KR20110032545A - Method of polishing substrate - Google Patents

Abstract

PURPOSE: A method of polishing a substrate is provided to remove an oxide film from the surface of a wafer by using a stock pad and final slurry in polishing. CONSTITUTION: In a method of polishing a substrate, stock grinding is performed to make the surface of a wafer even(S2). Final grinding is performed by making the surface of the wafer smooth(S3). The wafer is polished firstly using a first smooth polish pad and colloidal slurry containing a polymer(S31). The polished wafer is polished secondly by using a second polish pad that is smoother than the first polish pad(S32).

Description

Wafer Polishing Method {METHOD OF POLISHING SUBSTRATE}

The present invention relates to a wafer polishing method which can prevent the increase of frictional force and the polishing rate and improve the flatness of the wafer in the final polishing step due to the oxide film formed on the wafer surface after the stock polishing in the wafer manufacturing process.

Today, silicon wafers, which are widely used as materials for manufacturing semiconductor devices, refer to monocrystalline silicon thin films made of polycrystalline silicon as a raw material. The wafer fabrication process includes a slicing process that cuts grown silicon single crystal ingots into wafer form, a lapping process to uniformize and planarize the thickness of the wafer, and an etching process to remove or mitigate the damage caused. Process, a polishing process that mirrors the wafer surface, and a cleaning process that cleans the polished wafer and removes foreign matter adhering to the surface.

In general, the cleaning process is performed to remove contaminants such as particles, organic contaminants, and metal impurities generated in the mirror polishing process of the wafer. In general, the cleaning process is a wet cleaning method RCA method is commonly used. The RCA method uses a standard cleaning solution 1 (SC1) to oxidize and etch the surface of a mirror-polished wafer to remove particles and organics remaining on the surface of the wafer and a standard cleaning solution 2 (SC2). It can be divided into processes for removing metal impurities.

The polishing process is divided into stock polishing, which removes the surface deterioration layer of the wafer and improves thickness uniformity, and final polishing, which mirror-processes the surface of the wafer. Generally, stock polishing is generally performed at a rate of 0.5 to 0.8 μm / minute, and final polishing is performed at a small amount of polishing to a level at which an accurate polishing rate cannot be measured. The polishing process is performed by selecting a slurry and a polishing pad suitable for polishing characteristics, and the slurry is selected in consideration of polishing rate, friction characteristics, surface roughness, and the like on the wafer.

On the other hand, during the cleaning process before the wafer polishing process, the chemical oxide film due to the cleaning liquid or the natural oxide film due to exposure to the atmosphere grows while the wafer is cleaned, dried, and atmospheric. Here, since the polishing rate is smaller than that of silicon (Si), the oxide film (SiO2) has a smaller polishing rate, and thus, the oxide film causes excessive friction in the polishing process. May occur, resulting in overload and vibration of the drive of the polishing apparatus.

Wafers are processed in the form of conveyors, not at each unit process continuously, but at a minimum of one cassette (25 sheets / cassette). Even if the oxide film is completely removed in the cleaning process, the oxide film is formed again during the moving to the polishing process and during the atmospheric process.

The transition section due to the oxide film varies depending on the wafer surface state before the polishing process and the type of slurry used, but occurs in a similar form. Conventionally, a slurry containing an amine was used to increase the polishing rate and improve a glazing phenomenon in which a silica film is formed on a surface of a polishing pad. However, recently, a slurry without an amine has been widely used because copper contamination by an amine is a problem. However, in the case of using a slurry without amine, it is difficult to remove the oxide film, and thus the occurrence of the initial transition section of polishing is worsened.

On the other hand, the stock polishing process uses a double-sided polishing device, whereas the final polishing process uses a one-sided polishing device, so the waiting process is inevitable in the process of final polishing after stock polishing. However, since the final polishing rate is much lower than the stock polishing rate, the final polishing rate is more affected by the transition interval caused by the oxide film formed in the atmospheric process.

Embodiments of the present invention for solving the above problems are to provide a wafer polishing method that can prevent the increase in frictional force and the polishing rate of the initial polishing due to the oxide film.

In addition, embodiments of the present invention to provide a wafer polishing method that can prevent the increase in friction and the polishing rate in the final polishing process.

According to embodiments of the present invention for achieving the above object of the present invention, a wafer polishing method in which a stock polishing step for planarization of the wafer surface and a final polishing step for mirroring the planarized wafer surface are sequentially performed Is initiated. Final polishing step The final polishing step for removing the oxide film in the initial stage, the first polishing step of polishing the wafer using a colloidal slurry with a hard first polishing pad and a polymer added, and the first polished The second polishing step may be performed by polishing the wafer using a polishing pad softer than the first polishing pad.

