JP4623932B2 - Plasma processing equipment - Google Patents

Description

  The present invention relates to a plasma processing apparatus or method, and more particularly to generating a plasma in a first chamber, allowing diffusion of product ions and free radicals into a second chamber, and etching a silicon wafer or other workpiece in the second chamber. Alternatively, the present invention relates to a plasma processing apparatus or method for performing vapor deposition. The concept is to separate the plasma source and the processing chamber.

It is often advantageous to generate a high density plasma and increase the number of free radicals that can be used to speed up the required etching or deposition chemical treatment. However, in general, when generating a high density plasma, a large number of ions are generated in addition to a large number of free radicals, which leads to undesirable effects such as damage to the wafer or other workpiece.
US Pat. No. 5,501,893 US Pat. No. 6,051,503 International Publication No. 00/036631 Pamphlet Boswell and Porteous, "Etching in a pulsed plasma", Journal of Applied Physics, American Institute of Physics, (October 15, 1987), Volume 62, Issue 8, pp. 3123-3129

  One object of the present invention is to provide an apparatus capable of controlling the ratio of free radicals to ions so as to reduce the ratio of ions reaching the workpiece.

According to one aspect of the present invention, a first chamber provided with plasma inducing means designed to generate plasma therein, a second chamber in which the generated plasma diffuses and acts on the workpiece, and plasma inducing means A magnetic field generating means that can be controlled independently from each other, positioning the magnetic field generating means in relation to at least the first chamber in both the chambers, and diffusing into the second chamber and locating a part of the ion group approaching the workpiece. A permanent magnet group, an electromagnet group, or a solenoid having a structure in which the ion group is attenuated by being directed toward the loss surface of the chamber, the first chamber is annular, and is individually arranged along the inside and outside of the annular There is provided a plasma processing apparatus in which an annular magnetic field generating means is formed by a group .

  Control means incorporated in the apparatus by the magnetic field generating means relatively adjusts the number of ions and free radicals that enter the second chamber and reach the wafer. Thus, the use of a suitably oriented magnetic field can affect ion diffusion without affecting neutral free radical diffusion.

  Preferably, the magnetic field generating means includes a permanent magnet group or an electromagnet group installed around the side wall of the first chamber. The magnetic field generating means along the first chamber may be a variable output solenoid.

  The apparatus may be provided with additional plasma inducing means in the upper region of the second chamber. In that case, a permanent magnet group, an electromagnet group or a solenoid may be installed as an additional magnetic field generating means around the additional plasma inducing means in the upper region of the second chamber.

  The magnetic field generating means may include a magnetic structure formed at a coupling portion between the two chambers, and a dipole magnetic field may be formed at the portion.

  In addition to the gas supply inlet to the top of the first chamber, the apparatus may further include an annular gas supply port at a site below the coupling point of the two chambers in the second chamber.

  The apparatus can provide a variable output solenoid for the second chamber at a required position, and generate a magnetic field at the height portion of the workpiece in the second chamber to steer the ion group toward the workpiece.

A combination of an annular plasma source and a cylindrical plasma source may be provided in the first chamber.

  The first chamber may be formed of two or more dielectric cylindrical sections having different diameters and arranged vertically, and individual plasma inducing means may be provided in each section.

  A magnetic bucket can be provided in the second chamber by a magnet row along the chamber wall of the second chamber.

  The geometric shape of the first chamber can be formed by a cylinder, a stepped cylinder, a cone, a truncated cone, or a hemisphere, or a combination of these geometries.

According to another aspect of the present invention, the first chamber is provided with plasma inducing means designed to generate plasma by inductive coupling with a radio frequency power source , and the generated plasma diffuses to act on the workpiece. The first chamber is formed by two or more dielectric cylindrical sections having different diameters and arranged vertically, and plasma is generated in each section by inductive coupling with a radio frequency power source. There is provided a plasma processing apparatus provided with individually designed plasma induction means.

  The portions joining the individual areas of the first chamber are ideally made of metal or dielectric material and positioned so as to intersect or intersect perpendicularly with the areas.

  A structure in which the first chamber of the multiple zone is provided with magnetic field generating means associated with two or more of the zones, and each magnetic field generating means is diffused into the second chamber to attenuate the ion flow approaching the workpiece. It can be.

  Furthermore, an annular first chamber with a pair of attenuating magnetic field generating means arranged concentrically with each other can be provided in order to enable the processing in a large area.

  Ideally, the first chamber is provided with a dielectric plasma tube made of aluminum nitride, silicon carbide or other dielectric material having a thermal conductivity sufficiently higher than that of aluminum oxide, thereby causing damage in the dielectric material. It is possible to allow high power operation without causing a high degree of thermal gradient.

  In order to increase the area of active treatment, a plurality of said first chambers according to the invention can be provided across the top of said second chamber.

According to another embodiment of the present invention, a first chamber in which plasma inducing means designed to generate plasma is provided in the chamber, and a second chamber in which the generated plasma diffuses and acts on the workpiece. And providing a dielectric plasma tube made of aluminum nitride, silicon carbide or other dielectric material having a thermal conductivity sufficiently higher than that of aluminum oxide in the first chamber, which may cause damage in the dielectric material. Plasma processing that uses a plasma processing apparatus that allows high power operation without causing a high degree of thermal gradient, and that the plasma induction means is operated so as not to cause a high degree of thermal gradient that can cause damage in the dielectric material. method Ru is provided.

