WO2001083852A1

WO2001083852A1 - Method and apparatus for distributing gas within high density plasma process chamber to ensure uniform plasma

Info

Publication number: WO2001083852A1
Application number: PCT/US2001/011733
Authority: WO
Inventors: Wayne L. Johnson
Original assignee: Tokyo Electron Limited
Priority date: 2000-04-28
Filing date: 2001-04-27
Publication date: 2001-11-08
Also published as: AU2001255309A1

Abstract

An improved plasma processing chamber (20) is provided, which includes plural rotatable arms (105). Each rotatable arm (105) of the plurality of rotatable arms (105) has plural orifices for distributing at least one processing gas into the plasma processing chamber (20). In one embodiment, the gas distributor (100) is immersed in the plasma and is located in relatively close proximity to the semiconductor wafer (70) or wafers to be processed. In another embodiment, the spacing between the gas distributor (100) and the wafer (70) additionally may be adjusted. In an alternative embodiment, the gas distributor (100) is electrically insulated from the rest of the plasma processing chamber (20) and is otherwise designed to facilitate RF biasing so it may be cleaned in situ by RF means (30).

Description

TITLE OF THE INVENTION

METHOD AND APPARATUS FOR DISTRIBUTING

GAS WITHIN HIGH DENSITY PLASMA PROCESS

CHAMBER TO ENSURE UNIFORM PLASMA

CROSS-REFERENCE TO OTHER CO-PENDING APPLICATIONS This application is related to the following: U.S. Provisional Application Serial No. 60/059,173, filed September 17, 1997, entitled "Apparatus and Method For Adjusting Density Distribution Of A Plasma"; PCT Application No. PCT US98/ 18496, filed September 17, 1998, now WO 99/14394; U.S. Application Serial No. 09/508,102, filed September 17, 1998, entitled "Device and Method for Detecting and Preventing Arcing in RF Plasma Sources"; U.S. Provisional Application Serial No. 60/144,880, filed July 20, 1999, entitled "Electron Density Measurement And Plasma Process Control System Using A Microwave Oscillator Locked To An Open Resonator Containing the Plasma"; U.S. Provisional Application Serial No. 60/144,833, filed July 21, 1999, entitled "Electron Density Measurement And Plasma Process Control System Using Changes In The Resonate Frequency Of An Open Resonator Containing The Plasma"; U.S. Provisional Application Serial No. 60/144,878, filed July 20, 1999, entitled "Electron Density Measurement And Control System Using Plasma-Induced Changes In The Frequency Of A Microwave Oscillator"; U.S. Provisional Application Serial No. 60/166,418, filed November 19, 1999, entitled "Stabilized Oscillator Circuit For Plasma Density Measurement"; PCT Application No. PCT/US98/21622, filed October 15, 1998, now WO 99/19526; and PCT Application No. PCT/US98/21623, filed October 15, 1998, now WO 99/19527. All of the above-mentioned patent applications are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention generally relates to the production of semiconductor wafers and more particularly, to a method of and apparatus for distributing a gas within a high density plasma process chamber to improve the uniformity of a plasma applied to the surface of a semiconductor wafer.

Discussion of Background

A number of steps in the manufacture of semiconductor wafers may use plasma processing. For instance, resist-stripping, etching, depositing, and passivating, may use plasma processing to produce integrated circuits (hereinafter "ICs") on a semiconductor wafer. Because the features of the ICs are so small, a uniform plasma density is required for satisfactory resolution thereof. A high plasma density is also necessary in order to maintain process throughputs within a commercially viable range.

Typically, plasmas are established in low-pressure gas environments by causing electrons to collide with individual atoms or molecules, thereby producing additional free electrons and ions. In order to generate the plasma, radio frequency (hereinafter "RF") power is inductively or capacitively applied to a gas by an inductive or capacitive plasma coupling element, respectively. Examples of inductive coupling elements include conductive, helical, and solenoidal coils that are place outside of, but in close proximity to, the walls of the process chamber and surround a cylindrically-shaped process chamber. Known inductive plasma generating systems are described in U.S. Patent No. 5,234,529 (hereinafter "the '529 patent"), issued to Wayne L. Johnson, U.S. Patent No. 5,534,231 issued to Savas, and U.S. Patent No. 5,811,022 issued to Savas et al. However, the inductor may also be a planar coil of wire or tubing so as to be placed against the flat top of the cylindrically-shaped process chamber as disclosed in U.S. Patent No. 5,280,154 issued to Cuomo et al. The coils may be excited by a radio-frequency (RF) source such that a time varying magnetic field, in accordance with Faraday's Law, becomes associated therewith. The time varying magnetic field produces an electric field that accelerates electrons and it is the acceleration of the electrons which makes the establishment of the plasma possible as disclosed in U.S. Patent No. 4,431,898 issued to Reinberg et al. The contents of the five above-mentioned patents are herein incorporated by reference.

In capacitively coupled systems, a RF field may be produced between a pair of opposed electrodes, wherein the electrodes are nominally parallel to the surface of the semiconductor wafer or wafers to be processed. In fact, the semiconductor wafer(s) to be processed are often located on one of the electrodes. An example of such a plasma processing system is disclosed in U.S. Patent No. 4,209,357 (hereinafter "the '357 patent"), issued to Gorin et al. , which is herein incorporated by reference.

Plasma processors often require feed gas or gases to be introduced into the plasma processing chamber. Conventionally, feed gas or gases are introduced into the plasma chamber through gas inlet tubes which are located around the periphery of the region in which the plasma is to be established. A distribution manifold may also be used to introduce gas into a plasma processing chamber. Examples of such plasma processors are disclosed in the '357 patent, U.S. Patent No. 5,624,498 issued to Lee et al. , U.S. Patent No. 5,614,026 issued to Williams, and U.S. Patent Nos. 5,614,055 and 5,976,308 both issued to Fairburn et al.

The gas distribution systems of the prior art plasma processors discussed above have a number of drawbacks. More particularly, the feed gas distribution systems of prior art plasma processors are typically fixed with respect to the plasma processing chambers.

Another drawback of prior art feed gas distribution systems is that the physical configuration of the gas distribution systems in the plasma process chambers requires atoms or molecules of each feed gas to have essentially the same residence time within the plasma. For procedures using multiple feed gases, it is known that a reduction of the residence time within the plasma for the atoms or molecules of one of the feed gases could be advantageous.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method of and apparatus for distributing at least one gas in a high density plasma process chamber to improve plasma flux uniformity at the surface of at least one semiconductor wafer.

It is another object of the present invention to facilitate in situ RF cleaning to control contamination by particulates so that only one cleaning is necessary for the entire processing chamber and the contents thereof.

It is an object of the present invention to provide an adjustable feed gas distribution system to permit different spacings between the feed gas distribution system and the surface of the semiconductor wafer to be processed.

It is another object of the present invention to reduce or increase, as appropriate, the residence time of the feed gas within the plasma.

These objects and other advantages of the present invention are addressed by injecting at least one gas into the plasma processing chamber using a multi-armed, rotating, gas dispenser-diffuser or distributor. In one embodiment, the gas distributor is immersed in the plasma and is located in relatively close proximity to the semiconductor wafer or wafers to be processed. The gas distributor allows the at least one gas to be introduced into the plasma processing chamber. When using plural gases, it is possible to limit the number of collisions with electrons, ions, atoms, or molecules sustained by the atoms or molecules of one of those gases before the electrons, ions, atoms, or molecules impinge upon the surface of the at least one semiconductor wafer. In one embodiment, the spacing between the plural arms of the gas distributor and the semiconductor wafer additionally may be adjusted. In an alternative embodiment, the gas distributor is electrically insulated from the rest of the plasma processing chamber and is otherwise designed to facilitate RF biasing so it may be cleaned in situ by RF means.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the present invention and many of the attendant advantages thereof will become readily apparent with reference to the following detailed description, particularly when considered in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic showing the plasma processing chamber of the present invention, including an apparatus for introducing gas into the plasma processing chamber to maintain a uniform plasma flux on the surface of the semiconductor wafer to be processed;

FIG. 2 is a bottom plan view of the apparatus for introducing gas into the process chamber to maintain a uniform plasma flux on the surface of the semiconductor wafer to be processed; and

FIG. 3 is a side elevational view of the apparatus for introducing gas into the process chamber to maintain a uniform plasma flux on the surface of the semiconductor wafer to be processed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, in which like reference numerals designate identical or corresponding parts throughout the several views.

