JPH0963996A - Silicon wafer polishing method - Google Patents

Abstract

(57) Abstract: Chemical mechanical polishing method (CMP method (Chem-Mech Poli
In polishing the silicon wafer by the shing method), the surface of the silicon wafer is polished and flattened while preventing the contamination of the silicon wafer by the alkali metal. SOLUTION: From a slurry introducing pipe 26, colloidal silica is mixed, and tetramethylammonium hydroxide (T having a concentration of 0.1 wt% or more and 5.0 wt% or less) is used.
MAH) aqueous solution is supplied, and the surface of the silicon wafer 21 is polished by interposing the TMAH aqueous solution between the silicon wafer 21 and the polishing pad 24. Since TMAH contains no alkali metal, the silicon wafer 21 is not contaminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for polishing a silicon wafer, and more particularly, it is used for polishing a silicon wafer by a chemical mechanical polishing method (CMP (Chem-Mech Polishing Method)) to flatten the surface of the wafer. Is suitable.

[0002]

2. Description of the Related Art In recent years, with higher integration and miniaturization of elements in semiconductor devices, in order to achieve higher speed operation of the device and higher performance of electrical characteristics, multi-layers such as aluminum wiring and polycrystalline silicon wiring have been formed. Is being promoted. As the wiring becomes multi-layered in this way, the upper layer wiring formed on the lower layer wiring and on the interlayer insulating film such as a silicon oxide film having unevenness on the surface is disconnected due to the step due to the unevenness. Alternatively, a defect such as a short circuit between wirings due to a poor resolution of photolithography at the step portion may occur. In order to avoid such a situation and realize multi-layer wiring, it is necessary to flatten the surface of the interlayer insulating film formed on the lower wiring.

On the other hand, regarding the element isolation technique, the conventional L
A trench isolation method suitable for high integration of devices has been proposed instead of the device isolation by the OCOS method. In this trench isolation method, a deep groove (trench) formed in a silicon substrate is filled with an insulating film for element isolation, and then the insulating film deposited outside the groove is removed to flatten the surface of the silicon substrate. It is necessary to prepare for later element formation.

As one of the techniques for flattening the surface of such an interlayer insulating film or the surface of a silicon substrate, Japanese Patent Laid-Open No. 60-39 is available.
A method called CMP method described in Japanese Patent No. 835, etc. is known. The CMP method is used for polishing a silicon wafer by interposing a slurry (slurry) in which polishing particles having a hardness about the same as or slightly higher than that of a material to be polished are dispersed and mixed in a liquid between a silicon wafer and a polishing pad. It is a method of polishing and flattening the surface of a silicon wafer by rotating it relative to the pad. According to the CMP method, the polishing efficiency can be improved by the synergistic effect of the mechanical polishing action of the polishing particles and the chemical polishing action of the slurry liquid, and the polishing efficiency can be accurately controlled by adjusting the pH of the slurry liquid. You can

When an attempt is made to polish a silicon-based material such as a silicon substrate or a silicon oxide film by the CMP method,
As the polishing particles, silica powder having a particle size of about 10 nm is used, and as the slurry liquid, an aqueous solution of a substance composed of an alkali metal such as potassium hydroxide (KOH) or sodium hydroxide (NaOH) and a hydroxyl group (OH) is used. It is common. Thus, in order to use an aqueous solution of a substance having a hydroxyl group as the slurry liquid, silicon is bonded to the hydroxyl group on the surface of the silicon substrate or the silicon oxide film,
This is because these surfaces are easily polished.

[0006]

However, as a slurry liquid, potassium hydroxide (KOH) or sodium hydroxide (N) composed of an alkali metal and a hydroxyl group (OH) is used.
When an aqueous solution such as aOH) is used, alkali metals such as potassium and sodium are deposited in the silicon oxide film and at the interface between the silicon substrate and the silicon oxide film, so that they are contaminated. When such contamination occurs, the fixed charges in the silicon oxide film increase and the interface state between the silicon substrate and the silicon oxide film also increases, so that the device may malfunction or the electrical condition of the device may increase. There is a problem that the characteristics are deteriorated.

Therefore, when an aqueous solution of potassium hydroxide (KOH) or sodium hydroxide (NaOH) is used as a slurry liquid as in the prior art, after polishing, sufficient washing is performed to remove potassium, sodium, etc. Had to remove the alkali metal. However, due to the miniaturization of elements, it has become difficult to sufficiently remove potassium and sodium, which are the pollution sources, and eventually, malfunctions of the elements and deterioration of electrical characteristics have occurred.

