JPH06132253A - Reactive ion etching for silicon nitride film - Google Patents

Abstract

PURPOSE:To provide a reactive ion etching method for a silicon nitride film which can fulfill the anisotropy and the high selectivity of Si3N4 to a base SiO2 film at the same time, using ECR-RIE. CONSTITUTION:In reactive ion etching method for etching the silicon nitride film of the sample put on a sample susceptor, using microwave plasma having a magnetic field, the plasma is one of chloric gas 0.6 mtorr or over in pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reactive ion etching of a silicon nitride film, and more particularly to ECR-RI.
The present invention relates to a reactive ion etching method for a silicon nitride film using an E apparatus.

[0002]

2. Description of the Related Art One of LSI (Integrated Circuit Device) manufacturing processes is an element isolation process, and in recent years, LOCOS (Local Oxid)
ation of Silicon) process is mainly used. In this process, when forming the Si ₃ N ₄ pattern (during etching) that serves as an oxidation resistant mask, the SiO ₂ that is the base of Si ₃ N ₄ is formed.
It requires highly selective etching for the membrane.

FIG. 7 shows the relationship between the etching rates of polysilicon Si ₃ N ₄ and SiO ₂ in CDE (chemical dry etching) and the oxygen concentration in CF ₄ (1
983 Industrial Research Committee, Junichi Nishizawa, "Semiconductor Research, Vol. 19" P
231) and FIG. 8 show the relationship between the etching rates of Si ₃ N ₄ and SiO ₂ in CDE and the Cl ₂ flow rate when NF ₃ is set to 30 sccm (J. Electrochem. Soc. Vol. 13).
6, No. 7 (1989)). F3 or C for etching Si ₃ N ₄
l-based gas is used, and as shown in FIG. 7 and FIG.
The selection ratio of Si ₃ N _{4 to} the underlying SiO ₂ film in DE was high.

This is because the binding energy of SiO ₂ is larger than that of Si ₃ N ₄ , and F ₃ or FCl causes Si ₃ N.
₄ is etched, but SiO ₂ is not easily etched.

However, the CDE is a method of transporting radicals generated by microwave discharge and introducing them into the etching chamber. Since etching is mainly composed of radicals, anisotropy cannot be obtained and dimensional control is difficult. . Therefore, RIE was used because it has excellent anisotropy and is easy to control in size.
Etching of Si ₃ N ₄ has been reported. FIG. 9 shows RIE using RF power of 150 W and CF ₄ flow rate of 21 cc / mi.
n, H ₂ flow rate 12 cc / min, gas pressure 1 × 10 ^-2 Tor
set to r, Si ₃ N ₄ with respect to the amount of N ₂ added to CF ₄ + H ₂ ,
3 is a graph showing changes in etching rates of SiO ₂ and Si (edited by Junichi Nishizawa, 1983 Industrial Research Group, “Semiconductor Research 19
Vol. ”P233). In this case, since the substrate is negatively biased, ions are incident in the vertical direction, and the impact effect of the ions causes remarkable anisotropic etching.

[0006]

However, in the above-mentioned conventional etching method, when CDE is used, it is not possible to impart anisotropy to the etching processed shape. On the other hand, the etching processed shape is anisotropic. When RIE is used for the purpose, high selectivity of Si ₃ N ₄ with respect to the underlying SiO ₂ film cannot be obtained. As described above, the conventional method has a problem that anisotropy and high selectivity cannot be satisfied at the same time.

The present invention has been made in view of the above problems, and uses ECR-RIE to obtain anisotropy and an underlying SiO ₂ film.
It is an object of the present invention to provide a reactive ion etching method for a silicon nitride film which can simultaneously satisfy the high selectivity of Si ₃ N ₄ with respect to Si.

[0008]

In order to achieve the above object, a method for reactive ion etching a silicon nitride film according to the present invention is to use a magnetic field microwave plasma to form a sample silicon nitride on a sample stage. In the reactive ion etching method for etching a film, the plasma is characterized by being a plasma of chlorine-based gas at a pressure of 0.6 mtorr or more, and using a magnetic field microwave plasma, a sample of a sample placed on a sample stage is used. In the reactive ion etching method for etching a silicon nitride film, the plasma is a chlorine-based gas plasma, and high-frequency power of 30 W or less is applied to the sample stage.

