Dielectric films for narrow gap-fill applications

Dielectric film for filling narrow gaps

The present invention generally relates to a dielectric material for semiconductor devices, specifically, a dielectric material prepared from a colloidal dispersion that has high thermal stability and etching resistance and completely fills the gaps.

In order to provide integrated circuits (ICs) with increased performance, the feature size of the device and the space on the ICs continue to decrease. The manufacture of this device often requires the deposition of dielectric materials into the parts of the material layer on the jacquard silicon substrate. In most cases, it is important that the dielectric material completely fills the components that can be as small as 0.01 to 0.05 microns or even smaller in next-generation devices. Filling the narrow part, so-called gap filling, provides strict conditions on the materials used, for example, for pre-metal dielectric (PMD) or shallow trench isolation (STI) applications. The pre-metal dielectric layer on the integrated circuit is electrically isolated from the structure of the metal interconnection layer and is electrically isolated from the pollution mobile ion that degrades the electrical properties. The PMD layer needs to fill narrow gaps with an aspect ratio of 5 or more. After deposition, the dielectric material needs to be able to resist processing steps such as high temperature annealing, etching, and cleaning steps.

Dielectric materials are commonly deposited by chemical vapor deposition (CVD) or by spinning. Various methods have certain restrictions on filling extremely narrow gaps. The plasma enhanced chemical vapor deposition (PECVD) method provides a high deposition rate at a relatively low temperature (about 400°C). The main disadvantage is that the PECVD method has a lower deposition rate inside the gap than other locations on the surface. The differential deposition rate can produce a structure of overhanging slit openings, resulting in voids in the slits. Generally, for spaces below 0.25 microns, depending on the aspect ratio, it is difficult to use standard PECVD methods to achieve gap-free gap filling.

Phosphosilicate glass (PSG) and borophosphosilicate glass (BPSG) are used together for pre-metal dielectric applications. This film is usually deposited using atmospheric pressure CVD (APCVD), low pressure CVD (SACVD) or low pressure CVD (LPCVD). Depending on the processing conditions and the precursors used, these methods can achieve almost conformal coatings. The gap filling is achieved by the post-deposition reflow method, in which the material is processed at a high temperature, usually 800-1200°C. Phosphorus and boron, especially boron contained in the glass will reduce the glass transition and flow temperature. However, the use of CVD and subsequent reflow in future development devices will be limited by the high temperature required by the reflow method, and it cannot be compatible with specific materials and methods such as cobalt silicide used at the contact level. Regarding extremely narrow gaps below 0.2 micrometers, there is a risk that gaps will remain, even under high-temperature processing.

Some workers use high-density plasma chemical vapor deposition (HDP CVD) to improve the gap filling of PSG and BPSG. In the high-density plasma method, deposition and etching occur simultaneously. Etching is most effective at the top corners of narrow openings to compensate for the lower deposition rate inside the gap. HDP CVD deposition does not require high temperature processing, but an annealing step can be used if a denser film is desired. The HDP CVD method has the disadvantage that for narrower structures, the lower deposition-to-etch ratio that must be used results in a rather slow overall filling rate. Improved gap filling also requires modification of the design of device components such as rounded corners and oblique side walls. Finally, it is also about the damage of plasma to the device during HDP CVD processing.

Spinning glass and spinning polymers such as silicate, siloxane, silamine or silsesquioxane usually have good gap filling properties. Films of these materials are usually formed by applying a coating solution containing a polymer, followed by baking and thermal curing processes. However, the practicality of these spinning materials is limited by material shrinkage during thermal processing. Thermal shrinkage is the main consideration for materials that must resist high processing temperatures, such as those used in pre-metal dielectrics and/or shallow trench isolation applications that can involve processing temperatures exceeding 800°C. High shrinkage can lead to unacceptable film rupture and/or formation of porous materials, especially inside the slit. Cracked or porous materials can have unfavorable high wet etch rates in subsequent processing steps.

Therefore, there is still a need for a dielectric material that provides gap-free gap filling of narrow parts at a processing temperature lower than the reflow temperature currently used. The gap filling material needs to have high thermal stability and reasonable resistance to etching solutions in order to continue to be used in subsequent processing steps.

A colloidal particle dispersion composed of dense materials dispersed in a solvent is used to form gap-filling dielectric materials with low thermal shrinkage. The particles preferably have a nanometer size and are called small particles. The dense material is a dielectric material or can be converted into a dielectric material by oxidation or nitridation. Dielectric materials are particularly useful for pre-metal dielectric and shallow trench isolation applications. Silicon oxides and nitrides, aluminum oxides and nitrides, and boron oxides and nitrides can be used as small-grain materials. Colloidal silica is particularly useful as a colloidal dispersion. The dielectric material optionally includes dopants such as arsenic, antimony, phosphorus or boron.

According to the method of forming the dielectric material, the colloidal dispersion is deposited on the substrate, and the deposited film is dried to form a porous intermediate layer. The intermediate layer is percolated by the liquid-phase matrix material and then solidified. In all cases, solidification includes annealing, percolation by the gas-phase matrix material, and then solidified, or only solidified and modified to fill the gap, heat Stability and etching resistance dielectric material.

