JP3246707B2 - Ferroelectric film etching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nonvolatile memory device,
The present invention relates to a ferroelectric film etching method for finely processing a ferroelectric film used for a volatile memory capacitor, a light modulation element, a piezoelectric element, a pyroelectric infrared sensor, and the like.

[0002]

2. Description of the Related Art In recent years, ferroelectric nonvolatile memory devices using a ferroelectric film having spontaneous polarization for a capacitor have been actively developed. The ferroelectric material is PZ
T (Pb (Zr, Ti) O ₃ , lead zirconate titanate), PbTiO ₃ (lead titanate), BaTiO ₃ (barium titanate), PLZT ((Pb, La) (Zr, T
i) Oxides such as O ₃ (lead lanthanum zirconate titanate)) are mainly used. Among them, PZT is currently regarded as the most promising material for nonvolatile memory, and energetically studied.

When a ferroelectric film is applied to a ferroelectric nonvolatile memory, fine processing of the ferroelectric film is important. Conventionally, wet etching (S. Trolier, et.al, Proc. Sixth IEEE In) has been used for etching a ferroelectric film such as a PZT film.
t. Symp. on Appl. of Ferroelectrics, Bethlehem, PA. (1
986) p. 107), ion milling using Ar (S. Lee, e
t.al., Optical Engineering 25 (1986) p.250), CC
Chemical etching with l ₂ F ₂ mixed gas (Dilip P, et.a
l., J.Electrochem.Soc., Vol.140, No.9, (1933) p2635) or HCl / CF ₄ chemical etching with a mixed gas (MRPoor, et.al., Mat.Res.Soc.Symp.Proc .vol.200 (19
92) p. 211) and chemical etching using CCl ₄ (K. Sait
o, et.al., Jpn, Appl. Phys. Vol. 31 (1992) p. L1260).

[0004]

However, when a ferroelectric nonvolatile memory having a high degree of integration is formed, very fine processing is required, so that it is difficult to cope with wet etching. In addition, ion milling using an inert gas such as argon has a low etching rate, and causes problems such as contamination due to re-adhesion of the etched substance and a dimension shift due to re-adhesion to a mask side wall. On the other hand, in order to reduce this re-adhesion, when the pressure is increased to reduce the number of ions vertically incident on the ferroelectric film and the side wall is tapered, the line width is accurately controlled by the presence of the taper. There is also a problem that can not be.

Further, even in the case of chemical etching using fluorine gas or chlorine gas, particularly in the case of a ferroelectric film such as PZT or PLZT, it is difficult to form a halide having a high vapor pressure with respect to lead. There have been problems that the rate is slow and dimensional shift occurs due to deposits on the mask side wall.

For example, as shown in FIG. 14, when sputter etching using an argon gas or chemical etching using only SF ₆ is performed, a non-volatile deposit adheres to the mask side wall, causing a dimensional shift. FIG. 14 is a diagram for explaining the problems of the conventional technology, in which 21 is a silicon substrate, 22 is NSG (Non-doping Silicate Glass).
Film, 23 a Ti film, 24 a TiN film, 25 a Pt / Ti
Reference numeral 26 denotes a Pt film, 27 denotes a PZT film, and 28 denotes a side wall deposition film.

SUMMARY OF THE INVENTION The present invention has been made to solve such problems of the prior art, and has as its object to provide a method of etching a ferroelectric film which can suppress or prevent the occurrence of dimensional shift at a high etching rate. Aim.

[0008]

According to a first aspect of the present invention, there is provided a method for etching a ferroelectric film according to the present invention, wherein an etching resistant film serving as a mask is patterned on a ferroelectric film made of a compound with lead. in the dry etching method of a ferroelectric film to etch the ferroelectric film in the region not covered with the film, as an etching gas, a mixed gas of inert gas and a halogen gas or halide gas, the mixed gas Halogen gas or
Are those flow ratio of the halide gas is characterized der Rukoto 50% or less.

[0009] The etching process of the ferroelectric film of the present invention according to claim 2, characterized in that the temperature during etching is in the range of 100 ° C. or higher 400 ° C. or less, claims
1 SL is an etching method of mounting of the ferroelectric film.

[0010] The etching process of the ferroelectric film of the present invention according to claim 3, characterized in that the halogen gas or the halide gas is chlorine gas or chloride gas, according to claim 1 or claim Item 3. A method for etching a ferroelectric film according to Item 2 .

Furthermore, the etching process of the ferroelectric film of the present invention described in claim 4, claim 1, characterized in that a silicon oxide film in the etch-resistant film, according to claim 2 or claim 3 It is a method of etching a ferroelectric film as described above.

According to a fifth aspect of the present invention, there is provided a method of etching a ferroelectric film according to the present invention, wherein an etching-resistant film serving as a mask is patterned on a ferroelectric film made of a compound with lead, and is not covered with the etching-resistant film. In the method of etching a ferroelectric film for etching a ferroelectric film in a region, dry etching is performed using a mixed gas of an inert gas, a halogen-based first gas, and a halogen-based second gas as an etching gas. Then, the compound formed on the side wall of the etched ferroelectric film is removed by wet treatment with an aqueous solution.