In an embodiment, the first polishing pad may be a polishing pad of the same material as the polishing pad used in the stock polishing step. For example, the first polishing pad may be formed by foaming a polyurethane resin, or a polishing pad formed by impregnating a urethane resin with a nonwoven fabric may be used. And the slurry may be used colloidal silica containing a water-soluble polymer. Here, the second polishing step may use the same slurry as the first polishing step.

In addition, the primary polishing step may be performed at the same polishing rate or lower polishing rate as the stock polishing step, and the secondary polishing step may be performed at a lower polishing rate than the primary polishing step. For example, the first polishing step may be performed at a polishing rate of 0.1 ~ 0.8 ㎛ / min. The secondary polishing step may be performed at a polishing rate of 0.1 μm / minute or less.

As described above, according to embodiments of the present invention, the oxide film may be effectively removed using a colloidal silica slurry to which a hard polishing pad and a polymer are added in the first polishing step. In addition, it is possible to prevent a decrease in polishing rate due to the oxide film and a decrease in surface roughness after polishing.

In addition, since the same slurry as the secondary and tertiary polishing is used in the primary polishing, the surface roughness after the final polishing can be prevented from deteriorating.

In addition, since it is not necessary to use a separate slurry for removing the oxide film, it is possible to suppress the increase in cost and reduce the production cost.

In addition, since it is not necessary to add a separate pretreatment process for removing the oxide film, it is possible to shorten the process time and cost, and to prevent contamination and oxide regeneration that may occur when transitioning to the final polishing step from the additional pretreatment process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, but the present invention is not limited to or limited by the embodiments. In describing the present invention, a detailed description of well-known functions or constructions may be omitted for clarity of the present invention.

Hereinafter, a wafer polishing apparatus 10 according to an embodiment of the present invention will be described with reference to FIG. 1.

The wafer polishing apparatus 10 is equipped with a polishing head 12 for mounting the wafer 1 to be polished and a polishing pad 111 for polishing the surface of the wafer 1 in contact with the wafer 1. It consists of the surface plate 11 and the slurry supply part 13 for supplying the slurry 131 for polishing the wafer 1.

The polishing head 12 is mounted on the back surface of the polishing treatment surface on the wafer 1 and presses the wafer 1 against the polishing pad 111 and the surface plate 11 at a predetermined pressure and rotates at a predetermined speed. ) Is polished. Here, the polishing head 12 and the surface plate 11 may rotate in the same direction or in opposite directions to each other.

The polishing pad 111 is a mechanical polishing element for selectively planarizing protrusions and protrusions on the processing surface of the wafer 1 while being in direct contact with the processing surface of the wafer 1, and various grooves may be formed on the surface thereof. For example, the polishing pad 111 may be a relatively hard polishing cloth such as a polishing cloth impregnated with a urethane resin or a polishing cloth formed by foaming a polyurethane resin.

The slurry 131 is a chemical polishing element provided between the wafer 1 and the polishing pad 111 to selectively planarize the uneven portion of the processing surface of the wafer 1 as it chemically reacts with the surface of the wafer 1. It is a sol solution containing abrasive particles such as silica (colloidal silica).

On the other hand, the detailed technical configuration of the wafer polishing apparatus 10 can be understood from the known technology and are not the gist of the present invention, and thus detailed description and illustration are omitted.

Generally, a wafer polishing process for manufacturing a wafer is divided into stock polishing to improve thickness uniformity of the wafer 1 and final polishing to mirror-process the surface of the wafer 1.

First, after cleaning the wafer 1 (S1), a stock polishing step S2 for planarizing the cleaned wafer 1 surface is performed. In the stock polishing step S2, a relatively hard polishing pad (hereinafter referred to as a "stock pad") and a basic slurry (hereinafter referred to as a "stock slurry") are used to planarize the wafer 1. In the stock polishing step S2, polishing is performed at a removal rate of 0.1 μm / minute or more, typically 0.5 to 0.8 μm / minute, and a constant pressure is applied to perform polishing for a predetermined time.

Next, a final polishing step S3 for mirror processing of the stock polished wafer 1 is performed. In the final polishing step S3, polishing is performed at a very slow polishing rate compared with the stock polishing step S2 for mirror processing of the wafer 1.

When the mirror polishing of the wafer 1 is completed, a cleaning process for removing residual slurry and particles generated during the polishing process is performed on the wafer 1 (S4), and the wafer polishing process is completed.

On the other hand, the stock polishing step (S2) is performed using a double-side polishing apparatus and the final polishing step (S3) is performed using a single-side polishing apparatus, so that the wafer 1 is exposed to the atmosphere during the transition to final polishing after stock polishing. On the surface of the stock polished wafer 1, a chemical oxide film due to a cleaning liquid or a natural oxide film due to exposure to the atmosphere may grow. Hereinafter, a chemical oxide film and / or a natural oxide film formed on the wafer 1 will be referred to collectively as an oxide film.

