CA2029518A1 - Method for deposition and etching of thin films for microelectronic applications - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The present invention relates to a method for deposition or etching of thin films for microelectronic applications. In particular, it relates to the low temperature deposition of high quality silicon dioxide thin films suitable for gate oxide in MOS technology for VLSI applications. The method solves the problems derived from the harmful effects of energetic particle bombardment and photonic radiation emanated from the plasma, while at the same time makes use of the active species generated in the plasma before they are significantly deactivated, resulting in the achievement of high quality oxide films with low bulk and interface defect densities as well as high breakdown strengths.

Description

2~df~l`J` ;: ;J 1 TlTI.F. (1~ lNVFNT-ON
~E~OD FOl~ l)EPOS~TISlN ANl~_~TC~lNG OF THlN Fll~l~S FOR
MICROEI.ECTRONlC APPl~lCATlONs S F~FLD OF lNVENTlON
The present invendon relates to the deposidon on substrates of thin films of semiconductor, dielectrric, polymeric, metallie and alloy materials and the etehing thereof.
~ACK(~ROUNI) TO THE INV~,NT~ON
Various techniques have been proposed for the deposition of thin films on substrates, including thermal evaporadon, chemical vapor deposidon, sputtering, plasma enhanced chemical vapor deposidon (PECVD), and plasma acdvated chemical vapor deposition (PACVD). Among these techniques, PECVD has proved to be one of the most flexible for deposidng dieleetric and alloy films of different composidons and properdes. Reeendy, PACVD, a version of PECVD, where the deposition occurs downstream from the plasma region (between the plasma region and dhe pump), has been proposed as a soludon for avoiding the harmful effeets of plasma radiation on the growing film with various degrees of success. Another denominations for the same process are "remote PECVD" and "indireet PECVD", signifying the topologieal separadon between the acdve plasma region and the deposidon region. In addition, plasma etching has become a key process in integrated cireuit manufacturing. Although the plasma proeessing kineties is notwell understood, it is well known that varadon of the plasma parameters affects both thin film deposidon and etching characterisdcs. PECVD techniques and plasmaetching teehniques used in industry employ radio-frequency plasma excitadon of a gas mixture. Recentdy, ultra-high fsequency and microwave frequency radiadons have been used for plasma excitadon. One pardcular condidon for plasma exeitadon at a minimal energy is the so-ealled electron cyclotron resonance (ECR) condition. When a plasma is subjeeted to a magnedc field peIpendicular to the electric field of the eleetromagnetic excitadon, electrons and ions are forced to assume circular orhelical paths around the lines of force of the magnede field and hence the electrons and ions are confined in the direcdon perpendicular to the -magnedc field veeto,r. When the magnede field intensity is increased, the angular frequewyoftheele~nrotadon~so increascs and mayreach the value of the 3S angular frequency of tbe microwave electromagnedc excitadon. This condidon is ealled electron eyelotron resonanee. Microwave plasmas under ECR eondidons have been used as ion sources and, subsequently, these ion sources have been developed into plasma enhanced or aedvated ehemieal vapour deposidon and plasma etching systcms based on thc intcracdon of relativcly cnergetic ions and .

