KR101581469B1 - Method of polishing substrate - Google Patents

Abstract

Disclosed is a wafer polishing method capable of preventing an increase in frictional force and a decrease in polishing rate due to an oxide film on a wafer surface and improving the flatness of the wafer. The final polishing step for removing the oxide film at the beginning of the final polishing step in the wafer polishing step in which the stock polishing and the final polishing are sequentially performed is performed by using a hard first polishing pad and a colloidal slurry to which the polymer is added, And a secondary polishing step of polishing the primary polished wafer by using a polishing pad that is softer than the first polishing pad.

Final polishing, transition section, slurry

Description

[0001] METHOD OF POLISHING SUBSTRATE [0002]

The present invention relates to a wafer polishing method capable of preventing a rise in frictional force and a decrease in polishing speed and an improvement in flatness of a wafer in a final polishing step due to an oxide film formed on the wafer surface after polishing the stock in a wafer manufacturing process.

Silicon wafers, which are widely used today as materials for manufacturing semiconductor devices, refer to monocrystalline silicon thin plates made of polycrystalline silicon as a raw material. The process for manufacturing a wafer includes a slicing process for cutting a grown silicon single crystal ingot into a wafer shape, a lapping process for uniformizing and flattening the thickness of the wafer, an etching process for removing or mitigating the generated damage, A polishing process for mirror-polishing the surface of the wafer, and a cleaning process for cleaning the polished wafer and removing foreign matter adhered to the surface.

In general, the cleaning process is performed for the purpose of removing contaminants such as particles, organic contaminants, and metal impurities generated in the mirror polishing process of the wafer. Generally, the RCA method, which is a wet cleaning method, is commonly used in the cleaning process. The RCA method uses a standard cleaning solution (Standard Cleaning 2, SC2) to remove residual particles and organic matter on the surface of the wafer by oxidizing and etching the surface of the polished wafer using Standard Cleaning 1 (SC1) And a step of removing metal impurities.

The polishing process is divided into stock polishing, which removes the surface alteration layer of the wafer and improves the thickness uniformity, and final polishing which polishes the surface of the wafer to the mirror surface. In general, the stock polishing generally proceeds at a rate of 0.5 to 0.8 탆 / min, and the final polishing progresses a minute amount of polishing with a level at which it is impossible to accurately measure the polishing rate. The polishing process is performed by selecting a slurry and a polishing pad suitable for the polishing characteristics, and the slurry is selected in consideration of the polishing rate, the friction characteristics, the surface roughness, and the like for the wafer.

Meanwhile, during the cleaning process of the wafer before the polishing process of the wafer, the natural oxide film due to the chemical oxide film due to the cleaning liquid or the exposure to the air is grown while the wafer is cleaned, dried and stood. Here, since the polishing rate of the oxide film (SiO 2) is smaller than that of silicon (Si), the oxide film causes excessive frictional force in the polishing process, and a transition period in which the polishing rate abruptly decreases at the beginning of polishing Resulting in overload and vibration of the driving part of the polishing apparatus.

The wafers are produced in the form of a conveyor, and each unit process is not a continuous process. Instead, the wafer is processed in a unit of at least one cassette (25 sheets / cassette) and then moved to the next process Even if the oxide film is completely removed in the cleaning process, an oxide film is formed again while moving to the polishing process and during the waiting process.

The transition period due to the oxide film differs depending on the wafer surface state before the polishing process and the type of slurry used, but occurs in a substantially similar form. Conventionally, in order to increase the polishing rate and improve the glazing phenomenon in which a silica film is formed on the surface of the polishing pad, a slurry containing an amine is used. Recently, however, copper contamination due to amines has been a problem, and thus an amine-free slurry has been widely used. However, when an amine-free slurry is used, it is difficult to remove the oxide film, so that the generation of the transition zone at the initial stage of polishing is deteriorated.

On the other hand, the stock polishing process uses a double-side polishing device, whereas the final polishing process uses a single-side polishing device, so that the waiting process is inevitable in the process of finishing after finishing the stock polishing. However, since the final polishing rate is much lower than the stock polishing rate, it is more influenced by the generation of the transition region due to the oxide film formed in the waiting process in the final polishing process.

