JPH0774147A - Method and apparatus for dry etching - Google Patents

Abstract

PURPOSE:To remove a lower resist layer with the etching while keeping excellent shape anisotropy and selectivity for lower layer in a triple-layer resist process. CONSTITUTION:Using a high density plasma apparatus which can achieve the plasma such as ECR plasma, inductively coupled plasma, etc., having the ion density of 10<11>ion/cm<2> or higher, a lower resist layer 10 is etched with an etching gas which can generate carbonic deposit and oxygen active seed. A sidewall protective film 13 can be formed with good efficiency with contribution of both C element generated by the primary dissociation of the etching gas and C element generated by re-dissociation under the high density plasma ambience of COx which is a reaction product of the etching. Thereby, the incident ion energy which is required for anisotropic processing can be reduced and high selectivity can also be achieved. Since the sidewall protective wall 13 can easily be eliminated at the time of ashing, no particle-contamination can be found.

Description

Detailed Description of the Invention

The present invention relates to a dry etching method and apparatus applied to the manufacture of semiconductor devices and the like, and more particularly to a technique for etching a lower resist layer while maintaining a high selection ratio with respect to a base material layer in a multi-layer resist process. .

[0002]

2. Description of the Related Art In recent years, as semiconductor devices have been highly miniaturized in design rules, the surface steps of wafers have increased due to the complexity of integrated circuits, and the exposure wavelength in photolithography has become shorter, the multilayer resist process has become Hiring is becoming essential. This multi-layer resist process uses a combination of at least two resist layers, a lower resist layer thick enough to absorb surface steps of the substrate and a thin upper resist layer sufficient to achieve high resolution. is there.

A well-known method is described in J. Vac.
Sci. Tech. , 16 , p. 1620 (1979)
There is a three-layer resist process reported in. this is,
Three types of layers: a lower resist layer on the wafer, an extremely thin intermediate layer made of a silicon oxide (SiO _x ) based material such as SOG (spin on glass), and a thin upper resist layer directly patterned by photolithography. Is used. In this process, first, the upper resist layer is patterned into a predetermined shape by lithography, and the intermediate layer thereunder is patterned by RIE.
Patterning is performed by (reactive ion etching), and the lower resist layer is dry-etched using the intermediate layer as a mask.

By the way, dry etching of the lower resist layer described above is usually performed using O ₂ gas.
The essence of this etching mechanism is the combustion reaction of the resist material due to O ^* (oxygen radical), which essentially proceeds isotropically. Therefore, in order to prevent the cross-sectional shape of the pattern from deteriorating, it is necessary to adopt a condition in which the ion incident energy is increased to some extent. That is, the mean free path of ions and the self-bias potential V _dc are increased under conditions of low gas pressure and high bias power, and the contribution of the sputtering reaction by the ions having large incident energy is increased to achieve high anisotropy. Of.

However, the adoption of such etching conditions, on the contrary, also causes the practical application of the multilayer resist process. This is because the sputtered products of the underlying material layer are redeposited on the pattern sidewalls during overetching, which makes it difficult to remove them in a later step. Examples of such problems include, for example, Proceedings of the 33rd Joint Lecture on Applied Physics (Spring Annual Meeting 1986) p. 542, Al pointed out in abstract number 2p-Q-8
There are known cases of redeposited (aluminum),
In addition to this, SiO _x interlayer insulating film and W (tungsten)-
Reattachment of polycide wiring causes serious problems such as dust generation.

[0006]

It is obvious that the reduction of incident ion energy is effective for suppressing the above-mentioned spatter reattachment, but the above-mentioned isotropic combustion reaction becomes dominant. , The anisotropy is lowered, and the etching rate in the vertical direction is lowered. As a technique for solving this problem, it has been proposed to reduce incident ion energy to such an extent that a practical etching rate is not impaired by using sidewall protection together. For example, a mixed gas of halogen-based gas such as Cl ₂ and HBr and O ₂ is used, and CCl _x polymer and CB which are reaction products are used.
An example is a dry etching technique in which r _x polymer or the like is deposited on the pattern side wall surface.