The matrix material implemented in the liquid phase of the percolation is a spinning polymer, including oligomers and monomers, which can be cured at high temperatures and, if necessary, converted into silicon oxide or similar ceramic materials in the presence of oxygen or steam. Matrix materials include, but are not limited to, hydrogen silsesquioxane, organosilsesquioxane, organosiloxane, silsesquioxane-silicate copolymer, base material based on silamine, polycarbosilane And acetoxysilane. The liquid matrix material optionally includes dopants such as arsenic, antimony, phosphorus or boron. In liquid phase percolation, the coating solution of the matrix material is coated on the colloidal film.

Vapor infiltration uses a chemical vapor deposition (CVD) method to seal the top surface of the slit before the impact molecule has a low viscosity and/or high surface diffusivity to prevent the volume porosity of the intermediate layer from decreasing. The materials deposited by CVD include dopants as needed. Other vapor deposition methods such as atomic layer deposition can also be used for vapor infiltration.

The dried or percolated intermediate layer is cured, for example, in an oven at a temperature between about 600 and 800°C or by rapid thermal processing at a temperature between about 700 and 900°C. As needed, for example, one or more baking steps at a temperature between about 75 and 300°C may precede the curing step. In addition, curing may also be after the higher temperature annealing step. Curing and optionally annealing cause sintering of the pellets and reflow of the percolating matrix material. The inclusion of dopants in the pellets or matrix materials can reduce the reflow temperature.

The film prepared according to the present invention fills narrow gaps with a width of less than 100 nanometers and as small as 50-60 nanometers without voids or cracks. It does not show delamination of cracks, even after heat treatment at 900°C. This cured film has the lowest open porosity, as evidenced by its resistance to etching solutions in caulking. In addition, the average etch rate of the cured film on the blanket wafer is about the same as the average etch rate of the silicon dioxide film produced by chemical vapor deposition. Therefore, the thin film prepared according to the present invention can be advantageously used as a pre-metal dielectric and shallow trench isolation material.

The method of forming a gap-filling dielectric material with low thermal shrinkage uses a colloidal dispersion of dense particles. The coating solution of the colloidal dispersion is deposited on the substrate to form a thin film, which is modified by one or more methods. Dielectric materials can be advantageously used for pre-metal dielectric and shallow trench isolation applications.

The key to the present invention lies in the nature of the colloidal dispersion. Colloid is generally defined as a system in a suspension with two or more phases. In a colloidal suspension, one of the phases, called the dispersed phase, is distributed in the other phase, called the continuous phase. A similar type of colloid is composed of a dispersion of small particles in a liquid.

According to one aspect of the present invention, nanometer-scale particles are used, and colloidal dispersions called small particles are composed of dense materials dispersed in a solvent. Dense materials are dielectric materials or materials that can be converted into dielectric materials by reaction with oxygen or nitrogen. In addition, the physical size of the pellets needs to be thermally processed to be substantially unchanged. The size of the pellets should not decrease to more than 10% when exposed to a temperature of about 700°C. In the case where the small particles are composed of materials that can be converted into dielectric materials by oxidation or nitridation, such as silicon or aluminum, the particle size will increase somewhat during curing in the presence of oxygen or nitrogen.

Silicon and aluminum, and refractory oxides and nitrides of silicon and aluminum are useful small particles. Additional useful materials include nitrides such as boron nitride and gallium nitride, as well as boron oxide and boron nitride. Suitable dense silicon-containing materials for small particles include silicon oxide, silicon, silicon nitride, silicon oxynitride, and combinations and mixtures thereof. For example, colloidal silica can be advantageously used as a colloidal dispersion. The method of forming colloidal silica is known in this art, as described in, for example, U.S. Patent No. 3,634,558 and Van Helden et al. (J. Colloid Interface Sci.<b>81</b>, 354 (1981)), which are incorporated into this article by way of citations. In addition, colloidal silica is also available on the market. The general rule is that, in addition to the oxidation or nitridation described above, the pellets undergo little or no chemical changes. However, as long as the low shrinkage criterion is met, the pellets can additionally contain a small amount of silicon polymer such as hydrogenated silsesquioxane, organosiloxane, organosilsesquioxane, and perhydrosilazane.

The pellets have a characteristic size between about 2 nanometers and about 50 nanometers. Colloidal dispersions have excellent gap-filling capabilities limited only by particle size. For any particular application, choose a particle size smaller than the width of the opening to be filled. The size distribution of the pellets can be monodisperse, bimodal or polydisperse. The bimodal distribution can be tailored to provide a higher packing density of small particles, where the smaller particles are suitable for the voids created by the packing of larger particles. Small particles are dispersed in organic solvents or inorganic solvents such as aqueous solvents or solvent mixtures, or dispersed in supercritical fluids. Suitable organic solvents include those commonly used in coating solutions for spinning polymers such as methanol, ethanol, isopropanol, methyl isobutyl ketone, cyclohexanone, acetone, and anisole. The solid content of the pellets in the colloidal dispersion usually ranges from as little as 0.5% by weight to as much as 20%. A higher or lower concentration can be used to adjust the coating thickness. Additional additives such as surfactants or binders may also be present in the dispersion. The following percolation matrix materials can be used as binders when added to the dispersion in a small amount such as a ratio of pellets to binder greater than about 10:1.

