JPH07240402A - Dry etching method - Google Patents

Abstract

PURPOSE:To conduct the dry etching process ensuring excellent reproducibility and throughput by changing distance between a plasma generating section and a substrate during the dry etching process of an organic material film. CONSTITUTION:An organic material film on a substrate is selectively etched by introducing an etching gas which can produce an oxygen-based active species under the discharge dissociation condition into a plasma apparatus comprising a plasma generating section to produce the plasma with an ion density of 10<11>ion/cm<3> or more and then changing distance between the substrate held in the plasma apparatus and plasma generating section. This distance is set relatively short in the just etching process to substantially etch the organic material film as much as the thickness but is set relatively longer in the over etching process to each the remaining part of the organic material film. Moreover, this distance can be changed by moving up and down a substrate stage on which the substrate is placed along the axial direction of the plasma apparatus.

Description

Detailed Description of the Invention

The present invention relates to a dry etching method applied to fine processing such as manufacturing of semiconductor devices, and particularly to a high speed anisotropic anisotropic etching of a lower resist film while maintaining a high selection ratio with respect to a base material layer in a multi-layer resist process. Method for conductive etching.

[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 types of resist films, a lower resist film thick enough to absorb the surface step of the substrate and a thin upper resist film sufficient to achieve high resolution. is there.

A well-known method is a journal
Of Vacuum Science and Technology (J. Vac. Sci. Tech., 16 , p. 162)
0 (1979)). This is the lower resist film, SOG on the wafer.
(Spin-on-glass) silicon oxide (Si
An extremely thin intermediate film made of an O _x ) -based material and a thin upper layer resist film which is directly patterned by photolithography are used. In this process, the upper resist film is first patterned into a predetermined shape by lithography, the intermediate film thereunder is patterned by RIE (reactive ion etching), and the lower resist film is used as a mask. Are dry-etched.

By the way, dry etching of the lower resist film is usually performed by using O ₂ gas.
The essence of this etching mechanism is the combustion reaction of the organic polymer material by O ^* (oxygen radicals), 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 where 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. There is a need.

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 described 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]

Obviously, the reduction of incident ion energy is effective for suppressing the above-mentioned reattachment of sputter, but this reduces the etching rate in the vertical direction and the throughput. Besides being impaired, the above-mentioned isotropic combustion reaction becomes predominant, which causes a problem that anisotropy is lowered.

In particular, when a high density plasma having an ion density of 10 ¹¹ / cm ³ or more, which has been proposed one after another as a new plasma, is used, the etching reaction product C
Degradation of the anisotropic shape due to the re-dissociation of O _x is likely to appear remarkably. That is, in a plasma having a high electron temperature, such as ECR plasma (electron cyclotron resonance plasma), helicone wave plasma, inductively coupled plasma, etc., CO _x , which is a reaction product of combustion of resist, rides on a high vacuum exhaust flow and enters the chamber. Before being discharged to the outside, a re-dissociation reaction represented by the following formula CO _x → CO _x-1 + O ^* occurs. O generated here
^* Deteriorates the anisotropic shape of the lower resist pattern.

As a method of 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 in combination. For example, a dry etching method in which a mixed gas of halogen-based gas such as Cl ₂ and HBr and O ₂ is used and CCl _x polymer, CBr _x polymer and the like, which are reaction products, are deposited on the pattern sidewall surface is one example.

However, this method realizes anisotropic processing in a practical temperature range, but on the other hand, depending on the type of the underlying material layer, the halogen-based gas added contributes to the reaction formation which has a complicated composition and is difficult to remove. It created a new problem of depositing things. For example, Proceedings of the 40th Joint Lecture on Applied Physics (Spring Annual Meeting 1993) p. 5
78, Abstract No. 30a-ZE-8, when the lower resist film on the polysilicon film was etched using a HBr / O ₂ mixed gas, a deposit containing C, O, Si and Br as constituent elements was found. It is described that they are abnormally deposited to cause a microloading effect. Since this deposit contains Si, even if an attempt is made to remove it by performing O ₂ plasma treatment or the like after completion of etching, Si changes to SiO _x ,
There is a great risk of worsening the particle level. The above-mentioned collection of abstracts also states that such abnormal deposition can be suppressed by reducing the amount of halogen-based gas added.

