High efficiency plasma source for plasma processing

Abstract

A plasma source for plasma treatment is disclosed. The source includes a gas injection insert defining a plasma source interior volume and a plasma generation region or active region with enhanced electron confinement between the chamber wall and the insert. The source includes a pair of induction coils disposed around the active region. The gas injection insert includes a first set of gas injection ports at the top of the active region above the top coil and the second set of gas injection ports disposed in the lower half of the active between the first and the second induction coils. In at least one embodiment the first feed gas entering the active region through the first gas injection inlet is a noble gas and the second feed gas injected into the active region through the second gas injection inlet is one of the processing gases.

Description

High Efficiency Plasma Source for Plasma ProcessingPRIORITY CLAIM

[0001] The present allocation claims the benefit of priority of U.S. Provisional Patent Application No.63 / 725, 453, entitled "High efficiency plasma source for plasma processing," filed on November 26, 2024, which is incorporated herein by reference for all purposes.CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] The present disclosure relates generally to plasma generation for semiconductor plasma processing and, more particularly, to a plasma treatment and dry strip.PRIOR ART

[0003] V. Nagorny, D. Lee, A. Kadavanich, "Inductively coupled plasma source for plasma processing", US 9,653,264 (2017)

[0004] K. Obuchi, "Apparatus for plasma treatment", US 6,770,165, (2004).

[0005] V. Nagorny, C. Crapuchettes, "High efficiency plasma source", US 9,214,319, (2015).

[0006] V. Nagorny, V. Vaniapura, V. Surla, "Validation of High Efficiency ICP SourcePerformance for Advanced Resist Ashing", Proc, of Advanced Semiconductor Manufacturing Conference ASMC 2015, 978-l-4799-9930-9 / 15 / $31.00 ©2015 IEEE.

[0007] V. Nagorny "High Efficiency Plasma Source with Chemistry Conversion" PCT patent Application PCT / US25 / 23039, filed on April 3, 2025.BACKGROUND OF THE INVENTION

[0008] Plasma processing is widely used in the semiconductor industry for deposition, etching, mask removal, plasma treatment and related processing of semiconductor wafers and other substrates. Inductive plasma sources are often used for plasma processing to produce high density plasma and reactive species for processing wafers. For instance, inductive plasmasources can easily produce high density plasma using standard 13.56 MHz and lower frequency power generators.

[0009] For certain plasma processes such as a plasma treatment, or a dry strip it is not desirable to expose the semiconductor wafers directly to plasma ions. In these processes, a plasma source is used mainly as an intermediate for modification of a gas composition and to create some chemically active radicals for processing wafers. The plasma is formed remotely from the processing chamber and desired particles are channeled to the semiconductor wafer, for example, through a grid that is transparent to neutral particles and not transparent to charged particles. As long as one accepted the use of the grid, one can also use it for providing process uniformity on the wafer. So, here we will assume that one uses the grid and the process uniformity is not an issue.

[0010] Because rates of processes on the wafer directly relate to the rate with which these new species are created and delivered to the surface of the wafer, these processes typically require high RF power (e.g. about 3-10 kW) and in some cases high gas flows (e.g. about 5-25 slm) and high pressure (e.g. about 1 Torr or higher) and a large diameter of the plasma source. When gas and energy consumption demands are that high, the efficiency of the plasma source becomes increasingly important. Efficiency of the plasma source affects both capital and operational costs. In addition, large size of the source at increased pressure creates additional problems for plasma ignition and sustaining.

[0011] In order to overcome these problems two similar, but slightly different solutions (US 6,770,165, and US 9,214,319) were proposed earlier. The first one (US 6,770,165) suggested to use an insert, to create a separate plasma generation region near antenna with reduced volume - that would increase the power density in that region, improve electron confinement in the electron heating area and thus simplify both plasma ignition and sustaining. The second one (US 9,214,319), named a High Efficiency Plasma Source (HES), suggested that choosing a correct gap between the insert and the wall will make all the feed gas to flow through the region with high density of energetic electrons and then one can optimize the efficiency of radical generation by adjusting position of the coil with respect to the insert (overlapping size of the insert and the coil) that controls the size of the active region. Typically that would require a positioning of antenna near the bottom of the insert (Nagorny, et al., ASMC2015).

