JP5385714B2 - Polishing pad - Google Patents

Description

  The present invention relates to a polishing pad, and more particularly to a polishing pad suitable for polishing a semiconductor wafer such as a silicon wafer or a glass substrate.

  A chemical mechanical polishing (CMP) technique is used for planarization processing of a semiconductor wafer or the like, and various CMP apparatuses using the CMP technique have been proposed. FIG. 3 is a schematic configuration diagram of a conventional CMP apparatus. A polishing slurry 3 is supplied from a slurry supply device 4 to a polishing pad 2 attached to the surface of the surface plate 1. As an object to be polished, for example, a semiconductor wafer 5 is held by a polishing head 6 via a backing film 7. When a load is applied to the polishing head 6, the semiconductor wafer 5 is pressed against the polishing pad 2.

  The slurry 3 supplied onto the polishing pad 2 spreads on the polishing pad 2 and reaches the semiconductor wafer 5. The surface plate 1 and the polishing head 6 rotate in the same direction and move relatively as indicated by an arrow A, and the slurry 3 enters between the polishing pad 2 and the semiconductor wafer 5 to perform polishing. . Reference numeral 8 denotes a dresser for conspicuous the surface of the polishing pad 2.

  As the polishing pad 2, one using foamed polyurethane excellent in wear resistance or the like is known (for example, see Patent Document 1).

  In such a polishing pad, it is necessary to generate fine bubbles, for example, a main agent containing an isocyanate group-containing compound, a curing agent containing an active hydrogen group-containing compound such as an aromatic amine, and water as a foaming agent, There is a production method in which mixing and stirring are performed for curing.

JP-A-2005-236200

  In such a conventional polishing pad, there are few closed cells, and most of the open cells occupy. When there are many open cells in this way, polishing residues and slurry accumulate in the open open cells during polishing. There is a problem in that the elastic modulus changes, the flatness of the object to be polished is deteriorated, and the edge of the object to be polished is excessively polished (edge roll-off).

  The present invention has been made in view of the above points, and an object thereof is to improve the flatness of an object to be polished and to prevent end face sagging.

  As a result of earnest research to achieve the above object, the present inventor can improve the flatness of the object to be polished by considering the three-dimensional relationship between closed cells and open cells in the polishing pad, and can also improve the end face. The inventors have found that anyone can be suppressed and completed the present invention.

  That is, conventionally, image analysis based on an image of a scanning electron microscope (SEM) is mainly used for evaluation of bubbles in the polishing pad, and since the evaluation is based on a two-dimensional SEM image, Evaluation with a simple structure is difficult, and in particular, the three-dimensional relationship between closed cells and open cells has not been considered.

  On the other hand, the present inventors have found that the above object can be achieved by appropriately defining the closed cell ratio in the polishing pad in consideration of the three-dimensional relationship between closed cells and open cells in the polishing pad, The present invention has been completed.

  That is, the present invention is a polishing pad having a polishing layer pressed against an object to be polished, wherein the polishing layer is made of a foam having closed cells and open cells, and the closed cells and the open cells are combined. The closed cell ratio, which is the ratio of the volume of closed cells to the total volume of the combined cells, is 0.3% or more and 10% or less.

  Here, an independent bubble refers to a bubble that is not in communication with another bubble, and an open cell refers to another bubble or a bubble that is in communication with the outside.

  In a preferred embodiment, the closed cell ratio is calculated based on a measurement result of the polishing layer by an X-ray CT apparatus.

  In one embodiment, the foam is a foamed polyurethane.

  In another embodiment, the foamed polyurethane is obtained by mixing and stirring an isocyanate group-containing compound, an active hydrogen-containing compound, and water as a foaming agent to foam and cure.

  According to the polishing pad of the present invention, the three-dimensional relationship between closed cells and open cells in the polishing layer made of a foam is grasped as the closed cell rate, and this closed cell rate is 0.3% or more and 10% or less. Since it is defined in the range, it is possible to improve the flatness of the object to be polished and to suppress the end face drooping.