As described above, the etching of the lower resist film is performed while satisfying all the practical etching rate, high underlayer selectivity, excellent shape anisotropy, suppression of microloading effect, suppression of particles, etc. Although it is not easy to carry out, it is considered necessary to take an approach in which the amount of halogen-based gas added is zero or as small as possible.

On the other hand, it is known that the etching characteristics of ECR plasma and some types of inductively coupled plasma change depending on the positional relationship between the plasma generating portion and the substrate. For example, Japanese Journal of Applied Physics, Vol. 29, No. 4 (Japanese Journal
of Applied Physics, vol. 29, no.4) p. 792-7
97 (1990) examined the etching characteristics of the polyimide interlayer insulating film while changing the distance between the ECR position and the wafer stage. As a result, the ion current density increased as the substrate (wafer) approached the ECR position. The etching rate is increased and the anisotropy is improved.
On the contrary, when the ECR position is deviated, radicals having a longer lifetime than ions are predominant and the anisotropic shape is deteriorated.

Also, in 1993, the dry process symposium
CF for the proceedings_Four/ H ₂Using mixed gas
SiO₂The etching characteristics of the interlayer insulating film are determined by the inductive coupling
The high-frequency antenna and the wafer screen above the chamber of the Zuma device.
The results of the examination while changing the distance to the
It is listed. According to this description, the substrate is a high frequency antenna.
If it is placed in the plasma generation area close to
The reaction product, HF, is re-dissociated by the action of high-energy electrons.
Therefore, the selection ratio to Si is not improved. However,
Place the plate in the plasma diffusion area, which is slightly away from the high-frequency antenna.
When placed, HF re-dissociation is reduced and part is exhausted
Therefore, the F atom concentration is reduced and the selection ratio to Si is improved.
It

From these facts, as a future approach to dry etching, it is possible to positively utilize the above-mentioned change in etching characteristics depending on the substrate holding position in the plasma apparatus for highly selective anisotropic processing. , Considered to be extremely effective. Therefore, the present invention provides a method capable of satisfying each condition such as high speed, anisotropy, high selectivity and low contamination at a high level in dry etching of an organic material film represented by a lower resist film. The purpose is to provide.

[0014]

As a result of a study in view of the above-mentioned object, the present inventor has found that the amount of O ^* generated in a high-density plasma device is a plasma generation part and a substrate held in the device. It has been found that it is effective for shape control to change the amount of O ^* that can come into contact with the substrate by changing this distance during etching by utilizing the fact that it shows a distribution according to the distance between The present invention has been completed.

That is, according to the dry etching method of the present invention, an etching process capable of generating oxygen-based active species under discharge dissociation conditions in a plasma device having a plasma generation unit for generating plasma having an ion density of 10 ¹¹ ions / cm ³ or more. A gas is introduced to selectively etch the organic material film on the substrate while changing the distance between the substrate held in the plasma apparatus and the plasma generation unit.

The organic material film is typically an organic resist film. Moreover, since the patterning is performed by dry etching instead of solution development treatment, one of the most important practical uses of the organic resist film is a lower layer resist film in a multilayer resist process.

As a concrete mode of changing the distance,
A mode is set to be relatively small in the just etching step of etching the organic material film substantially by the film thickness and relatively large in the overetching step of etching the remainder of the organic material film. Also,
The simplest means for realizing this change is to move the substrate stage on which the substrate is placed along the axial direction of the plasma device.

The plasma having a high ion density as described above includes ECR plasma, helicon wave plasma,
Any of the inductively coupled plasmas can be used. Among these, several types with different device configurations are known for inductively coupled plasma.
ICP excited around the insulating cylinder constituting a part of the axial cylindrical chamber a high-frequency multi-turn antenna in the apparatus by winding (I nductively C o
upled P lasma), TCP excited in the apparatus which is disposed a spiral RF antenna on an insulating plate of the chamber top (T ransformer C oup
led P lasma), a helical resonator plasma or the like which is excited in a helical resonator wound spiral RF antenna around an insulating cylinder.

When using ECR plasma,
A method is known in which a solenoid coil for generating a magnetic field has a plurality of stages, and the ECR position is moved in the chamber axial direction by controlling the amount of electric power supplied to each stage solenoid coil. In the present invention, the ECR position may be moved together with the elevation of the substrate stage described above.

In the present invention, the etching of the organic material film
As the gas, a gas containing at least one compound selected from O ₂ , O ₃ , carbon oxide, nitric oxide, sulfur oxide, and carbonyl sulfide (COS) is used. Here, CO (carbon monoxide), CO ₂ (carbon dioxide), C ₅ O ₂ (pentacarbon dioxide) is used as the carbon oxide, and N ₂ O (dinitrogen monoxide), NO (is used as the nitrogen oxide. Nitric oxide), N
₂ O ₃ (dinitrogen trioxide), and as sulfur oxides, SO (sulfur monoxide), SO ₂ (sulfur dioxide), SO
₃ (sulfur trioxide) can typically be used.

[0021]

[Function] Generally, ECR plasma, helicon wave plasma,
In high-density plasma such as inductively coupled plasma, the ion current density is high in the vicinity of the plasma generation part, and re-dissociation of etching reaction products is promoted to generate a large amount of radicals. However, as the distance from the plasma generating portion increases, the electron temperature decreases, which lowers the ion current density and relatively decreases the radical density. However,
Since the re-dissociation of etching reaction products is also reduced, the radicals are not in excess. Such changes in the plasma characteristics along the axial direction of the plasma device are naturally reflected in the etching characteristics. That is, it is possible to perform high-speed anisotropic etching using high ion energy and radicals generated in a large amount near the plasma generation portion. On the other hand, highly selective anisotropic etching using a proper amount of radicals can be performed at a place away from the plasma generation unit.

The point of the present invention is to make it possible to hold the substrate in regions having different plasma characteristics by changing the distance between the plasma generating part and the substrate during dry etching of the organic material film. The point is that the advantages of etching in the region are obtained at the same time. In particular, O ₂ , O ₃ , carbon oxide, which can generate oxygen-based active species,
In the process of etching the organic material film using an etching gas containing nitric oxide, sulfur oxide, carbonyl sulfide, etc., CO _x is generated as a reaction product, and this CO
O in each region of the plasma depending on the degree of re-dissociation of _x
^{* The} density will change. Therefore, if etching is performed while holding the substrate near the plasma generating portion, high-speed anisotropic etching is possible due to abundant ions and O ^* . This process is suitable for just etching. On the other hand, if the substrate is held in a region away from the plasma generating unit, highly selective anisotropic etching can be performed. This process is suitable for overetching.

By changing the distance between the plasma generating part and the substrate by raising and lowering the substrate stage, the substrate is placed in plasma regions having different O ^* densities by only mechanical operation without changing the plasma excitation conditions. You can Therefore, dry etching excellent in reproducibility and throughput becomes possible.

[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 performing bit line processing of SRAM, and 10 ¹¹ ions /
This is an example of etching the lower resist film on the second-layer polycide film using ECR plasma having an ion density of cm ² level.

First, the magnetic field my used in this embodiment was used.
FIG. 1 shows the configuration of the black plasma etching apparatus.
The basic components emit microwaves at 2.45 GHz.
Living magnetron 1, Rectangular waveguide 2 for guiding microwaves
And circular waveguide 3, ECR using the microwave
(Electron cyclotron resonance) ECR
Razma P_EBell jar made of quartz for producing
4. Circling the circular waveguide 3 and the bell jar 4
Placed at 8.75 × 10^-2Magnetic field strength of T (875G)
Solenoid coil 5 that can achieve
High vacuum exhaust in the direction of arrow A through the exhaust hole 8.
Etching chamber 6, this etching chamber
The gas required for processing is supplied to the bar 6 and the bell jar 4 respectively.
Mark B₁, B₂Gas introduction pipe 7 and wafer W supplied from the direction
Wafer stage 9 for mounting the wafer
It is buried in the tage 9 and supplied from the cooling equipment such as a chiller.
Arrow C₁, C ₂The wafer W by circulating it in the direction
Cooling pipe 10 for cooling to a constant temperature, the wafer
Matching to apply the substrate bias to the stage 9
-Group connected via network (M / N) 11 etc.
The RF power source 12 for plate bias application and the like.

The solenoid coil 5 is divided into an upper coil 5a and a lower coil 5b, each of which is independently supplied with electric power to control the magnetic field intensity distribution in the bell jar 4. By this control, the position of the ECR position 13, which is the resonance absorption point of the ECR plasma P _E , can be shifted in the axial direction of the bell jar 4. Here, the distance from the bottom surface of the lower coil 5b to the ECR position 13 is h _E.

On the other hand, the wafer stage 9 can be moved up and down in the direction of arrow D in the figure by a drive mechanism (not shown). Here, the bottom surface of the lower coil 5b and the wafer
The distance to the surface of the stage 8 is h _S. Therefore, the distance d between the ECR position 13 and the wafer stage 9 is represented by d = h _E + h _S. Since the wafer W is very thin, this distance d is approximated to the ECR position 13
And the wafer W.

This magnetic field microwave plasma etch
The lower layer resist film is actually etched using
It was Figure 2 shows the wafer used as an etching sample.
Show. This wafer is a shallow trench device
SiO is formed on the Si substrate 21 on which the isolation region 22 is formed. ₂Or
By the first layer polycide film through the gate oxide film consisting of
The gate electrode 25 is formed. This gate electrode 25
The lower layer side is a polycrystalline silicon layer 23, the upper layer side is WSi
_x(Tungsten silicide) layer 24. Furthermore
In addition, the entire surface of the wafer is S deposited by, for example, CVD.
iO_xIt is covered with an interlayer insulating film 26 and 2
A layer polycide film 29 is formed. This second layer
The sidewall film 29 is a portion forming the SRAM bit line.
The lower layer side is the polycrystalline silicon layer 27, and the upper layer side is WS.
i_xIt consists of layer 28.

Further, on the second-layer polycide film 29, a lower resist film 3 for patterning the second polycide film 29 is formed.
0 is formed on the entire surface, and the SOG intermediate film 3 is further formed on this.
1 and the upper layer resist film 32 are patterned.
The upper resist film 32 is, for example, a chemically amplified negative type three-component resist (manufactured by Shipley Co .; trade name S).
After forming a coating film having a thickness of about 0.5 μm using AL-601), it is patterned with a line width of about 0.35 μm using a KrF excimer laser stepper.

The SOG intermediate film 31 is a coating film of SOG (manufactured by Tokyo Ohka Kogyo Co., Ltd .; trade name OCD-Type2) (film thickness of about 1).
00 nm) is patterned by dry etching using the pattern of the upper resist film 32 as a mask. This dry etching was performed using a RIE (Reactive Ion Etching) apparatus and a CHF ₃ / O ₂ mixed gas.

Further, as the lower resist film 30, a novolac-based positive photoresist (manufactured by Tokyo Ohka Kogyo Co., Ltd .; trade name OFPR-800) is used as an example, and a film capable of substantially absorbing the surface step of the wafer W and flattening it. Thickness (about 1.0μ
m).

This wafer was set on the wafer stage 9 of the above-mentioned magnetic field microwave plasma etching apparatus, and the lower resist film 10 was just etched under the following conditions as an example. O ₂ flow rate 20 SCCM Cl ₂ flow rate 5 SCCM Gas pressure 0.27 Pa Microwave power 1000 W (2.45 GH
z) RF bias power 200 W (800 kHz) Wafer stage temperature −50 ° C. (using alcohol-based refrigerant) Temperature inside bell jar 150 ° C. distance h _E 60 mm distance h _S 200 mm distance d (= h _E + h _S ) 260 mm

In this process, CO _x is produced as an etching reaction product, but this causes re-dissociation with a high probability in the vicinity of the ECR position 13 to increase the O ^* density in the plasma. At the above wafer position, rapid anisotropic etching progressed due to the contribution of high density and high energy ions and radicals. The Cl ₂ is added in a small amount in order to promote the deposition of a carbon-based polymer side wall protective film (not shown) under wafer cooling conditions.

