JPH05275326A - Method for ashing resist - Google Patents

Abstract

PURPOSE:To make it possible to strip resist where a hardened layer is formed without giving damage to a wafer by eliminating resist at a portion in which ions are injected and eliminating the remaining resist with the use of oxygen plasma. CONSTITUTION:A wafer S having a hardened resist layer is placed on a sample shelf, and an ashing chamber 25 is set to the specified degree of vacuum. Next, mixed gas of oxygen and CF4 is supplied from a supplying pipe 13, and microwave is introduced to an induction line 12 to generate plasma, and then the hardened resist layer is turned into ash. After that, a non-hardened resist layer is turned into ash by changing the mixed gas of oxygen and CF4 with mixed gas of oxygen and N2. As a result, ashing speed increases and processing time can be shortened, without giving damage on the wafer, despite of resist having the hardened layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resist ashing method, and more particularly, to a resist suitable for ashing a resist which has been hardened by ion implantation among resists mainly formed in a semiconductor wafer processing step. Ashing method.

[0002]

2. Description of the Related Art In a semiconductor manufacturing process, the photoresist applied to a wafer is frequently peeled and removed. In recent years, due to measures against pollution problems and the like, the semiconductor manufacturing process has shifted from a wet process to a dry process, and ashing using oxygen plasma has become the mainstream also in resist stripping.

In the conventionally used ashing method using plasma, a barrel type apparatus capable of processing a large number of sheets at one time has been used. However, in the barrel type apparatus, since the wafer is directly exposed to plasma, the damage of the wafer due to the charged particles is becoming a problem with the high integration of semiconductor devices. Therefore, a downstream type ashing device using microwave plasma or the like has been used as a device that is less damaged by charged particles.

In this downstream type plasma ashing apparatus, the plasma generation chamber and the processing chamber for ashing the wafer are separated by a partition plate having holes, and only the radicals among the ions and radicals generated in the plasma generation chamber are mainly separated. By introducing the
Allows ashing with little damage.

A plasma ashing apparatus of this type is shown in FIG. In the figure, 11 indicates a hollow rectangular parallelepiped reactor,
The reactor 11 is made of metal such as stainless steel,
The surrounding wall has a double structure, and a cooling chamber 21 for allowing cooling water to flow therethrough is formed therein. A plasma generation chamber 24 and an ashing processing chamber 25 are formed inside the cooling chamber 21. The plasma generation chamber 24 and the ashing process chamber 25 are partitioned by a partition plate 23 having a hole 27, and the upper part of the plasma generation chamber 24 is transparent to microwaves such as quartz glass and Al ₂ O ₃ and has a dielectric loss. A heat resistant plate 22 having a small size is placed and sealed. Inside the ashing processing chamber 25, a sample table 26 for mounting the sample S is arranged at a position facing the partition plate 23. An exhaust port 14 connected to an exhaust device (not shown) is formed on the lower wall of the ashing processing chamber 25.
A gas supply pipe 13 for supplying a required reaction gas into the reactor 11 is connected to one side wall of the plasma generation chamber 24.

On the other hand, the dielectric line 1 is provided above the reactor 11.
2 is provided, and the upper part of the dielectric line 12 is a metal plate 1
2a, and the dielectric layer 12 is attached to the lower surface of the metal plate 12a. The dielectric layer 12b is formed using fluororesin, polyethylene, polystyrene, or the like, which has a small dielectric loss. A waveguide 15 is provided on the dielectric line 12.
Is connected, and the microwave oscillator 16 is further connected to the waveguide 15, so that the microwave from the microwave oscillator 16 is introduced into the dielectric line 12.

A resist removing process using the ashing apparatus thus configured will be described with reference to FIG. A pattern of a resist 32 is formed on the substrate 31 (FIG. 2A). For ion implantation into the substrate 31 using the pattern of the resist 32 as a mask, for example, phosphorus ions 33 are ion energy 80 keV and the implantation amount is 1 × 10 ¹⁶
The implantation is performed under the condition of ions / cm ² (FIG. 2 (b)). At the time of this ion implantation, the kinetic energy of the ions is converted into thermal energy, the resist 32 is heated and thermally deteriorated, and the hardened layer 34 is formed (FIG. 2C). When the resist 32 having the hardened layer 34 thus formed is removed, conventionally, the hardened layer 34 is removed by using oxygen plasma (FIG. 2D), and the non-hardened resist remaining below the hardened layer 34 is used. The layer 35 was also removed by oxygen plasma (FIG. 2).
(E)).

[0008]

However, in the conventional oxygen radical-based ashing method using the downstream type plasma ashing apparatus, it takes a long time to ash the hardened layer 34 that is ion-implanted and hardened. ..

That is, the hardened layer 34 has a larger activation energy than the normal resist 32, and the conventional ashing method mainly using oxygen radicals has a problem that the reaction rate is low and the ashing rate is low.