[0012] While these ideas proved to work well and the efficiency of the HES design is noticeably higher than of a regular ICP plasma source, some modern applications require even higherdischarge efficiency, especially at high discharge power. Thus, a need exists for an efficient and high power plasma source providing a large supply of desired reactive species to the wafer.SUMMARY OF THE INVENTION

[0013] Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. Embodiments of the present disclosure generally relate to inductively coupled plasma sources and plasma processing apparatus and methods.

[0014] In at least one embodiment, plasma source includes a dielectric chamber sidewall and a gas injection insert at the top of the source. The gas injection insert together with the chamber sidewall define a plasma chamber, including a plasma generation region between the sidewall and the insert. The plasma source further includes a top and a bottom radio frequency (RF) antennas adjacent to the plasma chamber around the dielectric sidewall, both operating in the area of the plasma generation region. The gas injection insert includes a first set of gas injection ports at the top of the plasma generation region above the top RF antenna and a second set of gas injection ports between the first and the second RF antennas. The plasma source includes a first RF generator coupled to the first antenna and the second RF generator coupled to the second antenna. In at least one embodiment the RF antenna is an induction coil. In at least one embodiment the top coil uses magnetic field concentrators (ferrites).

[0015] In at least one embodiment, plasma source includes a dielectric chamber sidewall and a gas injection insert at the top of the source. The gas injection insert together with the chamber sidewall define a plasma chamber, including a plasma generation region between the sidewall and the insert. The plasma source further includes a pair of RF antennas adjacent to the plasma chamber about the dielectric sidewall, generating plasma from gases passing them in the plasma generation region. The gas injection insert has two sets of gas injection ports introducing gases into the plasma generation region. The first set of gas injection ports introduces a first gas at the top of the plasma generation region above the first antenna. The second gas enters the plasma generation region through the second set of gas injection ports in the lower half of the plasma generation region below the first RF antenna and close to the second antenna. In at least one embodiment the second RF antenna is positioned at the bottom of the plasma generationregion - close to the bottom edge of the gas injection insert. Species generated by the second RF antenna then pass the main plasma volume and a grid to the processing chamber.

[0016] In at least one embodiment, plasma source includes a first dielectric sidewall and a gas injection insert defining a plasma source interior volume, including a plasma generation volume between the first sidewall and the insert. The gas injection insert includes two sets of gas injection ports injecting two feed gases into different parts of the plasma generation volume. The plasma source includes a first induction coil disposed around the first sidewall between gas injection ports and a second induction coil below the first coil and close to the bottom edge of the insert. In at least one embodiment the second coil is disposed below the second gas injection port. The plasma source includes a first RF power generator coupled with the first induction coil and a second RF power generator coupled with the second induction coil.

[0017] Another exemplary aspect of the present disclosure is directed to a method for generating plasma for processing a substrate. In at least one embodiment, a plasma processing method includes introducing a first gas into a plasma generation volume between the first sidewall and a gas injection insert and generating a first gas plasma in that volume by energizing a first induction coil. The method further includes introducing a second gas into the plasma generation volume below the first induction coil, mixing the second gas with the first gas modified by the first plasma and generating second plasma from that mix by a second coil positioned downstream from the second injection point. The method further includes delivering plasma species to a substrate placed in the processing chamber. In at least one embodiment ions are filtered out by a grid separating plasma and processing chambers. In at least one embodiment the first gas is a noble gas (e.g. Ar), and the second gas is a molecular gas or a mix of molecular gases providing radicals.

[0018] Variations and modifications can be made to these exemplary embodiments of the present disclosure. For instance, in a particular embodiment, a Faraday shield can be placed between induction coils and the dielectric chamber sidewall. In another particular embodiment, the gas injection insert can include a metal / conductive portion. In another particular embodiments RF generators may operate at different frequencies, for example, 2 MHz and 13.56MHz.

[0019] These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification,illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.BRIEF DESCRIPTION OF DRAWINGS

[0020] The appended drawings only illustrate exemplary embodiments and are not to be considered limited of its scope.

[0021] Figure 1 - Illustration of the principle of the current invention

[0022] Figure 2 - High Efficiency plasma Source US 9,214,319 (Prior art).