[0013] The etching process of the ferroelectric film of the present invention described in claim 6, the flow ratio of the inert gas to the total flow rate of the first and second gas of the inert gas and the halogenated 6. The method for etching a ferroelectric film according to claim 5 , wherein the content is less than 50%.

[0014] The etching process of the ferroelectric film of the present invention of claim 7,8, wherein, when performing the dry etching, a gas pressure in the vacuum chamber during discharge 1m
An etching method of a ferroelectric film according to any one of claims 1 to 6, characterized in that in the 10mTorr following range of Torr.

According to a ninth aspect of the present invention, in the method for etching a ferroelectric film according to the present invention, the inert gas is Ar gas, and the first halogen-based gas is CF ₄ gas or SF ₆ gas.
A gas, according to claim 5, wherein the second gas of the halogen system is CHF ₃ gas, as an etching method of a ferroelectric film according to claim 6 or claim 8, wherein.

According to a tenth aspect of the present invention, there is provided a method for etching a ferroelectric film according to the present invention, wherein the halogen-based first gas and the halogen-based second gas have a halogen-based second gas flow rate. The flow ratio to the flow rate of one gas is 7
The method for etching a ferroelectric film according to claim 9 , wherein the content is less than 0%.

[0017] The etching process of the ferroelectric film of the present invention of claim 11 wherein the etching of the ferroelectric film according to claim 5, wherein the aqueous solution used in the wet process is H ₂ O Is the way.

[0018] The etching process of the ferroelectric film of the present invention according to claim 12, claim 11, wherein the temperature of the aqueous solution used in the wet process characterized in that it is a range of 100 ° C. or higher 25 ° C. Is a method of etching a ferroelectric film.

[0019]

According to the first aspect of the present invention, as the etching gas,
By performing etching using a mixed gas of an inert gas and a halogen gas or a halide gas, a bonding force between lead oxygen contained in a PZT film or the like which is a ferroelectric film is increased by an inert gas sputtering action. The ferroelectric film can be etched by weakening, promoting the halogenation of lead with a halogen gas or a halide gas, and evaporating the halide gas by raising the atmosphere during etching to a high temperature.

In the second invention, the PZT film or the like is etched using a mixed gas of an inert gas, a halogen-based first gas, and a halogen-based second gas as an etching gas. Thereby, the bonding force between lead and oxygen contained in the PZT film or the like is weakened or beaten out by the sputtering action of the inert gas to promote the halogenation of lead with the halogen-based first gas and the second gas, Evaporate as halide gas. At this time, the compound which is halogenated and adheres to the side wall is removed by treating with warm water.
Further, by using the halogen-based first gas and the second gas, it is possible to improve the selectivity with respect to the resist and protect the side wall of the resist, thereby suppressing the dimensional shift due to the receding of the resist.

Further, in the reference example , the ferroelectric film is etched using an inert gas and a halogen gas or a mixed gas of a halide gas and a hydrocarbon gas as an etching gas. Pb, Z contained in ferroelectric film
Each element such as r and Ti is weakened in bonding force with oxygen by sputtering with an inert gas. Thereby, the halogenation of each element contained in the ferroelectric film is promoted, and the element is volatilized as a halide gas. Further, by using the hydrocarbon gas, the etching can be performed while suppressing the erosion of the side wall of the photoresist, thereby increasing the etching rate and suppressing the dimensional shift. At this time, the compound which is halogenated and adheres to the side wall can be removed with water or the like.

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 1 is a sectional view showing an etching process of a ferroelectric film in this embodiment, and FIG. 2 is a schematic view of an ECR (Electron Cyclotron Resonance) plasma etching apparatus used in this embodiment. FIG. 3 is a diagram showing a change in the etching rate of the mask when the amount of chlorine gas added is changed.
Is a diagram showing the relationship between RF output and etching rate,
FIG. 5 is a diagram showing the relationship between RF output and selectivity. In FIG. 1, 1 is a silicon substrate, 2 is an NSG film, 3 is a Ti film,
Is a TiN film, 5 is a Pt film, 6 is a PZT film, 7 is Pt / T
In FIG. 2, 9 is a microwave, 10 is a high frequency power supply, 11 is a solenoid coil, and 1 is an SOG film.
2 is a wafer, 13 is an electrode, 14 is a Cl ₂ gas inlet, 1
5 is an Ar gas inlet. The present invention can be implemented by using an apparatus capable of generating high-density plasma (for example, HWP (helicon wave), ICP (inductive coupling) plasma) under low pressure as generated by an ECR plasma etching apparatus. is there.

Hereinafter, a method of etching a ferroelectric film according to this embodiment will be described with reference to FIG.

