WO1997011207A1

WO1997011207A1 - Dry etching method

Info

Publication number: WO1997011207A1
Application number: PCT/JP1995/001846
Authority: WO
Inventors: Naoyuki Kofuji; Kazunori Tsujimoto
Original assignee: Hitachi, Ltd.
Priority date: 1995-09-18
Filing date: 1995-09-18
Publication date: 1997-03-27
Also published as: JP3429776B2; TW364168B

Abstract

An etching method such that the selectivity of etching with respect to the mask and the substrate is not impaired when the bias voltage applied to a sample is boosted to improve the etching rate. A voltage having a positive pulse waveform is applied to the sample as the bias voltage and the interval of the pulse waveform is controlled to a prescribed value. In addition, a plasma is produced by applying a voltage having a positive waveform as the bias voltage and adding a gas containing such light elements as H, He, etc., to a process gas. Since the energy distribution of ions made incident on the sample can be made narrow, the selectivity of etching of the substrate material and the mask material can be improved while the high etching rate and anisotropy of the etching are maintained.

Description

Description Dry etching method

Technical field

The present invention relates to etching using plasma, and particularly to a method for applying a bias voltage to a sample. Background art

A typical bias applying method in plasma etching is a bias applying method called RF's. Figure 2 shows an example of this biasing device. The sample 1 to be etched is connected to a high frequency power source 3 via a capacitor 2. A high-frequency power supply 3 applies a sinusoidal voltage as shown in FIG. Due to the application of the pressure, a negatively shifted negative pressure appears in Sample 1 as shown in FIG. This negative pressure accelerates positive ions in the plasma and impinges on the sample, causing an etching reaction, thereby performing etching.

In the etching method using RF bias, ions are incident on the sample at the timing shown in Fig. 4. Ab in Fig. 4 is the maximum and minimum moments of the bias voltage. Since the energy of the ions incident on the sample is almost proportional to the magnitude of the bias voltage applied to the sample, ions with high energy are incident on the sample at the moment of a in FIG. At a moment, ions with low energy are incident on the sample, and the energy distribution is wide-ranged as shown in Fig. 8. Therefore, ions with high energy are incident on the sample in multiple layers. Such ions are incident on a sample having the structure shown in Fig. 9. In this case, the mask 5 and the base 6 are sputtered, and the selectivity with the material 7 to be etched is reduced. Also, if the bias pressure is reduced to keep the selectivity from decreasing, the average energy of ions decreases, and the etch rate and anisotropy decrease. In other words, there was a problem that the etch rate and anisotropy had a trade-off relationship with the selectivity when applying an RF bias.

As an alternative to the above-mentioned RF bias application method, as disclosed in Japanese Patent Application Laid-Open Nos. 56-13480 and 6-61182, a pulse waveform voltage is used as a bias voltage. The method used (hereafter referred to as pulse bias) has been devised. Fig. 5 shows an example of this bias application device. In this device, pulse power supply 4 is connected instead of RF power supply. The pulse S source 4 applies a positive pulse voltage as shown in FIG. It is predicted that the application of this overpressure causes a overpressure of the bias waveform as shown in Fig. 7 on the sample. It is believed that the positive pressure accelerates the positive ions due to the ¾-pressure of this bias waveform and enters the sample.

In the above-described pulse bias application method, as shown in Fig. 7, since the sample potential during ion acceleration is constant, the energies of ions incident on the sample are uniform, and it is expected that no high-energy ions will be generated. . Therefore, high selectivity was expected to be obtained compared to RF bias. However, as a result of actually applying the pulse bias, as shown in Fig. 10, when the pulse such as the sample bias ¾ waveform falls, the voltage drop based on the electron current during pulse application (hereinafter, referred to as Overshoot) was found to occur. Due to this overshoot, it was found that a large amount of high energy ions were generated in the ion energy distribution as shown in Fig. 11. It can be seen that this large amount of high energy ions does not provide sufficient selectivity improvement compared to RF bias. Power, _t0

Disclosure of the invention

An object of the present invention is to improve the selectivity of etching by reducing overshoot generated in plasma etching with pulse bias application.

In order to solve the above problems, the present invention is achieved by using, as a bias voltage applied to a sample, a voltage having a pulse waveform of i whose pulse waveform interval is controlled to a predetermined value.

Further, the above problem can be solved by applying a voltage having a positive pulse waveform to a sample as a bias voltage and adding a gas containing a light element as a processing gas for generating plasma. .

