POLISHING AGENT AND PROCEDURE FOR THE PRODUCTION OF PLANAR ONES LAYERS

The available invention concerns a polishing agent on SiO2-Basis and a procedure for the production of planar layers.

Integrated monoliths (Integrated Circuits, IC) consist of structured semiconducting, non conductive and electrically conductive thin layers. These structured layers are manufactured usually by the fact that a layer material is applied, e.g. by evaporating and structured by a microlithographic procedure. The electronic Schaltungselcmente of the IC, like transistors, is e.g. produced by the combination of the different semiconducting, not leading and leading layer materials condensers, resistances and wirings.

The quality of a IC and its function hang in crucial Maß e from the precision, with which the different layer materials can be applied and structured.

With rising number of layers however the Planarität of the layers decreases clearly. This leads starting from a certain number of layers to the failure of one or several functional elements of the IC and thus to the failure of the entire IC.

The decrease of the Planarität of the layers is consequence of the structure of new layers, if these must be applied on layers already structured. From the structuring result differences in height, which can amount to up to 0,6 µm per layer. These differences in height add themselves from layer to layer and cause that no more separate the following layer on a planar on an uneven surface be applied must. A first consequence is that those in the following applied one ungleichmäß ige thickness exhibits. In extreme cases develop in such a way defects, defects in the electronic functional elements and unsatisfactory contacts. Uneven surfaces lead besides to problems with the structuring. In order to be able to produce sufficiently small structures, an extremely high registration (depth OF focus, DOF) in the microlithographic process step is necessary. These structures can be illustrated however only in one level sharply; the more strongly places of this level deviate, are the illustration the more in a diffuse way.

For the solution of this problem so-called chemical-mechanical polishing (CMP) is accomplished. The CMP causes a global Planarisierung of the structured surface by erosion of increased layer parts, until an even layer will receive. Thereby the next layer structure on an even surface without differences in height can take place and the precision of the structuring and the Funktionsfähigkcit of the elements of the IC remains.

A CMP step is accomplished by special buffing machines, polishing cloths (Pads) and polishing agents (Polierslurries). A Polierslurry is a composition, which in combination with the polishing cloth, which so-called PAD, on which Pollermaschine causes a erosion of the material which can be polished.

An overview of the technology of the CMP is e.g. in B.L. a Mueller, J.S. Steckenrider Chemtech (1998) P. 38 - 46 described.

CMP Slurries affect crucially the behavior during polishing during the polishing process. So far is assumed both chemical and mechanical procedures take influence. For this reason specific Polierslurries is needed for different polishing steps.

In principle one differentiates between polishing non conductive layers, e.g. from silicon dioxide, and polishing electrically conductive layers, predominantly metals such as tungsten, aluminum and copper. Polishing silicon dioxide is called oxide CMP.

In the oxide CMP is there beyond that a set of different polishing steps, which differ by the task of the silicon dioxide in the respective layer structure and number and kind of the Schichtinaterialien taken part in the layer structure.

An important step during the oxide CMP process is the so-called ILD Polierschritt (more interlayer dielectric), in which the silicon dioxide isolating between two wiring levels is polished. Beyond that however the meaning of further oxide CMP steps, e.g. the so-called STI step (shallow trench isolation) increases, in which insulating layers are polished by semiconductor elements.

In particular in polishing steps, in which semiconductor layers are involved, the requirements are particularly gro&szlig to the precision of the polishing step and thus to the Polierslurry;.

Bewertungsmaß staff for the effectiveness of Polierslurries are a set of Größ EN, with which the effect of the Polierslurry is characterized. To it belong the erosion rate, i.e. the speed with the material which can be polished are cleared away, the selectivity, i.e. the relationship of the erosion speeds of material which can be polished to other present materials, as well as Größ EN for the Gleichmäß igkeit the Planarisierung. As Größ EN for the Gleichmäß igkeit the Planarisierung become usually the Gleichmäß igkeit the remainder layer thickness within a wafer (WIWNU, within wafer non uniformity) and the Gleichmäß igkeit from wafer to wafer (WTWNU, wafer ton wafer non uniformity) as well as the number of defects per unit area used. A wafer is a polished silicon wafer, on which integrated circuits are developed.

When Polierslurries for oxide CMP become strongly alkaline formulations of abrasiven particles such as alumina, silicon dioxide and cerium oxide used, whereby Polierslurries on the basis of silicon dioxide found in practice special spreading.

