JPH10209092A - Wafer abrasives and manufacture of semiconductor device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of plug loss and microscratch, by properly setting the average grain diameter of silica and the amount of NH4 OH. SOLUTION: Silica whose average primary grain diameter is 40-110nm, NB4 OH of 0.01-0.03mol/l and organic oxidizing agent are contained in wafer abrasives for chemically and mechanically polishing a tungsten film, a tungsten plug free from plug loss is formed, and generation of microscratch can be prevented. When the amount of NH4 OH exceeds 0.03mol/l, the wet-etching rate becomes high, and a large plug loss is formed. When the amount of NH4 OH is at most 0.01mol/l, the abrasive rate becomes too low. A practical abrasive rate can be ensured in the condition that the average primary grain diameter of silica is 40nm. When the average primary grain diameter of silica exceeds 110nm, microscratch is generated on the surface of an oxide film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an abrasive used when a tungsten film on a semiconductor wafer is polished and removed by a chemical mechanical polishing method, and a method for manufacturing a semiconductor device using the abrasive.

[0002]

2. Description of the Related Art The aspect ratio of connection holes (contact holes and via holes) for connecting upper and lower conductor layers has been gradually increased due to recent miniaturization of semiconductor devices and multi-layered wiring. It has become difficult to bury the inside of the connection hole with the Al film caused by this. As a means for compensating for this, a tungsten plug method of filling the inside of a connection hole with tungsten (W) by a CVD method having good step coverage has been widely adopted.

In this case, a method is used in which after depositing a tungsten film, tungsten other than in the via holes is removed by using etch back by dry etching. However, this method uses W
When removing, it is necessary to remove a little more so as not to cause a residue to be removed, so that tungsten in the upper portion in the via hole is also slightly removed, so that a so-called plug loss is formed. This plug loss becomes a depression on the wiring when the wiring is formed in a later step, so that good conduction cannot be obtained even if the next via hole is formed thereon. That is, the via holes cannot be stacked. Therefore, as a means for eliminating plug loss, chemical mechanical polishing (hereinafter, referred to as C) of tungsten on a wafer is performed.
(Also referred to as MP) method.

FIG. 3 is a cross-sectional view in the order of steps for explaining an example of forming a tungsten plug by a CMP method. Lower Al wiring layer 3 on first interlayer insulating film 2 on semiconductor substrate 1
Is provided, and the upper surface is covered with a second interlayer insulating film 4 [FIG.
(A)]. The second interlayer insulating film 4 is selectively etched using a photolithography method and an RIE (reactive ion etching) method to form a via hole 5 exposing the surface of the lower Al wiring 3 (FIG. 3B). ]. After the barrier metal layer 6 is formed by depositing titanium (Ti) and subsequently depositing titanium nitride (TiN) or only titanium nitride by sputtering, a tungsten film filling the via hole 5 by CVD. 7 (FIG. 3C).

The surface of the wafer is polished using an alkaline colloidal silica solution containing silica having an average particle diameter of about 30 nm and a pH of about 9 to 12 to polish and remove the tungsten film 7 on the second interlayer insulating film 4 to form a via hole. 5, a tungsten plug 7a is formed to bury the inside of FIG.
(D)]. Next, an aluminum alloy film is deposited by a sputtering method, patterning is performed using a photolithography method and a dry etching method, and an upper Al wiring 8 connected to the lower Al wiring 3 through a via hole is formed [FIG. e)).

[0006]

In a conventional example in which a tungsten film on a wafer surface is polished and removed by a CMP method, a slurry having a high pH is used as a polishing agent. Etching results in plug loss as in the case of using the etch-back method. In order to avoid this, when using a slurry whose pH is lowered to near 7 (for example, pH 7.2, silica average primary particle size 20 to 110 nm)
In this case, the tungsten is hardly polished, the throughput is reduced, and the tungsten is not practical. Further, as a method of improving the mechanical polishing ability, the average primary particle size of silica is set to 200 nm
Methods of increasing the size or using an acidic abrasive containing alumina as a main component (for example, pH 3.2, alumina average primary particle size of 230 nm, etc.) have been proposed, and CMP is performed using these abrasives. As a result, micro-scratch occurs frequently on the surface of the silicon oxide film exposed after the removal of the tungsten film. Therefore, the problem to be solved by the present invention is to provide a wafer polishing agent for chemical mechanical polishing of a tungsten film, which can prevent the occurrence of plug loss and micro-scratch without lowering the throughput.