According to another aspect of the present invention, the small particles include dopants such as arsenic, antimony, phosphorus or boron. The inclusion of the dopant can enhance the material properties of the film formed from the colloidal dispersion. For example, dopants are introduced to increase the mobile ion collection and lower the glass transition temperature. Among other reasons, boron is used to produce dielectric materials with increased corrosion resistance.

A thin film of colloidal dispersion is usually formed on a substrate by spin coating. Other methods known in this art for applying the coating solution, such as dip coating or spray coating, can be used alternately. The solvent in the dispersion is evaporated to dry the coated film. The coated film can be dried during the spin-coating process, for example, by rapid spin-coating or during the dwell period after the dispensing step. Alternatively, the coated film can be heat-treated by a process such as lamp heating, hot plate baking at one or more temperatures between about 75 and 300°C, or heat treatment by other methods known in this art. In addition to evaporating the solvent, heat treatment can be used to keep the particles attached to the substrate so that they will not be removed/washed off during subsequent percolation. The heat treatment can also have the effect of reflecting the adhesive material as needed. The thin film thus formed on the substrate is generally porous in nature and an open-pore structure. Regarding coating such as PMD or STI layers, it is desirable to minimize the porosity of the film to minimize heat shrinkage and moisture sensitivity and maximize thermal stability and corrosion resistance. It is also desirable to change the open pore structure to a closed pore structure. Elimination of open porosity can improve chemical resistance such as the corrosion resistance of the material during subsequent processing steps. In order to minimize the open porosity, the film formed from the colloidal suspension is modified in one or more ways. These processes include the percolation of the matrix material applied in the liquid phase, the percolation of the matrix material applied in the gas phase, and the curing/annealing process.

The percolation matrix material applied in the liquid phase is a spinning polymer, which can be converted into silica or similar ceramic materials during the curing process. One example is high temperature curing, in the presence of oxygen or steam as necessary. The term spinning polymer as used herein includes oligomers and monomers as well as polymers. Matrix materials include, but are not limited to, silicate, hydrogen silsesquioxane, organosilsesquioxane, organosiloxane, organohydrogensiloxane, silsesquioxane-silicate copolymer, silsesquioxane Alkane-based materials, polycarbosilane and acetoxysilane. Appropriate commercial substrate materials include T11 and T14 series of silicate, spinning glass Accuspin^TM, And organic hydrogen siloxane HOSP^TM, Are provided by Honeywell International, Inc. (Morristown, NJ).

In liquid phase percolation, the coating solution of the matrix material is usually coated on the colloidal film by spin coating, but alternative coating processes can also be used. The low-molecular-weight matrix material has easier penetration of the narrow space between the small particles. Matrix materials with molecular weights ranging from hundreds to thousands of atomic mass units (amu) are popular. Percolating molecules with a hydrogen dynamic diameter of less than 1-2 nanometers are beneficial to percolating pores. The solids content of the diafiltration solution can range from almost 100% solids to as low as 2% solids. The percolating matrix material occupies a small space to minimize open porosity. In addition, depending on the molecular weight of the matrix polymer, the matrix material can also form a covering layer on top of the percolated colloidal layer, as described in Example 5 below.

In some specific examples, the above-mentioned dopants such as arsenic, antimony, phosphorus or boron are contained in the host material. For example, dopants are introduced to increase the collection of mobile ions and reduce the glass transition temperature of the gap-filling dielectric material. The introduction of phosphorus can provide better gap filling properties and among other reasons, the use of boron to produce dielectric materials with increased corrosion resistance and to provide coating solutions for coating dielectric materials with longer shelf life. Dopants can also be provided for other reasons. Specifically, silicate and silsesquioxane doped with boron and phosphorus are useful host materials. Suitable phosphorous doped silicates include phosphorous silicate products P062A, P082A, P112A, P064A, P084A, and P114A, all provided by Honeywell International, Inc. (Morristown, NJ). The boron-doped silsesquioxane is prepared, for example, by adding a solution of boron oxide in isopropanol to the silsesquioxane solution, as described in Example 3 below. The boron and/or phosphorus doped silicate is prepared by the synthesis of silicate polymers including boron and/or phosphorus precursors. Suitable phosphorus precursors include but are not limited to P₂O₅, H₃PO₄, And trialkyl phosphates such as trimethyl phosphate and triethyl phosphate. Suitable boron precursors include but are not limited to B₂O₃, H₃BO₃, And trialkyl borate such as trimethyl borate and triethyl borate. Boron and/or phosphorus doped silicate uses P₂O₅With B₂O₃The synthesis as a reactant is illustrated in Example 7 below. Alternatively, the matrix material may comprise a mixture of undoped spinning polymer and the aforementioned boron and/or phosphorous precursors. Additional dopant-containing molecules that can be used in dopant/host material mixtures include phosphorus<img file="TW200529356A_D0001.tif" />, Borazine and borophosphate.

