JPS6235265B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a processing method using plasma and a processing apparatus therefor in a semiconductor device manufacturing process, and more particularly to a processing method and processing apparatus using a plasma flow transport method. .

First, the principle of the plasma flow transport method and its equipment will be explained. FIG. 1 is an explanatory diagram of the principle of a conventional plasma flow transport method. The vacuum container 1 is evacuated to a high vacuum through a vacuum exhaust hole 2 by a vacuum exhaust device (not shown). A plasma source, which is a plasma generation chamber 3, is placed in this chamber, and a neutral gas (marked with a circle) is introduced through a neutral gas introduction hole 4 to a pressure suitable for plasma generation (~10 ^-2 Torr), and a discharge means (not shown) is introduced into the chamber. Plasma (ⓓ mark) 8 is generated in the plasma source by, for example, high frequency discharge, microwave discharge, low voltage discharge by a thermal filament). The generated plasma is
Plasma outflow hole 5 drilled at one end of the plasma source
Due to the difference in plasma density between the inside and outside of the plasma source, the plasma flows out by diffusion at the speed of thermal movement in the vacuum container. Therefore, it diverges into the vacuum container and hardly reaches the collector 6 located at one end of the vacuum container. When a coaxial air-core electromagnet 7 is installed outside the vacuum vessel and a coaxial magnetic field is applied to the vacuum vessel, the divergent plasma is focused and reaches the collector 6 as a plasma stream 9.

Now, let n _p be the plasma density at the plasma source outflow hole 5, Z be the distance between the outflow hole and the collector, B be the strength of the magnetic field, K be the constant related to plasma, and n be the plasma density on the collector, then n is as follows. It is given by the formula.

n=n _p (1-KZ/B ² ) (1) In this equation, when B is increased, the second term becomes 0.
, so n≒n _p (2) holds true. The plasma density n _p of this plasma source
The fact that n became equal to the plasma density on the collector is interpreted to mean that the plasma in the plasma source was transported to the collector as a plasma flow, and that the plasma in the plasma source was formed by the flux of the coaxial magnetic field. It is also interpreted that the plasma flowed through the magnetic field pipe to the collector at a thermal velocity.

Specific inventions have been devised regarding the operation and configuration of this plasma flow transport device, and its application to semiconductor devices. It has also been confirmed that a silicon nitride film was deposited, and that a photoresist film was removed by an oxygen plasma stream and a polycrystalline silicon film was etched by a carbon tetrafluoride (CF ₄ ) plasma stream. The configuration and operation of the apparatus as shown in FIG. 1 is called the first mode of the plasma flow transport method. However, this first mode has various limitations. For example, in order to form a plasma flow of silicon or silicon nitride, the neutral gas introduction hole 4 in Fig.
When monosilane gas (SiH ₄ ) or monosilane gas and nitrogen are introduced as a neutral gas for discharge and plasma is generated by discharge to form a plasma flow, a large amount of silicon film or silicon nitride film is formed on the inner wall of the plasma source. Because they are deposited at the same time and often require cleaning, and because the silicon oxide film is deposited, if monosilane gas and oxygen are introduced as neutral gases, the monosilane gas and oxygen will react before generating a discharge and forming plasma, resulting in oxidation. The point is that it is not possible to obtain a silicon plasma flow.

A device configuration and operation method called the second mode was devised to eliminate these constraints.
The figure is an explanatory diagram thereof. The structural feature of this system is that a charge exchange chamber 10 is provided for the three plasma sources, and these are connected by a plasma drift tube 11. In operation, plasma generated in the plasma source 3 (referred to as primary plasma) is guided to the charge exchange chamber 10 by the plasma drift tube 11 as 12 plasma flows (referred to as primary plasma flow). Neutral gas introduction hole 1 to this charge exchange chamber
When the neutral gas is introduced from step 3, charge exchange (also called charge transfer) occurs between the introduced primary plasma flow and the neutral gas, and inside the charge exchange chamber, the primary plasma flow and the newly charged Secondary plasma, which is a mixture with ions generated from the exchange, is generated. This secondary plasma is transported from the plasma outflow hole 14 to the collector 6 as a secondary plasma flow 15. This second
The configuration and operation shown in the figure is called the second mode. Specifically, if nitrogen plasma is used as the primary plasma flow and monosilane gas is used as the neutral gas, a secondary plasma flow of silicon nitride can be obtained. , when a silicon nitride film is formed on the silicon wafer on the collector, and monosilane gas is used as the neutral gas and oxygen plasma is used as the primary plasma flow,
It has been found that a silicon oxide plasma stream is obtained and also deposits a silicon oxide film on the collector silicon wafer. Furthermore, by using helium plasma as the primary plasma flow and introducing cadmium or magnesium metal vapor as a neutral gas into the charge exchange chamber, a secondary plasma flow of these metals is obtained, and cadmium or magnesium is deposited on the silicon wafer of the collector. It has been confirmed that a magnesium metal film is deposited.

