JP4109135B2 - Etching method for difficult-to-etch materials - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for etching difficult-to-etch materials such as Pt, Ru, Ir, PZT, and HfO2, a semiconductor integrated circuit device including the hardly-etched material, and a method for manufacturing the same. The present invention relates to a technique effective for etching.
[0002]
[Prior art]
Conventionally, as a means for treating the surface of a semiconductor element, there is known a method of etching using a photoresist having a tapered shape or a round head.
[0003]
A method of etching using a tapered mask is disclosed in US Pat. Nos. 5,818,107 (JP-A-10-214826) and JP-A-10-223855. A method of etching using a round photoresist is disclosed in US Pat. No. 6,570,081 (JP-A-10-98162).
[0004]
However, the etching of a nonvolatile material that is a material that is difficult to etch (hereinafter simply referred to as a difficult-to-etch material) is performed at a high temperature of 300 ° C. or higher, and a photoresist may not be used.
[0005]
[Problems to be solved by the invention]
By the way, with the miniaturization of semiconductor elements and the speeding up of the operation, the gate insulating film of MOS (metal-oxide-semiconductor) transistors, the gate electrode, or the capacitor of the memory part, the capacitor electrode, alumina, zirconium oxide, hafnium oxide, The use of materials such as ruthenium, platinum, tantalum oxide, BST, SBT, and PZT has been studied. Moreover, iron, nickel, cobalt, manganese, or an alloy thereof is used in a memory (MRAM: magnetic random access memory) using magnetism.
[0006]
Examples of the difficult-to-etch material include the following.
Magnetic material: (Applications: magnetic disk, MRAM, etc.) Fe, Co, Mn, Ni, etc.
Precious metals, etc .: (Application: Various electrodes, etc.)
Pt, Ru, RuO2, Ta, Ir, IrO2, Os, Pd, Au, Ti, TiOx, SrRuO3, (La, Sr) CoO3,
Cu etc.
High dielectric: (Application: DRAM capacitor (accumulates charge), etc.)
BST: (Ba, Sr) TiO3, SRO: SrTiO3, BTO: BaTiO3, SrTa2O6, Sr2Ta2O7,
ZnO, Al2O3, ZrO2, HfO2, Ta2O5, etc.
Ferroelectric: (Application: FeRAM capacitor, etc.)
PZT: Pb (Zr, Ti) O3, PZTN: Pb (Zr, Ti) Nb2O8, PLZT: (Pb, La) (Zr, Ti) O3,
PTN: PbTiNbOx, SBT: SrBi2Ta2O9, SBTN: SrBi2 (Ta, Nb) 2O9,
BTO: Bi4Ti3O12, BiSiO_{x ,}BLOT: Bi_4-xLa_xTi_ThreeO₁₂  etc
Compound semiconductor: GaAs, etc.
ITO and others: InTiO, etc.
[0007]
These difficult-to-etch materials are difficult to etch compared to aluminum, silicon, silicon oxide, and the like, and in particular, it is difficult to process the side walls of the difficult-to-etch material into a shape perpendicular to the substrate. .
[0008]
None of the above-mentioned known documents suggests that the side wall of the difficult-to-etch material is processed into a shape perpendicular to the substrate.
[0009]
Next, when chemically stable materials such as iron, cobalt, manganese, nickel, platinum, ruthenium, tantalum, alumina, hafnium oxide, zirconium oxide, and gallium arsenide are etched using plasma, vertical etching is performed on the material to be etched. The reason why it is difficult to obtain the shape will be described below.
[0010]
In materials that are difficult to etch, such as the above-mentioned difficult-to-etch materials, a reaction product is generated by etching, and the reaction product jumps out of the sample surface into the gas phase and then adheres to the wall of the material to be etched. There is an easy nature. Therefore, if the reaction product adheres only to the position where the etching proceeds in the material to be etched, the etching rate is substantially reduced, but the reaction product is actually located at any position of the material to be etched. Adhere to. That is, the reaction product adheres to the side wall where the etching hardly progresses in the material to be etched, and as a result, the etching of the bottom surface where the etching proceeds and the deposition of the deposition material on the side wall proceed simultaneously. A shape perpendicular to the substrate cannot be obtained on the sidewall of the etching material. The above is the reason why the etching shape perpendicular to the substrate surface cannot be obtained in the etching of the difficult-to-etch material.
[0011]
The reason why an etching shape perpendicular to the substrate cannot be obtained on the side wall of the material to be etched will be described in more detail with reference to FIGS. 1A to 2G.
[0012]
FIG. 1A and FIG. 2A show the initial state of etching, in which the arrow in the right direction indicates the deposition direction of the deposit and the arrow in the lower direction indicates the etching direction. Here, the angle (taper angle) θ of the side wall of the mask 10 with respect to the upper surface of the substrate is 90 degrees. When a minute unit time Δt elapses from the initial state, the bottom surface (the upper surface 21 of the etching target material 20 exposed to plasma) is etched by Δe, and a deposit 25 is deposited on the side walls of the mask 10 and the etching target material 20 by Δd ( 1B, 2B). Actually, since the upper surface portion 30 of the deposit is also etched, the angle (taper angle) φ formed by the portion with respect to the substrate surface is the deposition amount (deposition rate) Δd of the deposit per unit time. It is determined by the etching amount per hour (etching rate) Δe.