activated species with the substra~e surface. The following referenc~s dcscribe tcchniques that make use of energetic particles generated in ECR microwavc plasmas:
(a) Sakudo et al, "Microwave ion source", Rev. Sci. Instrum., 48, pp. 762-- 5 766, (1977).
(b) Matsuo et al, U.S. Patent No. 4,401,0S4.
(c) Matsuo et al, "Reactive Ion Beam Etching Using a Broad Bcam ECR Ion Source", Jap.J. of Appl. Phys., 21, pp. L~L6, (1982).
(d) Matsuo et al, "Low temperature Chemical Vapor Deposidon Method Utilizing an Electron Cyclotron Resonance Plasma", Jap. J. of Appl.
Phys., 22, pp. L210-L212, (1983).
(e) Ono et at, "Elec~on Cyclotron Resonance Plasma Deposition Technique Using Raw Material Supplied By Sputtering", Jap.J. of Appl.Phys., 23, pp.LS34-LS36, (1984).
The ionic bombardment mentioned in this prior art may wcll damage the growing film during the deposition process or the previously fabricated filmlayers during the etching process. Plasma is also a source of energedc photon radiadons such as soft X-ray and ultra violet light. These radiadons have been known to be harmful to the properdes of electronic devices fabricated using silicon based materialæ Descripdon of these negadve effects on deposidon and etching as well as ionic damage of devioe properties are given in the the following references:
(f) L M. Ephrath and DJ.DiMaria, " Review of RIE Induced Radiation Damage in Silicon Dioxide", Solid State Tech., 24, pp. 182-188, (1981).
(g) K H. Ryden, H Norstrom~ C.Nender, and S.Berg, "Oxide Breakdown due to Charge Accumuladon during Plasma Etching", J. Electrochem. Soc., 134, pp. 3113-3118, (1987).
(h) J. Bos and M.Hendriks, "Plasma-induced fixed oxide charge", J. Appl.
Phys., 66, pp. 1244-1251, (1989), (i) J. Kassabov, E.Atanassova, D.Dimitrov, and E.Goranova, "Electrical Prope~ies of Si-SiO2 Structures Treated in Helium Plasma", Microelectronics J., 18, pp. 5-12, (1987) (j) N. B. Zhitene~, " Chemical Potendal Shift in Si (100) MOS-Structure Induced by Submillimeter Radiadon", Solid State Com., 71, pp. 351-354, (1989).
In the present art, a plasma deposition process has been developed in a configuration that avoids the hamlful effects of energetic particle bombardment or radiation induced by plasmas, but making full use of the activated spccies. Foursciendfic publications have reported the physical and electrical properties of SiO2 filn~ depositcd by this lecl~ique and on MOS capacitors built using these films:

(k) T. T. Chau, S. R. Mejia, and K. C. Kao, " High Quality SiO2 Film deposition using New ECR microwave Plasma" Electronic Icttcr, 2S, pp.
1088-1089, (1989).
(I) T.T. Chau, S. R. Mejia, and K. C. Kao, " High q~ality 100 A SiO2 films fabricated by a new ECR microwave OECVD process", ( to bc published in the J. Electrochemical Soc. 1991).
(m) T.T. Chau, S. R. Mejia, and K. C. Kao, " Thickness dependence on properties of SiO2 deposited by PECVD microwave ECR plasman, (to bc published in the J. Vac. Sci. Soc., 1991).
(n) T.T. Chau, S. R. Mejia, and K. C. Kao, " The effects of deposition temperature on properties of SiO2 films fabricated by a new ECR
microwave PECVD process", presented at the 5th canadian semiconductor technology conference in Otawa, Aug 1~16, 1990 (to be published in Canadian Journal of Physics, 1991).
Silicon dioxide films have been deposited by the present art with quality equivalent to or better than thermally oxidized silicon. In order to distinguishbetween the present art and the previous art, we have named this method the "close proximity plasma acdvated chemical vapor deposidon" (CP-PACVD), for reasons that will become apparent in the secdon below.
~iIlMM~RX OF ~lNVENTION
In accordance with the present invcndon, a plasma generates acdve species that are allowed to react with a silicon-containing gas (e.g. silane) fed in a phvsicallv separated region where the substrates are also located in order to prevent the film from damaging by energedc pardcle bombardrnent and photonic radiadon. At the same dme the method makes use of energedc activated species ~2fi2E they are de-enagized by many collisional processes. This is the reason why the method can beimplemented Ieadily at low pressures. In the "remote PECVD" or "PACVD"
methods the plasma and substrates are separated by a distance of many mean free paths at the pressure of operadon, and the acdvated species generated in the plasma are deacdvated considerably by the dme they reach the substrate. In some systemsthe plasma and substrates are not at straight view from each other, and thus thepho~nic radiadon of thc substrate is avoided, but at the expense of increasing the 3~ plasma-substrate distance and deacdvadng many of the acdvated species. In the present art the substrates are placed in "close proximity" to the plasma region, but they are protected from the damaging bombardment and radiadon created in the plasma Therefore, we denominate this prccess "Close Proximity Plasma Activated Chemical Vapo.r Deposidon" (CP-PACVD), and the system "Close Proximity 2 ~ 4 Plasma Processing System" (CP-PPS). Far from the plasma region, the specie energies and compositions are very different, which affect the film quality. This method is unique and is the only one that can produce silicon dioxidc films withquality cquivalent to or better than thermally oxidized silicon, as shown in reference (k), (1), (m) and (n) above.The system consists of two major compartmcnts; onc is for the plasma excitation called "the plasma chamber" and the other for the filmdeposition or etching called "the processing chamber". These two chasnbcrs arc æparated by a novel cont~oller. In term of technology, we narne this contro!lcr "the specics selector and energy controller (SSEC)" The specics selector and encrgy controller (SSEC) is uæd for film deposidon to filter out charged particles, which are known to be harmful to deposited insuladng films; while for etching, the SSEC
can cont~ol the energy of both the charged and the neutral etchant species for the opdmizadon of the etching process.Furthermore, it avoids also photonic radiadon effects.
RRTEF DESCRlPT~Ol~l OF DRAWINGS