  According to the present invention, the three-dimensional relationship between closed cells and open cells of the polishing layer made of a foam is grasped as the closed cell rate, and the closed cell rate is in the range of 0.3% to 10%. Since it stipulates, it is possible to improve the flatness of the object to be polished and to suppress the end face drooping.

It is sectional drawing which shows typically the bubble of the polishing pad of an Example. It is sectional drawing which shows typically the bubble of the polishing pad of a comparative example. It is a schematic block diagram of CMP apparatus.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  In the polishing pad of this embodiment, an isocyanate-terminated prepolymer that is an isocyanate group-containing compound and an aromatic amine that is an active hydrogen-containing compound are mixed and stirred together with water that is a blowing agent, and cast into a predetermined mold. A molded product of polyurethane foam is obtained by reaction curing.

  In this embodiment, the foamed polyurethane molded body is further cut into a sheet having a predetermined thickness and punched out to obtain a polishing pad.

  The isocyanate-terminated prepolymer is obtained by reacting a polyisocyanate and a polyol under commonly used conditions. This isocyanate-terminated prepolymer may be a commercially available one, or may be synthesized from a polyol and a polyisocyanate.

  Examples of the polyisocyanate include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, naphthalene-1,5-diisocyanate, and the like.

  Examples of the polyol include polyether polyols such as poly (oxytetramethylene) glycol and poly (oxypropylene) glycol, polycarbonate polyols, and polyester polyols.

  For polishing, an ether-based polyol that does not cause hydrolysis is preferable. As an ether-based polyol, -O- bonds such as PPG (polypropylene glycol), PTMG (polytetramethylene ether glycol), and PEG (polyethylene glycol) are used. Among them, a PTMG system having good physical properties (tensile properties) is preferable. In particular, PTMG having a molecular weight MW = 500 to 5000 is preferable.

  Examples of the aromatic amine that is an active hydrogen-containing compound include diamine compounds such as 3,3′-dichloro-4,4′-diaminodiphenylmethane (MOCA), chloroaniline-modified dichlorodiaminodiphenylmethane, 3,5-bis ( And methylthio) -2,4-toluenediamine and 3,5-bis (methylthio) -2,6-toluenediamine.

  The polishing pad of the present invention made of foamed polyurethane has closed cells and open cells, and has a closed cell ratio that is a ratio of the volume of closed cells to the total volume of the bubbles including the closed cells and the open cells. 0.3% or more and 10% or less.

  This closed cell ratio is calculated by measuring with an X-ray CT measurement device as described later.

  Thus, by appropriately defining the three-dimensional bubble structure of the polishing pad as the closed cell ratio, the flatness of the object to be polished can be improved and the end face droop can be suppressed.

  Hereinafter, the present invention will be described in more detail based on examples and comparative examples.

  In the above production method, by adjusting the amount of water as a blowing agent and the stirring speed, Examples 1 and 2 in which the closed cell ratio is 0.3% to 10%, and the closed cell ratio is less than 0.3% Four types of polishing pads of Comparative Example 1 and Comparative Example 2 having a closed cell ratio exceeding 10% were manufactured.

  Calculation of the closed cell ratio of each polishing pad of Examples 1 and 2 and Comparative Examples 1 and 2 was performed as follows.

  That is, each polishing pad was cut into 3 mm square and fixed to the sample stage with an adhesive tape, measured with an X-ray CT measurement device, binarized by image analysis after measurement, and the closed cell ratio was calculated. In the image analysis, a range corresponding to a sample volume of 1.6 × 1.6 × 0.45 mm (357 × 357 × 100 voxel) is cut out from the obtained X-ray CT image and binarized to obtain the closed cell ratio. Calculated. Table 1 below shows the measurement conditions of the X-ray CT measurement apparatus.

