JPH09167761A - Deposition of sog film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate crack from the protective film for underlying metallization. SOLUTION: After dripping SOG(spin on glass) liquid 4, a wafer 50 is turned at a low speed of 50-1000r.p.m. to spread the SOG liquid 4 flatly on an Al metallization 2 and an Si substrate. Subsequently, it is turned at a high speed of 4800r.p.m. or above within 5sec thus removing the SOG liquid 4 from the upper part of Al metallization 2. Consequently, substantially same quantity of SOG is deposited on the side A of Al metallization 2 contiguous to an adjacent Al metallization and the flat surface B side thereof.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for flattening an interlayer insulating film in a semiconductor device manufacturing process.
The present invention relates to a method for forming an OG film.

[0002]

2. Description of the Related Art In the process of manufacturing a semiconductor device, flattening of an interlayer insulating film between wirings is carried out in accordance with implementation of multilayer wiring. As a technique for flattening the interlayer insulating film, a method using SOG (Spin On Glass) has been conventionally known. For example, one of the flattening techniques using SOG is disclosed in Japanese Patent Laid-Open No. 7-142464. As shown in FIG. 13, the SOG film having excellent insulation and adhesion is formed by decomposing and removing the organic matter on the protective film covering the lower layer wiring, and then applying and baking the SOG liquid. The method is described.

When the interlayer insulating film is flattened, after forming a thick SOG film that completely covers the lower layer wiring in this way,
There is a method in which the entire surface of the wafer is etched back to flatten the upper surface of the SOG film. Alternatively, without etching back, the wafer is rotated at a relatively high speed before baking the applied SOG liquid to remove the SOG having a concave surface in the gap between the lower layer wirings or the stepped portion of the lower layer wirings. There is a way to leave.

The former method is a method for uniformly flattening a wafer, but has a drawback that the number of steps is increased because etching back is required. On the other hand, the latter method is not to flatten the wafer uniformly, but to make the level difference of the lower layer wiring smooth, and since it can be easily performed only by spin at the time of applying the SOG liquid, this method is used in the semiconductor manufacturing process. The method is often used.

[0005]

However, the conventional SOG film forming method has the following problems. Hereinafter, description will be made with reference to FIG. FIG. 2 is a diagram showing a conventional method of forming an SOG film. As shown in FIG. 2A, a wiring pattern 2 made of Al is formed on a wafer made of a Si substrate 1. The film thickness of the Al wiring 2 is 700 to 1000 nm, the line width is 0.8 to 1.0 μm, and the wiring interval is 0.8 to 1.2 μm.

Next, as shown in FIG. 2B, a film thickness of 100 to 300 is formed on the surface of the Si substrate 1 and the surface of the Al wiring 2.
A CVD film 3 having a thickness of about nm is formed. As the CVD film 3, PSG or P-SiO is used, which is Al
It serves as a protective film for the wiring.

Then, as shown in FIG. 2C, CVD
The SOG liquid 4 is applied on the film 3. At this time, SOG liquid 4
When is dropped, the SOG liquid 4 easily collects between the wirings 2 and does not easily collect in a flat portion. Then SO
When the wafer on which the G liquid 4 is dropped is rotated at a rotation speed of about 4500 rpm, as shown in FIG.
The amount of the OG liquid 4a does not change so much, but the S
The OG liquid 4b is shaken off and remains only on the side wall of the Al wiring 2.

Thereafter, the SOG film 4 is dehydrated by baking the wafer. In this baking process, 3
By performing a heat treatment for about 60 minutes at a temperature of 00 to 500 ° C., a dehydration reaction occurs in SOG to complete the interlayer insulating film.

By the way, in this baking step, an internal stress is generally generated in the Al wiring in the direction in which it expands, and an internal stress is generated in the CVD film and the SOG film in the direction in which it shrinks. However, as shown in FIG. 2D, when looking at the upper part of one Al wiring 2, the side where the adjacent Al wiring is adjacent (denoted by reference numeral A in the figure) and the flat surface side (denoted by reference numeral B in the figure). The amount of SOG present in that portion is significantly different from that shown in FIG.

In the CVD film 3 on the flat surface B having a small amount of SOG, the tensile stress generated by the expansion of Al is dispersed, so that no problem occurs. On the other hand, in the CVD film 3 on the side A of the Al wiring adjacent to a large amount of SOG, the tensile stress due to the expansion of Al is suppressed by the compressive stress of the SOG film 4a and cannot escape. Furthermore, on this side, the CVD film 3 and SO
The stress due to the difference in coefficient of thermal expansion from the G film 4a also increases. Therefore, stress imbalance occurs between the A wiring adjacent side A and the flat surface side B, and stress concentrates on the corner portions of the CVD film 3 on the Al wiring adjacent side A, so that this portion pops off on the CVD film 3. Cracks 5 occur. As a result, the insulation property and reliability of the Al wiring 2 are deteriorated.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for forming an SOG film which does not cause cracks in a protective film of a metal wiring as an underlayer. To do.

[0012]

In order to achieve the above object, a method of forming an SOG film according to the present invention covers a metal wiring formed on a substrate with a protective film, and forms a metal wiring on the protective film. In a method of forming an SOG film for reducing a step difference from the upper surface of a substrate by spin coating, after the SOG liquid is dropped on the substrate, S is dropped by rotating the substrate at a low speed.
The OG liquid is spread over the metal wiring and the substrate so that the upper surface thereof is flat, and then the substrate is rotated at a high speed so that at least the S portion above the metal wiring is exposed.
The feature is that the OG liquid is removed.

More specifically, after the SOG liquid is dropped on the substrate, the number of rotations when the substrate is rotated at a low speed is 500 to.
It is desirable to set the rotation speed to 1000 rpm, and thereafter to rotate the substrate at a high speed at 4800 rpm or more, and to set the time interval between the low speed rotation and the high speed rotation of the substrate to 5 seconds or less.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a diagram sequentially showing a method of forming an SOG film according to the present embodiment.

As shown in FIG. 1A, a wiring pattern 2 of Al is formed on a 5-inch diameter wafer made of a Si substrate 1.
Are formed. The thickness of the Al wiring 2 is 700 to
The thickness is 1000 nm, the line width is 0.8 to 1.0 μm, and the wiring interval is 0.8 to 1.2 μm.

Next, as shown in FIG. 1B, a film thickness of 100 to 300 is formed on the surface of the Si substrate 1 and the surface of the Al wiring 2.
A CVD film 3 having a thickness of about nm is formed. As the CVD film 3, PSG or P-SiO is used, which is Al
It serves as a protective film for the wiring 2. The steps up to this point are the same as in the conventional method.

Then, as shown in FIG.
The SOG liquid 4 is applied on the film 3. Normally, the SOG liquid 4 easily enters a narrow space such as between the Al wirings 2,
It has a property that it is hard to remain on a relatively wide flat portion such as the 1 wiring 2 or the Si substrate 1. Therefore, the SOG liquid 4 is dropped so as to completely cover the CVD film 3 and sufficiently remain on the Al wiring 2 and the Si substrate 1. For example, the diameter is 5
Inch wafer has 2-3 cc.

Then, the wafer on which the SOG liquid 4 has been dropped is rotated at a low speed, for example, at a rotation speed of about 500 to 1000 rpm for 0.2 to 0.5 seconds, whereby the Al wiring 2 is formed.
The SOG liquid 4 is spread so that the upper surface of the film becomes substantially flat regardless of the presence or absence of the pattern. Then, turn off the power of the rotary motor and lower the rotation speed until the rotation stops completely, that is, normally, within 5 seconds, rotate at a high speed, for example, increase the rotation speed to 4800 rpm or more to obtain an extra SOG liquid. Only 4 is shaken off, and as shown in FIG. 1D, the same amount of SOG liquid 4 remains on the narrow side A between the Al wirings 2 and the wide flat side B. It should be noted that, while the speed is increased to the high speed rotation, the low speed rotation is performed again, but since this is a very short time, this can be ignored.

For example, when the rotation speed of the low speed rotation is less than 500 rpm, the SOG liquid dropped on the central portion of the wafer does not spread sufficiently, so that the thickness of the SOG film 4 of the central chip of the wafer and the SOG film 4 of the peripheral chip of the wafer are reduced. The thickness difference of the SOG film 4 on the wafer peripheral chip becomes extremely large, as shown in FIG. 1C.
It does not reach the D film 3. That is, the SOG film 4
2 has the same form as that shown in FIG. 2C shown as the prior art. Therefore, the SO on the Al wiring 2 is rotated by rotating this wafer.
The G film 4 is removed, and as shown in FIG.
The same amount of SOG film 4 cannot be left on the narrow side A and the wide flat part side B. Therefore, the lower limit of the rotation speed at low speed rotation is set to 500 rpm.

On the other hand, when the rotation speed of the low-speed rotation is 1000 rpm or more, the centrifugal force acting on the wafer increases as the rotation speed increases, and the ratio of the SOG that is flown outside the wafer to the SOG dropping amount increases. Therefore, the amount of SOG remaining in the wafer, especially in the portion excluding between the Al wirings 2, is reduced. Then, the thickness of the SOG film 4 does not reach the CVD film 3 on the Al wiring 2 after all, and like the above, only the thin SOG film 4 on the wide flat portion side B can be formed. Therefore, the upper limit of the rotation speed at low speed rotation is set to 1000 rpm.

When the rotation speed of the high speed rotation is set to less than 4800 rpm, the SOG film 4 remains on the CVD film 3 on the Al wiring 2 and the SOG film 4 between the Al wirings 2 and the SOG on the flat portion side. Since the films are continuously connected, the desired semiconductor structure cannot be obtained. Therefore, the lower limit of the rotation speed at the time of high speed rotation is set to 4800 rpm.

Regarding the time interval between the low speed rotation and the high speed rotation, when the time interval exceeds 5 seconds, the rotation of the wafer stops completely, so that the dropped SOG liquid is not splashed to the outside of the wafer. Penetrates to the back side of the wafer. However, if the SOG liquid permeates the back surface of the wafer, the SOG liquid permeated in the subsequent drying process, wafer transfer process, or the like becomes a powder state and causes particles, which is not preferable. Therefore, the upper limit of the time interval between the low speed rotation and the high speed rotation is set to 5 seconds. It should be noted that this 5 seconds is a case of a typical spin coater and may be any time as long as the rotation of the wafer is not completely stopped.

After forming the SOG film 4 into a predetermined shape, the wafer is baked to dehydrate the SOG film 4. In this baking process, 300-500 ° C
When the heat treatment is performed at the temperature of about 60 minutes, a dehydration reaction occurs in SOG to complete the interlayer insulating film.

According to the SOG film forming method of the present embodiment, as shown in FIG. 1D, when one Al wiring 2 is viewed, the side A adjacent to the adjacent Al wiring and the flat surface are formed. The amount of SOG present in that portion can be the same on side B. Therefore, when heat is applied to the wafer in the baking process, the tensile stress of the CVD film 3 due to the thermal expansion of Al causes SOG.
The degree of suppression by the compressive stress of the film 4 is almost the same on the side A adjacent to the Al wiring and the side B on the flat surface, and the CVD film 3 and the SO
The stress due to the difference in the coefficient of thermal expansion of the G film 4 is about the same for both.

That is, the stress is balanced between the side A adjacent to the Al wiring and the side B on the flat surface, and the stress is not concentrated on one side as in the case of using the conventional forming method, so that the CVD film 3 is cracked. Never. Therefore, it goes without saying that the SOG film fulfills its original purpose of flattening.
The insulation and reliability of the Al wiring can be improved as compared with the conventional forming method.

The technical scope of the present invention is not limited to the above embodiment, and various changes can be made without departing from the spirit of the present invention. For example, in the present embodiment, the case where a 5-inch wafer is used is shown as an example. However, even if the diameter of the wafer is slightly increased, if the drop amount of SOG is about several cc, the amount of SOG remaining on the wafer after the wafer is rotated. Becomes saturated,
The effect of the present invention can be obtained similarly. Therefore, even for wafers having different diameters, the method of the present invention can be realized by setting only the number of rotations of the wafer during low speed rotation and high speed rotation within the above-mentioned range.

[0027]

As described above in detail, according to the method for forming an SOG film of the present invention, S existing in the portion of the metal wiring adjacent to the adjacent metal wiring and on the flat surface side.
Since the amount of OG can be made approximately the same, the tensile stress due to the thermal expansion of the metal wiring and the compressive stress of the SOG film that occur in the protective film when heat is applied to the wafer during the baking process are applied to the metal wiring side and the flat surface. Can be balanced on the side. Therefore, unlike the case where the conventional forming method is used, stress is not concentrated on one side, so that the protective film covering the metal wiring is not cracked, and the insulating property and reliability of the metal wiring are improved. You can

[Brief description of the drawings]

FIG. 1 is a diagram sequentially showing a method of forming an SOG which is an embodiment of the present invention.

FIG. 2 is a diagram sequentially showing a conventional SOG forming method.

[Explanation of symbols]

 1 Si substrate 2 Al wiring (metal wiring) 3 CVD film (protective film) 4, 4a, 4b SOG film (SOG liquid) 5 Crack

Claims (3)

[Claims] 1. A method of coating a metal wiring formed on a substrate with a protective film, and forming an SOG film for reducing the step between the metal wiring and the upper surface of the substrate on the protective film by spin coating. After the SOG liquid is dropped on the substrate, the substrate is rotated at a low speed to spread the dropped SOG liquid over the metal wiring and the substrate so that the upper surface thereof is flat, and then the substrate is rotated at a high speed. By doing so, at least a portion of the SOG liquid above the metal wiring is removed, thereby forming a SOG film. 2. The method for forming an SOG film according to claim 1, wherein after the SOG liquid is dropped on the substrate, the rotation speed when the substrate is rotated at a low speed is 500 to 1000 rpm,
After that, the rotation speed when rotating the substrate at a high speed is 4800.
A method for forming an SOG film, characterized in that the speed is at least rpm. 3. The method for forming an SOG film according to claim 1, wherein the time interval between the low speed rotation and the high speed rotation of the substrate is within 5 seconds.