In order to solve the above-described problems, the embodiments of the present invention are to provide a wafer polishing method capable of preventing an increase in frictional force and a decrease in polishing rate due to an oxide film at the initial stage of polishing.

Embodiments of the present invention are also intended to provide a wafer polishing method capable of preventing an increase in frictional force and a decrease in polishing rate in a final polishing process.

According to embodiments of the present invention for achieving the object of the present invention described above, a wafer polishing method in which a stock polishing step for planarizing the wafer surface and a final polishing step for mirror-polishing the flattened wafer surface are sequentially performed . The final polishing step for removing the oxide film at the beginning of the final polishing step includes a first polishing step of polishing the wafer using a rigid first polishing pad and a colloidal slurry to which a polymer is added, And a second polishing step of 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 nonwoven fabric with a urethane resin may be used. The slurry may be colloidal silica containing a water-soluble polymer. Here, the secondary polishing step may use the same slurry as the primary polishing step.

Further, the primary polishing step is performed at the same polishing rate or at a low polishing rate as the stock polishing step, and the secondary polishing step can be performed at a lower polishing rate than the primary polishing step. For example, the primary polishing step may be performed at a polishing rate of 0.1 to 0.8 μm / min. And the secondary polishing step may be performed at a polishing rate of 0.1 m / min or less.

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

Further, since the same slurry as the secondary and tertiary polishing is used in the primary polishing, deterioration of the surface roughness after the final polishing can be prevented.

In addition, since it is not necessary to use a separate slurry for removal of the oxide film, the increase in cost can be suppressed and the production cost can be reduced.

In addition, since there is no need to add a separate pretreatment step for removing the oxide film, it is possible to shorten the process time and cost, and to prevent the contamination and the oxide film regeneration that may occur during the transition from the additional pre-treatment step to the final polishing step.

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.

The wafer polishing apparatus 10 includes a polishing head 12 for mounting a wafer 1 to be polished and a polishing pad 111 for polishing the surface of the wafer 1 in a state of being in contact with the wafer 1 And a slurry supply unit 13 for supplying the slurry 131 for polishing the wafer 1.

The polishing head 12 is mounted on the back surface of the polishing surface of the wafer 1 and presses the wafer 1 against the polishing pad 111 and the table 11 at a predetermined pressure and rotates at a predetermined speed, Is polished. Here, the polishing head 12 and the table 11 can rotate in the same direction or in mutually opposite directions.

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

The slurry 131 is a chemical polishing element that is provided between the wafer 1 and the polishing pad 111 to selectively planarize the irregularities on the wafer 1 treated surface as it chemically reacts with the surface of the wafer 1, Sol solution containing abrasive particles such as colloidal silica.

The detailed description of the wafer polishing apparatus 10 can be understood from known techniques and is not a gist of the present invention.

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

First, after the wafer 1 is cleaned (S1), a stock polishing step S2 for planarizing the surface of the cleaned wafer 1 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 "stock slurry") are used for planarizing the wafer 1. Then, the stock polishing step S2 is performed at a removal rate of 0.1 mu m / min or more, usually 0.5 to 0.8 mu m / min, and a constant pressure is applied to perform the polishing for a certain period of time.

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

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

On the other hand, since 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, the wafer 1 is exposed to the atmosphere during transition to final polishing after stock polishing The surface of the stock polished wafer 1 may have a chemical oxide film due to the cleaning liquid or a natural oxide film due to exposure to air. Hereinafter, the chemical oxide film and the natural oxide film formed on the wafer 1 are collectively referred to as an oxide film.

In order to remove such an oxide film, the final polishing step (S3) is subdivided into a first to third polishing step.

In the primary polishing step S31, a first polishing pad having the same hardness as in the stock polishing step S2 is used to remove the oxide film on the surface of the wafer 1, and the same polymer as in the final polishing step S3 is included (Hereinafter referred to as " final slurry ") composed of abrasive grains can be used as the colloidal silica having a size of several nanometers.