[0013]
Further, in the portion 32 immediately below the mask side wall, at the moment when deposition of the deposit 25 on the side wall of the mask starts, the bottom surface portion 33 of the deposit on the side wall of the mask (the etching target 20 exposed to the plasma). The etching on the upper surface 21) stops. However, when the exposed portion of the material to be etched 20 is etched under the side wall of the deposit 25 on the side wall of the mask and the side wall of the new material to be etched 20 is exposed, the deposit is deposited on the exposed surface. . Therefore, the etching proceeds obliquely downward (FIGS. 1C and 2C).
[0014]
1C and 2C, when the unit time Δt further elapses, deposition of the deposit 25 further proceeds on the side wall of the deposit 25, and etching is also performed on the exposed portion of the material to be etched 20 below the side wall of the deposit 25. Proceed (FIGS. 1D, 1E, 2D-2F). In this way, the etching progresses obliquely downward, and the etching shape shown in FIGS. 1F and 2G is obtained. Thus, the side wall of the material to be etched forms a taper angle φ (φ <90 degrees) with respect to the substrate surface.
[0015]
  The object of the present invention is to etch a difficult-to-etch material that can solve the problems of the prior art.The lawIs to provide.
[0016]
  Another object of the present invention is to meet the demand for miniaturization of semiconductor elements and the like, a surface of a sample that can be processed stably on a plurality of wafers, or the taper angle of a material to be etched can be set to an angle close to vertical. How to processThe lawIs to provide.
[0017]
[Means for Solving the Problems]
  A feature of the present invention is that when a film formed on a substrate is etched using plasma.,sideTapered angle formed by the wall with respect to the substrate surfaceθButtan θ = (re−rd) / ((rd - (recos θ) × sin θ) (where re is the mask etch rate, and rd is the mask side wall deposition at this time).With maskThe difficult-to-etch materialIt is in the surface treatment method of the sample to be etched.
[0018]
That is, according to one aspect of the present invention, a method of etching a film using plasma using a film of a difficult-to-etch material formed on a substrate and a mask formed thereon, the sidewall of the mask is Etching with a mask having an angle of less than 90 degrees to the surface of the substrate.
[0019]
Therefore, according to the present invention, in etching of a material in which it is difficult to obtain a processed shape with a vertical sidewall, an etching shape with a sidewall substantially vertical can be obtained by using a tapered mask or the like. A highly integrated semiconductor device can be produced.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0021]
FIG. 3 is a diagram showing an example of the overall configuration of a plasma etching apparatus to which the present invention is applied. A high frequency current is supplied to the coil 103 from the high frequency power source 101 via an automatic matching unit 102 to generate a plasma 105 in the vacuum vessel 104. The vacuum vessel 104 includes a discharge unit 104a made of an insulating material and a processing unit 104b that is grounded. An etching gas such as chlorine is introduced into the vacuum vessel 104 through the gas introduction unit 106, and the gas is exhausted by the exhaust device 107.
[0022]
The sample 108 is placed on the sample table 109. In order to increase the energy of ions incident on the sample 108, a bias power source 110, which is a second high-frequency power source, is connected to the sample stage 109 via a high-pass filter 111. An insulating film 112 such as ceramic is provided on the surface of the sample table 109. The sample stage 109 is connected to a DC power source 113 via a low-pass filter 114, and holds the sample 108 on the sample stage 109 by electrostatic force.
[0023]
Further, a heater 115 and a refrigerant channel 116 are provided on the sample stage 109 in order to control the process by adjusting the temperature of the sample 108.
[0024]
Typical conditions for etching chemically stable materials such as iron, cobalt, manganese, nickel, platinum, ruthenium, tantalum, alumina, hafnium oxide, zirconium oxide, gallium arsenide using this device are as follows: Street. The pressure of the apparatus is 0.5 Pa, and the introduced gas is mainly chlorine. The temperature of the sample 108 is 200 ° C. or more and 500 ° C. or less, although it varies depending on the material to be etched. Although this depends on the required etching rate or the semiconductor device to be manufactured, the temperature of the sample 108 is higher than the typical temperature when etching a silicon film, an aluminum film or a silicon oxide film is 0 ° C. to 100 ° C. Is kept at a high temperature. Therefore, a photoresist cannot be effectively used as an etching mask material, and a silicon oxide or metal hard mask is often used.
[0025]
In order to perform the above-described problem in the etching of difficult-to-etch materials, that is, an etching process in which the taper angle φ of the material to be etched can be made an angle close to perpendicular to the substrate surface, the amount of deposits attached to the side wall of the mask It is important to suppress.
[0026]
As a method for suppressing the deposition of the deposit, it is conceivable to lower the pressure in the reaction vessel and increase the flow rate of the gas introduced into the reaction vessel. However, in many cases, the pressure and the flow rate of the gas are limited to an appropriate range in order to obtain desirable etching characteristics, and the limits of the pressure and the flow rate are determined by the exhaust capacity. Therefore, it is difficult to suppress deposition of deposits by pressure, flow rate, and the like.
