JPH0817804A - Plasma etching method - Google Patents

Abstract

PURPOSE:To eliminate instability of a process due to the deposit of a reaction product onto the inner wall of an etching chamber by removing natural oxide film on the surface of Si material layer by the plasma discharge of treatment gas including F gas, cleaning the inner wall surface of the chamber, and then performing plasma etching. CONSTITUTION:A substrate 1 to be etched is set onto a substrate stage 2. In this case, SiBrx reaction product 6 generated by a previous Si trench etching is adhered to the inner wall surface of a bell jar 4. Then, plasma discharge 5 by the F gas is performed for five seconds. Radical reaction due to plasma 7 generated by the dissolution of SF6 disappears since a strong natural oxide film is broken through by a mechanism which is assisted by the incidence of such ions as SFx<+>, thus exposing the surface of the Si substrate 1. At the same time, the reaction product 6 adhering to the inner wall surface of the bell jar 4 is also cleaned. Trench etching is successively performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma etching method, and more particularly to a Si-based material layer capable of obtaining stable and uniform etching characteristics even if a plurality of etching treatments are successively repeated in the same etching chamber. The present invention relates to a plasma etching method.

[0002]

2. Description of the Related Art As semiconductor device design rules such as LSI are miniaturized from a level of half micron to quarter micron, requirements for microfabrication techniques such as plasma etching are becoming more severe. Above all,
MIS using polycrystalline silicon or refractory metal silicide
A plasma etching method capable of satisfying various requirements such as high anisotropy, high selection ratio, high etching rate, low pollution and low damage at a high level is required in the trench processing of a gate electrode of a FET or a Si substrate. It

In recent years, Cl (chlorine) -based gas, Br (bromine) -based gas or I (iodine) -based gas has been used as an etching gas that achieves both high anisotropic etching without side etching and high selectivity with respect to the underlying insulating film. The etching gas containing it is said to be effective. This is Br radical (Br ^* ) or C
Since the chemical activity of the l radical (Cl ^* ) or the I radical (I ^* ) is smaller than that of the F radical (F ^* ) generated from an F (fluorine) -based gas such as CF _{4 which} is usually used,
This is because it is possible to suppress isotropic etching caused by radical reaction.

SiB which is a reaction product of etching
Since r _x , SiCl _x, or SiI _x is deposited on the substrate to be etched and remains on the side surface of the pattern with a small amount of ion incidence to form a side wall protective film, the side surface of the pattern may be attacked by radical attacks or incident ions from directions other than the vertical direction. It is also because the effect of protection is expected.

In order to promote the deposition of these reaction products and further reduce the radical reaction, low temperature etching for cooling the substrate temperature to be etched to, for example, 0 ° C. or lower is performed. For this purpose, the substrate to be etched is brought into close contact with the substrate stage cooled to a low temperature with a coolant or the like by an electrostatic chuck, and a small amount of heat-conducting gas such as He is flowed from the surface of the substrate stage toward the back surface of the substrate to be etched to heat the substrate. Increasing the conduction efficiency is performed. As the electrostatic chuck, a single-pole type electrostatic chuck is generally used from the viewpoint of in-plane uniformity of etching. After the plasma etching is completed, the electric charges remaining on the substrate to be etched are removed by plasma discharge of a rare gas such as He, and then the substrate to be etched is separated from the substrate stage and conveyed. For details of this method, refer to Japanese Patent Application No. 5-2 filed previously by the applicant of the present application.
No. 58614.

Even when plasma etching is performed using these Cl-based gas, Br-based gas and I-based gas,
In order to perform uniform and stable patterning, it is desirable to perform patterning after previously removing a natural oxide film such as SiO ₂ formed on the surface of the layer to be etched.

[0007]

By the way, SiBr _x
An etching reaction product such as SiCl _x or SiI _x deposits on the substrate to be etched and also adheres to the inner wall surface of the etching chamber. In particular, during continuous processing on a mass production line, the amount of reaction products attached is added, so the amount of accumulated reaction products is conversely sputtered out and released into the plasma atmosphere. Becomes an atmosphere of excess reaction products.
Therefore, in this case, it is one of the factors that cause the instability of the process such as the reduction of the etching rate of the layer to be etched and the occurrence of the dimensional conversion difference due to the taper of the pattern.

Further, since the above-mentioned reaction product is a substance which is easily oxidized, it is converted to an oxide when the inside of the etching chamber is exposed to the atmosphere after the plasma etching is completed or the resist mask is ashed, and this is exfoliated to form particles. It was also the cause of pollution.

A method is adopted in which these reaction products adhering to the inner wall of the etching chamber are removed by performing dry cleaning with an F-based gas at the end of each lot in which several tens of substrates to be etched are continuously processed. ing. However, the current situation is that it is not possible to deal with process fluctuations due to reaction products that gradually accumulate during continuous processing.

Therefore, the object of the present invention is to provide a Cl type gas and Br.
In a plasma etching method for etching a Si-based material layer on a substrate to be etched with an etching gas containing a system gas or an I-based gas, process instability resulting from deposition of reaction products on an inner wall of an etching chamber is eliminated, Accordingly, it is an object of the present invention to provide a plasma etching method capable of obtaining a stable and uniform pattern shape.

Another object of the present invention is to remove the natural oxide film on the Si-based material layer and to remove the residual charge on the substrate to be etched after the etching in the etching method using a monopolar electrostatic chuck. The purpose of the present invention is to provide the above-described plasma etching method that also serves as the above. Other problems of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0012]

The plasma etching method of the present invention was devised to solve the above-mentioned problems, and any one selected from Cl-based gas, Br-based gas and I-based gas can be used. In a plasma etching method for etching a Si-based material layer on a substrate to be etched with an etching gas containing the same, a natural oxide film on the surface of the Si-based material layer is removed by plasma discharge of a processing gas containing an F-based gas, and etching is performed. After cleaning the inner wall surface of the chamber, plasma etching is performed.

Further, the plasma etching method of the present invention is
While holding the substrate to be etched by a monopolar electrostatic chuck, the Si-based material layer on the substrate to be etched is etched by an etching gas containing any one selected from Cl-based gas, Br-based gas and I-based gas. In this plasma etching method, after performing the plasma etching, the plasma discharge of the processing gas containing the F-based gas causes
It is characterized in that the residual charge of the substrate to be etched is removed and the inner wall surface of the etching chamber is cleaned.

Here, the Si-based material layer contains a layered material such as a silicon material including amorphous Si, polycrystalline Si and a Si substrate, a refractory metal silicide and a refractory metal polycide. Further, the processing gas containing the F-based gas means S
Gases containing non-depositing F atoms such as F ₆ , NF ₃ , N ₂ F ₄ , HF, F ₂ and XeF ₂ or mixed gases of these gases, and mixed gases of these with other non-depositing gases To point to.

[0015]

The point of the present invention resides in that the dry cleaning with the F-based gas, which has been conventionally performed at the end of each lot, is performed before or after the end of each plasma etching. That is, for example, in the case of a single wafer etching apparatus, the inner wall surface of the etching chamber is cleaned for each substrate to be etched.

In the present invention, this cleaning is F
This is performed by plasma discharge of a processing gas containing a system gas, and at this time, a step of removing the natural oxide film formed on the surface of the layer to be etched is simultaneously performed. As a result, the reaction products deposited on the inner wall surface of the etching chamber by the previous plasma etching are removed, and stable and uniform treatment can be performed in the clean chamber in the plasma etching of this time.

Further, in the plasma etching using the unipolar electrostatic chuck, this cleaning is performed by plasma discharge of the processing gas containing the F-based gas, and at the same time, the residual charge removing step of the substrate to be etched is performed. As a result, the reaction products deposited on the inner wall surface of the etching chamber by the plasma etching of this time are removed, and stable and uniform processing can be performed in the clean chamber in the next plasma etching.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described below with reference to the drawings. First, FIGS. 1A to 1C and FIGS. 3A to 3C are schematic cross-sectional views showing a usage state of the RF bias application type ECR plasma etching apparatus used in the examples. That is, a microwave of 2.45 GHz is introduced into the bell jar 4 made of a dielectric material such as quartz via the waveguide 3, and the ECR is introduced into the bell jar 4 by the magnetic field of 0.0875T generated by the solenoid coil 5. Plasma 7 is generated by the discharge. The bell jar 4 is a main part of the etching chamber, and the substrate stage 2 on which the substrate to be etched 1 is placed is arranged below the bell jar 4.
In both figures, details of the temperature control means of the substrate stage 2, the electrostatic chuck, the gas introduction hole, the vacuum pump, etc. are omitted.

Example 1 This example is an example in which the present invention is applied when a trench is formed in a Si substrate by using a Br type gas.
A description will be given with reference to (a) to (c) and FIGS. 2 (a) to (c). The substrate to be etched used in this example is shown in FIG.
As shown in (a), a resist mask 13 having an opening diameter of 0.35 μm is formed on the Si substrate 1.
A natural oxide film 12 made of SiO ₂ is thinly formed on the Si substrate 1, and the thickness, film quality, etc. of the natural oxide film 12 are irregular. Therefore, S in this state
When the i-trench etching is started, there is a possibility that a stable and uniform trench processing may be hindered.

Therefore, first, the natural oxide film 12 is removed. The substrate 1 to be etched shown in FIG.
It is set on the substrate stage 2 of the etching apparatus shown in (a). At this time, the SiBr _x reaction product 6 produced by the previous Si trench etching is attached to the inner wall surface of the bell jar 4. Needless to say, Figure 1
This reaction product 6 is shown exaggerated in (a). Next, as an example, plasma discharge using an F-based gas is performed for 5 seconds under the following conditions. SF ₆ 50 sccm Gas pressure 1.0 Pa Microwave power 850 W (2.45 GHz) RF bias power 40 W (2 MHz) Substrate temperature 0 ° C. In this plasma discharge step, radicals generated by plasma 7 generated by dissociation of SF ₆ A strong natural oxide film with a mechanism in which the reaction is assisted by the incidence of ions such as SF _x ⁺
2 breaks through and disappears, and the surface of the Si substrate 1 is exposed as shown in FIG. At the same time, Fig. 1 (b)
As shown in FIG. 5, the reaction product 6 attached to the inner wall surface of the bell jar 4 is also cleaned.

Subsequently, as an example, trench etching of the Si substrate 11 is performed under the following conditions. HBr 120 sccm Gas pressure 0.5 Pa Microwave power 850 W (2.45 GHz) RF bias power 30 W (2 MHz) Substrate temperature 0 ° C. In this etching step, as shown in FIGS. 1 (c) and 2 (c). Then, the plasma 7 is generated by HBr, and the Si substrate 11 is etched in such a manner that the radical reaction by Br ^* is assisted by the incident Br ⁺ . A sidewall protection film (not shown) made of a reaction product of SiBr _x system is formed on the side surface of the formed trench 14, and anisotropic etching is achieved. The side wall protective film partially contains a decomposition product of the resist mask 13. At the same time Si
The Br _x reaction product 6 adheres to the inner wall surface of the bell jar 4. After the etching is completed, the processed substrate to be etched is carried out, a new substrate to be etched is carried in, and the process shown in FIG.
The state of (a) is obtained.

According to this embodiment, the natural oxide film 12 on the surface of the Si substrate 11 is removed before the start of the trench etching, and the reaction product 6 on the inner wall surface of the bell jar 4 is removed.
Since it is also removed, stable and uniform Si trench etching can be continuously performed without receiving the history of the previous etching step, that is, without forming an atmosphere of excess reaction products.

Example 2 This example is an example in which the present invention is applied to the case of etching a refractory metal polycide layer with a Cl-based gas using an etching apparatus having a monopolar electrostatic chuck. A description will be given with reference to a) to (c) and FIGS. 4 (a) to (c). The etching apparatus used in this example is basically the same as the RF bias application type ECR plasma etching apparatus used in Example 1, but FIG.
The apparatus shown in (c) includes a substrate stage 2 equipped with a monopolar electrostatic chuck (not shown).

As shown in FIG. 4A, the substrate to be etched used in this example is a Si substrate 11 having a gate insulating film 15 such as SiO ₂ , a polycrystalline silicon layer 16 doped with impurities, WSi _x. Layers 17 are deposited in sequence, 0.35 nm
A resist mask 13 having a width is formed, and is applied to, for example, patterning of gate electrode wiring.
The thickness of each layer is, for example, 10 nm for the insulating layer 15 and 100 for the polycrystalline silicon layer 16 and the WSi _X layer 17.
nm. The substrate 1 to be etched is set on the substrate stage 2 which is cooled at a low temperature in the etching apparatus shown in FIG. 3A, and the substrate to be etched is suction-held by a monopolar electrostatic chuck. Next, as an example, the refractory metal polycide gate electrode is patterned under the following conditions. Cl ₂ 70 sccm O ₂ 10 sccm Gas pressure 0.4 Pa Microwave power 850 W (2.45 GHz) RF bias power 40 W (2 MHz) Substrate temperature 0 ° C. Plasma of Cl ₂ / O ₂ mixed gas is used in this etching process. 7 is generated, and the radical reaction by Cl ^{* is} caused by Cl ⁺ , O
High-speed anisotropic etching proceeds in a form assisted by ⁺ ion injection. The reaction product SiCl _x adheres to the pattern side surface of the refractory metal polycide to be patterned as a side wall protective film 18, and contributes to the improvement of anisotropy. The side wall protection film 18 also contains a decomposition product of the resist mask 13. At the same time, the reaction product 6 also adheres to the inner wall surface of the bell jar 4.

Even after the etching of the polycide layer is completed and the high voltage DC power supply of the unipolar electrostatic chuck is turned off, residual charges remain on the substrate to be etched 1 and the substrate stage 2
If it is forcibly removed from the substrate, the substrate to be etched 1 may be damaged. Therefore, next, as the step of removing the residual charges, plasma discharge is performed for 5 seconds under the following conditions, for example, by using a processing gas containing an F-based gas. SF ₆ 30 sccm O ₂ 20 sccm Gas pressure 0.5 Pa Microwave power 850 W (2.45 GHz) RF bias power 0 W Substrate temperature 0 ° C. In this plasma discharge step, as shown in FIG.
Plasma 7 is generated by the ₆ / O ₂ mixed gas, and the reaction product 6 on the inner wall surface of the bell jar 4 is removed. At the same time, the residual charge on the substrate to be etched 1 is also neutralized, and the substrate stage 2
It becomes easy to remove from and transport. Further, the sidewall protection film 18 on the side surface of the etched polycide electrode pattern is also removed by this F-based plasma. Since the RF discharge power is 0 W and the ion energy is low under this plasma discharge condition, damage to the gate insulating film 15 is at a negligible level. This state is shown in FIG. After the processed substrate to be etched is carried out of the etching apparatus, a new substrate to be etched is carried in, and the state shown in FIG.

According to the present embodiment, since the etching is started from the state where the reaction product 6 on the inner wall surface of the etching chamber is also removed at the same time as the step of removing the residual charges on the substrate to be etched after the etching is completed, It is possible to continuously perform stable and uniform polycide gate etching without receiving a history of the etching process, that is, without creating an atmosphere of excess reaction products. Further, the removal of the side wall protective film is also achieved at the same time, which contributes to the improvement of the throughput of the whole process.

Although the present invention has been described with reference to the two examples, the present invention is not limited to these examples, and various embodiments are possible.

For example, a Cl type gas is used as an etching gas.
Although Br-based gas is shown as an example, HI and I ₂Including I-based gas such as
When etching a Si material layer with an etching gas
It is also applicable to the case. Even in this case, the reaction product
And relatively low vapor pressure SiI_xThe reaction product of the system is
The inner wall surface of the ching chamber is easily attached.

SF ₆ is exemplified as the F-based gas, but NF
₃ , N ₂ F ₄ , HF, F ₂ and XeF _{2 and the} like, a gas containing non-depositing F atoms, a mixed gas of these gases, or a mixed gas of these and another non-depositing gas is appropriately used. Good.

Although the single crystal Si substrate and the refractory metal polycide layer have been exemplified as the Si-based material layer, the present invention may be applied to patterning of amorphous Si, polycrystalline Si, refractory metal silicide or the like.

Although the substrate bias application type ECR plasma etching apparatus is used as the etching apparatus, a parallel plate type RIE apparatus or a magnetron RIE apparatus may be used. Helicon wave plasma etching equipment, TCP (Tr
Transformer Coupled Plasma)
Etching equipment, ICP (Inductive C)
If a high-density plasma etching device such as an open plasma etching device is used, further low damage, high etching rate, and uniformity in the substrate to be etched can be expected.