[0023] Figure 3 - Plasma source according to at least one embodiment.

[0024] Figure 4 - Plasma source according to at least one embodiment.

[0025] Figure 5 - Faraday shield pattern according to at least one embodiment.DETAILED DESCRIPTION OF THE INVENTION

[0026] It is well known that plasma ignition and sustaining is very different in processing gas mixes. In some gas mixes plasma ignition and sustaining require relatively small power, while in others they require high power. It is especially pronounced if one compares noble gases and molecular gases. It takes about half energy for ionization in noble gases compared to molecular gases. Plasma density in argon can be one to two orders of magnitude higher than in majority of processing gases when using the same plasma source at the same power. Minimum power required for sustaining plasma in a noble gas like argon or helium is much lower than what is necessary for molecular gases. The reason for high efficiency of discharge in noble gases is the absence of low energy electron excitation levels in noble gases, negligible losses on gas heating (elastic collisions between electrons and atoms) and relatively narrow range between ionization and the first electron excitation levels (metastable level). Another feature of discharges in noble gases at high pressures is enormous amount of metastables in the discharge. These features can be used for generation of radicals at high pressures.

[0027] Of all noble gases, the most interesting for that purpose is argon (Ar). Besides being inexpensive, argon excitation and ionization levels are relatively low (compared to He and Ne, but in the right range for Penning like processes, so one can use products of Ar plasma fordissociation or ionization of most of molecular gases used in plasma processing for generation of radicals. Indeed, ionization level of Ar , 1=15. 755eV is higher than most of ionization levels for processing gases, and the metastable level Em=l 1.55eV is between dissociation and ionization levels for vast majority of processing gases. That means that collisions of argon metastables with molecules will efficiently dissociate these molecular gases generating radicals, and argon ions can efficiently ionize those gases through non-resonant charge exchange process.

[0028] The idea how one can use these properties of Ar is illustrated in the Figure 1. One can imagine a simple channel 100 between two flat surfaces and ID flow starting as pure Ar (110), changing to Ar plasma (111) as it passes a first "antenna" 121 generating plasma about it. Downstream from the antenna plasma slowly converts back to Ar, mostly due to recombination of ions and quenching of metastables on the surfaces. However if downstream from the first antenna one injects into this flow a molecular gas B (112) then argon metastables will efficiently dissociate this molecules into radicals^ and B, and Ar* ions will exchange charge with molecular gas generating ions ^4B+in the area 113 adjacent to the injection point. The^r plasma will be converted in to completely different plasma. Compared to argon metastables Ar*, radicals A and B do not quench on the walls of the channel 100 and flow freely downstream toward the exit of the channel. Obviously, the closer injection point 112 of the gas AB to the antenna 121 the more radicals and molecular ions are generated. One has to remember, though, that it they are too close then the upstream diffusion of the molecular gas^B from the injection point 112 may "poison" the A' plasma. Gas mix coming from the mixing area 113 is completely different from the original gas AB - it is rich on radicals A, B and Ar, so one can obtain even higher level of dissociation if right after or about the mixing point uses another antenna and generate plasma from that mix. If areas 111 and 114 are not too far from each other, then electrons can travel from one plasma area to another helping with plasma generation in the area 114. The latter effect was observed by the author earlier and mentioned in his Patent US 9,653,264.

[0029] One can easily realize this idea using axial flow between two large diameter cylinders and induction coils for antennas wrapped around the outer dielectric cylinder. Details of preferred embodiments are described below.

[0030] It is worth noting that recently author filed a Patent Application PCT / US2025 / 023039, with a dual gas injection and only one coil between gas ports. While there are clearly some similarities between these approaches, there are also fundamental differences between them.The main purpose of PCT / US2025 / 023039 invention was to propose a way to avoid plasma contamination caused by a source wall being etched by a reactive process gas radicals (especially hydrogen H or fluorine F) produced in plasma while achieving good efficiency. Since the wall etching strongly depends on the wall temperature, which is highest near the coil, the second gas injection port with that particular gas (e.g. hydrogen) must be downstream from the coil and separated from the coil by a quite a large distance (l-5cm), compared to the current case, where this distance must be as short as possible as long as it doesn't affect Ar plasma generation. For the same reason one cannot have another antenna downstream from the second gas injection - that will create a hot spot on the wall in the presence of etching gas. That method / design sacrificed efficiency for non-contamination.

[0031] In the current invention the first stage - generation of Ar plasma and mixing its products with a second gas is only a preliminary step designed for modification of a gas, "feeding" the second (main) coil. The modified "feed" gas enters the active region of the second coil with significantly lower percentage of molecules in the mix and with some level of ionization. That makes the plasma generation there much more efficient. The question of reactions between walls and reactants / radicals generated in plasma is out of question here and we don't have to worry about the wall temperature in the presence of radicals. So, the current invention can only be used with gases, which radicals do not chemically react with a source sidewall, or these reactions could be ignored, by some reasons. These are gases like oxygen, nitrogen and many other processing gases.DETAILED DESCRIPTION OF THE PEREFERRED EMBODIMENT

[0032] While one can come up with many embodiments, we will focus on detailed description of a two exemplary embodiments simply to describe the key elements of this invention for better understanding of main ideas.

[0033] For convenience we start with the original design of a High Efficiency plasma Source from US 9,214,319, as it demonstrates a mentioned earlier realization of a ID flow passing antenna. Figure 2 (based on Fig.2 from US 9,214,319) shows a plasma processing system consisting of the plasma source 200 and a processing chamber 250 with a substrate holder 252 and a wafer 254, separated by a grid 256. The plasma source 200 comprises a chamber wall 201,chamber cap 216 with a feed gas inlet 203-204, RF coil 210 with RF power supply 214 and a matching network 216. Finally, the plasma source comprises gas injecting insert 202. The insert 202 together with the sidewall 201 form a gas injection channel 204 and a plasma generation region 241 near the coil with enhanced electron confinement in the region with high electric field, leading to a high plasma density rich on "hot" electrons, and directs all the gas flow through that region, increasing probability for every molecule to be transformed into desired species. The efficiency of the source depends on the overlapping length A between the coil (electron heating area) and the insert sidewall (area of enhanced confinement), and the gas velocity (flow <t> over pressure p), so that one has to optimize the combination overlapping and the gas flow. The value of A in the Fig.2 is close to the coil's vertical size. The gas injection channel in Fig.2 has a form of a slit between the wall 201 and the insert 202, but one can use a different way of gas injection into the plasma chamber as long as the injection happens above the active plasma generation region near the coil.

[0034] So, the insert is a key element that must be present in ANY high efficiency design for a high pressure source. It was shown in US 9,214,319 and in presentation ASMC2015 (Nagorny, et al.) that the optimum position of the coil is around the bottom edge of the insert. As this invention relates to a plasma source, all figures below will show only the plasma chamber - above the grid separating plasma chamber and the processing chamber.

[0035] Figure 3 depicts a plasma source 300 according to an exemplary embodiment of the present disclosure. As shown, the interior 340-341 of the plasma source 300, including a plasma generation region 341 are defined by a dielectric sidewall 301 forming a cylinder and the gas injection insert 302. A gas injection insert 302 has two gas inlets 303 and 307, with multiple gas injection ports 304 and 308 for injecting gases into the plasma generation region. Gas injection ports 304 and 308 are distributed uniformly along the annular gas distribution channel 305 and the insert's sidewall from the gas distribution volume 309. This gas injection system provides a gas flow similar to the one described in the Figure 1 between 2 close surfaces (insert and the chamber sidewall) in the plasma generation region 341 of the plasma source interior.

[0036] Two ICP coils 310 and 320 are placed around the dielectric sidewall 301 for plasma generation from the gas passing these coils in adjacent to them areas "a" and “b" of the plasma generation volume 341. Two RF power generators 314 and 324 with matching networks 316 and 326 apply power to the coils 310 and 320, respectively. Grounded disk 327 is for separating electromagnetic fields of the induction coils. RF generators for different coils preferably operateat different frequencies. Grounded Faraday shield 330 can also be used to reduce capacitive coupling between coils and plasma and reduce sputtering of the dielectric sidewall by ions.