First, an NSG film 2 having a thickness of about 300 nm is formed on a silicon substrate 1 by a CVD method.
In order to improve the adhesion between the NSG film 2 and the TiN film 4,
A Ti film 3 having a thickness of about 20 nm is formed using a sputtering method. This sputtering was performed at a flow rate of argon = 85 SCCM, R
The test was performed under the conditions of F power = 3 kW and pressure = 2.5 mTorr.

Next, a TiN film 4 having a thickness of about 200 nm was formed as a barrier layer by using a sputtering method. In this sputtering, the argon flow rate was 58 SCCM, and the nitrogen flow rate was 76 SC.
CM, RF power = 5 kW, pressure = 4 mTorr were performed. Thereafter, in order to improve the adhesion between the TiN film 4 and the Pt film 5, the Ti film 3 is formed under the above conditions, and then the Pt film 5 is formed as a lower electrode of the ferroelectric film capacitor by sputtering. A film of about 100 nm was formed. In this sputtering, argon flow rate = 120 SCCM, RF power =
The test was performed under the conditions of 2 kW and pressure = 4 mTorr.

Next, a PZT film 6 as a ferroelectric film was formed by a sol-gel method. In this film forming method, a PZT sol-gel solution is formed on a Pt film 5 by a spin coater,
Preliminary baking was performed at 00 ° C. for 1 hour (see FIG. 1A).
Thereafter, RTA (Rapid Thermal) is performed as annealing at 600 ° C. for 30 seconds as main firing of the PZT film 6.
Anneal). The thickness of the PZT film 6 after the main baking was about 250 nm. At this time, the Ti film 3 between the Pt film 5 and the TiN film 4 is eutectic with Pt, and P
A t / Ti film 7 is formed (see FIG. 1B). Further, the Pt film 5 as an electrode is in a state like an aggregate of grains.

Next, an SOG (Spin On Glass) film 8 is formed on the PZT film 6 as an anti-etching film by a spin coater to a thickness of 1 μm and baked.

For use as a mask, the reaction between the mask material and the PZT film 6 during film formation must be suppressed. For example, when an SOG film is used as a mask as in this embodiment, no interface reaction occurs even when the temperature at the time of film formation rises to near 350 ° C., and when an NSG film is used as a mask, 400 It is known from TEM analysis that no interfacial reaction occurs even when the temperature rises to about ° C.

Thereafter, patterning of 0.8 μm to 2.5 μm square is performed by photolithography using a resist, and the SOG film 8 is etched to
The SOG film 8 was used as a mask. The etching conditions for the SOG film 8 were as follows: a microwave plasma etching apparatus was used, the flow rate of CF ₄ was 50 SCCM, the pressure was 5 mTorr, the microwave output was 200 mA, and the RF output was 40 W. After that, the resist was removed by an ashing process (see FIG. 1C).

Next, using an ECR plasma etching apparatus as shown in FIG. 2, as an etching gas, Ar was introduced at a flow rate of 63 SCCM, Cl ₂ was introduced at a flow rate of 27 SCCM, the pressure was 1.4 mTorr, the microwave output was 1000 W, and
Assuming that the RF output is 100 W and the substrate surface temperature is 300 ° C.
The PZT film 6 is etched (see FIG. 1D).

The substrate surface temperature is preferably 100 ° C. or higher in order to volatilize the halide of lead. No reaction occurs at the interface between the etching mask and the PZT, and the quality of the PZT film 6 is reduced. Since it is necessary to keep the temperature unchanged, 400 ° C. or less is appropriate. Further, as the halogen gas, it is appropriate to use chlorine (Cl ₂ ) gas or chloride which is easier to volatilize than other halogen gases. As the chloride, CCl ₄ , CHCl ₃ or the like can be used. The degree of vacuum at the time of etching is 1 to 10 mTorr as a range in which stable plasma can be obtained by microwave (ECR). Further, as shown in FIG. 3, when the flow rate ratio of chlorine gas to the total flow rate of the etching gas is in the range of 50% or less, the etching rate of the SOG film 8 serving as a mask tends to decrease, but the etching rate of the PZT film 6 is reduced. It is appropriate that the flow rate ratio of chlorine gas to the total flow rate of the etching gas is less than 50% as a range that can be used as a mask so that the selectivity (SOG film 8 / PZT film 6) is considered in this embodiment. The flow rate ratio was set to 30%. Further, as the RF output increases as shown in FIG. 4, the etching rate increases, but when the selectivity is considered as shown in FIG.
The range of (W) is more appropriate. 100-150 (W)
The reason is that the selectivity (PZT / Pt) between the PZT film 6 to be etched and the Pt film 5 thereunder is 100 W
However, considering the uniformity of the surface shape of the Pt film 5 after etching, the selectivity of PZT / Pt is 1
This is because it needs more.