Figure 1 is a general schemadc diagram of a closc proximity plasma processing system (CP-PPS) for deposidon or etching of thin f~lms at low temperatures.
Figure 2 is a schemadc diagram of a CP-PPS with a microwave ECR plasrna source for thin film deposidon or etching.
Figure 3 shows a schemadc diagram for several SSECs already designed which can be used for thin films deposidon or etching.
Flgure 4 is a graphical representadon of the magnetic field profile along the axis of the plasma chambcr and the funcdon of the SSEC during thin film deposidon.
Figure S is an overall schemadc diagram of an ECR rnic~owave plasma system that has been used for the present art.
Figure 6 is a graphical presentadon of the electron currents measured by a probe biased at +10 V, (a) without the SSEC and (b) with the SSEC, which shows that elec~on collecdon is significantly reduced after traveling through the SSECFigure 7 is a graphical rcpresentadon of the typical inf~ed spec~um of SiO2 films deposited by the present art (curve b), the corresponding spectrum ofconvendonal ECR PECVD films deposited in contact with the plasma (curve a), and ` that of high quality thermal o~ude (curve c).
Figure 8 is a graphical re~resentadon of the I-V chr~sdcs for MOS
capacitors fabricatcd using silicon dioxide deposited by the present method.
Figure 9 shows a histogram of a typical breakdown distribudon from 30 MOS devices ta~en randon~y frorn 100 MOS devices in one substrate fabricated using silicon dioxide deposited by the present method.