  Control means associated with specific aspects of the etching or deposition stage are required via a functional relationship that depends on time or other parameters. For example, the number of ions reaching the surface to be etched needs to be reduced once the surface layer is removed, but the number of free radicals reaching the surface may be kept constant. After the time required to remove the surface layer, the control level can be readjusted to shift the free radical to ion ratio to the new required value. The controlled variable can include a function of distance, and the relative ratio of the number of ions to the number of free radicals can be varied as a function of wafer position.

  To etch deep trenches in silicon or other suitable material, a switched process (Robert Bosch GmbH, US Pat. No. 5,501,893 or Surface Technology, US Pat. No. 5,051,503 (Patent Document). 2)) can be used. In such a construction method, the steps of material etching and vapor deposition are alternately performed, and as a result, a structure is formed in the wafer by anisotropic etching. More particularly, in the deposition step, a polymer is deposited on both the sidewalls and bottom of the groove or other structure. In subsequent etching steps, the polymer is preferentially removed from the bottom of the trench by directional ion bombardment, followed by chemical etching of the exposed silicon. Although chemical etching is essentially isotropic, the entire etching process is anisotropic because the polymer is removed only from the bottom of the groove and the silicon etch depth at each etching step. Because it is shallow. In order to define the geometry of the structure surface to be etched, a suitable pattern mask, for example made of photoresist, is applied to the wafer before the start of the etching step. It is an important aspect of the overall process that ion bombardment aimed at removing the polymer from the bottom of the trench does not erode the mask before reaching the required etch depth, otherwise the structure is accurate. Sex is harmed.

  In the international patent application PCT / GB99 / 04168 (see “Plasma Processing Apparatus” in Patent Document 3), the present applicant has decided to control the relative number of free radicals and ions allowed to reach the wafer. A number of examples of permanent magnet and electromagnet arrangements have been described. In the switched etching process, the magnetic field generated by the electromagnet is set at a certain level for the etching stage and at a different level for the vapor deposition stage. Under certain circumstances, it is advantageous to change the magnetic field strength during either or both of the etching and deposition steps. For example, in the etching stage, the magnetic field strength may be kept low at the initial portion to allow a high level of ion flux to reach the wafer and remove the polymer deposited on the bottom of the trench. At the end of polymer removal, the magnetic field strength can be increased to reduce the ion flux reaching the wafer and reduce the mask etch rate. In addition, the relative number of ions to free radicals as the groove etch progresses by adjusting the magnetic field strength from one etching stage to the next and / or from one deposition stage to the next. Can be adjusted gradually.

  The present application details various features that enable high-speed etching while maintaining good uniformity of the etching rate across the wafer in the plasma processing apparatus, and also enables high-precision control of the shape of the structure to be etched. Describe. The description of this application relates in particular to etching performed by the switched etching process. This is because, from this application, a continuous etching process or a continuous deposition process (where “continuous” means that the process is “rather than the implied that the processing rate or other processing surface is constant over time” It is not intended to exclude "not being able to switch between the etching and deposition steps".

  A plasma processing apparatus consists of two or more chambers, typically a larger second chamber on which a wafer or other workpiece is placed on a suitable support. The support can include a mechanism for cooling or heating the wafer during or before or after processing. The support also allows a continuous or pulsed radio frequency or direct current voltage to be applied from the chamber to the wafer, allowing acceleration of ions toward the wafer. A mechanism capable of remotely controlling the insertion or withdrawal of the wafer can be included in the support base. The chamber walls are usually provided with openings for pressure gauges and other diagnostic means, and one or more relatively large openings for gas outflow to the vacuum pump device used to maintain the chamber at the required pressure. Wear.

  Typically, the volume of one or more first chambers is small compared to the second chamber in which the wafer is mounted. A plasma is created and maintained in this first chamber, and ions and free radicals diffuse into the second chamber. Control means such as a magnetic attenuator can be used to limit the flux of ions and free radicals going into the second chamber. Reference to one first chamber excludes the use of multiple chambers for plasma formation and the combined use of multiple control means to control the flux of ions and free radicals towards the second chamber where the wafer is mounted. It is not a thing. When plasma is formed in multiple first chambers, it means that all chambers are operated at the same time, the supply gas is the same, or the input level to each plasma is the same, etc. do not do.

According to another aspect of the present invention, in a method for controlling the transmission of plasma to a workpiece, the plasma is generated in the first chamber by a plasma inducing means, and the plasma acts on the workpiece to be processed. Diffusing into the second chamber with magnetic field generating means positioned relative to at least the first chamber of both chambers and controllable independently of the plasma inducing means. A part of the ion group approaching the object is directed to the loss surface of one of the chambers so that the ion group is attenuated , and the first chamber is formed in an annular shape, and is individually arranged along the inside and the outside of the annular shape. There is provided a plasma transmission control method in which an annular magnetic field generating means is formed by a permanent magnet group, an electromagnet group, or a solenoid group .

  Although the present invention can be implemented in various modes, preferred embodiments will be described below with reference to the accompanying drawings.

  In the single first chamber A of the apparatus schematically shown in FIG. 1, plasma is generated and allowed to flow into the second chamber where the wafer is to be placed. The wafer 1 is placed on the wafer support 2 in the lower chamber B. Maintain good thermal contact between the wafer and the temperature controlled portion of the support by means of a mechanical clamp 2A for the wafer, or an electrostatic clamp, or other suitable means suitable for this situation. In order to improve the heat conduction between the two surfaces of the wafer back surface and the surface of the support base 2, a pressurized gas such as helium is injected through the inlet 3 to fill the narrow gap between the two surfaces as a thin layer. To do. An appropriate part of the support is connected to a radio frequency or DC continuous or pulsed power source such as a radio frequency power source 4 via an appropriate impedance matching device 5, and a control potential difference is formed in a sheath formed on the wafer. Thereby controlling the energy of ions impinging on the wafer. The normal processing height position in the room is indicated by symbol 6. The gas is discharged through the pumping port 7.

  A group of permanent magnets 21g (see FIG. 2) is arranged in a column shape on the peripheral wall of the chamber B (and also on the peripheral wall of the chamber A if necessary) to form a “magnetic bucket”. The “multiple tip” or “pile shelf” arrangement has the effect of reducing the diffusion of ions and free radicals into the chamber wall. Historically, “magnetic buckets” have been used to increase the plasma density in a room, because the rate of production of a given ion and free radical inside the room is greater than when there is no “magnetic bucket”. The loss rate to the wall was to decrease. If magnetic confinement is applied to chamber A, it is primarily for this purpose and to contribute to the formation of a high density plasma with a high density of neutral free radicals.

Adding a magnetic confinement to chamber B may seem illogical when the number of ions reaching the wafer needs to be reduced relative to the number of free radicals, but in the absence of a “magnetic bucket” This is because ions that diffuse into the chamber B can be confined more effectively. However, for chamber B, the purpose of using magnetic confinement is primarily to increase the uniformity of the ion flux reaching the wafer. If there is no magnetic confinement around chamber B, there will be a loss of ions and electrons to the walls of chamber B before reaching the wafer position during the diffusion of the plasma descending from chamber A into chamber B. As the distance from chamber A to the wafer increases, the plasma density decreases, non-uniformity increases, and the density is maximized at the chamber axis. Magnetic confinement around chamber B ensures a substantial increase in plasma uniformity at the wafer location as it reduces plasma loss to the wall. The proposal to provide magnetic confinement around chamber B is not intended to exclude the use of devices that do not have magnetic confinement around chamber B. That is, it is used only when there is an advantage to using a “magnetic bucket”.

  To reduce the number of ions at the wafer position to increase the number of neutral free radicals and to maintain a high degree of spatial uniformity of ions, not only provide good ion confinement in chamber B, but simultaneously leave chamber A It is necessary to significantly reduce the number of ions diffusing to the number of free radicals. To obtain the required result, a magnetic plasma attenuator that is integrated with chamber A or in the middle of both chambers can be used in combination with chamber B plasma confinement. For this purpose, a bipolar magnetic plasma attenuator can be formed by permanent magnets or electromagnets.

  Preferably, a solenoid magnetic field is formed in the chamber B by the electromagnet 9 at the height level at which the wafer is processed, and the electromagnet 9 is provided outside (in the illustrated example) or indoors. The magnetic field strength is controlled so that different magnetic field strength values are taken for different stages of the switching process, and the magnetic field intensity value changes in an upward or downward gradient depending on which processing stage is performed as the process proceeds. You may make it do. The purpose of this magnetic field is to control the directionality of ions reaching the wafer surface and to assist in the uniformity of ion flux over the wafer surface.

  The processing plasma is formed in the upper chamber A. In the following description of this specification, reference is made to a plasma generated and maintained by inductive coupling with a radio frequency power source. However, this excludes the use of other plasma generation means such as microwaves (including electron cyclotron resonance type), helicon waves, direct current means with or without a heated filament as an electron source. Of course not. An antenna 10 shown in FIG. 1 is positioned around a cylindrical tube 11 made of a dielectric material, and radio frequency power (from a power point 21) is inductively coupled to plasma formed in the tube via the antenna. The The geometrical shape of the tube may be other than shown, for example, a pentagonal cross section or other shapes. The geometric shape may be a conical shape 11A, a truncated conical shape 11B, a hemispherical shape 11C, or a combination thereof (see FIG. 3) instead of the above. In many cases, a single antenna 10 is used to couple power to the plasma. However, improvement in the uniformity of the etching process or the vapor deposition process can be achieved by using two or more antennas 10A and 10B, particularly by attaching the dielectric tube 11 to different diameter portions (see FIG. 3B).

  The dielectric material for forming the tube 11 is alumina, quartz, or other suitable material as a suitable material that is compatible with the processing gas. The use of a material such as silicon carbide is advantageous because it has a higher thermal conductivity than alumina and therefore better heat transfer from the inner wall surface in contact with the plasma to the outer cooling means. Silicon carbide, because of its high conductivity, helps reduce capacitive coupling into the room when inductive coupling of radio frequency power is the desired mode. Aluminum nitride is another available material that combines high and low thermal conductivity and allows good heat transfer, but has little impact on the radio frequency power coupling from the external antenna 10 to the plasma. When the plasma density is high, the high thermal conductivity of aluminum nitride or silicon carbide is particularly advantageous. This is because the temperature gradient between the inside and outside of the tube is reduced as compared with a material having a relatively low thermal conductivity such as alumina. Significant expansion differences in dielectric tubes can cause cracking and propagation and loss of vacuum maintenance.

