JP4110801B2 - Semiconductor wafer polishing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for polishing a semiconductor wafer capable of obtaining ultrahigh flatness at low cost.
[0002]
[Prior art]
The manufacturing process of a semiconductor wafer, such as a silicon wafer, consists of chamfering, mechanical polishing (lapping), etching, mirror polishing (polishing) and cleaning of a wafer obtained by cutting and slicing from a pulled silicon single crystal ingot. , Produced as a wafer with high precision flatness. Depending on the purpose, some of these steps are replaced, repeated a plurality of times, or other steps such as heat treatment and grinding are added or replaced to perform various steps.
[0003]
Of these, mirror polishing is a process for producing a mirror-surface wafer having optical gloss and no processing distortion. Conventionally, mirror polishing of silicon wafers has generally been performed by a single-side polishing method.
[0004]
However, as the miniaturization and high integration of semiconductor devices progress, it is required to manufacture a silicon wafer having higher precision flatness, and there is a limit in the conventional silicon wafer single-side mirror polishing method. As one measure for solving this problem, a double-sided mirror polishing method for silicon wafers has been proposed. This is a method in which a silicon wafer is loaded into a carrier slightly thinner than the finished thickness and mirror-polished by a mechanism similar to double-sided lapping. With this double-side polishing apparatus, both the front and back surfaces of the wafer are mirror-polished to obtain extremely high accuracy flatness and uniform thickness.
[0005]
[Problems to be solved by the invention]
However, the mirror polishing method using the above-described double-side polishing apparatus is a very useful method because high-accuracy flatness is obtained. However, in the current semiconductor device process, it is possible to use a single-sided mirror wafer in which only one side is mirror-polished. In most cases, double-sided mirror wafers obtained by double-sided simultaneous polishing are manufactured by mirror-polishing the front and back surfaces of the wafer at the same time, making it difficult to distinguish between the front and back surfaces. For example, the presence or absence of a wafer in the transport system in the device process Since the back surface is polished, problems such as difficulty in inspection and erroneous detection occur.
[0006]
For this reason, there is a demand for a wafer having high flatness similar to that obtained by mirror-polishing only one side and not both surfaces of the wafer being mirror-polished. In order to meet such a demand, a technique for polishing only one side using a double-side polishing apparatus effective as a high planarization processing method has been proposed. For example, a method has been proposed in which an oxide film or a nitride film is formed on a non-polished planned surface of a wafer before performing double-sided mirror polishing, and mirror polishing is performed only on the planned surface of the wafer by performing double-side polishing on the wafer. Kaihei 10-303154). In this method, an oxide film or a nitride film which is a protective film is formed by a CVD method or a thermal oxidation process.
[0007]
However, the polishing technique disclosed in the above publication has a problem in that the manufacturing cost increases and the throughput decreases because the film forming and removing steps are added. In addition, there is a possibility that problems such as contamination due to the heat process and generation of particles during film removal may occur.
[0008]
On the other hand, the polishing cloth used for polishing is usually made hydrophilic in order to have the polishing ability. However, when only one side is polished using a double-side polishing machine, hydrogen bonding occurs between the polishing cloth and the non-polished surface, increasing the contact resistance during polishing and reducing the stability in processing. It was happening.
[0009]
An object of the present invention is to provide a semiconductor wafer polishing method capable of obtaining a single-sided mirror wafer having a high degree of flatness at low cost.
[0010]
[Means for Solving the Problems]
As shown in FIG. 1, the invention according to claim 1 holds a semiconductor wafer 19 having a thin film formed on both sides in a carrier hole 16a formed in a carrier plate 16 on its both surfaces, and is a polishing liquid. A surface parallel to the surface of the carrier plate 16 between the upper surface plate 11 to which the first polishing cloth 13 is attached and the lower surface plate 12 to which the second polishing cloth 14 is attached. This is an improvement of a method for polishing a semiconductor wafer in which the plate 16 is moved in the wafer to planarly polish the wafer 19. This characteristic configuration includes a step of removing the thin film on the wafer surface in contact with the upper surface plate 11 by leaving the thin film on the wafer back surface in contact with the lower surface plate 12 among the thin films on the front and back surfaces of the wafer 19. The polishing rate for the material is higher than the polishing rate for the thin film, the first polishing cloth 13 has hydrophilicity, and the second polishing cloth 14 has water repellency.
According to the second aspect of the present invention , a semiconductor wafer having a thin film formed on both sides thereof in a carrier hole formed in a carrier plate is held on the both surfaces, and a first polishing liquid is supplied to the wafer surface while supplying a polishing liquid to the wafer surface. Polishing of a semiconductor wafer in which the wafer is planarly polished by moving the plate in a plane parallel to the surface of the carrier plate between the upper surface plate to which the polishing cloth is attached and the lower surface plate to which the second polishing cloth is attached. It is an improvement of the method. The characteristic configuration includes a step of removing the thin film on the wafer surface in contact with the lower surface plate by leaving the thin film on the wafer back surface in contact with the upper surface plate among the thin films on the front and back surfaces of the wafer, and the polishing liquid is applied to the material of the wafer. higher than the polishing rate polishing rate for the thin film, the first polishing cloth has a water repellency, the second polishing cloth is in place with a hydrophilic.