, ~ , ' ' 29~ f Figure 10 is a graphical represenlation of the high fi~qoency and the quasi-stadc C-V charactelistics measured after post-metallization annealing (PMA) in forming gas (10% H2 in N2) at 400 C for 30 rnin.
(~.ENERAl. I)FSCRlPr-ON OF lNVFNTll)N
The present art makes use of a device that we have dubbed the "species selector and energy controller", SSEC, inserted between the plasma and the processing chambers. Its main funcdon is to elirninate the damage to the film under deposidon or to the substrate under etching caused by the ionic bombardment and the photonic radiadon originated in the plasma The innovadon and the uniqueness of this system configoradon are as follows:
(i) A species selector and energy controller (SSEC) is used for film deposidon to filter out charged pardcles, which are known to be harmful to deposited insulating films; while for etching, the SSEC can control the energy of both the charged and the neutral etchant species for the opdmizadon of the etching process.
(ii)The SSECcan control the energy of the acdvated (possibly neutral) precursor species for the opdmizadon of the deposidon process.
(iii) The SSEC can prevent all high energy photons such as ultra violet lights and soft X-rays generated by plasmas from irradiating the substrate and the growing filn~
(iv) The system configuradon provides a bi-level pressure in the system, that is, the pressure in the film deposidon or etching compartment is lower than that in the plasma eompartment.
(v) The SSEC provides a low pressure chemical vapor deposidon (LPCVD) condidon whieh is one of the pre-requisites for high quality SiO2 film deposidon at low temperatures (no gas phase reaetdons and powder formadon), and also helps in improving the uniformity of the deposited filrns.
The system consists of two major compartments; one is for the plasma exeitadon ealled "the plasma ehamber" and the other for the film deposidon or etehing ealled "the proeessing ehamber". These two ehambers are separated by theSSEC whieh is eapable of performing effeedvely the five funedons Iistçd in (i~(v) 3S above. Depending on the applieadon of the system (e.g. for the deposidon of insuladng or semiconduetor films, or for etehing), a specially designed SSEC with suitable openiogs and eleetrieal bias has to be used for seleedng the right species and eontrolling their energy for a partieular applieation. It is this SSEC whichenables the low ~ (270 C) deposidon of SiO2 films with physical and 2 ~ 6 electrical properties approaching those of thermal oxidcs grown at 1000 C in oxygen as described in example 2 below and in references (k) and (1) above. The SSEC also enables the low temperature deposidon and etching of any material films for very large scale integration (VLSI) and other applicadons. Therefo~e, we claim S that our invented SSEC is novel and unique and has a great potential impact to the electronic industry.
The plasma can be excited in any gas mixture and by any energy source, sueh as dc, radio frequency (rf), microwave frequency, or eleetron cyelotron resonance (ECR). There are also rnany ways of designing the SSEC depending on 10 the purpose for which the plasma is used. However, although the design of the SSEC may be different from case to case, the basic principles remain unchanged.The only difference from case to case is the emphasis on certain functions described in (i)-(v) above. For a pardcular applicadon the design should be aimed at emphasizing one or more panicular functions for that parlicular 15 applicadon. In the following, we shall confine ourselves to describe how to use our SSEC to deposit high quality thin SiO2 filrns and to use this as a good example for any other applicadons.
Thegases are divided into two separate categories depending on their funcdon, and they are (A) A gas mixture conta ning oxygen or nitrogen, and (B) A20 gas mixture eontaining silicon. The gas mixture containing oxygen or nitrogen(which may consist of 2. N20, N2, or CO2 gases) is fed into the plasma chamber and excited by an extemal energy source. In our case, we use the microwave ECR
excitadon. We purposely make the gas pressure in this plasrna chamber reladvely higher than that in the processing chamber. The gases containing silicon are SiH4, 25 SiF4, Si2H6, or mixture of one of these gases with inert gases such as Ar, He, etc.
The gas mixture containing silicon is fed to the processing chamber via a gas injecdon shower as shown in figure 1. In order to produce films uniform in thickness and homogeneous in composidon, a special nozzle can be designed which will provide a gas mixture containing silicon with a uniform density distribudon30 over the substrate surface. In the processing chamber, the substrates are placed on a thermostadcally controlled table (we use a lamp inserted beneath the table surface to heat the substrate), which is located approximately 5-7 cm away from the SSEC.
As has been mentioned, there are many ways of designing the SSEC
depending on what funcdons we want the SSEC to act opdmally. Figure 3(A) shows two possible designs which are intended to bloek completely the photon 35 radiation direeted to the substrates, and to suppress the charged pardcles (e.g.
eleetrons and ions) that may enter the processing chamber. Thus, we can avoid the impingement of both photons and eharged parlicles on the growing films, which are the major eauses of the defects in the deposited 01ms. The energy of the precurso.r species can be controllcd by the shields in the SSEC, their energy tends to decrease as the number of shields is increased or as the separation betwecn thcm is increased. The energy of precursor species can also bc controlled by regulating the gas pressure difference bctween the plasma and the processing chambers, o~ thc 5 scparation betwecn shidds if the number of shields is fixcd. Flgure 3(B) shows that the individual shiclds can be isolatcd from the chamber so that thcy can be biased with positive or negativc voltage to eliminatc complctely thc clectron or ionic particles. Figure 3(C) shows that we can use a mask screen with tiny windows instead of a solid shield so that we can study the effects of photon radiation. If wc 10 use these three designed SSEC, we should be able to isolate the effects of photon radiation, ionic bombardment and electron bombardment on the properties of the deposited SiO2 films. If all these bombardments can be avoided by using a properly designed SSEC with suitable bias, the reaction in the processing chamber is mainly a CVD process. With the CVD process optimally adjusted, high qualiq thin films can be deposited at low temperatures (lower than 300 C) provided that the substrate 15 surface is well prepared.
DESCRIPI'~ON OF PREFF.RRED FMROD MENT
Referring now to the drawings, a microwave ECR plasma system provided 20 in acco~dance with one embodiment of the invendon is shown in figure 1 and figure 2. A stainless steel waveguide chamber 12 is vacuum sealed at both ends bj quartz windows 14 and a steel substrate supporter flange 16. The waveguide 12 is dhrided into plasma chamber 18 and deposidon chamber 20 by a SSEC 22. The plasma chamber 18 and the prccessing chamber 20 can be heated to an elevated 25 temperature, typically about 400 C by a thermostadcally-controlled heating element 24 surrounding the chamber, or by any other convenient heating means. Gases inlet 26 and 28, vacuum port 30, and electrical feed through 32 may be provided to facilitate plasma characterizadon, deposition or etching control. A substrate supporter 34 ~s mounted in such a way that substrate surface is perpendicular to the 30 gas flow direcdon along the chamb axis. The substrate supporter 34 is also heated by a thermostatically40ntrolled tungsten lamp inserted beneath the table surface.
Typically the table can be heated to temperatures of 400 C. A pair of coils 38 are-mounted coaxially to the cbamber 12 in order to produce a magnetdc fidd that confines the plasma along the plasma chamber 18. The magnedc cor~inement 3S avoids the bombar~ment of the sur ounding structures by energetic electrons and ions and it also rcduces the electron loss to the walls with the consequent Ieduction in electromagnetic power requilement for sustaining the plasma.
The SSEC 22 is placed right after the edge of the magnetic field coils or behind the plasma discharge volume. The SSEC 22 can be designed in liffercnt 2~
ways depending on what function we want the SSEC to act optimally. Pigure 3 shows some of the possible designs. The SSEC æ eonfines the energetic eleelrons,ions, and photons to an isolated region in order to avoid their bombardment on the growing film or on the substrate to be etehed. This effeet is seen most dramadeally in figure 4. The use of the SSEC also creates a bi-level pressure difference and a gradient that opposes the flow of the reactant gas, redueing its diffusion from the deposition chamber into the plasma chamber. The ineorporation of a SSEC into a system provides the means of eontrolling and tailoring the gas dist~ibution to the requirements of composition and thickness uniformity of the deposited films, o~ the desired uniformity of the chemieal eomposition of the reactants for the etching of the substrate su~face.
An overall schematie diagram of an ECR microwave plasma system embodying the present invendon is shown in figure 5.
Figure 6 is a graphical representadon of the electron current collected by a Langmuir probe biased at +10 V and placed at the substrate posidon 34 in the ECRmicrowave plasma system shown in Figure 2, while a hydrogen plasma is sustained in the plasma chamber 18, as a funcdon of absorbed microwave power.
The SSEC 22 design used for this experiment is shown in Figure 3 (A) The two curves shown in figure 6 correspond to the electron current with and without theSSEC device.
Figure 7 is a graphical representation of the infrared speetrum of films deposited by the present art (curve b), the corresponding spectrum of convendonal ECR PECVD films deposited in contact with the plasma (curve a), and ~at of high quality thermal oxide (curve c).
Figure 8 is a graphical representadon of the I-V eharacterisdes for MOS
capaeitors with the silicon dioxide layer deposited using the present method.
Figure 9 shows a histogram of a typieal breakdown distribudon from 30 MOS devices taken randomly from 100 MOS devices in one substrate, the silicon dioxide being deposited using the present method.
Figure 10 is a graphieal representadon of the quasi-stadc and the high frequewy C-V characterisdcs measu~ed after post-metallizadon annealing (PMA) in forming gas (10% H2 in N2) at 400 C for 30 min. -- -F,X AMPl .FS