The above dry etching method is practical
It has attracted attention as a technology that can realize highly anisotropic processing in the temperature range.
However, depending on the type of base material layer, the added halo
Reaction products of complex composition are deposited due to the contribution of gen-based gas
I knew that I would do it. For example, 40th Applied Physics
Proceedings of the Lectures of the Association (Spring Annual Meeting 1993) p.
578, Abstract No. 30a-ZE-8, Polysilicon
HBr / O is used as the lower resist layer on the film.₂With mixed gas
When etched, C, O, Si, Br are constituent elements
Abnormal deposits and micro loading effect
It has been reported to produce fruit. This deposit contains Si
Therefore, after the etching is completed, O ₂Plasma treatment
Even if you try to remove it by_xTo generate
-There is a great possibility that it will deteriorate the tickle level.

In view of the above, the present invention utilizes a sidewall protective material that can be easily removed in a subsequent step, and dry-etches the lower resist layer with high underlayer selectivity, high shape anisotropy and a practical etching rate. It is an object of the present invention to provide a method and a dry etching apparatus therefor.

[0009]

The present inventors have considered that a halogen-free carbon-based deposit is suitable as a material for forming a sidewall protective film that can be easily removed in a subsequent step.
However, in order to deposit such a carbon-based deposit in the etching reaction system in which the combustion reaction by O ^* proceeds, some kind of ingenuity is required. The inventors of the present invention have focused on re-dissociation of carbon oxide in so-called high-density plasma and devised to deposit a carbon-based deposit generated thereby on the sidewall surface of the pattern.

The dry etching method of the present invention is proposed in accordance with the above-mentioned concept, and a carbon-based deposit and an oxygen-based active material are applied to an etching apparatus capable of generating plasma having an ion density of 10 ¹¹ ions / cm ³ or more. An etching gas capable of generating seeds is introduced, and the organic material layer formed on the substrate is etched using the inorganic material layer patterned in a predetermined shape as a mask.

Here, the high-density plasma is a plasma that has been devised to increase the number of collisions of electrons and gas atoms as compared with conventional plasma.
Conventional plasma is, for example, RF between parallel plate electrodes.
It is excited by applying power to cause glow discharge or by supplying microwave to the waveguide to cause microwave discharge. On the other hand, the high-density plasma, for example, uses electron cyclotron resonance based on the interaction between the microwave electric field and the magnetic field, or the microwave propagation mode in the magnetic field called the Whistler mode, to highly dissociate the gas. It has been promoted and achieved a high ion density.

Specific examples of such a plasma having an ion density of 10 ¹¹ ions / cm ³ or more include ECR plasma, helicon wave plasma, ICP (Inductive).
lyCoupled Plasma), TCP (Tra
nsformer Coupled Plasma),
Hollow / anode type plasma, helical resonator plasma and the like can be mentioned, and both are suitable for application to the present invention.

The carbon-based deposit and the oxygen-based active species may be supplied from a single compound contained in the etching gas, may be supplied separately from a plurality of types of compounds, or may be further or a plurality of types. It does not matter whether they are supplied in duplicate from the compound. As an example, when a compound having a carbon-oxygen multiple bond in the molecule is used, both can be supplied from this single compound. Examples of such compounds include CO (carbon monoxide), CO
₂ (carbon dioxide), C ₅ O ₂ (pentacarbon dioxide), COS
(Carbonyl sulfide) and the like.

Of course, it does not matter if O ₂ which is the basic component of the etching gas for the conventional organic material layer is contained. Further, a nitrogen-based compound may be included.

Further, generally, in dry etching, the anisotropic shape is deteriorated during overetching in which radicals are relatively excessive. Therefore, as a process ingenuity, the above etching is performed in a just etching step and an overetching step. It is also effective to increase the generation ratio of carbon-based deposits in plasma in the latter case.

Alternatively, a device for supplying carbon to the hardware side may be provided without depending on the etching gas composition. For example, in the dry etching apparatus capable of generating high density plasma as described above, At least the surface layer of the internal components of the etching chamber,
It is effective to use a carbon-based material. In this case, SiC (silicon carbide), graphite or the like can be used as the carbon-based material layer.