Here, when the water-soluble polymer is added to the slurry, the polymer improves the dispersion among the abrasive grains and facilitates formation of laminar flow during polishing. Polymers are adsorbed on the surface of the wafer 1 to be polished, and peaks protruding from the surface due to a pressure difference depending on the surface shape can be selectively polished. In addition, the final slurry has a chemical erosion action relative to the surface of the wafer 1 relative to the stock slurry, so that the step width of the center portion and the edge portion of the wafer can be reduced during polishing of the wafer 1 and the flatness of the wafer can be improved , It is possible to improve the nanotopology of the surface of the wafer after completion of final polishing.

In detail, the first polishing pad used in the primary polishing step S31 is normally used as a stock pad as in the stock polishing step S2, for example, the first polishing pad is a polyurethane resin Or a stock pad formed by impregnating a nonwoven fabric with a urethane resin may be used.

Further, in the primary polishing step S31, polishing can be performed at a high polishing rate as compared with the usual final polishing step S3, but polishing at the same polishing rate or low 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 of 0.5 to 0.8 mu m / min as in the stock polishing step, or polishing may be performed at a polishing rate of 0.1 to 0.5 mu m / min.

In the secondary polishing step (S32) and the tertiary polishing step (S33), a second polishing pad that is softer than the first polishing pad can be used. For example, in the secondary polishing step (S32) and the tertiary polishing step (S33), a soft polishing pad can be used as in the usual final polishing step (S3). In the secondary polishing step S32 and the tertiary polishing step S33, mirror polishing of the wafer 1 is performed using the final slurry in the same manner as in the primary polishing step S31.

In the secondary polishing step S32 and the tertiary polishing step S33, polishing is performed at a polishing rate which is very low compared to the primary polishing step S31. For example, in the secondary polishing step S32 and the tertiary polishing step S33, polishing can be performed at a low speed of 0.1 m / min or less.

Hereinafter, the wafer polishing method according to one embodiment of the present invention as described above, and the polishing result of the wafer according to the comparative example and the oxide film removing result according to the polishing method will be described in comparison with FIG. 3 to FIG.

First, in Example, polishing was performed using a polishing pad impregnated with a urethane resin in a polyester nonwoven fabric and colloidal silica added with a polymer. Polishing was carried out under the conditions of a polishing pressure of 260 g / cm 2, a polishing speed of 120 rpm, a polishing time of 300 seconds, and a slurry flow rate of 0.5 LPM. In the Comparative Example, polishing was performed under the same polishing conditions as those of the Example except for the slurry because the slurry used colloidal silica.

Then, an oxide film was grown on the surface of the wafer by using ozone water (O3), polishing was performed under the polishing conditions according to the examples and the comparative examples, and the change of the friction force with time was measured. The measurement results are shown in Figs. 3 and 4, respectively.

Referring to FIGS. 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 stage of polishing (that is, before 30 seconds) due to the oxide film. It can also be seen that the difference in the removal time of the oxide film hardly occurs in both the comparative example and the embodiment.

Here, since the difference in PV (peak to valley) of the surface of the wafer is small and the thickness of the oxide film is about 10 to 20 Å after the stock polishing, it is easy to remove the oxide film, .

Figs. 5 and 6 are graphs showing the results of measurement of the wafer shape before and after polishing in Examples and Comparative Examples.

Generally, in the single-side polishing apparatus, the polishing progresses while the polishing table and the polishing head rotate in the opposite directions or in the same direction. In this case, the pressure is concentrated on the dedection portion as compared with the center portion of the wafer, have.

As shown in FIG. 5, it can be seen that the edge portions and the central portion of the wafer are relatively uniform in height, so that the edge portions are not completely etched, the wafer is evenly polished as a whole, and the level of flatness is improved have.

On the other hand, as shown in Fig. 6, in the case of the comparative example, it is known that the edge portion (the portion indicated by the dotted circle) has a height difference larger than the center portion, the edge portion is finished and the flatness level is low . In addition, as shown in FIG. 6, in the case of the comparative example, nano topology is worsened as compared with the embodiment, since portions having a large P-V value appear locally.