The present invention proposes two methods of reducing the overshoot: a method of controlling the HI between pulses and a method of adding a gas containing a light element.

First, to explain how to reduce the overshoot by controlling the pulse interval ra, the relationship between the magnitude of the overshoot and the pulse interval is elucidated. When a rapid pulse is applied to the sample, a pressure drop occurs at the substrate potential based on the electron current during the pulse application, as shown in Figure 12. This is overshoot, and its magnitude is given by Equation 1 below.

And.

····

Δνβ, U-position drop during pulse application

J, child current during pulse application

Area O 97/11207

Four

C ₀ Capacitance of capacitor due to electrostatic mechanism

n _t plasma density

Τ · Rouge i¾K

簏の

k Boltzmann constant

V pnln The magnitude of the pulse mane pressure

-The magnitude of the voltage drop of the sample with respect to the pulse source pressure On the other hand, during the period when the pulse application is off, the following formula is applied due to the ion flow.

A ¾ pressure rise represented by 2 occurs. x pulse interval pulse interval

C, ',' ^m

… (Number 2)

厶Vi _H pulse-off in ^! Cry of descent

J, child current during pulse-off application

m _{ ion quality! : Therefore, in one cycle, a pressure drop of AV e! — AV it occurs. The pressure drop of this return Ku is, the voltage drop AV e _n - steady state is reached where the delta [nu i _n becomes 0. Thus when considering the steady state, the magnitude AV e _n of over one chute are summer as large as the Δ ν i _π. That is, the magnitude of the overshoot in the steady state can be expressed by the following equation (3).

_Δνβ- ^ 1χ pulse interval, 'X pulse interval and _β C, Υ exp (ljm,

… (Equation 3)

△ Ve Because of the magnitude of overshoot in the steady state, the magnitude of overshoot is reduced by the amount of overshoot used in etching. To less down the standard bias voltage magnitude 1 0 ² V 1 0% ie 1 0 V may be required to control the pulse interval cormorants by satisfying the following formula 4.

△ WX pulse interval 10 (V)

… (Number 4)

The pulse interval, the plasma density, electron temperature, © c area, key Yapashita due to capacity, the plasma density 1 0 ^{1 1} as a standard value, the electron temperature 3 e V © Hasaizu 6 inches, capacitance 5 n When F is used, the condition of Equation 4 is

Lus spacing <5 s

Can be harmed. It is considered that shortening the pulse interval in this way reduces the issue. In addition, the lower limit of the pulse interval is 0.1 μs, which is the lower limit at which ions can follow the bias voltage. The relationship with the potential waveform was examined. Figure 13 shows the results. As the pulse interval is shortened,

Is smaller. As a result, it is predicted that the energy distribution of the energy distribution of ions incident on the sample will be reduced. Figure 14 shows the relationship between the ion incident energy distribution of the ions at the actual pulse interval. By shortening the pulse interval, the high-energy components of ions are reduced, and the energy distribution is sharpened. For this reason, highly selective etching becomes possible.

As described above, under standard conditions, by setting the pulse interval between 0.1 s and 5 s, the size of the oscilloscope can be suppressed to 10% or less of the bias voltage. Highly selective etching becomes possible. Next, the change in overshoot when a light element such as H or He is added to reduce overshoot will be described. Icons such as H and He are

Since the mass is smaller than the ions of the etching element such as C 1 +, the ions of the etching element can enter the sample from the plasma in a sufficiently short time compared to the time required for the ions of the etching element to reach the sample. Therefore, at the moment of O-bar one chute of falling of the pulse is, H + also previously Ri good such as C 1 ^+, the ion such as H e ⁺ is incident on the sample, the sample bias potential waveform of FIG. 1 5 As shown in the figure, the sample size rises rapidly and falls to a constant value in the short time described above. Since the ions of the etching element are incident after this increase in the pressure, the high-energy etching ions generated during overshoot are reduced as shown in the ion incident energy distribution of the ions in Fig. 16. For this reason, the mask and the base are scraped by the etching ion, thereby being greatly reduced. In addition, the ability of the added H and He ions to form a snnotter is better than that of etching ions. Since it is sufficiently small in comparison with the sputtering capability, the scraping of the mask and the background by H and He ions can be ignored, and the selectivity to the mask material and the base material can be greatly improved. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram showing the change in average energy dependence of the selectivity of P o 1 y -S i with respect to the base S i O ₂ due to the addition of NH ₃ and He gas.