In the invention according to claim 1 or 2, the back surface of the wafer on which the thin film remains by selectively polishing the front surface side of the semiconductor wafer by supplying a polishing liquid whose polishing rate for the material of the wafer is higher than the polishing rate for the thin film On the side, the polishing rate is low and polishing hardly progresses, whereas the wafer surface side from which the thin film has been removed has a high polishing rate and good polishing is performed. Further, by imparting water repellency to the second polishing cloth 14, hydrogen bonding does not occur between the back surface of the wafer where the thin film, which is a non-polished surface, remains, and therefore contact resistance with the thin film during polishing is reduced. Can be small. Therefore, even a thin film generated during natural standing or during cleaning functions sufficiently as a protective film, and does not require a process for providing an oxide film in particular, so that it is possible to suppress an increase in cost due to additional processes in film formation and removal, and a thermal process. It is possible to suppress the generation of particles due to contamination and film removal. As a result, the stability in processing is improved, and a wafer having high precision flatness can be obtained in high yield.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of the present invention will be described based on an example of polishing a silicon wafer based on the drawings.
As shown in FIG. 1, the double-side polishing apparatus 10 affixes a first polishing cloth 13 to the upper surface plate 11 and a second polishing cloth 14 to the lower surface plate 12 on the upper surface plate 11 and the lower surface plate 12, respectively. In the meantime, a thin disk called a carrier plate 16 having a thin film slightly thinner than the finished thickness of a silicon wafer having a thin film generated during natural standing or cleaning is set on the entire surface plate. Reference numeral 21 in FIG. 1 indicates a pipe for supplying a polishing liquid between the upper surface plate and the lower surface plate. As shown in FIG. 2, the carrier plate has four carrier holes 16a having a diameter about 0.5 to 2 mm larger than the outer diameter of the wafer, and has a structure in which the wafer 19 can be loaded into the carrier hole 16a. .
As shown in FIG. 3, the carrier plate 16 is held in mesh with a sun gear 17 located at the center of the surface plate 12 and an internal gear 18 located around the outer periphery of the surface plate. After the silicon wafer 19 is set in the carrier hole 16a, while the wafer 19 is sandwiched between the upper surface plate 11 and the lower surface plate 12 and a predetermined pressure is applied, rotation of the upper and lower surface plates, rotation of the carrier, and rotation of the wafer itself are referred to. Polishing the front and back of the wafer using complex motion. FIG. 3 shows only one carrier plate held on the surface plate.
[0012]
The characteristic configuration of the present invention includes a step of removing the thin film on the wafer surface in contact with the upper surface plate 11 by leaving the thin film on the back surface of the wafer in contact with the lower surface plate 12 among the thin films on the front and back surfaces of the wafer 19. The polishing rate for the material of the wafer is higher than the polishing rate for the thin film, the first polishing pad 13 has hydrophilicity, and the second polishing pad 14 has water repellency.
[0013]
Of the oxide film of the silicon wafer produced by cleaning by ozone cleaning or the like before polishing or natural oxidation, the oxide film on the wafer surface in contact with the upper surface plate 11 is removed in advance by a hydrofluoric acid-based etching solution. Since this oxide film is an extremely thin oxide film, it can be easily removed with a hydrofluoric acid-based etching solution. An alkaline solution having a polishing abrasive concentration of 1% by weight or less is used as the polishing liquid whose polishing rate for the wafer material is higher than that for the thin film. Since this polishing liquid has almost no mechanical polishing action by the abrasive grains and has only a chemical polishing action by an alkaline solution, that is, an etching action, an oxide film remaining on the back surface of the wafer even if polishing is performed using this polishing liquid. Is hardly polished, and only the wafer surface exposed by removing the oxide film is polished.
[0014]
In the polishing apparatus, the polishing cloth attached to the upper surface plate and the lower surface plate is usually hydrophilic so as to have a polishing ability. Accordingly, the resistance during polishing can be reduced by making the polishing cloth hydrophilic without conferring hydrophilicity. Therefore, by making the second polishing cloth 14 attached to the lower surface plate 12 in contact with the back surface of the wafer 19 water-repellent and making the first polishing cloth 13 attached to the upper surface plate 11 in contact with the wafer surface hydrophilic. Since the polishing resistance is reduced without generating a hydrogen bond between the oxide film 19a remaining on the back surface of the wafer 19 and the second polishing pad 14, it is possible to suppress detachment or loss of the oxide film 19a due to polishing. Since a large polishing resistance is obtained between the surface 19 and the first polishing cloth 13 having hydrophilicity, the surface is polished to a mirror surface. Therefore, it is possible to manufacture a wafer in which only one of which maintains high precision flatness is mirror-polished.
Examples of the water-repellent abrasive cloth of the present invention include a nonwoven fabric in which a nonwoven fabric is impregnated with a fluorine-based resin, a nonwoven fabric whose surface is coated with a fluorine-based resin, urethane foam, and suede. Examples of hydrophilic abrasive cloth include nonwoven fabric, urethane foam, and suede that are not specially subjected to resin processing or chemical processing. Suede is a fabric or knitted fabric with a surface finish resembling suede leather, or a base material using a sheet of polyester felt impregnated with polyurethane. And a foamed layer provided with a feather-like opening.