5 and FIG. 6, when the center portion of the wafer was compared before and after polishing, it can be confirmed that polishing was selectively performed at a relatively high portion before and after polishing.

7 is a graph showing the measurement results of the surface roughness after polishing in Examples and Comparative Examples. Referring to FIG. 7, it can be seen that the surface roughness of the embodiment has an RMS value of 0.5 to 3 Å, while that of the comparative example has an RMS value of 6 to 10 Å. The surface roughness value according to the embodiment is similar to the surface roughness of the wafer after the final polishing is completed. On the contrary, in the comparative example, the surface roughness is larger than that in the embodiment, and the polishing quality is low. Also, in the case of the embodiment, there is almost no deviation of the surface roughness according to the measurement position, whereas in the comparative example, the surface roughness varies greatly depending on the measurement position.

Referring to FIG. 7, in the embodiment, the surface roughness is 3 Å or less at a cutoff range of 1 to 25 탆, the surface roughness is 4.5 Å or less at a cutoff range of 25 to 80 탆, the cut- Mu m, the surface roughness is 6 A or less.

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

According to the present invention, since the primary slurry of the colloidal silica to which the polymer is added is used in the primary polishing step, adverse effects that may occur when the slurry is changed in the secondary and tertiary polishing steps can be prevented and the surface roughness after polishing can be improved . In addition, since it is not necessary to use a separate slurry for oxide film removal to remove the oxide film, an increase in cost due to the use of the additional slurry can be prevented.

Since the primary polishing is performed in the final polishing apparatus and the secondary polishing can be performed immediately after the primary polishing, it is possible to proceed to a continuous process, and there is no need to carry out the atmospheric process of the wafer between the processes, Generation or contamination can be prevented. In addition, since it is not necessary to add a separate pretreatment step to remove the oxide film before performing the final polishing step, it is possible to shorten the processing time and cost, and to prevent contamination and oxide film The regeneration can be prevented.

Further, it is possible to prevent the edge portion of the wafer from being excessively smoothed and the flatness of the wafer to be lowered during the single side polishing.

In addition, by removing the oxide film, it is possible to prevent the polishing rate from being lowered due to the oxide film and the generation of the transition section, thereby improving the surface roughness.

As described above, the present invention has been described with reference to particular embodiments, such as specific elements, and specific embodiments and drawings. However, it should be understood that the present invention is not limited to the above- It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Accordingly, the spirit of the present invention should not be construed as being limited to the above-described embodiments, and all matters that are equivalent to or equivalent to the claims of the present invention are included in the scope of the present invention.

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

2 is a flow chart for explaining a wafer polishing method according to an embodiment of the present invention;

FIGS. 3 and 4 are graphs for comparing frictional force changes over time in the embodiment and the comparative example;

FIGS. 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 measurement of surface roughness after polishing in Examples and Comparative Examples.

Description of the Related Art

1: wafer 10: wafer polishing apparatus

11: Platen 111: Polishing pad

12: polishing head 13: slurry supply part

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, In the final polishing step, A first polishing step of polishing the wafer using a rigid first polishing pad and a colloidal slurry to which a polymer is added; And A secondary polishing step of polishing the primary polished wafer using a second polishing pad softer than the first polishing pad; ≪ / RTI > The method according to claim 1, Wherein the first polishing pad is a polishing pad of the same material as the polishing pad used in the stock polishing step. 3. The method of claim 2, Wherein the first polishing pad is a polishing pad formed by foaming a polyurethane resin or formed by impregnating a nonwoven fabric with a urethane resin. The method according to claim 1, Wherein the slurry is colloidal silica containing a water-soluble polymer. 5. The method of claim 4, Wherein the secondary polishing step uses the same slurry as the primary polishing step. The method according to claim 1, Wherein the primary polishing step is performed at the same polishing rate or a lower polishing rate as the stock polishing step and the secondary polishing step is performed at a lower polishing rate than the primary polishing step. The method according to claim 6, Wherein the primary polishing step is performed at a polishing rate of 0.1 to 0.8 mu m / min. The method according to claim 6, Wherein the secondary polishing step is performed at a polishing rate of 0.1 m / min or less.

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