In an alternative embodiment, the matrix material is included as a component of the colloidal dispersion. Pre-mixing the colloidal dispersion and the matrix material has the advantage of eliminating the processing step of coating the coating solution of the matrix material. In the case of pre-mixing, the part of the matrix material added makes most of the volume in the gap occupied by small particles to minimize the thermal shrinkage of the dielectric material. For example, the ratio of small particles to matrix material is greater than or about 1:1. It should be noted that when the matrix material is used as the binder in the colloidal dispersion, the ratio of small particles to the matrix material is much larger than when the matrix material is premixed in the colloidal suspension.

Gas-phase percolation using matrix materials provides a second way of thickening. Vapor percolation methods include chemical vapor deposition (CVD) and atomic layer deposition. Regarding use as a percolation method, adjust the CVD conditions to prevent the top surface from being sealed before reducing body porosity. Therefore, for example, the CVD method is performed in a processing system where the reaction rate is limited by the condition that the impact molecule has a low adhesion coefficient and/or a high surface diffusivity. The adhesion coefficient is the probability that the arriving molecule will react on the surface. A bonding coefficient of 1 means that each molecule remains on the surface. For successful infiltration using CVD, the adhesion coefficient must be less than 0.01. Regarding the thermal CVD method, this can usually be achieved by choosing a deposition temperature lower than the standard processing temperature. Regarding the typical CVD deposition of material layers on a plane, these conditions can result in unacceptably low deposition rates. However, in the deposition on the highly porous film of the present invention, the surface area can be many times larger than the area of the flat substrate, enhancing the effective deposition rate to the actual level. A typical vapor phase thickening method is CVD deposition of tetraethoxysilane (TEOS) and oxygen at a temperature between about 400 and 600°C. The deposition temperature of percolation is significantly lower than the traditional CVD method used in TEOS/oxygen system of about 600 to 700°C. The above-mentioned dopants can be included in the CVD percolation method by including the dopant precursor gas together with the CVD reaction gas. Examples of dopant precursors may include boron oxide, triethyl borate, alkyl borane, and diborane for boron doping, and triethyl phosphate, trimethyl phosphate, and phosphine for phosphorus doping.

Atomic layer deposition (ALD) provides an alternative to vapor infiltration. In ALD, each atomic layer is deposited by alternately supplying reactive gas and cleaning gas. Therefore, ALD is an excellent method for forming a conformal uniform coating of the entire pore surface structure of the colloidal dispersion layer. Al deposition₂O₃The ALCVD method uses Al(CH₃)₃And water vapor as a precursor. ALCVD coatings composed of less than 20-30 atomic layers can be advantageously used in the present invention. A larger number of atomic layers can also be used.

The curing method, which may include thermal processing or annealing methods such as electron beam annealing or ion beam annealing or a combination thereof, provides a third method of modifying the open-pore structure. The curing method can be applied to the colloidal dispersion thus deposited, or applied to the thin film after liquid or gas phase percolation. All methods of forming gap-filling dielectric materials according to the present invention include a curing step. Depending on needs, one or more baking steps at a temperature between about 75 and 300°C can precede the curing method. The film can be cured in a vacuum or in an atmosphere of common gases such as nitrogen, oxygen, ozone, steam, ammonia, argon, carbon monoxide, carbon dioxide, nitrous oxide, nitrogen oxide, helium, hydrogen, forming gases or mixtures thereof. Regarding materials that can be converted into dielectrics by oxidation or nitridation, such as small particles of silicon, a curing atmosphere containing oxygen or nitrogen is used.

A typical curing process is curing in a nitrogen/oxygen atmosphere in a furnace at a temperature between about 600 and 800°C for a period of less than about 2 hours. Alternatively, the film is cured by rapid thermal processing (RTP) at a temperature between about 700 and 900°C for about 10 seconds to 5 minutes. Depending on needs, especially for methods in which the small particles or the matrix material are non-doped materials, the curing can be performed after the higher temperature thermal annealing step. The typical annealing process uses a temperature between about 800 and 1000°C in nitrogen. In the method of the present invention, the curing effect improves the dielectric film on the substrate included in the inner side of the slit and the open area.

The method of the present invention is used to deposit a dielectric material on a substrate when manufacturing an integrated circuit device. Integrated circuit devices include, but are not limited to, silicon-based devices, gallium arsenide-based devices, optoelectronic devices, focal plane arrays, photovoltaic cells, and optical devices. As is well known, integrated circuit devices usually include a substrate, conductive circuit wires, and dielectric materials. In addition, barrier layers, corrosion stop layers, and conductive gates such as polysilicon gates can also be included in the device. The interconnection circuit lines can function to distribute electrical signals within the device and provide power input to the device and output signals from the device. Integrated circuit devices usually include multiple layers of circuit lines, which are interconnected by vertical metal bolts, which are metal filled vias. Suitable substrates include, but are not limited to, silicon, silicon dioxide, glass, silicon nitride, ceramics, and gallium arsenide. The substrate as used herein means any layer that is planarized or has a surface state, including semiconductor wafers, dielectric layers, gates, barrier layers, corrosion stop layers, and metal lines found in integrated circuit devices.