FIG. 1 illustrates a plasma processing system including a plasma source 10 and a process chamber 20. A gas is supplied to the process chamber 20 via a shaft 115 and a gas distributor 100 that helps to maintain a uniform plasma flux on the surface of the semiconductor wafer 70 to be processed. In the preferred embodiment, the gas distributor 100 is a multi-armed, rotatable, gas dispenser-diffuser. The gas distributor 100 is located within the process chamber 20 to enable the gases to be couple to the RF power.

A RF power source 30 is shown on the left-hand side of FIG. 1. The RF power source 30 has an output impedance Rs. The radio-frequency (RF) power source 30 is for supplying radio-frequency (RF) power to a helical coil 40 acting as an inductive coupling element. The coil 40 couples energy into the gas and excites it into a plasma within a plasma region 50 of the process chamber 20. The plasma and energetic and/or reactive particles produced by the plasma (e.g., ions, atoms, or molecules) can then be released through an output 60 of the plasma source 10 and used to process a substrate, such as a semiconductor wafer 70 or a flat panel display substrate.

FIG. 2 illustrates the underside (i.e. , the side facing a semiconductor wafer 70 to be processed) of the gas distributor 100. The gas distributor 100 is typically mounted above the semiconductor wafer or wafers 70 to be processed within an inductively coupled plasma (hereinafter 'TCP") processor. In one embodiment of the present invention, the ICP processor includes at least one of an electrostatic shield and a bias shield. The gas distributor 100 of the present invention is used to introduce a feed gas into the process chamber 20 in relatively close proximity to the semiconductor wafer or wafers 70 to be processed.

The gas distributor 100 includes a number of radially outwardly extending arms 105. The gas distributor 100 illustrated in FIG. 2 has four arms 105. As would be appreciated, the number of arms 105 may be adjusted according to different design constraints. It is desirable that the number of arms 105 be kept small enough so that the plasma flux at the surface of the semiconductor wafer or wafers 70, when in the presence of the gas distributor 100, is between 60% and 90% (and preferably not less than about 70%) of the plasma flux that would exist in the absence of the gas distributor 100. Applicants believe that four to six symmetrically spaced arms 105 represent the preferred embodiment.

Each of the plural arms 105 of the gas distributor 100 shown in FIG. 2 is represented as being rectangular in cross-section, but alternate embodiments use other cross-sections. Each of the plural arms 105 has a predetermined area 120, which is shown in FIG. 2 as being shaded and as delineated by the dashed lines 125. This predetermined area 120 includes a plurality of orifices (not shown individually). The plurality of orifices allow a feed gas to enter the plasma process chamber 20. The orifices need not be of the same size, nor need they be uniformly distributed throughout the predetermined areas 120, shown as being trapezoidal solely for illustrative purposes in FIG. 2.

The size, shape, spacing and distribution of the orifices are determined by the requirement that processing be uniform over the entire surface of the semiconductor wafer or wafers 70. It is to be expected that details of the design of the gas dispenser-diffuser apparatus 100 will depend on the particulars of either the inductively coupled plasma (ICP) processor or the electrostatically shielded radio-frequency (ESRF) processor in which the gas distributor apparatus 100 is to operate.

The size and spacing of the orifices in the arms 105 of the gas distributor 100 is important to establishing and maintaining a uniform plasma flux. Therefore, the size and spacing of the orifices are chosen so that the feed gas emerging from the orifices provides a uniform plasma flux at the surface of the semiconductor wafer or wafers 70.

The gas distributor 100 also includes a hub 110. The hub 110 distributes process gas or gases to the arms 105 so that the process gas or gases may then be dispensed/diffused through the orifices thereof to create a uniform plasma flux that contacts the surface of the semiconductor wafer or wafers 70.

The gas distributor 100 connects to a shaft 115 (e.g. , a hollow cylindrical sleeve). The shaft 115 facilitates mounting of the gas distributor 100 on a drive system 200 (see FIG. 1). The drive system 200 may include a motor and a drive train or assembly for rotating the shaft 115 in at least one direction. Additionally, process gases enter the gas distributor 100 through the shaft 115 and leave the arms 105 of the gas distributor 100 via the plurality of orifices in each arm 105. At least a portion of the shaft 115 may be rotated by the drive system 200 in either clockwise or counterclockwise directions 116. Normally, the gas distributor 100 is oriented with the plane of the arms 105 being horizontal and the orifices on the underside of the arms 105. In such an orientation, the shaft 115 extends upwardly from the plane of the arms 105. Preferrably, the drive shaft is suspended from a bearing of a type chosen to minimize the generation of particulates (e.g. , a Ferrofluidic^® bearing).