As mentioned above, plasma flow transport methods include first mode and second mode operation methods and device configurations, and each has been proven to have its own features and effects.As a result of more detailed research, plasma flow The present inventor has discovered that there is an operation and device configuration called a third mode in the transportation method. The operation and device configuration of this third mode constitute the main subject of the present invention, and an explanatory diagram thereof is shown in FIG.

In the figure, a neutral gas introduction hole 4 is inserted into the plasma source 3.
A gas pressure suitable for plasma generation is introduced through the pump to generate primary plasma, and as shown in the figure, a plasma flow 16 is generated and reaches the surface of the collector 6. At the same time, when a neutral gas 18 is introduced at a constant pressure into the vacuum vessel 1 through the neutral gas introduction hole 17, on the surface of the collector 6, a substance is supplied by diffusion from the introduced gas 18, and a plasma flow 1
7 is supplied with plasma. As a specific example, consider the deposition of a silicon film on the collector surface. As the primary plasma, an inert gas such as helium (He), neon (Ne), argon (Ar), krypton (Kr), or xenon (Xe) is used. Monosilane (SiH ₄ ) gas is used as a neutral gas for depositing the introduced silicon film. The monosilane gas that has arrived on the collector surface by diffusion receives energy from radicals (states of high internal excitation of atoms and molecules) generated by the inert gas plasma transported by the plasma flow, and is separated into silicon and hydrogen. Deposit as a silicon film on the wafer.
In other words, the role of this inert gas plasma flow is to cause a plasma chemical reaction by supplying radicals to the collector surface and the space in its vicinity, although it does not itself participate in film formation as a deposition material. It has also been found that the action of radicals caused by this inert gas is particularly strong for helium and neon, which have a high ionization voltage. In this case, if an arbitrary deposition is given to the primary plasma flow, the ions in the arriving plasma will arrive on the substrate with the given deposition energy, increasing the decomposition efficiency of monosilane gas, but causing sputtering on the collector. In this case, the bonding energy is preferably 30ev or less, which is lower than the bonding energy of silicon. In this case, if the wafer on the collector is heated to about 300℃ or higher,
The deposited silicon atoms move more easily on the wafer, resulting in a smooth and uniform deposition film without pinholes. In addition, by appropriately selecting the plasma potential and wafer temperature mentioned above, the crystalline state of the deposited silicon film can be changed from amorphous to polycrystalline, using the effect of making it easier for silicon atoms to move on the silicon wafer.
It can be controlled into a single crystal.

If we consider the above numerically, we get the following. If the density of the neutral gas (monosilane) just introduced in the vacuum container is N, and the diffusion rate is _VN , then the number of neutral gases (monosilane) supplied per unit area on the collector surface, D ₁ , is given by the following formula: Given.

D ₁ = 1/4Nv _N (3) On the other hand, the intensity of the plasma flow per unit area of the plasma outlet hole 5 is n, since this plasma flow moves at the thermal diffusion rate v _p within the plasma source, assuming that the plasma density is n _p . It is given by _p v _p . In addition, this plasma flow passes through a neutral gas of density N for a distance Z,
When the charge exchange cross section with the neutral gas arriving at the collector is σ, the intensity D ₂ per unit area on the collector is given by the following equation.

D ₂ = n _p v _p e ^- 〓 ^NZ = e ^- 〓 (4) Here, λ is the mean free path and is given by (σN) ^-1 . The neutral gas, which is newly ionized by this charge exchange, is transported to the collector together with the primary plasma as a secondary plasma flow. Since the amount D ₃ transported to the collector is equal to the amount of decrease in the primary plasma, D ₃ is given by the following equation.