Exanu)le 1 The ECR microwave plasma system used in this experiment was as 5 illustrated in figure 5. The microwavc power was generatcd by a magnetron operating in a continuous mode at a frequency of 2.45 GHz. Details of thc chambers are shown in Figure 2. The plasma chamber 18 and the dcposition chamber 20 were constructed as a stainless steel waveguide, which is 34 cm long and with standard dimensions of WR-284 waveguidc. Both chambers were 10 separated by the SSEC 22 designed in accordance with Figure 3 (A) (ii)., The chambers were vacuum sealed at both ends by a quartz window 14 and a substrate supporter flange 16 with respecdve Viton O-rings. A bottom port 30 connected thechamber to a turbo molecular pump for evacuatdon to a base prcssurc of 10-6 Torr.
A gas mixture containing Oxygen, i.e. N20 was fed to the plasma chamber via 15 inlet 26. The microwave power was fed through the quartz window in the TE 10 mode. A coaxially mounted coil 38 encircling the plasma chamber to produce an axial magnedc field for plasma confinernent. The funcdons of the SSEC are to select from the plasma chamber the suitable activated species and to guide them into the processing chamber. Once in theprocessing chambcr the actdvated species 20 will travel unobstrucdvely to the substrates since the mean free path is larger than the SSEC-substrate distance, at the pressure of operadon. Diluted Silane gis (10%
SiH4 in Argon) is also fed to the processing chamber by a gas injectdon shower to provide a uniform SiE~4 distribudon over the substrate surface. The gas mixture cont~ining silicon is fed into the processing chamber via gas inlet 28 in front of the 25 substrates. Silane gas and the activated species will react on the wafer surface to.generate SiO2 and to liberate voladle H2 that is pumped out from the chamber.To optimize the plasma excitatdon, the plasma is formed under mic~owave ECR
condidons. The axial magnedc field required to create the ECR condidon is 875 Gausswhichisproducedbyan external dc magnedc field coil su~unding the 30 plasma chamber. The proccssing chamber is connected to a vacuum system which consists of a turbo-molccularpump backed by a chemical rotary pump.
The plasma chamb~ contains a mixture of ions, electrons, neutrsl molecules, actdvatcd molecules, activated and oxidizing species, as well as photons of various cncrgics, as illustrated in Fig~re4. Thcsc paniclcs diffuse to thc proccssing 35 chamber through a SSEC in which all photons, ions and electrons are filtered out.
Figure 6 shows the clectron currcnt vcrsus microwave absorbed power. It can be sccn that thc ions and clectrons reaching the substrates are suppressed as indicatcd by 34 o~ders of magnitude reducdon in clec~on current mcasured by a Langmuir probc whcn a SSEC is inscncd bctwecn thc two chambers. The probc was placcd at 2 ~ ' 1 0 the substrate position and was biased at +10 V. The particles that can reach theother side of the SSEC (i.e. the processing chamber) are mainly neutral molecules, activated molecules, neutral and acdvated oxidizing species. It is these activatcd oxidizing species which are believed to be the major reactant species interacting S efficiently with SiH4 to form SiO2 for CVD on the substrate surfaee.

E?~atnDle 2 Themicrowave ECR system described in Example 1 was usedforthe deposition of SiO2 films at 270 C. The gases employed were 10% SiH4 in Argon and N2O with flow rates of 1 and 10 sccm, respectively. The gases were injected to the system as described in Example 1 Silicon wafers (100) oriented were used as substrates. The wafers were cleaned using RCA method prior to being loaded to the chamber. Two sets of samples were prepared: for electronie measurements the 15 substrates used were n-type, 2-4 ohm-cm in resisdvity, and for optdcal characterization the substrates used were p-type, 60 100 ohm-cm in resistdvity.The electronic and the structural properdes of the SiO2 films deposited by our newlydeveloped CP-PACVD proeess in conjuncdon with SSEC are shown in Figures 7 to 10. In Figure 7 we compare the infrared speetrum of our films (eurve b) with the 20 eorresponding speetrum of eonvendona ECR PECVD films deposited in eontaet with the plasrna (eurve a), and that of high quality the~mal oxide (eurve e). The shoulder height, the full width at half maximum (E;W~), and the stretehing frequency of the speetrum (b) and (c) are elearly eloser to eaeh other than the same features from speetrum (a). Flgure 8 shows the I-V eharaeterisdcs for MOS
25 eapaeitors fabncated with the present method, in both accumuladon and depledon modes. No trapping ledge is observed and the resisdvity at a steady de field of S
MV/em is about 1017 ohm-em, whieh is of the same order as that for the high quality themlal oxide. The similarity in the I-V eharaeterisdes between our films and the high quality thermal oxide eonfirms that our filrns are of high qualiq eontaining 30 only a low eoneentradon of oxide traps. Figure 9 shows a histogram of a typieal breakdown distribution from 30 deviees taken randomly from 100 deviees in one substrate. The brcakdown measurements were made with the gate at negative polarity. Of the 100 devices only 13 of them were shorted due mainly to dust ` partieles, no low field b~eakdown eaused by damaging structures being obseI~ved.
35 The average b~alSdown field is about lQ5 MV/em which is in the same order as that for high qudity themlal oxide. The high frequeney and the quasi-statie C-V
eharaeterisdes measurcd after post-metallizadon annealing (PMA) in fo~ming gas (10% H2 in N2) at 400 C for 30 min are shown in Fig~e 10. Clearly, in terms of electrical integrity and film qudity, our SiO2 films are mueh eloser to the high quality thermal oxides than other SiO~ films deposited at low tempcraturcs by othcr methods. The I-V, C-V, and breakdown characteristics are very similar to thosc of high quality thermal oxides. To the bcst of our knowlcdgc, our mcthod for producing high quality SiO2 films at low tempcratures (~300 C) is the first mcthod S that can achieve that quality ever ~eportcd. The advantages of our mcthod can bc summarized as follows:
a. We use a bi-level pressure system, the plasma chambcr is at a high gas pressure (gas mixture containing mainly oxygen) and the proccssing chamber is at a low gas pressurc This prcvents SiH4 from diffusing toward the plasma chamber, thus suppressing the gas phase nuclcation.
b The SSEC prcvents radiation damage of the growing films by the high energy photons as well as bombardment damage of the growing films by energedc charged particles.
c. The low prcssurc deposidon chambcr providcs a long mean frce path, thus reducingthechance of collision of the incoming spccies. Thisin turn provides a favorable environment for a complete CVD proccss which is supposed to involve only the reaction between activated oxidizing spccies and neutral molecules containing silicon at the substrate surface. This enables the deposition of high quality films at low temperaturcs.
Other apl~lications of thi~ method.

