CN101255286B - Abrasive particles, slurry for polishing and method of manufacturing the same - Google Patents

Abstract

The present invention discloses a polishing slurry for use in an STI CMP process, necessary for fabricating ultra highly integrated semiconductors of 256 mega D-RAM or more (Design rule of 0.13 mu or less), which can polish wafers at a high removal rate, having an excellent the removal selectivity of oxide compared to nitride. The polishing slurry can be applied to various patterns required in the course of producing ultra highly integrated semiconductors, and thus excellent removal rate, removal selectivity, and within-wafer-nonuniformity (WIWNU), which indicates removal uniformity, as well as minimal occurrence of micro scratches, can be assured.

Description

Abrasive particles, polishing slurry and method of manufacturing the same

This application is a divisional application of a patent application with an application date of December 16, 2005, an application number of 200510134775.9, and an invention title of "abrasive particles, polishing slurry and its manufacturing method".

technical field

The present invention relates to a slurry used in chemical mechanical polishing (hereinafter referred to as "CMP") process. Especially relate to a kind of polishing slurry that is used for shallow trench isolation (STI, shallow trench isolatein) CMP process, and this polishing slurry is for the manufacture of 256M (mega) or higher D-RAM ultra-high integration semiconductor (design standard is less than or equal to 0.13 μm), which can polish wafers at a high removal rate, and the polishing slurry has excellent oxide removal selectivity compared to nitride. In addition, the present invention also relates to abrasive grains, and methods for producing the abrasive grains and polishing slurry.

Background technique

Chemical Mechanical Polishing (CMP) is a semiconductor processing technique that uses abrasive particles between the wafer and polishing pad for mechanical processing and slurry for chemical etching. This method has been successfully developed by the IBM company of the United States since the 1980s, and has become the core process of the overall surface technology in the global production of submicron semiconductor wafer manufacturing.

The types of polishing slurry can be roughly divided into three types according to the objects to be processed: oxide polishing slurry, metal polishing slurry and polysilicon wafer polishing slurry. The oxide polishing slurry is suitable for polishing the surface of the interlayer insulating film and the silicon dioxide (SiO ₂ ) layer in the shallow trench isolation (STI, shallow trench isolation) process, and it roughly includes polishing particles, deionized water, pH stabilizer and ingredients such as surfactants. The role of the polishing particles in the polishing process is to mechanically polish the surface of the workpiece through the pressure generated by the polishing machine. The composition of the polishing particles may be silicon dioxide (SiO ₂ ), cerium oxide (CeO ₂ ), or aluminum oxide (Al ₂ O ₃ ).

Specifically, in the STI process, ceria slurry is usually used to polish the silicon dioxide layer, and at this time, the silicon nitride layer can be mainly used as the polishing stop layer. Typically, additives can be added to the ceria slurry to reduce the removal rate of the nitride layer, thereby improving the oxide layer to nitride layer polishing rate selectivity. However, the use of additives is disadvantageous because it can reduce the removal speed of the oxide layer as well as the removal speed of the nitride layer. In addition, the polishing agent particles of the ceria slurry are usually larger than the polishing agent particles of the silica slurry, which scratches the wafer surface.

However, if the selectivity of the polishing rate of the oxide layer to the nitride layer is low, since the excess oxide layer is removed, the pattern of the adjacent nitride layer is destroyed, resulting in dishing on the processed surface. Therefore, it is impossible to achieve uniform surface flatness.

Therefore, the polishing slurry used in STI's CMP process must have high selectivity, high polishing speed, high dispersion, highly stable micro-scratch distribution, and highly concentrated and uniform particle size distribution range. In addition, the number of particles with a particle size ≥ 1 μm must be controlled within a predetermined range.

The two patented technologies of U.S. Patent Nos. 6,221,118 and 6,343,976 of Hitachi Corporation of Japan provide the conventional technology used in STI CMP, that is, the method of preparing cerium oxide, and the polishing slurry with high selectivity when using cerium oxide as polishing particles The preparation method of the material. These two patents describe the properties that polishing slurries must possess in the STI CMP process, types of polymers containing additives, and methods of using them in various special cases and in general. It is particularly worth mentioning that these two patents also proposed that the range of the average particle size of the polishing particles, primary polishing particles and secondary particles, and the change of the calcination temperature can lead to changes in the particle size of the polishing particles and changes in the scratches on the polishing surface. Another conventional technology, U.S. Patent No. 6,420,269, belongs to Hitachi, which provides us with a method for preparing a variety of ceria particles and a polishing slurry with high selectivity when using ceria as polishing particles. . At the same time, US Patent No. 6,615,499, a patented technology belonging to Hitachi, also provides us with the change rate of the peak density of polishing particles and the change of polishing removal rate depending on the heating rate of calcination within the predetermined X-ray radiation range. In addition, in the technology provided by the US Patent Nos. 6,436,835, 6,299,659, 6,478,836, 6,410,444 and 6,387,139 belonging to Showa Denko Co., Ltd. of Japan in the early period, it also pointed out the method of preparing ceria and the use of ceria to make A method for preparing a polishing slurry with high selectivity when polishing particles. Most of these patents describe additives to polishing slurries, their effects on polishing performance, and coupling additives.

However, the above-mentioned prior art only discloses the average particle size and range of the abrasive grains constituting the polishing slurry, but lacks the types and characteristics of the raw materials of the abrasive grains, the calcination process involving these characteristics, and the carbon dioxide obtained in this way. The characteristics of cerium particles and other details.