[0007]

The above objects of the present invention can be solved by appropriately setting the average particle size of silica and the amount of NH ₄ OH to be added.

[0008]

DETAILED DESCRIPTION OF THE INVENTION A wafer abrasive for chemical mechanical polishing of a tungsten film according to the present invention has an average primary particle diameter of 40 to 1.
10 nm silica, 0.01-0.03 mol / l N
It is characterized by containing H ₄ OH and an organic oxidizing agent. And, preferably, the pH is 8.0 to 8.0.
8.5, oxidation-reduction potential (ORP) is + 550-650m
V (liquid temperature 23 ° C.).

[Action] To 1250 ml of a silica slurry (20 wt%) having an average primary particle diameter of 80 nm, 20 g of an organic oxidizing agent (for example, hexamethylenetetramine) and 500 ml of pure water are added, and the amount of the 3% ammonia aqueous solution is changed. To prepare an abrasive, and then performed CMP. FIG. 1 shows the relationship between the amount of NH ₄ OH in the slurry and the polishing rate together with the wet etching rate using the same polishing agent.
When the amount of NH ₄ OH exceeds 0.03 mol / l, the wet etching rate increases and a large plug loss is formed. In addition, the amount of NH ₄ OH is 0.01 mol /
If it is less than 1, the polishing rate will be too low to be practical. Next, the polishing rate dependence of the average primary particle size of silica was examined. In the CMP with the above-mentioned wafer abrasive, 20
Although a polishing rate of 0 ° / min was obtained, the average primary particle size was 3
When silica having a particle diameter of 0 nm was used (the other conditions
nm), the polishing rate was reduced to 100 ° / min. However, it has been found that a polishing rate of 140 ° can be obtained with a particle size of 40 nm, and a polishing rate that can be practically used can be secured. When the average primary particle size of silica exceeded 110 nm, micro scratches were observed on the surface of the silicon oxide film after polishing.

It is desirable to add an organic oxidizing agent to the wafer polishing agent to impart a certain oxidizing ability. Figure 2 shows the oxidation reduction potential of the abrasive.
ORP) (liquid temperature 23 ° C.) and the tungsten polishing rate. By maintaining the ORP at +550 to 650 mV (at a liquid temperature of 23 ° C.), a high polishing rate can be obtained. The pH of the wafer polishing agent is almost governed by the concentration of NH ₄ OH, but also changes depending on the amount of the organic oxidizing agent added. By adjusting the addition amount of NH ₄ OH and the organic oxidizing agent to keep the pH within the range of 8 to 8.5,
A more preferable abrasive can be obtained.

[0011]

【Example】

[First Example] 20 g of an organic oxidizing agent (for example, hexamethylenetetramine) and 500 g of pure water were added to 1250 ml of a silica slurry (20 wt%) having an average primary particle diameter of 80 nm.
Then, the pH was adjusted to 8.2 by adding 40 ml of a 3% ammonia aqueous solution, and the tungsten film on the silicon wafer was subjected to CMP under the following conditions. Slurry dripping amount = 50 cc / min Polishing pad rotation speed = 35 rpm Wafer holding head rotation speed = 35 rpm Wafer pressure = 0.44 kg / cm ² The polishing rate of tungsten is 200 ° / min.
The polishing rate of the silicon oxide film under the same conditions is about 180 ° /
min. As a result of this polishing, the dissolution of tungsten in the via hole and the micro scratch on the silicon oxide film did not occur.

[Second Embodiment] A commercially available alkaline slurry (for example, PLANERLI manufactured by Fujimi)
TE5101, average primary particle diameter 30 nm, pH 9.6
4, oxidation-reduction potential +555 mV), and the tungsten film on the wafer was subjected to CMP under the following conditions. Slurry dripping amount = 50 cc / min Polishing pad rotation speed = 35 rpm Wafer holding head rotation speed = 35 rpm Wafer pressure = 0.44 kg / cm ² The polishing rate of tungsten was about 1100 ° / min.

However, since the slurry under the above conditions dissolves even the tungsten in the via hole, the CMP is temporarily stopped in a state where the tungsten still remains on the entire surface of the wafer, and then the silica slurry having an average primary particle diameter of 100 nm (20 wt% ) 1250 ml of organic oxidizing agent (for example, hexamethylene theramine etc.) 20 g and pure water 500
The slurry was adjusted to pH = 8.3 and oxidation-reduction potential = 595 mV by adding 40 ml of a 3% ammonia aqueous solution, and tungsten was finally left only in the via hole. In this method, it is troublesome to use two kinds of slurries, but the throughput is improved. As a result of this polishing, the dissolution of tungsten in the via hole and the micro scratch on the silicon oxide film did not occur.

[0014]

As described above, by performing CMP of tungsten with the slurry according to the present invention, it is possible to prevent the tungsten in the via hole from being dissolved while maintaining the polishing rate in a practically usable range. Can be formed without any tungsten plug. Further, it is possible to prevent the occurrence of micro-clutch on the silicon oxide film, and to improve the product yield. Further, according to the embodiment in which the tungsten film is partially polished with a slurry that is usually used, and thereafter the slurry according to the present invention is used, a semiconductor device without plug loss and micro scratch can be obtained with high throughput.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between NH ₄ OH added to a slurry and a polishing rate for explaining the operation of the present invention.

FIG. 2 is a graph showing the relationship between the oxidation-reduction potential of a slurry and the polishing rate for explaining the operation of the present invention.

FIG. 3 is a sectional view in order of process for describing a manufacturing process of a tungsten plug.

[Explanation of symbols]

 Reference Signs List 1 semiconductor substrate 2 first interlayer insulating film 3 lower layer Al wiring 4 second interlayer insulating film 5 via hole 6 barrier metal layer 7 tungsten film 7a tungsten plug 8 upper layer Al wiring

Claims (5)

[Claims] 1. A wafer polishing agent for chemical mechanical polishing comprising silica having an average primary particle diameter of 40 to 110 nm, NH ₄ OH of 0.01 to 0.03 mol / l, and an organic oxidizing agent. . 2. The wafer polishing agent according to claim 1, wherein the pH is 8.0 to 8.5. 3. The oxidation-reduction potential (ORP) is + 550-6.
2. The wafer polishing agent according to claim 1, wherein the polishing agent has a temperature of 50 mV (liquid temperature: 23 [deg.] C.). 4. A step of: (1) depositing an interlayer insulating film on a lower conductive layer; and (2) connecting holes for selectively etching away the interlayer insulating film to expose the surface of the lower conductive layer. (3) a step of depositing tungsten on the entire surface to form a tungsten film filling the connection holes, and (4) silica having an average primary particle diameter of 40 to 110 nm.
The tungsten film on the interlayer insulating film is polished and removed by chemical mechanical polishing using a wafer abrasive containing 01 to 0.03 mol / l of NH ₄ OH and an organic oxidizing agent, and tungsten is formed only in the connection holes. And (5) a step of depositing a metal film and patterning the same to form an upper wiring layer connected to the lower conductive layer. 5. After the step (3), the step (4)
5. The method according to claim 4, wherein, prior to the step, the tungsten film is chemically and mechanically polished using an alkaline colloidal silica solution having a pH of 9 or more as an abrasive to the extent that the surface of the interlayer insulating film is not exposed. A method for manufacturing a semiconductor device.