The main method of forming the gap-filling dielectric material according to the present invention is summarized in the processing flow chart of FIGS. 1-3. Figure 1 illustrates a process 10 for forming a membrane that is not percolated by a matrix material. The colloidal dispersion of small particles is deposited on the substrate in step 12 and then baking step 14 as necessary. The pellets can be doped or undoped. The final step of the process 10 is the curing process 16 described above. The processing step 16 of Figures 1-3 does include higher temperature annealing if necessary. FIG. 1 also illustrates an alternative process of forming a dielectric material, in which the matrix material is pre-mixed in the colloidal dispersion in step 12. When depositing the premix dispersion, the baking step 14 is included in the process.

Figures 2 and 3 illustrate that processes 20 and 30 include percolation and gas phase processes with a liquid matrix material, respectively. In the processes 20 and 30, the deposition of the colloidal dispersion, step 12, is after the baking process 14 if necessary. Regarding liquid phase percolation, in step 26 process 20, the coating solution of the matrix material is coated on the thin film formed from the colloidal dispersion. The coating solution of step 26 may contain dopants, including but not limited to boron and/or phosphorus. Step 26 may optionally include multiple coatings of the coating solution of the matrix material. The coating of the matrix material is after the baking step 28 and the curing step 16. In the vapor percolation process 30, after depositing the colloidal dispersion in step 12 and optionally baking in step 14, the matrix material is deposited on the small molecules by chemical vapor deposition in step 36. Materials containing dopants such as boron and phospholipids can be advantageously used in step 36. The curing step 16 completes the process 30. Processes 20 and 30 provide a composite gap-filling dielectric material composed of a matrix material surrounding a small particle filler.

The material of the present invention is particularly useful for filling narrow gaps with dielectric in the pre-metal layer and filling trenches in shallow trench isolation structures, as shown in FIGS. 4 and 5, respectively. The pre-metal layer 40 in FIG. 4 includes a polysilicon gate 43 and a barrier layer 44 on the substrate 45. The gap 42 may even be narrower than the "minimum part size", as defined by the limitations of the photocopying method. The specific example illustrated in FIG. 4 shows a dielectric layer 46 comprising small particles 47 covered by a cover layer 48 of a cured percolating matrix material. The matrix material also occupies the space between the small particles (not shown). The use of colloidal silica to provide small particles and boron-doped sesquioxane as the percolation matrix material, less than 100 nanometers, as small as 50-60 nanometers in width (0.05-0.06 microns) gap has been completely filled without loss Layer, as described in Example 5 below.

The typical shallow trench isolation structure 50 shown in FIG. 5 includes a substrate 52, a spacer oxide layer 53, a hard mask 54, a spacer oxide 55, and a trench 56 filled with the dielectric material of the present invention. The characteristic size 57 of the shallow groove is usually 1-2 times the "minimum part size". Therefore, STI applications also need materials to fill narrow openings. Regarding STI applications, small particles are usually composed of silicon oxide, silicon or a mixture thereof. Percolation is in the liquid or gas phase, preferably oxides or oxide-forming matrix materials such as SiO₂Or Al₂O₃conduct. Regarding vapor phase percolation, silicon oxide can be deposited using standard CVD precursors, including but not limited to tetraethoxysilane (TEOS) and oxygen or ozone, or silicon can be deposited using precursors including dichlorosilane or trichlorosilane.

The advantages of the gap-filling dielectric material of the present invention can be understood from the subtle conversion of the material during the curing step 16, which is mainly the process of sintering and reflow. Sintering is traditionally defined as the process of heating and compacting the powder at a temperature below the melting point of the powder or at the glass transition temperature to fuse the particles together into a single rigid shape.

Reflow occurs at a temperature above the glass transition temperature and causes a physical conformal change. The reflow effect of PSG and BPSG materials is described in RALevy (J. Electrochem. Soc., Vol 133, No. 7, pp. 1417 (1986)). The reflux is driven by surface tension. The surface tension and σ/R²It is proportional, where σ is the surface tension and R is the radius of curvature. Regarding the traditional BPSG reflow, the curvature radius of the conformal coating for the narrow slit is about 100 to 500 angstroms, but the radius of curvature between the particles of the porous film is about 5 to 50 angstroms, depending on the particle size. The surface tension on the inside of the porous film can be several orders of magnitude greater than that of traditional coatings, so it can cause backflow at even higher viscosities. Therefore, the reflow can convert the initial open pore structure into a closed pore structure at a lower temperature (or a shorter time at the same temperature) than that required by the traditional reflow.

Regarding the process 10 that does not include percolation with the matrix material, the deposited colloidal dispersion after removing the solvent is mainly composed of small particles. In these cases, solidification can induce sintering of the pellets. The use of small particles containing phosphorus or boron dopants can reduce the minimum temperature requirement for sintering. The use of doped pellets can also lower the glass transition temperature, so that the reflow of the doped pellets can occur at the above-mentioned oven curing and RTP temperature.