The internal components of the etching chamber may include the inner wall of the etching chamber, a wafer clamp, a wafer cover and the like. In particular, from the viewpoint of efficiently supplying carbon by the ion-sputtering action, wafer clamps or wafers that are arranged near the wafer and that have an ion vertical incidence surface parallel to the wafer surface.
The cover is particularly effective.

[0018]

In the present invention, the oxygen-based active species represented by O ^* acts as an etchant for the organic material layer, and as a result, C in the organic material layer represented by photoresist is used.
The (carbon) atom causes the following combustion reaction. C + xO → CO _x ↑ Here, when the above reaction proceeds in a conventional plasma having an ion density of up to about 10 ¹⁰ ions / cm ³ , the generated CO _x is directly stored in the etching chamber. It is removed outside the chamber by riding on the existing high vacuum exhaust flow. However, it has recently been clarified that the generated CO _x is re-dissociated in the plasma having an ion density of the order of 10 ¹¹ ions / cm ³ or more. The C component generated by this re-dissociation is added to the C component generated by the primary dissociation of the etching gas, so that the plasma is carbon-rich (carbon-rich) than the conventional plasma.
Therefore, it is advantageous for the formation of carbonaceous deposits. Since this abundant carbon-based deposit provides a sufficient side wall protection effect, it is possible to reduce the incident ion energy required for anisotropic processing and suppress the sputtering of the base material layer.

Moreover, since the carbon-based deposit does not contain a component such as halogen that reacts with the underlying material layer and can be easily removed by O ₂ plasma treatment such as ashing after the etching is completed, the micro-loading is carried out. The effects and particle contamination are not revealed.

The most simple etching gas usable in the present invention is a compound having a carbon-oxygen multiple bond in the molecule. If this compound dissociates, both carbon that contributes to sidewall protection and oxygen-based active species that serves as an etchant can be supplied. Therefore, the etching gas composition may basically be a single composition. However, depending on the conditions, this compound may increase the C / O ratio (ratio of the number of C atoms and the number of O atoms) of the etching reaction system and may reduce the etching rate. In such a case, if O ₂ is appropriately added, the deposition of carbonaceous deposits can be slightly suppressed and a practical etching rate can be secured.

On the contrary, the addition of nitrogen compounds to the etching gas promotes the deposition of carbon deposits. In the etching reaction system to which the nitrogen-based compound is added, in addition to the compound having a C—O bond as a reaction product,
A compound having a C—N bond is produced. Comparing the interatomic bond energies of diatomic molecules, the C—N bond (770 kJ / mol) has a higher C—O bond (1077 kJ / mol).
It is smaller than (J / mol) and is likely to be re-dissociated. Therefore, the higher the production ratio of the compound having the C—N bond is, the more the plasma becomes carbon rich, and the deposition of the carbon-based deposit is promoted.

Further, if the production ratio of carbonaceous deposits is increased in the over-etching step, a good anisotropic shape can be maintained throughout the process, and the underlayer selectivity can be increased. Generally, in the dry etching process, it is in the over-etching stage where the number of the objects to be etched decreases that the radicals are excessive compared with the initial setting conditions. Further, the underlayer selectivity becomes a problem in the over-etching stage. Therefore, if the deposition of the carbon-based deposit is enhanced only at this stage, good anisotropy and selectivity can be achieved although the etching rate is slightly lowered. In addition, since the carbonaceous deposit formation ratio is kept relatively low in the just etching stage before that, the etching proceeds at a normal rate. Therefore, the total etching time is not significantly extended.

Alternatively, as a device of the hard wafer surface, when at least the surface layer portion of the internal constituent members of the etching chamber is made of a carbon-based material, it may come into contact with the radicals in the plasma or may have an ion sputtering action. By receiving the carbon, the carbon can be supplied also from the surfaces of these members. Therefore, the C / O ratio can be controlled without resorting to the composition of the etching gas.

[0024]

EXAMPLES Specific examples of the present invention will be described below.