[0027]
  Next, by using a mask having a taper angle (angle of the side wall of the mask 10 with respect to the upper surface of the substrate) θ of less than 90 degrees (that is, a tapered mask), the taper angle of the material to be etched (the side wall of the material to be etched) The reason why a processed shape having an angle (φ with respect to the substrate surface) close to vertical is obtained will be described with reference to FIGS. 5A shows a case where the taper angle θ of the mask is 90 degrees, and the deposit 25 is deposited in parallel on the side wall of the mask 10 as described in FIGS. 1A to 2G. 4A shows that the taper angle θ of the mask is 90 degrees.Less thanIn this case, the state before etching is shown.
[0028]
First, when the process conditions are determined, the etching rate of the bottom surface of the sample (the surface 21 of the material to be etched exposed to plasma) is determined. When etching is performed using chlorine as a main etching gas, chloride (reaction product) of the material to be etched out of the sample jumps out of the substrate (material) into the etching apparatus (reaction vessel). The reaction product that has jumped into the etching apparatus is incident on the substrate again, and some of the reaction product incident on the substrate is deposited as a deposit on the substrate surface (the side wall of the mask and the side wall of the material to be etched) (FIG. 4B). . In many cases, this depot can be approximated isotropic. The deposition rate of this deposit (hereinafter simply referred to as the deposition rate) is denoted by rd. On the other hand, since etching is mainly due to the action of ions, the incident direction of ions at the etching target position greatly affects the etching rate at that position. If the etch rate is simply determined by the ion flux, assuming that the etch rate at the bottom of the sample where ions are incident substantially perpendicularly is re, the etch rate when the ion incident angle is α is re × sin α. Here, re is a true etch rate when the deposit is not deposited.
[0029]
That is, when the side wall of the mask is perpendicular to the substrate surface, the deposition rate of the deposit on the side wall of the mask is rd, and the apparent etch rate of the sample bottom surface 21 is re-rd (see FIG. 4D). At this time, the taper angle φ of the material to be etched is
tan φ = (re−rd) / rd
It is.
[0030]
On the other hand, as shown in FIGS. 4B and 5B, when the side wall of the mask is slightly inclined from the direction perpendicular to the substrate surface (the taper angle θ of the mask is less than 90 degrees), the deposition on the side wall of the mask is isotropic. Therefore, rd, and the etch rate of the side wall of the mask is re × cos θ. Accordingly, rd−re × cos θ is a deposition on the side wall when the taper angle of the mask is θ. Therefore, the taper angle φ of the material to be etched is as shown in FIG. 4D.
tan φ = (re−rd) / ((rd−re × cos θ) × sin θ)
It is.
[0031]
Thus, under the condition where deposition of deposits proceeds on the sidewall of the mask, the taper angle φ of the etched material after etching increases as the mask taper angle θ decreases. FIG. 4C shows a state in which the deposit is removed after the etching process as shown in FIG. 4B.
[0032]
When the taper angle θ of the mask is made smaller than 90 degrees and the taper angle θ is made smaller than that in FIG. 5B, the taper angle θ and the taper angle φ of the material to be etched become as shown in FIG. 5C. Agree (θ = φ). This state is a condition in which deposits do not progress on the mask. That is, even if deposits adhere to the mask, the deposits are instantaneously removed by etching, and as a result, deposits do not adhere to the mask. If the taper angle of the mask at this time is θ0 and the taper angle of the material to be etched is φm, as shown in FIG. 5D, even if the taper angle θ of the mask is further reduced (that is, θ <θ0), The taper angle of the material does not become larger than φm. That is, as shown in FIG. 5D, when θ <θ0, θ <φm is satisfied, and therefore, the taper angle θ0 of the mask is the limit for setting the taper angle φ of the material to be etched to the maximum (φm). Value. In the state shown in FIG. 5D, the mask or the base (the material to be etched) is exposed.
[0033]
The relationship between the taper angle θ of the mask and the taper angle φ of the material to be etched is as shown in FIG. Here, rd / re is uniquely determined by the mask, the material of the material to be etched, and the etching conditions (pressure in the reaction vessel, flow rate of gas introduced into the reaction vessel, etc.). In general, the rd / re decreases as the pressure in the reaction vessel increases, and the rd / re decreases as the flow rate of the gas introduced into the reaction vessel increases.
[0034]
As shown in FIG. 6, for example, when rd / re = 0.5, when the taper angle θ of the mask is decreased from 90 degrees, the taper of the material to be etched is approximately proportional to the taper angle θ of the mask. The angle φ increases. When the taper angle θ of the mask is reduced to about 72 degrees, the taper angle φ of the material to be etched is also increased to about 72 degrees (θ = φ), and the state shown in FIG. 5C is obtained. That is, θ = θ0 = φ = φm. Therefore, even if the taper angle θ of the mask is further reduced (θ <θ0), the taper angle of the material to be etched remains φm.
[0035]
  Therefore, in FIG. 6, the line L indicates the limit value θ0 of the taper angle of the mask.AhThe Therefore, the region A is a region where θ> θ0, and deposits adhere to the mask, and the taper angle φ of the material to be etched is determined by the taper angle θ of the mask.(FIG. 7A). On the other hand, the region B is a region of θ ≦ θ0, and deposits do not adhere to the mask, and the taper angle φ of the material to be etched becomes a constant value φm regardless of the taper angle θ of the mask.(Fig. 7B). Therefore, for example, when rd / re = 0.4, if the taper angle φ of the material to be etched is set to 70 degrees, the taper angle θ of the mask may be set to about 82 degrees.
[0036]
Next, a method for forming a mask having a side wall taper angle of less than 90 degrees will be described.