Regarding the processes 20 and 30 including percolation with the matrix material, the curing process can cause chemical changes in the matrix material. For example, using the above-mentioned spinning polymer containing silicon for liquid phase percolation, the solidification in an oxygen-containing atmosphere can transform the matrix material into silicon oxide or silicon oxynitride. In addition, when the pellets are composed of a material that can transform a dielectric, such as silicon, the curing in an oxygen or nitrogen atmosphere can also cause chemical changes in the pellets. The reflow and sintering characteristics of the matrix material can be adjusted by doping. For example, the use of a matrix material containing phosphorous or boron can lower the reflow temperature and cause the curing to induce chemical and physical changes. In this case, reflow occurs at a temperature lower than that required for traditional BPSG glass. Without being limited by any theory, the inventors concluded that the lower reflow temperature is that the driving force for reflow is surface energy, which is inversely proportional to the radius of curvature. Regarding the colloidal dispersion of the small particles of the film of the present invention, the relevant radius of curvature is angstroms, while for the traditional BPSG reflow process, it is hundreds of angstroms. In addition, in the present invention, the required flow distance is more than an order of magnitude smaller.

Therefore, it can be seen that thermal processing can improve the gap filling of the dielectric material by sintering the pellets together and/or by causing reflow in the pellets and/or matrix material, minimizing the open porosity, reducing its porosity, and in some cases , Increase its density. The higher the processing temperature, the greater the improvement in the pore structure. Reducing open porosity can increase the resistance of the dielectric material to shared buffered oxide etchant (BOE) solutions, for example, solutions containing ammonium fluoride and/or hydrogen fluoride. As described in the following example, only thermal processing, process 10, a dielectric material formed from a colloidal dispersion of silica particles, and percolation of boron-doped hydrogen silsesquioxane, process 20, self-oxidation A dielectric material formed from small silicon particles is used to fill the gaps in the jacquard wafer. The infiltrated and non-infiltrated materials in the gap are resistant to the standard 500:1 BOE solution. However, the high processing temperature is related to the shrinkage rate of the material that can cause the material to crack or delamination in the slit. The use of dense granules in the method of the present invention can minimize the heat shrinkage rate. Regarding colloidal silica without percolation, for example (refer to Example 2 below), after annealing at 900°C, it can be seen that the overall thickness shrinkage of the baked film is only 4.5%. Therefore, the thermal processing temperature can be selected according to the method of the present invention to provide a crack-free and etching-resistant gap-filling dielectric material.

The characteristics and advantages of the present invention are further illustrated but not limited by the following experimental examples.

Analytical test method

In the results of characterization experiments, the refractive index and film thickness are measured using Woollam variable-angle spectroscopic ellipsometer model MMA. The film thickness samples are measured after baking, curing and annealing. The shrinkage percentage is calculated by dividing the change in film thickness by the thickness after baking. After baking, the coated jacquard wafer is cracked to show the size of the part. The cross section is gold contaminated with a thin layer of gold. Use JOEL JSM model 6330F SEM device to obtain scanning electron microscope (SEM) images with magnification ranging from 40,000 to 100,000.

Example 1: Preparation of colloidal dispersion of silica

A 1.8% by weight colloidal silica dispersion in cyclohexanone was prepared by combining 50.3 g of a 10% by weight colloidal silica stock solution in cyclohexanone (Catalyst and Chemical Industries Co, Japan) and 225 g of cyclohexanone. The average particle size of colloidal silica is 10.5 nanometers. The analysis of the metal concentration of the solution is: Ca: 4.8 ppb; Cr: &lt;1 ppb; Cu: 4.2 ppb; Fe: &lt;5 ppb; Mg: 0.7 ppb; Mn: &lt;1 ppb; Ni: &lt;0.5 ppb; K: &lt; 5 ppb; and Na: 16 ppb.

The 3.5% by weight colloidal silica dispersion in cyclohexanone was prepared by mixing 90.6 g of 10% colloidal silica stock solution and 170 g of cyclohexanone. The solution is homogenized by ultrasonic agitation for 30 minutes, and then filtered through a 0.1 micron filter before being used for spin coating on covered or jacquard wafers.

Example 2: Coating of colloidal silica solution

1.8% by weight of the colloidal silica solution of Example 1 was spin-coated on an 8-inch silicon cover wafer, hereinafter referred to as the cover wafer, and spin-coated on parts with a size range of 50 nanometers to several microns with a step height of 0.2 Jacquard wafers up to 0.4 microns. The spin coating conditions included dynamic dispensing with a dispensing volume of 2 ml at 300 rpm for 3 seconds, followed by an acceleration of 50 rpm/sec at 2000 rpm and finally spin coating for 20 seconds. The coated wafers were baked at 80°C, 150°C, and 250°C for 1 minute, cured, and annealed. During curing, the temperature was increased from 450°C to 700°C at a rate of 5°C/min, and then kept at 700°C for 30 minutes. Curing atmosphere is N₂Under 16 liters/min and O₂At 4 liters/minute. The wafer was annealed in flowing nitrogen at 900°C for 20 minutes.