The drive system 200 rotates the gas distributor 100 about an axis in either a clockwise or counterclockwise direction 116, as is represented in FIG. 2 by the curved arc with an arrow head at each end. The axis of rotation of the gas distributor 100 is usually vertical and usually coincident with the center of the plasma process chamber 20. The speed of rotation of the gas distributor 100 is not critical to maintaining a uniform distribution of the plasma. Satisfactory performance of the system has been obtained with rotational speeds of approximately 100 revolutions per minute.

Besides rotating the gas distributor 100, the drive system 200 is also capable of making the gas distributor 100 translate in an up and down direction (i.e. , the vertical line 130 with an arrow head at each end in FIG. 3) by increasing or decreasing the distance between the gas distributor 100 and a surface of the semiconductor wafer or wafers 70 to be processed.

The gas distributor 100 may be fabricated from any one or a combination of the following: (1) a metal (e.g. , aluminum, having an untreated surface, except if necessary to ensure cleanliness); (2) a metal coated with a non-conducting surface film (e.g. , aluminum with an anodized surface); or (3) a non-conducting material.

The gas distributor 100 of the present invention is advantageous for use in both etch and deposition steps related to plasma processing. In etch processes which use an electrostatically shielded radio-frequency (hereinafter "ESRF") high density plasma processor at pressures in the order of 1-10 mTorr, the plasma densities are typically greater than the plasma densities associated with capacitively excited plasma processors by a factor of 50 to 100. The high densities are necessary to achieve a commercially viable etch rate. Furthermore, the high densities assure a sufficiently great ion flux at the bottom of small features (e.g., <0.5 micrometer) of the IC formed from the semiconductor wafer 70.

However, the high plasma densities have the drawback that any atom or molecule that enters the plasma processing chamber 20 through either a typical gas inlet tube or a conventional gas distribution manifold and that impinges on the surface of a semiconductor wafer will have experienced 50 tolOO times the number of collisions that an atom or molecule traversing a similar path through the less dense plasma of a capacitively coupled plasma processor would have experienced.

As a consequence of the increased number of collisions of the atom or molecule due to the high plasma densities, the relative concentration of the atoms, molecules, and ions arising from the feed gas, which impinge upon the surface of the semiconductor wafer 70 (or the wall of other substrates), will not be the same as the relative concentration of the atoms, molecule, and ions arising from the feed gas in a plasma processor that operates at a lower pressure. Typically, the dissociation of molecules in the feed gas subjected to the higher plasma densities will be many times greater than the dissociation of molecules in the feed gas in plasma processors operating at lower pressures. Thus, the plasma processing done at higher plasma densities may not to proceed in the optimum way.

One way to reduce the number of electron collisions that the feed gas atoms or molecules undergo before impinging on the substrate, and consequently improving the efficacy of the plasma processing, is by introducing the feed gas closer to the wafer surface, although still within the plasma, by using the gas distributor 100 of the present invention.

The same above-described considerations with respect to atoms and molecules in the etching process apply to the atoms and molecules in the deposition processes. The molecules in a molecular feed gas are substantially dissociated in the plasma before those molecules impinge upon the surface of the semiconductor wafer 70. Estimates predict (and measurements confirm) that in ESRF plasma processors operating at high plasma densities (e.g. , those approximately greater than 10¹² cm ³) and at low pressures (e.g. , those less than 10 mTorr), more than 80% of the molecules in the molecular feed gas will be dissociated before impinging upon the surface of the semiconductor wafer 70.

The molecules that become deposited have a low surface mobility after landing on the surface of the semiconductor wafer. This is because the chemical groups that tend to inhibit incorporation of the molecule into the surface of the semiconductor wafer 70 are removed when the molecular bond is broken. The reduced surface mobility results in a deposited layer containing a greater concentration of defects. The problem of a deposition layer containing a greater concentration of defects can be alleviated by injecting the feed gas closer to the surface of the semiconductor wafer 70, although still within the plasma, using the adjustable gas distributor 100 according to the present invention.

