JP2005238359A - Polishing pad and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing pad with almost no edge droop carrying out polishing with high profile precision without causing a new problem such as the increase of process costs and a process time. <P>SOLUTION: A fibrous layer is erected on a hard substrate so as to cover its surface. The fibrous tip of the fibrous layer is formed so as to have a length of being laid down by pressing. Therefore, the sinking of a wafer is reduced during polishing and excessive pressure is not applied to the peripheral part of the wafer. Consequently, the occurrence of the edge droop is prevented or the edge droop is made to hardly occur. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a precision polishing pad for semiconductor wafers, liquid crystal glass, hard disks, and the like, and more specifically, chemical mechanical polishing used mainly in the manufacturing process of semiconductor devices capable of polishing with high shape accuracy with less fringing. The present invention relates to a polishing pad.

  As semiconductor integrated circuits are highly integrated and miniaturized, wiring is stacked. That is, a process is employed in which a wiring material is patterned on the surface of a semiconductor wafer, and the wiring material is covered with an insulating film such as silicon oxide, the next wiring material is patterned, and this is repeated sequentially.

  As the number of wiring layers increases, there will be a step in the insulating film such as silicon oxide, so it is necessary to flatten the insulating film before patterning the next wiring material. Chemical mechanical polishing is performed to polish a wafer flat.

  In a polishing process using a conventional polishing pad, there is a problem of a work piece (processed sample) coming out. Edges are thought to occur for the following reasons.

  Since the polishing pad is a viscoelastic body, it is deformed by the pressure applied to the wafer during polishing, and the pressure applied to the wafer increases exponentially toward the periphery. At the periphery of the wafer, the polishing pad is in a transition state in which the polishing pad changes from the deformed state to the released state, and it is considered that the processing pressure is applied to the wafer edge at the same time as being applied to the wafer surface. As a result, the polishing amount increases and the shape accuracy deteriorates in the peripheral portion within a range of several millimeters in the radial direction from the edge of the wafer to which high pressure is applied.

  FIG. 1 is an explanatory diagram of the cause of the occurrence of fringing at the periphery of the wafer, and schematically shows the contact state between the periphery of the wafer and the polishing pad when polishing the wafer using a viscoelastic polishing pad. It is shown. FIG. 1 shows a platen rotor type general polishing method, in which a polishing pad is rotated, and a wafer placed on a polishing head is simultaneously rotated to perform polishing. The wafer is subjected to a vertical load on the pad, which causes the entire wafer to sink into the pad. For this reason, since a large polishing pressure is generated in the peripheral portion of the wafer as compared with the central portion of the wafer, the polishing rate is increased and the stagnation occurs.

  In order to solve this problem, (1) a method of installing a surrounding retainer ring outside the periphery of the processed sample and pressing the polishing pad with pressure applied to the retainer ring part, (2) in-plane of the processed sample A method for controlling the pressure distribution and (3) a method for changing the shape of the work sample chuck surface have been developed. However, both methods require the addition of new devices, equipment, and control systems, and it is necessary to set control values and chuck shapes for each processing target. Therefore, new methods such as an increase in process cost and process time are required. It is causing a problem.

  In addition, in order to reduce the occurrence of the above-mentioned flickering, it is conceivable to use a so-called hard pad having a small viscoelastic coefficient. On the other hand, since the ability to unevenly distribute the polishing pressure distribution of the wafer becomes poor, the accuracy of the polishing surface of the entire wafer is deteriorated.

  The present invention has been made paying attention to such points, and provides a polishing pad that can be polished with a high degree of shape accuracy without causing a new problem such as an increase in process cost and process time. The purpose is to provide.

  In order to achieve the above object, as a result of intensive studies, the present inventors have used a so-called hard pad having a small viscoelastic coefficient, and erected fibers on the surface of the hard pad to reduce the polishing pressure distribution of the wafer. It has been found that a polishing pad that can be polished with high shape accuracy and less wobbling can be obtained by imparting a uniform relaxation capability and forming the fiber to fall down by pressing, and has reached the present invention.

  That is, the present invention is characterized in that a fiber layer is erected on a hard substrate so as to cover the surface, and the fiber tip of the fiber layer is formed to have a length that collapses when pressed.

  In short, the fiber layer has a function of buffering the polishing pressure of the fiber layer, and when high pressure is applied to the periphery of the polishing sample, the fiber moves laterally (falls down) The fiber length is such that the pressure is relaxed.

  It is preferable to use a hard base material having a compression ratio of the hard base material of 0.5% or less.

  The fiber diameter of the fibers is preferably 1 to 20 μm, and the average fiber length is preferably not less than twice the fiber diameter and not more than 500 μm.

  The fiber may be a polyester fiber having high hydrophilicity, high strength, excellent chemical resistance and various elastic properties (Claim 4).

  The hard base material is formed by binding inorganic or high-hardness synthetic resin abrasive fine powder with a synthetic resin, and is preferably made of a material more brittle than the fibers constituting the fiber layer. This is because when the surface is ground with a diamond dresser or the like, the fiber remains on the pad surface even if the hard substrate is scraped, and a fiber layer can be formed on the pad surface.

  In the production method of the present invention, a hard base material obtained by binding an inorganic or synthetic resin fine powder with a synthetic resin is impregnated into a woven or non-woven fabric and cured, and this is rolled, laminated or bundled with the fiber direction aligned. Then, the fiber layer is cut from the direction crossing the length direction of the fiber, and the fiber layer erected so as to cover the surface of the hard base material by dressing the cut surface is such that the tip of the fiber falls down by pressing. It is formed.

  In short, the present invention reduces the sinking of the wafer by using a hard substrate, and provides a fiber layer on the surface thereof, whereby the fiber of the fiber layer has a polishing pressure buffering function. By using it, the gist is that the uniformity in the surface of the processed sample is good and the deterioration of the shape accuracy due to stagnation is improved.

  According to the polishing pad of the present invention, this type of conventional polishing pad is capable of polishing with a high shape accuracy with little fluttering without causing new problems such as an increase in process cost and process time. There is no remarkable effect.

  Next, embodiments of the present invention will be described with reference to the drawings.

  FIG. 2 schematically shows the structure of the polishing pad of the present invention, which is a structure in which fibers are combined with a hard pad base so that the fibers stand on the polishing surface, and the surface of the hard pad base is The fiber layer is formed so as to cover, and the tip of the fiber protrudes from the hard pad surface to a length that can move in the horizontal direction (the direction perpendicular to the polishing surface is the vertical direction).

  In the above embodiment, the fibers are erected perpendicularly to the polishing surface, but may be erected obliquely. In short, the upper end of the fiber may be above the polishing surface, and it may be configured to contact or approach the polishing surface by pressing.

  By using the polishing pad having such a structure, fluffing is alleviated and non-uniformity of the polishing pressure distribution can be alleviated, so that polishing with high shape accuracy can be performed.

  In the polishing pad of the present invention, for example, as shown in the method for producing a polishing pad of JP-A-2002-36129, a hard base material is impregnated and cured on a woven or non-woven fabric, wound, and then crossed with a wind axis. It is obtained by dressing after slicing (preferably a vertical method) to form a pad. In addition, a woven fabric or a non-woven fabric having the same fiber direction is laminated or bundled, and this is filled and hardened by a method such as impregnation, and sliced in a direction crossing the fiber direction (preferably a vertical method). It can also be manufactured by dressing after forming into a pad.

  Since the polishing pad after slicing is at the same level as the surface of the hard pad base material, the polishing pad is ground by a diamond dresser or the like so that the fiber extends from the surface of the hard pad base material. There must be. For this purpose, the hard pad base material needs to be made of a material that is more brittle than the fibers.

  Grinding with the diamond dresser may be performed by a method similar to the break-in process performed before using the urethane foam pad, but the diamond dresser can form a state in which the fibers extend from the hard substrate surface. It is desirable to adjust the fiber and the rigid substrate so that there is a difference in wearability with respect to.

  The break-in process is an operation called dressing performed as a break-in operation before polishing in order to ensure a sufficient polishing rate and in-plane uniformity. The dressing method may be performed according to the method of removing the surface layer of the pad with a diamond dresser, as in the case of the foam pad.

  As the hard substrate used in the present invention, it is preferable to use a material obtained by binding inorganic or synthetic resin fine powder with a synthetic resin (such as a synthetic polymer or a binder material). As the inorganic or synthetic resin fine powder, a conventionally known one used for this purpose may be used.

  Inorganic or synthetic resin fine powder bound with synthetic resin is impregnated into a woven or non-woven fabric and cured, and if necessary, a binder is used to roll and laminate the fibers in the same direction. Alternatively, the polishing pad of the present invention can be obtained by forming a bundle, cutting from the direction intersecting (preferably orthogonal) with the length direction of the fiber, and dressing the cut surface. As the binder, a synthetic polymer having adhesive strength may be used.

Next, the present invention will be further described with reference to examples and comparative examples of the present invention, but the present invention is not limited to these examples.
Example 1: Production Example of the Polishing Pad of the Present Invention The polishing pad of the present invention having a structure in which a hard pad base material and a fiber are combined so that the fibers are perpendicular to the polishing surface was produced as follows.

A polyester nonwoven fabric (average fiber diameter: 3 microns) having a basis weight of 60 g / m ² is impregnated with a mixture of 90% by weight of silica fine particles and 10% by weight of a urethane resin binder, and cured to form a sheet having a thickness of 0.3 mm. did.

  Coat the urethane resin between the sheets so that the thickness is 0.02 mm, heat cure while winding, form into a roll shape with an outer diameter of 610 mm, and make the thickness 3 mm perpendicular to the roll axis A polishing pad was made by slicing. At this stage, the fiber layer on the pad surface is not formed. A fiber layer is formed in the next break-in process.

The conditions for dressing by break-in are not special conditions, but the following conditions can be easily set by the equipment used in the semiconductor wafer polishing process.
(Break-in condition)
Used dresser φ270-Ring type diamond dresser # 150 equivalent Platen rotation speed 20rpm
Dresser speed 16rpm
Dresser load 120 N
Pure water supply 1000 cc / min
Break-in time 15min
Sectional SEM photographs of the pad after break-in (Example 1) and the pad after slicing (Comparative Example 1) obtained as described above are shown in FIG. 8 (Example 1) and FIG. 9 (Comparative Example 1). Show.

  8 and 9, it can be seen that the fiber layer is formed on the pad surface of Example 1, but the fiber layer is not formed on the pad surface of Comparative Example 1.

Example 2: Example of use of polishing pad of the present invention The pad of the present invention obtained in Example 1 (Example), the pad of Comparative Example 1 and a commercially available urethane foam pad (Comparative Example 2) were used. In this way, the wafer was polished.

  Using the platen rotor type polishing apparatus shown in FIG. 3, the pads 1 of Examples, Comparative Example 1 and Comparative Example 2 were fixed on the platen 2 under the polishing conditions shown in the following Table 1, respectively. The TEOS blanket wafer (film pressure 1000 nm) 3 was polished on the pad 1, and the polishing rate was measured at 81 points in the diameter direction of the wafer. The measurement results are shown in the following Table 2 and FIGS. In FIG. 3, 4 is a dresser, and 5 is a head for pressing the wafer.

(Table 1) (Polishing conditions)

(Table 2) (Measurement results)

  FIG. 4 shows the wafer profile at the polishing rate when using the polishing pad of the example, FIG. 5 shows the wafer profile at the polishing rate when using Comparative Example 1, and FIG. 6 shows the polishing when using Comparative Example 2. The velocity wafer profile is shown.

  From the above measurement results, it can be seen that the example has a polishing rate comparable to that of the comparative example 2, but the in-plane uniformity is excellent in each step, and almost no edge is observed from FIG.

  On the other hand, in Comparative Example 1, almost no flickering is observed, but the in-plane uniformity is equivalent to that of Comparative Example 2, and the polishing rate is greatly reduced as compared with Example 1 and Comparative Example 2.

  From this result, the polishing pad of Example 1 can prevent a decrease in the polishing rate and can be polished with high shape accuracy while preventing a decrease in polishing rate due to the effect of the fiber layer on the pad surface shown in FIG. I understand.

  Table 3 below shows the viscoelasticity of the pads of Examples, Comparative Example 1 and Comparative Example 2 in comparison with the compression rate and the compression recovery rate.

圧縮率及び圧縮回復率をつぎのように定義した。図7に、圧縮率及び圧縮回復率の測定方法の説明図を示す。 (Table 3) (Results of comparing viscoelasticity with measured values of compression rate and compression recovery rate)

The compression rate and compression recovery rate were defined as follows. FIG. 7 is an explanatory diagram of a method for measuring the compression rate and the compression recovery rate.

Working indenter: φ5 mm flat indenter Compression rate: T2 / T1 × 100
Compression recovery rate: ΔT / T2 × 100
Here, T1 is the thickness of the pad when a load of 300 g / cm ² is applied to the flat indenter. T2 is from T1 when a load of 1400 g / cm ² is applied to the flat indenter.
The compression dimension T is the recovery dimension when the load is returned from 1400 to 300 g / cm ²

  From the above results, it can be seen that Example 1 and Comparative Example 1 have a smaller viscoelastic coefficient than Comparative Example 2. This indicates that the wafer is polished in a state in which the wafer hardly sinks into the pad, and it is determined that this result is reflected in the profile of the wafer edge portion in FIGS.

  When Example 1 and Comparative Example 1 are compared, Example 1 is slightly compressed and Comparative Example 1 is lower in compression rotation rate than Comparative Example 1. This is judged to be the influence of the fiber layer on the pad surface, and this is judged to be reflected in the polishing with high shape accuracy.

FIG. 6 is an explanatory diagram of occurrence of fringing at a wafer peripheral portion. It is the figure which showed typically the structure of the polishing pad of this invention. It is a perspective view which shows an example of the grinding | polishing apparatus used for this invention. 2 is a diagram showing a wafer profile at a polishing rate using the polishing pad of Example 1. FIG. 6 is a diagram showing a wafer profile at a polishing rate using the polishing pad of Comparative Example 1. FIG. It is a diagram which shows the wafer profile of the polishing rate using the polishing pad of the comparative example 2. It is explanatory drawing of the measuring method of a compression rate and a compression recovery rate. 2 is a cross-sectional SEM photograph of the pad of the present invention obtained in Example 1. FIG. 3 is a cross-sectional SEM photograph of a pad of Comparative Example 1.

Explanation of symbols

1 ... Pad 2 ... Platen 3 ... Wafer 4 ... Dresser 5 ... Head

Claims (6)

A polishing pad, wherein a fiber layer is erected so as to cover a surface of a hard substrate, and a fiber tip of the fiber layer is formed to a length that can be collapsed by pressing. The polishing pad according to claim 1, wherein the compression ratio of the hard base material is 0.5% or less. The polishing pad according to claim 1 or 2, wherein the fiber has a fiber diameter of 1 to 20 µm, and an average length of the fiber is not less than twice the fiber diameter and not more than 500 µm. The polishing pad according to claim 1, wherein the fiber is a polyester fiber. The polishing pad according to claim 1, wherein the hard base material is obtained by binding inorganic or synthetic resin abrasive fine powder with a synthetic resin. A hard base material in which fine powder of inorganic or synthetic resin is bound with synthetic resin is impregnated into a woven or non-woven fabric and cured. A fiber layer cut from a direction crossing the vertical direction and dressed on the cut surface so as to cover the surface of the hard base material is formed to have such a length that the tip of the fiber falls down by pressing. Manufacturing method of polishing pad.

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