FIG. 2 is a diagram showing the configuration of a conventional etching apparatus used for RF bias application.

FIG. 3 is a diagram showing a bias input voltage waveform when a conventional RF bias is applied.

Figure 4 shows a sample bias waveform when a conventional RF bias is applied. It is.

FIG. 5 is a diagram showing a configuration of an etching apparatus used for pulse bias application.

FIG. 6 is a diagram showing a bias input voltage waveform when a pulse bias is applied.

FIG. 7 is a diagram showing an ideal sample bias waveform when a pulse bias is applied.

FIG. 8 is a diagram showing a distribution of ion incident energy of a sample when a conventional RF bias is applied.

FIG. 9 is a diagram showing an example of a sample structure used for plasma etching.

FIG. 10 is a diagram showing an actual sample bias waveform when a conventional pulse bias is applied.

Fig. 11 is a diagram showing the actual incident energy distribution of the sample in the case of the conventional pulse bias application.

Fig. 12 is a diagram showing the change of the sample bias waveform from the start of the application of the pulse bias to the steady state.

FIG. 13 is a diagram showing a change in a sample bias waveform due to a difference in pulse interval when a pulse bias is applied.

Fig. 14 is a diagram showing the change in the ion incident energy distribution of ions due to the difference in pulse interval when a pulse bias is applied.

Figure 15 shows the change in the sample bias waveform due to the addition of H and He when a pulse bias is applied.

Fig. 16 is a diagram showing the change in the ion incident energy distribution of ions due to the addition of H and He when a pulse bias is applied.

FIG. 17 shows a microcontroller capable of performing the pulse bias application of the present invention. FIG. 3 is a diagram illustrating an example of a mouthpiece etching apparatus.

FIG. 18 is a diagram showing the structure of a sample used for polysilicon processing in Example 1.

Figure 19 shows c. FIG. 6 is a diagram showing a change in the sample bias waveform due to the addition of NH ₃ or He when a lus bias is applied.

Figure 20 is a diagram showing the change in ion incident energy distribution due to NH ₃ and He addition in the case of pulse bias application.

FIG. 21 is a diagram showing the change in the average ion energy dependence of the polysilicon etching rate due to the addition of NH ₃ and He.

FIG. 22 is a diagram showing a structure of a sample used for A 1 -Cu-Si processing in Example 2.

FIG. 23 is a diagram illustrating a change in the sample bias waveform due to a difference in pulse interval when pulse bias is applied.

Figure 24 is a diagram showing the change of the ion incident energy distribution of the ion due to the difference in the pulse interval when the pulse bias is applied.

Fig. 25 is a diagram showing the variation of the average energy-dependence of the resist mask selection ratio of Po1y-Si with respect to the pulse interval due to the difference in pulse interval.

FIG. 26 is a diagram showing the change in the average ion energy dependence of the polysilicon etching speed due to the difference in the pulse interval. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. <Example 1>

FIG. 17 shows an example of a micro mouth wave etching apparatus capable of performing the pulse pulse application of the present invention. In this device, the microwave generated in the magnetron 8 is introduced into the discharge tube 10 through the waveguide 9 and the introduced magnet Gas plasma 13 can be generated from the processing gas introduced from the gas introduction section 12 by the electron cyclotron resonance of the magnetic field created by the open mouth wave and the coil 11. The structure is as follows. As a sample 1 to be etched, a polysilicon film 1 was formed on Si 0 ₂ 15 formed by thermally oxidizing a 6 inch Si 14 wafer. 6 was deposited, and a resist mask 17 was formed on the polysilicon film 16 to have a structure as shown in FIG. 18.

The sample 1 is connected to a constant voltage source 19 for electrostatic adsorption and a pulse power supply 4 for bias via an insulating ceramic 18 for electrostatic adsorption having a capacitance of 5 nF. Here, the capacitance of the electrostatic attraction mechanism was almost equivalent to the capacity of the insulating ceramic.

In this device, a negative voltage of 150 V is supplied from a constant voltage source 19, and a pulse width 1 s, a pulse interval 20 βs, and a peak value 10 are supplied from a pulse power supply 4 for bias. Sample 1 was etched by applying a 0 V pulse voltage. Etching is performed in three cases: chlorine gas alone, helium added to chlorine, and ammonia added to chlorine containing ammonia. The differences in characteristics were evaluated.

First, the sample bias potential waveform was examined. Figure 19 shows the results. The width of the overshoot in the waveform becomes smaller in the order of chlorine gas alone, helium, and ammonia added. From these results, it is predicted that the C 1 + ion of the high energy plant has been reduced.

