CN1188817A - Control of SiO2 etch rate using dilute chemical etchants in presence of megasonic field - Google Patents
Control of SiO2 etch rate using dilute chemical etchants in presence of megasonic field Download PDFInfo
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- CN1188817A CN1188817A CN97122693A CN97122693A CN1188817A CN 1188817 A CN1188817 A CN 1188817A CN 97122693 A CN97122693 A CN 97122693A CN 97122693 A CN97122693 A CN 97122693A CN 1188817 A CN1188817 A CN 1188817A
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Abstract
Processes for cleaning a silicon body and for controllably decreasing the thickness of a silicon dioxide layer overlying a silicon substrate are disclosed. The processes comprise chemically etching a silicon dioxide layer with a dilute etchant in the presence of a megasonic field. The concentration of the etchant is preferably less than its diffusion-rate-limiting threshold concentration at a given temperature. When aqueous alkaline hydroxyl ion etchants are employed, the concentration of etchant is preferably less than about 300 ppm by weight relative to water. The etching is discontinued before the silicon substrate is exposed to the etchant. The etch rate is controlled to within about 2x10-5 mu m/min (0.2 ANGSTROM /min) of a target etch rate which ranges from about 3x10-5 mu m/min (0.3 ANGSTROM /min) to about 4x10-4 mu m/min (4.0 ANGSTROM /min). A simpler, more cost-effective chemical process for robustly cleaning silicon bodies or for producing very thin gate oxides is achieved.
Description
Generally speaking the present invention relates to the preparation of silicon body, or rather, relate to from the surface of such silicon body the controllably method of etch silicon dioxide.In preferred embodiment, The present invention be more particularly directed to clean for example method of silicon chip surface of monocrystalline silicon body.
Generally, preparation semiconductor microelectronics element on monocrystalline silicon piece, this monocrystalline silicon piece is to be prepared by the single crystal rod by the growth in enormous quantities of well-known caochralski method.Silicon chip generally prepares by a series of step, wherein single crystal rod is trimmed to have accurate diameter,, is etched with and removes mechanical defect to determine the crystal orientation along one or more limit equating, is cut into unfinished silicon chip along specific direction then.Unfinished silicon chip comprises that by other procedure of processing round edge, abrasive disc, etching and polishing are accurately shaped.
The productive rate of microelectronic device and performance characteristic mainly are subjected to the pollutant effect of silicon chip surface.Usually, because the above-mentioned procedure of processing and the relevant treatment of silicon chip, general organic and metal pollutant can be physically or chemically attached to the surface.Along with the geometrical dimension of installing diminishes sharp, it is more sharp-pointed that this point becomes.Correspondingly, between the processing and forming step of silicon chip, after polishing and equally to remove such pollutent at the production period that installs be necessary.
The chemical process that various surface cleaning from the silicon body is fallen pollutent is known in the prior art." RCA method " is a kind of industrial method of well-known cleaning silicon chip.In the method, silicon chip sequentially is exposed in two kinds of different chemical solutions, and generally these two kinds of chemical solutions are called as " standard cleaning 1 " (SC1) and " standard cleaning 2 " (SC2) solution.Referring to F.Shimura, semiconductor silicon crystal technology (Semiconductor Silicon Crystal Technology), the 189th page, the Academic Press of press of institute (San Diego CA, 1989).
SC1 solution is respectively parts by volume by ratio) 1: 2: 7～1: 1: 5 ammonium hydroxide, hydrogen peroxide and water forms, and these reagent are commercial available, usually with the NH of 28～30 weight %
4The H of the aqueous solution of OH and 30～35 weight %
2O
2The aqueous solution provide.With water is the ratio that benchmark is represented ammonium hydroxide and hydrogen peroxide, but they are independently mutually.That is to say, in typical SC1 solution, NH
4OH: H
2The ratio of O is about 1: 7～1: 5, H
2O
2: H
2The ratio of O is about 2: 7～1: 5, these two ratio (NH
4OH: H
2O and H
2O
2: H
2O) be separate.With with respect to 1,000,000 of the weight of water/a expression, NH in SC1
4The concentration of OH generally is about 35,000ppm～50,000ppm.Ratio of reagents is about 1: 4: 20 NH
4OH: H
2O
2: H
2O (about 13,300ppm NH
4OH) or about 1: 20: 100 (about 2,800ppm NH
4OH) SC1 solution is known equally in the prior art.Meuris etc., " a kind of remove particle on the silicon face and the new cleaning program of metal " (A New Cleaning Concept for Particle and MetalRemoval on Si surfaces), Electrochem.Soc.Proc. 94-7 phase, 15-24 page or leaf (1994).
Ammonium hydroxide and hydrogen peroxide are distinguished the silicon base of etch silicon dioxide layer and oxidation bottom simultaneously in SC1 solution.When ammonium hydroxide etch, it removes organic pollutant, and complexed metal pollutent for example copper, gold, nickel, cobalt and cadmium.Yet alkaline etching is NH for example
4OH if it is with the contact of the silicon base of bottom, with anisotropic, relevant with crystal orientation mode etching silicon, and seriously makes surperficial roughen.Hydrogen peroxide prevents the silicon base of ammonium hydroxide etch bottom in SC1 solution.In the SC1 cleaning system speed of etch silicon dioxide generally be about 1～5 dust/minute.Yet the etch-rate of conventional SC1 solution changes significantly in time, thereby causes the cleaning heterogeneous of silicon body.In addition, the high oxidation gesture and the overbasic combination that have in SC1 solution will cause separating out of iron and aluminum oxide.
Second step of RCA method is promptly used the SC2 solution-treated, mainly is that purpose is to remove the iron that produces in the SC1 step and the remedial steps of aluminum oxide.SC2 solution generally comprises spirit of salt, hydrogen peroxide and the water that ratio is respectively (parts by volume) 1: 2: 8～1: 1: 6 to be formed, and these reagent are commercial available, supplies the aqueous solution of HCl of 28～30 weight % and the H of 30～35 weight % usually on the market
2O
2The aqueous solution.With water is the ratio that benchmark is represented spirit of salt and hydrogen peroxide, but they are independently mutually.SC2 solution and basic metal and transition metal form the soluble metal title complex.
For fear of or reduce the problem that iron and aluminium separates out and attempted other method.A kind of method is to use ultra-pure reagent preparation SC1 solution.Yet,, also need the SC2 step even use the reagent of the concentration of wherein iron and aluminium less than 10ppt.Because most metallic impurity came from hydrogen peroxide during SC1 bathed, another kind of method is to use other oxygenant, for example the ozone of commercial available no metallic impurity.Yet it is unsuccessful using ozone to replace the trial of hydrogen peroxide, because ozone layer destroying ammonium hydroxide.
The improvement of RCA method and variation are known in the prior art equally.For example, remove the cleaning that silicon dioxide layer on the silicon base is considered to be convenient to the surface that covers of natural generation fully.For this reason, can between the SC1 of RCA method and SC2 step, adopt instantaneous ground etching silicon chip in very rare highly purified hydrofluoric acid solution.Beyer and Kastl, " rinsed with deionized water is to the influence of Silicon Surface Cleaning " Impact of Deionized Water Rinses on Silicon Surface Cleaning, electrochemical society magazine J.Electrochem.Soc.129,1027-29 (1982).As at U.S. Patent number 4,804, report is the same in 007, another kind of improve to relate to using ultrasonicly bathe with SC1 and SC2.
The non-SC1 cleaning program that ultrasonic cleaning machine is used for other for example is described in U.S. Patent number 3,893, and among 869 (Mayer etc.), it discloses the acoustic energy that uses ultrasonic frequency so that become flexible the lip-deep particle of semi-conductor silicon chip.United States Patent (USP) 4 as Bran, 804,007 and 5,286,657 and cited the same of the United States Patent (USP) 5,279,316 of Mrianda, carried out other improvement and the application of ultrasonic cleaning device, they relate separately to improved ultrasonic tr-ansducer, high-intensity single silicon-chip system and the rapid method system of mono bath/multistep.Improve although have these, the problem of the level of the impurity relevant with conventional SC1/SC2 cleaning system and the change of etch-rate still exists.
Therefore the purpose of this invention is to provide a kind of chemical process of better simply, thorough cleaning silicon body that expense is cheaper, or rather, is a kind of method that can not introduce the metal precipitate pollutent by cleaning reagent.The purpose that the present invention is correlated with is the control that improves SiO 2 etch rate, with preferably to obtain relative low temporary transient etch-rate uniformly.Another object of the present invention is that controllably etch silicon dioxide can not make the silicon substrate of bottom be exposed to etching reagent with the thickness that reduces silicon dioxide layer.
Therefore, briefly the objective of the invention is to clean the method for the silicon body of the silicon dioxide layer that has on the silicon base of covering.This method is included under the temperature T, in the presence of ultrasonic field, uses etchant chemistry etch silicon dioxide layer, and the concentration of etching reagent is less than its rate of diffusion restriction threshold concentration under T.Preferably a kind of aqueous alkaline etching reagent that comprises hydroxide ion of etching reagent, etching reagent with respect to the concentration of water weight preferably less than about 300ppm.
This method comprises that the use etching reagent is to be controlled in about 2 * 10 in addition
-5The target etch speed R of μ m/min
EtchingInterior etch-rate chemical milling silicon dioxide layer, target etch speed R
EtchingAbout 3 * 10
-5μ m/min and about 4 * 10
-4Change between the μ m/min, before silicon base is exposed to etching reagent, end etching, the silica-based then end.
The present invention also aims to provide a kind of reduction to cover the method for the silicon-dioxide layer thickness on the silicon base.This method is included in temperature T
1Down, in the presence of ultrasonic field, use etchant chemistry etch silicon dioxide layer, the concentration of etching reagent less than it at T
1Under rate of diffusion restriction threshold concentration.Preferably a kind of aqueous alkaline etching reagent that comprises hydroxide ion of etching reagent, etching reagent with respect to the concentration of water weight preferably less than about 300ppm.Before being exposed to etching reagent, silicon base ends etching.
These methods of cleaning the silicon body are compared with ordinary method with the method that reduces the silicon-dioxide layer thickness has significant advantage.Accessing uniformly, its value is about 3 * 10
-5μ m/min (0.3 dust/min)～about 4 * 10
-4(etch-rate of 0.4 dust/min), these etch-rates can be controlled in about 2 * 10 to μ m/min
-5μ m/min (the target etch speed R of 0.2 dust/min)
EtchingIn.The etching reagent that controlled, uniform and low etch-rate can use causticity is NH for example
4OH comes the etch silicon dioxide layer and can not penetrate silicon base.Therefore, in order to make anisotropically etching silicon substrate of etching reagent, in etching solution, do not need for example H of SC1 of oxygenant
2O
2In preferred embodiment, additional advantage is exposed to two kinds of etching reagent and oxygenants and obtaining in the independent bath by the silicon body.At SC1 NH
4OH/H
2O
2Iron and aluminum oxide precipitate very general in the system no longer occur.Because do not need to remove the oxide compound of de-iron and aluminium, so can save the SC2 step.Usually the middle HF step that adopts between SC1 and SC2 step also can be removed.Another advantage that etching and oxidizing reaction are separated be other oxygenant for example with NH
4The inconsistent ozone of OH environment can replace H
2O
2Therefore, eliminated the donor of known impurity.Therefore, can know obtain in the present invention and use controlled, all even low etch-rate is compared with the ordinary method of cleaning the silicon surface and is produced many advantages.
Further feature of the present invention and purpose part to those skilled in the art will be significantly, and part will be pointed out hereinafter.
The part sectioned view of the silicon body in the etching reagent is immersed in accompanying drawing 1 expression.
Just as used herein the same, term " silicon " is defined as in and comprises silicon single crystal and polysilicon in its scope.Term " etch-rate " is meant the variation of time per unit silicon-dioxide layer thickness, and the thickness of being measured is the vertical range to the silicon-dioxide substrate surface here.Term " silicon body " is meant and covers the silicon of the silicon dioxide layer on the silicon base comprising of any structure and shape.Though silicon chip is the example that is included within term " silicon body " scope, purposes of the present invention is not limited to silicon chip.
With reference to accompanying drawing 1, etch silicon-dioxide the silicon dioxide layer 25 on covering silicon base 15, wherein silicon base contains silicon at reaction surface 27 places.Reaction surface 27 is the interfaces between silicon dioxide layer 25 and the etchant solutions.Along with the carrying out of etching reaction, etching reagent reduces gradually in the concentration at reaction surface 27 places, forms concentration boundary layer 37 within the solution 35 between reaction surface 27 and the bulk solution 39.In order to make etching reagent and silicon dioxde reaction at reaction surface 27, etching reagent must be by concentration boundary layer 37 diffusions.The etch-rate of silicon dioxide layer can be by etching reaction speed or diffusion of reagents limit to the speed of reaction surface 27.If etching reagent can spread by concentration boundary layer 37 with the speed faster than etching reagent wear rate in the etching reaction, will cross at reaction surface 27 place's etching reagents so, etch-rate will be by the rate limiting of etching reaction.Yet, if etching reagent from bulk solution to reaction surface 27 diffusion can not catch up with consumption at the reaction surface etching reagent, etch-rate will be subjected to the restriction of rate of diffusion so.Rate of diffusion directly is directly proportional with the concentration of etching reagent in the bulk solution 39.Just as used herein the same, for given temperature, the rate of diffusion of etching reagent restriction threshold concentration is defined as such concentration in the bulk solution 39, promptly be higher than the restriction that this concentration etch-rate is subjected to etching reaction speed, be lower than this concentration etch-rate and be subjected to etching reagent to be diffused into the rate limiting of reaction surface 27.If etch-rate is subjected to the restriction of etching reaction speed.So can be by controlling etch-rate with the temperature of the irrelevant solution 35 of etchant concentration.On the contrary, if the restriction that etch-rate is spread so the control of etch-rate depend on temperature, depend on the thickness of the concentration boundary layer of determining diffusion path length and depend on the concentration of etching reagent in the bulk solution 39.
According to the present invention, in the presence of ultrasonic field, by etchant chemistry etch silicon dioxide layer.Any chemical etchant be can use, acidity and alkaline etching comprised.For example ammonium hydroxide, Tetramethylammonium hydroxide, potassium hydroxide or sodium hydroxide are gratifying for many purposes generally to comprise the alkaline etching of hydroxide ion.The aqueous solution of ammonium hydroxide is the example of alkaline hydroxide ion etching reagent, and said here alkaline hydrogen oxonium ion etching reagent is dissociated into hydroxide ion basically under the wherein known in the prior art and condition used.
Ultrasonic field can produce by method well known in the prior art, for example comprises using single barrel of formula or dual pail type ultrasonic cleaning equipment.The preferably about 700kHz of the frequency of ultrasonic field is to about 1200kHz, most preferably from about 840kHz～about 875kHz.The power that is applied to the ultrasonic field on the etched silicon body is not crucial, but it generally is about 2W/ silicon body～about 30W/ silicon body, preferably 5W/ silicon body～10W/ silicon body.Therefore, supplying with the preferably about 100W of total power～about 200W that 25 etched silicon chips are bathed, most preferably is about 150W.Yet owing to operation limit, the calorific loss loss in efficiency relevant with various ultrasonic cleaning equipment with other, the total power of supplying with sonac generally is greater than the total power that is applied in the bath of wherein placing silicon chip.For example, the power of supplying with rated output and be the single barrel of ultrasonic cleaning equipment of 300W generally is restricted to the about 90% of its rated output, promptly about 270W.Suppose that calorific loss and other loss in efficiency relevant with such device further reduces by 20% with the power that discharges, the power of supplying with etchant bath so is about 216W, and the ultrasonic power that is applied in this bath on 25 silicon chips is about 9W/ silicon chip.When applying ultrasonic wave, the silicon body preferably is positioned in the etch bath by this way, and the acoustic streaming of promptly being convenient to etching reagent is applied on the etched silicon dioxide layer.When the silicon body was silicon chip, silicon chip preferably was positioned in the etch bath like this, i.e. the surface of silicon chip (that is to say parallel) in alignment with the direction that sound wave passes etching reagent.
The etch silicon dioxide layer has obviously changed the mode and the mechanism of control etch-rate in the presence of ultrasonic field.For example, accompanying drawing 2 and 3 is illustrated in similar temperature and the concentration range etch-rate and NH when ultrasonic wave is opened and close respectively
4The graph of relation of OH concentration.When ultrasonic wave is closed (accompanying drawing 2), etch-rate depend on ☆ concentration and the diffusion control under.When ultrasonic wave is opened (accompanying drawing 3), etch-rate and NH
4The concentration of OH is irrelevant and under the control of speed of reaction.Without being limited by theory, as if ultrasonic field reduces the thickness of concentration boundary layer 37 to produce short diffusion path length.Or rather, in SC1 bathed, the thickness of concentration boundary layer 37 was not about 50～100 μ m when having ultrasonic field, yet was about 1 μ m at the thickness of the following interlayer of existence of ultrasonic field.As the result than short diffusion paths who exists in the presence of ultrasonic field, the rate of diffusion of the etching reagent in the bulk solution 39 restriction threshold concentration is lowered there not being value in the presence of the ultrasonic field to compare with it.That is to say that when applying ultrasonic field, under the bulk concentration of relatively low etching reagent, SiO 2 etch rate becomes and is subjected to diffusional limitation (promptly from being subjected to speed of reaction restriction transition).
After this manner, can use lower etchant concentration, still within the scope that is subjected to speed of reaction control, operate simultaneously.For example, when ultrasonic wave is opened, use a kind of concentration less than about 3000ppm but when being higher than dilution ammonium etching reagent to the rate of diffusion of etching reagent under fixed temperature restriction threshold concentration, can irrespectively control SiO 2 etch rate with concentration.Aspect low expense and low corrosion, compare with method of the prior art, operation is favourable under low like this concentration.As shown in Figure 3, under 30～80 ℃ temperature, working concentration can obtain less than 5 * 10 less than the ammonium hydroxide etch agent of about 5000ppm
-5μ m/min (0.5 dust/min) to about 4 * 10
-4μ m/min (the etch-rate of 4 dusts/min).Especially, in the SC1 system, can obtain these etch-rates, wherein NH in SC1
4OH: H
2O
2: H
2The ratio of O is respectively (parts by volume) 1: 100: 500～1: 10: 50, and these reagent solutions are commercial available, supplies the NH of 28～30 weight % usually on the market
4The H of the aqueous solution of OH and 30～35 weight %
2O
2The aqueous solution.With water is the ratio that benchmark is represented ammonium hydroxide and hydrogen peroxide, but they are independently mutually.That is to say, in above-mentioned SC1 solution, NH
4OH: H
2The ratio of O is about 1: 500～1: 50, H
2O
2: H
2The ratio of O is about 1: 5, these two ratio (NH
4OH: H
2O and H
2O
2: H
2O) be separate.To represent NH in above-mentioned SC1 solution with respect to 1,000,000 of water weight/portion
4The concentration of OH generally is about 550ppm～5,500ppm.When using aqueous alkaline etching within the scope of speed of reaction control, to operate, the concentration of etching reagent with respect to the weight of water preferably less than about 3000ppm with more preferably less than about 1000ppm.The ratio that the typical ammonium hydroxide etch agent aqueous solution will have is (volume) commercial available reagent N H
4OH: H
2O is 1: 100 (about 3000ppm) and 1: 300 (1000ppm).
In addition, when within the scope of diffusion control, operating, in the presence of ultrasonic field with acceptable speed etch silicon dioxide layer, here the concentration of etching reagent less than silicon-dioxide the diffusional limitation threshold concentration under the temperature when etched.When alkaline hydrogen oxonium ion etching reagent when for example ammonium hydroxide is used in the presence of ultrasonic field etch silicon dioxide with the form of the aqueous solution, the concentration of etching reagent less than about 300ppm (with respect to the weight of water), more preferably is less than about 100ppm preferably under about 30～80 ℃ temperature.The preferably about 10ppm of the concentration of aqueous alkaline hydroxide ion etching reagent～about 100ppm and more preferably be about 30ppm～about 100ppm under about 30～80 ℃ temperature.Under about 70 ℃ temperature, the concentration of such etching reagent most preferably is about 50～80ppm.When under these preferred concentrations and temperature, using the ammonium hydroxide etch agent of dilution, can obtain about 3 * 10
-5μ m/min (0.3 dust/min) to about 4 * 10
-5μ m/min (the SiO 2 etch rate of 4 dusts/min).In addition, these etch-rates can be controlled at about 2 * 10
-5μ m/min (the desirable or target etch speed R of 0.2 dust/min)
EtchingSo very rare etchant solutions uses together with ultrasonic system is convenient to low relatively etch-rate and corresponding higher degree ground control etching process.Use the etching reagent of dilution also can cause the with low uncertainty of etchant concentration, and therefore cause uniform etching.Control in general, uniformly, and low etch-rate provides with chance accurate and that controllable mode is ended etching reaction.In addition, the weaker concn of etching reagent is low expense and low causticity basically.
The control etch-rate is about 3 * 10
-5μ m/min (0.3 dust/min) to about 4 * 10
-4μ m/min is (within the value of 4.0 dusts/min) and about 2 * 10
-5μ m/min (offers an opportunity for ended etching reaction before silicon base 15 is exposed to etching reagent within the desired etch-rate of 0.2 dust/min), and therefore eliminates anisotropically etching silicon substrate.The same permission etching in rational time range in this scope of control etch-rate reaches the silicon-dioxide 25 of 0.1 μ m (1000 dust).Though the present invention can use in requiring the application of silicon dioxide layer 25 thickness reduction more than 0.1 μ m, the present invention needing preferably to be suitable for thickness to reduce less than 0.1 μ m, most preferably reduces about 5 * 10
-4μ m (5 dust) is to about 5 * 10
-3In the application of μ m (50 dust).The control etch-rate is to about 2 * 10
-5μ m/min (can further be convenient to controllably reduce the thickness of silicon dioxide layer and controllably end etching before silicon base is exposed to etching reagent within the desired etch-rate of 0.2 dust/min).When the thickness of silicon dioxide layer about 5 * 10
-4In the time of within an individual layer of the thickness t of μ m (5 dust)～be equivalent to silicon-dioxide or the thickness of two individual layers, controllably end etch-rate.
The uniform like this and controllably low etch-rate that obtains by the method for describing in detail above can directly be applied in from the surperficial removal of contamination of silicon body.In the embodiment of preferably being made up of a kind of step that departs from the conventional SC1 step of RCA method basically, the alkali etching of silicon body and oxidation sequentially take place in independent bath.Especially, in first ultrasonic bath, do not having under the condition of oxygenant, the surface of silicon body covers the surface that silicon dioxide layer on the silicon body cleans the silicon body by using etching reagent chemical milling for the first time.The surface of silicon body is preferably hydrophilic before etching, if its surface is hydrophobic, so preferably this surface is exposed to before obtaining coming down to hydrophilic surface oxygenant for example in the ozone being etched with.Etching preferably is subjected to rate of diffusion restriction restriction rather than that be subjected to speed of reaction.In preferred embodiment, in ultrasonic bath, carry out etching, the concentration of etching reagent is the diffusional limitation threshold concentration under the temperature when etched less than silicon-dioxide.The preferred etched thickness of silicon dioxide layer up to silicon dioxide layer be about 0.2nm (2 dust) to 1.0nm (10 dust), still under any circumstance, before silicon base is exposed to etching reagent, end etching.Etched result obtains etched silicon body.
After washing etched silicon body by quick removing flushing or other technology well known in the prior art, use the silicon base of oxygenant oxidation etching silicon body in second bathes, preferably the thickness up to silicon dioxide layer is that about 1.0nm (10 dust) is to 1.5nm (15 dust).Though can use any oxygenant, oxygenant preferably includes the ozone of concentration for about 50ppb to 50ppm.Most preferably, at room temperature, etched silicon body is exposed to concentration and reaches about 5 minutes in the ozone of about 15ppm.The result of oxidation obtains the silicon oxide body.Wash the silicon oxide body then, preferably, repeat above-described several times etching and oxidation step to guarantee to remove up hill and dale the surface of silicon body.Etching-flushing-oxidation-flush cycle can be repeated needed number of times to realize the removing of silicon surface.For the cleaning as the monocrystalline silicon piece of the part in silicon chip or the component fabrication process, general two-six etching-oxidation cycle are enough.After last etching-oxidation cycle, wash the silicon oxide body again, dry then, preferably in the IPA vapor moisture eliminator.
Can measure the thickness of silicon dioxide layer by several direct or indirect methods well known in the prior art.Typical direct method comprises ellipsometry and photoelectron spectroscopy assay method.In a kind of round-about way, be determined at the needed time of etch silicon dioxide layer under the known etch-rate, calculate mean thickness then thus.In another kind of indirect method, from the whole silicon dioxide layer of substrate etching, and the silicone content of calculating etchant solutions.Vepa etc. " a kind of native oxide Determination of thickness method " (A Method for Native Oxide Thickness Measurement), Electrochem.Soc.Proc., 95-20 volume, the 358th～365 page (1995).
Another embodiment of the invention relates to the improvement of the SC1 cleaning step of well-known RCA method.In this embodiment, clean the silicon surface by the silicon dioxide layer that in the ultrasonic bath of etching reagent that comprises concentration dilution and oxygenant, uses the etchant chemistry etching to cover on the silicon base.When the etch silicon dioxide layer, the oxygenant simultaneous oxidation silicon base in this is bathed.Using ammonium hydroxide aqueous solution and hydrogen peroxide respectively in the system as etching reagent and oxygenant, etching reagent preferably with respect to the weight of water for about 10ppm extremely the concentration of about 100ppm be to use NH
4OH: H
2O
2: H
2O is respectively (parts by volume) 1: 100: 28, and 000～1: 100: 3000 ratio obtains, and these reagent solutions are commercial available, supplies the NH of 28～30 weight % usually on the market
4The H of the aqueous solution of OH and 30～35 weight %
2O
2The aqueous solution.That is to say that these preferred concentration are to use a kind of SC1 solution to obtain, in this solution, NH
4OH: H
2The ratio of O is about 1: 28,000～1: 3000, and H
2O
2: H
2The ratio of O is about 1: 280 to about 1: 30, these two ratio (NH
4OH: H
2O and H
2O
2: H
2O) be separate.Etching reagent with respect to the weight of water for about 30ppm extremely the concentration of about 100ppm be to use NH
4OH: H
2O
2: H
2O is respectively (parts by volume) 1: 100: 9, and 000～1: 100: 3000 ratio obtains, and these reagent solutions are commercial available, supplies the NH of 28～30 weight % usually on the market
4The H of the aqueous solution of OH and 30～35 weight %
2O
2The aqueous solution.After the SC1 step, then can the silicon body be exposed in the SC2 solution according to known RCA method.
The present invention has found the secondary purpose in the gate oxide preparation.Gate oxide is known in the prior art and is used in the element for example NMOS and pmos fet (FETS).Gate oxide comprises the thin silicon dioxide layer that covers on the silicon body.Generally, the thickness of the silicon dioxide layer on such thin gate oxide is 8 * 10
-3μ m (80 dust) is to 5 * 10
-2μ m (100 dust).The thickness that needs silicon dioxide layer in the latest developments of gate oxide technical elements is 4 * 10
-3μ m (40) is to 5 * 10
-3μ m (50 dust).Need eventually and 5 * 10 in the further progress of this technical elements
-4The ultra-thin silicon dioxide layer that μ m (5 dust) is equally thin.Can obtain so ultra-thin silicon dioxide layer by method of the present invention.
Embodiment described herein can be used in many baths system, wherein adopts one method steps in each is bathed, or is used in the mono bath system, wherein adopts a plurality of method stepss in this mono bath.In addition, embodiments of the present invention can be used as continuation method or act on a plurality of or single silicon body as batch process.
Also there be other purposes in the chemical milling system and feature in the present invention.Generally, the present invention can be used to anyly need remove that a certain amount of silicon-dioxide reoxidizes simultaneously or not in the purposes at the silica-based end with controllable mode.These other purposes is obvious for a person skilled in the art.
Claims (15)
1, a kind of reduction covers the method for the thickness of the silicon dioxide layer on the silicon base, and this method comprises:
In the presence of ultrasonic field, use etchant chemistry etch silicon dioxide layer, the concentration of etching reagent is the rate of diffusion restriction threshold concentration under the temperature when etched less than silicon dioxide layer; With
Before being exposed to etching reagent, silicon base ends etching.
2, according to the process of claim 1 wherein that etching reagent is a kind of aqueous alkaline etching that comprises hydroxide ion, less than about 300ppm, the temperature of etching reagent is about 30～about 80 ℃ to etching reagent with respect to the concentration of water weight.
3, according to the process of claim 1 wherein that etch-rate is controlled in about 2 * 10
-5In the target etch speed of μ m/min, target etch speed is about 3 * 10
-5μ m/min and about 4 * 10
-4Change between the μ m/min.
4, according to the process of claim 1 wherein that the thickness of working as silicon dioxide layer is about 5 * 10
-4End etching in the time of in the target thickness of μ m.
5, a kind of method of cleaning the silicon surface wherein is coated with silicon dioxide layer on the silicon body, and this method comprises:
In the presence of ultrasonic field, use etchant chemistry etch silicon dioxide layer forming the etching silicon body, the concentration of etching reagent is the rate of diffusion restriction threshold concentration under the temperature when etched less than silicon dioxide layer;
Before being exposed to etching reagent, silicon base ends etching; With
Use oxygenant oxidation silicon base to form the silicon oxide body.
6, according to the method for claim 5, wherein etch silicon dioxide layer and silicon oxide body in the bath that comprises etching reagent and oxygenant.
7, according to the method for claim 5, wherein do not have etch silicon dioxide layer in the first bath of oxygenant comprising etching reagent, comprise oxygenant second bathe in the silica-based end.
8, according to the method for claim 7, wherein chemical milling silicon dioxide layer, termination etching and the step at the silica-based end repeat once at least.
9, according to the method for claim 7, wherein the etch silicon dioxide layer is about 0.2nm～about 1.0nm up to the thickness of silicon dioxide layer, and the thickness of the silica-based end up to silicon dioxide layer is about 1.0nm～about 1.5nm.
10, according to the method for claim 5, wherein etching reagent is a kind of aqueous alkaline etching that comprises hydroxide ion, and less than about 300ppm, the temperature of etching reagent is about 30～about 80 ℃ to etching reagent with respect to the concentration of water weight.
11, according to the method for claim 10, wherein do not have etch silicon dioxide layer in the first bath of oxygenant comprising etching reagent, comprise oxygenant second bathe in the silica-based end.
12, according to the method for claim 10, wherein etching reagent comprises that concentration is the ammonium hydroxide of about 50ppm～about 80ppm, and the temperature of first bath is about 70 ℃, and oxygenant comprises ozone.
13, according to the method for claim 10, wherein the etch silicon dioxide layer is about 0.2nm～about 1.0nm up to the thickness of silicon dioxide layer, and the thickness of the silica-based end up to silicon dioxide layer is about 1.0nm～about 1.5nm.
14, according to the method for claim 10, it further comprises step: flushing etching silicon body; Flushing silicon oxide body; At least repeat the step of chemical milling silicon dioxide layer, flushing etching silicon body, the silica-based end and a flushing silicon oxide body.
15, a kind of method of cleaning the silicon surface wherein is coated with silicon dioxide layer on the silicon body, and this method comprises:
Use etching reagent to be controlled in about 2 * 10
-5Etch-rate chemical milling silicon dioxide layer in the target etch speed of μ m/min, target etch speed is about 3 * 10
-5μ m/min and about 4 * 10
-4Change between the μ m/min;
Before being exposed to etching reagent, silicon base ends etching; With
Use oxygenant oxidation silicon base to form the silicon oxide body.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN97122693A CN1188817A (en) | 1996-11-15 | 1997-11-13 | Control of SiO2 etch rate using dilute chemical etchants in presence of megasonic field |
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| Application Number | Priority Date | Filing Date | Title |
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| US749906 | 1996-11-15 | ||
| CN97122693A CN1188817A (en) | 1996-11-15 | 1997-11-13 | Control of SiO2 etch rate using dilute chemical etchants in presence of megasonic field |
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| Publication Number | Publication Date |
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| CN1188817A true CN1188817A (en) | 1998-07-29 |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN100415934C (en) * | 2003-12-22 | 2008-09-03 | 硅电子股份公司 | High-purity alkali etching solution for silicon wafers and alkali etching method for silicon wafers |
-
1997
- 1997-11-13 CN CN97122693A patent/CN1188817A/en active Pending
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN100415934C (en) * | 2003-12-22 | 2008-09-03 | 硅电子股份公司 | High-purity alkali etching solution for silicon wafers and alkali etching method for silicon wafers |
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