Subsequently, as an example, over-etching was performed under the following conditions to remove the remaining portion of the lower resist film 30. O ₂ flow rate 20 SCCM Cl ₂ flow rate 2 SCCM Gas pressure 0.27 Pa Microwave power 1000 W (2.45 GH
z) RF bias power 200 W (800 kHz) Wafer stage temperature −50 ° C. (using alcohol-based refrigerant) Belljar internal temperature 150 ° C. distance h _E 90 mm distance h _S 300 mm distance d (= h _E + h _S ) 390 mm

In this process, the distance between the wafer W and the ECR position 13 was enlarged as compared with that during just etching. At this wafer position, the re-dissociation of CO _x is not so large, so the amount of O ^* produced does not become excessive, and therefore high-speed high-selective etching proceeds without impairing the anisotropic shape. As a result, as shown in FIG. 3, the lower layer resist pattern 30a having an anisotropic shape could be formed.

In this over-etching step, the Cl ₂ flow rate is lower than that in the just-etching step, but this is achieved by adjusting the distance d as described above.
By performing the etching under the condition of less ^* , it is not necessary to reinforce the side wall protective film so much. Since Cl ₂ is in contact with the underlying WSi _x layer 28, the fact that the flow rate can be reduced in this way is extremely advantageous from the viewpoint of securing the underlying selectivity.

Example 2 In this example, the same etching of the lower resist film 30 was performed with an IC having an ion density of the order of 10 ¹² ions / cm ^2.
Performed using P. First, the IC used in this example
The structure of the P etching apparatus is shown in FIG.

This apparatus comprises a cylindrical etching chamber 46, a ceiling portion of the etching chamber 46, a conductive upper lid 41 which functions as a large-area DC ground electrode for plasma, and the etching chamber. 46
, A non-resonant multi-turn antenna 45 that surrounds the quartz cylinder 44, and a first matching network (M / N) 42 in the multi-turn antenna 45. An RF power source 43 for plasma excitation connected through the above, an exhaust hole 50 connected to an external exhaust system for high-vacuum exhaust of the inside of the etching chamber 46 in the direction of arrow E, an etching
A gas supply pipe 47 for introducing an etching gas into the chamber 46 from the direction of the arrow F, a wafer stage 48 on which the wafer W is mounted, an alumina clamp 49 for fixing the wafer W on the wafer stage 48, An RF power source 53 for applying a substrate bias, which is capacitively coupled to the wafer stage 48 via a second matching network (M / N) 52 for impedance matching, and arrows G ₁ and G ₂ inside the wafer stage 48. Cooling pipe 5 for cooling the wafer W by supplying and circulating a coolant in the direction
The first component is the main component.

The RF frequencies of the plasma exciting RF power source 43 and the substrate bias applying RF power source 53 are set to values slightly different from each other in order to prevent interference between them, and the former is, for example, 2.2 MHz. , The latter is 2.0MH
z. The wafer stage 48 can be moved up and down in the direction of arrow H in the figure by a drive mechanism (not shown). Here, the distance h between the multi-turn antenna 45 and the lower end and the wafer mounting surface of the wafer stage 48 is h.
Consider _I as a parameter that controls the O ^* density.

In such a structure, RF for plasma excitation
When a high frequency is applied to the antenna 45 from the power source 43, 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. As a result, 10 ¹² ions / cm ² An inductively coupled plasma P _I having a high ion density of is generated.

Next, using the above-mentioned ICP etching apparatus, just etching of the lower resist film 30 was performed on the same sample wafer as that used in Example 1 under the following conditions as an example. CO flow rate 50 SCCM Gas pressure 0.27 Pa Antenna output 1200 W (2.2 MH
z) RF bias power 200 W (2.0 MH
z) Wafer stage temperature −20 ° C. (using alcohol-based coolant) Distance h _I 50 mm In this process, the wafer W is O in the inductively coupled plasma P _I.
^* High-speed anisotropic etching progressed because it was placed in a relatively dense area.

At this time, if the ICP etching device is a device in which a heater is built in the upper lid 41, the heater is operated during the etching to suppress the deposition of the carbon-based polymer on the chamber wall and to remove particles. In addition to reducing the number, the sidewall protection film can be efficiently formed on the wafer W.

Subsequently, over-etching was performed under the same conditions except that the wafer stage 48 was lowered to set the distance h _I to 200 mm. In this process, the wafer W is O ^*
Since it is placed in a region having a relatively low density, highly selective anisotropic etching could be performed. Finally, as in Example 1, the lower layer resist pattern 30a having a good anisotropic shape could be formed.

As described above, the fact that the etching characteristics can be changed only by mechanically raising and lowering the wafer stage 48 without changing the plasma excitation conditions is an extremely excellent merit of the present invention.

Example 3 In this example, the same etching of the lower resist film 30 was carried out by using a helicon wave plasma having an ion density of 10 ¹³ / cm ³ . First, the configuration of the helicon wave plasma etching apparatus used in this example is shown in FIG.

The plasma generation part of this apparatus has a bell jar 61 made of quartz for generating helicon wave plasma P _H inside, and two loops that circulate around the bell jar 61, and couples RF power to the plasma. The main components are a loop antenna 62 for making the chamber 61, a solenoid coil 63 provided so as to circulate around the chamber 61, and generating a magnetic field along the axial direction of the chamber 61.

Here, the solenoid coil 63 further includes an inner circumference side solenoid coil 63a mainly contributing to the propagation of a helicon wave and an outer circumference side solenoid coil 6 mainly contributing to the transport of the helicon wave plasma P _H.
3b.

A high frequency is applied to the loop antenna 62 from an RF power source 74 for plasma excitation through a first matching network (M / N) 73 for impedance matching, and the upper and lower two loops rotate in opposite directions. Current flows. Here, the frequency of the plasma excitation RF power supply 74 is set to 13.56 MHz. The distance between both loops is optimized according to the desired wave number of the helicon wave.

The bell jar 61 is connected to the etching chamber 67, and the inner peripheral side solenoid coil 63a is connected.
The helicon wave plasma P _H is drawn into the etching chamber 67 along the divergent magnetic field formed by the outer solenoid coil 63b. The side wall surface and the bottom surface of the etching chamber 67 are made of a conductive material such as stainless steel. The inside thereof is evacuated to high vacuum in the direction of arrow I through an exhaust hole 68 by an exhaust system (not shown), and the gas required for dry etching is supplied in the direction of arrow J from a gas supply pipe 65 opened in the top plate portion. Receive. Further, the side wall surface thereof is connected to, for example, a load lock chamber (not shown) via a gate valve 66.

Further, inside the etching chamber 67, a conductive wafer stage 69 electrically insulated from the wall surface is housed, and the wafer W is held on the conductive wafer stage 69 to perform a predetermined dry etching. Has been done.
The wafer stage 69 has a wafer W in process.
In order to maintain the temperature at a desired temperature, a cooling pipe 70 for supplying a coolant from a chiller (not shown) and circulating the coolant in the directions of arrows K ₁ and K ₂ is inserted.

A second matching network (M / M) is applied to the wafer stage 69 in order to control the energy of the ions entering from the helicon wave plasma P _H.
An RF power source 72 for applying a substrate bias is connected via (N) 71. Here, this substrate bias application RF
The frequency of the power supply 72 was 13.56 MHz. further,
Outside the etching chamber 67, a magnet 64 capable of generating a multicusp magnetic field is arranged as an auxiliary magnetic field generating wafer stage in order to converge the divergent magnetic field in the vicinity of the wafer stage 69.

The wafer stage 69 can be moved up and down in the direction of arrow L in the figure by a drive mechanism (not shown). Here, the lower end of the bell jar 61 and the wafer stage 6
The distance h _H from the wafer mounting surface of No. 9 is considered as a parameter for controlling the O ^* density. In this configuration, when a magnetic field is formed in the inner space of the bell jar 61 and a high frequency is applied to the loop antenna 62 wound around the bell jar 61 to generate a helicon wave in the bell jar 61, the helicon wave is generated. Electrons are accelerated by energy transport through the Landau decay process, and the accelerated electrons collide with gas molecules to generate high-density plasma. With a helicon wave plasma, a high ion density of about 10 ¹³ / cm ³ can be achieved.