  In some cases, from the viewpoint of uniformity of wafer processing, it is advantageous to use a geometric shape in which the chamber A is formed by two or more cylindrical dielectric sections 11X and 11Y (see FIG. 5) having different diameters. . In that case, the radio frequency power supply can be coupled to the plasma by two or more individual antennas 10A and 10B provided around each cylindrical section. It may be a single dielectric material structure or may be constituted by two or more areas 11X, 11Y with a conductive or non-conductive interface flange portion 12 and suitable vacuum sealing means. Although a cylindrical section has been described, this does not exclude other geometric shapes such as square or hexagonal cross sections. Two or more individual antennas use individual impedance matching units and individual radio frequency power sources or single power sources with split outputs. Referring to FIG. 5, the power coupled to the plasma via the antenna 10A has a stronger influence on the flux of ions and free radicals that reach the center of the wafer, and is coupled to the plasma via the other antenna 10B. The electric power has a stronger influence on the flux of ions and free radicals that reach the outer periphery of the wafer. The lateral diffusion of ions and free radicals means that the effect is not obvious, but the effect is true unless the distance between the upper chamber A and the wafer is large. By adjusting the relative level of the radio frequency power supplied to two or more antennas, the plasma cross-section in this chamber and the effect of the plasma on the wafer can be adjusted. The relative power level is adjusted to a different value depending on whether an etching or deposition phase of the process is in progress.

  Referring to FIG. 1, the upper chamber A is formed by a dielectric cylindrical tube 11 forming a side wall and a plate 13 closing the top and a suitable vacuum sealing means for the cylinder. The top plate is usually made of metal and has suitable connection means 14 that allow the supply of process gas into the chamber. Appropriate means are incorporated so that the gas distribution in the room is uniform. For example, a window indicated by symbol 15 in FIG. 4 or FIG. 5 is provided in the top plate to allow observation of plasma or wafer for measurement purposes at the final point of processing. The lower end of this dielectric cylindrical tube serves as an interface to the lid 17 of the lower chamber B, either directly or through an intermediate short tube region, usually made of metal, which short tube region is grounded or electrically Floated or biased to a selected potential.

  The above description includes the supply of the processing gas via the lid of the upper chamber A, but in addition or alternatively, the chamber is directed upward from the gas ring 16 provided in a portion near the lower chamber lid 17 inside the lower chamber B. It may be desirable to supply gas to A. In some cases, one gas is supplied through the lid of the upper chamber A, and different gases are supplied from the gas ring 16 provided in the lower chamber B. If the upper chamber A has a hemispherical or conical shape and is entirely made of a dielectric material, it is not possible to supply gas to the top of the upper chamber A, and the gas ring 16 in the lower chamber is indispensable. It is.

In the case of switchable processing (switched- process) is a proper process gas depending on whether the etching step, or passivation (passivation) stage of processing what is implemented, the supply port of the cover of the upper chamber A, Alternatively, there may be advantages in supplying from the gas supply ring 16 in the lower processing chamber B, respectively. Rather, it may be desirable to supply gas via both routes in some process stages and only one route in other process stages. In each of the two processing stages, proper control of the gas inlet can be performed by the mass flow controller when using any route to supply process gas into the apparatus. Automatic pressure control (APC) can be used to control the gas flow conductance from the process chamber to the vacuum pump, which allows control of the process chamber pressure.

  Under certain circumstances, it may be desirable to use significantly different process chamber pressures for each of the two stages of the switching process. For example, high pressure in the etching stage and low pressure in the passivation stage. This can be achieved by appropriate high-speed control of a mass flow controller for supplying gas to the processing chamber and a pressure control valve for controlling gas conductance between the processing chamber and the vacuum pump.

  In order to form plasma in the upper chamber A, it is necessary to supply radio frequency power to the antenna 10 surrounding the upper chamber and to introduce the required processing gas through the associated inlet means. Neutral free radicals are formed by the collision of active electrons from the plasma with the neutral gas, so ions, electrons, free radicals and unseparated feed gas will be mixed in the upper chamber A. All of these species diffuse into the lower chamber B, but the number is reduced by recombination in the volume and on the wall. Ions and electrons recombine easily at the chamber walls, but free radicals will survive after multiple collisions. If there is magnetic confinement in the lower chamber B, the loss of ions and electrons to the wall of this chamber is significantly reduced.

  The opening of the lid 17 of the lower chamber B to which the upper chamber A is to be attached, or the limitation on the inner diameter of the intermediate short tube area, if present, allows a higher pressure difference between the upper chamber and the lower chamber. . This improves the processing efficiency because the higher pressure in the upper chamber favors the formation of ions and free radicals because it increases collisions, and the reduction in pressure in the lower chamber is within its volume. Reduce the occurrence of recombination at This treatment can obviously only be used when the gas supply is directed into the upper chamber and can have undesirable consequences if the above-mentioned limitations increase the loss of ions or free radicals. An automatic pressure control (APC) mechanism with variable aperture can be included in this position. However, depending on the physical design of the APC mechanism, the ion flow, especially the uniformity of it reaching the wafer, is degraded.

  A magnetic plasma attenuator is applied by applying a dipole magnetic field formed using a permanent magnet 8 or electromagnet across the lower end of the upper chamber A (or across the intermediate short tube region, if present), if necessary. It may be formed. The permanent magnet or electromagnet used for generating the magnetic field is generally positioned outside the chamber, but a part or all of the permanent magnet or electromagnet may be provided in the chamber. The effect of this magnetic field is to deflect electrons and then ions to the wall (loss surface) where they are to be lost, thus allowing control of the number of ions traveling into the lower chamber, but with radial flow. The bundle is not lowered.

  If the magnet structure is in the chamber, it is expected to increase the local loss area for free radicals slightly according to its geometry. Control of the relative number of ions relative to free radicals migrating into the lower chamber allows greater control of the overall process. In particular, when using electromagnet or permanent magnet / electromagnet mixture for switching control, control is performed so that the relative number of ions to free radicals is a different appropriate ratio value for each of the two stages of processing. It becomes possible.

  Control of the radio frequency power toward the plasma in the upper chamber A determines the number of ions and free radicals to be formed, but generally both increase with increasing input power. Process gas flux and pressure are also affected. There is also an increasing demand for high etch rates, and the chemical reaction therefore requires a very large number of free radicals, while the number of ions must be limited to reduce unwanted damage to the structure and mask after etching. is there. The combination of plasma density control to generate a large number of ions and free radicals and a “magnetic plasma attenuator” that reduces the ionic content that reaches the wafer, overwhelmingly reduces chemical high-speed etching to ion-related undesired Allows to be achieved with reduced effect. Undesirable effects associated with large ion flow to the wafer include high speed mask etching and post-etch structure sidewall cross-section control issues.

  The dipole shape of the “magnetic plasma attenuator” has the disadvantage that application of a magnetic field across the upper chamber induces a perpendicular deflection of ions and free radicals, and the flow of ions during descending from the plasma generation region to the wafer. This is accompanied by a decrease in cylindrical symmetry. For this reason, the uniformity of the process added to a wafer may occur.

  The solenoid magnetic field generated by the coil 18 shown in FIG. 4 along the upper chamber A has an advantage as a “magnetic plasma attenuator” with respect to the dipole magnetic field. The cylindrical symmetry is maintained by careful adjustment of the magnetic field strength, and the high-density plasma region 19 formed in a portion adjacent to the antenna 10 in the tube 11 is confined by the field lines 20. The magnetic field lines intersect with the wall surface of the upper chamber A at or near the lid 13 and intersect with the base portion of the upper chamber A or the lid 17 of the lower chamber B or the upper portion of the side wall thereof. The exclusion of the magnet 8 (for generating a dipole magnetic field) removes what may cause plasma non-uniformity. A significant number of free radicals can be generated in the upper chamber A and they diffuse into the lower chamber. However, the associated ion flow is reduced due to losses at the intersection of the magnetic field lines and the walls, thus ensuring a reduction in the required aspect of the ratio of ions to free radicals reaching the wafer. As shown in FIG. 5, separate solenoid coils 18A and 18B may be provided for the two cylindrical tubes 11X and 11Y, respectively, so that plasma control can be enhanced. Two individual high-density plasma regions 19A and 19B are formed by the two antennas.

  When magnetic confinement is applied in the lower chamber B, some of the electrons confined in the magnetic field lines from the solenoid coil 18 around the upper chamber A will encounter a strong magnetic field on the wall of the lower chamber B. This causes local mirroring of the electrons that survive and participate in further excitation and ionization collisions with the gas molecules. Thus, a situation may occur where the magnetic field strength from the solenoid around the upper chamber A is sufficient to significantly reduce the ion flux towards the wafer 1 and at the same time increase excitation and ionization collisions. Increasing the rate of free radical formation by this mechanism has the potential to increase the chemical etch rate of the wafer.

  An experimental operation was attempted on the separation of the plasma source and the processing chamber, including some of the features already described. The configuration is shown in FIG. In the upper chamber A for plasma generation, a dielectric tube 11 with a radio frequency antenna 10 held by appropriate support means is provided in the vicinity of the center thereof. Radio frequency power from the radio frequency power source 21 was supplied to the antenna 10 via the matching device 22, and the matching device 22 matched the plasma impedance to the 50 ohm impedance of the power source. An electromagnetic solenoid 18 is disposed around the plasma chamber A, and a magnetic field pattern indicated by a representative magnetic field line 20 is generated when the electromagnetic solenoid 18 is energized. The electromagnetic solenoid 18 was the only magnetic ion attenuating means incorporated in a plasma source / processing chamber separation type apparatus. No type of dipole magnetic ion attenuator was provided between the plasma source and the processing chamber.

  The processing chamber B is provided with a “magnetic bucket” (similar to FIG. 2) with a group of small magnets arranged around the periphery to improve plasma confinement. No electromagnet was provided at 6 or in the vicinity thereof.

  A specific experiment to measure the effectiveness of the solenoid-type magnetic field formed by the electromagnetic solenoid 18 around the chamber A where the plasma is formed in attenuating the ion flux reaching the wafer 1 attached to the processing chamber B went. In this experimental work, a silicon wafer was used as the workpiece, but it should be understood that other material wafers or alternative objects that are subject to plasma-induced processing can also be workpieces. is there.

  A small Langmuir probe 23 was inserted through the entrance of the wall of processing chamber B and allowed to move along the chamber diameter over the surface diameter of the test wafer loaded in the chamber. The Langmuir probe 23 was used to measure the ion flux just above the wafer as a function of the position on the chamber diameter.

  The experimental results of ion flux measured as a function of position on the diameter of the processing chamber are shown in FIG. The plurality of curves are for different values of the current flowing through the electromagnetic solenoid around the chamber A where the plasma is formed. The strength of the magnetic field increases with increasing current through the solenoid. From the graph, it can be seen that as the magnetic field strength increases, the ion flux reaching the wafer processing height decreases, and the uniformity of the ion flux size in the main part on the diameter of the processing chamber increases to some extent. it is obvious.

  Experimental measurements of ion flux with a Langmuir probe were reinforced by further experiments. That is, the use of an electromagnetic solenoid around chamber A reduced ion related effects on the wafer being processed and achieved a high chemical etch rate.

  The use of an electromagnetic ion attenuator is effective for reducing the flux of ions reaching the wafer while keeping the neutral free radical flux reaching the wafer high. This approach is clearly useful when the etching process is primarily chemical and driven by free radical flux, but mask erosion is primarily done by the flux of ions reaching it.

  In some cases, it is desirable to reduce the number of similar ions relative to the number of neutral free radicals reaching the wafer to a level lower than that obtained by a magnetic attenuator alone. In other cases, there are reasons why it is desirable to operate a magnetic attenuator under high magnetic field strength. One way to obtain the required results for a particular process is to pulse the plasma formed in chamber A on and off in the same manner as the magnetic attenuator is operated.

In the specific case of etching silicon with SF ₆ gas, it is understood that the etching of silicon is primarily due to chemical reactions of fluorine free radicals formed in the plasma. It is also known that under certain conditions, fluorine free radicals formed by plasma can survive for a considerably long time after plasma extinction. However, the ion density usually decreases at a very high rate after the plasma is switched off. If the plasma is turned on and off with a pulse at a suitable speed and a suitable mark space ratio, the difference in the lifetimes of these two species can be used to advantage. Boswell and Porteous (see J. Appl. Phys. 62 (8), American Insti. Of Phys. 1987), Non-Patent Document 1), a period of 10 milliseconds for a pulse group of 2 milliseconds, An SF ₆ plasma pulsing operation in which the average etch rate of silicon is essentially equal to the rate for a continuous plasma is described. The lifetime of the charged species was found to be less than 1 millisecond, which is typical for this type of low pressure discharge. For pulsed plasma only, Boswell and Porteos results show that the time-average ratio of ion flux to free radical flux can be reduced to less than 0.3 times that for continuous plasma. Indicates that Therefore, the combined concept of pulsed plasma and magnetic attenuator has the potential to make the ratio of ion flux to free radical flux reaching the wafer lower than that of either technique alone.

  The use of the separation method of the plasma source and the wafer processing chamber as shown in FIG. 1 or FIG. 6 has a great effect on a specific process for a wafer having a certain size. In general, neutral free radicals generated in a plasma source diffuse down to the wafer where they chemically react with the wafer surface. The ion flux reaching the wafer surface can be controlled by the use of a magnetic attenuator and, if necessary, pulsed operation in the plasma source. The use of an electromagnetic solenoid ion attenuator 18 around the plasma source helps to reduce the ion flux reaching the wafer, helping to equalize the ion flux along the wafer diameter within a certain limit, Plasma source separation has certain limitations due to its geometric shape.

  In order to efficiently form a high density plasma in the plasma source chamber when the applied radio frequency power is below an acceptable level, its volume should be reasonably small. The electromagnetic solenoid around the source can also be made reasonably small by lowering its current duty. Neutral free radicals generated at the plasma source diffuse down to the wafer and reach the wafer, and the free radical flux as a function of its radius is partially processed by the plasma chamber geometry and processed elsewhere. Determined by chamber vacuum pump and other regulators.

  The size and uniformity of the ion flux on the wafer surface is determined by a magnetic attenuator, and whether the geometry of the plasma source chamber and the magnet for promoting plasma confinement are located at the periphery of the processing chamber B or not. It depends on what. In the case of a plasma source that is small relative to the diameter of the wafer, it may be difficult to maintain a substantially uniform ion flux from the center to the periphery of the wafer. In the case of a single separated plasma source that is coaxial with the wafer, the ion flux density reaching the wafer tends to decrease from the central portion toward the peripheral portion.

  In many cases, the ion flux density gradient between the center and periphery of the wafer does not cause any appreciable problems, especially when the process is overwhelmingly chemically driven. If the process is driven by ions or depends on the exact definition of the ion flux impinging on the wafer at right angles to the wafer surface in at least part of the process, the geometry of the processing apparatus described above However, sufficient uniformity and directivity of ion flux will not be obtained. In such cases, additional measures may need to be taken to improve the uniformity of the ion flux reaching the wafer.

  An example of a specific configuration of a plasma processing apparatus designed to contribute to alleviating the above problems is shown in FIG. This configuration is based on the use of a separate plasma source with a shape similar to that described above in this document. The plasma is formed together with neutral free radicals in the same plasma source chamber A, and the neutral free radicals diffuse and descend into the processing chamber B where the wafer is supported. Similarly, ions from the plasma diffuse and descend into the processing chamber, but the magnetic ion attenuator 18 operates to make the required reduction to the ion flux. In order to improve the uniformity of the ion flux towards the wafer, magnetic plasma confinement on a portion of the wall of the processing chamber B is utilized.

  The alternative configuration of the separate processing apparatus differs from that previously described in the secondary plasma formed in the processing chamber by the use of radio frequency power internally coupled by the antenna 24 around the upper area of the processing chamber B. is there. This description of inductive coupling of radio frequency power to a secondary plasma is given by way of example and does not exclude other means, such as secondary plasma generation in the process chamber using microwave power.

  The antenna around the upper area of the processing chamber B forms an annular plasma in the chamber which then diffuses throughout the chamber volume. In general, the power supplied to this antenna is significantly less than that supplied to the antenna 10 around the smaller plasma source chamber A. The primary purpose of forming this secondary plasma is to make additional ions near the periphery of the plasma chamber, thereby increasing the ion flux towards the wafer periphery. By careful adjustment of the power supplied to the secondary plasma, the additional ions supplement the shortage in the ion flux reaching the peripheral edge of the wafer from the plasma source chamber A via the magnetic ion attenuator 18. Can do. In most cases, the secondary plasma is used to increase the ion flux towards the wafer edge, and the extra free radicals that are generated are of little importance, but in some cases these extra free radicals are beneficial for the ongoing process. is there. If necessary, a solenoid type magnetic ion attenuator can be provided around the region of the processing chamber B where the antenna 24 of the processing chamber B is located, and ions entering the main volume of the processing chamber. The ratio between the number of and the number of free radicals can be controlled.

  For the alternative configuration of the plasma source separation type plasma processing apparatus, processing gas is generally supplied through an inlet 14 in the lid of the plasma chamber A. However, it can instead be supplied through the gas ring 16 located in the vicinity of the lid in the processing chamber B. Depending on the situation, process gas is supplied simultaneously from both inlet 14 and gas ring 16, or different gases are supplied from each route.

  When performing a switchable process, gas is supplied to either or both inlets 14 and 16 depending on which process stage is being performed. For example, when performing an etching step, gas is supplied primarily to the top of plasma chamber A via inlet 14, where the gas is exposed to a high density plasma and generates a large number of etching free radicals. When performing the passivating step, the gas is supplied primarily through the gas ring 16 to form a plasma using the antenna 24 around the upper area of the processing chamber B, in which no plasma is formed. Or a weak plasma is formed. This example describes one possible scenario, but is not intended to limit the gas supply route or plasma generation region options for any stage of the switched process in any way.

  As described above for the basic separation source type apparatus, the pressure in the processing chamber B is controlled to be significantly different in each of the two stages of the switching process.

  The above description is for the antenna 24 around the outside of the upper portion of the processing chamber B and for coupling the power to the secondary plasma. It does not exclude use. In order to serve the same purpose as externally mounted antennas, such internally mounted antennas are generally positioned on a large diameter near the periphery of the processing chamber. The inner mounting antenna requires suitable feed-through connection means in part of the walls of the processing chamber, thereby connecting radio frequency power and circulating the cooling medium through the hollow antenna when possible.

  Another embodiment of a separation source type plasma processing apparatus with a magnetic ion attenuator is shown in FIG. The processing chamber in this configuration is basically shown in FIG. 1 or FIG. 6, but the plasma source chamber is different. In this case, the plasma source chamber is annular and uses one antenna 101 located radially outside the outer dielectric cylinder 111 and a second antenna 102 located radially inside the inner dielectric cylinder 112. . These two antennas are supplied with radio frequency power from two separate power sources or one power source with suitable power branching means. Under certain conditions, it may be advantageous to adjust the relative power supplied to each antenna to fine-tune the plasma characteristics, but in most cases the two antennas are co-driven with a fixed power ratio. .

Two electromagnetic solenoids are incorporated into the structure, one solenoid 181 is located radially outside the outer antenna 101 and the other solenoid 182 is located radially inside the inner antenna 102. By appropriately adjusting the current flowing through each of the solenoids, an electromagnetic ion attenuator for the annular plasma source can be formed. It should be noted that the current flowing through the two solenoids 181 and 182 to form the magnetic field line pattern 20 shown in FIG. 9 (which is effective in attenuating the ion flux reaching the wafer). Must be such that they produce a magnetic field in the opposite direction inside each solenoid. Each of the two solenoid electromagnets may be driven from a separate current source to obtain the required magnetic field strength. However, in many cases it is desirable to use a single current source with a means to divide the current between both solenoids at a constant ratio.

  When processing large wafers, it may be advantageous to use an annular plasma source for a separate source plasma processing apparatus rather than a simple small cylindrical plasma chamber. The reason is that this geometry ensures that free radicals and ions from the plasma chamber enter the process chamber with a larger diameter, and that different diffusion characteristics can be achieved by properly selecting the wafer processing height. It is in advantageous use. This is particularly important in order to achieve a uniform ion flux reaching the wafer surface.

  Although the above structure has been described for the case of a cylindrical annulus, this is not intended to exclude similar structures having square, hexagonal or other polygonal ring configurations.

  Those skilled in the art will consider repeating the annular plasma source spring structure of FIG. 9 with two or more diameters in one or more planes when it is necessary to supply ions and free radicals into a large processing chamber. It is not unreasonable. Combining an appropriate diameter annular plasma source and a simple cylindrical plasma source on an axis of symmetry may have application under certain circumstances.

  When using an annular plasma chamber, it is considered unlikely that it will be necessary to provide an additional antenna around the upper area of processing chamber B, but this option is still considered if necessary. be able to.

  When operating the apparatus to perform processing within the apparatus of the present invention, the decay field, which varies as a function of time, and therefore the time variability of ion decay, depending on the field strength of one or more electromagnets used. ) Is possible.

It is explanatory drawing of the isolation | separation form of the plasma source by the present invention, and a processing chamber. It is a horizontal sectional view of the processing chamber of FIG. FIG. 2 shows alternatives to the first chamber geometry of the system of FIG. FIG. 2 shows a further different shape of the first chamber of the system of FIG. 1 with a magnetic field formed therein. FIG. 3 illustrates another embodiment of the system of FIG. 1 with a magnetic field formed therein. It is a figure which shows the other Example of the apparatus of FIG. It is a figure which shows the analysis of the experimental result performed using the apparatus of FIG. It is a figure which shows the other Example of the apparatus of FIG. It is a figure which shows the other Example of the apparatus of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Wafer 2 ... Support stand 3 ... Inlet 4 ... Power supply 5 ... Matching unit 6 ... Normal processing height 7 ... Pumping port 8 ... Lower chamber 9 ... Electromagnet
10 ... Antenna 11 ... Cylindrical tube
12… Flange 13… Plate
14 ... Process gas connection means 15 ... Window
16 ... Gas ring 17 ... Lid
18 ... solenoid coil 19 ... high density plasma region
20 ... Magnetic line 21 ... Power supply
21g ... Permanent magnet

Claims (23)

A first chamber provided with plasma inducing means designed to generate plasma inside, a second chamber in which the generated plasma diffuses and acts on the workpiece, and can be controlled independently of the plasma inducing means. A magnetic field generating means, positioning the magnetic field generating means in relation to at least the first chamber of the two chambers, and losing a portion of an ion group that diffuses into the second chamber and approaches the workpiece to a chamber; A structure in which the ion group is attenuated by being directed to the surface, the first chamber is annular, and an annular magnetic field is formed by a permanent magnet group, an electromagnet group, or a solenoid group individually disposed along the inner side and the outer side of the annular shape. A plasma processing apparatus formed with generating means . 2. The plasma processing apparatus according to claim 1, wherein the magnetic field generating means includes a permanent magnet group or an electromagnet group installed around a side wall of the first chamber. 3. A plasma processing apparatus according to claim 1, wherein said magnetic field generating means along said first chamber is a variable output solenoid. The apparatus according to any one of claims 1 to 3, wherein an additional plasma inducing means is provided in an upper region of the second chamber. 5. The plasma processing apparatus according to claim 4, wherein a permanent magnet group, an electromagnet group, or a solenoid is installed as additional magnetic field generating means around the additional plasma inducing means in the upper region of the second chamber. 6. The plasma processing apparatus according to claim 1, wherein the magnetic field generating means includes a magnetic structure formed at a coupling portion of the two chambers, and a dipole magnetic field is formed at the portion. . In the apparatus according to any one of claims 1 to 6, in addition to the gas supply inlet to the top of the first chamber, an annular gas supply port is provided at a portion below the coupling point of the two chambers in the second chamber. Including a plasma processing apparatus. 8. The apparatus according to claim 1, wherein a variable output solenoid for the second chamber is provided at a required position, and a magnetic field is generated at a height portion of the workpiece in the second chamber. Plasma processing equipment that steers the ion group heading to 9. The plasma processing apparatus according to claim 1, wherein a magnetic bucket is provided in the second chamber by a magnet row along a chamber wall of the second chamber. 10. Apparatus according to any one of claims 1 to 9, wherein the geometric shape of the first chamber is formed by a cylinder, a stepped cylinder, a cone, a truncated cone, or a hemisphere, or a combination thereof. A plasma processing apparatus. 11. The plasma processing apparatus according to claim 1, wherein a combination of an annular plasma source and a cylindrical plasma source is provided in the first chamber. The apparatus of any of claims 1 to 10, damping the magnetic field generating means to-group and the plasma processing apparatus the first chamber of the annular portion group and a plasma inducing means, which are concentrically disposed to each other. 13. The plasma processing apparatus according to claim 1, wherein the plasma inducing means is designed to generate plasma by inductive coupling with a radio frequency power source in the first chamber. 14. The apparatus according to claim 1 , wherein a dielectric plasma tube formed of aluminum nitride, silicon carbide, or other dielectric material having a thermal conductivity sufficiently higher than aluminum oxide is provided in the first chamber. A plasma processing apparatus that allows high power operation so as not to cause a high degree of thermal gradient that may cause damage in the dielectric material. The apparatus according to any one of claims 1 to 14, formed by providing a plurality of the first chamber across the top of the second chamber plasma processing apparatus. In a method for controlling the transmission of plasma to a workpiece, plasma is generated in the first chamber by plasma inducing means, allowing the plasma to diffuse into the second chamber for acting on the workpiece and then said One of a group of ions that is positioned in relation to at least the first chamber in both chambers and diffuses into the second chamber and approaches the workpiece by means of magnetic field generating means that can be controlled independently of the plasma inducing means. A permanent magnet group, an electromagnet group, or a solenoid group, each of which is made to act so as to attenuate the ion group by being directed toward the loss surface of the chamber, and the first chamber is annular, and is individually arranged along the inside and outside of the annular A plasma transmission control method in which an annular magnetic field generating means is formed . The method according to claim 16 , wherein in addition to the gas supply inlet to the top of the first chamber, the plasma is transmitted by supplying gas to the ring gas supply port in the second chamber below the coupling portion of the two chambers. Control method. 18. The plasma transmission control method according to claim 17 , wherein different gases are supplied to the gas supply inlet and the ring gas supply port. 19. The plasma transmission control method according to claim 17 , wherein an inlet gas flow to the gas supply inlet and the ring gas supply port is controlled by an individual mass flow meter. 20. The plasma transmission control method according to claim 17 , wherein the processing chamber pressure is set to a different level for each of the different processing stages. 21. The plasma transmission control method according to claim 16 , wherein the plasma inducing means is operated so that the plasma is turned on and off in a pulsed manner during a processing operation. The method according to any one of claims 16 to 21 , wherein a magnetic confinement is provided in the second chamber by a magnetic bucket generated by a magnet array around the chamber. 23. The plasma transmission control method according to claim 21 , wherein the magnetic field strength of one electromagnet provided for generating the attenuation magnetic field is changed as a function of time.

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