In fact, the characteristics of the finished ceria slurry, including specific surface area, porosity, crystallinity, and uniformity of particle size distribution, can change according to material properties and calcination conditions, resulting in very different STI CMP result. Specifically, the number of large abrasive particles and their agglomerations that can cause micro-scratches changes as design criteria decrease. Therefore, it is extremely important to specify and limit the characteristics of the raw materials and the calcination process according to these raw material characteristics.

Contents of the invention

Therefore, the present invention is produced in view of the above-mentioned problems occurring in the prior art.

The object of the present invention is to provide a method for manufacturing a bulk precursor material with uniform size distribution through a multi-step calcination process.

The present invention provides a method of manufacturing slurry abrasive particles, which includes: preparing a precursor material; and calcining the precursor material in at least two or more stages.

In the method of making slurry abrasive particles, the calcining step comprises: first calcining the precursor material; crushing or crushing the first calcined precursor material to produce smaller secondary precursor materials; and secondly calcining the secondary precursor material body material.

According to the method for manufacturing slurry abrasive particles according to a preferred embodiment of the present invention, further comprising: pulverizing or crushing the second-calcined precursor material to form a third-level precursor material; and calcining the third-level precursor for the third time body material.

In the method of manufacturing slurry abrasive grains, the calcining step may be performed at a temperature from 500 to 1,000°C.

The present invention further provides a method for manufacturing a polishing slurry, the method comprising: preparing the above-mentioned manufactured abrasive grains; grinding the abrasive grains in a grinding mixture comprising deionized water, a dispersant and additives; and filtering the grinding mixture to Remove larger particles from it.

The present invention further provides abrasive grains and polishing slurry produced by the above method.

The abrasive particles preferably comprise ceria and the precursor material preferably comprises cerium carbonate.

The above description is only an overview of the technical solutions of the present invention. In order to understand the technical means of the present invention more clearly and implement them according to the contents of the description, the preferred embodiments of the present invention and accompanying drawings are described in detail below.

Description of drawings

FIG. 1 is a flow chart illustrating the process of polishing slurry according to an embodiment of the present invention.

FIG. 2 is a flow chart illustrating a process for manufacturing a precursor material according to an embodiment of the present invention.

Figure 3 shows the definition of Dl, D50 and D99 depending on the particle size.

Figure 4 shows a distribution diagram of the size of cerium carbonate secondary particles.

Fig. 5 is a graph plotting the size of cerium carbonate secondary particles versus calcination temperature.

Figure 6a is a schematic diagram illustrating the formation of particles when calcining dispersed precursor materials.

Figure 6b is a schematic diagram illustrating the formation of particles when calcining a bulk precursor material.

Figures 7a to 7c are TEM photographs of abrasive grains calcined at 800°C with different secondary grain sizes.

FIG. 8 is a schematic diagram illustrating the calcination process of the precursor material according to the present invention.

Figure 9a is a SEM photo of the dispersed precursor material.

Figure 9b is a SEM photo of the bulk precursor material.

Figure 10 is a graph of density and specific surface area plotted against particle size for dispersed and bulk precursor materials when calcined.

Figure 11a is a TEM image of a slurry prepared from dispersed precursor materials.

Figure 11b is a TEM image of a slurry prepared from bulk precursor material.

FIG. 12 is a graph showing the particle size of slurries 1 and 2 before and after the milling process.

Fig. 13a is a graph showing the change in particle size distribution before and after forcibly dispersing slurry 1.

FIG. 13b is a graph showing the change in particle size distribution before and after the slurry 2 is forcibly dispersed.

Figure 14 is a graph showing CMP results.

Detailed ways

The preparation method of the polishing slurry in the present invention and the analysis of the properties of the polishing slurry will be described in detail below. Specifically, changes in polishing slurry properties will be analyzed separately when the size of raw material agglomerates changes and when a multi-step calcination process is introduced. In addition, the present invention will also illustrate the preparation method of polishing slurry using cerium oxide as polishing particles, and the method of using deionized water and anionic polymer as dispersant. Also, CMP results depending on production process conditions, such as oxide film polishing speed and selectivity, will be given. Any person skilled in the art can use the structures and technical contents disclosed below to make some changes or modify them into equivalent embodiments with equivalent changes, and the scope of the present invention is not limited to the following descriptions.

[Manufacturing method of ceria slurry]

The ceria slurry of the present invention comprises ceria powder, deionized water, anionic polymer dispersant and an additive such as a weak acid or a weak base. The preparation method of the polishing slurry includes the following steps (see FIG. 1 ). First, a precursor such as cerium carbonate is pretreated to synthesize solid ceria powder (S1). Alternatively, a multi-step calcination process including drying, calcination, pulverizing and/or crushing steps may be performed prior to solid state synthesis. After that, the cerium oxide powder is mixed with deionized water in a vessel (S2), and the resulting mixture is ground in a grinder in order to reduce the particle size and achieve a desired particle size distribution (S3). An anionic polymer dispersant is added to the slurry obtained by the above method to increase the dispersion stability of the polishing particles (S4). Add additives such as weak acid and weak base to the high-speed mixer to control the pH value of the slurry, and then stabilize the dispersion by grinding (S5) to determine the weight percentage (wt%) of solids in the slurry, that is, the solid content (S6) to reach the desired value. Large particles are removed by filtration to prevent precipitation and scratches from the polishing process (S7). Afterwards, the slurry is stabilized by aging (S8). The preparation method of the ceria polishing slurry in the present invention will be described in detail below.

1. Manufacture of ceria powder

In the present invention, the first step of preparing the ceria slurry is: preparing ceria powder from the precursor by using a solid generation method. Precursors such as cerium carbonate can be calcined to produce ceria powder, but before calcination, the moisture should be removed by drying process alone to ensure the heat transfer and manufacturability. Depending on the properties of precursor materials such as cerium carbonate, ceria slurries may vary according to specific properties including specific surface area, porosity, crystallinity, particle size distribution, etc., which are explained in detail below.

