JPS63211631A - Plasma treatment device - Google Patents

Abstract

PURPOSE:To make ions having aimed effective energy to reach to a substrate by providing a means in which ACs are applied to the substrate. CONSTITUTION:A means in which ACs are applied to a substrate is provided in order to regulate the potential of plasma in a vacuum vessel to the substrate and control energy in which ions in plasma reach to the substrate. The frequency of a low-frequency oscillator 12 is made sufficiently lower than that of a high-frequency oscillator 3, and ions in plasma 9 can follow up enough owing to the changing electric field. High impedance viewed from the high-frequency side such as introduction through an induction coil of an output from the low-frequency oscillator is formed so that high-frequency power does not leak to the low-frequency oscillator side at that time. Accordingly, ions having aimed effective energy can be made to reach to the substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a processing apparatus using plasma generated by high-frequency discharge, and mainly relates to a processing apparatus for performing deposition or etching processing on a semiconductor substrate using plasma.

In order to understand the problems of conventional plasma processing apparatuses, a conventional plasma deposition and etching apparatus using high frequency discharge will first be explained.

FIG. 1 is a configuration diagram of a plasma deposition apparatus using high frequency discharge. Material gas at an appropriate pressure is introduced into the first discharge tube through the second gas introduction hole. A vacuum chamber 5 is evacuated by a vacuum evacuation system (not shown), and a substrate 6 to be deposited is held on a holding plate 7 and connected to a ground potential 8 .

Now, when high-frequency power is applied to the discharge tube 1 using the high-frequency oscillator 3 and the discharge coil 4 inductively coupled to the high-frequency oscillator 3, if the internal pressure of the discharge tube 1 is an appropriate pressure of about 10-1 Torr, a voltage will be generated inside the discharge tube. A non-polar discharge is generated to generate discharge plasma 9. Monosilane (8iH4) is now used as the discharge gas.
By introducing nitrogen (N) and heating the substrate 6 to about 300 to 400 DEG C. by a heating means (not shown), a silicon nitride (S'8H4) film is deposited on the substrate.

FIG. 2 similarly shows a configuration diagram of another conventional deposition apparatus. Electrodes 10 and 11 capacitively coupled to the oscillator 3 are introduced into the vacuum chamber 5 which is evacuated by a vacuum evacuation system (not shown), and the electrodes 11 serve as a holding plate for the substrate 6 and are connected to the ground potential 8. By introducing an appropriate pressure through the gas introduction hole 2 and generating discharge plasma 9, a desired substance can be deposited on the substrate 6 in the same manner as in the case of FIG.

Next, FIG. 3 is a block diagram in the case of plasma etching using high frequency discharge. An electrode 10.11 capacitively coupled to the oscillator 3 is placed on the outside of the vacuum chamber 5, and a substrate 6 is placed on a holding plate 7 inside the vacuum chamber 5. For example, 7 Leon gas (CF4
) or oxygen gas at an appropriate pressure to generate discharge plasma 9, the silicon substrate and silicon oxide film will be etched by fluorine ions.

FIG. 4 shows another example with a configuration similar to that in FIG. 3, but with two capacitively coupled electrodes 10, 11 introduced into the vacuum chamber 5. A processing substrate 6 is attached to one electrode 10, held and grounded, and then discharge is caused by Freon gas at an appropriate pressure introduced between the electrode 11' and the other electrode 11'.
to occur.

The discharge is high frequency! Since Q is (several M to several + MH2) and one electrode is in contact with the plasma 9 at ground potential, ions with energy corresponding to the wave height of the applied high frequency arrive at the substrate 6. However, if the discharge gas is reactive, for example, energetic fluorine ions react with the substrate to cause reactive sputtering, etching the substrate. Even if the substrate in this case is an insulator, there is no problem because high frequency is applied.

FIG. 5 summarizes the various systems shown in FIGS. 1 to 4 for the case of capacitive coupling, with particular attention paid to the energy of ions reaching the substrate.