[0037] The first feed gas Gasl enters the plasma chamber through multiple ports 304 and then passes the first plasma generation region "a" near the auxiliary coil 320, which modifies that feed gas into a Gaslm. The modified in the region "a" gas, then mixes and reacts with the second feed gas Gas2 in the intermediate region "c", creating potentially very different gas Gas3, which then enters the second plasma generation region “b" related to the main coil 310. The second feed gas enters the plasma generation volume 341 through a gas inlet 307, followed by gas distribution volume 309 and multiple ports 308 between the coils. Figure 3 shows ports 308 entering the active region perpendicular to the surface of the insert. It is obvious that they can be directed under some angle to that direction, say 0-45 degrees downwards.

[0038] To demonstrate a method based on this embodiment, let's assume that the Gasl is Ar, and Gas2 is one of the typical processing feed gases, for example oxygen O2, or nitrogen N2. Then modified by plasma Gaslm(after region “a") consists of the argon rich on argon metastables ( Ar*) with excitation energy of Em=l 1.55eV , argon ions (Ar+) with ionization energy lAr=15. 755eV , and electrons. Since argon atoms don't quench argon metastables or ions (dominating processes are resonant excitation / charge exchanges), these species flow with the ground state Ar atoms toward the region "c" losses only on the walls) where they mix with the Gas2 entering reactive zone from second injection ports.

[0039] In case of O2as a second feed gas (ionization and dissociation energies are 1O2=12. 6eV, Edis,o2=8-4eV , respectively), the dominating reaction in the region “c" between argon metastables and O2molecules is dissociation of O2and dominating reaction between O2molecules and argon ions is a non-resonant charge exchange. That means that the Gas3, entering the region “b", is an oxygen plasma (diluted by Ar), rich on oxygen ions and radicals, poor on low energy excited oxygen molecules, and with significantly reduced molecular component compared to the feed gas entering the volume through ports 308. The second coil will now operate with the Gas3 generating radicals more efficiently than it would do with a simple mix Gasl+Gas2.

[0040] In case of N2as a second feed gas (IN2=15.6eV, Ea&N2=9. 76eV), the number of different reactions between argon metastables and N2is larger - besides dissociation there is a large number of highly excited molecular excitation levels of N2. So the Gas3 formed in the region "c" and entering the active region of the second coil (“b") is mostly highly excitednitrogen gas (diluted by argon), which was generated without large waste of energy on low energy vibrational excitations of nitrogen, nitrogen ions and argon atoms and which is very easy to convert into nitrogen plasma with large fraction of nitrogen radicals.

[0041] It is worth noting again, that in both cases (O2or N2for the second gas) the Gas3 significantly differs from a mix of feed gases Gasl+Gas2 , since the Gaslm, which enters the area of the second coil, is very reactive and it changes Gas2, which original Gasl does not. That makes the second discharge in Gas3 significantly more efficient than what it would be with original mix Gasl+Gas2. So, the purpose of the split of a feed gas into two components with Ar flowing from the top, generating argon plasma and then mixing it with the second component - is efficient modification of the feed gas for efficient plasma / radicals generation by the main coil 310.

[0042] Dimension of the plasma generation volume in radial direction was defined in the US 9,214,319. It is about 1-3 plasma skin layers. For typical plasma parameters at high pressures (0.5-5Torr) and high power deposition in plasma, it is about 2-5cm for most gases, but can be up to half of the radius of the plasma chamber. In a vertical direction dimension of the plasma generation volume 341 is mostly limited by sizes of coils and space between them and above the top coil. Realistically, the length of this area with standard 13.56MHz coils must be about 15- 20cm.

[0043] Material for the dielectric sidewall can be quartz, alumina, zirconia, aluminum nitride and many other dielectric materials, which can withstand plasma heat, chemistry and hold vacuum under atmospheric pressure. With respect to the material of the insert it can be ceramic or quartz, but the preferred material is a metal like aluminum alloy. It has to be well cooled to withstand large heat from plasma. Water cooling lines, for example, can be buried in the top cover 312 and in the cover 306 of the gas distribution volume 309 of the second gas injection.