In order to remove such an oxide film, the final polishing step S3 is divided into first to third polishing steps.

The first polishing step S31 uses the same hard first polishing pad as in the stock polishing step S2 to remove the oxide film on the surface of the wafer 1, and includes the same polymer as the final polishing step S3. Slurry (hereinafter referred to as "final slurry") consisting of a colloidal silica of several nanometers in size may be used.

Here, when the water-soluble polymer is added to the slurry, the polymer improves dispersion between the abrasive particles and facilitates the formation of laminar flow during polishing. In addition, the polymer is adsorbed on the surface of the wafer 1 to be polished, there is an advantage that can selectively polish the peak (peak) protruding from the surface by the pressure difference according to the surface shape. In addition, the final slurry has a smaller chemical erosion effect on the surface of the wafer (1) than the stock slurry, thereby reducing the step width of the center and edge portions of the wafer (1) and improving the flatness of the wafer. After final polishing, the nano-topology of the wafer surface can be improved.

Specifically, as the first polishing pad used in the primary polishing step S31, a stock pad is generally used as in the stock polishing step S2, for example, the first polishing pad is a polyurethane resin. Stock pads formed by foaming or impregnated with a urethane resin may be used.

In addition, in the primary polishing step S31, the polishing may be performed at a higher polishing rate than in the conventional final polishing step S3, but polishing may be performed at the same polishing rate or at a lower polishing rate as the stock polishing step S2. For example, in the primary polishing step S31, polishing may be performed at the same polishing rate as 0.5 to 0.8 μm / minute, or polishing may be performed at a polishing rate of 0.1 to 0.5 μm / minute.

In the second polishing step S32 and the third polishing step S33, a second polishing pad softer than the first polishing pad may be used. For example, in the second polishing step S32 and the third polishing step S33, a soft polishing pad may be used as in the conventional final polishing step S3. In the second polishing step S32 and the third polishing step S33, mirror polishing of the wafer 1 is performed using the final slurry in the same manner as the first polishing step S31.

Further, the secondary polishing step S32 and the tertiary polishing step S33 are performed at a very low polishing rate compared to the first polishing step S31. For example, in the second polishing step S32 and the third polishing step S33, polishing may be performed at a low speed of 0.1 μm / minute or less.

Hereinafter, referring to FIGS. 3 to 7, a wafer polishing method according to an embodiment of the present invention and a polishing result of a wafer according to a comparative example and an oxide film removal result by the polishing method will be described with reference to FIGS. 3 to 7.

First, 'Example' was performed by using a polishing pad impregnated with a urethane resin and a colloidal silica added with a polymer. In the polishing conditions of Examples, the polishing pressure was 260 g / cm 2, the rotational speed of the surface plate and the polishing head was 120 rpm, the polishing time was 300 seconds, and the slurry flow rate was 0.5LPM. In Comparative Example, the slurry used colloidal silica, and the polishing was performed under the same polishing conditions as in the example except for the slurry.

An oxide film was artificially grown on the wafer surface using ozone water (O3), and polishing was performed under polishing conditions according to Examples and Comparative Examples, and a change in friction force over time was measured. The measurement results are shown in FIGS. 3 and 4, respectively.

3 and 4, it can be seen that both the embodiment and the comparative example have a transition section in which the polishing rate is lowered at the initial polishing stage (ie, 30 seconds or less) due to the oxide film. In addition, it can be seen that the difference in oxide film removal time hardly occurs in both the comparative examples and the examples.

Here, after the stock polishing, the difference in peak to valley (PV) of the wafer surface is small and the thickness of the oxide film is about 10 to 20 microseconds, so that the oxide film is easily removed. .

5 and 6 are graphs showing the results of measuring wafer shapes before and after polishing in Examples and Comparative Examples.

In general, the single-side polishing device performs polishing while the surface plate and the polishing head are rotated in opposite directions or in the same direction, and pressure is concentrated on the edge portion compared to the center portion of the wafer, so that the edge portion may be relatively polished. have.

As shown in FIG. 5, in the case of the embodiment, the edges of the wafer and the center of the wafer were polished at a relatively uniform height, so that the edges were not over-polishing, the entire surface was polished uniformly, and the flatness level was improved. have.

On the contrary, as shown in FIG. 6, in the comparative example, the edge portion (the portion indicated by the dotted circle) has a greater height difference than the center portion, so that the edge portion is over-polishing and the flatness level is low. Can be. In addition, as shown in FIG. 6, in the case of the comparative example, since portions having a large P-V value appear locally, it can be seen that the nano topology is worse than that of the example.

In addition, when comparing the center portion of the wafer in FIG. 5 and FIG. 6 before and after polishing, it can be seen that the polishing was selectively performed at a relatively high portion before and after polishing in the case of the embodiment.