[0015]
In this embodiment, the double-side polishing apparatus in which the sun gear is incorporated is described. However, a double-side polishing apparatus in which the sun gear is not incorporated may be used.
[0016]
Further, the thin film 19a is left on the back surface of the wafer in contact with the lower surface plate 12, the thin film on the wafer surface in contact with the upper surface plate 11 is removed, and the first polishing cloth 13 having hydrophilicity and the second polishing cloth 14 having water repellency. However, the thin film 19a remains on the back surface of the wafer in contact with the upper surface plate 11, the thin film on the surface of the wafer in contact with the lower surface plate 12 is removed, and the first polishing cloth 13 having water repellency has hydrophilicity. The wafer may be polished with the second polishing cloth 14.
[0017]
【The invention's effect】
As described above, according to the present invention, the thin film remains by selectively polishing the surface side of the semiconductor wafer by supplying a polishing liquid whose polishing rate for the wafer material is higher than the polishing rate for the thin film. While the polishing rate is low on the back side of the wafer and polishing hardly proceeds, the polishing rate is high on the front side of the wafer from which the thin film has been removed, and good polishing is performed. Further, by providing the second polishing cloth with water repellency, hydrogen bonding does not occur between the non-polished thin film and the wafer back surface, so that the contact resistance with the thin film during polishing is reduced. can do. Therefore, even a thin film generated during natural standing or during cleaning functions sufficiently as a protective film, and it is not necessary to provide an oxide film. Can be suppressed. As a result, the stability in processing is improved, and a wafer having high precision flatness can be obtained in high yield.
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional view of a double-side polishing apparatus used in the present embodiment.
FIG. 2 is an explanatory top view of a carrier in a double-side polishing apparatus.
FIG. 3 is a top view of a surface plate on which a carrier is set in a double-side polishing apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Double-side polish apparatus 11 Upper surface plate 12 Lower surface plate 13 1st polishing cloth 14 2nd polishing cloth 16 Carrier plate 16a Carrier hole 17 Sun gear 18 Internal gear 19 Silicon wafer 21 Piping

Claims (8)

The semiconductor wafer (19) having a thin film formed on both sides in the carrier hole (16a) formed in the carrier plate (16) is held on the both sides, and the polishing liquid is supplied to the surface of the wafer (19). However, between the upper surface plate (11) to which the first abrasive cloth (13) is adhered and the lower surface plate (12) to which the second abrasive cloth (14) is adhered, the carrier plate (16) In the semiconductor wafer polishing method of polishing the wafer (19) by moving the plate (16) in a plane parallel to the surface,
Leaving the thin film (19a) on the wafer back surface in contact with the lower surface plate (12) among the thin films on the front and back surfaces of the wafer (19), and removing the thin film on the wafer surface in contact with the upper surface plate (11),
The polishing liquid has a higher polishing rate for the wafer material than the polishing rate for the thin film,
A method for polishing a semiconductor wafer, wherein the first polishing cloth (13) has hydrophilicity and the second polishing cloth (14) has water repellency. The semiconductor wafer (19) having a thin film formed on both sides in the carrier hole (16a) formed in the carrier plate (16) is held on the both sides, and the polishing liquid is supplied to the surface of the wafer (19). while, between the first polishing cloth (13) is pasted on the surface plate (11) and the second polishing cloth (14) is pasted lower surface plate (12), said carrier plate (16) In the semiconductor wafer polishing method of polishing the wafer (19) by moving the plate (16) in a plane parallel to the surface ,
Said back surface of the wafer in contact with the surface plate (11) out of the thin film on the front and back surfaces of the wafer (19) leaving a thin film (19a), comprising the step of removing the thin film of the wafer surface in contact with the lower surface plate (12),
The polishing liquid has a higher polishing rate for the wafer material than the polishing rate for the thin film,
The first abrasive cloth (13) has water repellency, and the second abrasive cloth (14) has hydrophilicity.
A method for polishing a semiconductor wafer . The polishing method according to claim 1 or 2, wherein the semiconductor wafer (19) is a silicon wafer and the thin film (19a) is an oxide film. The polishing method according to claim 1 or 2, wherein the polishing liquid is an alkaline solution having a polishing abrasive grain concentration of 1% by weight or less. The polishing method according to claim 1 or 2, wherein the thin film formed on the surface of the wafer (19) is removed with a hydrofluoric acid-based etching solution. The polishing method according to claim 1 or 2, wherein the water-repellent polishing cloth is a nonwoven fabric obtained by impregnating a nonwoven fabric with a fluorine resin. The polishing method according to claim 1 or 2, wherein the water-repellent polishing cloth is a nonwoven fabric, urethane foam or suede whose surface is coated with a fluorine resin. The polishing method according to claim 1 or 2, wherein the hydrophilic polishing cloth is a non-woven fabric, urethane foam or suede.

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