In any deposition processing equipment, contamination by particulates will occur unless the equipment is periodically cleaned. A cleaning technique that is especially suitable for a high density, ESRF plasma processors takes advantage of the processor's built-in capability for RF-assisted self-cleaning. For this reason, in one embodiment the gas distributor 100 is electrically insulated from the rest of the process chamber 20 and is otherwise designed to accommodate a suitable RF biasing so that the gas distributor 100 may be cleaned in situ by RF power at the same time that the rest of the process chamber 20 is being cleaned. In other words, only a single cleaning procedure is necessary for the entire process chamber 20 and its contents.

Alternate embodiments of the plasma source 10 include at least two gas distributors 100. In each such embodiment, each gas distributor 100 rotates about a shaft laterally displaced from the other, wherein the amount of displacement is either fixed or dynamically variable. Plural sets of arms 105 (either offset or aligned vertically) can likewise be rotated by plural concentric shafts 115, either rotated in the same or opposite directions. Moreover, the speed of rotation of each set of arms 105 need not be the same as every other set of arms 105. Similarly, the number of arms 105 and the sites and locations of the orifices may be different in different sets of arms 105.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein.

Claims

CLAIMS:

1. In a plasma processing chamber, the improvement comprising: plural rotatable arms, wherein each rotatable arm has plural orifices for distributing at least one processing gas into said plasma processing chamber.

2. The improved plasma processing chamber of claim 1, further comprising a drive system for rotating said plural arms.

3. The improved plasma processing chamber of claim 2, wherein said drive system comprises a motor for rotating said plural arms in at least one of a clockwise direction and a counterclockwise direction.

4. The improved plasma processing chamber of claim 2, wherein said drive system includes a motor for increasing and decreasing a distance between said plural arms and a surface of the semiconductor wafer to uniformly distribute a plasma across the surface of the semiconductor wafer.

5. The improved plasma processing chamber of claim 1 , further comprising a radio frequency power source and at least one of an inductively coupled coil and a pair of capacitively coupled plates for applying radio frequency power to said plasma processing chamber.

6. The improved plasma processing chamber of claim 4, further comprising an electrostatic shield.

7. The improved plasma processing chamber of claim 4, further comprising a bias shield.

8. The improved plasma processing chamber of claim 2, wherein said drive system includes a hollow, cylindrically-shaped shaft.

9. The improved plasma processing chamber of claim 1, wherein said plural orifices are distributed across a lower surface of said plural arms.

10. The improved plasma processing chamber of claim 1, wherein said plural orifices are distributed across a side surface of said plural arms.

1 1. The improved plasma processing chamber of claim 1 , wherein said plural orifices have at least two different diameters.

12. The improved plasma processing chamber of claim 1, further comprising: an electrical insulator for electrically insulating said plural arms from a remainder of said plasma processing chamber; and a biasing source coupled to the plural arms for RF biasing the plural arms during cleaning.

13. A method for generating, in a plasma processing chamber, a uniform plasma using a gas distributor including a plurality of arms extending outwardly from a center, said method comprising the steps of: injecting a gas from a gas source through a shaft and into said plurality of arms; rotating said plurality of arms; ejecting the gas through a plurality of orifices of each arm of said plurality of arms and into said plasma processing chamber; subjecting the gas distributed within said plasma processing chamber to radio- frequency excitation to create a plasma; and applying said plasma onto a surface of a semiconductor wafer.

14. The method of claim 13, wherein the step of ejecting the gas comprises ejecting the gas through the orifices located on a bottom surface of each arm of said plurality of arms.

15. The method of claim 13, wherein the step of ejecting the gas comprises ejecting the gas through the orifices located on side surfaces of each arm of said plurality of arms.

16. The method of claim 13, wherein the step of injecting comprises positioning said gas distributor vertically above the surface of the semiconductor wafer at a distance depending upon the gas being injected.

17. The method of claim 13, wherein the step of injecting the gas comprises injecting a combination of plural gases.

18. The method of claim 13, further comprising, after applying said plasma, at least one of: (1) etching the surface of the semiconductor wafer and (2) depositing on the surface of the semiconductor wafer.