[0044] It is obvious that the main coil 310 in the current disclosure behaves similar to the coil in the US 9,214,319. Thus, for the best efficiency this coil must be positioned at the very bottom of the insert. More specifically, the active area "b" should "partially overlap with the insert". Exact position of the coil can be found only experimentally, since it depends on process parameters like the gas flow, pressure and the gas. Taking into consideration a typical size of a regular 13.56MHz induction coil one could expect the center line of the coil to be about 0-3cm above the edge of the insert.

[0045] As we mentioned above, it is beneficial if coils 320 and 330 operate close to one another, so that electrons can diffuse between active regions "a" and “b" related to these coils. It is however difficult to realize if both coils are regular 13.56MHz ICP coils. One can reduce the distance between coils if the top coil (operating with Ar) is using magnetic field concentrators.

[0046] Figure 4 depicts a plasma source 400 according to an exemplary embodiment of the present disclosure. It shows essentially the same design as in Figure 3, but with the top coil 430 using magnetic field concentrators. Similar to Figure 3, the interior 440-441 of the plasma source 400 is defined by a dielectric sidewall 401 and the gas injection insert 402. A gas injection insert 402 has two gas inlets 403 and 407, with multiple gas injection ports 404 and 408 for injecting gases into the plasma generation volume. Gas injection ports 404 and 408 distributed uniformly along the annular gas distribution channel 405 and from the gas distribution volume 409. This gas injection system provides a gas flow similar to the one described in the Figure 1 between 2 close surfaces (insert and the chamber sidewall) in the plasma generation volume 441 of the plasma source interior.

[0047] Two ICP coils 410 and 420 are placed around the dielectric sidewall 401 for plasma generation from the gas passing these coils in adjacent to them areas "o" and “b" of the plasma generation volume 441. Two RF power generators 414 and 424 with matching networks 416 and 426 apply power to the coils 410 and 420, respectively. The top coil 420 comprises actual winding 421, magnetic field concentrators (ferrites) 422 and grounded metal shield 423 isolating this coil from the main coil 410. So, one can place these coils quite close to each other. Grounded Faraday shield 430 can also be used to reduce capacitive coupling between coils and plasma and reduce sputtering of the dielectric sidewall by ions. The coil with ferrites can advantageous if the first gas entering the plasma generation volume from the top ports 404 is argon.

[0048] Operation of the plasma source in this embodiment is exactly the same as in the previous embodiments with similar coils. The first feed gas Gasl enters the plasma chamber through multiple ports 404 and then passes the first active region "o" near the auxiliary coil 420, which modifies that feed gas into a Gaslm. The modified in the region “a" gas then mixes and reacts with the second feed gas Gas2 in the intermediate region "c", creating potentially very different gas Gas3, which then enters the second active region “b" related to the main coil 410. The second feed gas enters the plasma generation volume 441 through gas ports 408.

[0049] RF generators for different coils preferably operate at different frequencies. For example one can use 13.56MHz RF generator for 414 and around 2MHz RF generator for 424. This is the most cost effective choice, since generators of these frequencies are widely available.

[0050] Figure 5 shows a small section of an exemplary Faraday shield as it is seen from the inside of the plasma chamber. The Fig.5 also shows elements of both coils as one can see them through openings in the Faraday shield. The Faraday shield in this figure is designed to fit 2 coils of different kind and different frequencies. The upper one is a lower frequency (e.g. ~2MHz) coil with ferrites, and at the bottom one is a regular coil without ferrites (e.g. ~13.56MHz)), like in the plasma source shown in the Figure 4. A shaded area 530 is a metal body (e.g. copper, aluminum) of the Faraday shield. There are two different type of openings in the shield, a simple openings 531 are for the main coil 410 (black are the main coil windings), and 532 - are "lying / horizontal H"-shape openings for the coil with ferrites. Through horizontal opening of the "lying H" one can see elements of ferrite surfaces 422 and through the vertical openings of the "lying H"one can see wiring / winding 421.

[0051] The shapes of the openings for inductive field penetration don't have to be as shown in Fig. 5. There are many other possible shapes, which one chooses based on specific goals and restrictions. For example, one can use a similar "horizontal H"- shape of openings for the main coil, which slightly increases efficiency of the field penetration, but also slightly increases capacitive coupling. The shape of the opening is more important for the ferrite containing coil, where one should maximize the ratio of the horizontal opening of the "H" (532) to the distance between adjacent horizontal ends of "H" openings (533).

