JPS6346575B2 - - Google Patents

Description

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

In order to explain the present invention, first, a conventional plasma deposition and etching method using high frequency discharge and an apparatus therefor will be described.

FIG. 1 is a block 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 a suitable pressure of about 10 ^-2 Torr, a non-polar discharge will occur inside the discharge tube. is generated to generate discharge plasma 9. Now monosilane (SiH ₄ ) and nitrogen (N ₂ ) are introduced as discharge gases.
When the substrate 6 is heated to about 300 to 400° C. by a heating means (not shown), a silicon nitride (Si ₃ H ₄ ) film is deposited on the substrate.

FIG. 2 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 an evacuation system (not shown), and the electrode 11 serves as a holding plate for the substrate 6 and is connected to the ground potential 8. Gas introduction hole 2
By introducing a more appropriate pressure 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 of an etching apparatus using plasma using high frequency discharge. Electrodes 10 and 11 capacitively coupled to the oscillator 3 are 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. Gas introduction hole 2
For example, freon gas (CF ₄ ) and oxygen (O ₂ )
When gas is introduced at an appropriate pressure and discharge plasma 9 is generated, the silicon substrate and silicon oxide film are etched by fluorine ions.

FIG. 4 shows another example and has a configuration similar to that in FIG. 3, but two capacitively coupled electrodes 10 and 11 are introduced into the vacuum chamber 5. A substrate 6 to be processed is attached to and held by one electrode 10, and a Freon gas at an appropriate pressure is introduced between the electrode 11 and the other electrode 11, which is held and grounded.A discharge is caused to generate plasma 9.

The discharge is a high frequency discharge (several M to several tens of MHz),
In addition, since one electrode is in contact with the plasma 9 at ground potential, ions with an energy corresponding to the wave height of the applied high frequency arrive at the substrate 6, which causes general sputtering, but also causes the discharge gas to become reactive. In this case, 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, electrodes 10 and 1 are connected to the oscillator 3.
1 is capacitively coupled, and one of the electrodes 11 is 8
Assume that it is grounded. The vacuum container 5 is made of an insulating material, is evacuated by a vacuum evacuation system (not shown), and a suitable pressure gas is introduced through a gas introduction hole (not shown) and discharged by applied high frequency power to form plasma 9. do.

FIG. 5A corresponds to FIG. 3 in terms of the discharge format. The plasma 9 formed within the vacuum container is at a floating potential with respect to the outside world. Therefore, in both the case of deposition and etching, the potential of the plasma 9 relative to the insulating container 5, that is, 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. do.

Figure 5B is the discharge type shown in Figures 2 and 4.
Corresponds to the figure. In this case, one electrode 11 has 8
Since the sheath is grounded and in contact with the plasma 9, the potential of the plasma separates the sheath from the ground potential and becomes a potential corresponding to the plasma potential V _S . Therefore, when a substrate is placed on the ground side electrode 11 in _FIG . arrive.

On the other hand, the ten high-frequency electrodes in FIG.
If the output voltage waveform of this oscillator is represented by V ₀ sinωt, then this electrode 1
The potential changes to 0 at V ₀ sinωt. Here, V ₀ 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 ₀ sinωt is applied to the plasma 10, the average potential of the plasma 9 remains at V _S . However, in reality, the electrode 10
Since it changes with V ₀ sinωt, the electrode 10 and plasma 9
The sheath between the plasma and the electrode increases and decreases to maintain the potential difference between the plasma and the electrode. Therefore, when the potential of the electrode 10 reaches -V ₀ , ions arrive from the plasma with the highest energy (V ₀ +V _s ). Since V _O is typically on the order of several hundred volts, the substrate held on electrode 10 is bombarded with ions with energies of up to several hundred volts. Therefore, when performing normal deposition, as shown in Figure 2, the substrate is held on the ground side electrode and ions are allowed to arrive with the energy of V _S.
When sputtering is performed, the substrate is held by an electrode on the high frequency side, and ions are made to arrive at the energy of (V _S +V _O ).

In the discharge type shown in FIG. 5C, one electrode 11 is located 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 FIG. 5B, the plasma potential is equal to V _S and ions with energy V _S arrive on the 11th electrode. Looking at the other high-frequency electrode 10, this is equivalent to the case where the high-frequency electrode 10 in FIG. 5B 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 _VW . The surface potential of this insulator is
Since the energy changes as V ₀ sinωt, ions with the highest energy (V _O +V _W ) arrive and sputter the insulator. This is the principle of high frequency sputtering on insulators. The configuration of FIG. 4 can be considered similar to the configuration of FIG. 5C.

Considering the various deposition devices and etching devices currently in use as described above,
It can be seen that the energy of the deposition or etching ions deposited onto the substrate being processed is completely determined by the equipment conditions at the time, and has become an amount that is difficult to control. For example, in the depositions shown in FIGS. 1 and 2, the deposition energy is determined by the potential V _S of the plasma 9, and this potential is
It depends on the high frequency power applied and the 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 _FIG.
This high frequency voltage is the voltage required for discharge.

