JP3550466B2 - Plasma processing method - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a plasma processing method for a semiconductor device, and more particularly to a plasma processing method for etching a semiconductor surface using an apparatus using plasma.
[0002]
[Prior art]
An apparatus widely used at present for etching and film formation of a semiconductor element is an apparatus utilizing plasma. One of them is an apparatus called an ECR (Electron Cyclotron Resonance) system. In this method, plasma is generated by microwaves in a vacuum vessel to which a magnetic field is externally applied. Electrons perform cyclotron motion due to the magnetic field, and plasma can be efficiently generated by resonating this frequency with the frequency of the microwave. In addition, diffusion of the plasma to the wall is suppressed by the magnetic field, and high-density plasma can be generated. A bias voltage is applied to the sample to accelerate ions incident on the sample. For example, when etching is performed, a halogen gas such as chlorine or fluorine is used as a plasma gas. This device is used not only for etching but also for depositing films.
[0003]
Various types of this apparatus have been conventionally proposed, and for example, an example in which the frequency of a plasma generation power supply is set to 2.45 GHz is known in Japanese Patent Application Laid-Open No. 53-4795. Further, Japanese Patent Application Laid-Open No. 2-16731 discloses an example in which the frequency of a plasma generation power supply is set to 2 GHz or less and 100 MHz or more.
[0004]
The known apparatus has an advantage that the processing speed such as etching is high because high-density plasma can be generated.
[0005]
[Problems to be solved by the invention]
2. Description of the Related Art In a recent semiconductor device manufacturing process, higher cost performance has been required of a manufacturing apparatus more than ever due to an increase in clean room maintenance costs. In order to realize this, the device is required to be small and low power consumption, but it is particularly important that the frequency of maintenance such as replacement of parts is as small as possible.
[0006]
In particular, the ECR (Electron Cyclotron Resonance) type plasma in the region where the frequency band of the plasma generation power supply is 100 MHz or more and 1.2 GHz or less is about twice as high as the plasma density of 2.45 GHz ECR plasma which has been conventionally used. Is a new problem that the sample stage is sputtered by the incidence of ions in the plasma, and the sample stage is exchanged more frequently because the sample stage is sputtered due to the incidence of ions in the plasma. A study found.
[0007]
An object of the present invention is to solve this new problem and to provide a plasma processing method in which the frequency of sample stage replacement is low and the processing speed is high.
[0008]
[Means for Solving the Problems]
The bias power supply was modulated by making the output of the bias power supply applied to the sample intermittent or pulse-like.
[0009]
FIG. 2A is a diagram showing the sample table 9 exposed to the ions 12 in the plasma and the vicinity of the sample 8 placed thereon. FIG. 2B shows a continuous output with a voltage waveform of the bias power supply 10 applied to the sample stage 9. . In most cases, the sample stage 9 is made of ceramic such as alumina or silicon nitride, or quartz. These substances are sputtered and cut by the incidence of high energy ions. Since the sputtering rate is proportional to the number of ions, the sample stage is consumed more quickly in high-density plasma. This is the reason that the sample table 9 is intensely consumed in the apparatus using the ECR plasma in the frequency band of 100 MHz or more and 1.2 GHz or less (the portion indicated by the dotted line represents the consumed portion). The ions 12 are accelerated by the voltage of the bias power supply 10 applied to the sample stage and enter the sample 8 and the sample stage 9. If no bias is applied to the sample stage 9, the ions are not accelerated and the energy is low, so that the sample stage does not sputter.
[0010]
Therefore, when the bias applied to the sample stage is intermittently turned on and off, for example, as shown in FIG. 3C, the ions 12 are incident on the sample stage 9 with the bias on and the sample stage is sputtered (FIG. 3A). ), When the bias is off, the ions are not accelerated because they are not accelerated (FIG. 3 (b)), and the amount of collapse of the sample stage is smaller than in the case where the bias is applied continuously in one cycle in which the bias is turned on and off. It is proportional to time.
[0011]
On the other hand, the etching rate of the sample to be processed does not decrease in proportion to the off time of the bias as described below. FIG. 4 is an enlarged view of a cross section of the sample 8 in the plasma. The sample 8 is usually made of a semiconductor such as Si or a metal such as Al or W, and a portion not to be etched is covered with a resist 14. In a sample 8 such as a semiconductor or metal, active radicals 13 of halogens such as chlorine and fluorine generated in plasma are adsorbed on the sample 8 and ions 12 are incident thereon, and a chemical reaction is accelerated by the energy to be etched. . This is called ion-assisted etching. In ion assisted etching, the etching rate depends on the amount of accelerated ions 12 as well as the amount of radicals 13 adsorbed on the sample. The adsorption of the radical 13 occurs more efficiently when there is no ion acceleration, that is, when the bias is off. Therefore, as shown in FIG. 4A, the radicals 13 efficiently adsorb to the sample 8 when the bias is turned off. Next, as shown in FIG. 4B, when the bias is turned on, the ions 13 are accelerated and incident on the sample 8, and a chemical reaction occurs efficiently, and the etching proceeds. Even when the sample is made of silicon oxide, by making the sample stage less resistant to ion assist etching such as alumina, it is possible to suppress a decrease in the etching rate of the sample and to suppress sputter on the sample stage.