Therefore, an object of the present invention is to provide a method for polishing a silicon wafer which can polish the surface of the silicon wafer while preventing the contamination of the silicon wafer by an alkali metal when polishing the silicon wafer by the CMP method. That is.

[0009]

In order to achieve the above object, a method for polishing a silicon wafer according to the present invention comprises a tetramethylammonium hydroxide (hereinafter referred to as "TMAH") between a silicon wafer and a polishing pad. ) Polish the surface of the silicon wafer with an aqueous solution interposed.

In one embodiment of the present invention, the TMAH
TMAH concentration in aqueous solution is 0.1 wt% or more and 5.0 w
It is t% or less.

In one embodiment of the present invention, the TMAH
Silica powder is mixed in the aqueous solution at a concentration of 5 wt% or more and 10 wt% or less.

In one aspect of the present invention, the particle size of the silica powder is 7 nm or more and 40 nm or less.

In one embodiment of the present invention, the TMAH
Colloidal silica is mixed in the aqueous solution at a concentration of 5 wt% or more and 10 wt% or less.

In one aspect of the present invention, the particle size of the colloidal silica is 7 nm or more and 50 nm or less.

In one aspect of the present invention, the surface of the silicon wafer is polished at a polishing pressure of 50 g / cm ² or more and 600 g / cm ² or less.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings.

In the present embodiment, polishing is performed to flatten the surface of the silicon wafer according to the above-mentioned trench isolation method. FIG. 1 is a schematic diagram of a polishing apparatus (polisher) used for carrying out the polishing method of the present embodiment, and FIG. 2 is a partial view showing a silicon wafer to be polished by the polishing method of the present embodiment in process order. FIG.

In FIG. 1, the polishing apparatus 10 has a polishing plate (platen) 23, a wafer holding sample table 22 and a slurry introducing tube 26. The polishing plate 23 having a circular cross section is rotatably supported and fixed to the polishing plate rotating shaft 28 so as to be rotatable about the polishing plate rotating shaft 28. A polishing pad 24 is provided on the upper surface of the polishing plate 23, and a heater 29 for adjusting the polishing temperature is embedded in the polishing plate 23. In this embodiment, 30
Polishing plate 23 at a rotation speed of 80 rpm or more and 80 rpm or less
To rotate. This is because if the rotation speed is less than 30 rpm, sufficient polishing efficiency cannot be obtained, and if it exceeds 80 rpm, the stability of the entire polishing apparatus 10 is deteriorated and the polishing efficiency is rapidly reduced to the float polishing state. is there.

A wafer holding sample table 22 having a circular cross section of substantially the same shape as the silicon wafer 21 is rotatably supported and fixed to the sample table rotating shaft 27 so as to be rotatable around a sample table rotating shaft 27. Further, the silicon wafer 21 can be fixed to the lower surface of the wafer holding sample table 22 so as to face the polishing pad 24 by a vacuum chuck method. The polishing pressure of the silicon wafer 21 can be adjusted by changing the vertical position of the wafer holding sample table 22 together with the sample table rotating shaft 27.

The slurry introducing pipe 26 is connected to a slurry tank (not shown), and the slurry 25 stored in this slurry tank is fed from the tip of the slurry introducing pipe 26 to the central portion of the polishing pad 24 on the polishing plate 23. It is supplied, diffused to the peripheral portion by the rotation of the polishing plate 23, and comes to be interposed between the silicon wafer 21 and the polishing pad 24.

In this embodiment, the slurry is tetramethylammonium hydroxide (TMAH) with a concentration of 0.3 wt% and the particle size is 7 nm to 50 nm and the concentration is 5%.
An aqueous solution containing wt% of colloidal silica (colloidal silica) is used.

Next, the polishing method of this embodiment will be described in the order of steps.

The conditions for polishing the surface of the silicon wafer 21 were as follows. Rotational speed of polishing plate 23 35 rpm Rotational speed of wafer holding sample table 22 15 rpm Relative speed between silicon wafer 21 and polishing pad 24 (polishing relative speed) 6 cm / sec Polishing pressure 200 g / cm ² Slurry flow rate 200 ml / min Polishing temperature 32 ℃ Polishing time 30 seconds

First, as a pre-stage of polishing, the surface of the silicon wafer (silicon substrate) 1 is separated into elements by a trench isolation method. To do so, first, refer to FIG.
As shown in (a), a film thickness of 25 n is formed on the silicon wafer 1.
A silicon oxide film 2 having a thickness of about m and a silicon nitride film 3 having a thickness of about 30 nm are sequentially formed. Then, the silicon nitride film 3 and the silicon oxide film 2 in the portion where the groove is to be formed are selectively removed, and then the silicon wafer 1 is anisotropically etched using the silicon nitride film 3 as a mask to a depth of 300.
A groove 5 of about nm is formed. Thereafter, the silicon oxide film 4 having a film thickness of about 25 nm is formed on the side surface and the bottom surface of the groove 5 by thermal oxidation. The silicon oxide film 2 reduces the stress caused by the direct contact between the silicon wafer 1 and the silicon nitride film 3.