  Table 2 below shows the measurement results of the closed cell ratio of Example 1 and Comparative Example 1.

  In Table 2, the total bubble volume including closed cells and open cells, the volume of closed cells, and the closed cell rate are shown.

  For Examples 1 and 2 and Comparative Examples 1 and 2, the polishing rate, flatness, end face sag, (Edge Roll Off) and life (Life) are 4 stages (x: defective, Δ: slightly defective, ○: good, A: Relative evaluation was performed with “Excellent”. The flatness was evaluated for both GBIR (Global Back Ideal Range), which is the flatness of the entire wafer based on the back surface, and SFQR (Site Front Least Squares Range), which is the flatness of each surface based chip. The lifetime was defined as the lifetime until the polishing pad was replaced.

  The results are shown in Table 3 below together with the closed cell ratio.

  In Comparative Example 1, where the closed cell ratio is as low as 0.27%, the ratio of open cells is high. Therefore, during polishing, polishing residues and slurry accumulate in open open cells and the elastic modulus changes. The flatness of the object to be polished deteriorates and the evaluation is slightly poor (Δ).

  Further, as schematically shown in FIG. 2, since many of the open bubbles 10 are easily compressed, the sinking of the peripheral portion 5a of the wafer 5 becomes large, and the end surface where the peripheral portion 5a of the wafer 5 is excessively polished. The evaluation is slightly poor (Δ).

  On the other hand, in Example 1 with a closed cell ratio of 1.4% and Example 2 with 9.5%, the closed cell ratio is in the range of 0.3% to 10%. The evaluations of the degrees are all good (◯).

  Further, as schematically shown in FIG. 1, since the number of closed cells 11 is larger than that in the first comparative example, it is difficult to compress and the sinking of the peripheral portion 5 a of the wafer 5 is suppressed. As a result, the evaluation of the end face droop of Example 1 is excellent (◎), and the evaluation of the end face droop of Example 2 is good (◯). Since the closed cell ratio is higher in Example 2 than in Example 1, the hardness is slightly high and the life evaluation is slightly poor (Δ).

  Further, in Comparative Example 2 where the closed cell ratio is as high as 17.0%, the hardness is too high, the life is short, and it is evaluated as defective (x), the number of open cells is small, and the amount of slurry retained is small. For this reason, the evaluation of the polishing rate is slightly poor (Δ).

  As described above, in Examples 1 and 2 in which the closed cell ratio is in the range of 0.3% to 10%, both the flatness and the end face sagging can be improved as compared with Comparative Example 1, and the comparison is made. As in Example 2, the polishing rate does not decrease.

  In the above-described embodiment, the polishing pad is composed of only the polishing layer made of polyurethane foam. However, as another embodiment of the present invention, the polishing pad may be a laminate of the polishing layer and another layer (for example, a cushion layer). Good.

  In the above-described embodiment, the foam is formed using water as a foaming agent. However, other forming methods, for example, a method of dispersing and hardening a micro hollow body (micro balloon), heating after mixing thermally expandable fine particles For example, a method of foaming fine particles, a method of mechanically mixing bubbles and then curing may be used.

  The present invention is useful as a polishing pad used for polishing silicon wafers and glass substrates.

2 Polishing pad 10 Open cell 11 Closed cell

Claims (4)

A polishing pad having a polishing layer pressed against an object to be polished,
The polishing layer is made of a foam having closed cells and open cells. A polishing pad, wherein the polishing pad is 3% or more and 10% or less.   The polishing pad according to claim 1, wherein the closed cell ratio is calculated based on a measurement result of the polishing layer by an X-ray CT apparatus.   The polishing pad according to claim 1, wherein the foam is foamed polyurethane.   The polishing pad according to claim 3, wherein the foamed polyurethane is obtained by mixing and stirring an isocyanate group-containing compound, an active hydrogen-containing compound, and water as a foaming agent to foam and cure.

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