JPH0888216A - Ashing method - Google Patents

Abstract

(57) [Summary] [Object] To provide an ashing method for removing an organic substance on a substrate, particularly a resist film whose surface is hardened by doping or the like. [Structure] Boron is implanted by ion shower doping, and the ashing object 8 having a resist film 12 whose surface layer 13 is hardened is subjected to reactive ion etching in a mixed gas atmosphere of oxygen gas and nitrogen gas to be hardened. After removing the surface layer 13, the remaining resist film is removed by reactive ion etching under a high pressure condition in an oxygen gas atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ashing method for removing a mask made of an organic material on a substrate, particularly a resist film hardened by doping or the like.

[0002]

2. Description of the Related Art In a device manufacturing process such as a semiconductor device or a liquid crystal display, a resist film patterned by a photolithography technique is used as a mask for an etching process or a mask for an impurity implantation process.

A method of removing the resist film is called an ashing method, and conventionally, ashing by down-etching has been performed in a plasma atmosphere of oxygen gas.

A conventional ashing method will be described below with reference to the drawings. FIG. 4 shows a download etching apparatus. Reference numeral 15 is a gas supply port for introducing the reaction gas into the reaction chamber 14 for performing ashing. 1
Reference numeral 6 denotes a gas exhaust port, which is connected to an exhaust system (not shown) that controls the pressure in the reaction chamber 14 to an appropriate value while introducing air.

In the reaction chamber 14, a discharge region 17 for converting the reaction gas introduced from the gas supply port 15 into plasma by the high frequency power supplied from the high frequency power source 19 and the charged particles and excited particles forming the plasma are lost. The transport pipe 18 that activates and introduces only radicals into the reaction chamber 14 is
Are provided in sequence along with the flow of gas. An object to be ashed 20 is placed on the sample table 21 in the reaction chamber 14.

At the time of ashing, after the reaction chamber 14 is evacuated by the exhaust system having the exhaust port 16, the reaction gas is introduced into the reaction chamber 14 through the gas supply port 15 while the inside of the reaction chamber 14 is being evacuated. Control pressure to proper pressure. In this state, high-frequency power is supplied from the high-frequency power source 19 to turn the reaction gas into plasma in the discharge region 17, and this plasma ashes the resist film of the object 20 to be ashed.

In ashing with oxygen plasma using the above apparatus, oxygen plasma passes through the transport pipe 18 and the reaction chamber 1
4, the charged particles such as electrons and ions and the short-lived excited particles are deactivated in the process of transportation, and only neutral and long-lived oxygen radicals react with the ashed object 20 to form a resist film. To ash. In addition, the above reaction is a chemical reaction due to radicals, which enables etching with low damage.

[0008]

However, with the introduction of techniques such as ion beam etching and ion shower doping, the temperature of the resist film on the substrate rises in the etching process, the impurity implantation process, etc., and the surface layer of the resist film is formed. The situation has begun to change. For example, when implanting ions into a glass substrate with a patterned resist film,
The impact raises the temperature of the resist film. Furthermore, since glass has a low thermal conductivity, it does not cool sufficiently, and hydrogen atoms and oxygen atoms come out from the surface layer of the resist film, and the surface layer of the resist film is carbonized and hardened.

When the resist film containing the hardened surface layer is removed by conventional ashing with oxygen radicals, the removal process is chemical etching, so that the reaction does not proceed in the hardened surface layer of the resist film and the resist film is removed. There was a problem that it could not be removed.

In order to solve the above problem, it was found that the hardened layer can be removed by ion-centered etching.
Since this removal method is a physical reaction by ions, it was also found that the type of ions affects the underlying film below the resist film. In order to eliminate this effect, it was necessary to study the reaction gas used for removing the hardened layer and the method for removing the residual resist film after the hardened layer was removed depending on the state of the underlying film.

The present invention solves the above problems and provides an ashing method capable of removing a resist film including a hardened layer and performing low-damage etching with less influence on a device.

[0012]

In order to achieve the above object, the present invention provides a first method of removing a hardened layer of a resist film made of an organic material by reactive ion etching in a mixed atmosphere of oxygen gas and nitrogen gas. And a second step of removing the resist film remaining in the first step by reactive ion etching in a mixed gas atmosphere of oxygen gas or nitrogen gas mainly containing oxygen gas.