Next, as shown in FIG. 2B, TEOS
CV by plasma reaction of organic compounds such as ozone with ozone
A silicon oxide film 6 is formed on the entire surface by the D method and the groove 5 is filled. As a result, the silicon wafer 1 is element-separated by the groove 5. At this time, on the silicon nitride film 3,
A silicon oxide film 6 having a thickness of about 200 nm is deposited.

Next, as shown in FIG. 2C, the silicon wafer 1 is attached to the wafer holding sample table 22 shown in FIG. 1 by a vacuum chuck. Then, polishing of the surface of the silicon wafer 1 is started under the above conditions. Since the polishing efficiency under the above polishing conditions is 0.5 μm / min, by polishing the silicon wafer 1 for about 30 seconds, the silicon oxide film 6 except the inside of the groove 5 can be completely removed.
The surface of the silicon wafer 1 is flattened. At this time, since the silicon nitride film 3 serves as a stopper for polishing, the silicon oxide film 6 inside the groove 5 and the silicon wafer 1 may be polished even if polishing is performed for a long time with some margin. Absent. After that, after performing a simple cleaning to remove the slurry, elements such as MOS transistors (not shown) are formed on the convex portions of the silicon wafer 1 between the grooves 5.

In the present embodiment, CM using an aqueous solution containing TMAH and colloidal silica as a slurry
By performing the P polishing, a synergistic effect of the chemical polishing action of TMAH and the mechanical polishing action of colloidal silica occurs, so that the silicon oxide film 6 on the surface of the silicon wafer 1 can be removed by polishing with high polishing efficiency. Where TM
The chemical polishing action of AH occurs because the hydroxyl group (OH) in TMAH is bonded to the silicon of the silicon oxide film 6 and the surface thereof is easily polished. The polishing efficiency can be easily controlled by adjusting the concentration (pH) of TMAH.

Furthermore, since TMAH is composed only of oxygen, carbon, nitrogen and hydrogen and does not contain alkali metals such as sodium and potassium, it is different from conventional ones.
It is possible to prevent malfunctions of elements and deterioration of electrical characteristics due to contamination of the silicon oxide film 6 and the silicon wafer 1. Further, since the silicon oxide film 6 and the silicon wafer 1 are not contaminated, the step of cleaning and removing them is not required unlike the conventional case.

In this embodiment, the surface of the silicon wafer 1 is flattened by polishing when the elements are separated by the trench isolation method. However, the polishing method of the present invention uses an insulating film such as an interlayer insulating film, or polycrystalline silicon. Conductive films such as films and metal films, and single crystal silicon substrates (bare wafers)
It can also be applied to the flattening of

[0030]

EXAMPLES Next, examples in which the polishing conditions of the above embodiment are variously changed will be described.

Example 1 First, in the above embodiment, only the TMAH concentration condition was set to 0.
1, 0.2, 0.3, 0.5, 1.0, 2.0, 3.
A change in the polishing efficiency (μm / min) when changing to 0, 4.0, 5.0 and 6.2 (wt%) will be described. Table 1 shows the relationship between the TMAH concentration and the polishing efficiency at this time.
And FIG.

[0032]

[Table 1]

As is clear from Table 1 and FIG. 3, in order to maintain a realistic polishing efficiency of about 0.18 μm / min or more, the TMAH concentration in the slurry is 0.1 w.
It is preferably t% or more and 5.0 wt% or less. Further, by setting the TMAH concentration to 0.2 wt% or more and 0.6 wt% or less, a desired polishing efficiency of 0.3 μm / min or more can be obtained, and by setting it to about 0.3 wt%, 0.5 μm / min. It is possible to obtain an excellent polishing efficiency of about a minute.

Example 2 Next, how much the polishing efficiency (μm / min) changes when colloidal silica is used as the particles mixed in the TMAH aqueous solution and when silica powder is used in the above embodiment. explain.

When colloidal silica having a particle size of about 7 to 50 nm was mixed in the TMAH aqueous solution, a polishing efficiency of 0.5 μm / min could be obtained as described in the above embodiment. The polishing efficiency was 0.41 μm / min when silica powder having a particle size of about 7 to 40 nm was mixed in the TMAH aqueous solution under the same conditions except for the above.