The film thickness and shrinkage rate of the silicon oxide film on the cover wafer after each processing step are shown in Table 1. When deposited on a cover wafer, a crack-free transparent film with no visible defects can be obtained. The thickness of the film was measured with a JAWoolam VASE. The unevenness of the film is less than 2%.

<tables><img file="TW200529356A_D0002.tif" /></tables>

The refractive index of 1.24 shows that the deposited film has a porous silica structure. This refractive index value can be compared with the refractive index of 20% porous silica film of 1.36 and the refractive index of non-porous silica film of 1.45. The porous film shows very low shrinkage, even after heat treatment up to 900°C.

The gap-filling ability of colloidal silica in the narrow gap of the jacquard wafer is measured by the SEM image of the self-cracking wafer. SEM pictures are used for (i) after baking, (ii) after curing and (iii) after annealing the wafer. All three types of SEM images show that small silicon oxide particles uniformly fill gap sizes ranging from 50 nanometers to several nanometers. After curing and annealing, there is no delamination or cracking, and the small particles also fill the corners around the bottom of the gap.

Example 3: Preparation of boron-doped silsesquioxane solution

Add 8.2 grams of triethoxysilane, 0.60 grams of deionized water and 0.75 grams of 0.02 N nitric acid to 41 grams of acetone in a plastic bottle. The mixture was kept at room temperature for 18 hours, and then diluted with 50 grams of n-propoxypropanol and 20 grams of denatured ethanol to form a basic silsesquioxane solution.

3 grams of boron oxide (B₂O₃) Is dissolved in 100 grams of isopropanol to form a 3% boron oxide solution. 6.66 grams of 3% boron oxide solution was added to 100.55 grams of basic silsesquioxane solution. The molecular weight of the boron-doped silsesquioxane resin is 1256 atomic mass units separated from the gel permeation chromatography. The resin contains 2.0% by weight of boron. The molecular weight of the resin after 15 days at room temperature is 1797.

Comparative example 4: Coating of boron-doped silsesquioxane solution

The boron-doped silsesquioxane solution of Example 3 was coated on 6" covered wafers and jacquard wafers using the spin coating, baking and curing cycles of Example 2. The film properties are shown in Table 2. 1100 Angstroms of baking The post-film thickness is obtained by the baking cycle between the coating steps on the cover wafer from the two coating steps. A good quality film can be obtained on the cover wafer. The FTIR spectrum of the cured film shows that the sharp edge is at 2000- 2250 cm^-1And 800-900 cm^-1Silane (SiH) confirmed by the film after baking is converted into silicon oxide, thus producing a silicon oxide film doped with boron.

<tables><img file="TW200529356A_D0003.tif" /></tables>

The SEM pictures obtained after each processing step can see the gap filling effect of the material. The boron-doped silsesquioxane fills the gaps in the jacquard wafer without voids or delaminations, after baking, down to the narrowest dimension of about 50-60 nanometers. After curing at 700°C in nitrogen/oxygen, the formed cultivated silicon showed no delamination, but according to the SEM brightness of this area, low-density materials were confirmed around the corners under the gap. After annealing at 900°C in nitrogen, delamination and cracks occurred due to further shrinkage caused by annealing.

Example 5: Percolation of boron-doped silsesquioxane for colloidal silica film

The 1.8% by weight colloidal silica solution from Example 1 was used to coat the jacquard wafer, and then the spin coating and baking conditions of Example 2 were performed. After baking, the boron-doped silsesquioxane solution from Example 3 was spin-coated on the coated jacquard wafer using the spin-coating/baking sequence of Example 4. Then, the curing and annealing conditions of Example 2 were used to cure and anneal the percolated wafer.

The degree of gap filling in the jacquard wafer is determined by examining the SEM pictures of the gaps of various sizes. For all samples after baking, curing and annealing, there is no delamination inside the gap of all sizes down to the narrowest dimension of about 50-60 nanometers. A cover layer of boron-doped silicon oxide is formed on top of the percolated colloidal silicon oxide film. The thickness of the cover layer is about 200 nanometers.

Example 6: Corrosion resistance

The silicon oxide-coated cover wafer of Example 2 and the boron-doped silsesquioxane-coated wafer of Example 4 were immersed in 500:1 BOE (buffered oxide) containing ammonium fluoride at an etching temperature of 21°C. The etchant) solution lasts for 180 seconds. After etching, the processed wafer was cleaned with deionized water and the film thickness was measured. The etch rate of silicon oxide produced by CVD deposition of TEOS is used as a reference for comparison. The etching rate is calculated by dividing the reduction in film thickness by the etching time. The etching rate (Angstrom/sec) and the relative etching rate related to CVD TEOS are shown in Table 3. The average etch rate of CVD TEOS is about 0.45 angstroms/sec.

<tables><img file="TW200529356A_D0004.tif" /></tables>

The coated jacquard wafers of Examples 2, 4, and 5 were immersed in a 500:1 BOE solution for 20 seconds, and then washed with deionized water. Take out the SEM picture of the etched sample to check the corrosion resistance of the dielectric filled in the narrow gap. The results are summarized below.