D ₃ = n _p v _p e (1-e ^- 〓 ^NZ ) = n _p v _p (1-eZ/λ (5) In order to numerically consider the supply state of the material from the above equation, n _p = 5 ×10 ¹¹ cm ^-3 , v _p =1 × 10 ⁵ cm・
sec ^-1 , v _N =5×10 ⁴ cm・sec ^-1 , Z=50cm, σ=
Assuming 1×10 ^-14 cm ^-2 to 1×10 ^-15 cm ^-2 and the degree of vacuum due to the introduction of neutral particles to 1×10 ^-4 Torr, N=4
×10 ¹² cm ^-3 , so D ₁ = 5 × 10 ¹⁶・cm ^-2・sec ^-1 , D ₂ = 1 × 10 ¹⁶ ~
4.25×10 ¹⁶ cm ^-2・sec ^-1 , D ₃ =4×10 ¹⁶ ~7.75×
10 ¹⁵・cm ^-2・sec ^-1 is calculated. This D ₃ secondary plasma flow component is deposited on the collector surface or acts as new radicals. All the radicals due to the flow rate D ₂ of the plasma flow that now arrive at this collector surface contribute to the decomposition of monosilane gas,
Considering that this is all a deposit,
Since the D ₃ component is expected to partially contribute to the deposition, the growth of the deposition film is calculated to be 0.5 μm per minute per unit area. As described above, according to this method, a very high deposition rate can be achieved due to the action of radicals caused by plasma flow transport onto the collector.

Although the deposition of a simple silicon film has been exemplified above, the same applies to a compound film. For example, regarding the deposition of silicon nitride, as described above, an inert gas plasma flow may be used as the primary plasma flow, and a mixed gas of monosilane gas and nitrogen may be used as the neutral gas. Further, in order to impart tensile properties to the silicon nitride film, hydrogen may be added to the ammonia gas so that hydrogen is contained in the deposited film. It should be noted here that the primary plasma flow should not be limited to inert gas only; a nitrogen or ammonia plasma flow may also be used as the primary plasma flow to form the silicon nitride. Furthermore, a plasma flow containing a mixture of an inert gas and nitrogen or ammonia may be used. These must be determined based on the strength of radicals upon arrival at the collector, deposition speed, film quality, etc. Furthermore, in this case, when deposition is added to the primary plasma flow, components of the film structure arrive on the collector with the energy of the deposition, thereby further improving the efficiency of radical action. Furthermore, by heating the silicon wafer on the collector, the entire deposited film becomes smooth without pinholes.

As another example, when a mixed gas of titanium tetrachloride (TiCl ₄ ) and oxygen is used as the neutral gas, titanium oxide (TiO ₂ ) is deposited, but in this case, as the primary plasma flow, the same as in the above example is used. Other oxygen plasmas of inert gases or mixed plasmas of inert gases and oxygen may also be used. As yet another example, in the case of silicon oxide film (SiO ₂ ) deposition, when monosilane gas and oxygen are mixed,
Since the reaction occurs as it is, monosilane gas is used as the neutral gas, and oxygen or a plasma containing an inert gas and oxygen is used as the primary plasma. In this case, sufficient reaction cannot occur unless the amount of material supplied by the neutral gas is smaller than the amount of oxygen transported as a plasma flow, so care must be taken with the relationship between these amounts.

In the above film deposition, when it is desired to contain a specified impurity, for example, when it is desired to contain phosphorus (P) in a silicon film or a silicon oxide film,
A phosphorus compound gas such as osphine (PH ₃ ) or phosphorus trichloride (PCl ₃ ) may be added to the neutral gas or primary plasma flow. If boron (B) is desired to be included, diborane (B ₂ A boron compound gas such as H ₆ ) or boron trichloride (BCl ₃ ) may be added. The same applies to other impurities.