As raw material for the production of the Polierslurries usually pyrogene silicic acid serves, out groß EN aggregates of smaller Primärteilchen exists, i.e. small usually spherical Primärteilchen are firmly too grö&szlig in the pyrogenen silicic acid; eren, unregelmäß industrial union formed particles connected. For the production of a Polierslurry it is necessary to divide these aggregates into as small a particles as possible. One manages this by entry of Scherenergie, e.g. by intensive agitating, in mixtures from water or alkaline media and pyrogener silicic acid. The aggregates of the pyrogenen silicic acid are cut up by the Schercnergie. There however the effectiveness of the entry of the Scherenergie of the Teilchengröß e depends, is not it not possible, by the shearing stresses particles of the Größ to produce e and the form of the Primärteilchen. In such a way manufactured Polierslurries has from there the disadvantage that cutting up not completely effected and aggregates of silicic acid primary particles remain in the Slurry. This rough particle portion can lead surface which can be polished to increased formation of scratches and other unwanted defects on that.

EP-A-899 005 teaches to avoid the rough particle portion by filtration however this is complex and only partly solves the problem, since aggregates can remain below the filtration border and damage due to their not-spherical form further those surface which can be polished.

WHERE 96/027 2096, US-A-5 and EP-A-520 109 teach 376,222 the use of basic flint brines with a pH value between 9 and 12,5. This pH value is stopped by additive of alkali hydroxide or of amines.

This Polierslurries exhibits the advantage that her practically ausschließ lich of discrete spherical particles consist, only in small Maß e to scratches and other defects on that surface which can be polished lead.

The disadvantage of these Polierslurries exists in their smaller erosion rate. One tries this disadvantage with increased additive from basic Polierbeschleunigem to compensate i.e. alkali hydroxide and amines to. However borders are set to the additive of basic polishing accelerators with Polierslurries on the basis by silicon dioxide due to the chemical equilibrium for silicon dioxide. Starting from a certain quantity of hydroxyl ions these react with the silicon dioxide particles and solve these to Silicaten on (Peptisation). Therefore Polierslurries with a pH of over 12 are unstably and in the technology only with difficulty manageable.

In EP-A-874 036 and US-A-5 876,490 is tried to solve this problem by the fact that the silicon dioxide particles will provide with coats from polymers and/or Cerdioxid. In JP 09/324 174 for this organic polymers and Polysiloxane are suggested. In US-A-3 922,393 is described coats from alumina, in US-A-4 664,679 surface modifications for the reduction of the Silanolgruppen at the surface.

Thereby the Stabilitäten is increased by Polierslurries on the basis of silicon dioxide particles. However after past knowledge a certain quantity of freely accessible silicon dioxide surface is needed for the achievement of sufficient erosion rates. Even if so far not yet all too much admits over the chemical procedures running off at the surface is, the conception exists that these Kugel-Oberflächen are needed for the deposit of the material removed from the surface which can be polished. Thereby such Polierslurries exhibits unsatisfactory polishing rates despite increased quantities of polishing accelerators. Besides a surface treatment of the polishing agent particles raises the price of the Polierslurry and thus the total process of the I production.

In Research Disclosure (RD) 419,020 one describes that as a function of the middle Partikelgröß e the best polishing results with Kieselsol particles were received, some middle Größ e of 35 Nm exhibited.

There is however further a need of Polierslurries with improved characteristics. In particular for the STI step Polierslurries with sufficient high erosion rate, in particular between silicon dioxide and silicon nitride, are wished to high selectivity good Planarisierungswirkung and small defect densities.

This task becomes surprisingly by supply of polishing agents on basis of flint brines with bimodaler Teilchengröß enverteilung solved.

This is for the specialist surprising, since from RD it admits 419,020 was that Kieselsol particles of a middle Teilchengröß e of 35 Nm optimal polishing characteristics aurweisen are.

This is not however the case. The polishing agents found now exhibit improved erosion rates and increased Selektivitäten opposite polishing agents of the state of the art.

The subject of the invention from there polishing agents are containing spherical, discrete, not silicon dioxide particles, by the fact gekennzeichnct linked with one another over connections, that the polishing agent

1. a) 5 to 95 Gew. - %, preferably 20 to 80 Gew. - %, silicon dioxide particle of a Größ e from 5 to 50 Nm and
2. b) 95 to 5 Gew. - %, preferably 80 to 20 Gew. - %, silicon dioxide particle of a Größ e from 50 to 200 Nm

The subject of the invention are beyond that procedures for the production of planar layers with the help of these polishing agents.

Those erfindungsgemäß EN polishing agent contained over connections did not link silicon dioxide particles with one another. They point solid contents from 1 to 60 Gew. - % up, preferably 1 to 30 Gew. - %, particularly prefers 5 to 20 Gew. - %, whereby it is possible to stop desired solid contents by addition of water. Those erfindungsgemäß EN polling-determine can beside silicon dioxide particles still further additives as polishing accelerators, surface-active materials or connections to the viscosity attitude to be e.g. contained.

Basis that erfindungsgemäß EN polishing agents are flint brine. Flint brine contained over connections did not link silicon dioxide particles with one another. Flint brine are sedimentation-stable, colloidal solutions of amorphous SiO2 in water or also alcohols and other polar solvents. They are mostly water liquid, and the commercial products have partially high solid concentrations (up to 60 Gew. - %) and point one groß e stability against gelling up.

The flint brine are milchig cloudily over opaleszierend to colorless clearly depending upon Teilchengröß e of the silicon dioxide particles. The particles of the flint brine have diameters from 5 Nm to 250 Nm, preferably 5 Nm to 150 Nm. The particles are spherically, spatially limited and preferably electrically negatively charged. Inside the individual particles is usually present a stand of Siloxan connections, which itself from the linkage of - Tetraedem and/or of Polykieselsäuren results in. At the surface frequently SiOH groups are arranged. Sturdy flint brine with specific surfaces of approx. 30 to 1000 m2/g. the specific surfaces is preferential can either according to the praying method (S.S. Brunauer, P.H. Emmet and E. plate, J. to. Chem. Soc., 1938, 60, P. 309) at dried SiO2-Pulver or directly in solution by titration after G.W. Sears (S. Analytical Chemistry, Bd. 28, P. 1981, Jg. 1956) to be determined.

The used flint brine point usually a viscosity of less than 10 mPa·s with a solid content of 30 Gew. - % up. The viscosity of the flint brine hangs of the Teilchengröß e, the content of electrolytes, the silicon dioxide content and the Vemetzungsgrad of the particles off. Preferentially are unvernetzt and stable the used flint brine against gelling.

Stability in relation to irreversible gelling to the silicagel, which is based on a spatial Vemetzung under training of SI-O-SI-connections between the particles, takes with increasing silicon dioxide content, rising electrolyte pollution and removing Teilchengröß e off. Generally leave themselves purify-hasty flint brine (e.g. such with Teilchengröß EN smaller 6 Nm) only on lower solid concentrations (e.g. < 30 Gew. - %) adjust as grobteilige flint brine (with e.g. Teilchengröß EN größ it as 50 Nm) with those solid contents up to 60 Gew. - % to be reached can do.

The pH value of the used flint brine lies between 1 and 12. Preferred the pH value of the used flint brine lies between 9 and 11. The range between pH 5 and pH 6 is less preferential, since flint brine within this range only exhibit a small stability. At pH values above 12 then increasingly Peptisierung and dissolving the particles enters under formation of alkali silicate solution.

Unstable flint brine e.g. is in relation to electrolyte additive, like sodium chloride, ammonium chloride and potassium fluoride. For stabilization e.g. contain flint brine alkali, like Natronoder caustic potash solution, ammonia or other alkalis. From there flint brine without electrolyte additive is preferential.

Flint brine can be kept rarer by condensation from diluted silicic acid solutions freshly made of molecular silicate solutions, by Peptisierung from silicagels or manufactured over other procedures. The predominant part in the technical Maß staff accomplished procedures for the production of flint brines uses technical water glasses as raw material.

For the procedure Natronwassergläser or potash water glasses are suitable, whereby from cost reasons Natronwassergläser are preferential. Commercial Natronwasserglas has a composition of Na2O 3.34 SiO2 and by melts by quartz sand with soda or a mixture of sodium sulfate and coal is usually made, whereby one receives a transparent colorless glass, so-called piece glass. This piece glass reacts in gemahlener form with water at increased temperature and pressure to colloidal, strongly alkaline solutions, those anschließ end still another to cleaning to be submitted.

Admits is also procedure, with which purify-hasty quartz or other suitable SiO2-Rohstoffe under hydrothermalen conditions with alkalis is unlocked directly to aqueous water glasses.

For the production of the flint brine used in the polishing agents a distance of the ellkalikationen from the water glass is necessary. The most common method of the Entalkalisierung is the treatment of diluted water glass solutions with cation exchangers in the H+-form. Preferably water glass solutions with a silicon dioxide Gchalt under 10 Gew become. - % over exchanger columns led. Short retention times are important in the exchange zone, in which the pH value of the solutions amounts to 5 to 7, in order to avoid a gelling of the solutions and flints of the exchanger resin.

The resulting diluted silicic acid solution (so-called Frischsol) is very unstable and by renewed alkalization and by thermal treatment is stabilized preferably immediately and concentrated. Particularly preferred the Kieselsol is stabilized, by one the solution up to a SiO2: Na2O-Verhältnis from 60 to 130: 1 alkalisiert, a part of the solution to the Teilchenvergröß erung to 60 to 100°C warms up, and anschließ end to Frischsollösung continuously admits and on the already existing particles to grow up leaves. At the same time or in the following a concentration of the solution can be made on the desired concentration by evaporation.

By exact reaction guidance, pH control, temperature control or by a purposeful attitude of the retention times can a desired Teilchengröß enspektrum to be adjusted. It is likewise possible to add additionally to the Frischsol so-called germ brine. As germ brine know flint brine with defined Teilchengröß enverteilungen to be used.

It is likewise possible to manufacture the used flint brine in further procedures. For example this is possible by hydrolysis of Tetraethoxysilan (TEOS). Flint brine, which will receive in this procedure, to have only a limited employment as polishing agents in the semiconductor manufacturing due to their high price.

A detailed representation of the flint brine is in K.K. Iler, The Chemistry OF Silica, chapter 4, P. 312-461, Wiley & Sons, New York, 1979.

Preferentially flint brine, those is anschlie&szlig by Entalkalisierung of water glasses and; end to stabilization to be manufactured and some bimodale Teilchengröß exhibit enverteilung. The Teilchengröß EN of the used flint brine are present in a distribution, the 5 - 95 Gew. - %, preferably 20 - 80 Gew. - % at particles in a Größ enverteilung of 5,-50 Nm and the 95-5 Gew. - %, preferably 80 - 20 Gew. - % at particles in a Größ contain enverteilung from 50 to 200 Nm. Bimodal heiß t that at least one minimum between two maxima with the Teilchengröß enverteilung arises.

For the measurement of the Teilchengröß EN within the nanometer range are suitable beside electron microscope photographs still further different methods, like e.g. laser correlation spectroscopy, ultrasound measurements or measurements with an ultra centrifuge. The ultra centrifuge is particularly well suitable due to their high discrimination, bimodale Teilchengröß enverteilungen to recognize.

The special with the ultra centrifuge consists of the fact that before the actual measurement a cracking after the dispersion the Teilchengröß e takes place. In a homogeneous dispersion as well known those sedimentieren groß EN particle faster than the likewise existing mittelgroß EN and small particle. During radiography of the ultra centrifuge cell with laser light a clearly minted change of intensity arises as a function of the time. From this change of intensity the change of concentration of the particles and from this the Teilchengrö&szlig leave themselves; compute enverteilung. Source of light is a He-Ne-laser. The ultra centrifuge makes a high accuracy possible, a high resolving power, and the distributions are accurately assignable, which is particularly important with bimodalen distributions.

The production of bimodaler flint brine can take place via mixing monomodaler flint brine. Here mixtures with different quantities of flint brines monomodalen on are adjustable, whereby a Kieselsol component a Teilchengröß enmaximum between 5 and 50 Nm and the second Kieselsol component a Teilchengröß enmaximum between 50 and 200 Nm exhibits. The production of bimodaler flint brine can take place if necessary also during stabilization. The production of bimodaler flint brine is preferential by a mixture process, since in this the desired quantitative proportions of clearly reproducible can be adjusted. The formulation of the Sols to a Polierslurry takes place e.g. via diluting with water and the possible addition from additives. Additives can in quantities of 0,01 Gew. - % to 10 Gew. - %, related to the Polierslurry, to be added.

PH values from preferably 9 to 12, particularly preferentially exhibit the polishing agent flint brine from 10 to 11. The high pH values needed for polishing acceleration can be stopped e.g. by additive of alkali hydroxide, like e.g. Kaliumund sodium hydroxide, amines or ammonia and/or tetraalkyl ammonium hydroxides. Likewise suitably salts, which react with the hydrolysis alkalinely, e.g. are like Natriumcarbonat, Natriumhydrogencarbonat, potassium carbonate, potassium hydrogencarbonate as well as ammonium hydrogencarbonate. As amines are suitable e.g. primary amines, secondary amines, tertiary amines, hetero-cyclic amines, tri amines, Tetramine or Pentamine. As tetraalkyl ammonium hydroxides can be used e.g. Tetramethylammoniumhydroxid, Tetraethylammoniumhydroxid, Tetrapropylammoniumhydroxid and Tetrabutylammoniumhydroxid.

Further agents can be added for the improvement of the performance of the Polierslurries: e.g. surface-active materials, like alkyl sulfates, Alkylsulfonate, phenol, glycols or Fluortenside or e.g. the viscosity adjusting materials such as Polyclektrolytc, Polyacrylsäuren, polyethylene amines and Polysiloxane.

Surface-active materials are preferably anionische, kationische or nichtionische low-molecular, oligomere or polymere emulsifying agents, Tenside or Schutzkolloide.

Examples of anionischen low-molecular, oligomeren and/or polymere emulsifying agents or Tensiden are Alkalioder of alkaline-earth salts fatty acids with 10 to 21 carbon atoms, sodium salts of insatiated fatty acids with 12 to 18 carbon atoms, Alkylethersulfonate, satisfied by fatty acids, e.g. sodium salts of, such as Ethcr of Sulfo hydroxy polyethylene glycols with e.g. 1-Methylphenylethyl-phenol, Nonylphenol or Alkylethem with 12 to 18 carbon atoms, aryl alkyl sulfonate as for example Naphthalinsulfonsäuren or alkyl sulfates provided with geradkettigen or branched Butylgruppen like sodium salts of langkettigen Schwefelsäurealkylestem.

As well as examples of kationischen low-molecular, oligomeren and/or polymere emulsifying agents or Tensiden are amines with 8 to 22 carbon atoms, those, carrying the salts by langkettige alkane remainders, with acids or by alkylation to the ammonium compounds were converted similar Phosphorund sulfur connections.

Examples of nichtionischer ollgomerer and/or polymere emulsifying agents or Tenside are Alkylpolyglykolether or - ester like ethoxylierte satisfied or insatiated connections basic langkettige alcohols e.g. with 12 to 18 carbon atoms, ethoxyliertes castor-oil, ethoxylierte (Kokos) fatty acids, ethoxyliertes Sojabotulenöl, ethoxylierte Resinoder Rosinsäuren, more ethoxylierter and if necessary propoxylierter Butyldiglykol, ethoxylierte Alkylarylether like ethoxyliertes geradkettiges and/or branched Nonylphenol or Octylphenol or benzyliertes p-Hydroxybiphenyl, ethoxylierte Triund Diglyceride and Alkylpolyglykoside.

As emulsifying agents or Tenside further ethoxylierte langkettige Alkyloder of alkenyl amines, Lecithin, suitable with langkettigen alkyl isocyanates modified conversion products of polyethylene glycols and Diisocyanaten, is conversion products of Rapsölund Diethanolamin or ethoxylierte conversion products of Sorbitan and langkettigen Alkanoder alkene carbonic acids.

Suitably are besides so-called Schutzkolloide, like e.g. polyvinyl alcohols or water-soluble cellulose derivatives such as methyl cellulose.

In the following on the basis of examples the invention is described, whereby itself that erfindungsgemäß e polishing agent on the examples mentioned does not limit.

500 ml a Kieselsol with the middle Teilchengröß e of 15 Nm and a pH value of 9,3 become at ambient temperature with 1583 ml a Kieselsols with a middle Teilchengröß e mixed by 70 Nm and a pH value of 9,4. The bimodale Teilchengröß enverteilung this Kieselsols is shown in fig. 3. This bimodale Kieselsol with a pH value of 9,4 is used for the polishing attempt in example 2.

In the table the examples 2 to 4 with the erosion rates and Selektivitäten that are erfindungsgemäß EN flint brine and the comparison flint brine represented. The polishing conditions are in the following summarized. In the example 2 are erfindungsgemä&szlig the results of the polishing attempt with the Polierslurry with that; EN bimodalen Kieselsol from example 1 indicated. For the Polierslurry in the polishing attempt 3 a Kieselsol with a middle Teilchengrö&szlig becomes; e of 70 Nm (Abb.2) assigned. The Polierslurry in the polishing attempt 4 contains a purify-hasty Kieselsol with a middle Teilchengröß enverteilung of 15 Nm (Abb.1).

Are used unstructured (blank) wafer with 200 mm in diameter. The thickness of the oxide coating (TEOS) amounts to 10000 angstroms and the thickness of the nitride layer amounts to 6000 angstroms.

The erosion rate for the oxide (TEOS) is indicated in angstroms per minute, the selectivity indicates the relationship of the erosion rate of the oxide to the silicon nitride.

As is shown by the test results of the table, the Polierslurry with that points erfindungsgemäß EN bimodalen Kieselsol from example 1 a clearly higher erosion rate and an improved selectivity up than the two Polierslurries of the comparison examples with flint brines monomodalen in each case.