[0009]

[Function] Si-Cl bond energy is 77 kcal / mol, Si-
The binding energy of N is 105 kcal / mol, the binding energy of Si-O is 192 kcal / mol, and the magnitude relationship of the binding energies is Si-Cl <Si-N <Si-O. For this reason, it is usually difficult to etch SiN and SiO ₂ with Cl radicals. However, since chlorine ions are vertically incident on the substrate to be etched in the RIE apparatus, the energy due to the collision of the chlorine ions weakens the bond between Si and N and excites it so that the etching can proceed in the vertical direction. It will be possible.

FIG. 1 is a graph showing the potential distribution in the ECR-RIE plasma apparatus, and FIG. 2 is a graph showing the relationship between the gas pressure and the plasma potential under the conditions of microwave power of 1000 W and RF power of 0 W. . As is clear from FIGS. 1 and 2, the plasma potential (V _pp ) of the ECR-RIE plasma device largely depends on the gas pressure. FIG. 3 shows the applied RF when the Cl ₂ flow rate is set to 26 sccm and the gas pressure is set to 0.8 × 10 ⁻³ Torr.
It is a graph showing the relationship between power and self-bias, and as shown in FIG. 3, it can be seen that self-bias (V _DC ) greatly depends on the applied RF power. From this, it is predicted that if the ion energy obtained by V _PP + V _DC is controlled by the gas pressure and the RF power, the excited state of the bond can be changed by the energy of ion collision. However, when a normal RIE is used, it is difficult to obtain a high selection ratio because the ion energy is too large. Therefore, it can be said that it is desirable to use an ECR-RIE device that combines ECR that can generate plasma even when the gas pressure is low and that can obtain a high ionization rate, and RIE that is rich in anisotropic etching.

According to the above-mentioned method, in the reactive ion etching method of etching the silicon nitride film of the sample placed on the sample stage by using the magnetic field microwave plasma, the plasma is chlorine having a pressure of 0.6 mtorr or more. Since it is a plasma of a system gas, it is possible to change the excited state of the bond, and it is possible to obtain high selectivity for etching Si ₃ N ₄ with respect to SiO ₂ and to perform etching with excellent anisotropy. Becomes

Further, by using a magnetic field microwave plasma,
In the reactive ion etching method for etching a silicon nitride film of a sample placed on a sample stage, when the plasma is chlorine-based gas and a high frequency power of 30 W or less is applied to the sample stage, the same as the above method. the it is possible to vary the excited state of the binding, Si for SiO ₂
It becomes possible to obtain a high selectivity of ₃ N ₄ etching, and it is possible to perform etching having excellent anisotropy.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the reactive ion etching method for a silicon nitride film according to the present invention will be described below with reference to the drawings.
FIG. 4 is a sectional view showing a generally used ECR-RIE apparatus, and 11 in the figure shows a plasma generation chamber.

The peripheral wall of the plasma generating chamber 11 has a double structure, the inside of which is a cooling chamber 15 for allowing cooling water to flow therethrough, and a microwave introducing hole is provided substantially in the center of the upper wall of the plasma generating chamber 11. 11a is formed, a quartz plate 11b is disposed above the microwave introduction hole 11a, and a waveguide 12 is connected above the quartz plate 11b. A plasma extraction window 11d is formed below the plasma generation chamber 11, and a sample chamber 13 is disposed so as to face the plasma extraction window 11d. Turbo molecular pump 22, rotary pump 23 and oil cleaner 2 for setting the pressure of
4 is connected. Further, the exciting coil 14 is concentrically formed around the plasma generating chamber 11 and one end of the waveguide 12 connected to the plasma generating chamber 11 so as to surround them.
Is provided.

On the other hand, in the sample chamber 13, a sample holder 17 is arranged at a position facing the plasma extraction window 11d, and a sample 18 such as a wafer is placed on the sample holder 17. An electrode plate 25 is embedded inside the sample holder 17, and the electrode plate 25 is connected to an RF power supply 27 via a matching box 26 by a connecting wire 25a. Further, the cooling liquid pipe 16 is arranged so as to surround the connection line 25a in the sample holder 17, and the double magnetic coil 17a is arranged so as to further surround the cooling liquid pipe 16.