The performance of ceria powder depends on the calcination effect of cerium carbonate and the performance of calcination equipment. Cerium carbonate is hygroscopic and can crystallize with water, and the valence of its crystal water can be 4, 5 or 6. Therefore, the calcination effect of cerium carbonate is related to the valence of crystal water in its crystal and its water absorption. After calcination, the moisture in the cerium carbonate is removed. But as the temperature rises and heat builds up, a decarbonation reaction occurs, and the carbonates become carbon dioxide. Ceria powder also started to form. Second, an additional heat treatment is performed to cause recrystallization, thereby producing a ceria powder composed of particles of various sizes. The calcination process is preferably carried out at 500-1000°C. Here, the calcination temperature determines the degree of crystallinity as well as the particle size. The size of individual particles or crystals increases with the increase of calcination temperature.

Furthermore, calcination may be performed in multiple stages rather than a single stage, with comminution or crushing steps introduced in between. This multi-step calcination process determines the properties of the ceria slurry, such as specific surface area, porosity, crystallinity, particle size, etc., as well as oxide removal rate and selectivity, which are also described in detail below.

2. Mixing and grinding

After the ceria powder generated by the above calcination process is mixed with deionized water in a high-speed rotating mixer and humidified, the resulting mixture is sent to a high-power grinder for grinding to reduce its particle size and make the particles well dispersed. In order to generate nano-scale ceria polishing slurry. After mixing with water, a high-power grinder can be used to control the size of the polished particles and disperse the particles that have become agglomerated. The grinder can be wet or dry. However, due to the possibility of corrosion by the metal particles produced by the dry grinder during the grinding process, it is recommended to use a wet grinder made of ceramics. However, during the grinding process of the wet grinding machine, sediments formed by agglomeration of particles may appear, resulting in a wide range of large particles, and eventually the grinding efficiency will decrease. Therefore, it is necessary to control the concentration of the polishing particles, the pH value and conductivity of the slurry, and use a dispersant to improve the dispersion stability of the polishing particles.

3. Dispersion stability and addition of additives

An anionic polymer dispersant and other additives, such as weak acid or weak base, need to be added to the polishing slurry, so as to control the pH value of the polishing slurry and stabilize the polishing slurry. Thereafter, a high energy mill may be used to grind the mixture including dispersants and additives to reduce particle size and disperse the particles. Second, use a pump to transport the powdered and dispersed slurry into a separate tank, and then disperse it again with an appropriate dispersing device to ensure its dispersion stability and prevent re-agglomeration and sedimentation.

The anionic polymer compound used as a dispersant can be any material selected from the group consisting of: polymethacrylic acid, polyacrylic acid, ammonium polyethacrylate ), ammonium polycarboxylate, carboxyl-acryl polymer, and combinations thereof. The reason is that the slurry of the present invention is based on water, and the above-mentioned polymer compound is soluble in water at normal temperature. In addition, based on the amount of polishing particles, the content of the added anionic polymer compound is suitably 0.0001-10.0 wt%. The viscosity performance of the stabilized ceria slurry is preferably Newtonian performance.

4. Control of solid phase content (wt%) and removal of larger particles

As mentioned above, after the dispersion stabilization process, the solid content of the ceria slurry is controlled within a certain range, and the filtration method is used to remove large particles that can cause precipitation and agglomeration and scratches during the CMP process. When large particles exist, the gravitational force of the particles is greater than the repulsive force caused by the repulsion between particles, and the surface area of the large particles is smaller than that of the small particles, so the dispersibility of the large particles is smaller than that of the small particles. When the number of large particles per unit volume increases with the increase of solid content, it will lead to aggravation of precipitation and agglomeration. Based on the above two reasons, precipitation and agglomeration are easy to occur, resulting in unstable slurry, so it is necessary to remove large particles, and the degree of removal of large particles increases with the number of times of filtration.

5. Aging of slurry

In the vessel, the stability of the slurry was further increased by 24 hours of agitated aging. This step can also be implemented after the slurry is completely prepared, and can also be omitted as needed.

[Changes in properties of ceria slurry depending on precursor material properties]

As described below, in the case of producing ceria slurry through the above-mentioned production process, the influence of the characteristics of the precursor material cerium carbonate on the characteristics of the ceria slurry was analyzed. In particular, the variation of the properties of the ceria slurry according to the size of the agglomerated secondary particles of cerium carbonate will be described in detail.

Abrasive grains were prepared by pre-drying and calcining the precursor material as described above, and then mixed with DI water prior to grinding. After calcination, more extensive aggregation of the precursor cerium carbonate results in a broader particle size distribution. That is, upon calcination, fine ceria particles as well as larger particles can be produced.

However, if the polishing slurry contains larger particles with a size greater than 1 μm, the polishing slurry can cause micro-scratches, which, however, will have a fatal effect on semiconductor devices during the fabrication of ultra-highly integrated semiconductors of 0.13 μm or less. Therefore, it is extremely important to exclude larger particles as much as possible for the manufacture of ceria slurry. For this, the particle size and aggregation of the precursor material, cerium carbonate, must be controlled.

Cerium carbonate can be prepared according to the procedure shown in FIG. 2 as a precursor material for ceria slurry. First, raw ores of rare earth metals are mixed (S10), and dissolved in hydrochloric acid to obtain a rare earth chloride solution (S20). Multiple extraction and isolation cycles are performed to separate cerium chloride from other rare earth metals (S30). Cerium chloride is mixed with ammonium carbonate to form a cerium carbonate precipitate (S40), which is then washed and dried (S50) to provide the desired high-purity precursor material (S60).