On the other hand, if the energy of ions arriving at the processing substrate from plasma formed by high-frequency discharge can be controlled, the effect is considered to be significant.

Considering the case of deposition, if the material is deposited onto the substrate using thermal kinetic energy, it will simply adhere to the substrate. If the substrate is heated, it can gain kinetic energy from the substrate and move on the substrate.
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 are made to reach the substrate, most of that energy simply becomes thermal energy due to collision, but some (~several percent) 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. Furthermore, when the same material as the substrate is deposited, atoms arriving at the substrate can move to appropriate lattice points using this kinetic energy, so crystal growth can be performed at a considerably low temperature. The energy to be delivered 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.

Furthermore, in the case of etching, 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 volts is not necessary, and local etching cannot be achieved at such a high voltage. When etching is performed, the mask may be etched by sputtering, and the temperature of the substrate may rise, resulting in difficulties.

When performing reactive sputtering, in principle, the ion energy can be set to a value that promotes the chemical reaction;
The value is also preferably on the order of several volts to several tens of volts.

As seen from the above considerations, in an apparatus that generates plasma using high-frequency discharge and performs deposition or etching, it is possible to make ions arrive on a substrate with controlled energy ranging from several volts to several tens of volts. If possible, this could lead to significant advances in the processing process.

As described above, in order to control the target ions from within the plasma and make them arrive at the substrate at a specific energy V _T , a target positive potential is applied to the discharge electrode, or a probe is inserted into the plasma. An invention in which a specific positive potential is applied to plasma to cause ions to arrive at a substrate with controllable energy is described in JP-A-53-68171 (Children's No. 761037). Although this method has been found to be very effective in controlling the plasma potential, it has been found in numerous experiments that its application is limited in the following cases.

(1) When performing deposition, if the deposition material is an insulator, as the film thickness increases, charges accumulate on the surface of the deposited film, so the energy of ions no longer acts effectively. Therefore, the application of this potential is not effective for depositing thick films of insulators.

(2) In the case of etching, if the target is a thick insulating film, the same phenomenon as in the above-mentioned deposition occurs. In addition, in order to protect the etched substrate from surrounding contamination, the upper and lower discharge electrodes are covered with quartz plates, and the substrate is placed on a tetrafluoroethylene plate to accelerate the chemical reaction. Recently, a method has been used to insulate the terminal from ground potential, but in such cases, applying a potential is also not effective.

In other words, the configuration is as shown in Figure 5A. In such a case, even if a direct current potential is applied to the plasma, the entire substrate will be positively charged because the substrate is insulated from the ground potential, and the plasma potential will change. The substrate potential approaches, the ions do not arrive at the substrate with the desired energy, and the potential generated between the plasma and the wall of the insulating tube,
In other words, it arrives at the substrate at tube wall potential _VW . Since this tube wall potential is generally several eV or less, it is a much lower value 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.

Figure 6 shows this basic concept. This is a new low frequency oscillator 12 for control shown in Figure 5A.
This is a configuration in which these are 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 the simplest example of explanation shown in FIG. 7, when a rectangular wave is applied as shown in the figure by the low frequency oscillator 12,
The potential change of the substrate 6 in FIG. 6 corresponding to this is qualitatively shown. In this example, for simplicity of explanation, the so-called tube wall potential between the plasma and the insulating container is ignored. When a rectangular potential of +V _O of ABC is applied as shown in Fig. 7, the 10 electrodes in Fig. 6 become +V _O , so the potential of the substrate 6 becomes as shown by the dotted line because it is charged by ions from the plasma. The voltage increases with AK, and becomes equal to the electrode potential +V _O at K. In this case, the plasma also rises to a potential of +V _O like the substrate. This potential remains constant during KC, and then when the electrode potential reverses to CDE and -V _O , the substrate becomes negatively charged due to the influx of electrons from the plasma and rapidly drops to CLM and -V _O. And during ME-
V _O is strong. Next, the electrode potential changes from −V _O to +V _O
When EFG changes to EFG, the potential of the substrate becomes ENP and +
Continue to rise to V _O , and +V _O continues to rise during PG. This is repeated below.

Therefore, the arrival of ions to the substrate is limited by e.g. ME
The potential of the electrode, which has been sufficiently charged by electrons during this period and shows a value of -V _O , is reversed to EFG and +V _O ,
This is done only while ENP is rising from -V _O to +V _O. Therefore, the energy of the arriving ions is
This is the difference between +V _O , the potential of the electrode, and the potential of the substrate, which rises along ENP. Therefore, the energy of the ions arriving at the substrate changes from 2V _O to 0 eV during ENP.

Figure 8 shows the case where ABCDEFGHI and a sine wave are added instead of the rectangular wave. The potential of the substrate changes in a sine waveform AB'C'D'E'F'G'H'I' with a slightly shifted period based on the same logic as described above. Considering ions arriving at the substrate, for example, if the electrode potential is +V _O
Energy arrives at 0 electron volts from 2V _O during D'E'F' along with DEF changing to V _O.

In this way, ions flow into the substrate between ENP in FIG. 7 and between D′E′F′ in _FIG. Varies between. In the above discussion, we have ignored the so-called tube wall potential V _W that the plasma has with respect to the tube wall, which is an insulator, as mentioned above. This V _W
When the effect of is included, the substrate receives ions with an energy between (2V _O +V _W ) than V _W . Therefore, if ions with energy higher than V _T are effective for reactions against the target substrate, if (V _T > V _W ), particles with energy of (2V _O + V _W −V _T ) is effective for the specific purpose of plasma processing of substrates. This energy must not be infinitely large, and must be less than the maximum value V _M when considering damage to the substrate and the cross section of the reaction. Therefore, V _M > 2V _O + V _W > V _T (1) holds true, and the square wave applied in this way can increase the peak value V _O of the sine wave alternating current independently of the high frequency for the discharge that creates plasma. You can choose.

Now, in FIG. 7, when the potential of the rectangular wave applied to the electrode changes from -V _O of DM to +V _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 2V _O is d, the mass of the _O ion is M, and the charge of the _O ion is e, then the time t for the ions to arrive at the substrate from the plasma at the edge of the sheath is calculated by the following equation: will be given.

Now, assuming 2V _O = 50V, d _O = 0.5 cm, e = 1.6 × 10 ^-19 coulombs, and M _O with mass number 40, t = 6.4
×10 ^-7 (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 between 2V _O and 0, so among the ions arriving at the substrate, ions with energy higher than V _T , that is, the potential V of the substrate is between V2V _O −V _T …(3) Only those ions that arrive are useful for purposes of this invention. Assuming that 2V _O =50V and V _T =20V, the third equation effectively acts until the substrate potential reaches 30V. Therefore, if a square wave is applied as shown in Fig. 7, it is not effective in this case since it is about 1/2 between ENP when ions arrive at the substrate in the above example, but this is due to V _T and V _O Due to the relative value of
In other words, when V _T is small and V _O 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 V _T and V _O according to the relationship in the formula.

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

In the above discussion, we added a high-frequency power source for the main discharge, a power source for control to give effective control energy to the ions in the plasma generated by this discharge, and a power source for this control. By making the frequency low enough for ions in the plasma to follow, it is possible to protect the electrodes and vacuum chamber constituents from contamination, as shown in Figure 6, and for the purpose of certain chemical reactions. Therefore, in a structure in which the substrate is completely placed in an insulating container and a discharge gas is introduced into the container, it is possible to process the substrate by allowing ions of a specific energy to arrive on the substrate. This method is also extremely effective in cases where conventional methods are difficult to process with controllable ion energy because an insulating film exists on the substrate or the insulating film is deposited during processing. It is clear from the above discussion that

As described above, according to the present invention, it is possible to control the energy of ions in the plasma arriving at the substrate by preparing a low-frequency power source separately from the high-frequency power source for plasma generation, so that by varying the ion energy, The degree of freedom can be given to control of the processed shape of the substrate.

The present invention is particularly effective when applied when the object to be processed is an insulator.

When the present invention is applied as an etching process, it is possible to reduce the amount of undercut under the etching mask and perform directional etching. On the other hand, when the present invention is applied as a deposition process, a flattened substrate processing surface can be obtained by depositing, for example, on an uneven surface of the substrate.

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 block diagrams of conventional deposition equipment using plasma generated by high-frequency discharge, and Figure 3
Figure 4 is a configuration diagram of a conventional etching apparatus using plasma generated by high-frequency discharge, Figure 5 A, B,
C is a configuration diagram for explaining the operating principle, in which the configurations from FIG. 1 to FIG. 4 are classified into three types in order to explain from the operating principle, and FIG. 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 of the electrode and substrate that occurs when this is applied.
FIG. 2 is an explanatory diagram of a low frequency sine wave to be applied to the configuration shown in the figure and potential changes between an electrode and a substrate that occur when the sine wave is applied. 1...Discharge tube, 2...Gas introduction hole, 3...High frequency oscillator, 4...Inductively coupled discharge coil, 5...
Vacuum container, 6... Processing substrate, 7... Holding plate, 8...
...Earth potential connection, 9...Generated plasma, 10...
... Capacitive coupling electrode (high frequency electrode), 11... Capacitive coupling electrode, 12... Low frequency oscillator.

Claims (1)

[Claims] 1. A method for processing a substrate by generating plasma in a vacuum chamber and performing deposition or etching on the substrate, in which a pair of opposing electrodes are arranged to sandwich a plasma generation section generated in the vacuum chamber section. By applying an alternating current between the opposing electrodes, the energy of the ions from the plasma generating section reaching the substrate is controlled. On the other hand, a high-frequency alternating current power source with a higher frequency than the alternating current is prepared to apply high-frequency power to the substrate. A plasma processing method characterized by generating plasma by applying voltage to an electrode. 2. Applying the low frequency AC and the high frequency AC to the same electrode, configuring the low frequency AC power source to have high impedance when viewed from the high frequency AC side, and preventing high frequency power from leaking to the low frequency AC side. A plasma processing method according to claim 1, characterized in that: