KR20030034310A - Water-soluble polyurethane for chemical mechanical polishing pad, and process for preparing the same - Google Patents

Abstract

Hydrolyzable for pads for chemical mechanical polishing, consisting of 65 to 85% polyester polyols, isocyanates, low molecular weight diols, 1.5 to 10% ionic acid compounds, and neutralizers corresponding to 70 to 140 mol% of the ionic acid groups Polyurethane, and a method for producing the hydrolyzable polyurethane, characterized in that it comprises the step of synthesizing and emulsifying the NCO-terminal prepolymer using acetone and methyl ethyl ketone as a solvent.

According to the present invention, the foaming process for forming the pore structure of the conventional pad can be omitted, and the chemical mechanical polishing process without the conditioning process, which was necessary to ensure a constant polishing rate in the chemical mechanical polishing process, was accompanied by many problems. Yield can be increased.

Description

WATER-SOLUBLE POLYURETHANE FOR CHEMICAL MECHANICAL POLISHING PAD, AND PROCESS FOR PREPARING THE SAME}

The present invention relates to the manufacture of a pad, which is a type of consumable used in chemical mechanical polishing processes.

In the field of semiconductor manufacturing, it is recognized that planarization of the wafer surface is essential for lithography and subsequent processing due to the reduction of the minimum line width. For the planarization of the wafer, methods such as spin on glass (SOG), reflow, and etch-back have been used. However, the planarization technique is a planarization method for semiconductor structures having a minimum line width of 0.25 μm or less. There is a limit.

As an alternative method of the planarization, a chemical mechanical polishing (CMP) method has emerged, and is currently being applied and examined in industrialization.

As shown in FIG. 1, the polishing of the surface of the wafer by applying relative pressure to the wafer and the pad 12 while simultaneously applying pressure while the slurry in which the abrasive particles and the chemical liquid are suspended is supplied between the wafer and the pad 12. Processing takes place. The pad 12 used as the processing tool is generally formed by forming a pore on the surface of the pad 12 by using a polyurethane foaming technique. The surface of the pad 12 and the pore wall 1 are as shown in FIG. ) In general, the polishing pad 12 used for chemical mechanical polishing of a device wafer has a laminated structure such as a hard layer for local planarization in the die and a soft layer for wide area planarization in the wafer. On the other hand, the polishing pad 12 used to polish the surface of the silicon wafer is composed of a single soft layer, which can polish the surface roughness to several levels.

Currently, chemical mechanical polishing is divided into silicon wafer polishing and interlayer insulating film (ILD) and wiring (metal) in device wafers, and pad 12 is also optimized and applied according to each process and each target material. . In general, the pad applied to the interlayer dielectric chemical mechanical polishing is made of a material having a relatively high hardness, and the pad applied to the wiring has a relatively low hardness, but the physical properties of the pad vary depending on the processing material.

In the manufacturing process of the pad, a foaming process for producing a pore structure is followed after mixing of the materials, which is difficult to control depending on temperature and time, so that the yield of the pad production is low and the production cost itself is expensive.

The pore formed on the pad surface serves to supply the slurry to the surface of the wafer 14 as shown in FIG. 3, and the slurry supply varies depending on the state of the pore. Any difference in slurry feed to the surface of the wafer 14 results in a difference in removal rate across the wafer 14 front surface, which has a substantial impact on wafer 14 yield. However, in general, as the chemical mechanical polishing proceeds, a clogging phenomenon in which pores are blocked by abrasive particles on the pad surface occurs essentially. The clogging phenomenon hinders the slurry supply to the surface of the wafer 14, resulting in a reduction in polishing rate and a polishing irregularity. This leads to a state in which machining is no longer performed, and also causes substantial problems in process repeatability and stability during continuous processing of the wafer 14 in which semiconductor elements are integrated. In order to prevent this, a conditioning process using a diamond wheel is essential. The conditioning process is an essential process for chemical mechanical polishing, but it may cause defects on the surface of the wafer 14 due to shortening of pad life and dropping of diamond or bonding material. There is a risk, the increase of the overall consumables cost and the disadvantages of a complicated process, etc., resulting in a decrease in yield due to the process time and the occurrence of bad factors. Therefore, various methods have been studied and suggested in order to omit this conditioning process.

In order to solve the above problems, the present inventors do not need an expensive foaming process, but a conditioning process for preventing clogging while ensuring continuous supply of slurry into the wafer 14, reproducibility, and stability. Continuing research efforts on the production of a polishing pad without water, it was found that a polishing pad using a hydrolyzable polyurethane could achieve such an object, and the results were confirmed by experiments to complete the present invention.

1 is a block diagram of a conventional chemical mechanical polishing apparatus.

2 is a view showing a cross-sectional structure of a conventional chemical mechanical polishing pad.

3 is a conceptual diagram of polishing of a polishing pad by a conventional method.

4 is a view showing pore clogging phenomenon appearing in the conventional chemical mechanical polishing pad.

5 is a diagram showing the construction of the hydrolyzable polyurethane pad according to the present invention and the derivation of a new surface.

6 is a view showing the structure of the hydrolyzable polyurethane according to the present embodiment.

Aqueous polyurethane is a form in which polyurethane particles present in a dispersed phase are dispersed in water in a continuous phase, and various manufacturing methods are known, but industrially used methods are roughly classified into two types: acetone process and prepolymer mixing process. In the present invention, combining the advantages of the above two processes to synthesize a polyurethane by an improved acetone process (modified acetone process). In the improved acetone process, methyl ethyl ketone and acetone are mixed as a solvent, and an NCO-terminated prepolymer is synthesized to perform emulsification. The advantage of this process is that even if the viscosity of the prepolymer is increased by controlling the solvent methyl ethyl ketone and acetone, it is possible to vary the molecular weight of the NCO-terminal prepolymer. In addition, it is possible to synthesize a branched polyurethane or cross-linked polyurethane, which is an advantage of the prepolymer mixing process by emulsifying the chain extension reaction, and thus, polyurethane having various molecular structures can be synthesized.

The hydrolyzable polyurethane according to the present invention is synthesized by the polymerization reaction of isocyanate groups and polyols, and the hardness, compression recovery, and abrasion resistance of the surface among the physical properties of the pad may be important factors in the chemical mechanical polishing process. In the case of the hydrolyzable polyurethane pad, the mixing ratio of the isocyanate and the polyol is determined to maintain the properties of the existing pad. The components used in the synthesis of the hydrolyzable polyurethane of the present invention are as follows.

1) Polyol: The polyol used in the synthesis used a polyester polyol showing crystallinity. The polyol content was 65 to 85% by weight of the total reactants to show the proper hydrolyzability and physical properties for use as a pad for CMP. It was set as.

Poly (ethylene adipate) diol (PEAD), poly (tetramethylene adipate) diol (PTAD), poly (hexamethylene adipate) diol (PHAD) and the like are preferably used.

2) Isocyanate: The physical properties of polyurethane are highly dependent on isocyanate, and one or two or more kinds are used to obtain proper physical properties. The amount of isocyanate is determined by the amount of other reactants and the molecular weight of the prepolymer to be synthesized. Examples of isocyanate compounds which are preferably used in the present invention include 4,4'-diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), toluene diisocyanate (TDI) and the like. Can be mentioned.

3) Low molecular weight diols: Low molecular weight diols are used to control the desired molecular weight of the prepolymer to be synthesized, the type of which is determined by the viscosity of the reactants during the prepolymer synthesis. As an example used preferably, 1, 4- butanediol (1, 4-BD), 1, 3- butanediol (1, 3-diol), etc. are mentioned.

4) Ionic Groups: The amount of ionic groups determines the size and stability of the emulsified state of the polyurethane particles present in the dispersed phase in the water-dispersed polyurethane. In the present invention, 1.5 to 10% by weight of ionic groups were used relative to the total reactants. Dimethylol propionic acid (DMPA), dimethylol butionic acid (DMBA) and the like are preferably used.

5) Neutralizer: Neutralizer neutralizes the acid groups present in DMPA and DMBA introduced into ionic groups to form salts. The salt thus formed serves as an emulsifier to emulsify the polyurethane, and the neutralizing agent is used in an amount of 70 to 140% by weight relative to the total moles of acid used in the reaction, and depending on the degree of neutralization, The stability of the emulsified state is determined. Triethyl amine (TEA), sodium hydroxide (NaOH) and the like are preferably used.

When hydrolyzable polyurethane encounters water or chemicals based on water, the polymer network structure decomposes, although it varies depending on its environment. Polishing pads using hydrolyzable polyurethanes take advantage of these properties of polyurethanes. Conventional polishing pads consist of polyurethane foam, pore wall (1) and pore (2). In the case of the hydrolyzable polyurethane pad, the pore structure itself, which is decomposed by water on the polymer network, is not used as the pore function due to the pore function.