In FIG. 5, it is assumed that electrodes 10 and 11 are capacitively coupled to an oscillator 3, and one of the electrodes 11 is grounded to 8. The vacuum container 5 is made of an insulating material, is evacuated by a vacuum exhaust system (not shown), and a suitable pressure gas is introduced through a gas introduction hole (not shown), which is discharged by the applied high-frequency power to form plasma 9. shall be taken as a thing.

FIG. 5 (5) corresponds to FIG. 3 in terms of the discharge format. The plasma 9 formed within the vacuum chamber is at a floating potential with respect to the outside world. Therefore, in both deposition and etching, the potential of the plasma 9 with respect to the insulating container 5,
In other words, the energy of the plasma potential, called tube wall potential, reaches the substrate inserted in the vacuum container, which is also at a floating potential.

FIG. 5(B) corresponds to FIGS. 2 and 4 as the Fi discharge format. In this case, one electrode 11 is grounded at 8 and is in contact with the plasma 9, so that the plasma potential separates the sheath from the ground potential and becomes a potential corresponding to the plasma potential Vs. Therefore, Figure 5(B)
When a substrate is placed on the ground-side electrode No. 11, ions arrive at an ion energy Vs (usually about several volts or less) corresponding to the potential of this plasma, both in the case of deposition and in the case of etching.

On the other hand, the 10 high-frequency electrodes in FIG.
o 5ilIωt, this electrode 10
The potential changes by V o sin ωt. Here v.

is the highest value of the high frequency waveform, ω is the angular frequency, and t is the time. This electrode 10 is also in contact with the plasma 10, but when averaged over time, the potential of the electrode 10 is equal to the ground potential. Therefore, even if a high frequency voltage of V o sin ωt is applied to the plasma 10, the potential of the plasma 9 stops at VsK on average. However, since the electrode 10 actually changes by V o sinωt, the sheath between the electrode 10 and the plasma 9 increases or decreases to maintain the potential difference between the plasma and the electrode. Therefore, when the potential of the electrode 10 becomes -vo, it is the highest (Vo+
Plasma and ions arrive with the energy of Vs).

■.

Since the voltage is usually on the order of several hundred volts, the substrate held on the electrode 10 is bombarded with ions having an energy of up to several hundred volts. Therefore, when making a normal deposition, the second
As shown in the figure, when sputtering is performed by holding the substrate on the electrode on the ground side and allowing ions to arrive at the energy of vs, the electrode on the high frequency side should hold the substrate and (V
The ions are allowed to arrive with an energy of s + Vo ).

In the discharge type shown in FIG. 5(q), one electrode 11 is placed inside the vacuum chamber as a ground electrode and is in contact with the plasma 9, and the other high-frequency electrode 10 is located outside the vacuum chamber.

As in the case of ) in FIG. 5, the plasma potential is equal to V, and ions with an energy of vs arrive on the electrode 11. Looking at the other high-frequency electrode 10, this is equivalent to the case where the high-frequency electrode 10 in FIG. 5(B) is covered with an insulator so that it does not come into direct contact with plasma. Therefore, the plasma has a so-called tube wall potential ■w. The surface potential of this insulator is amazing! The maximum (V
Ions with an energy of o+Vw) arrive and sputter the insulator. This is the principle of high frequency sputtering for insulators. The configuration in FIG. 4 can be considered to be similar to the configuration in FIG. 5 (q).

Considering the various deposition and etching equipment currently in use as described above, the energy of the deposition or etching ions deposited onto the substrate to be processed is completely determined by the equipment conditions at that time, and is difficult to control. It can be seen that For example, in the depositions shown in FIGS. 1 and 2, the deposition energy depends on the potential of the plasma 9, and this potential is
Determined by the applied high frequency power and discharge gas pressure.

In addition, in the configuration shown in Fig. 3, the energy of etching ions is close to the tube wall potential due to the floating potential of the substrate, and
In the configuration shown in the figure, the energy of the etching ions is the high frequency voltage v of high frequency oscillation.

This high frequency voltage is the voltage required for discharge.

On the other hand, if it is possible to control the energy of ions arriving at the plasma formed by high-frequency discharge and the υ-treated substrate, the effect is considered to be significant.

Considering the case of deposition, if it is deposited onto a substrate with thermal kinetic energy, it is simply K that is attached to the substrate. If the substrate is heated, it is possible to obtain kinetic energy from the substrate and move on the substrate, but the substrate temperature during deposition is desired to be as low as possible due to limitations in device fabrication. When ions are given energy and made to arrive at the substrate, most of that energy simply becomes thermal energy due to collision, but some (~several inches) becomes kinetic energy on the substrate and can move on the substrate. .

Therefore, in the case of general deposition, it is possible to create a deposited film with good step coverage over steps and small holes on the substrate.

In addition, if the material number is the same as that of the substrate, the atoms arriving at the substrate can use this kinetic energy to move to an appropriate lattice point, so crystal growth can be performed at a considerably lower temperature. The energy to arrive is suitably in the range of several volts to several tens of volts, since if the value is too large, it may cause defects on the substrate due to collision or sputtering.

Consider the case of etching again! In the configuration shown in FIG. 4, ions usually arrive at the substrate with an energy of several hundred eV, causing crystal defects in the substrate at the same time as sputtering. In particular, when etching is performed by using a reactive gas (Freon, etc.) as the discharge gas to cause reactive sputtering, ion energy of several hundred square meters is not necessary, and at such a high voltage, local etching cannot be achieved. Difficulties arise when performing this process because the mask is etched by sputtering and the substrate temperature rises.

When performing reactive sputtering, in principle, the ion energy can be set to a value that promotes chemical reactions, and the value is preferably in the range of several volts to several tens of volts.As seen in the considerations above, high-frequency discharge is If it is possible to make the ions arrive on the substrate with a controlled energy of several volts to several tens of volts in an apparatus that generates plasma and performs deposition etching, this processing step will be possible. can bring about great progress.

As described above, in order to control the number of target ions in the plasma and make them arrive at the substrate at a specific energy VT, a target positive potential is applied to the emission r!1 electrode, or a probe is inserted into the plasma. JP-A-53-68171 describes an invention in which ions are inserted into the plasma, given a specific positive potential to the plasma, and are made to arrive at the substrate with controlled energy.This method is very effective in controlling the plasma potential. Although it has been found to be effective, it has been found in numerous experiments that its use is limited in the following cases.

(1) When performing deposition, in the case of an insulating material such as deboxing material, as the film thickness increases, charges accumulate on the surface of the deposition film, and the energy of ions no longer acts effectively. Therefore, application of this potential is not effective for depositing thick films of insulators.

(2) In the case of etching, if the object is a thick insulating film, the same phenomenon as the above-mentioned deposition occurs.

In order to protect the maku-etched substrate from surrounding contamination, the upper and lower discharge electrodes were covered with quartz plates, and the maku-etched substrate, which promotes chemical reactions, was placed on a tetrafluoroethylene plate. Recently, methods of insulating the substrate from ground potential have been developed, and in such cases, applying a potential is also not effective.

The configuration of the tab is as in the fifth position, and in such a case, even if a DC voltage is applied to the plasma, the substrate is insulated from the ground potential, so the entire substrate will be positively charged, and the plasma potential will increase. The ions approach the substrate potential, and the ions do not arrive at the substrate with the desired energy, but instead arrive at the potential generated between the plasma and the insulating tube wall, that is, the tube wall potential Vw. Since this tube wall potential is generally several eV or less, it has a value considerably lower than the target potential.

The present invention has been devised to improve upon these conventional methods and to allow ions to arrive at a substrate at a targeted and effective energy.

According to the plasma processing apparatus of the present invention, there is provided a vacuum container made of an insulating material for sealing a discharge gas, and a device for generating plasma in the vacuum container, which is passed through the vacuum container from outside the vacuum container. means for applying high frequency power; means for placing a substrate to be processed in the vacuum container;
and means for applying an alternating current to the substrate in order to regulate the potential of the plasma in the vacuum container with respect to the substrate and control the energy with which ions in the plasma reach the substrate. do.

FIG. 6 shows an embodiment of the invention. This is Figure 5 (5)
The configuration is such that a low frequency oscillator 12 for control is newly connected. It is assumed that the frequency of this low frequency oscillator 12 is sufficiently lower than the frequency of the high frequency oscillator 3, and the ions in the plasma 9 in FIG. 6 can sufficiently follow its changing electric field.

In this case, in order to prevent high frequency power from leaking to the low frequency oscillator side, it is necessary to make the output of the low frequency oscillator high impedance from the high frequency side, such as by passing the output through an induction coil.

As a simple explanatory example of FIG. 7, when a rectangular wave is applied as shown in the figure by the low frequency oscillator 12, the corresponding potential change of the substrate 6 in FIG. 6 will be qualitatively shown. In this example,
Here, to simplify the explanation, the so-called tube wall potential between the plasma and the insulating container will be ignored. When the +Vo rectangular potential of KABC is applied as shown in Figure 7, the 10 electrodes in Figure 6 become +
vo, the potential of the substrate 6 rises to AK as shown by the dotted line due to charging by ions from the plasma, and becomes K.
becomes equal to +vo of the potential of the electrode. In this case, the plasma also rises to the same potential as the substrate, <+Vo. This potential is between KC and then the potential of the electrode is CDE and -■
When the substrate is reversed to 0, the substrate becomes negatively charged due to the influx of electrons from the plasma and rapidly drops at CLM and -Vot, and during ME -■o becomes so. Then the electrode potential is -vo again
When +vo''1 changes to EFG, the potential of the substrate becomes E
Increase to NP and +Vo, and +Vo to low during PG. This is repeated below.

Therefore, when ions arrive at the substrate, for example, during ME, the potential of the electrode, which has been sufficiently charged with electrons and stains and exhibits a value of -vo, is reversed to EFG and +Vo, and from BNP and one This is done only while ascending to o. Therefore, the energy of the arriving ions is +Vo, which is the potential of the electrode, and E
This is the difference in potential of the substrate that rises along the NP. Therefore, the energy of the ions arriving at the substrate is between the BNPO and
It changes from 2Vo to 0 electron volt.

Fig. 8 shows a hidden gem by adding Al3CDEFGHI and a sine wave instead of the rectangular wave. The potential of the substrate changes in a sine waveform of A B'C'D'E'F/αH/I' with a slightly shifted period based on the same logic as described above. Considering the ions arriving at the substrate, for example, the electrode potential is -Mo to +
Along DEF changing to Vo, energy arrives at O electron volts from 2Vo between D'E/F'.

In this way, ions flow into the substrate between ENP in Figure 7 and between l)/p and /p/ in Figure 8, and these ions flow into the substrate from O The amount of 2Vo changes. In the above discussion, we have ignored the so-called tube wall potential ■w that the plasma has with respect to the tube wall, which is an insulator, as described above. When this 7W effect is included, the board becomes more than VW (2V).

+Vw). Therefore, if ions with energy greater than t, VT are effective in reacting with the target substrate, (VT
) Vw ), particles with an energy of (2 Vo + vw - vT) are useful for the specific purpose of plasma processing of substrates. This energy must not be infinitely large, and when considering substrate damage and reaction cross-section, the maximum value vM
Must be less than or equal to Therefore, VM ) 2 Vo +Vw > VT
``(1) holds true, and the peak value o of the rectangular wave and sine wave alternating current applied in this way can be selected independently of the high frequency for the discharge that creates plasma.

Now in Figure 7, the potential of the square wave applied to the electrode is DM
When the potential changes from -vo to +■o of FG, ions arrive at the substrate while the substrate potential rises to ENP as described above. In this case, if the thickness of the ion sheath formed by the potential difference of 2Vo is do, the mass of the ion is and the charge of the Mo ion is e, then the time for the ions to arrive at the substrate from the plasma at the edge of the sheath is given by the following equation: .

Now 2 V O=50 v* dO"' 0.5 Cm
g e=L 6X 10-10 coulombs and mass number 40
Assuming M, then t=6.4×10-tons (seconds). In FIG. 7, since PG is ineffective for the arrival of ions to the substrate, it is set to 0, and it is efficient to set t to 1/2 of the period T of the applied rectangular wave. On the other hand, the energy of the arriving ions is 2V.

and 0, so 77 of the ions arriving at the substrate
Ions with energy above, that is, the potential V of the substrate is V×2Vo VT...(3)
Only ions that arrive during this period will be effective for purposes of this invention. Assuming that 2.0=50V and vT=20V, the third equation effectively acts until the substrate potential reaches 30V. Therefore, if a square wave is applied as shown in FIG.
and v.

Due to the relative value of , VT is small and V.

If is large, a large area can be effectively used. The argument is exactly the same when a sinusoidal waveform as shown in Figure 8 is added as an electric field that acts on these ions. The usable area is determined by the relative values of VT and vo according to the relationship in the equation.

Although we have discussed rectangular waves and sine waves in Figures 7 and 8, the discussion is the same even if triangular waves and other alternating currents are added.

As mentioned in the above discussion, we add a high-frequency power source for the main discharge and a control power source to give effective control energy to the ions in the plasma generated by this discharge. If the frequency is set to a low frequency that the ions in the plasma can follow, it can be used to protect the electrodes and vacuum chamber constituents from contamination, as shown in Figure 6, or for the purpose of certain chemical reactions. In a structure in which the substrate is completely placed in an insulating container and a discharge gas is introduced into the container, ions of a specific energy can be caused to arrive on the substrate to process the substrate. That is, according to the present invention, the vacuum chamber container is formed of an insulating material with few impurities such as quartz, and an electrode for applying power for plasma generation can be used externally. Contamination from the material or the vacuum chamber material can be prevented, and conversely, products generated within the vacuum chamber can be prevented from adhering to the electrodes.

In addition, this method is extremely effective even in cases where an insulating film exists on the substrate or the insulating film is deposited during processing, making processing difficult due to the ion energy that can be controlled using conventional methods. It is clear from the above consideration that it works effectively.

Further, the application of this method is not limited to a parallel plate type plasma processing apparatus as shown in FIG.

In addition, when the plasma-generating discharge has a high frequency, the low-frequency alternating current to be applied can be generated by dividing the high-frequency voltage, converting the frequency, or the like.

[Brief explanation of the drawing]

Figures 1 and 2 are configuration diagrams of a conventional deposition apparatus using plasma generated by high-frequency discharge, and Figures 3 and 4 are configuration diagrams of a conventional etching apparatus using plasma generated by high-frequency discharge. (B) and (C) are configuration diagrams for explaining the operating principles classified into three types in order to explain the configuration from the operating principle from Fig. 1 to Fig. 4. Fig. 7 is an explanatory diagram of the low frequency rectangular wave to be applied to the configuration of Fig. 6, and the potential change between the electrode and the substrate that occurs when this is applied. FIG. 6 is an explanatory diagram of a low frequency sine wave to be applied to the configuration shown in FIG. 6 and potential changes between the electrode and the substrate that occur when the sine wave is applied.

Claims (1)

[Claims] 1. a vacuum container made of an insulating material and for sealing discharge gas; means for applying high frequency power from outside the vacuum container through the vacuum container in order to generate plasma in the vacuum container; means for placing a substrate to be processed in a vacuum vessel; and an alternating current applied to the substrate in order to regulate the potential of the plasma in the vacuum vessel with respect to the substrate and to control the energy with which ions in the plasma arrive at the substrate. 1. A plasma processing apparatus comprising: means for applying .