In the conventional chemical etching using a fluorine-based gas, when the thickness of the PZT film is 3000 Å, the taper angle is 45 ° and the dimensional shift is 0.3 μm.
However, in the present embodiment, when the above-described conditions were used,
The dimensional shift was suppressed to 0.05 μm or less.

In sputter etching using Ar gas, the pressure is set to 1.4 mTorr, and the microwave output is set to 1000 mTorr.
W, RF output 200W, substrate surface temperature 200-30
At 0 ° C., the etching rate was 300 Å, but the flow rate of Ar was 63 SCCM, Cl ₂
When a gas system with a flow rate of 27 SCCM was used, the etching rate increased to 520 Å.

When the substrate surface temperature is 100.degree.
In the range of not more than ° C., a resist can be used as a mask, but the side wall of the resist is etched and receded, so that a dimensional shift of 0.1 to 0.2 μm occurs. On the other hand, when a silicon oxide film is used as the etching resistant film, the substrate temperature during etching is 100 ° C. or more and 400 ° C.
In the following cases, the pattern is not deformed, the dimensional shift can be suppressed, and the volatilization of the halide can be further promoted.

As described above in detail, according to the present embodiment, a fine etching of a ferroelectric film containing a lead compound or the like can be performed at a high etching rate, with little or no dimensional shift, and with high precision. Becomes

In the case of this embodiment, when a resist is used as a mask in a temperature range where a resist mask can be used, a slight dimensional shift may occur, leaving room for improvement.

(Embodiment 2) This embodiment is a case in which a dimensional shift is completely prevented.

FIG. 6 is a cross-sectional view showing an etching process of the ferroelectric film of the present embodiment. In FIG. 6, 31 is a silicon substrate, 32 is an NSG film, 33 is a Ti film, and 34 is a Ti film.
N film, 35 is Ti film, 36 is Pt film, 37 is PZT film,
38 is a Pt / Ti film, 39 is a resist film, and 40 is a side wall deposition film.

In this embodiment, etching is performed as follows.

First, as shown in FIG. 6A, an NSG film 32 is formed on a silicon
m is formed thereon, and as an adhesion layer for improving the adhesion between the NSG film 32 and the TiN film 34, a T
An i film 33 was formed to a thickness of 20 nm. In this sputtering, Ar flow rate = 85 SCCM, RF power = 3 kW, pressure = 2.5 m
The test was performed under Torr conditions.

Thereafter, a 200 nm-thick TiN film 34 was formed as a barrier layer by sputtering. This sputter has N ₂ flow rate = 76 SCCM, Ar flow rate = 58 SCCM, R
The test was performed under the conditions of F power = 5 kW and pressure = 4 mTorr.

Thereafter, as an adhesion layer for improving the adhesion between the TiN film 34 and the Pt film 36, a 20 nm-thick Ti film 35 was formed under the same conditions as the above-mentioned Ti film 33.

Thereafter, a Pt film 36 having a thickness of 100 nm was formed as a lower electrode of the ferroelectric thin film capacitor by a sputtering method. This sputtering is performed at an Ar flow rate of 120 SCCM, RF
The test was performed under the conditions of power = 2 kW and pressure = 4 mTorr.

Thereafter, a PZT film 37 which is a ferroelectric thin film is formed.
Was formed using a sol-gel method. In this film formation, a sol-gel solution of PZT was formed on the above-mentioned Pt film 36 by a spin coater, and calcination was performed at 400 ° C. for 1 hour.

Next, after stacking in this manner, RTA (Rap) at 660 ° C. for 30 seconds is performed as the main firing of the PZT film 37.
id Thermal Anneal) (FIG. 6)
(B)). The thickness of the PZT film 37 after the main baking is 250
nm. After the main baking, the Ti film 35 between the Pt film 36 and the TiN film 34 becomes eutectic with Pt, and becomes a Pt / Ti film 38. Etching is performed on the sample wafer thus obtained.

Next, as shown in FIG. 6C, a resist film 39 is formed to a thickness of 2 μm on the PZT film 37 and a pattern of 0.8 to 2.5 μm square is formed by photolithography. Was used as a mask.

Next, the PZT film 37 was etched using the ECR plasma etching apparatus shown in FIG.
The etching conditions are Ar: CF ₄ as an etching gas.
(Halogen-based first gas): CHF ₃ (Halogen-based second gas) = 1: 1: 2 or Ar: SF ₆ (Halogen-based first gas)
Gas): CHF ₃ (halogen second gas) = 1: 1: 2
Pressure = 1.4 mTorr, μ wave output = 1000
W, RF output = 100 W, substrate surface temperature = 50 ° C. By this etching, as shown in FIG.
The side wall deposition film 40 was formed on the side wall of the PZT film 37.

Next, the side wall deposition film 40 was removed with warm water, and then the resist film 39 was removed by ashing (see FIG. 6E). It has been confirmed that the hot water can be removed in 10 minutes or more at 25 ° C. and 5 minutes or more at 100 ° C. By using hot water, it is possible to avoid an increase in cost when another processing liquid is used, and also possible to avoid damage due to the processing liquid. The degree of vacuum at the time of etching is preferably 1 to 10 mTorr as a range in which stable plasma can be obtained by microwaves (ECR), and it is desirable to use a high vacuum region as much as possible in order to obtain higher anisotropy. . Therefore, in this embodiment, the pressure is set to 1.4 mTorr.

As described above, according to the second embodiment, it is possible to eliminate the side wall deposition film, and it is possible to perform fine processing of PZT with high precision without dimensional shift.

In the first embodiment, it is necessary to increase the substrate temperature to about 300 ° C. in order to increase the vapor pressure. For this purpose, the SOG film is used as a mask. Therefore, a general resist film 39 can be used. Since the removal of the resist film 39 can be performed by ashing, the process can be simplified.

The selectivity can be improved by setting the flow rate ratio of the inert gas to the total flow rate of the inert gas and the halogen-based first gas and the second gas to less than 50%. For example, in the case of only Ar, PZT / P. Selectivity of R (photoresist) is _{0.5, Ar: CF 4 = 1} : 1 The PZT / P. The selection ratio of R is 2.4. Further, CH
The selectivity of the mixture of F ₃ and Ar: CF ₄ : CHF ₃ = 1: 1: 2 was 6.6. As described above, in the halogen-based first gas and the halogen-based second gas, the halogen-based second gas is used.
By setting the flow rate ratio of the gas flow rate to the flow rate of the halogen-based first gas to less than 70%, the selectivity can be further improved. The improvement of the selectivity is that the side etching of the resist serving as the mask is small. By performing the hot water treatment using the etching method of this embodiment, the dimensional shift can be suppressed to 0.05 μm or less.

In the Ar sputter etching, the etching rate is pressure = 1.4 mTorr, μ wave output = 1.
The etching rate was 300 Å / min at 000 W and RF output = 200 W, but the etching rate was increased to 550 Å / min when an Ar / CF ₄ / CHF ₃ gas system was used. When the Ar / SF ₆ / CHF ₃ gas system was used, the etching rate could be improved to 900 to 1000 Å / min. Therefore,
By using such an etching gas, rapid etching becomes possible.

( Reference Example ) This reference example (hereinafter referred to as Example 3) is a case where the dimensional shift is completely prevented by a method different from that of Example 2. Further, the method according to the present embodiment can be applied not only to the compound with lead as the ferroelectric film but also to PLZT, PNZT and other ferroelectric films containing impurities such as La and Nb. Further, the first and second embodiments can be applied to the above-described PLZT and PNZT.

In this embodiment, a sample wafer as shown in FIG. 7 was prepared, and etching was performed using etching containing a hydrocarbon gas. In FIG. 7, 41 is a silicon substrate, 42 is an NSG film, 43 is a Ti film, 44 is a TiN film,
45 is a Ti film, 46 is a Pt film, and 47 is a PZT film.

In this embodiment, etching was performed as follows.

First, an NSG film 42 having a thickness of about 300 nm is formed on a silicon substrate 41 by a CVD method.
A Ti film 43 having a thickness of about 20 nm was formed as a contact layer for improving the adhesion between the SG film 42 and the TiN film 44 by using a sputtering method. This sputtering was performed at an Ar flow rate of 85 SCCM, RF
The test was performed under the conditions of power = 3 kW and pressure = 2.5 mTorr.

Next, a TiN film 44 having a thickness of about 200 nm was formed as a barrier layer by a sputtering method. This sputter has a N ₂ flow rate of 76 SCCM, an Ar flow rate of 58 SCCM,
The test was performed under the conditions of RF power = 5 kW and pressure = 4 mTorr.

Thereafter, a Ti film 45 having a thickness of 20 nm was formed as an adhesion layer for improving the adhesion between the TiN film 44 and the Pt film 46 under the same conditions as the Ti film 43 described above.

Thereafter, a Pt film 46 having a thickness of about 100 nm was formed as a lower electrode of the ferroelectric thin film capacitor by a sputtering method. This sputtering is performed at an Ar flow rate of 120 SCC.
M, RF power = 2 kW, pressure = 4 mTorr.

Thereafter, a PZT film 47 as a ferroelectric thin film is formed.
Was formed using a sol-gel method. The PZT precursor solution is formed on the above-mentioned Pt film 46 with a spin coater,
Preliminary firing was performed at 400 ° C. for 1 hour. Furthermore, RTA (R
rapid Thermal Anneal), 66
The main baking was performed at 0 ° C. for 30 seconds. Etching is performed on the sample wafer thus obtained.

Next, a pattern of 0.8 to 2.5 μm square was formed by photolithography using a photoresist generally used in the manufacture of semiconductor devices, and this was used as a mask.

Next, the sample wafer was set in the ECR plasma etching apparatus shown in FIG. 2 and the PZT film 47 was etched. The etching gas is Ar gas flow rate =
59.5 SCCM, Cl ₂ gas flow rate = 25.5 SCC
M, CH ₄ gas flow rate was introduced at 5.0 SCCM. At this time, the gas inlets 14 and 15 are used to introduce Cl ₂ gas and Ar gas, and the gas inlet 1 is used to introduce CH ₄ gas.
4 and / or 15 were used. As another condition, the total pressure in the reaction chamber of the etching apparatus is 1.4 mTorr.
, The microwave power = 1 kW, the RF output = 100 W, and the substrate surface temperature was set to 8 with a current of 20 A of the solenoid coil.
0 ° C.

The total pressure in the reaction chamber at the time of the etching is within a range in which stable plasma can be obtained by ECR.
0.5 to 10 mTorr is desirable. Further, the total flow rate of the mixed gas is desirably 40 to 90 SCCM so that the pressure in the reaction chamber can be stably maintained by the variable valve.

FIG. 8 shows the relationship between the ratio of the flow rate of Cl ₂ gas to the total flow rate of the etching gas and the sectional profile angle of the ferroelectric film by etching. FIG. 9 shows the relationship between the total flow rate of the etching gas and the Cl ₂ gas. The relationship between the flow rate ratio and the etching rate is shown. As shown in FIG. 8, when the flow rate ratio of the Cl ₂ gas to the total flow rate of the etching gas exceeds 50%, the cross-sectional profile angle of the ferroelectric film by etching becomes small and the dimensional shift becomes large. Further, as shown in FIG. 9, when the flow rate ratio of the Cl ₂ gas to the total flow rate of the etching gas is less than 10%, the etching rate decreases. Therefore, the ratio of the flow rate of the Cl ₂ gas to the total flow rate of the etching gas is preferably in the range of 10% to 50%.

FIG. 10 shows the relationship between the flow rate ratio of the CH ₄ gas to the total flow rate of the etching gas and the selectivity of the ferroelectric film and the photoresist by etching. FIG. The relation between the flow ratio of CH ₄ gas and the thickness of the side wall deposition film is shown. As shown in FIG. 10, by adding CH ₄ gas to the etching gas, the side wall of the photoresist is protected, and the selectivity between the ferroelectric film and the resist is improved. However, as shown in FIG. 11, when the flow rate ratio of the CH ₄ gas to the total flow rate of the etching gas exceeds 10%, the deposition film (deposit) on the side wall increases and the dimensional shift increases. If the flow rate ratio is less than 2%, the side wall of the photoresist is etched and receded, so that the dimensional shift becomes large.
Therefore, it is desirable that the flow rate ratio of the CH ₄ gas to the total flow rate of the etching gas is in the range of 2 to 10%.

As an inert gas contained in such an etching gas, Ar gas or the like can be used, and thereby, an element such as lead contained in the ferroelectric film is sputtered to promote halogenation. Can be. Further, as the halogen gas or the halide gas, a chlorine gas or a chloride gas such as BCl ₃ , CCl ₄ , SiCl ₄ or the like is desirable, and the volatility of the halide is higher than when other halogen gas or halide gas is used. And rapid etching becomes possible. Further, as hydrocarbon gas,
_{C n H 2n + 2, C} n H 2n or C _n H _{2n-2 (n} is a positive integer)
And the like can be used, whereby the selectivity between the ferroelectric film and the mask can be improved.

The cross section of the PZT film etched as described above is as shown in FIG. 12, and the conventional etching method using ion milling is as shown in FIG. Comparing the two sections, it can be seen that according to the etching method of this embodiment, fine processing of a PZT thin film having a larger profile angle and a smaller dimensional shift is possible as compared with the case of using the conventional etching method. 12 and 15, 51 and 71 are Si substrates, 52 and 72 are NSG films, 53 and 73 are Ti films, 54 and 74 are TiN films, 55 and 75 are Ti films, and 56 and 76 are Pt films, 57 and 77 are PZT films, and 58 and 78 are side wall deposition films.

The etching rate in the third embodiment is 450 to 500 Å / min.
The etching rate by E was 1.5 times or more as compared with the etching rate of 300 Å or less.

Further, in the third embodiment, the use of the hydrocarbon gas can prevent the side wall of the photoresist from being eroded, and the use of the photoresist film simplifies the process. The substrate surface temperature is 150
If the temperature exceeds ℃, the photoresist is softened and deformed, so that high-precision fine processing becomes difficult. Therefore, it is desirable to keep the substrate surface temperature at 150 ° C. or lower by using a cooling device or the like.