I have explained the deposition above, and carbon tetrafluoride (CF ₄ ) gas is introduced as a neutral gas.
When an inert gas plasma flow is used as the primary plasma flow, carbon tetrafluoride decomposes into radicals on the collector, generating fluorine radicals, which destroy the polycrystalline silicon film deposited on the silicon substrate of the collector. or etching the silicon nitride film. In this case, naturally, fluorine radicals generated by the secondary plasma flow generated by charge exchange are also added to the etching process. Furthermore, as in the case of the above-mentioned deposition, even if a mixed gas of inert gas and carbon tetrafluoride is used in the primary plasma flow, the effect is large.
In addition, when only carbon tetrafluoride gas is used as the primary plasma flow, it looks similar to the first mode of plasma flow transport method, but in this third mode,
The second plasma flow generates more fluorine radicals on the collector, thereby increasing the etch rate. Also in this case, the addition of 5-10% of oxygen, both as a neutral gas and as a primary plasma stream, further increases the etching rate. In addition, adding deposition to the primary plasma stream not only increases the amount of fluorine radicals on the collector, but also adds energy to the area where spatter occurs, sputtering the reaction residue on the etched surface and exposing a new surface. This further increases the etching speed.
Heating the silicon wafer on the collector to be etched further accelerates the reaction and increases the etching rate. The (CF ₂ ) radicals in the decomposition products of carbon tetrafluoride are effective for etching silicon oxide films (SiO ₂ ), but this is because the F radicals that are generated at the same time usually etch silicon. The etching ratio of silicon is about 1:3. When 20% to 40% hydrogen is mixed in to suppress the action of F radicals, CF ₂ radicals work well and the above ratio can be reversed to 10:1. Carbon tetrafluoride (CCl ₄ ) and boron trichloride (BCl ₃ ) are used for etching aluminum (Al), and these can also be used in the same manner as described above. In addition, sputtering the etched surface by applying a potential to the primary plasma flow is effective in removing aluminum oxide (Al ₂ O ₃ ) naturally formed on the aluminum surface at the beginning of etching, and then sputtering the etched surface with trichloride. It is effective not only for removing aluminum by evaporation but also forcibly removing it by sputtering. Particularly when etching aluminum containing copper, removing copper spatter is effective in promoting the etching reaction.

Although the above explanation has mainly focused on the deposition and etching of inorganic substances and inorganic compounds, the operation in this third mode is also effective for the deposition and etching of organic substances. Regarding the deposition of organic films, for example, when ethylene gas (C ₂ H ₄ ) or tetrafluoroethylene gas (C ₂ F ₄ ) is introduced into a vacuum container and plasma is applied, a polyethylene film (C 2 F 4 ) is deposited on the collector _. H ₄ ) _o or polytetrafluoroethylene film (C ₂ F ₄ ) _o can be formed by polymerization. Regarding etching of organic films, the simplest method is to combine carbon and hydrogen, which are organic components, with oxygen. Therefore, when oxygen is introduced into a vacuum container and treated with a plasma flow, oxygen radicals are generated, which combine with carbon and hydrogen in organic matter to produce carbon dioxide and water, thereby etching the organic matter. . In order to locally etch an organic film, a metal film such as aluminum or an inorganic film such as silicon oxide may be suitable as a mask.

The generation of secondary plasma and radicals by this method has been explained above as an effect of ion components in the plasma flow. In addition to ionic components, there are also electronic components in the plasma flow, which maintains electrical neutralization as a whole. Now, if electrons have sufficient energy to ionize or decompose neutral gas, it is possible to consider the generation of secondary plasma and radicals by these electrons. The component of this electron is largely related to the plasma generation method in the plasma source, such as a discharge that has a discharge component in the direction of the plasma transport axis.
For example, in the case of plasma generation using discharge caused by a coaxial magnetic field from a thermal filament, this value is considered to be non-negligible, but in the case of plasma generation that has a discharge component perpendicular to the transport axis direction due to microwave discharge, it can be omitted. It is considered to be of a certain degree.

As described above, the third mode of operation of this plasma flow transport method has a much more effective effect on material deposition and etching than the first and second modes. The basic operation and device configuration of this third mode are shown in FIG. 3, and the specific device configuration is shown in FIG. 4.