[0032]

As is apparent from the above description, according to the present invention, when the Si-based material layer is etched by the etching gas containing Cl-based gas, Br-based gas and I-based gas, the inner wall surface of the etching chamber is Since the cleaning is performed for each etching process without accumulating the attached reaction products, the atmosphere of the reaction products does not become excessive in the etching chamber. Therefore, the problem of tapering of the pattern profile due to the decrease of the etching rate and the excess of the side wall protection film does not occur, and it is possible to always perform a stable and uniform etching process. In addition, a clean process can be realized without lowering the particle level due to separation of reaction products accumulated in the chamber.

Further, since the natural oxide film on the surface of the layer to be etched can be removed simultaneously with the chamber cleaning, this also contributes to the stabilization of the process. Furthermore, when the monopolar electrostatic chuck is used, it is possible to remove the residual charges on the substrate to be etched, and it is possible to improve the throughput.

According to the plasma etching method of the present invention, particularly when the substrate to be etched having a fine pattern of the sub-half micron class is continuously processed, the uniformity and stability of the process for each substrate to be etched can be improved. The effect is remarkably improved, and the contribution of the present invention to the semiconductor device manufacturing process is significant.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a usage state of an RF bias application type ECR plasma etching apparatus used in Example 1 to which the present invention is applied, in which (a) is a reaction generated on the inner wall surface of a chamber by the previous plasma etching. (B) is a state in which reaction products are removed from the inner wall surface of the chamber by plasma discharge of a processing gas containing F-based gas, and (c) is a state in which the inner wall surface of the chamber is etched by the plasma etching this time. The reaction product is in the attached state.

2A and 2B are schematic cross-sectional views illustrating a plasma etching method in Example 1 to which the present invention is applied in the order of steps, in which (a) shows a resist mask formed on a Si substrate plate on which a natural oxide film is formed. The state, (b) is a state in which the natural oxide film on the opening surface of the resist mask is removed by plasma discharge of a processing gas containing an F-based gas, and (c) is a state in which the Si substrate is subsequently subjected to trench etching.

FIG. 3 is a schematic cross-sectional view showing a usage state of an RF bias application type ECR plasma etching apparatus used in Example 2 to which the present invention is applied, and FIG. 3A shows a substrate to be etched having a unipolar electrostatic chuck. A state of being set on the substrate stage, a state of (b) performing plasma etching, and a state of (c) removing reaction products on the inner wall surface of the chamber by plasma discharge of a processing gas containing an F-based gas and on the substrate to be etched. This is a state in which the residual charge of is removed.

FIG. 4 is a schematic cross-sectional view for explaining a plasma etching method in Example 2 to which the present invention is applied in the order of steps, in which (a) is a WSi _x layer laminated on a polycrystalline silicon layer to form a resist mask. State (b) is a state in which the polycrystalline silicon layer and the WSi _x layer are patterned while depositing a side wall protective film, and (c) is a state in which residual charges are removed and side wall protection is performed by plasma discharge of a processing gas containing an F-based gas. The film is removed.

[Explanation of symbols]

1 Etched Substrate 2 Substrate Stage 3 Microwave Waveguide 4 Berge 5 Solenoid Coil 6 Reaction Product 7 Plasma 11 Si Substrate 12 Natural Oxide Film 13 Resist Mask 14 Trench 15 Gate Insulation Film 16 Polycrystalline Silicon Layer 17 WSi _X Layer 18 Side wall protection film

Claims (3)

[Claims] 1. A plasma etching method for etching a Si-based material layer on a substrate to be etched with an etching gas containing any one selected from Cl-based gas, Br-based gas and I-based gas, wherein F-based gas is used. By the plasma discharge of the processing gas containing the Si,
A plasma etching method, comprising removing the natural oxide film on the surface of the system material layer, cleaning the inner wall surface of the etching chamber, and then performing the plasma etching. 2. The substrate to be etched is held on the substrate to be etched by an etching gas containing any one selected from a Cl-based gas, a Br-based gas and an I-based gas, while holding the substrate to be etched by a monopolar electrostatic chuck. In a plasma etching method for etching a Si-based material layer, after performing the plasma etching, a residual gas is removed from the substrate to be etched by plasma discharge of a processing gas containing an F-based gas, and an inner wall surface of the etching chamber is cleaned. A plasma etching method comprising: 3. The plasma etching method according to claim 1, wherein the Si-based material layer is at least one selected from the group consisting of silicon, refractory metal silicide, and refractory metal layer polycide. .