Figure 20 shows the results of measuring the energy distribution of C 1 + ions incident on the sample. It can be seen that the high-energy components become smaller in the order of chlorine gas alone, followed by helium and ammonia-added ones, and the energy distribution is sharp. From these results, it is expected that the etching selectivity will be improved.

The average energy of the ion by changing the magnitude of the pulse voltage Was varied, and the relationship between the selectivity between the Po 1 y —S i layer and the underlying S i 0 ₂ layer of sample 1 and the average ion energy was measured. Figure 1 shows the results. It can be seen that even with the same average energy, higher selectivity can be obtained by adding Helium ammonia. Figure 21 shows the relationship between the Si etching speed and the average ion energy at this time. It can be seen that the same etching speed can be obtained at the same average energy regardless of the method. From the results shown in Fig. 1 and Fig. 21, it was confirmed that high-speed and selective processing can be performed by adding helium gas or ammonia gas.

In the present invention, He and ammonia gas are added, but other gases including He element and H element may be added, or H element may be included in the composition such as HC1 and HBr. The same effect can be obtained by using an etching gas.

Etching of the metal wiring was performed using the present invention. As a sample, TiN 2 2, Al-Cu-Si 2 3 .T Ν 4 24 were deposited on the CVD silicon oxide film 21 in this order, and A structure as shown in FIG. 22 in which a resist mask 17 was formed on a silicon film was used. This sample was processed in the etching apparatus of Example 1 using a mixed gas of C 12 gas and BC 13 as an etching gas. No., the change of the etching characteristic was measured by changing the pulse interval under the conditions of a pulse width of 1 s and a pulse voltage of 250 V.

First, the sample bias potential waveform was examined. Figure 23 shows the results. It can be seen that the magnitude of the overshoot voltage in the waveform decreases as the pulse interval decreases. From this result, it is predicted that high-energy C 1 + ions are reduced.

Figure 24 shows the results of measuring the energy distribution of C 1 + ions incident on the sample. Shorten the pulse interval to reduce high energy components It turns out that the energy distribution is sharp. From this result, it is expected that the etching selectivity will be improved.

The average energy of the ions is changed by changing the magnitude of the pulse S pressure, and the three-selectivity between the P o 1 y — S i layer and the underlying S i 0 ₂ layer of the sample and the average ion energy The relationship was measured. Figure 25 shows the results. It can be seen that the shorter the pulse interval, the higher the selectivity can be obtained with the same average energy. Figure 26 shows the relationship between the Si etching rate and the average ion energy at this time. It was confirmed that the same etching rate could be obtained if the average energy was the same regardless of the pulse interval. From the results of Fig. 25 and Fig. 26, it was confirmed that high-speed and high-selection processing can be performed by shortening the pulse interval.

As described above, according to the present invention, the overshoot can be reduced, so that the selection of the base material and the mask material can be improved while maintaining the high speed and high anisotropy of the etching. . Industrial applicability

As described above, the dry etching method according to the present invention is useful for an etching method using plasma, and is particularly suitable for performing high-speed and high-selectivity etching.

Claims

The scope of the claims

1. The object placed in the reduced-pressure processing chamber is supplied with the plasma discharged by introducing gas into the processing chamber, and the biased voltage is applied to the object to be processed. An etching method for etching an object, wherein a voltage having a positive pulse waveform is applied as the bias S pressure, and an interval between the pulse waveforms is controlled to a predetermined value.

2. The dry etching method according to claim 1, wherein the pulse interval of the second underpressure is controlled so as to satisfy a condition of Equation (4).

3. The dry etching method according to range 1, wherein the pulse interval of the second pressure is 0.1 s or more and 5 ^ s or less.

4. To the workpiece placed in the decompression processing chamber B, the plasma discharged by introducing gas into the processing chamber is supplied, and the workpiece is applied by applying a bias voltage to the workpiece. In an etching method for etching a processed object, it is preferable that a bias voltage having a positive pulse waveform is applied as the bias voltage, and that a gas introduced into the processing chamber contains two or more types of elements. Features Dry etching method.

5. A method according to claim 4, wherein at least one of the two or more elements contained in the gas is a 柽 element, and the light element is an H element or a He element. The dry etching method described.

6. The element contained in the above gas is HBr or HCL or

Doraietsu quenching method according to claim 4 and 5 according to this and the feature is NH _3.