In Fig. 4, 19 is a magnetron oscillation tube,
Microwaves that cause discharge in a plasma source are supplied from an antenna 20 to a waveguide 21 . The microwave propagates through the waveguide and is supplied to a discharge tube 22 made of quartz. A pressure suitable for gas discharge for primary plasma generation is introduced into the discharge tube 22 through the gas introduction hole 23, and discharge is started due to the applied microwaves. Reference numerals 24, 25, and 26 are coaxial air-core electromagnets for transporting plasma flow, and in particular 24 causes electron cyclotron resonance in the discharge tube together with the transport magnetic field to increase plasma density. The primary plasma generated using this discharge tube as a plasma source passes through a plasma drift tube 27 and reaches a silicon wafer 29 placed on a collector 28 as a plasma stream. Reference numeral 30 denotes a probe located at the plasma outflow hole which becomes the outlet of the plasma drift tube 27, and applies voltage to the probe 30 through a hermetic seal 31 to give a predetermined potential to the plasma flow. Reference numeral 32 denotes a vacuum vessel which is evacuated through a vacuum exhaust hole 33 by a vacuum exhaust pump (not shown), and a predetermined amount of neutral gas is introduced into the vacuum vessel through a neutral gas introduction hole 34. Magnetic shielding plates 35 and 36 prevent coaxial magnetism from leaking to the outside. In this way, when this device is operated, the plasma flow flows through the center of the coaxial transport magnetic field and reaches the collector 28.
Since only the center of the upper wafer 29 is reached, the deposition occurs only near the center of the wafer. For this purpose, a triangular wave current is applied to a pair of coaxial electromagnets 37 and 38 and a pair of coaxial electromagnets 39 and 40 at right angles thereto to periodically change the generated magnetic field, and to direct the plasma flow in the X direction (horizontal direction). By scanning in the Y direction (vertical direction), the surface of the arriving wafer can be uniformly scanned, and the deposition on the wafer can be uniformly performed. The same applies when this apparatus is used for etching. Although not shown in FIG. 4, if a means for automatically inserting and removing wafers is added, and an automated heating device is added to the collector 28, the ability of the plasma processing apparatus to automate both deposition and etching can be demonstrated. can do.

As mentioned above, the plasma flow transport method operates in three modes: the first mode, the second mode, and the third mode, and this application relates to the third mode, but when considered as an apparatus, It is possible to consider a device that can operate in any of these three modes. FIG. 4 is an explanatory diagram of a device that can operate these three modes with the same device. The plasma source 3 has four gas introduction holes, and when used in the first mode, the other gas introduction holes are do not use. The generated plasma flow passes through the charge exchange chamber 11 of the plasma drift tube 10, flows out from the plasma outlet hole 14 as a plasma flow, and reaches the collector 6. When used in the second mode, a neutral gas for charge exchange is introduced from the neutral gas introduction hole 13 into the charge exchange chamber 10, and the charge is exchanged with the primary plasma flow flowing from the plasma source 3 through the plasma drift tube 11. This is performed to form secondary plasma, which flows out as a secondary plasma stream from the plasma outflow hole 14 and reaches the collector 6. When used in the third mode, as in the first mode, the primary plasma flow is made to flow out through the plasma outflow hole 14, and at the same time, a neutral gas is introduced into the vacuum chamber 1 through the neutral gas introduction hole 17, and this neutral gas is The diffusion of the target gas causes the target gas to arrive at the collector 6, as well as the primary plasma flow to arrive at the collector 6. As described above, in this case, secondary plasma is generated by charge exchange as the primary plasma flow passes through the neutral gas, and this also arrives at the collector together with the primary plasma flow. The coaxial air-core electromagnet 7 outside the vacuum chamber 1 acts as a plasma flow transport magnetic field in both modes.