[0037]
Here, as an example, a case where Pt is etched using a silicon oxide hard mask will be described.
[0038]
(A) First, a method of controlling the taper angle of the side wall of the silicon oxide film as a mask by the etching gas component and the etching pressure will be described with reference to FIGS. 8A to 8E. A hard mask material 51 such as a silicon oxide film or a metal film is formed on the Pt 50, and a photoresist 52 is patterned into a predetermined pattern thereon (FIG. 8A). Next, silicon oxide is etched into a tapered shape mainly using a fluorocarbon-based gas and an additive gas such as oxygen (FIG. 8B). At this time, the silicon oxide can be etched into a tapered shape by changing the composition of the gas introduced into the etching chamber or changing the etching pressure.
[0039]
Etching to such a tapered shape is described, for example, in J. Vac. Sci. Technol. A 14, 1832 (1996). According to this document, a method is described in which the taper angle of a silicon oxide film is controlled by the etching gas component and the etching pressure. Specifically, a taper angle of a silicon oxide film formed by using a photoresist having a taper angle of 86 °, changing the pressure from 40 mTorr to 300 mTorr under an etching condition in which the flow rate of CF 4 is 20 sccm and the bias power is 100 W. Changes from 80 ° to 51 °. Further, by changing the component ratio (CHF3 in CF4 (%)) from 0% to 50% under an etching condition in which the pressure is 40 mTorr and the total flow rate of CHF3 and CF4 is 20 sccm, the taper angle of the silicon oxide film is 66 °. To 84 °.
[0040]
Thus, while the etching rate of the lateral method of the silicon oxide film is almost independent of the pressure, it can be seen that the taper angle of the oxide film can be controlled by utilizing the fact that the etching rate in the vertical direction decreases as the pressure increases. .
[0041]
When the taper angle of the silicon oxide film can be formed to be less than 90 degrees (FIG. 8B), the photoresist 52 is removed (FIG. 8C). Next, the substrate is transported to a predetermined position in the etching apparatus, etching is performed (FIG. 8D), and then the mask 51 is removed (FIG. 8E).
[0042]
Another etching method for forming the mask taper angle below 90 degrees is shown in U.S. Patent No. 5,856,239.
[0043]
(B) Next, a method of forming the taper angle of silicon oxide as a mask to less than 90 degrees by wet etching will be described. Such a method is disclosed in, for example, Jpn. J. Appl. Phys., Vol. 34 (1995), pp.2132-2136. That is, as shown in FIG. 9A, a polysilicon film 52 having a predetermined pattern is formed on a silicon oxide film 51 as a mask for etching Pt 50, and this is immersed in an aqueous HF solution under a certain condition. Although the polysilicon film 52 is not etched with the HF aqueous solution, the silicon oxide film 51 is isotropically etched with the HF aqueous solution to form a tapered shape as shown in FIG. 9B. Thereafter, when the polysilicon film is etched using chlorine Cl 2, fluorine F 2, hydrogen hexafluoride SF 6, or the like, a silicon oxide mask 51 having a shape as shown in FIG. 9C is finally formed. Therefore, etching is performed using such a tapered mask (FIG. 9D), and then the mask 51 is removed (FIG. 9E).
[0044]
10A to 13D are diagrams showing several methods for forming masks of silicon oxide films having the same width (size) and different taper angles.
[0045]
First, in the method shown in FIGS. 10A to 10I, masks having the same width (size) and different taper angles are formed by the thickness of the silicon oxide film 51 as a mask and the wet etching time corresponding thereto. For example, as shown in FIGS. 10A, 10D, and 10G, silicon oxide films 51 having different thicknesses T1, T2, and T3 are formed, and then wet etching with HF is performed for a time corresponding to the thickness of the silicon oxide film. As a result, masks having different taper angles can be formed as shown in FIGS. 10B, 10E, and 10H. Therefore, when the polysilicon film 52 is subsequently removed, as shown in FIGS. 10C, 10F, and 10I, masks having the same width (size) and taper angles θ1, θ2, and θ3 (here, θ1> θ2> θ3), respectively. Can be formed. That is, the greater the thickness of the silicon oxide film 51 as a mask, the smaller the taper angle of the mask can be set.
[0046]
The method shown in FIGS. 11A to 11I is to form masks having the same width (size) and different taper angles with the width (size) of the polysilicon film as the mask and the wet etching time corresponding to the width. For example, as shown in FIGS. 11A, 11D, and 11G, forms having different widths (sizes) W1, W2, and W3 and a polysilicon film 52 that is a resist are formed, and then wet etching using HF is performed on the polysilicon film. If only the time corresponding to the width (size) is performed, masks having different taper angles can be formed as shown in FIGS. 11B, 11E, and 11H. Therefore, after that, when the polysilicon film 52 is removed, as shown in FIGS. 11C, 11F, and 11I, masks having the same width (size) and taper angles θ4, θ5, and θ6 (here, θ4> θ5> θ6), respectively. Can be formed. That is, the smaller the width (size) of the polysilicon film 52, the smaller the taper angle of the mask can be set.
[0047]
12A-13D show a method of controlling the taper angle of the mask by dry etching and wet etching.
[0048]
In the method shown in FIGS. 12A to 12C, first, the polysilicon film 52 is patterned to a predetermined width (size) W4 (FIG. 12A), and then a part of the silicon oxide film 51 is almost vertical by dry etching. The thickness Th1 is cut (FIG. 12B), and then wet etching is performed to taper the silicon oxide film 51 (FIG. 12C).
[0049]
In the method shown in FIGS. 13A-13D, first, the polysilicon film 52 is patterned to a predetermined width (size) W5 different from the width (size) W4 (FIG. 13A), and then the silicon oxide film 51 is dry-etched. A portion of the silicon oxide film 51 is cut substantially vertically by a thickness Th2 different from the thickness Th1 (FIG. 13B), and then wet etching is performed to taper the silicon oxide film 51 (FIG. 13C).
[0050]
Thus, assuming that the thickness of the polysilicon film 52 used in FIGS. 12A and 13A is the same Th, the taper angle of the mask can be set smaller as the width (size) of the polysilicon film 52 is smaller. The taper angle of the mask can be set smaller as the thickness of the cut 51 is thinner.
[0051]
The taper angle of the mask can be controlled by combining these taper mask forming methods.
[0052]
Here, a case where a Pt film having a thickness of 0.5 μm is etched using the etching apparatus of FIG. 3 using a SiO 2 mask will be described with reference to FIG.
[0053]
As described above, the gas used for etching is mainly chlorine, and etching is performed by applying a bias voltage to the wafer. At this time, the etching rate of SiO2 and the etching rate of Pt are approximately the same, so the thickness of the SiO2 mask The thickness should be equal to or more than the thickness of Pt, and is 0.5 μm here.
[0054]
In the apparatus of FIG. 1, rd / re is a certain value or more under the condition that the plasma can be stably maintained, and the minimum value is 0.4 here. At this time, according to FIG. 6, when the taper angle of the SiO 2 mask is 90 °, the taper angle of the Pt film becomes 57 ° by etching Pt.
[0055]
That is, the width y of the bottom surface of Pt is larger by about 0.3 μm on each of the one side x1 and x2 than the width of the SiO2 mask. This is obtained from x1 = x2 = 0.5 μm / tan φ = 0.5 μm / tan 57 °. Therefore, if the total width of the mask is 0.5 μm, if the Pt film is etched by 0.5 μm, the width y of the bottom surface of Pt becomes y = 0.5 μm + x1 + x2 = 1.1 μm.
[0056]
However, if the SiO2 mask is given a taper angle of 80 ° by any of the methods described above and etched under the same conditions, the taper angle of the Pt film after etching is 70 ° and the width y of the bottom surface of the Pt film is , Larger by about 0.2 μm on one side than the width of the mask. Therefore, the total width y of the bottom surface of the Pt film is about 0.9 μm (y = 0.5 μm + 0.2 μm + 0.2 μm).
[0057]
By reducing the taper angle of the mask in this way, the taper angle of the Pt film after etching is increased. In other words, the etching shape can be controlled by the taper angle of the mask.
[0058]
Further, when the mask taper angle is reduced (for example, 60 °), the taper angle of etching is increased, but it is a condition that deposits do not adhere to the mask.
[0059]
Accordingly, the condition for increasing the taper angle and maintaining the size of the bottom surface of the mask before etching is that the taper angle of the mask is θ0.
[0060]
The taper angle θ0 of the mask can be predicted from the etching result using a vertical mask. That is, assume that φ (for example, 60 °) is obtained as a result of etching using a vertical mask. At this time, the rd / re value (0.37) under the conditions can be estimated from FIG. Formula to predict the taper angle of the above etching
[0061]
tan φ = (re−rd) / ((rd−re × cos θ) × sin θ)
The estimated value (0.37 in this case) is substituted into rd / de, and θ (77 °) satisfying φ = θ may be obtained.
[0062]
(C) Next, a silicon oxide mask having substantially vertical sidewalls (that is, a taper angle of approximately 90 degrees) is used, and a method in which the effect of the taper mask is substantially obtained will be described with reference to FIGS. explain. First, a predetermined amount, for example, half of a desired etching amount of Pt50, which is a material to be etched, is etched using a mask of silicon oxide 51 whose side walls are substantially vertical (FIG. 14B). As described above, in this state, the deposit 55 is attached to the side wall of the mask of the silicon oxide 51 (FIG. 14B). Next, the deposit is removed (FIG. 14C). As a method for removing this deposit, a wet treatment using pure water, aqueous ammonia, sulfuric acid, hydrochloric acid, alcohol or a mixture thereof is typical. After removal of the deposit 55, the taper angle of the projection 50a of Pt50, which is the material to be etched, becomes φ1. After removing the deposit, the remaining amount of Pt50 is etched again to perform the desired amount of etching (FIG. 14D). At this time, the deposition film 56 is deposited on the mask of the silicon oxide 51 and the side wall of the convex portion 50a of the Pt 50, and the deposition film is deposited almost in the same manner as the first deposition film 55. Pt is exposed on the side wall of the convex portion 50b of the Pt 50 that has been shaved by the second etching. The taper angle of the convex portion 50b of Pt50 thus obtained is φ2 (where φ1 <φ2). In this way, the first etching and removal of the deposited material immediately after that, as shown in FIG. 14C, a substantial taper mask having a taper angle of φ1 made of the silicon oxide 51 and the convex portion 50a of Pt50 is obtained. . By using such a substantial taper mask, the taper angle of the material to be etched can be made an angle close to vertical.
[0063]
It should be noted that by repeating such etching and deposit removal a plurality of times, the taper angle of the material to be etched can be made closer to a perpendicular angle. If Pt, which is a material to be etched, is exposed on the side wall instead of a deposit in the shape obtained immediately after etching, there is an advantage that Pt is etched immediately upon overetching. When the deposition film is exposed, the deposition film is first etched at the time of overetching, and then Pt as the material to be etched is etched. Therefore, there is an advantage that the overetch time can be shortened.
[0064]
Next, a method for removing deposits will be described.
[0065]
As a method for removing the deposit, in addition to the wet process, a process using supercritical water or CO2 or a dry process using an appropriate gas system may be considered. This dry process may be performed using the same processing apparatus (same reaction vessel) as the Pt etching process. Furthermore, the same etching apparatus (the same reaction vessel) or another etching apparatus (another reaction vessel) may be used for a certain number of times of etching and another number of times of etching.
[0066]
As the dry treatment, for example, oxygen, hydrogen, ammonia, chlorine, hydrogen chloride, and alcohol may be introduced to generate plasma, and the sample may be plasma treated.
[0067]
As another method of wet treatment, for example, there is a method of exposing to supercritical carbon dioxide added with ammonia, alcohol, hydrochloric acid, hydrogen peroxide water, etc., thereby removing chloride adhering to the side wall. .
[0068]
Moreover, you may put the rinse and the drying process before or after the removal process of a deposit as needed. For example, when a wet process using a chemical solution is performed as a method for removing deposits, a cleaning process using pure water may be performed thereafter, followed by a drying process. When etching is performed in this manner, there is a point where the taper angle changes (rapidly) in the middle of the side wall of the mask or the material to be etched. Alternatively, it is possible to provide a portion having a clearly different taper angle in the middle of the side wall of the mask or the material to be etched. Most metal chlorides are water-soluble.
[0069]
Next, a case where the present invention is applied to a semiconductor device manufacturing apparatus will be described with reference to FIGS. 15A and 15B.
[0070]
The semiconductor manufacturing apparatus shown in FIG. 15A is a multi-chamber semiconductor device manufacturing apparatus, and includes an etching processing chamber 901, a wafer transfer robot 903, a load lock chamber 904, an unload lock chamber 905, a loader 906, and a stocker 907. A cassette 908 is placed on the stocker 907. When a wafer is processed in the processing chamber 901, the wafer 105 placed in the cassette 908 under substantially atmospheric conditions is carried by the loader 906 to the load lock chamber 904 under almost atmospheric conditions, and the load lock chamber is closed. After reducing the pressure in the load lock chamber 904 to an appropriate pressure, the wafer 105 is transferred to the processing chamber 901 by the wafer transfer robot 903 and etched halfway. Thereafter, the wafer 105 is transferred to the deposit removal processing chamber 902 by the wafer transfer robot 903, and the deposit on the side wall is removed. Next, the wafer 105 is again transferred to the etching chamber 901 ′ by the wafer transfer robot 903 and etched by a desired amount. After that, the wafer 105 is transferred to the deposit removal processing chamber 902 ', and the deposit on the side wall is removed. Then, the wafer 105 is transferred to the unload lock chamber 905 by the wafer transfer robot 903. After the pressure in the unload lock chamber 905 is raised to almost atmospheric pressure, it is inserted into the cassette 908 by the loader 906.
[0071]
Thus, FIG. 15A shows a wafer transfer device (903), a plurality of processing chambers (901, 901 ′) and a plurality of post-processing chambers (902, 902 ′) connected to the wafer transfer device, and a plurality of locks. A chamber (904, 905) and an atmospheric transfer device (906) adjacent to the lock chamber, the atmospheric transfer device connected to the plurality of lock chambers and a wafer cassette (908) adjacent to the atmospheric transfer device; A semiconductor manufacturing apparatus capable of etching a material to be processed in any one of the plurality of processing chambers, performing a post-processing in any one of the plurality of post-processing chambers, and then performing the plurality of processes. Etching is performed in any one of the chambers, and further, post-processing is performed in any one of the plurality of post-processing chambers.
[0072]
In the example of FIG. 15A, an atmospheric cassette is used, but a vacuum cassette may be used as shown in FIG. 15B. That is, FIG. 15B shows a wafer transfer device (903), a plurality of processing chambers (901, 901 ′) connected to the wafer transfer device, a plurality of lock chambers (904, 905), and adjacent to the lock chamber. An atmospheric transfer device (906), and the atmospheric transfer device is a semiconductor manufacturing apparatus connectable to the plurality of lock chambers, a post-processing chamber (902) adjacent to the atmospheric transfer device, and a wafer cassette (908). Then, after the material to be processed is etched in any one of the plurality of processing chambers, post-processing is performed in the post-processing chamber, and then etching is performed in any one of the plurality of processing chambers. Post-processing may be performed in the chamber.
[0073]
Furthermore, for the sake of explanation, the deposit removal process is performed under vacuum conditions, but may be performed under atmospheric pressure conditions.
[0074]
In the above example, the etching process is performed twice using different etching chambers 901 and 901 ′, but only the same processing chamber 901 may be used a plurality of times. An advantage of using another processing chamber as an etching processing chamber is that, when a laminated film is etched, it can be stably etched under different conditions for each film type. It is also possible to perform etching and removal of deposits in the same chamber.
[0075]
Next, using the method (c) shown in FIGS. 14A to 14F, a stacked film such as Pt / PZT / Pt which is a memory portion of the ferroelectric memory is etched using a substantially tapered mask. The method will be described with reference to FIGS. 16A-16D. In this case, when the Pt / PZT / Pt film 61-63 shown in FIG. 16A is processed by one etching, deposition of deposits inevitably progresses on the side walls of these layers 61-63, and the shape shown in FIG. 16D. It becomes. That is, the difference between the dimension of the mask 64 and the dimension of the material to be etched is increased. This dimensional difference hinders miniaturization.
[0076]
Therefore, immediately before etching the conductor (for example, Pt) film 61 positioned under the insulating film (PZT) 62, the etching is interrupted and the deposition is removed (FIG. 16B). Then, the taper angle of the PZT / Pt film 62-63 becomes φ3. Thereafter, when etching is performed again, a shape as shown in FIG. 16C is obtained. In this case, the taper angle of the Pt film 61 is φ4 (here, φ3 <φ4). Characteristically, conductors (for example, Pt films 61 and 63) of the same material are formed above and below the insulating film (PZT) 62, but their taper angles φ3 and φ4 are different. Of course, the taper angle φ4 can be set larger than the taper angle φ5 shown in FIG. 16D.
[0077]
In this way, by the first etching and removal of the deposited material immediately after that, as shown in FIG. 16C, the taper angle of φ3 consisting of the insulating film (PZT) 62 and the conductor (for example, Pt) film 63 is substantially reduced. A taper mask is obtained. By using such a substantial taper mask, the taper angle of the material to be etched can be set to an angle close to vertical in the laminated film.
[0078]
Further, by using the method (c) shown in FIGS. 14A-14F or the method shown in FIGS. 16A-16C, a stacked film of MRAM (magnetic random access memory) expected as a next-generation memory device is substantially formed. A method of etching using a tapered mask will be described with reference to FIGS. 17A to 17D.
[0079]
The MRAM has a laminated film as shown in FIG. 17A. That is, from the top, a ferromagnetic material (for example, Co) 76, an insulating film (for example, Al2O3) 75, a ferromagnetic material (for example, Co) 74, an antiferromagnetic material (for example, FeMn) 73, a base material (for example, Co and Si) 72, 71. Reference numeral 70 denotes a silicon oxide film 70, for example. In MRAM, it is required to etch these films 71-76 using one mask.
[0080]
In this case, for example, when adhesion of the reaction product of the FeMn film 73 is more intense than adhesion of other materials, the etching is interrupted and depot removal is performed immediately before the etching of the FeMn film 73 is started (FIG. 17B). Then, the taper angle of the film 74-76 becomes φ6. Thereafter, when the etching is resumed, the FeMn film 73 can also be etched in a shape close to vertical (FIG. 17C). At this time, the taper angle of the FeMn film 73 is φ6 <φ7. As described above, the first etching and the removal of the deposit immediately after that, and the second etching and the removal of the deposit immediately after that, as shown in FIG. An altered, substantially tapered mask is obtained. By using such a substantial taper mask 73-77, the taper angle φ8 of the materials to be etched 71, 72 can be made to be nearly vertical in the laminated film such as MRAM (where φ6 <φ7). <Φ8).
[0081]
In addition, what is considered as a ferromagnetic material is mainly Fe, Co, Ni, Mn, or a compound thereof, all of which are known as difficult-to-etch materials. In the figure, reference numeral 77 denotes a mask.
[0082]
In the above example, a method of devising a mask shape or a substantially tapered mask shape in order to make the side wall of the material to be etched substantially vertical has been described. However, the present invention described below is a modification of etching conditions. Thus, the side wall of the material to be etched can be made vertical.
[0083]
As described above, the taper angle of etching is determined by the ratio rd / re of the deposition rate rd to the side wall of the mask or the material to be etched and the etching rate re of the bottom surface, and the smaller the rd / re, the more the side wall of the material to be etched. The taper angle can be close to vertical.
[0084]
Up to now, etching has been performed under the condition that deposits do not easily adhere to the wall of the vacuum vessel (104 in FIG. 3). To reduce deposition deposits, the concentration of reaction products in the vacuum vessel is reduced. Lowering is effective. Under conditions where deposits do not adhere to the wall of the vacuum vessel, the reaction product in the gas phase can be reduced by exhausting the reaction product in the gas phase out of the vacuum vessel, or by a mask or material to be etched. The only way is to attach it to the side wall. Therefore, in practice, the concentration of the reaction product in the gas phase is kept high under the condition that the deposit does not adhere to the wall of the vacuum vessel.
[0085]
  However, in FIG.119By reducing the impedance of the electrostatic coupling antenna 118, the reaction product can be easily attached to the wall of the vacuum vessel 104. At this time, since the concentration of the reaction product in the gas phase is reduced by adhering to the wall of the vacuum vessel, the amount of the reaction product incident on the wafer from the gas phase is reduced. As a result, deposition of deposits on the mask and the side wall of the material to be etched is reduced. Therefore, even when a mask having a side wall of approximately 90 degrees is used, the shape of the side wall of the material to be etched is nearly vertical.
[0086]
However, if deposits adhere to the wall of the vacuum vessel, the state of the plasma may change or particles may be generated. Therefore, the deposits need to be removed periodically. Therefore, for example, every time one or more wafers are processed, a deposit removal process (that is, a process such as increasing the current flowing through the electrostatic coupling antenna 118) is performed.
[0087]
At this time, the temperature of the wafer support table (sample table) 109 is set higher than that at the time of etching, so that the deposits do not adhere to the wafer support table 109, and the deposits are quickly exhausted out of the vacuum vessel 104. You can make it. Or, conversely, the temperature of the wafer support 109 is lowered and the deposit is positively attached to the wafer placed on the support or the support, and the deposit is placed on the support or the support. It is also possible to prevent the deposits from re-adhering to the wall of the vacuum vessel and prevent the deposits from being reflected from the wafer to facilitate the exhaust of the deposits.
[0088]
【The invention's effect】
According to the present invention, in etching of a material in which it is difficult to obtain a processed shape with a vertical sidewall, an etching shape with a sidewall substantially vertical can be obtained by using a tapered mask or the like. High-quality semiconductor devices can be created.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view for explaining an etching process using a mask having a vertical sidewall.
FIG. 2 is a cross-sectional view for explaining an etching process using a mask having a vertical sidewall.
FIG. 3 is a diagram showing an example of the overall configuration of a plasma etching apparatus to which the present invention is applied.
FIG. 4 is a cross-sectional view for explaining an etching process when the taper angle θ of the mask is less than 90 degrees.
FIG. 5 is a cross-sectional view for explaining the relationship between the deposition state of deposits on the mask side wall and the taper angle φ of the material to be etched when the taper angle θ of the mask is gradually decreased from 90 degrees.
FIG. 6 is a diagram showing a relationship between a taper angle of a mask and a taper angle of a material to be etched.
FIG. 7 is a diagram showing the relationship between the taper angle of the mask and the taper angle of the material to be etched in a region where the taper angle of the mask is less than the limit value and a region where the taper angle is greater than or equal to the limit value.
FIG. 8 is a diagram for explaining a method of controlling the taper angle of a mask by using an etching gas component and an etching pressure.
FIG. 9 is a diagram for explaining a method of controlling the taper angle of a mask by wet etching.
FIG. 10 is a view for explaining a method of controlling the taper angle of a mask by wet etching.
FIG. 11 is a diagram for explaining another method for controlling the taper angle of a mask by wet etching.
FIG. 12 is a diagram for explaining a method of controlling a taper angle of a mask by dry etching and wet etching.
FIG. 13 is a diagram for explaining another method for controlling the taper angle of a mask by dry etching and wet etching.
FIG. 14 is a diagram for explaining a method of obtaining the effect of a substantially tapered mask by using a mask having a taper angle of approximately 90 degrees.
15A is a block diagram showing a configuration example of a semiconductor device manufacturing apparatus to which the present invention is applied, and FIG. 15B is a block diagram showing another configuration example of a semiconductor device manufacturing apparatus to which the present invention is applied.
FIG. 16 is a diagram for explaining a method for obtaining the effect of a substantially tapered mask by using a mask having a taper angle of approximately 90 degrees in a ferroelectric memory;
FIG. 17 is a diagram for explaining a method in which the effect of a substantially tapered mask can be obtained using a mask having a taper angle of approximately 90 degrees in the MRAM;
FIG. 18 is a cross-sectional view for explaining an etching process using a mask having a vertical sidewall.
[Explanation of symbols]
10 Mask
20 Material to be etched
21 Top surface of material to be etched
25 Depot
30 Top surface of the deposit

Claims (2)

Pt formed on a substrate, Ru, Ir, PZT, either aluminum HfO _2, silicon, a film of etching hardly difficult to etch material than the oxide silicon down, silicon oxide was formed on the film or In the etching method of a difficult-to-etch material using a mask made of metal and etching using plasma generated using a gas containing at least chlorine that can etch the difficult-to-etch material,
Taper angle θ that the side walls with respect to the surface of the substrate is tanθ = (re-rd) / - in ((rd recosθ) × sinθ) ( here, re mask etch rate, rd the mask side wall of the case Etching the mask to be equal to an angle θ given by
Removing deposits deposited during etching of the mask during etching;
Thereafter, the step of etching the mask again to form the mask,
A method of etching a difficult-to-etch material, comprising the step of etching the difficult-to-etch material using the mask. Pt formed on a substrate, Ru, Ir, PZT, either aluminum HfO _2, silicon, a film of etching hardly difficult to etch material than the oxide silicon down, silicon oxide was formed on the film or In a method of etching a difficult-to-etch material using a mask made of metal, etching using plasma generated using a gas containing at least chlorine that can etch the difficult-to-etch material, and attaching a reaction product to the wall of the etching apparatus,
Taper angle θ that the side walls with respect to the surface of the substrate is tanθ = (re-rd) / - in ((rd recosθ) × sinθ) ( here, re mask etch rate, rd the mask side wall of the case Etching the difficult-to-etch material using a mask that is equal to an angle θ given by
Etching the difficult-to-etch material while reducing the current flowing through the capacitively coupled antenna that generates the plasma and attaching the reaction product to the wall of the etching apparatus. An etching method for a difficult-to-etch material, wherein the angle of the side wall with respect to the surface of the substrate is maximized toward 90 degrees.

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