When the base film is a thin film, after the first step, the resist film left by the plasma etching in the mixed gas atmosphere of oxygen gas or nitrogen gas mainly containing oxygen gas, or the organic solvent. A second step of removing

[0014]

In the first step, oxygen and nitrogen ions are generated in the plasma atmosphere of oxygen and nitrogen in addition to oxygen radicals, and these ions participate in the reaction.

Specifically, first, nitrogen ions are accelerated by an electric field and collide with a hardened layer of a resist film made of an organic material.
At this time, atoms on the surface portion of the hardened layer are repelled by the effect of spattering, and the surface portion is chemically activated. In this state, oxygen ions and oxygen radicals having kinetic energy hit the surface portion of the hardened layer and ashing proceeds to remove the hardened layer.

Then, in the second step, the remaining resist film is ashed by chemical etching using oxygen radical centers or an organic solvent.

[0017]

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

(Embodiment 1) FIG. 1 shows the overall structure of a reactive ion etching apparatus.

In the figure, 5 is a gas controller,
The reaction gas involved in the ashing is introduced into the reaction chamber 1 in which the ashing is performed while controlling the flow rate to a predetermined mixing ratio. An exhaust system 2 controls the pressure in the reaction chamber 1 to a predetermined pressure while introducing air.

An anode 3 is provided above the reaction chamber 1.
However, a cathode (cathode) 4 is provided in the lower part, and an object 8 to be ashed is arranged on the cathode 4. A high frequency power supply 7 is connected to the cathode 4 via an impedance matching circuit 6, and a high frequency discharge is generated between the anode 3 and the cathode 4 to generate plasma. The material of the cathode 4 is aluminum, and the surface thereof is anodized. A push-up mechanism 9 lifts the ashing target 8 when the ashing target 8 is transported. Although not shown, the object to be ashed 8 is cooled by cooling the cathode 4 with cooling water.

After the reaction chamber 1 is evacuated by the exhaust system 2, the reaction gas is introduced into the reaction chamber 1 through the gas controller 5, and the exhaust system 2 controls the pressure to a predetermined pressure.

Next, high frequency power is supplied from the high frequency power supply 7 through the impedance matching circuit 6 to the anode 3 and the cathode 4.
And a plasma of a reaction gas is generated between them and the object to be ashed by the plasma.

Next, the ashing method in this embodiment using the above apparatus will be described. FIG. 2A shows a sectional view of the object to be ashed used in this example. In this embodiment, a glass substrate 10 having a thickness of 1 mm has a thickness of 100 n.
m polycrystal silicon film 11 is formed, a 1.7 μm thick resist film 12 is patterned by photolithography, and then boron is implanted by ion shower doping to form a hardened layer 13 on the surface of the resist film. Item 8 was used.

In order to form the polycrystalline silicon film, after forming amorphous silicon by the plasma CVD method,
A method of melting and recrystallizing with a laser was used. The acceleration voltage for ion shower doping was changed between 0 and 150 kv.

In ashing, first, the object 8 to be ashed is placed on the cathode 4 in the reaction chamber 1 shown in FIG.

Next, after the pressure in the reaction chamber 1 is set to a vacuum state of about 0.7 mTorr by the exhaust system 2, the gas controller 5 is introduced into the reaction chamber 1 and oxygen gas having an inflow rate of 60 cc per minute is added. While the gas mixed with 30 cc of nitrogen gas is introduced, the pressure in the reaction chamber 1 is set to 3 by the exhaust system 2.
It was controlled to 00 mTorr.

Next, 300 W of high frequency power is applied from the high frequency power supply 7 through the impedance matching circuit 6 to generate plasma of the reaction gas, and the hardened layer 1 of the object 8 to be ashed.
3 and the resist film 12 were ashed for 3 minutes by reactive ion etching using oxygen and nitrogen ions. Further, the object 8 to be ashed is kept at 20 ° C. by the cooling water.

Since the above etching is ion-centered etching by oxygen and nitrogen ions, if the etching is continued even after the hardened layer is removed, the polycrystalline silicon film 11 is also etched, which may adversely affect the device. is there.

Therefore, after the first step, reactive ion etching under a high pressure condition was performed in an oxygen gas atmosphere, and the remaining resist film was removed by oxygen radical center etching.

In this embodiment, using the above-mentioned apparatus, the reaction chamber 1 pressure was set to 600 mTorr with oxygen gas having an inflow rate of 90 cc per minute, and high-frequency power of 150 W was applied to the reactive ion of oxygen gas. Ashing was performed for 5 minutes by etching. Here, the object to be ashed 8 is cooled by the cooling water.
Was kept at 20 ° C.

As a result, as shown in FIG. 2 (b), low damage etching with little influence on the polycrystalline silicon film 11 was performed.

As a comparative example, 1 was used as the reaction gas in the first step.
The above-described series of ashing was performed using a mixed gas of oxygen gas having an inlet air flow rate of 90 cc, oxygen gas of 60 cc, and CF ₄ gas of 300 cc.

[0033]

[Table 1]

Table 1 shows the removal state of the resist film in the ashing, the removal state by the ashing of the present invention using the mixed gas of oxygen gas and nitrogen gas, and the acceleration voltage of the ion shower doping of 0 to 0. 150
It is described in the range of kv. In the table, the polycrystalline silicon film 11 after ashing is shown in 3 by an electron microscope.
As a result of observing at a magnification of 10,000 times, as a result, the resist film 12 can be completely removed, and the polycrystalline silicon film 11 is hardly etched. The case where the silicon film is etched is Δ, and the resist film 1 including the hardened layer 13
The case where 2 was not removed was represented as x.

As a result, in the reactive ion etching of oxygen gas, the acceleration voltage of the ion shower doping is 20.
It was found that only the resist film including the hardened layer generated at less than kv can be removed.

With a mixed gas of oxygen gas and CF ₄ gas, the acceleration voltage for ion shower doping is 120 kv.
The cured resist film can be completely removed within the following range, but at that time, the polycrystalline silicon film may be etched, which may adversely affect the device.

On the other hand, in the reactive ion etching in the mixed atmosphere of oxygen gas and nitrogen gas, the resist film hardened in the range where the acceleration voltage of the ion shower doping is 120 kv or less can be completely removed, and the polycrystalline film can be removed. It was possible to perform low-damage etching with almost no etching of the silicon film.

Next, with respect to the object to be ashed doped with the acceleration voltage of the ion shower doping of 60 kv, the mixing ratio of the oxygen gas and the nitrogen gas in the above-mentioned first step was changed to examine the state of removal of the surface hardened layer. It was The results are shown in (Table 2).

[0039]

[Table 2]

In the table, as a result of observing the polycrystalline silicon film 11 after ashing at a magnification of 30,000 with an electron microscope, the resist film 12 can be completely removed, and the polycrystalline silicon film 11 is almost etched. The case where the resist film 12 including the hardened layer 13 was not removed was represented by ◯, and the case where the resist film 12 including the cured layer 13 was not removed was represented by x.

From the table, it was found that the flow rate of nitrogen used for ashing was 15 to 85% of the total flow rate of oxygen gas and nitrogen gas, and the effect of removing the hardened layer was obtained. It should be noted that this range had almost no effect even if the acceleration voltage of the ion shower doping was changed.

(Embodiment 2) In Embodiment 1, since a small amount of ions are involved in etching even in the second step, there is a possibility that the base film such as a silicon film may be etched to some extent. In the case of a thin film, it may affect the device. To solve this problem, in this example, plasma etching was performed in an oxygen gas atmosphere in the second step. In this etching, the plasma etching apparatus shown in FIG. 3 is additionally required, but by performing chemical etching by radicals, it is possible to perform etching with lower damage than that in the first embodiment without etching the base film. did it.

In the figure, reference numeral 22 is a flow meter, and 23 is a valve, and the reaction gas involved in the ashing is introduced into the reaction chamber 34 in which the ashing is performed while controlling the flow rate to a predetermined mixing ratio. A vacuum pump 26 controls the pressure in the reaction chamber 34 to a predetermined pressure while introducing air. here,
The introduction pipe 24 is a passage for introducing the reaction gas, and the exhaust pipe 25 is a passage for exhausting the reaction gas.

Two pairs of electrodes 29 are provided around the reaction chamber 34, and a high frequency power source 27 is connected to the electrodes 29 via an impedance matching circuit 28.
A high frequency discharge is generated between 9 and 9 to generate plasma.
Further, a heater (not shown) for adjusting the temperature of the reaction chamber is provided on the outer periphery of the reaction chamber 34. Reference numeral 33 is an etch tunnel for performing etching.

Next, a plasma etching method using the apparatus shown in the figure will be described. The introduction pipe 2 is introduced into the reaction chamber 34 while controlling the flow rate of the reaction gas by the flow meter 22 and the valve 23.
4, and the pressure in the reaction chamber 34 is kept constant through the exhaust pipe 25 by the vacuum pump 26. Next, high frequency power is applied to the electrode 29 from the high frequency power supply 27 through the impedance matching circuit 28 to etch the sample 32 on the board 31. Here, the reaction chamber 34 is kept at a constant temperature by a heater.

