JPS63211630A - plasma processing equipment - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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 depositing or etching 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. 6 A material gas at an appropriate pressure is introduced into a discharge tube 1 through a gas introduction hole 2. 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 by the high-frequency oscillator 3 and the discharge coil 4 inductively coupled to the high-frequency oscillator 3, a group 1
! If the pressure inside the pipe is a suitable pressure of about 10 Torr, this release is possible! A non-polar discharge is generated in the tube to generate discharge plasma 9
generate. Currently, monosilane (SIH) is used as the discharge gas.
, ) and nitrogen (N) are introduced and the substrate 6 is heated to about 300 to 400 DEG C. by a heating means (not shown), thereby depositing a silicon nitride (Si, H,) film on the substrate.

Figure 2 shows another conventional deposition device as well! Show the cause. 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 of an etching apparatus using plasma 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. From the gas introduction hole 2, for example, Freon gas (CF4
) and oxygen (Ol) gas at an appropriate pressure to generate discharge plasma 9
If fluorine ions are generated, the silicon substrate and silicon oxide film will be etched by the fluorine ions. is introduced into the vacuum chamber 5. A processing substrate 6 is attached to and held by one electrode 10, and plasma 9 is generated by a discharge caused by 7 Leon gas introduced at an appropriate pressure between the electrode 10 and the grounded electrode 11.

Since the discharge is a high frequency discharge (several M to several tens of MHz) 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. This causes general sputtering, but if the discharge gas is reactive, for example, energetic fluorine ions react with the substrate, causing reactive sputtering and 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 emphasis on 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 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.

Figure 5 corresponds to Figure 3 in terms of discharge format.

The plasma 9 formed within the vacuum container 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, 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. .

FIG. 5 (■) corresponds to FIGS. 2 and 4 in terms of the 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 is higher than the ground potential through the sheath, and the plasma potential Vg
The potential corresponds to . Therefore, if a substrate is placed on the ground-side electrode 11 in Figure 5), ions arrive with ion energy Vs (usually less than a few volts) corresponding to the potential of this plasma, both in the case of deposition and in the case of etching. do.

On the other hand, the 10 high-frequency electrodes in FIG. 5(G) are connected to the oscillator 3, so the output voltage waveform of this oscillator is now V.

If it is expressed as sin (k)t, then the potential of this electrode 10 is . It changes by 5inQ1t. Here ■.

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 wave of yosinQ't is applied to the plasma 10, the potential of the plasma 9 remains at Vs on average. However, in reality, the voltage of the electrode 10 is V. Since the voltage changes with a sinusoid, the sheath between the electrode 10 and the plasma 9 increases or decreases to maintain the potential difference between Prada i and the electrode. Therefore, it is highest when the potential of electrode 10 becomes -v0 (V00Vg)
Ions arrive from the plasma with the energy of

Since vo is typically on the order of several hundred volts, the substrate held on the electrode 10 is bombarded with ions with energies of up to several hundred volts. Therefore, when performing normal deposition, the substrate is held on the ground side electrode as shown in Figure 2.
When sputtering is performed by making the energy ion of 8 arrive, the substrate is held by the electrode on the high frequency side,
The ions are made to arrive with an energy of (V 3 10V,).

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

Same as the case in FIG. 5 (g) (the plasma potential is equal to Vs, and ions with energy of Vs arrive on the electrode 11. Looking at the other high frequency electrode 10, this is the high frequency [410 is covered with an insulator so that it does not come into direct contact with the plasma.Therefore, the plasma has a so-called tube wall potential V.The potential of this insulator also changes with VosinQ)t, so the maximum ( V0+V
Ions with an energy of w ) 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 deposition shown in FIGS. 1 and 2, the deposition energy is determined by the potential 8 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 Figure 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 etching ions is determined by the high frequency voltage v0 of high frequency oscillation, and this high frequency voltage is the voltage necessary 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 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 restrictions 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, defects may be formed on the substrate due to collisions and sputtering may occur.

Furthermore, in the configuration shown in FIG. 4 considering the case of etching, 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 a reactive gas (such as 7 Leon) is used as the discharge gas and etching is performed by causing reactive sputtering, an ion energy of several hundred volts is not necessary, and such a high voltage can cause local etching. When carrying out this process, difficulties arise because the mask is etched by sputtering and the substrate temperature increases.

When performing reactive sputtering, the ion energy may in principle be at a value that promotes the chemical reaction, and the value is also preferably in the range of several volts to several tens of volts.

As can be seen from the above considerations, in an apparatus that generates plasma using high-frequency discharge and performs deposition or etching, it is possible to have ions arrive on the substrate with controlled energy ranging from several volts to several tens of volts. If you can,
Significant advances can be made in this 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 vT, a target positive potential is applied to the discharge electrode, or a globe is inserted into the plasma. An invention is described in Japanese Patent Application Laid-Open No. 53-68171 in which a specific positive potential is applied to plasma and ions are caused 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 deposition film, so that 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 addition, in order to protect the etched substrate from surrounding contamination, the upper and lower 11 poles were imitated with quartz plates, and the substrate was placed on a tetrafluoroethylene plate to promote chemical reactions. In recent years, a method of insulating the substrate from ground potential has become popular; in such cases, applying a potential is also ineffective.

In other words, the configuration is as shown in Figure 5. In this case, even if a direct current potential is applied to the plasma, the substrate is insulated from the ground potential, so the entire substrate is positively charged, and the plasma potential 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 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 container, and a magnetic field created in the vacuum container by the coaxial electromagnet,
The apparatus is characterized in that it comprises means for arranging a substrate to be processed in the vacuum chamber, and means for applying an alternating current to the substrate in order to control the energy with which ions in the plasma reach the substrate.

Furthermore, according to an embodiment of the present invention, the coaxial electromagnet is configured from a plurality of coaxial electromagnets arranged overflowing in the axial direction, so that the strength of the axial magnetic field by the coaxial electromagnet can be adjusted to It is characterized by being constructed so that it becomes weaker from the front surface side toward the back surface side 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 substrate is evacuated from the back side.

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 type plasma device shown in Fig. 6 is
This is a configuration in which a low-frequency oscillator 12 for control is newly connected to the configuration shown in FIG. This low frequency oscillator 120 frequency is 3
Assume that the frequency of the high-frequency oscillator is sufficiently lower than the frequency of the high-frequency oscillator. To prevent leakage, it is necessary to make the output of the low frequency oscillator high impedance from the high frequency side, such as by passing it 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, to simplify the explanation, the so-called tube wall potential between the plasma and the insulating container is ignored. ABC + as shown in Rin 7
When a rectangular potential of v0 is applied, the 10 electrodes in FIG.
. Therefore, the potential of the substrate 60 rises to AK as shown by the dotted line due to charging by ions from the plasma, and becomes equal to +v0 of the electrode potential at K. In this case, the plasma also rises to a potential of +v0 like the substrate. This potential is lowered between KC and then the potential of the electrode is CDE and -V0
When the substrate reverses to
ME's "Group -■. Gulps. Next, the electrode potential becomes -v0 again.
When EFG changes from +v0 to +v0, the potential of the substrate becomes gN
Between P and +V0, +V0 is between PG (this is repeated hereafter).

Therefore, ions arrive at the substrate only while the potential of the electrode, which is sufficiently charged by electrons during ME and exhibits a value of -V0, is reversed to EFG and +V0 and is rising from ENP and -vo to +v0. It will be done. Therefore, the energy of the arriving ions is +V, 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 2 during ENP.
■. It changes to 0 electron volts.

FIG. 8 shows a case where ABCDgFGHI and a sine wave are added instead of the rectangular wave. The potential of the substrate changes in a sine waveform of AB CD'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, the electrode potential is +V from -v0. The energy is 2v0 between D'E'F' along DEF which changes to
From 01 [arrive at child bolt.

In this way, ions flow into the substrate between ENP in FIG. 7 and D'E'F' in FIG.
. The amount of changes. In the above discussion, we have ignored the so-called tube wall potential Vw that the plasma has with respect to the tube wall, which is an insulator, as described above. When this effect of Vw is included, the board becomes V
From W, ions with energy between (2v0 and Vw) arrive. Therefore, if ions with energy higher than VT are effective for reactions against the target substrate, then (VT > VW) Noj11%, (2V0
Particles with energies of 10 Vw-Vt) are useful for certain purposes in plasma processing of substrates. This energy must not be unlimited, and must be below the maximum value of 7M, considering substrate damage and reaction cross-section. Therefore, VM , >2 V0+Vw >VT ”” (
1) is established, and the peak value vo of the sine wave alternating current can be selected independently of the high frequency of the discharge reservoir that creates plasma using the rectangular wave applied in this way.

Now in Figure 7, the potential of the square wave applied to the electrode is DM
+V of FG from -v0 of. As described above, ions arrive at the substrate while the substrate potential increases to ENP. In this case, if the thickness of the ion sheath formed by the potential difference of 2vo is d0, the mass of the ion is M0, and the charge of the ion is e, then the time t for the ions to arrive at the substrate from the plasma at the end of the sheath is given by the following equation: .

Now 2V0 = 50V, d6 = 0.5cm, e = 1.6
Assuming Mo with a mass number of 40 and XIO-"-coulombs, it becomes t -6,4 Then, this t is the period T of the rectangular wave to be applied.
It is efficient to set it to 1/2 of that. On the other hand, the energy of the arriving ions is 2■.

and O, of the ions arriving at the substrate, Vt
Only ions with energy above, that is, ions that arrive between 3J and 3J when the potential of the substrate is v<2 Vo -Vt "", will work effectively for the purpose of this invention. Now assuming that 2V0 = 50V and Vt = 20V. , it acts effectively until the substrate potential reaches 30 V according to the third equation. Therefore, when a square wave is applied as in the seventh case, in the above example, the ions arrive at the substrate at about 1/2 of the ENP. Although this is not effective in this case, it depends on the relative values of vT and Vo, that is, when vT is small and vo is large, a large area can be effectively used. The argument is exactly the same when adding a sine waveform as shown in the figure.
In the figure, the usable region is determined by the relative values of vT and vo according to the relationship of the third equation during the period during which ions arrive at the substrate of D'E'F'.

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.

As mentioned in the above discussion, we added a high-frequency power source for the main discharge and a power source for controlling the ions in the plasma generated by this discharge to effectively control the energy. If the frequency of the power source is set to a low frequency so that the ions in the plasma can follow it,
As shown in Figure 6, in order to protect the electrodes and vacuum chamber constituents from contamination, and for the purpose of some kind of chemical reaction, the substrate is completely placed in an insulating container, and a discharge gas is placed inside the container. In this structure, ions of a specific energy can be delivered onto the substrate to process 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

The inventor of the present application has confirmed that using such a parallel plate type plasma processing apparatus, it is possible to control the energy with which ions in the plasma reach the substrate to be processed using an AC power source that is separate from the high-frequency power source that serves as the plasma generation source. . Therefore, the inventor of the present invention considered applying this principle to a plasma processing apparatus 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 container is surrounded by a coaxial electromagnet 15, in which a gas source 16 is positioned, and an appropriate amount of gas is introduced through a discharge gas introduction hole 17, and a discharge means (not shown), such as a direct current This plasma is discharged by arc discharge, microwave discharge, etc. and generates plasma No. 18. This plasma flows out from the plasma outlet hole No. 19 as a plasma flow No. 20, forms a plasma flow, and is transferred to the collector (substrate) No. 21.
arrive at. If the plasma flow includes a deposition material, the material will be deposited on the substrate 21, and if the plasma flow includes an etching component, the substrate will be etched. The basic configuration before this invention was applied was disclosed in Japanese Patent No. 611184 (Japanese Patent Publication No. 45-38801).
No. 2). This patent clarifies the operation of each part of the above-mentioned basic configuration. That is, the ninth
In the figure, a plurality of coaxial electromagnets 15 arranged along the axial direction are configured to weaken the strength of the magnetic field in the axial direction from the front side of the substrate 210 to the back side of the substrate, and this magnetic gradient is From the plasma source 16 to the substrate 21
A plasma flow is formed towards the The reason why the coaxial electromagnet 15 is divided in this way is to provide a magnetic field gradient.

And, in accordance with the present invention, in order to control the energy with which ions in the plasma stream 20 arrive at the processing substrate 21,
A controllable potential is applied to the plasma stream 20. That is,
If an AC power source 22 with a frequency that the ions can follow is placed between the plasma source 16 and the substrate 21, ions with controlled energy can be made to reach the substrate in accordance with the above discussion.

In particular, similar to the above-mentioned parallel plate method, if the material deposited on the substrate 21 is an insulating material or a high-resistance material, or if there is an insulating film on the substrate, or if there is a need to protect the substrate itself, Even if the substrate is insulated, ions can be made to reach the substrate with the above-mentioned controllable energy.

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 applying the present invention 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. can have a stimulatory effect such as increasing the amount of

[Brief explanation of the drawing]

FIGS. 1 and 2 are block diagrams of a conventional deposition apparatus using plasma generated by high-frequency discharge, and FIG. Fig. 4 is a block diagram of a conventional etching apparatus using plasma generated by high-frequency discharge, and Fig. 5 (A), 03), (Q
is a configuration diagram for explaining the operating principle, which categorizes the configurations from Fig. 1 to Fig. 4 into three types in order to explain the operating principle from the operating principle.
Figure 6 is a block diagram of the plasma device devised at the study stage of the present invention, and Figure 7 shows the low frequency rectangular wave to be applied to the configuration of Figure 6, and the potentials of the electrodes and substrate that occur when this is applied. FIG. 8 is an explanatory diagram of the low frequency sine 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. 9 is a diagram of the plasma flow according to the present invention. FIG. 1 is a configuration diagram of a plasma processing apparatus using a transportation method and an explanatory diagram when the present invention is applied thereto. DESCRIPTION OF SYMBOLS 1... Discharge tube, 2... Gas introduction hole, 3... High frequency oscillator, 4... Inductively coupled discharge coil, 5... Vacuum container, 6... Processed 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. Figure 6 B Figure 8

Claims (5)

[Claims] (1) 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 discharge space within the vacuum vessel surrounded by the coaxial electromagnet. plasma generation means for turning discharge gas into plasma by discharge; means for arranging a substrate to be processed within a magnetic field created within the vacuum container by the coaxial electromagnet; and ions in the plasma. means for applying an alternating current to the substrate in order to control the energy reaching the substrate. (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 controlled from the surface side of the substrate to be processed. 2. The plasma processing apparatus according to claim 1, wherein the plasma processing apparatus is configured to become weaker toward the back side. (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.