The side wall deposition film generated by the etching in the third embodiment can be removed by washing in pure water at room temperature for 20 minutes. As shown in FIG. 13, the profile angle is large, the dimensional shift is small, and the precision is high. Fine processing was realized. Since normal-temperature water can be used, an increase in cost can be avoided, and no damage is caused by the processing liquid. In FIG. 13, 61 is an Si substrate, 62 is an NSG film, 63 is a Ti film, 64 is a TiN film, and 65 is a TiN film.
Reference numeral 66 denotes a Pt film, and 67 denotes a PZT film.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. For example, the inert gas, the halogen gas, the halide gas, the halogen-based first gas, the halogen-based second gas, and the hydrocarbon gas may be other than those described in the above embodiment. In the above embodiment, the etching of the PZT film has been described. However, the same effect can be obtained for PLZT, PNZT, and other ferroelectric films containing impurities such as La and Nb. It can be applied to etching of a film.

[0073]

As is clear from the above description, the first embodiment
According to the invention, by using a mixture of an inert gas and a halogen gas or a halide gas as an etching gas, a high etching rate, no dimensional shift,
It is possible to finely process a ferroelectric film made of a lead compound with little, if any, and high precision. Also, in the first invention,
And halogen gas or halogen as etching gas
Flow rate ratio to the total flow of
%, The choice between the mask and the ferroelectric film
Improves the precision, enabling more precise micromachining.
You.

Further, in the first invention, by setting the substrate surface temperature at the time of etching to 100 ° C. or more and 400 ° C. or less, the interface between the PZT film and the etching mask does not react, and the ferroelectric film The volatilization of the halide can be promoted without changing the film quality.

Further, in the first invention, by using a chlorine gas or a chloride gas as the halogen gas or the halide gas, the volatility of the halide is improved as compared with the case where another halogen gas or a halide gas is used. ,
Further, the etching rate can be increased or the etching can be performed at a low temperature.

Further, in the first invention, by using a silicon oxide film as the etching resistant film, pattern deformation does not occur even when the substrate temperature at the time of etching is 150 ° C. or more and 400 ° C. or less. Since the dimensional shift is suppressed as compared with the case where the etching is performed, the etching rate can be further increased.

According to the second aspect of the present invention, by using a mixed gas comprising an inert gas, a halogen-based first gas, and a halogen-based second gas as an etching gas,
A fine etching of a ferroelectric film made of a lead compound can be performed at a high etching rate, with no dimensional shift, and with high precision.

Further, in the second invention, the mask, the ferroelectric film, and the flow rate of the inert gas with respect to the total flow rate of the inert gas and the halogen-based first and second gases are less than 50%. Can be improved, so that fine processing can be performed with higher precision.

Further, in the second invention, the pressure of the gas in the vacuum chamber at the time of discharge is set to 1 mTorr or more and 10 mTo
By setting it within the range of rr or less, plasma can be stabilized and high anisotropy can be obtained, so that fine processing with higher precision can be performed.

In the second invention, Ar gas is used as the inert gas, CF ₄ gas or SF ₆ gas is used as the first halogen-based gas, and CH 4 gas is used as the second halogen-based gas.
The use of the F ₃ gas enables more rapid etching.

In the second invention, in the halogen-based first gas and the halogen-based second gas, the flow ratio of the flow rate of the halogen-based second gas to the flow rate of the halogen-based first gas is less than 70%. As a result, the selectivity between the mask and the ferroelectric film is further improved, so that more precise fine processing can be performed.

Further, in the second invention, the deposition film formed on the side wall of the ferroelectric film at the time of dry etching can be removed by wet treatment with an aqueous solution, so that etching can be performed at a lower temperature. , The size shift can be reduced.

In the second aspect of the present invention, since the aqueous solution used for the wet treatment is H ₂ O, it is possible to avoid an increase in cost and also to avoid damage to the ferroelectric film due to the chemical solution.

Further, in the second invention, by setting the temperature of the aqueous solution used for the wet treatment in the range of 25 ° C. or more and 100 ° C. or less, the side wall deposition film can be sufficiently removed.

[Brief description of the drawings]

FIGS. 1A to 1D are process cross-sectional views illustrating a method of etching a ferroelectric film according to a first embodiment.

FIG. 2 is a schematic diagram of an ECR (Electron Cyclotron Resonance) plasma etching apparatus used in Examples 1 to 3.

FIG. 3 is a graph showing a relationship between a flow rate ratio of a Cl ₂ gas to a total flow rate of an etching gas and an etching rate of an SOG mask in Example 1.

FIG. 4 is a graph showing a relationship between an RF output and an etching rate in Example 1.

FIG. 5 is a graph showing the relationship between RF output and selectivity in Example 1.

FIGS. 6A to 6E are process cross-sectional views illustrating a method of etching a ferroelectric film according to a second embodiment.

FIG. 7 is a cross-sectional view showing a sample wafer etched by the method for etching a ferroelectric film of Example 3.

FIG. 8 is a graph showing the relationship between the flow rate ratio of Cl ₂ gas to the total flow rate of etching gas and the cross-sectional profile angle in Example 3.

FIG. 9 is a graph showing the relationship between the ratio of the flow rate of Cl ₂ gas to the total flow rate of etching gas and the etching rate in Example 3.