Further, the ashing speed has a large temperature dependency, and a method of raising the temperature of the substrate 31 to increase the ashing speed can be considered. However, in this case, since the hardened layer 34 and the non-hardened resist layer 35 have different thermal expansion coefficients, the hardened layer 34 bursts, and the burst pieces are left on the substrate 31 as a residue that cannot be removed even when a wet resist removing method is used. However, there is a problem that it becomes a cause of lowering the yield of LSI.

The present invention has been made in view of the above problems, and when the resist having the hardened layer formed by ion implantation is removed, the resist can be efficiently removed without damaging the wafer. It is an object of the present invention to provide a resist ashing method.

[0012]

In order to achieve the above object, a method of ashing a resist according to the present invention is a method of ashing a resist, which utilizes plasma and mainly radicals to ash the resist. The method is characterized by including a step of removing the resist in the ion-implanted portion by using plasma with a mixed gas of and a step of removing the remaining resist by using oxygen plasma.

[0013]

With respect to the effect of the fluorine radicals, the present inventor speculates that it lowers the activation energy in the ashing reaction of the resist. This is because, in oxygen radical-based ashing in which fluorine is not added, the wafer temperature needs to be 150 ° C. or higher to ash a normal resist at a rate of about 2 μm / min. On the other hand, as shown in FIG. 4, when CF ₄ which is a fluorine-based gas is added to oxygen, it becomes 2 μm / mi even at room temperature.
This is because an ashing speed of about n can be obtained.

Therefore, by adding the fluorine-based gas to the hardened layer of the resist formed by ion implantation, the activation energy of the hardened layer can be lowered and the ashing speed can be increased.

However, when the fluorine-based gas is added, the underlying oxide film other than the resist is also etched, resulting in a problem that the electrical characteristics of the device are adversely affected.

Therefore, for the ashing of the hardened layer, a mixed gas of oxygen and a fluorine-based gas is used, and for the ashing of the remaining ordinary resist, an oxygen gas is used to suppress the etching of the oxide film. it can.

At this time, in order to switch the gas, it is necessary to judge the end of the ashing of the hardened layer, which can be judged by the change of the emission intensity of CO in the plasma. That is, it can be seen that when the ashing of the hardened layer is completed, the ashing speed rapidly increases, and the emission intensity rapidly increases as the speed increases. Therefore, this change in emission intensity can be used to determine the end of ashing of the cured layer.

According to the above-mentioned method, by mixing a fluorine-based gas with oxygen, it is possible to lower the activation energy in the portion which is ion-implanted and becomes a hardened layer, and to increase the ashing rate. Moreover, since the remaining non-cured resist layer is ashed using only oxygen plasma, the resist can be removed without damaging the wafer.

[0019]

Embodiments of the resist ashing method according to the present invention will be described below with reference to the drawings. The ashing device used in the embodiment is the downstream ashing device shown in FIG. 1 as described in the section [Prior Art].
The description of the device will be omitted. The ashing method according to the embodiment will also be described based on the process diagram of FIG. 2 described above. First, an 8-inch wafer is placed as a sample S on the sample table 26 of the ashing apparatus shown in FIG. 1, and then, cooling water is allowed to flow into the cooling chamber 21 and, at the same time, exhausted from the exhaust port 14. , The ashing chamber 25 is set to a required degree of vacuum. Next, a mixed gas of oxygen and CF ₄ is supplied as a gas for ashing from the gas supply pipe 13. Then, microwaves are introduced into the dielectric line 12 from the microwave oscillator 16 via the waveguide 15, and an electric field is formed below the dielectric line 12. The formed electric field passes through the heat resistant plate 22 and reaches the inside of the plasma generation chamber 24 to generate plasma, and the charged particles in the generated plasma are captured by the partition plate 23, and mainly neutral particles such as radicals are mainly captured. The resist on the sample S is guided to the periphery of the sample S in the ashing processing chamber 25 through the hole 27, and the resist on the sample S is ashed.

The sample stage 26 has a heating mechanism so that the temperature can be controlled. In addition, an emission spectroscopic analyzer (not shown) is provided.

When the hardened layer 34 shown in FIG. 2C is to be ashed, a mixed gas of oxygen gas and 1% CF ₄ is flowed at a total flow rate of 1000 sccm, the pressure in the ashing processing chamber 25 is set to 2 Torr, and the substrate is processed. Set the temperature to 180 ° C. When the ashing of the hardened layer 34 is completed and then the uncured resist layer 35 is ashed, oxygen gas and CF are used.
Switch the gas from the mixed gas of ₄ to the mixed gas of oxygen gas and 5% N ₂ gas, and make the total flow rate of oxygen gas and N ₂ gas 1
The pressure in the ashing processing chamber 25 is set to 2 Torr, and the substrate temperature is set to 180 ° C.