The first mode, second mode shown in FIG. 4,
The specific device configuration for common use in the third mode is to connect a charge exchange chamber indicated by a dotted line 41 to the plasma drift tube 27 in FIG. What is necessary is to allow more primary or secondary plasma to flow out.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the operation and configuration of the first mode in the plasma flow transport method, Figure 2 is an explanatory diagram of the operation and configuration of the second mode in the plasma flow transport method, and Figure 3 is the main points of the present invention. An explanatory diagram of the operation and configuration of the third mode in the plasma flow transport method, FIG. 4 is a configuration diagram of an apparatus for specifically performing the operation of the third mode, which is the main point of the present invention,
Figure 5 shows the first mode and the second mode of the plasma flow transport method.
FIG. 2 is an explanatory diagram of a device configuration that allows the same device to perform operations in either mode or third mode. 1... Vacuum vessel, 2... Vacuum exhaust hole, 3... Plasma source, 4... Neutral gas introduction hole, 5... Plasma outflow hole, 6... Collector, 7... Coaxial air-core electromagnet, 8... Primary plasma, 9... Primary plasma flow, 10... Charge exchange unit, 11... Plasma drift tube, 12... Primary plasma flow, 13... Neutral gas introduction hole, 14... Plasma outflow hole, 15...
Secondary plasma flow, 16...Primary plasma flow, 17
...Neutral gas introduction hole, 18...Neutral gas, 19...
...Magnetron oscillator tube, 30...Antenna, 21
... Waveguide, 22 ... Discharge tube, 23 ... Neutral gas introduction hole, 24, 25, 26 ... Coaxial air-core electromagnet,
27... Plasma drift tube, 28... Collector, 29... Silicon wafer, 30... Probe, 31... Probe introduction part, 32... Vacuum horizontal outer wall, 33... Vacuum exhaust hole, 34... Neutral gas Introduction hole, 35, 36... Magnetic shielding plate, 37, 38...
Y direction scanning electromagnet, 39, 40...X direction scanning electromagnet, 41...Charge exchange unit, 42...Neutral gas introduction hole, 43...Plasma outflow hole.

Claims (1)

[Claims] 1. In a plasma flow transport method in which plasma generated in a plasma generation chamber is transported as a plasma stream to a collector in a vacuum container using a magnetic field, the plasma generation chamber and the vacuum container in which the collector is installed are separately provided. A plasma characterized by introducing a gas and causing a plasma reaction that decomposes or polymerizes the gas in the vacuum container by the action of radical atoms and molecules generated from the plasma flow on and near the collector. Processing method. 2. Using an inert gas as the gas introduced into the plasma generation chamber, a gas containing the substance to be deposited is introduced into the vacuum container, and by the action of radical atoms and molecules generated from the plasma flow on and near the collector, The plasma treatment according to claim 1, wherein a plasma reaction such as decomposition or polymerization of the gas containing the substance to be deposited is caused, and a film of the target substance is deposited on the collector or a wafer positioned on the collector. Method. 3. The plasma processing method according to claim 1, wherein a predetermined potential is applied to the plasma flow to improve reactivity. 4. The plasma processing method according to claim 1, wherein the collector is heated to improve reactivity. 5. The plasma processing method according to claim 1, wherein a gas containing a part of the deposition material or a mixed gas of this and an inert gas is used as the gas introduced into the plasma generation chamber. 6. The plasma processing method according to claim 1, wherein the plasma flow is scanned by magnetic means. 7. Using an inert gas as the gas introduced into the plasma generation chamber, the gas containing the etching substance is introduced into the vacuum container, and the etching substance is removed on and near the collector by the action of radical atoms and molecules generated by the inert gas. 2. The plasma processing method according to claim 1, wherein a plasma reaction is caused to decompose a gas containing a gas, and a material on a collector or a wafer placed on the collector is etched. 8. The plasma processing method according to claim 7, wherein a gas containing an etching substance or a mixed gas of an etching substance and an inert gas is used as the gas introduced into the plasma generation chamber. 9 In a plasma flow transport device configured to transport plasma generated in a plasma generation chamber as a plasma stream through a magnetic field pipe to a collector in a vacuum container, a method for introducing neutral gas into the vacuum container in which the collector is installed is provided. A plasma processing apparatus having a neutral gas introduction means. 10 Claim 9 comprising magnetic scanning means for uniformly scanning the plasma stream over the collector
The plasma processing apparatus described in Section 1. 11. The plasma processing apparatus according to claim 9, which includes a heating device for heating the collector. 12 In order to perform any of the first mode, second mode, and third mode of the plasma flow transport method, a charge exchange chamber is connected to the plasma outlet hole of the plasma processing apparatus, and a neutral gas supply means is connected to the charge exchange chamber. 10. A plasma processing apparatus according to claim 9, wherein the plasma processing apparatus is provided with: