JPH033380B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a plasma processing apparatus 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 be explained first.

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 we introduce monosilicate (SiH ₄ ) and nitrogen (N ₂ ) 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 a vacuum 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. Freon gas at an appropriate pressure is introduced between one electrode 10 and a grounded electrode 11 to which a processing substrate 6 is attached and held, causing discharge and plasma 9 to be generated.

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 methods 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 is 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.
Since the output voltage waveform of this oscillator is expressed by V _p sinωt, this electrode 1
The potential changes to 0 at V _p sinωt. Here, V _p 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 _p sin ωt is applied to the plasma 9, the average potential of the plasma 9 remains at V _s . However, in reality, the electrode 10 is V _p
Since it changes by 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, the potential of the electrode 10 is −
When V _p is reached, ions arrive from the plasma with the highest energy (V _p + V _S ). Since V _p 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 _P ).

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 _p sinωt, ions with the highest energy (V _p +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 arriving at the substrate to be processed is determined entirely by the equipment conditions at the time and is a quantity 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. Furthermore, in the configuration shown in FIG. 3, the energy of the 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 made to arrive at 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 too large a value may cause collision defects and sputtering on the substrate.

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 (such as Freon) as the discharge gas and causing 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 substrate temperature may rise, causing 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 is described in JP-A-53-68171, in which a specific positive potential is applied to plasma to cause ions to arrive at a substrate with controllable energy. 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. In recent years, methods have been used to insulate wires from ground potential. In such cases, application of potential is also ineffective.

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.

According to the plasma processing apparatus of the present invention, a vacuum vessel having a vacuum exhaust hole, a coaxial electromagnet disposed so as to surround at least a part of the outer periphery of the vacuum vessel, and a coaxial electromagnet surrounded by the coaxial electromagnet. a plasma generating means for turning discharge gas into plasma by discharge in a discharge space in the vacuum vessel, and a magnetic field created in the vacuum vessel by the coaxial electromagnet, and
means for arranging a substrate to be processed within the vacuum container; and a member electrically connected to the substrate and the plasma generated in the discharge space in order to control the energy with which ions in the plasma reach the substrate. and means for applying alternating current at a frequency that the ions can follow between the two.

Furthermore, according to an embodiment of the present invention, by configuring the coaxial electromagnet from a plurality of coaxial electromagnets arranged along the axial direction, the strength of the axial magnetic field by the coaxial electromagnet can be controlled by the coaxial electromagnet. It is characterized by being constructed so that it becomes weaker from the surface to be treated toward the back surface of the substrate.

Further, according to an embodiment of the present invention, the evacuation hole is provided on the back side of the substrate so that the vacuum is evacuated from the back side of the substrate. Furthermore, the embodiment has the following features.

(1) The plasma generating means is characterized in that it utilizes microwave discharge.

(2) In place of (1) above, the plasma generation means:
It may also be one that utilizes DC arc discharge.

Next, in order to understand the solution principle of the present invention, a parallel plate type plasma processing apparatus, which was studied by the inventor of the present invention at the stage of studying the plasma processing apparatus of the present invention, will be explained with reference to FIG. The parallel plate plasma apparatus shown in FIG. 6 has a configuration similar to that shown in FIG. 5A, in which 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 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, to simplify the explanation, the so-called tube wall potential between the plasma and the insulating container is ignored. When a rectangular potential of +V _p of ABC is applied as shown in Fig. 7, the 10 electrodes in Fig. 6 become +V _p , 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 _p at K. In this case, the plasma also rises to a potential of +V _p like the substrate. This potential remains constant during KC, and then when the electrode potential reverses to CDE and V _p , the substrate receives a negative charge due to the influx of electrons from the plasma and rapidly drops to CLM and -V _p . , between ME−V _p
It's tough. Next, when the electrode potential changes EFG from -V _p to +V _p again, the substrate potential changes to ENP and +Vo.
+V _p continues to rise until PG. This is repeated below.

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

A case is shown in which ABCDEFGHI and a sine wave are added instead of the rectangular wave in FIG. The potential of the substrate changes in a sinusoidal waveform AB′C′D′E′F′G′H′I′ with a slightly shifted period based on the same logic as above. Considering the ions arriving at the substrate, for example, along DEF where the electrode potential changes from _-Vp to + _Vp , and D'E'F', the energy arrives at 0 electron volts from _2Vp .

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 the arrival of ions with an energy between (2V _p + 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 _p + 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 _p + V _W > V _T (1) holds true, and the square wave applied in this way makes the peak value V _p of the sinusoidal alternating current independent 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 _p of DM to +V _p 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 a potential difference of 2V _p is d, the mass of the _p ion is M, and the charge of the _p 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 given by the following equation: Given.

Now, assuming 2V _p = 50V, d _p = 0.5 cm, e = 1.6 × 10 ^-19 clone, and M _p 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 waveform. On the other hand, the energy of the arriving ions is between 2V _p and 0, so among the ions arriving at the substrate, ions with energy higher than V _T , that is, the potential of the substrate is between V2V _p −V _T ……(3) Only ions that arrive at will work effectively for purposes of this invention. Assuming that 2V _p =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 where ions arrive at the substrate in the above example, but this is due to the difference between V _T and V _p Due to the relative value of
In other words, when V _T is small and V _p 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 _p according to the relationship in the equation.

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 the ions in the plasma to follow, as shown in Figure 6, it is possible to protect the electrodes and vacuum chamber components from contamination, and for the purpose of certain chemical reactions. In order to do this, 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 and the substrate can be processed. 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

The inventor of the present application has found that, by using such a parallel plate type plasma processing apparatus, the energy with which ions in the plasma reach the substrate to be processed can be controlled by an AC power source that is separate from the high frequency power source that serves as the plasma generation source. It was confirmed. Therefore, the inventor of the present application,
We studied the application of this principle to plasma processing apparatuses other than the parallel plate type, and completed the plasma processing apparatus of the present invention described below.

FIG. 9 shows an embodiment of the plasma apparatus of the present invention. In FIG. 9, a vacuum container 13 is evacuated through a vacuum exhaust hole 14 by a vacuum exhaust system (not shown). This vacuum vessel is surrounded by a coaxial electromagnet 15, in which a plasma source 16 is positioned, gas is introduced at an appropriate pressure through a discharge gas introduction hole 17, and discharge means (not shown), such as a DC arc, is used. This plasma, which generates plasma 18 by discharging by electric discharge, microwave discharge, etc., flows out from the plasma outlet hole 19 as a plasma stream 20, forms a plasma stream, and reaches the collector (substrate) 21. If the plasma stream contains a deposition substance, the substance will be deposited on the substrate 21, and if the plasma stream includes an etching component, the substrate will be etched. The basic configuration before the present invention is applied is known from Japanese Patent No. 611184 (Japanese Patent Publication No. 38801/1983). This patent clarifies the operation of each part of the above-mentioned basic configuration. That is, in FIG. 9, a plurality of coaxial electromagnets 15 arranged along the axial direction are configured so that the strength of the magnetic field in the axial direction becomes weaker from the front side of the substrate 21 toward the back side of the substrate. A plasma flow is formed from the plasma source 16 toward the substrate 21 by the action of this magnetic gradient. The reason why the coaxial electromagnet 15 is divided in this way is to provide a magnetic field gradient.

In accordance with the present invention, a controllable potential is then applied to the plasma stream 20 in order to control the energy with which the ions in the plasma stream 20 reach the processing substrate 21 . That is, if an AC power source 22 with a frequency that can be followed by ions is connected between the plasma source 16 and the substrate 21, ions with controllable energy can be made to reach the substrate according to the above discussion.

In particular, similar to the above-mentioned parallel plate method, the substrate 21
If the material deposited on the substrate is an insulating material or a high-resistance material, or if there is an insulating film on the substrate, or even if the substrate is insulated to protect the substrate itself, the above controlled energy can be used. Ions can be allowed to reach the substrate.

As described above, according to the present invention, an AC power source separate from the energy of the plasma generation means, that is, the energy of arc discharge and microwave discharge, is prepared to create a potential between the plasma generation section and the substrate to be processed. By applying this, it is possible to control the energy of the ions in the plasma that arrive at the substrate, and by varying the ion energy, it is possible to have a degree of freedom in controlling the processed shape of the substrate. In particular, the present invention is effective when applied to cases where the substrate to be processed is an insulating film. When the present invention is applied as a plasma etching process, the undercut amount (side etching amount) under the etching mask can be extremely reduced, and directional etching can be performed. On the other hand, when the present invention is applied as a deposition process, for example, by depositing on an uneven surface of the substrate, a flattened substrate processing surface can be obtained.

Furthermore, according to the above-described plasma processing apparatus of the present invention, as is clear from FIG. 9, since the vacuum is evacuated from the back side of the substrate in the direction of the plasma flow, the plasma flow from the plasma generation section toward the substrate is It can have a stimulatory effect such as increasing the amount.

[Brief explanation of drawings]

Figures 1 and 2 are configuration 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 principles of the configurations from FIGS. 1 to 4 classified into three types in order to explain the operating principles, and FIG. 6 is a plasma device devised at the study stage of the present invention. 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, and Fig. 8 is the configuration of Fig. 6. FIG. 9 is an explanatory diagram of a low-frequency sine wave to be applied to the sine wave and the potential change between the electrode and the substrate that occurs when this is applied. It is an explanatory view when the invention 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, 13... Vacuum container, 14... Vacuum exhaust hole, 15... Coaxial electromagnetic coil, 16... Plasma source , 17...Discharge gas introduction hole, 18...Discharge plasma, 19...Plasma outflow hole, 20...Plasma flow, 21...Collector (substrate), 22...Low frequency oscillator.

Claims (1)

[Scope of Claims] 1. A vacuum container having a vacuum exhaust hole, a coaxial electromagnet disposed so as to surround at least a part of the outer periphery of the vacuum container, and the vacuum surrounded by the coaxial electromagnet. Plasma generation means for turning discharge gas into plasma by discharge in a discharge space in the container, and a magnetic field created in the vacuum container by the coaxial electromagnet, and a substrate to be processed is placed in the vacuum container. and an alternating current having a frequency that the ions can follow between the substrate and a member electrically connected to the plasma generated in the discharge space in order to control the energy with which ions in the plasma reach the substrate. 1. A plasma processing apparatus comprising: means for applying voltage. 2. By configuring the coaxial electromagnet from a plurality of coaxial electromagnets arranged along the axial direction, the strength of the axial magnetic field by the coaxial electromagnet can be spread from the front side of the substrate to be processed to the back side of the substrate. 2. The plasma processing apparatus according to claim 1, wherein the plasma processing apparatus is configured to become weaker toward the sides. 3. The plasma processing apparatus according to claim 2, wherein the vacuum exhaust hole is provided on the back side of the substrate so that the vacuum is evacuated from the back side of the substrate. 4. The plasma processing apparatus according to claim 2, wherein the plasma generating means utilizes microwave discharge. 5. The plasma processing apparatus according to claim 2, wherein the plasma generating means utilizes DC arc discharge.