Specifically, the temperature inside the reaction chamber was kept at 100 ° C. by using the apparatus shown in FIG.
The pressure of the reaction chamber 1 is 600 mTorr with 0 cc of oxygen gas.
Then, high frequency power of 400 W was applied, and ashing was performed for 20 minutes by plasma etching of oxygen gas.

In the second step, the remaining resist film can be removed by a chemical reaction with an organic solvent. When the resist film is removed by a chemical reaction after the step of removing the hardened layer, the effect on the base film is small, so that it is effective when the base film is a thin film or the like.

In each of the above embodiments, the object to be ashed is the cured resist film on the surface layer of the resist film, but the same applies to the object to be ashed having a hardened layer other than the surface layer of the resist film. It goes without saying that the effect of can be obtained.

Further, in the present embodiment, the resist film can be completely removed even when the range of hardening and alteration of the resist film is large.

Although oxygen gas was used in the second step in each of the above-mentioned embodiments, it goes without saying that low-damage etching can be performed by using a mixed gas of oxygen gas and nitrogen gas.

[0051]

As described above, the present invention provides an ashing method for removing a resist film in which a part of an organic film layer on a substrate is hardened by reactive ion etching in a mixed gas atmosphere of oxygen gas and nitrogen gas. The hardened layer is removed, and the remaining resist film is removed by reactive ion etching in a mixed gas atmosphere with oxygen gas or nitrogen gas containing oxygen gas as a main component. Can be etched.

When the underlying film is a thin film, after removing the hardened layer, the remaining resist film is removed by plasma etching in a mixed gas atmosphere containing oxygen gas as a main component and nitrogen gas, or by an organic solvent. As a result, etching can be performed with lower damage.

[Brief description of drawings]

1] Overall configuration diagram of a reactive ion etching apparatus

FIG. 2 (a) is an enlarged cross-sectional view of an object to be ashed having a resist film whose surface portion is hardened. (B) Reactive ion etching is performed in a mixed gas atmosphere of oxygen gas and nitrogen gas in Example 1 of the present invention. Sectional view of the ashed object

FIG. 3 is an overall configuration diagram of a plasma etching apparatus

FIG. 4 is an overall configuration diagram of a downflow etching apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Reaction chamber 2 Exhaust system 3 Anode (anode) 4 Cathode (cathode) 5 Gas controller 6 Impedance matching circuit 7 High frequency power supply 8 Object to be ashed 10 Substrate 11 Sio ₂ film 12 Resist film 13 Hardened resist film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mamoru Furuta 1006 Kadoma, Kadoma City, Osaka Prefecture, Matsushita Electric Industrial Co., Ltd.

Claims (6)

[Claims] 1. An ashing method for removing a resist film made of an organic material, which is formed on a semiconductor substrate or a glass substrate and partially hardened by doping, etching or heating, wherein the hardened portion of the resist film is removed. The first step of removing by reactive ion etching in a mixed gas atmosphere of oxygen gas and nitrogen gas, and the remaining resist film by reactive ion etching in a nitrogen gas atmosphere mainly containing oxygen gas or oxygen gas An ashing method comprising a second step of removing. 2. An ashing method for removing a resist film formed on a semiconductor substrate or a glass substrate and made of an organic material partially cured by doping, etching or heating, wherein the cured portion of the resist film is removed. First step of removing by reactive ion etching in a mixed gas atmosphere of oxygen gas and nitrogen gas, and the remaining resist film is removed by plasma etching in oxygen gas or a nitrogen gas atmosphere mainly containing oxygen gas An ashing method including the second step. 3. An ashing method for removing a resist film made of an organic material, which is formed on a semiconductor substrate or a glass substrate and is partially hardened by doping, etching or heating, wherein the hardened portion of the resist film is removed. An ashing method comprising a first step of removing by reactive ion etching in a mixed gas atmosphere of oxygen gas and nitrogen gas, and a second step of removing the remaining resist film with an organic solvent. 4. The ashing method according to claim 1, wherein silicon or a silicon compound is contained between the glass substrate and the organic substance on the substrate. 5. The resist film portion cured by doping with an acceleration voltage of 120 kv or less is removed.
The ashing method described in 2, 3, or 4. 6. The ashing method according to claim 1, wherein the nitrogen flow rate of the mixed gas in the first step is 15 to 85% of the total flow rate of oxygen and nitrogen.