[0012]
By the above operation, when the bias applied to the sample is turned on and off, only the amount of shaving of the sample stage is reduced, and the etching rate of the sample is not so reduced. Therefore, it is possible to reduce the consumption of the sample table without lowering the processing speed of the sample, and to reduce the frequency of maintenance for replacing the sample table.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
(Example 1)
An embodiment will be described below with reference to FIG. FIG. 1A is an overall configuration diagram of a plasma etching apparatus. An electromagnetic wave is introduced into the vacuum vessel 4 from the plasma power supply 1 via the waveguide 2 and the introduction window 3. The frequency of the electromagnetic wave is 915 MHz, and the material of the vacuum vessel 4 is metal and the inner surface thereof is insulatingly coated. The material of the introduction window is a material that transmits electromagnetic waves, such as quartz, silicon nitride, and ceramic. The magnetic field strength of the electromagnets 6 and 7 is 325 Gauss. Since the cyclotron motion of the electrons in the plasma 5 resonates with the frequency of the electromagnetic wave at this magnetic field intensity, the energy of the electromagnetic wave is efficiently supplied to the plasma, and a high-density plasma is generated. In this frequency range, a plasma density approximately twice as high as that of the 2.45 GHz microwave conventionally used is obtained, and the etching rate is correspondingly increased. The sample 8 is placed on a sample table 9. A bias power supply 10 is connected to the sample stage 9 to accelerate ions incident on the sample. Normally, the frequency of the bias power supply is set to 20 MHz or less. FIG. 1B shows a voltage waveform 11 of the bias power supply 10. According to the invention, the voltage is turned on and off at some suitable interval.
[0014]
The result of etching aluminum, which is often used as a wiring material for a semiconductor element, with this apparatus will be described below. A mixed gas of Cl2 and BCl3 was used as an etching gas. The pressure inside the vacuum vessel 4 was 2 Pa. The output of the plasma power supply 1 was 600 W. The output of the bias power supply 10 was 80 W, the frequency was 800 Khz, the on / off repetition frequency was 1 KHz, and the ratio between the on time and the off time was 50%. At this time, the etch rate of aluminum was 1.2 mm / min. Although this value is 10% lower than that when the bias power supply is continuously output, the consumption of the electrode is suppressed to about one half as compared with the case where the bias power supply is continuously used. Furthermore, when these values are compared with the case where a conventional 2.45 GHz plasma power supply is used, the etch rate was about 1.5 times and the electrode consumption was about the same. That is, the present invention increases the throughput of the apparatus.
[0015]
Next, the on / off time ratio of the bias power supply 10 will be described. Since the consumption of the electrode 9 is almost proportional to the on-time, the shorter the on-time, the longer the electrode life. However, as shown in FIG. 5, when the on-time is too short, the etch speed decreases. The optimum value of the ratio of the ON time in one cycle is 10% to 60%.
[0016]
(Example 2)
Next, further effects of the present invention will be described. In this embodiment, the apparatus configuration is the same as that of FIG. 1, and a rare gas is added to the gas, for example, Ar (100 cc) + Cl2 (80 cc) + BCl3 (20 cc). Assuming that the pressure is 2 Pa, which is the same as in the first embodiment, the amount of chlorine radicals is reduced by the mixing of Ar, and argon ions occupy a large amount. In this gas system, the ratio of Cl and B is reduced, so that the corrosion and dirt of the vacuum vessel 4 are reduced. Therefore, there is an advantage that the frequency of cleaning maintenance is reduced. On the other hand, by turning on and off the bias power supply as shown in FIG. 4, after the chlorine radicals 13 are sufficiently adsorbed on the sample 8 in the off cycle (FIG. 4A), the bias power supply is turned on to perform ion-assisted etching. (FIG. 4B), so that a decrease in etch rate due to the addition of a rare gas can be suppressed.
[0017]
(Example 3)
FIG. 6 shows an embodiment in which the power source 14 for plasma and the bias power source 19 are changed. In this embodiment, a frequency of 500 MHz is used as the power source 14 for plasma. The bias power supply 19 is modulated in a pulse shape. A coaxial cable 15 and a disk antenna 16 are used as means for introducing an electromagnetic wave into the vacuum vessel 4. The container upper cover 18 is a portion for introducing the coaxial cable 15 into a vacuum. A quartz plate 17 for preventing the antenna from being worn is placed on the front surface of the antenna 16. The thickness of the quartz plate 17 is adjusted so as to transmit electromagnetic waves radiated from the antenna. The coaxial cable 15 has the advantage of being smaller than a waveguide. When the output of the bias power supply 19 is pulsed as shown in FIG. 6B, electrons enter the sample 8 with a positive pulse on, and ions enter with a pulse off. Since the ions are incident in the same amount to neutralize the electrons, if the off cycle is lengthened, there occurs a time when the ions are not accelerated. As a result, the sample stage is not sputtered as described with reference to FIG.