Beside thin film deposidon, our new method can also be used for etching applicadons. Tn this case, the processing chamber beco~es an etching chamber.
Suppose we want to etch silicon based materials using CF4 and 2 gas mixture. The gas mixture is fed to the plasma chamber where a microwave ECR
plasma is generated at a pressure reladvely higher than that in the etching chamber.
The plasma chamber is a rich source of active radicals. The funcdon of the SSEC in this case is to filter ou~ all photons, electrons and ions, allowing only the neutra~ but 30 acdvated radicals to be injected into the processing chamber toward the substrate to be etched. We use neutral and acdvated radicals instead of ions because the latter cause severe damage due to energcdc ion bombardment. Since the etching chamber--is under a lower pressure and the radical residence time is short, fluoIide radicals andthevoladleproductsresuldng f~om the reaction can be easilyremoved,thus 35 redwing the chancç for lateral etching. Our method, whilc avoiding the damageintrinsic to reactive ion etching, might provide the directionality requued for VLSI
technology, ~t~ ` 12 SuMkI~Y OF D-SCLOSI~

In summary of this disclosure, the present invention provides a novel method for low temperature microwave plæma thin film deposidon and etching S wherein the charge species and photons can be eliminated by the SSEC so æ to avoid thc damaging effects of these particles on the substrate or the growing film.
Modificadons are possible within the scope of this invention.

Claims (5)

1. The method of microwave plasma thin film deposition or etching, wherein a device called the "species selector and energy controller (SSEC)" is inserted between the plasma chamber and the processing chamber, provides means of controlling or eliminating the charge particle bombardment and the photonic radiation of the film being deposited (or the substrate being etched), as well as preserving the activated species that are the bases for high quality deposited films.

2. The method of claim 1 for thin film deposition or etching wherein the reaction in the processing chamber is due to a mixture of only neutral reactive species.

3. The method of claim 1 for thin film deposition or etching wherein the plasma is in close proximity to the substrates, without any direct physical contact, but at sufficiently close distance to allow the activated neutral species to react with the substrate surface and the gas injected to the processing chamber, before the said activated neutral species are deactivated. This method is called "close proximity plasma activated chemical vapor deposition" CP-PACVD.

4. The method of claim 1 wherein an additional function of the SSEC is to prevent the silicon containing gas, (i.e. SiH4) ,. from diffusing toward the plasma chamber and reacting there with the oxygen containing plasma.

5. The method of claim 1 wherein the said SSEC device creates a pressure difference between the said plasma chamber and the said processing chamber.
The improvement is that the pressure in the said plasma chamber is higher as compared to the pressure in the said processing chamber. The effect is to increase the concentration of generated species in the said plasma chamber, while the mean free path remains large in the said processing chamber, allowing for the deposition reaction to occur at the substrate surface.6. The method of claim 1 wherein the SSEC is designed to optimize the gas flow distribution in order to improve the uniformity of the film thickness and the film composition in the deposition process, and to improve the etching performance in the etching process