When using this co-precipitation method to prepare the precursor material cerium carbonate, the precipitation reaction conditions such as pH value, temperature, time, etc. can all determine the characteristics of the precipitate. Specifically, the tendency of the precursor to precipitate and the particle size of the resulting precursor have a critical impact on the properties of the finished ceria slurry.

Referring to Fig. 3, it is a schematic diagram illustrating the definition of D1, D50 and D99, ie classifying particles according to size.

As shown in Figure 3, D50 corresponds to a particle size where this particle size is smaller than 50% of the population distribution of particles, and D1 corresponds to a particle size where this particle size is the larger 1% of the population distribution particles size, and D99 corresponds to a particle size where this particle size is the size of the smaller 1% of the overall distribution of particles. Therefore, D1 occupies a larger secondary particle size than the other two, and more extensive aggregation and poorer dispersion stability will result in higher D1 values.

In order to better understand that the properties of the ceria slurry depend on the properties of the precursor material, many examples of particle size distributions are given below.

Table 1

D1 (larger size) D50 (medium size) D99 (smaller size) Precursor material 1 36 5.3μm 120.5μm 2.4μm Precursor material 2 107.7μm 34.9μm 2.5μm Precursor material 3 51.9μm 6.483μm 1.5μm

FIG. 4 plots the particle size distribution of the precursor materials cerium carbonate given in Table 1. As shown in Figure 4, Precursor Material 1 contains larger sized particles compared to Precursor Material 2 or Precursor Material 3 due to the higher degree of aggregation. After calcination at high temperature, the cerium carbonate particles of the precursor materials 1 to 3 were found to have the particle size shown in FIG. 5 as measured using an X-ray diffractometer (XRD). To reproduce the data in Fig. 5, two particles were randomly selected from various precursor materials and their dimensions were measured. As can be seen in Figure 5, as the calcination process proceeds and the particle size of the precursor material increases, the size of these particles will increase.

Cerium carbonate powder can be produced during the calcination process, while decarburization occurs to remove the carbonic acid functional group (carbonate functional group) in the form of carbon dioxide. At higher calcination temperatures, the cerium carbonate powder recrystallizes to produce larger sized particles. Furthermore, an increase in particle size due to the high tendency of cerium carbonate to agglomerate will produce larger particle sizes for the following reasons.

In densely agglomerated nano-sized powders, many primary particles are in contact with each other. At the necking point between adjacent primary particles, mass diffusion and lattice motion easily occur, so that larger particles can be formed by thermal degradation even at low temperatures. That is, as shown in Figure 6a, when the particles are dispersed from each other, they remain separated from each other even after calcination. Conversely, as shown in Figure 6b, when the particles are in contact with each other, calcination allows them to form larger particles centered at the necking point. Thus, even if calcined at the same temperature for the same time, particles of different sizes will be produced.

As shown in FIG. 5 , in the case where the precursor material 1 having a relatively large particle size is formed due to aggregation of cerium carbonate, larger particles may be formed, resulting in abnormal grain growth of ceria abrasive grains.

Referring to FIGS. 7 a to 7 c , they are photographs showing the results of calcination of precursor materials 1 to 3 at 800° C., respectively. As shown in the photographs, the number of larger particles in the abrasive grains increases proportionally to the particle size of the precursor material, cerium carbonate.

At the same time, when the particles are agglomerated, the precursor material appears as larger particles. At this time, due to incomplete calcination, very small particles can be formed in the larger agglomerate. The bulk precursor material is more resistant to mass transfer, thus delaying mass transfer and diffusion of reactant gas oxygen and by-product carbon dioxide, resulting in incomplete calcination. This phenomenon will be described in detail in the following section "Ceria slurry properties changes depending on the multi-step calcination process". For this reason, the precursor material particles appear as larger particles as they aggregate more widely, wherein the precursor material has fine particles, thus providing a broad particle size distribution.

In order to control the particle size of cerium carbonate, as previously mentioned, it is necessary to minimize powder aggregation during the precipitation process of the precursor material fabrication method. Aggregation occurs depending on the reaction conditions of powder preparation. Cerium carbonate precipitates are less likely to aggregate as more uniform precipitates are produced. A homogeneous precipitation can be obtained by adjusting the concentration of the CeCl3 solution, the mixing rate, the reaction temperature and/or by passing through an appropriate dispersant.

[Changes in properties of ceria slurry depending on multi-step calcination process]

Here, in the case of using the above-mentioned process to manufacture ceria slurry, the effect of the multi-step calcination process on the properties of ceria slurry will be described in detail, specifically, the CMP rate and the number of micro-scratches. describe.

As shown in Figure 8, the calcination process includes five steps. First, oxygen in the air reacts with cerium carbonate. Subsequently, oxygen diffuses into the cerium carbonate through pores and adsorbs at the reaction sites. Second, the oxygen reacts to calcine the cerium carbonate. Thereafter, products such as carbon dioxide are released from the reaction site, and the carbon dioxide diffuses out of the cerium carbonate and into the air through the pores. This calcination process can be expressed from the following reaction equation 1.

[Reaction Equation 1]

It can be appreciated that during the calcination process, the diffusion rate of oxygen and carbon dioxide through the pores depends on the morphology of the cerium carbonate, thereby determining the overall reaction rate. Therefore, even if calcination is performed at the same temperature for the same time period, the resulting particles may exhibit different particle growth or crystallinity.