[0018]
The combination of the method of introducing power from the plasma power supply 14 and the method of turning on and off the bias power supply is arbitrary, and is not limited to the above embodiment.
[0019]
(Example 4)
FIG. 7 shows another embodiment of the output waveform of the bias power supply of the device shown in FIG. 1 or FIG. 6, which is obtained by amplitude-modulating a high-frequency voltage 21 of several hundred KHz to several tens of MHz with a modulation wave 22 of several KHz. . Even with this bias power supply, when the amplitude is small, the acceleration of ions is stopped, and the electrode life is extended as described in the operation.
[0020]
(Example 5)
FIG. 8 shows another embodiment in which the plasma power source 23 is also turned on and off. The frequency of the plasma power supply is 915 MHz, and the bias power supply 10 is 2 MHz. Both are turned on and off at a frequency of 1 KHz and both are synchronized. When the plasma power supply 23 is turned on and off, the amount of ions and radicals attenuates with a certain time constant during the off period. Synchronized with the period, the output of the bias power supply 11 is turned on, and the timing of turning on the bias power supply 10 just before the output 24 of the plasma power supply 23 is turned off as shown in FIG. It is possible to finely adjust the amount of ions and radicals incident on the substrate, and there is an advantage that the degree of freedom increases according to conditions.
[0021]
【The invention's effect】
As described above, according to the present invention, in a dry etching apparatus using high-density plasma, consumption of an electrode due to ion sputtering can be reduced. Therefore, the frequency of maintenance for changing the sample table of the apparatus can be reduced.
[Brief description of the drawings]
FIG. 1A is a configuration diagram of an etching apparatus to which the present invention is applied, and FIG. 1B is an output waveform of a bias power supply 10;
2A is an enlarged view of the vicinity of a sample stage of an etching apparatus, and FIG. 2B shows a voltage waveform of a bias power supply 10 of a conventional system.
3 (a) is an enlarged view of the vicinity of a sample stage of an etching apparatus, showing a state when bias is turned on, FIG. 3 (b) shows a state when bias is turned off, and FIG. 3 (c) shows a bias power supply 10 according to the present invention. 3 shows a voltage waveform.
4A is an enlarged view of a sample cross section on a sample stage and shows a state when a bias is turned off, FIG. 4B shows a state of the sample cross section when a bias is turned on, and FIG. 2 shows a voltage waveform of a power supply 10.
FIG. 5 shows an etching rate of a sample (metal) and a scraping rate of a sample stage.
6A is a configuration diagram of an etching apparatus using a plasma power supply of 500 Mhz to which the present invention is applied, and FIG. 6B is a pulse output-modulated bias output waveform of the power supply 19;
FIG. 7 shows another example of the waveform of the bias voltage applied to the sample stage.
8A is a configuration diagram of an etching apparatus to which the present invention is applied, and FIG. 8B shows an embodiment in which a bias output waveform and a power supply for plasma are modulated on and off.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Power supply for plasma, 2 ... Waveguide, 3 ... Introduction window, 4 ... Vacuum container, 5 ... Plasma, 6 ... Magnet, 7 ... Magnet, 8 ... Sample, 9 ... Sample stage, 10 ... Bias power supply, 11- Voltage waveform, 12 ion, 13 radical, 14 resist, 15 coaxial cable, 16 antenna, 17 quartz plate, 18 container lid, 19 bias power supply, 20 voltage waveform, 21 high frequency voltage , 22: modulated wave, 23: power supply for plasma, 24: output waveform of electromagnetic wave.

Claims (2)

A rare gas is added to an etching gas in which active radicals are generated in plasma using an electromagnetic wave having a frequency of 100 MHz or more and 1.2 GHz or less to form a plasma, and ions of the rare gas occupy a large amount of ions in the plasma. The rare gas is added , a bias having a frequency of 20 MHz or less is applied to the sample stage on which the sample is placed, and the ratio of the on time occupied in the cycle is changed from 10% to 60%, and the bias is repeatedly turned on and off. characterized in that said active radicals to prevent sample stage sputtering by ions with adsorbed to the sample to etch the desired film formed on the sample to result resist the ion assisted etching as a mask to accelerate ions during biased on Te Plasma processing method. A rare gas is added to an etching gas in which active radicals are generated in plasma using an electromagnetic wave having a frequency of 100 MHz or more and 1.2 GHz or less to form a plasma, and ions of the rare gas occupy a large amount of ions in the plasma. The rare gas is added, a sample on which a semiconductor or a metal film of a material to be etched by ion assisted etching is formed is placed on an alumina sample table, and a bias having a frequency of 20 MHz or less is applied to the sample table and the bias is applied. The on / off is repeated at a frequency of 1 kHz and the ratio of the on time occupied in one cycle from 10% to 60% is repeated to adsorb radicals to the sample at the time of bias off and to prevent sputtering of the alumina sample table by ions due to ions. accelerating the ions when on the ion-assisted etching The plasma processing method characterized by etching a desired semiconductor or metal film formed on the sample I.

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