EXAMPLE 1 In this example, the present invention is applied to a three-layer resist process for bit line processing of SRAM, and EC of CO gas is used.
1 generated by R (electron cyclotron resonance) discharge
This is an example of etching the lower resist layer on the second polycide film using ECR plasma having an ion density of the order of 0 ¹¹ ions / cm ² . This process will be described with reference to FIG.

First, the wafer used as an etching sample is shown in FIG. In this wafer, a gate electrode 5 made of a first-layer polycide film is formed on a silicon substrate 1 on which a shallow trench type element isolation region 2 has been formed, with a gate oxide film made of SiO ₂ interposed. The gate electrode 5 differs from that of the polycrystalline silicon layer 3 of the lower side and upper side of the WSi _x (tungsten silicide) layer 4 are stacked. Further, the entire surface of the wafer is covered with an SiO ₂ interlayer insulating film 6 formed by depositing SiO ₂ by CVD, for example, and a second-layer polycide film 9 is formed thereon. The second-layer polycide film 9 is formed by laminating the lower-layer side polycrystalline silicon layer 7 and the upper-layer side WSi _x layer 8 and is a portion forming the bit line of the SRAM.

Further, in order to pattern the second-layer polycide film 9, first, a lower resist layer 10 is formed to a thickness capable of substantially absorbing and flattening the surface step of the wafer, and a thin SOG intermediate layer 11 is formed thereon. And the upper resist pattern 12 is sequentially formed. Here, the lower resist layer 10 was formed by using, for example, a novolac-based positive photoresist (manufactured by Tokyo Ohka Kogyo Co., Ltd .; trade name OFPR-800). At this time, a region having a large layer thickness and a region having a small layer thickness occur depending on the arrangement of the gate electrode 5, but the average layer thickness in the former case is about 1.
It was set to 0 μm.

The SOG intermediate layer 11 is, for example, SO
G (manufactured by Tokyo Ohka Kogyo Co., Ltd .; trade name OCD-Type 2)
It is formed by applying. The upper resist pattern 12 is, for example, a chemically amplified negative type 3
Component resist (made by Shipley Co., Ltd .; trade name SAL-601)
After forming a coating film with a thickness of about 0.5 μm using
It is patterned using an excimer laser stepper with a line width of about 0.35 μm.

Next, the upper resist pattern 12 described above is used.
The SOG intermediate layer 11 was etched using the as a mask. A hex type RIE device was used for etching, and the etching conditions were set as follows as an example. CHF ₃ flow rate 75 SCCM O ₂ flow rate 8 SCCM gas pressure 6.5 Pa (= 50 mTorr) RF power 700 W (13.56 MHz) By this etching, as shown in FIG.
The OG intermediate layer pattern 11a was formed.

This wafer was set on the wafer mounting electrode of the RF bias application type magnetic field microwave plasma etching apparatus, and as an example, the lower resist layer 10 was etched under the following conditions. CO flow rate 20 SCCM Gas pressure 0.27 Pa Microwave power 900 W (2.45 GH
z) RF bias power 50 W (800 kHz) Wafer mounting electrode temperature −50 ° C. Over etching 100%

In this etching process, the etching proceeds due to the contribution of O ^* , O ^+, etc. dissociated from CO. On the other hand, carbon-based deposits are also produced by C similarly produced from CO and C produced by re-dissociation of the etching reaction product CO _x , and the sidewall protective film 13 as shown in FIG. 1C. Was efficiently deposited on the side wall surface of the pattern. As a result, the lower layer resist pattern 10a having an anisotropic shape was formed even under a relatively low bias condition. Further, since the ion sputtering action is controlled to the necessary minimum due to this low bias, the re-deposited layer derived from the underlying WSi _x layer 8 is formed even after performing overetching up to 100%. Was not done.

Furthermore, since no highly reactive halogen-based active species are present in the etching reaction system, the abnormal formation of deposits, which was observed in some of the prior art, did not occur.

Thereafter, the lower resist pattern 10 is formed.
The second-layer polycide film 9 was etched using a as a mask, and after the etching was completed, the SOG intermediate layer pattern 11a was removed by RIE, and then ordinary ashing was performed to remove the lower layer resist pattern 10a. The sidewall protective film 13 was removed at the same time as this ashing, and no particle contamination was left on the wafer.

Example 2 In this example, a similar underlayer resist etch was performed with O ₂
/ COS mixed gas was used, and the mixing ratio of this gas was changed between the just etching step and the over etching step. First, the same wafer as that used in Example 1 was set in a magnetic field microwave plasma etching apparatus, and as an example, the lower resist layer 10 was just-etched under the following conditions.

O ₂ flow rate 10 SCCM COS flow rate 10 SCCM Gas pressure 0.27 Pa Microwave power 900 W (2.45 GH)
z) RF bias power 50 W (800 kHz) Wafer mounting electrode temperature −50 ° C. The etching mechanism at this stage is basically as described in the first embodiment. However, as a constituent component of the sidewall protective film 13, a small amount of S (sulfur) generated by dissociation from COS is included.

Next, as an example, overetching was performed under the following conditions. CO flow rate 5 SCCM COS flow rate 15 SCCM Gas pressure 0.27 Pa Microwave power 900 W (2.45 GH
z) RF bias power 25 W (800 kHz) Wafer mounting electrode temperature −50 ° C. At this stage, the flow rate ratio of COS gas was increased more than in the just etching stage, so that the sidewall protection effect was enhanced. Therefore, it is possible to maintain the good anisotropic shape of the lower layer resist pattern 10a and improve the underlayer selectivity even during overetching in which O ^* is relatively excessive.

Example 3 In this example, a similar lower layer resist etching was performed with I
It was performed using a CP etching apparatus and a CO ₂ / N ₂ mixed gas. First, before explaining the etching process,
The configuration of the ICP etching apparatus will be described with reference to FIG.

This apparatus comprises a cylindrical etching chamber 26, a ceiling portion of the etching chamber 26, a conductive lid 21 having a built-in heater 22, and an upper electrode integrated with the lid 21. 23, above etching
A quartz window 24 forming the upper part of the side wall surface of the chamber 26, a non-resonant antenna 25 that surrounds the quartz window 24, an RF power supply 27 that supplies RF power to the antenna 25, and an arrow A inside the etching chamber 26. A gas supply pipe 30 for introducing the etching gas into the etching chamber 26 in the direction of the arrow B and discharging it from a ring-shaped blow-out port, in order to evacuate the chamber to a high vacuum in a direction. A wafer stage 28, which is arranged to face the upper electrode 23 and also serves as a lower electrode, an alumina clamp 29 for fixing the wafer W on the wafer stage 28, and a matching stage for impedance matching on the wafer stage 28. RF power source 33 capacitively coupled through box 32, and arrows C ₁ and C inside wafer stage 28. A cooling pipe 31 for cooling the wafer W by supplying and circulating a coolant in _two directions is a main component.

In this structure, when power is applied from the RF power supply 27 to the antenna 25, the electrons rotate in a plane substantially parallel to the electrodes in the induced magnetic field to increase the probability of collision with gas molecules. An inductively coupled plasma P having a high ion density on the order of 10 ¹² ions / cm ² is generated. Here, the RF frequencies of the RF power source 27 and the RF power source 33 are set to be slightly lower in the latter in order to prevent interference between them.

Using the ICP etching apparatus, the lower resist layer 10 was etched under the following conditions as an example. CO ₂ flow rate 10 SCCM N ₂ flow rate 20 SCCM Gas pressure 0.4 Pa Antenna output 2500 W (2.2 MH
z) RF bias power 200 W (2.0 MH
z) Wafer stage temperature −50 ° C. Upper electrode temperature 250 ° C. Over-etching 100% Here, in addition to the etching mechanism described in the previous embodiment,
The reaction product having a C—N bond generated from N ₂ is effectively re-dissociated, and the density of the inductively coupled plasma P generated here is higher than that of the ECR plasma used in the previous example, The production rate of the carbon-based deposits increased due to the high probability of re-dissociation, the fact that the heating of the upper electrode suppressed the deposition of the carbon-based deposits on portions other than the wafer W surface. As a result, the excellent shape anisotropy of the lower resist pattern 10a and high underlayer selectivity were maintained even during 100% overetching.

