves to ignite plasma. However, the embodiments of the invention are not limited to this, instead, they include applications using different apparatuses, including those that use different principles to support a plasma, such as, for example, CCP (Capacitively Coupled Plasma), or ICP (Inductively Coupled Plasma).

[0052] The aspects that may constitute the content of the present invention are described below; however, they are not limited thereto. (Aspect 1) A plasma processing method comprising: a 1ststep of providing, to a sample stage within a processing chamber, a wafer including a substrate having an etching mask disposed on a target layer to be etched with an aspect ratio of width to depth; a 2ndstep of etching the wafer with a certain gas pressure; a 3rdstep of gas exchange with a lower gas pressure than the 2ndstep, during which the plasma is pulsed, and a 4thstep of deposition or passivation, with a higher gas pressure than the 3rdstep, wherein the plasma source power of the 3rdstep is smaller than that of the 2ndstep, and the 3rdstep is of shorter duration than the 2ndand 4thsteps. (Aspect 2) The plasma processing method according to aspect 1, wherein the gas inserted during the 3rdstep includes inert gas or gas that is used during the 4thstep. (Aspect 3) The plasma processing method according to aspect 1 or aspect 2, wherein the plasma source power is turned-off or pulsed during the 3rdstep, such that the plasma-off time exceeds 1 ms. (Aspect 4) The plasma processing method according to any one of aspects 1 to 3, wherein the plasma source power of the 3rdstep is smaller than that of the 4thstep. (Aspect 5) The plasma processing method according to any one of aspects 1 to 4, wherein the gas pressure of the 3rdstep is determined based on the 2ndor 4thstep’s pressure and on the aspect ratio of the structure that is processed. (Aspect 6) The plasma processing method according to any one of aspects 1 to 5, wherein the gas pressure of the 3rdstep (PΔPX) does not exceed the lower pressure of the 2ndand 4thsteps divided by the sum of the neutral gas particle desorption probability, which is the complement of the sticking coefficient (s), and the product of the sticking coefficient (s) and said aspect ratio as expressed by Inequality (1). (Aspect 7) The plasma processing method according to any one of aspects 1 to 6, wherein the 2nd, 3rdand 4thsteps are repeated.

[0053] 101… vacuum container 102… shower plate 103… dielectric window 104… processing chamber 105… gas supply device 106… vacuum exhaust device 107… waveguide 108… electromagnetic wave generating power supply 109… magnetic field generating coil 110… sample mounting electrode 111… wafer 112… matching circuit 113… radio frequency bias power supply 114… radio frequency filter 115… DC power supply 116… exhaust on-off valve 117… exhaust rate variable valve 118… matching unit 119… control unit 120… pulse generating unit 201… SiO2etching mask 202… Si layer to be etched 203… Width CD 204… Depth 301… Width CD 302… Depth 303… Side-wall etching 304… Wall damage

Claims

1. A plasma processing method comprising: a 1ststep of providing, to a sample stage within a processing chamber, a wafer including a substrate having an etching mask disposed on a target layer to be etched with an aspect ratio of width to depth; a 2ndstep of etching the wafer with a certain gas pressure; a 3rdstep of gas exchange with a lower gas pressure than the 2ndstep, during which the plasma is pulsed, and a 4thstep of deposition or passivation, with a higher gas pressure than the 3rdstep, wherein the plasma source power of the 3rdstep is smaller than that of the 2ndstep, and the 3rdstep is of shorter duration than the 2ndand 4thsteps.

2. The plasma processing method according to claim 1, wherein the gas inserted during the 3rdstep includes inert gas or gas that is used during the 4thstep.

3. The plasma processing method according to claim 1, wherein the plasma source power is turned-off or pulsed during the 3rdstep, such that the plasma-off time exceeds 1 ms.

4. The plasma processing method according to claim 1, wherein the plasma source power of the 3rdstep is smaller than that of the 4thstep.

5. The plasma processing method according to claim 1, wherein the gas pressure of the 3rdstep is determined based on the 2ndor 4thstep’s pressure and on the aspect ratio of the structure that is processed.

6. The plasma processing method according to claim 1, wherein the gas pressure of the 3rdstep (PΔPX) does not exceed the lower pressure of the 2ndand 4thsteps (Pmin) divided by the sum of the neutral gas particle desorption probability, which is the complement of the sticking coefficient (s), and the product of the sticking coefficient (s) and said aspect ratio as written by Inequality (1).

7. The plasma processing method according to claim 1, wherein the 2nd, 3rdand 4thsteps are repeated.

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