The timing of switching the gas is
Judgment is made by using the emission spectral analysis of plasma. The spectral wavelength used at this time is 309 nm of CO, and as shown in FIG.
(B) shows the results of monitoring emission spectra during ashing by the conventional method and the results of monitoring emission spectra during the method according to the example. In the case of FIG. 3A, the result is that after the emission intensity gradually increases, the concave portion appears, and then the emission intensity increases again, and then decreases with time. The concave portion shows the ashing process of the hardened layer, and the point at which the increase thereafter starts the end point of the hardened layer 34. That is, in the hardened layer 34, the reaction speed is low, so that the emission intensity becomes low,
When the ashing is completed, the reaction rate increases and the emission intensity starts to increase. The total resist removal time at this time was 240 seconds.

Meanwhile FIG. 3 (b), to determine the end point of the hardened layer 34 by the time to move to a sharp increase from the concave portion of the emission intensity as described above, switches the gas at this point from the O ₂ + CF ₄ to O ₂ + N ₂ The case where the uncured resist layer 35 is removed thereafter is shown. At this time, the time required for removing the cured layer 34 is 40 seconds, the switching time is 10 seconds, the removal time for the non-cured resist layer 35 is 90 seconds, and the total resist removal time is 140 seconds. 10 in comparison
It was possible to reduce the time to 0 seconds.

C in a mixed gas of oxygen and CF ₄
Relationship between F ₄ concentration and ashing speed and resist S
The relationship with the selectivity for the iO ₂ film is shown in FIG. At this time, the ashing conditions are as follows: microwave power 1.5 kW, pressure 0.9 Torr, total flow rate 800 sccm, substrate temperature 3
It was 0 ° C. As a result, it was confirmed that the higher the CF ₄ concentration in the mixed gas of oxygen and CF _4, the higher the ashing rate, but the lower the selectivity of the resist for the SiO ₂ film. From this result, it seems that the amount of CF ₄ added is appropriately in the range of 0.1 to 5%, but it is necessary to select it according to the allowable etching amount of the base film according to the degree of integration of the device. In the above embodiment,
Although ashing was performed with the substrate temperature set to 180 ° C., when the substrate temperature was set to 200 ° C., the hardened layer 34 burst and the resist could not be completely removed.

When the change in the electrical characteristics of the sample subjected to the ashing treatment in this way was measured, the shift amount of the flat band voltage was 0.03 V or less, which means that it reached a level without problems. confirmed. It was also confirmed that the etching amount of the base film in the case of the above-mentioned embodiment was 10 Å or less, and that it could be practically used even in 16 MDRAM or more.

In the above embodiment, C is used as the fluorine-based gas.
Although F ₄ is used, the fluorine-based gas is not limited to CF ₄ , and any gas containing fluorine such as NF ₃ , SF ₆ , C ₄ F ₈ may be used. In addition, the uncured resist layer 35
At the time of removing, in the above example, a mixed gas of oxygen and N ₂ was used, but it is not limited to this, only oxygen,
Alternatively, instead of N ₂ , it is possible to use He, Ar, or the like, which can promote the generation of oxygen radicals.

As described above, in the resist ashing method according to the embodiment, when removing the hardened layer 34 having high activation energy, CF ₄ is added to oxygen to activate the activation energy. It can be lowered to increase the ashing speed. Further, whether or not the hardened layer 34 has been removed can be judged by the change in the CO plasma emission intensity, and after the hardened layer 34 is removed, ashing with oxygen can be performed to prevent damage to the wafer. .. Therefore, by using such a method, the ashing speed can be increased and the processing time can be shortened even with the resist on which the hardened layer 34 is formed, without damaging the wafer.

[0028]

As described above in detail, in the resist ashing method according to the present invention, in the resist ashing method in which plasma is used and the resist is mainly ashed using radicals, oxygen and fluorine-based materials are used. Since the method includes a step of removing the resist in the ion-implanted portion using plasma using a mixed gas, and a step of removing the remaining resist using oxygen plasma, the activity of the cured layer that is the ion-implanted portion is It is possible to lower the energy of ashing and increase the ashing speed. The remaining resist can be removed by using oxygen plasma without damaging the wafer.

Therefore, even when the resist on which the hardened layer is formed by ion implantation is removed, the resist can be efficiently removed without damaging the wafer.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a downstream type plasma ashing apparatus.

2A to 2E are schematic cross-sectional views of a wafer showing a resist removing step in order.

FIG. 3A is a graph showing an emission spectral waveform during resist ashing by a conventional method, and FIG. 3B is a graph showing an emission spectral waveform during resist ashing according to an example. is there.

FIG. 4 is a graph showing the ashing rate with respect to the concentration of the fluorine-based gas in the mixed gas and the selectivity of the resist with respect to the SiO ₂ film.

Claims (1)

[Claims] 1. A method of ashing a resist using plasma, wherein a step of removing the resist in the ion-implanted portion by using plasma of a mixed gas of oxygen and fluorine is used, and a remaining resist is removed by using oxygen plasma. And a step of removing the resist.