Thus, when the colloidal silica is mixed in the TMAH aqueous solution, the polishing efficiency is excellent.
For one, colloidal silica forms an electric double layer and repels each other, and secondary particles due to agglomeration are less likely to be formed, so that the particles remain relatively small in size and have a large mechanical polishing action. It is thought to be from. Furthermore, it is considered that negative ions in the electric double layer of colloidal silica act to enhance the chemical polishing action of TMAH.

Example 3 Next, the polishing efficiency (μm / m 2) was obtained when only the polishing temperature conditions were changed to 32, 25 and 20 (° C.) in the above embodiment.
Minutes) will be described. Table 2 shows the relationship between the polishing temperature and the polishing efficiency at this time.

[0038]

[Table 2]

As is clear from Table 2, it is preferable that the polishing temperature is high, and in reality, the polishing temperature is preferably about 30 to 40 ° C.

Example 4 Next, in the above embodiment, only polishing pressure conditions of 50 and 20 were used.
The change in the polishing efficiency (μm / min) when it is changed to 0, 300 and 600 (g / cm ² ) will be described. Table 3 shows the relationship between the polishing pressure and the polishing efficiency at this time.

[0041]

[Table 3]

As is clear from Table 3, the higher the polishing pressure is, the higher the polishing ability can be obtained, but if the polishing pressure is less than 50 g / cm ² , the sufficient polishing ability cannot be obtained. If it exceeds 600 g / cm ² , scratches may be formed on the surface of the silicon wafer. Therefore, the polishing pressure is preferably 50 g / cm ² or more and 600 g / cm ² or less.

In the present invention, the concentration of colloidal silica or silica powder in the slurry is not particularly limited, but it is preferably 5 wt% or more and 10 wt% or less in reality.

As the particles mixed in the slurry, aluminum oxide (Al ₂ O) having a particle diameter of about 7 nm to 40 nm may be used in addition to colloidal silica and silica powder.
₃ ) or silicon carbide (SiC).

[0045]

As described above, according to the present invention,
When polishing a silicon wafer by the CMP method, TMA
The surface of the silicon wafer can be polished and planarized with sufficient polishing efficiency by the chemical polishing action of the H solution, and the silicon wafer is not contaminated because the TMAH solution does not contain an alkali metal. Therefore, it is not necessary to perform an extra step of sufficiently cleaning the silicon wafer to remove the alkali metal,
The element formed on the silicon wafer does not malfunction, and the electrical characteristics of the element are stable and hard to deteriorate. Therefore, it is possible to obtain a highly reliable semiconductor element by a simple process.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a polishing apparatus used for carrying out a polishing method according to an embodiment of the present invention.

FIG. 2 is a partial cross-sectional view showing a silicon wafer polished by a polishing method according to an embodiment of the present invention in the order of steps.

FIG. 3 is a graph showing the relationship between TMAH concentration and polishing efficiency in the present invention.

[Explanation of symbols]

 1, 21 Silicon wafer (silicon substrate) 2, 4, 6 Silicon oxide film 3 Silicon nitride film 5 Groove 10 Polishing device 22 Wafer holding sample stage 23 Polishing plate (platen) 24 Polishing pad 25 Slurry 26 Slurry introducing pipe 27 Sample stage Rotating shaft 28 Polishing plate Rotating shaft 29 Heater

Claims (7)

[Claims] 1. A tetramethylammonium hydroxide (hereinafter,
A method for polishing a silicon wafer, which comprises polishing the surface of the silicon wafer with an aqueous solution (referred to as "TMAH") interposed. 2. The method for polishing a silicon wafer according to claim 1, wherein the TMAH concentration in the TMAH aqueous solution is 0.1 wt% or more and 5.0 wt% or less. 3. The TMAH aqueous solution contains 5 wt% or more 1
The method for polishing a silicon wafer according to claim 1 or 2, wherein silica powder is mixed at a concentration of 0 wt% or less. 4. The method for polishing a silicon wafer according to claim 3, wherein the particle size of the silica powder is 7 nm or more and 40 nm or less. 5. The TMAH aqueous solution contains 5 wt% or more 1
The method for polishing a silicon wafer according to claim 1, wherein colloidal silica is mixed at a concentration of 0 wt% or less. 6. The particle size of the colloidal silica is 7 nm.
The method of polishing a silicon wafer according to claim 5, wherein the thickness is not less than 50 nm. 7. The surface of the silicon wafer is 50 g / c
The method for polishing a silicon wafer according to claim 1, wherein the polishing is performed at a polishing pressure of m ² or more and 600 g / cm ² or less.