Specifically, there is a large difference in crystallinity between the exterior and interior of cerium carbonate agglomerates having a size of several hundred μm, so that the particles exhibit a broad particle size distribution.

Referring to Figures 9a and 9b, which are SEM pictures of dispersed and bulk precursor materials, respectively. In Fig. 10, when the dispersed precursor material and the bulk precursor material are calcined, the relationship curves of the density and the specific surface area relative to the particle size are drawn for the dispersed precursor material and the bulk precursor material, wherein respectively from Fig. 9a Samples A and B were obtained for the dispersed precursor material and the bulk precursor material in Figure 9b. It can be easily drawn from the graph that bulk cerium carbonate has a larger specific surface area and lower density than dispersed cerium carbonate despite having the same particle size. The reason for this is that in the case of bulk cerium carbonate as shown in Figure 9b, its exterior crystallizes well and thus appears as larger particles, while its interior exhibits low crystallinity due to incomplete calcination which does not allow crystal growth .

Referring to Figures 11a and 11b, TEM photographs are shown of slurries prepared by calcining dispersed cerium carbonate and bulk cerium carbonate, respectively. As shown, the slurry prepared from bulk cerium carbonate exhibited a non-uniform particle size distribution with many fine particles. This is due to incomplete crystallization within the precursor material. That is, the particle size distribution of the bulk precursor material increases because there is a larger size difference between the inner and outer particles, eg, the outer particles are larger and the inner particles are smaller.

In addition, the smaller particles generated inside the larger particles are prone to agglomeration due to their larger specific surface area, and cause the outer larger particles to have micro-scratches. Furthermore, smaller particles have poor oxide polishing rates due to their low internal crystallinity, thereby enhancing the polishing rate selectivity of the oxide layer over the nitride layer.

Since microscratches have a fatal effect on semiconductor devices during the fabrication of ultra-highly integrated semiconductors of 0.13 μm or less, microscratches must be avoided. Considering the degree of aggregation of the precursor material cerium carbonate, the particle size must be adjusted.

To this end, the bulk cerium carbonate is uniformly calcined using a multi-step calcining process according to an embodiment of the present invention. The difference in crystallinity between the exterior and interior of the bulk cerium carbonate can be overcome by the multi-step calcination of the present invention to produce abrasive grains of uniform particle size in a controllable manner.

First, the primary precursor material of cerium carbonate is dried and primary calcined. Second, smaller secondary precursor materials are obtained by crushing or milling, exposing the interior with low crystallinity. A secondary calcination step is performed on the powdered or ground secondary precursor material to provide abrasive particles.

The primary and secondary calcination steps can be performed at the same or different temperatures. For the crushing or crushing process, various dry crushing or crushing devices, such as classifiers, crushers, air jet mills, etc., can be utilized.

Further improvements were obtained using a three-step calcination process. In this regard, the step of pulverizing or milling the precursor material is performed just before the subsequent calcination step. Specifically, after initial drying and calcination, the precursor material is pulverized or crushed to obtain smaller secondary precursor materials, exposing their interiors with low crystallinity. After undergoing secondary drying and calcination, the secondary precursor material is further pulverized or crushed into smaller tertiary precursor materials exposing their interiors with low crystallinity. Finally, a tertiary drying and calcination step is performed on the tertiary precursor material to provide abrasive particles.

The multi-step calcination process results in similar crystallinity on the exterior and interior of the bulk precursor material, thereby maintaining uniform particle size within a narrower particle size distribution compared to conventional single-step calcination processes. Thus, larger particles that can cause micro-scratches that form on the outside of the bulk precursor material can be broken down into smaller particles by multiple crushing or crushing steps. In addition, since the crystallinity of the entire precursor material becomes uniform, it is calcined to produce abrasive particles with a narrow size distribution.

Table 2 below presents crystallinity measurements for abrasive grains prepared from bulk cerium carbonate in Figure 9b by a multi-step calcination process and a single-step calcination process. In Table 2, slurry 1 is obtained by performing primary calcination, crushing or crushing, and secondary calcination as in a multi-step calcination process, while slurry 2 is obtained by a single-step calcination process. The particle size was measured using XRD immediately after calcination and after the wet milling process followed by calcination.

Table 2

  Average particle size (nm) Reduction (nm) Before grinding After grinding slurry 1 29.8 28.7 1.1 slurry 2 29.6 22.6 7

From Table 2 and Figure 12, it can be seen that Slurry 1 prepared by the multi-step calcination process has almost no change immediately after calcination and after grinding, while Slurry 2 prepared by the single-step calcination process shows a change in particle size after grinding. decreased sharply.

In X-ray diffraction, the depth to which X-rays penetrate a sample is only 10 μm or less. However, as shown in Fig. 9b, as in slurry 2, the bulk cerium carbonate was up to hundreds of μm in diameter and maintained this morphology even after single-step calcination. Therefore, when XRD is applied to clotted cerium carbonate, its exterior can be measured but its interior cannot be analyzed. That is, XRD is applicable to outer particles with high crystallinity, but not to inner particles with low crystallinity. After performing the wet milling process, XRD can analyze smaller internal particles, thus reducing the average particle size by 7nm.

In contrast, as in Slurry 1, since the multi-step calcination process can fully calcine the interior, the size of the particles is uniform, and their average size decreases by only 1 nm even after grinding.