FIG. 7 is a graph showing measurement results of surface roughness after polishing in Examples and Comparative Examples. FIG. Referring to FIG. 7, in the case of the embodiment, the surface roughness has a root mean square (RMS) value of 0.5 to 3 ms, while in the comparative example, the surface roughness has an RMS value of 6 to 10 ms. The surface roughness value according to the embodiment is at a level similar to the surface roughness of the wafer after final polishing is completed. On the contrary, in the case of the comparative example, the surface roughness is larger than that of the example, indicating that the polishing quality is low. In addition, in the case of the embodiment there is almost no variation in the surface roughness for each measurement position, in the case of the comparative example it can be seen that the surface roughness is very large deviation for each measurement position.

Referring to FIG. 7, the embodiment has a surface roughness of 3 μs or less at a cutoff range of 1 to 25 μm, a surface roughness of 4.5 μs or less at a cutoff range of 25 to 80 μm, and a cutoff range of 80 to 250. It is understood that the surface roughness is 6 kPa or less at 탆.

As described above, the semiconductor wafer polishing method according to the present invention can effectively remove the oxide film on the wafer surface by performing the polishing using the stock pad and the final slurry similarly to the stock polishing in the early stage of the final polishing. In addition, the desired polishing rate can be secured in a short time in the primary polishing step by using the stock pad and the final slurry.

Here, according to the present invention, in the first polishing step, the final slurry of colloidal silica to which the polymer is added is used to prevent adverse effects that may occur when the slurry is changed in the second and third polishing steps, and to improve the surface roughness after polishing. Can be. In addition, since it is not necessary to use a separate oxide film removal slurry to remove the oxide film it is possible to prevent the increase in cost by using an additional slurry.

In addition, the primary polishing may be performed in the final polishing apparatus and the secondary polishing may be performed immediately after the primary polishing. Therefore, the primary polishing may be performed in a continuous process, and there is no need to have a standby process of the wafer between the processes. Formation or contamination can be prevented. In addition, there is no need to add a separate pretreatment process to remove the oxide film before performing the final polishing step, which can reduce the process time and cost, and contamination and oxide film that may occur when transitioning from the additional pretreatment process to the final polishing step. Regeneration can be prevented.

In addition, it is possible to prevent over-polishing of the edge portion of the wafer during single-side polishing and thereby lowering flatness of the wafer.

In addition, as the oxide film is removed, the surface roughness may be improved by preventing a decrease in the polishing rate and the transition section caused by the oxide film.

As described above, the present invention has been described by specific embodiments such as specific components and the like, but the embodiments and the drawings are provided only to help a more general understanding of the present invention, and the present invention is limited to the above-described embodiments. In other words, various modifications and variations are possible to those skilled in the art to which the present invention pertains. Therefore, the spirit of the present invention should not be limited to the above-described embodiments, and all the things that are equivalent to or equivalent to the scope of the claims as well as the claims to be described later belong to the scope of the present invention.

1 is a schematic view of a wafer polishing apparatus according to an embodiment of the present invention;

2 is a flowchart illustrating a wafer polishing method according to an embodiment of the present invention;

3 and 4 are graphs for comparing the frictional force change with time in the Examples and Comparative Examples;

5 and 6 are graphs for comparing wafer shape changes before and after polishing in Examples and Comparative Examples;

7 is a graph showing the results of surface roughness measurement after polishing in Examples and Comparative Examples.

<Explanation of symbols for the main parts of the drawings>

1: wafer 10: wafer polishing apparatus

11: surface plate 111: polishing pad

12: polishing head 13: slurry feed section

131: slurry

Claims (8)

A wafer polishing method in which a stock polishing step for planarizing a wafer surface and a final polishing step for mirroring a planarized wafer surface are sequentially performed, The final polishing step, A first polishing step of polishing the wafer using a hard first polishing pad and a colloidal slurry to which a polymer is added; And A second polishing step of polishing the first polished wafer using a second polishing pad softer than the first polishing pad; Wafer polishing method comprising a. The method of claim 1, And the first polishing pad is a polishing pad of the same material as the polishing pad used in the stock polishing step. The method of claim 2, And the first polishing pad is a polishing pad formed by foaming a polyurethane resin or impregnated with a urethane resin in a nonwoven fabric. The method of claim 1, The slurry is a colloidal silica containing a water-soluble polymer wafer polishing method. The method of claim 4, wherein The second polishing step is a wafer polishing method using the same slurry as the first polishing step. The method of claim 1, And the first polishing step is performed at the same polishing rate or lower polishing rate as the stock polishing step, and the second polishing step is performed at a polishing rate lower than that of the first polishing step. The method of claim 6, The first polishing step is a wafer polishing method performed at a polishing rate of 0.1 ~ 0.8 ㎛ / min. The method of claim 6, The secondary polishing step is a wafer polishing method performed at a polishing rate of 0.1㎛ / min or less.

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