FIG. 10 is a graph showing a relationship between a flow rate ratio of a CH ₄ gas and a selectivity to a total flow rate of an etching gas in Example 3.

FIG. 11 is a graph showing the relationship between the flow rate ratio of the CH ₄ gas to the total flow rate of the etching gas and the thickness of the side wall deposit in Example 3.

FIG. 12 is a cross-sectional view showing a sample wafer etched by the method for etching a ferroelectric film of Example 3.

FIG. 13 is a cross-sectional view showing a sample wafer on which etching has been performed by the method for etching a ferroelectric film of Example 3 and sidewall deposits have been removed by a water washing process.

FIG. 14 is a cross-sectional view showing a substrate etched by a conventional etching method.

FIG. 15 is a cross-sectional view showing a substrate etched by a conventional etching method.

[Explanation of symbols]

1, 21, 31, 41, 51, 61, 71 Si substrate 2, 22, 32, 42, 52, 62, 72 NSG film 3, 23, 33, 35, 43, 45, 53, 55, 6
3, 65, 73, 75 Ti film 4, 24, 34, 44, 54, 64, 74 TiN film 5, 26, 36, 46, 56, 66, 76 Pt film 6, 27, 37, 47, 57, 67, 77 PZT film 7, 25, 38 Pt / Ti film 8 SOG film 9 Microwave 10 High frequency power supply 11 Solenoid coil 12 Sample wafer 13 Electrode 14, 15 Gas inlet 28, 40, 58, 78 Side wall deposition film 39 Resist film

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Jun Kudo 22-22, Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Keizo Sakiyama 22-22, Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Sharp Corporation (72) Inventor Jin Urashima 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) References JP-A-6-151383 (JP, A) JP-A-6-13357 (JP, A) JP-A-6-295993 (JP, A) JP-A-7-94471 (JP, A) JP-A-8-195377 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/3065 C23F 4/00 H01L 27/04

Claims (12)

(57) [Claims] An etching resistant film serving as a mask is patterned on a ferroelectric film made of a compound with lead, and the ferroelectric film in a region not covered with the etching resistant film is etched. In the dry etching method, a mixed gas of an inert gas and a halogen gas or a halide gas is used as an etching gas, and the halogen gas or the ha gas relative to the total flow rate of the mixed gas is used .
Strong etching method of a dielectric film you wherein a flow ratio of androgenic compound gas is 50% or less. 2. The method according to claim 1, wherein the substrate temperature during the etching is 100 ° C.
2. The method for etching a ferroelectric film according to claim 1, wherein the temperature is in a range of not less than 400 ° C. 3. The halogen gas or halide gas
Wherein the gas is chlorine gas or chloride gas ,
The method for etching a ferroelectric film according to claim 1 or 2. 4. A silicon oxide film as said etching resistant film.
Characterized by using, according to claim 1, claim 2 or claim 3 etching method of a ferroelectric film according. 5. The method according to claim 1, wherein the ferroelectric film is made of a compound with lead.
Pattern the etching-resistant film to be
Etch the ferroelectric film in the area not covered by the etching film
In the method of etching a ferroelectric film to be etched, an inert gas and a halogen-based first gas are used as etching gases.
Using a mixed gas consisting of gas and a halogen-based second gas
Perform dry etching and etch the above ferroelectric
Wet compound formed on the side wall of body film with aqueous solution
A method for etching a ferroelectric film, wherein the method is removed by a treatment . 6. An inert gas and a halogen-based first gas.
Of the inert gas with respect to the total flow rate of the inert gas and the second gas
6. The method according to claim 5 , wherein the amount ratio is less than 50%.
The method for etching a ferroelectric film according to the above. 7. The method according to claim 6, wherein the dry etching is performed.
When the pressure of the gas in the vacuum chamber is less than 1 mTorr
The method for etching a ferroelectric film according to any one of claims 1 to 4, wherein the upper limit is 10 mTorr or less . 8. The method according to claim 8, wherein the dry etching is performed.
When the pressure of the gas in the vacuum chamber is less than 1 mTorr
7. The method for etching a ferroelectric film according to claim 5 , wherein the upper limit is 10 mTorr or less . 9. The method according to claim 1, wherein the inert gas is Ar gas.
First gas halogen system CF ₄ gas or SF ₆ Gasudea
9. The method for etching a ferroelectric film according to claim 5, wherein the halogen-based second gas is CHF ₃ gas . 10. The halogen-based first gas and halogen.
Of the flow rate of the halogen-based second gas in the system-based second gas
The flow rate ratio to the flow rate of the first logen gas is less than 70%
Characterized in that it is a full,請 Motomeko 9 etching process of the ferroelectric film according. 11. An aqueous solution used for the wet treatment is H
Characterized in that it is a ₂ O, the etching method of a ferroelectric film according to claim 5, wherein. 12. The temperature of an aqueous solution used for the wet treatment.
The method for etching a ferroelectric film according to claim 11 , wherein the temperature is in a range of 25C to 100C .