Furthermore, the particle size distribution has an influence on the dispersion stability of the resulting slurry. As a valid standard for measuring slurry aggregation, dD15 or dD50 can be used. In other words, the particle size was measured using LA910 manufactured by Horiba Corporation, Japan, and the result was used for its calculation. It is defined as follows.

dD1 = before D1 sonication - after D1 sonication

dD15 = before D15 sound crack - after D15 sound crack

dD50＝D50 before sound cracking-D50 after sound cracking

Among them, each is defined as follows:

Before D1 sonication: D1 particle size measured before exposure to ultrasound;

After D1 sonication: D1 particle size measured after exposure to ultrasound;

D15 pre-sonic cracking: D15 particle size measured before exposure to ultrasound;

D15 after sonication: D15 particle size measured after exposure to ultrasound;

D50 pre-sonic cracking: D50 particle size measured before exposure to ultrasound;

D50 after sonication: D50 particle size measured after exposure to ultrasound.

In the case of measuring the particle size using model LA910 produced by Horiba Corporation, if the measurement is performed by ultrasonic waves, the lumped slurry is redistributed so that the particle size in a dispersed state can be measured. On the other hand, if the measurement is not performed by ultrasound, the clump of slurry is not redistributed and thus the particle size of the clump of slurry is measured. Therefore, the particle size deviation dD1, dD15, or dD50 increases with increasing precursor material aggregation, or increases with decreasing slurry dispersion stability.

Table 9b below shows the comparison between the dispersion stability of the multi-step calcination process and the single-step calcination process applied to the bulk cerium carbonate in Fig. 9b respectively.

table 3

dD1(nm) dD15(nm) dD50(nm) Slurry 1 4 3 3 Slurry 2 234 110 43

Based on these data, the degree of dispersion of slurries 1 and 2 could be measured and the results are shown in Figures 13a and 13b, respectively. In Figure 13a, Slurry 1 prepared by the multi-step calcination process has no change in the particle size distribution of the secondary slurry particles regardless of the forced dispersion by ultrasonic waves. In contrast, as shown in Fig. 13b, slurry 2 prepared by the single-step calcination process has a large difference in the particle size distribution of the secondary slurry particles before and after the forced dispersion. In slurry 2, due to the difference in crystallinity between the outside and inside of the precursor material, smaller particles with a larger specific surface area coexisted with larger particles with a smaller specific surface area, making the slurry have poor dispersion stability and Extensively caked. Therefore, there is a larger difference in the particle size distribution between slurries with and without forced dispersion.

[Changes in CMP characteristics]

Hereinafter, ceria abrasive grains and slurries were produced from ceria powders under respective predetermined conditions by the method described above, and slurry characteristics such as particle size and dispersion stability of each ceria slurry were analyzed, as well as, for example, migration. CMP characteristics such as removal rate and micro-scratch.

First, the characteristic analytical instruments are as follows:

1) Particle size: measured by RINT/DMAX-2500 manufactured by Japan Rigaku Company;

2) Particle size distribution: measured using LA-910 manufactured by Horiba Corporation of Japan;

3) TEM: Measured using JEM-2010 manufactured by Japan JEOL Co., Ltd.

Objects were polished using ceria slurries prepared as described above and evaluated with respect to removal rate, number of microscratches, and removal selectivity. The CMP polishing performance test was performed using 6EC manufactured by Strasbaugh Corporation, USA. An 8" wafer coated with PE-TEOS (Plasma Enhanced Chemical Vapor Deposition TEOS Oxide) to form an oxide film on its entire surface and coated with Si ₃ N ₄ to form an oxide film on its entire surface Another 8" wafer formed with nitride film was used for CMP polishing performance test. The test conditions and substances used are as follows:

1) Gasket: IC1000/SUBAIV (purchased from Rodel, USA);

2) Film thickness measurement device: Nano-Spec 180 (purchased from Nano-metrics, USA);

3) Table speed: 70rpm

4) Spindle speed: 70rpm

5) Downforce: 4psi

6) Back pressure: 0psi

7) Slurry supply: 100ml/min

8) Measurement of residual particles and scratches: use Surfscan SP1 manufactured by KLA-Tencor, USA for measurement.

A wafer with an oxide film (PE-TEOS) or a nitride film (Si ₃ N ₄ ) formed on the entire surface was polished for 1 minute using a ceria slurry, and then the removal rate was determined according to the thickness change of the film after polishing, And micro-scratches were measured using Surfscan SP1. The polishing performance of each slurry was tested in such a manner that the polishing characteristics were measured after polishing the semi-finished wafer three times or more.

[Ceria slurries 1 to 3: Comparison of properties depending on particle size of precursor material]

(1) Preparation of ceria abrasive particles 1 to 3

High-purity ceria powders 1 to 3 (corresponding to precursor materials 1 to 3, respectively) were charged into each container, the amount of each ceria powder was 800 g, and heated in a tunnel furnace (tunnel kiln) at 800° C. Calcined for 4 hours. Ceria powders 1 to 3 have the same characteristics as precursor materials 1 to 3 given in Table 1, respectively. All ceria powders 1 to 3 were made of cerium carbonate and exhibited smaller and smaller particle size distributions. Calcination was performed at a temperature increase rate of 5°C/min. After reaching the maximum temperature, the ceria powder was allowed to cool. The gas was flowed at a rate of 20 m ³ /hour in the opposite direction to the direction of motion of the saggar, effectively removing the CO ₂ by-product. When analyzed by an X-ray diffractometer, the thus-calcined ceria powders 1 to 3 were found to be high-purity ceria (cerium oxide) abrasive grains 1 to 3 .

(2) Preparation of ceria slurry 1 to 3

In a high-speed mixer, 10 kg each of high-purity ceria abrasive grains 1 to 3 synthesized from ceria powders 1 to 3 under the aforementioned conditions were mixed with 90 kg of deionized water for 1 hour or more , so as to achieve sufficient wetting, thereafter each 10% of the slurry thus obtained was ground using a channel milling process, which was intended to control the particle size within the desired range and disperse the agglomerated particles of the slurry. Subsequently, 1 wt% of ammonium polymethacrylate, which acts as an anionic dispersant, was added, based on the weight of the ceria powder. In consideration of adsorption, mixing was continued for 2 hours or more to disperse the slurry, followed by filtration to prepare ceria slurries 1 to 3 .

(3) Comparison of ceria slurry 1 to 3

Analysis of ceria slurries 1 to 3 prepared from high-purity ceria abrasive grains 1 to 3, respectively, showed that the precursor material, cerium carbonate, ceria powder, was extensively agglomerated and larger particles The size leads to the formation of more abnormally enlarged grains in the ceria abrasive grains.

(4) CMP test results

The CMP polishing performance of ceria slurries 1 to 3 prepared as described above was tested.

Table 4

Slurry serial number Precursor material (nm) particle size

/min)removal rate (

/min) Removal Ratio (Oxide:Nitride) (Selectivity) WIWNU(%) Oxide film residual particles (>0.20μm, #) Scratches (#) D1 D50 Oxide nitride 1 (comparative example) 365.3 120.5 50.2 2750 54 50.9 1.1 420 5 2 107.7 34.9 44.0 2682 52 51.6 1.1 293 2 3 51.9 6.483 30.7 2586 51 50.7 1.0 160 0

CMP tests were performed under the same CMP conditions using ceria slurries 1 to 3 prepared from ceria powders 1 to 3 (i.e., precursor material cerium carbonate with different particle sizes), and the results are presented in the above given in Table 4.

From the data in Table 4, it can be seen that ceria slurry 1 prepared from the precursor material with D1 greater than 350 μm exhibited a greater removal rate, but produced significantly more residual oxide film particles, and was therefore comparable to ceria slurry 2. or 3 produced more scratches. The reason for this is that as the particle size of cerium carbonate increases, the particle size also increases, which leads to the formation of larger particles that cause micro-scratches during the polishing process. On the other hand, a smaller D1 of the precursor material can reduce the number of oxide film residual particles and micro-scratches, but reduces the removal rate, degrading the polishing performance.

A D50 exceeding 100 μm has a high removal rate, but produces a large amount of oxide film residual particles and scratches caused by these particles. Since a D50 in excess of 100 μm means that more than 50% of the particles are larger than 100 μm, a large number of larger particles are formed, resulting in a proportionate number of microscratches. On the other hand, if the D50 of the precursor material is small, the removal rate will decrease, resulting in poor polishing performance.

As mentioned above, the removal rate and the number of oxide film residual particles and scratches are extremely important factors in the ultra-high integration semiconductor manufacturing process, which depends on the particle size of the precursor material.

Ceria slurries 2 or 3, prepared from the precursor material cerium carbonate with properly controlled particle size, exhibited excellent removal rates, while oxide film residual particles and micro-scratches were kept at significant levels compared to the comparative examples. lower level.

Therefore, by providing a precursor material with a D1 between 10 and 350 μm and a D50 between 4 and 100 μm, excellent removal rate, polishing selectivity or removal rate and as few scratches as possible can be obtained. More preferably the D1 of the precursor material is between 20 and 200 μm, and more preferably the D50 is between 5 and 40 μm.

[Cerium oxide slurries 4 and 5: comparison of characteristics depending on calcination conditions]

(1) Preparation of ceria abrasive particles 4 and 5

High-purity cerium carbonate powders 4 and 5 (both corresponding to the bulk precursor material of Fig. 9b) were charged into respective containers, wherein the amount of each ceria powder was 800 g. First, the cerium carbonate powder 4 was calcined twice in a tunnel furnace, initially at 750° C. for 4 hours, and secondly at 650° C. for another 4 hours, during which pulverization was performed. On the other hand, the cerium carbonate powder 5 was calcined once at 780° C. for 4 hours. In both cases, calcination was performed at a temperature increase rate of 5°C/min. After reaching the maximum temperature, the cerium carbonate powder was allowed to cool. The gas was flowed at a rate of 20 m ³ /hour in the direction opposite to the direction of motion of the cauldron, effectively removing the CO ₂ by-product. The ceria powders thus calcined were found to be high purity ceria (ceria) abrasive grains 4 and 5 with mean particle sizes of 29.8 nm and 29.6 nm, respectively, as analyzed by X-ray diffractometer.

(2) Preparation of ceria slurry 4 and 5

Using a high-speed mixer, 10 kg each of high-purity ceria abrasive particles 4 and 5 synthesized from ceria powders 4 and 5 under the aforementioned conditions were mixed with 90 kg of deionized water for 1 hour or more, thereby Adequate wetting was achieved and thereafter each 10% of the slurry thus obtained was ground using a channel milling process to control the particle size within the desired range and to disperse the agglomerated particles of the slurry. Subsequently, based on the weight of the ceria powder, 1 wt% of ammonium polymethacrylate, which can be used as an anionic dispersant, was added. Considering its adsorption, mixing was continued for 2 hours or more to disperse the slurry, followed by filtration to prepare ceria slurries 4 and 5 .

(3) Comparison of ceria slurry 4 and 5

As is readily apparent from Table 2 and Figure 12, analysis of ceria slurries 4 and 5 prepared from high-purity ceria abrasive grains 4 and 5, respectively, shows that ceria slurry 4 exhibits a significant difference in particle size before and after grinding. There was little change, whereas ceria slurry 5 had a dramatic particle size reduction after milling. The reason is: due to the extensive agglomeration of the precursor cerium carbonate, the particle size distribution between the inside and outside of the precursor cerium carbonate of ceria slurry 5 has a large difference, thus forming larger particles on the outside, while the inside is not completely The case of calcination.

In addition, the dispersion stability of the ceria slurries 4 and 5 were analyzed using a light scattering method by a particle size analyzer (LA-910 manufactured by Horiba). As shown in Figure 13a, the ceria slurry 4 subjected to the multi-step calcination process showed no change in the particle size distribution of the secondary slurry particles regardless of whether forced dispersion was performed. In contrast, as shown in Figure 13b, the ceria slurry 5 prepared by the single-step calcination process had a large difference in the particle size distribution of the secondary slurry particles before and after forced dispersion. In ceria slurry 4, smaller inner particles coexisted with larger outer particles, so that the slurry had poor dispersion stability and extensively agglomerated.

(4) CMP test results

The CMP polishing performance of ceria slurries 4 and 5 prepared as described above was tested.

table 5

Serial number of slurry Removal rate (L/min) selectivity WIWNU(%) Oxide film residual particles (>0.20μm, #) Scratches (#) Oxide nitride 4 2332 49 47.6 1.1 440 3 5 (comparison example) 2521 49 51.4 1.1 150 1

The data in Table 5 and Figure 14 demonstrate that Slurry 4 prepared by the multi-step calcination process has sufficiently uniform crystallinity to allow high rates of oxide film removal, whereas incomplete calcination within the bulk cerium carbonate Slurry 5 had poor crystallinity and poor oxide removal rate. Furthermore, for nitride films on which a sufficient amount of surfactant is electrically adsorbed, the removal rate does not differ between Slurry 4 and Slurry 5, resulting in better removal selectivity using Slurry 4 sex.

Slurry 4 is significantly less agglomerated, in other words, more dispersed, and thus achieves better flatness during wafer polishing than Slurry 5; whereas Slurry 5 There are more agglomerates and larger particles in Slurry 4 than in Slurry 4, so Slurry 5 will obviously produce more residual oxide particles and micro-scratches.

Therefore, the application of a multi-step calcination process is effective to achieve excellent removal rate, polishing selectivity or removal rate and minimum number of micro-scratches. In other words, by calcining precursor materials of ceria abrasive grains in a multi-step manner, desired slurry properties can be readily obtained.

Therefore, the present invention controls the particle size of the ceria slurry precursor material within a predetermined range, so that the ceria slurry can have excellent removal rate and selectivity, and has the ability not to cause micro scratches or make micro The ability to minimize the number of scratches. Thus, desired slurry properties can be easily obtained by controlling the calcination process in a multi-step manner.

As described above, according to the present invention, it is possible to manufacture a polishing slurry having various excellent characteristics that are necessary for STI CMP abrasives used in semiconductor manufacturing. In particular, when the polishing slurry of the present invention is applied, a significantly reduced amount of scratches and residual particles that have fatal effects on semiconductor devices can be maintained after CMP.

In addition, the present invention can produce a slurry that can maintain a high removal rate while reducing the number of scratches that can cause defects by performing a calcination process that takes into account the properties of the precursor material.

Furthermore, the present invention makes it possible to produce a slurry with the excellent physical properties necessary for STI CMP polishes. Thus, the polishing slurry of the present invention can be applied to various patterns required in the manufacturing process of ultra-highly integrated semiconductors, thereby ensuring excellent removal rate, removal selectivity, and intra-wafer non-uniformity (WIWNU), It indicates uniformity of removal and minimizes the occurrence of micro-scratches.

The above description is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. Anyone familiar with this field Those skilled in the art, without departing from the scope of the technical solution of the present invention, may use the structure and technical content disclosed above to make some changes or modifications to equivalent embodiments with equivalent changes, but any content that does not depart from the technical solution of the present invention, Any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims (7)

1. method of making the ceria sizing agent abrasive grain is characterized in that comprising:

Preparation cerous carbonate persursor material comprises:

Obtain rare-earth chloride solution;

Carry out a plurality of extractions with isolation cycle so that the Cerium II Chloride in the described rare-earth chloride solution separate with other rare earth metal;

Described Cerium II Chloride is mixed with volatile salt to form the cerous carbonate throw out; And

Described cerous carbonate throw out is washed with dry to form high purity carbonic acid cerium precursor material; And

Calcine described cerous carbonate persursor material with at least two above stages.

2. according to the method for the described manufacturing ceria sizing agent of claim 1 abrasive grain, it is characterized in that described incinerating step comprises:

At first calcine described cerous carbonate persursor material;

Pulverize or pulverize described through incinerating cerous carbonate persursor material at first to produce less secondary persursor material; And

Next calcines described secondary persursor material.

3. according to the method for the described manufacturing ceria sizing agent of claim 2 abrasive grain, it is characterized in that further comprising:

Pulverize or pulverize described secondly described secondary persursor material of incinerating to form third stage persursor material; And

The described third stage persursor material of third firing.

4. according to the method for the described manufacturing ceria sizing agent of claim 1 abrasive grain, it is characterized in that described calcining step is to carry out under 500 ℃ to 1000 ℃ temperature.

5. method of making polishing slurries is characterized in that comprising:

Method according to each described manufacturing ceria sizing agent abrasive grain in the claim 1 to 4 prepares described cerium dioxide abrasive grain;

In the grinding mixture that comprises deionized water, dispersion agent and additive, grind described cerium dioxide abrasive grain; And

Filter described grinding mixture with from wherein removing larger particles.

6. cerium dioxide abrasive grain according to the method manufacturing of each described manufacturing ceria sizing agent abrasive grain in the claim 1 to 4.

7. the polishing slurries of the method manufacturing of a manufacturing polishing slurries according to claim 5.

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