Embodiment 4 This embodiment is an example in which the deposition efficiency of carbonaceous deposits is improved by supplying the C component into the plasma from the internal constituent members of the etching chamber. The apparatus used here is made from alumina to SiC (silicon.
Carbide).

An example of etching conditions is shown below. CO ₂ flow rate 20 SCCM Gas pressure 0.4 Pa Antenna output 2500 W (2.2 MH
z) RF bias power 200 W (2.0 MH
z) Wafer stage temperature -50 ° C Upper electrode temperature 250 ° C Overetching 100%

In this etching process, the C component is also supplied from the surface of the clamp 29, so that the side wall protection effect is enhanced. Therefore, even though the composition of the etching gas was a single composition of CO ₂ unlike Example 3, it was possible to perform extremely excellent high selection, high anisotropy and low contamination etching.

Although the present invention has been described based on the four examples, the present invention is not limited to these examples, and the structure of the sample wafer, the type and structure of the etching apparatus, the etching, and the like. It goes without saying that the conditions can be changed as appropriate.

[0045]

As is apparent from the above description,
When the present invention is applied, the carbon-based deposit is efficiently deposited by utilizing the re-dissociation of the carbon-based reaction product that occurs in the high-density plasma, and thus the highly anisotropic and highly selective gas composition is achieved by the extremely simple gas composition. It is possible to etch the organic material layer with good properties and low contamination. In addition, abnormal deposition or the like which occurs when a halogen-based active species is used does not occur.

Particularly, by applying the present invention, a three-layer resist
The significance of providing a process as a practical process is
It is extremely large.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of a process in which the present invention is applied to the formation of a resist pattern for bit line processing of an SRAM in the order of steps, (a) being a lower layer resist on a second layer polycide film. Layer, SOG intermediate layer, upper layer resist pattern are sequentially laminated, (b) is a state in which the SOG intermediate layer is etched using the upper layer resist pattern as a mask, and (c) is sidewall protection by carbon-based deposits. While showing, the respective states in which the lower layer resist pattern is formed are shown.

FIG. 2 is a schematic cross-sectional view showing a configuration example of an ICP etching apparatus to which the present invention has been applied.

[Explanation of symbols]

 9 ・ ・ ・ Second layer polycide film 10 ・ ・ ・ Lower resist layer 10a ・ ・ ・ Lower resist pattern 11a ・ ・ ・ SOG intermediate layer pattern 12 ・ ・ ・ Upper resist pattern 13 ・ ・ ・ Sidewall protection film 23 ・ ・・ Top electrode 24 ・ ・ ・ Quartz window 25 ・ ・ ・ Antenna 26 ・ ・ ・ Etching chamber 28 ・ ・ ・ Wafer stage 29 ・ ・ ・ Clamp W ・ ・ ・ Wafer P ・ ・ ・ Inductively coupled plasma (ICP)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H01L 21/31 C

Claims (6)

[Claims] 1. An etching apparatus capable of generating a carbon-based deposit and oxygen-based active species is introduced into an etching apparatus capable of generating a plasma having an ion density of 10 ¹¹ ions / cm ³ or more to form a plasma on a substrate. A dry etching method, wherein the organic material layer is etched using the inorganic material layer patterned into a predetermined shape as a mask. 2. The etching gas is carbon in the molecule.
The dry etching method according to claim 1, further comprising a compound having a multiple bond between oxygen atoms. 3. The dry etching method according to claim 1, wherein the etching gas contains O ₂ . 4. The dry etching method according to claim 1, wherein the etching gas contains a nitrogen-based compound. 5. In the just etching step of etching the organic material layer substantially by the thickness of the organic material layer during the etching step, the production ratio of carbonaceous deposits in the plasma is made relatively small. 5. The dry etching method according to claim 1, wherein the overetching step for removing the remaining portion of the layer is made relatively large. 6. An etching chamber has a constituent member in which at least a surface layer portion is made of a carbon-based material, and an ion density generated in the etching chamber is 10 ¹¹ ions / cm ³ or more. A dry etching apparatus adapted to supply a carbon component into the plasma from the surface of the constituent member by contacting with the plasma.