Reference numeral 11c in the drawing denotes a reaction gas supply pipe communicating with the plasma generation chamber 11, and 13b denotes a reaction gas supply pipe communicating with the plasma generation chamber 11.
Reference numerals 5a and 15b denote a cooling water supply pipe and a cooling water discharge pipe,
Reference numerals 16a and 16b denote a supply pipe and a discharge pipe for the cooling liquid.

Further, a sample loading chamber 19 is provided on one side of the sample chamber 13, and the sample loading chamber 19 is provided.
A cassette 19a on which the sample 18 is placed is arranged inside. A turbo molecular pump 20 and a rotary pump 21 are connected to the sample loading chamber 19 in order to maintain the same pressure in the sample loading chamber 19 as in the sample chamber 13.

In order to etch the sample 18 by using the ECR-RIE apparatus having the above-mentioned structure, first, the Turb molecular pump 22 and the rotary pump 23 are operated in the plasma generation chamber 11 and the sample chamber 13, respectively. After setting a predetermined degree of vacuum, R on the electrode plate 25 in the sample holder 17
The F power supply 27 is applied, a current is passed through the double magnetic coil 17a, a cooling liquid is passed through the cooling liquid pipe 16, and cooling water is also passed through the cooling chamber 15. Then, Cl-based gas is supplied as a reaction gas into the plasma generation chamber 11 through the reaction gas supply pipe 11c. Then, a microwave is introduced into the plasma generation chamber 11 while applying a current to the exciting coil 14 to form a magnetic field, and the gas is resonantly excited by using the plasma generation chamber 11 as a cavity resonator to generate plasma. The generated plasma has a divergent magnetic field whose magnetic flux density decreases toward the side of the sample chamber 13 formed by the exciting coil 14, and thus the sample chamber 13
The surface of the sample 18 in the sample chamber 13 is etched by being projected onto the periphery of the sample 18 inside. Etched sample 1
8 is carried into the sample loading chamber 19 and the cassette 19
The unprocessed sample 18 stored in a is carried to the sample holder 17.

FIG. 5 is a graph showing the relationship between chlorine gas pressure and etching rate. These measurements are based on the EC
Using R-RIE equipment, microwave frequency 2.45G
The H _Z, the microwave power to 1 KW, the applied RF frequency 13.56MH _Z, 10 ℃ sample stage circulating chiller temperature
I set it to. As the etching conditions, the gas pressure was set to 0.45 to 3.1 mtorr, the RF power was set to 0 W, and the Si ₃ N ₄ etching rate, SiO ₂ etching rate and selectivity were measured under each condition. The measured results are shown in the graph.

[0020] As shown in FIG. 5, the etching rate the Si ₃ N ₄ is greater than the etching rate of SiO _2, Si ₃ N ₄
The etching rates of SiO ₂ and SiO ₂ tend to decrease as the chlorine gas pressure increases, and the selection ratio is 1 mt.
It is 5 or more at orr or higher. Normally, a selection ratio of 4 or more is required, and when RF is applied as shown in FIG. 6, the selection ratio becomes small. As a result of taking these factors into consideration, it is desirable that the chlorine gas pressure be set to 0.6 mtorr or more.

FIG. 6 is a graph showing the relationship between the applied RF power and the etching rate. These measurements, in the same manner as described above using an ECR over RIE apparatus, a microwave frequency 2.45 GHz _Z, the microwave power to 1 KW, the applied RF frequency 13.56MH _Z, 10 ℃ sample stage circulating chiller temperature I set it to. The etching conditions are RF power of 0 to 100 W and chlorine flow rate of 15 sc.
cm, and the chlorine gas pressure is 0.45, 1.0, 2.
0, mtorr, and Si under each condition
The etching rate of ₃ N _4, the etching rate of SiO ₂ , and the selection ratio were measured, and the measurement results are shown in the graph.

As shown in FIG. 6, the etching rate of Si ₃ N ₄ is higher than that of SiO ₂ , and the etching rates of Si ₃ N ₄ and SiO ₂ tend to increase as the RF power increases. However, the selection ratio shows a decreasing trend. Since the required selection ratio is 4 or more, when the selection ratio is taken into consideration, the RF power applied is preferably 30 W or less.