<tables><img file="TW200529356A_D0005.tif" /></tables>

The inclusion of small silicon oxide particles in the dielectric shows two main advantages: (1) elimination of cracking or delamination caused by 700-900°C heat treatment and (2) a significant improvement in the corrosion resistance of the gap dielectric to BOE etching. These advantages are due to the low shrinkage and high density achieved by the inert filler compound method.

Example 7: Synthesis of doped silicate

0.38 g B₂O₃Dissolved in 10.0 g of 5% P₂O₅In the solution in 2-propanol, and stir for 1 hour. Add 9 grams of TEOS to 9.5 grams of acetone, followed by 1.38 grams of 1N HNO₃And 0.5 g of water. The mixture was heated to boiling at about 66°C and kept for 3 hours. The molecular weight is about 2000 amu. The silicate was evaluated to have 8% by weight phosphorus and 4% by weight boron. The solid content of the solution is 8% by weight.

Example 8: Percolation of doped silicate for colloidal silica film

The colloidal silica film was deposited on the cover wafer using 1.8% by weight of the colloidal silica solution of Example 1. The spin-coating procedure was to dynamically dispense 2 ml of solution at 300 rpm for 5 seconds, followed by spin-coating at 2000 rpm for 20 seconds. The wafers were baked at 80°C, 150°C, and 250°C for 1 minute each. The film thickness is 520 angstroms and the refractive index is 1.23.

The porous silica film was percolated with the doped silicate solution of Example 7. Prepare a cleaning solution consisting of 50% by weight of 2-propanol and 50% by weight of acetone. Use the following percolation and cleaning procedures: (1) Dynamically distribute 4 ml of doped silicate solution on the wafer for 5 seconds at 300 rpm; (2) Distribute the liquid for 1 second at 1000 rpm; (3) Let stand still 5 seconds; (4) Dynamic cleaning with 4 ml cleaning solvent at 300 rpm for 5 seconds; and (5) Final spin coating at 2000 rpm for 20 seconds.

The diafiltration membrane was baked at 80°C, 150°C and 250°C for 1 minute each. The film thickness after baking was 517 angstroms and the refractive index was 1.43. The increase in the refractive index to a value of 1.43 shows that a solid non-porous film is produced.

Example 9: Percolation of doped silicate for colloidal silica film

The jacquard wafer was coated with the 1.8% by weight colloidal silica solution of Example 1 using dynamic dispensing of 3 ml at 300 rpm for 3 seconds, followed by spin coating at 2000 rpm for 20 seconds. One minute after spin coating without baking, 3 ml of the doped silicate solution of Example 7 was dispensed on the wafer and spin-coated at 300 rpm for 3 seconds, followed by a final distribution at 2000 rpm for 20 seconds. Then, according to the procedure described in Example 2, the percolated membrane was baked, cured, and annealed. The SEM image of the annealed film shows that there are no cracks in the film in the gaps and the top layer of the infiltrated material. The diafiltration wafer is immersed in BOE 500:1 solution for 20 seconds. Under 80,000 magnification, no etching is seen around the corners of the wide and narrow slits in the SEM image.

Example 10: Pre-mixing of colloidal silica and doped silicate solution

The 4% by weight colloidal silica solution was prepared by adding 23 grams of cyclohexanone to 15 grams of 10% colloidal stock solution. 9 grams of TEOS was mixed with 9.5 grams of acetone, and then 1.38 grams of 1N nitric acid and 0.58 grams of deionized water were added. 10g 5wt%P₂O₅The solution was added to isopropanol (IPA) and stirred well. The mixture was stirred at room temperature for 72 hours. Then, the solution was diluted with 15.23 grams of acetone and 15.23 grams of IPA to obtain a final solid content of 4% by weight of P-doped silicate.

The following three solutions were prepared and spin-coated on the cover wafer, and then baked, cured and annealed as in Example 2: Solution 10A: 10 grams of 4% silicate and 10 grams of 4% P-doped silicate solution solution 10B: 16 grams of 4% silicate and 4 grams of 4% P-doped silicate solution solution 10C: 18 grams of 4% silicate and 2 grams of 4% P-doped silicate solution. The results are shown in Table 5 below .

<tables><img file="TW200529356A_D0006.tif" /></tables>

Although the present invention has been described based on specific materials and conditions, the description is only an example of the application of the present invention. Various adjustments and changes of the method shown are all within the scope of the present invention defined in the following claims.

<p>10Process</p><p>12The step of depositing colloidal dispersion</p><p>14Baking steps</p><p>16Curing process</p><p>20Process</p><p>26Liquid phase percolation step</p><p>28Baking steps</p><p>30Process</p><p>36Liquid phase percolation step</p>

Figures 1-3 are flowcharts of a method of forming a dielectric material according to a specific example of the present invention.

Fig. 4 is a pre-metal layer filled with a dielectric material formed according to an embodiment of the present invention.

FIG. 5 is a shallow trench isolation structure filled with a dielectric material formed according to a specific example of the present invention.