Hydrolysable polyurethane pads exhibit hydrolysis by breaking the linkage of the polymer as the hydrophilic groups attached to the isocyanate groups in aqueous solution penetrate into the structure forming network of the hydrolyzable polyurethane. When the hydrolysis state is reached, the polymer network has a structural shape similar to the pore of a conventional pad, which is used in place of the role of the pore. As the structure of the top layer of the hydrolyzed pad is decomposed during the process, water penetrates into the lower layer to continue the hydrolysis reaction. When the top layer structure is completely decomposed, a new pore structure is formed in the lower layer. Thus, the polishing pad of the present invention maintains a constant polishing rate by the repeated derivation of the new surface (see FIG. 5) and the generation of the pore structure. In addition, the production rate of the new surface can be controlled by the blending ratio of the polyurethane material, the processing liquid supplied to the process, ultraviolet irradiation and the like. The preparation of the hydrolyzable polyurethane polishing pad of the present invention generally does not require a foaming process, but it is also possible to add a pore structure by means of a foaming process if desired.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

<Example>

Depending on the total amount of reactant (200 g) and the molecular weight of the designed prepolymer (10000 g / mol), firstly 140 g of polyol (70% by weight of total reactant), ionic groups (5% by weight of total reactant) and 4.33 g of 1,4-BD and 36.1 g of HDI thus determined were added to the reactor, followed by reaction at 90 ° C. for 2 hours. At this time, 60 g of methyl ethyl ketone was added as a solvent to proceed with the reaction. After 2 hours, 140 g of acetone was added to reduce the viscosity of the reactant, cooled to 50 ° C., then a neutralizing agent was added and stirred for 30 minutes. The neutralizer was emulsified by slowly adding water to the salt-formed reaction through neutralization. The emulsified reactant was polymerized through chain extension reaction at 60 ° C. for 1 hour 30 minutes and then the solvent was removed. Here, the molecular weight of the prepolymer is determined according to the physical properties of the polyurethane required in the molecular design, the size and decomposition rate of the particles of the hydrolyzable polyurethane, etc., are prepared according to the 2,000 ~ 20,000g / mol, according to the NCO reverse titration The progress of the reaction and the molecular weight of the prepolymer were checked. The final molecular weight is determined between 10,000 and 60,000 g / mol depending on the design of the molecule and the molecular weight of the prepolymer.

The size of the particles of the hydrolyzable polyurethane produced according to this embodiment is determined between about several nm and 500 nm depending on the amount of ionic groups used, the type of ionic groups, the amount of neutralizing agent, and the molecular weight of the prepolymer. In addition, the appearance is a colloidal solution with turbidity, the degree of turbidity varies depending on the size of the particles. When the particles are as small as a few nm, they are close to a blue-green transparent liquid. When the particles reach several hundred nm, they become a white, completely opaque liquid.

The structure of the hydrolyzable polyurethane according to the present embodiment is as shown in FIG. 6.

In order to shape the hydrolyzable polyurethane obtained as described above in the shape of a pad, a synthetic liquid was added to a pad-shaped mold and dried by heat drying. The proper time and temperature were maintained to obtain a good pad surface. The temperature holding conditions are dried for 4 hours from room temperature 25 ℃ to final temperature 65 ℃. The temperature is increased by 15 ° C. per hour for the first 2 hours and 5 ° C. per hour for 2 hours for the effect of defoaming.

According to the method of the present invention, the foaming process for forming the pore structure of the conventional pad can be omitted, and the chemical mechanical polishing without the conditioning process, which was necessary to ensure a constant polishing rate in the chemical mechanical polishing process, but accompanied many problems The yield of the process can be increased.

Claims (4)

65 to 85 weight percent polyester polyol, 10 to 25 weight percent isocyanate, 0 to 10 weight percent low molecular weight diol, 1.5 to 10 weight percent ionic acid compound and 70 to 140 moles of the ionic acid group A hydrolyzable polyurethane for pads for chemical mechanical polishing, comprising a corresponding neutralizing agent. The method of claim 1 wherein the polyester polyol is selected from the group consisting of poly (ethylene adipate) diol (PEAD), poly (tetramethylene adipate) diol (PTAD) and poly (hexamethylene adipate) diol (PHAD) Isocyanate is at least one compound selected from the group consisting of 4,4'-diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI) and toluene diisocyanate (TDI), Low molecular weight diols are selected from the group consisting of 1,4-butanediol (1,4-BD) and 1,3-butanediol (1,3-diol), the ionic acid compounds being dimethylol propionic acid (DMPA) and dimethylol A hydrolyzable polyurethane for pads for chemical mechanical polishing, characterized in that it is selected from the group consisting of butyric acid (DMBA). 65 to 85% by weight polyester polyol, 10 to 25% by weight isocyanate, 0 to 10% by weight low molecular weight diol 1.5 to 10% by weight ionic acid compound, corresponds to 70 to 140 mol% of the ionic acid group A method for producing a hydrolyzable polyurethane by polymerizing a neutralizing agent, wherein the NCO-terminated prepolymer is synthesized and emulsified using acetone and methyl ethyl ketone as a solvent. Method of producing urethane. The method of claim 3, wherein the viscosity of the prepolymer is adjusted during the process by adding acetone or methyl ethyl ketone solvent.