In this way, the case where the chlorine gas pressure of 1 mtorr or more or the RF power of 30 W or less which can obtain a high selection ratio is set as an example, and the chlorine gas pressure and the RF power which are out of the range are set as a comparative example. Table 1 shows the results of these comparisons in which the anisotropy of is also taken into consideration.

[0024]

[Table 1]

As is clear from Table 1, in the reactive ion etching method for the silicon nitride film according to the example, the Si
It can be seen that the selection ratio of Si ₃ N ₄ to O ₂ is high, and the anisotropy becomes higher as the RF power approaches 30W.

On the other hand, as in Comparative Examples 1 and 2, when the chlorine gas pressure and the RF power are out of the claimed range, the anisotropy is relatively high but the selectivity is poor. The same applies to Comparative Examples 3 to 6. .

As described above, in the reactive ion etching method for the silicon nitride film according to the embodiment, the ECR
-Using RIE equipment, chlorine is used as the etching gas species, chlorine-based gas plasma is ignited at a chlorine gas pressure of 0.6 mTorr or more, and RF power is applied to the sample stage at 30 W or less for etching. This makes it possible to obtain not only excellent anisotropy but also a high selection ratio of Si ₃ N ₄ with respect to SiO ₂ .

[0028]

As described above in detail, in the reactive ion etching method of the silicon nitride film according to the present invention, the silicon nitride film of the sample placed on the sample stage is used by using the magnetic field microwave plasma. In the reactive ion etching method for etching, since the plasma is a chlorine-based gas plasma having a pressure of 1 mtorr or more, it becomes possible to change the excited state of the bond, and it is possible to highly selectively etch Si ₃ N ₄ with respect to SiO ₂ . And etching with excellent anisotropy can be performed.

Further, by using a magnetic field microwave plasma,
In the reactive ion etching method for etching a silicon nitride film of a sample placed on a sample stage, when the plasma is chlorine-based gas and a high frequency power of 30 W or less is applied to the sample stage, the same as the above method. the it is possible to vary the excited state of the binding, Si for SiO ₂
It is possible to obtain high selectivity of ₃ N ₄ etching and perform etching with excellent anisotropy.

[Brief description of drawings]

FIG. 1 is a graph showing a distribution of potential energy in an ECR-RIE device.

FIG. 2 is a graph showing the relationship between chlorine gas pressure and plasma potential in ECR-RIE.

FIG. 3 is an applied RF when the microwave power is changed.
6 is a graph showing the relationship between power and self-bias.

FIG. 4 is a sectional view showing a commonly used ECR-RIE device.

FIG. 5 is a graph showing the relationship between chlorine gas pressure and etching rate with RF power as a parameter.

FIG. 6 is a graph showing the relationship between applied RF power and etching rate with chlorine gas pressure as a parameter.

FIG. 7: Polysilicon, Si ₃ N ₄ , Si in a CDE device
It is a graph showing the relationship between the O ₂ concentration of the etching rate and the CF ₄ in O _2.

FIG. 8 is a graph showing the relationship between each etching rate of Si ₃ N ₄ and SiO ₂ in CDE and the Cl ₂ flow rate when the NF ₃ flow rate is set to 30 sccm.

FIG. 9 is a graph showing changes in etching rates of Si ₃ N ₄ , SiO ₂ , and Si with respect to the amount of N ₂ added to CF ₄ + H ₂ in RIE.

[Explanation of symbols]

 17 sample holder (sample table) 18 sample

Claims (2)

[Claims] 1. In a reactive ion etching method of etching a silicon nitride film of a sample placed on a sample stage using a magnetic field microwave plasma, the plasma is 0.6
A reactive ion etching method for a silicon nitride film, which is a plasma of chlorine-based gas at a pressure of mtorr or higher. 2. A reactive ion etching method for etching a silicon nitride film of a sample placed on a sample stage by using a magnetic field microwave plasma, wherein the plasma is a chlorine-based gas plasma and A reactive ion etching method for a silicon nitride film, characterized in that a high frequency power of 30 W or less is applied.