Claims

ClaimsWhat is claimed is:

1. A plasma source comprising:- a dielectric sidewall forming a cylinder;- a gas injection insert disposed within the dielectric sidewall and located at an upper end of the cylinder, the gas injection insert and the dielectric sidewall defining a plasma source interior volume, including a plasma generation region between the sidewall and the insert;- the gas injection insert comprising a first gas injection line with a first set of gas injection ports coupled to the top part of the plasma generation region and the second gas injection line with a second set of gas injection ports coupled to the lower half of the plasma generation region;- a first radio frequency antenna disposed around the dielectric sidewall opposite to the gas injection insert sidewall between the first and the second sets of gas injection ports and the second radio frequency antenna disposed around the dielectric sidewall opposite to the bottom part of the insert, below the second set of gas injection ports;2. The plasma source of claim 1, wherein the bottom radio frequency antennas is an induction coil.

3. The plasma source of claim 2, wherein the top radio frequency antennas is an induction coil.

4. The plasma source of claim 3, wherein the top inductive coil uses magnetic field concentrators (ferrites).

5. The plasma source of claim 3, wherein the bottom inductive coil is placed at the very bottom of the plasma generation region, so that the centerline of the coil is within 0-3cm above the bottom edge of the insert.

6. The plasma source of claim 5, wherein the distance between the second coil and the second gas injection is less than 1cm.

7. The plasma source of claim 3, wherein the gas injection insert comprises a metal.

8. The plasma source of claim 3, wherein the dielectric sidewall comprises a quartz, or alumina or zirconia or aluminum nitride ceramics.

9. The plasma source of claim 1, wherein the length of the gas injection channel is between 10 and 20cm.

10. The plasma source of claim 3, wherein a Faraday shield is place between the coils and the dielectric sidewall.

11. The plasma source of claim 10, wherein the Faraday shield is grounded.

12. An apparatus for plasma treatment comprising:- a processing chamber having a substrate holder operable to hold the substrate at chosen temperature and a plasma source of claim 1 separated from the processing chamber by a grid.

13. A method for generating plasma for plasma treatment of a substrate, comprising:- providing a downstream gas flow in a plasma generation region of a plasma volume by injecting a first feed gas into a plasma generation region through a gas line coupled to a top set of gas injection ports, and injecting a second feed gas into the plasma generation region through a second gas line with a second set of gas injection ports coupled to the lower half of the plasma generation region;- energizing a first induction coil positioned between the first and the second sets of gas injection ports and generating the first gas plasma;- energizing a second induction coil positioned downstream from the second set of gas injection ports at the bottom part of the plasma generation zone and generating plasma from the gas passing the second coil;14. A method of claim 13, wherein the first feed gas injected through the first (top) set of gas injection ports is mainly an inert gas, like argon, or helium.

15. A method of claim 13, wherein the second feed gas injected through the second set of second gas injection ports is mainly a molecular gas or a mix of molecular gases.

16. A method of claim 13, wherein the second coil is placed at the bottom part of the plasma generation region close to the bottom edge of the gas injection.

17. A plasma source comprising:- a first sidewall forming a dielectric cylinder;- a gas injection insert disposed within the cylinder forming a second sidewall of the diameter smaller than the first sidewall, and located at an upper end of the dielectric cylinder, the gas injection insert and the first sidewall defining a plasma generation volume located between the first and the second sidewalls;- a first induction coil disposed around the first sidewall, against the second sidewall of the gas injection insert;- a second induction disposed around the first sidewall, against the second sidewall of the gas injection insert below the first radio frequency antenna;- the gas injection insert comprising a first gas injection line with a first set of gas injection ports coupled to the top part of the plasma generation region and the second gas injection line with a second set of gas injection ports coupled to the lower part of the plasma generation region between the first and the second RF coils;18. The plasma source of claim 17, wherein the gas injection insert comprises a metal.

19. The plasma source of claim 17, wherein the dielectric sidewall comprises a quartz, or alumina or zirconia or aluminum nitride ceramics.

20. The plasma source of claim 17, wherein a grounded Faraday shield is placed between the coils and the dielectric sidewall.

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