Next, using this helicon wave plasma etching apparatus, the same sample as that used in Example 1
As an example, the lower resist film 30 was just-etched on the wafer under the following conditions. NO ₂ flow rate 20 SCCM Gas pressure 0.1 Pa Antenna output 2000 W (13.56)
MHz) RF bias power 200 W (13.56)
MHz) Wafer stage temperature −30 ° C. (using alcohol-based coolant) Distance h _H 250 mm In this process, the wafer W is placed in a region with a relatively high O ^* density in the helicon wave plasma P _H , so that high-speed anisotropy is achieved. Etching progressed.

Then, the wafer stage 69 is lowered to set the bell jar-wafer stage distance h _H to 450 mm.
Other than the above, overetching was performed under the same conditions.
In this process, since the wafer W is placed in the region having a relatively low O ^* density, high selective anisotropic etching can be performed. Finally, as in Example 1, the lower layer resist pattern 30a having a good anisotropic shape could be formed.

As described above, the fact that the etching characteristics can be changed only by mechanically raising and lowering the wafer stage 69 without changing the plasma excitation conditions is an extremely excellent merit of the present invention.

The present invention has been described above based on the three embodiments, but the present invention is not limited to these embodiments. For example, in the above embodiment, etching
Although O ₂ , CO, and NO ₂ were used as the gas, basically the same result can be obtained by using carbon oxide or nitrogen oxide other than these, or sulfur oxide or carbonyl sulfide.

In addition to the above, it goes without saying that the structure of the sample wafer, the type and structure of the etching apparatus, the etching conditions and the like can be changed as appropriate.

[0059]

As is apparent from the above description, according to the present invention, the substrate is placed in the plasma region having different O ^* densities only by the mechanical operation without changing the plasma excitation condition and the reproducibility is improved. Further, it becomes possible to perform dry etching having excellent throughput.

In particular, since the high speed and high selective anisotropic etching of the lower resist film in the three-layer resist process becomes possible, the present invention greatly promotes the practical use of the process.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a configuration example of a magnetic field microwave plasma etching apparatus used in a dry etching method of the present invention.

FIG. 2 is a schematic cross-sectional view showing a state in which an SOG intermediate film is etched by using a pattern of an upper resist film as a mask in a process of forming a resist pattern for processing a bit line of SRAM.

FIG. 3 is a schematic cross-sectional view showing a state in which the lower layer resist film of FIG. 2 is anisotropically etched to form a lower layer resist pattern.

FIG. 4 is an ICP used in the dry etching method of the present invention.
It is a schematic sectional drawing which shows the structural example of an etching apparatus.

FIG. 5 is a schematic sectional view showing a configuration example of a helicon wave plasma etching apparatus used in the dry etching method of the present invention.

[Explanation of symbols]

1 magnetron 4,61 bell jar 5,63 solenoid coil 6,46,67 etching chamber 9,48,69 wafer stage 12, 53,72 substrate bias application RF power supply 13 ECR position 30 lower resist film 30a lower resist film Pattern 31 SOG intermediate film 32 Upper resist film 45 Multi-turn antenna 43,74 RF power supply for plasma excitation 44 Quartz cylinder 62 Loop antenna P _E ECR plasma P _I Inductively coupled plasma P _H Helicon wave plasma W Wafer

Claims (5)

[Claims] 1. An etching gas capable of generating oxygen-based active species under discharge dissociation conditions is introduced into a plasma device having a plasma generation unit for generating plasma having an ion density of 10 ¹¹ ions / cm ³ or more, and the plasma is generated. A dry etching method characterized by selectively etching an organic material film on a substrate while changing a distance between the substrate held in the apparatus and the plasma generation part. 2. The distance is set relatively small in a just etching step of etching the organic material film by substantially the film thickness thereof, and relatively set in an overetching step of etching the remainder of the organic material film. The dry etching method according to claim 1, wherein the dry etching method is large. 3. The dry etching according to claim 1, wherein the distance is changed by raising and lowering a substrate stage on which the substrate is placed along an axial direction of the plasma device. Method. 4. The dry etching method according to claim 1, wherein the plasma is any one of ECR plasma, helicon wave plasma, and inductively coupled plasma. 5. The etching gas according to claim 1, wherein the etching gas contains at least one compound selected from O ₂ , O ₃ , carbon oxide, nitric oxide, sulfur oxide, and carbonyl sulfide. The dry etching method according to claim 1.