JPH04296018A - Metal plug forming method - Google Patents

Abstract

PURPOSE:To form a highly reliable metal plug by suppressing the overhang of a close-adhesion layer in a metal plug forming method in a semiconductor integrated circuit. CONSTITUTION:Close adhesion layers 15a and 15b are formed on an insulating film 13, containing connection hole 14, using a method with which a metal plug 16A is formed in the connection hole 14 of an insulating film 13. The close adhesion layer on the shoulder part of the connection hole 14 is selectively removed, the close adhesion layer 15a in the connection hole 14 and the close adhesion layer 15b on the insulating film 13 are separated. Then, a blanket tungsten layer 16 is formed in deposition, the blanket tungsten 16 and the close adhesion layer 15b on the insulating film 13 are removed, and a highly reliable metal plug 16A is formed.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] With the miniaturization and high integration of semiconductor integrated circuits, the present invention is suitable for use in connection, for example, in via holes that connect layers of multilayer wiring, or in contact holes that connect semiconductor substrates and wiring. The present invention relates to a method of forming a so-called metal plug in which metal is embedded.

0002

[Background Art] In semiconductor integrated circuits such as next-generation ultra-super LSIs, as they become smaller and more highly integrated, via holes that connect layers of multilayer wiring, contact holes that connect semiconductor substrates and wiring, etc. The opening diameter of the connection hole is becoming smaller and smaller, for example, 0.35 μm□. Therefore, with the conventional Al bias sputtering method, it has become impossible to reliably form wiring within the connection hole from the viewpoint of step coverage. Therefore,
Metal plug technology is being put into practical use as a method to improve step coverage. This technique is a method of selectively embedding metal plugs into connection holes such as the above-mentioned via holes or contact holes. In this metal plug technology, as the aspect ratio of the connection hole increases, the resistance of the plug itself becomes a problem, so tungsten plugs with low resistance, for example, are attracting attention. In the formation of this tungsten plug, selective tungsten CVD is also used.
There are two methods, the blanket tungsten CVD method and the blanket tungsten CVD method, but the blanket tungsten method is attracting attention because it is advantageous in terms of process stability and plug formation in connection holes of different depths.

FIG. 4 shows a conventional method for making wiring connections using the metal plug technology described above. That is, as shown in FIG. 4A, after forming a lower layer wiring 2 using a diffusion layer on a silicon substrate 1, for example, a lower layer wiring 2 is formed on the upper surface of the silicon substrate 1.
After forming an insulating film 3 such as the above, and forming a contact hole 4 in this insulating film 3, an adhesion layer 5 made of, for example, a TiN film is formed on the entire upper surface of the insulating film 3, including the inside of the contact hole 4. . Next, as shown in FIG. 4B, a blanket tungsten layer 6 made of a high melting point metal, for example, is deposited on the entire surface including the inside of the connection hole 4 by CVD. Next, as shown in FIG. 4C, tungsten is etched back so that it remains only in the connection hole 4, thereby forming the metal plug 6A. After that, upper layer wiring 7 connected to metal plug 6A is formed. Note that it is possible to form a TiSi2 film 8, which is a heat-resistant layer, on the surface of the lower wiring 2 formed by the diffusion layer by the SITOX (silicization through oxide) method.

0004

However, since the method of forming the metal plug 6A using blanket tungsten includes an etch-back process, the stability of the etch-back process is a problem. In particular, as shown in FIG. 5, the coverage of the adhesion layer (TiN film) 5 that also serves as a barrier metal is poor, and overhang 10 is likely to occur. On the other hand, when etching the adhesion layer 5, the etching rate changes due to the macro loading effect (an extreme change in the etching area ratio).In particular, in the case of the adhesion layer, since its thickness is thin, the decrease in the area ratio is extreme. Due to the combination of the following two points: (1) and the difficulty in controlling over-etching, there are cases where the adhesive layer 5 is over-etched compared to the tungsten plug 6A when the adhesive layer 5 is etched, as shown in FIG. Therefore, concerns remain about the reliability of the process when forming the upper layer wiring 7.

In view of the above points, the present invention provides a method for forming a metal plug suitable for miniaturization and high density.

[0006]

[Means for Solving the Problems] The present invention provides a method for forming a metal plug 16A in a contact hole 14 of an insulating film 13, in which an adhesive layer 15 is formed on the insulating film 13 including the inner surface of the contact hole 14.
a step of selectively removing the adhesion layer 15 at the shoulder of the connection hole 14 to separate the adhesion layer 15 inside the connection hole 14 and on the insulating film 13; and after forming the metal layer 16. The method is characterized in that it includes a step of etching back to form a metal plug 16A in the connection hole 14.

[0007]

[Operation] In the present invention, after forming the adhesive layer 15 including the inside of the connection hole 14, the adhesive layer 15 at the shoulder part of the connection hole 14 is selectively removed to insulate the adhesive layer 15a inside the connection hole 14. By separating the adhesive layer 15b from the film 13, only the adhesive layer 15b on the insulating film 13 will be removed when the deposited metal layer 16 is etched back and the adhesive layer 15 is further etched away. You can have sex back. That is, the adhesive layer 15a in the connection hole 14 is not over-etched. Therefore, the reliable metal plug 1
6A, and the reliability of the process when forming the upper layer wiring 17 thereafter is improved.

[0008]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 3.

In this example, first, as shown in FIG. 1A, a lower layer wiring 12 made of a diffusion layer is formed on one surface of a semiconductor substrate 11, for example. In this case, a TiSi2 film 18, which is a heat-resistant layer, is formed by the SITOX method on the surface of the diffusion layer. An insulating film 1 of SiO2 etc. is formed on this substrate 11.
3 is formed, and a connection hole 14 is formed by dry etching through a resist mask (not shown).

Next, as shown in FIG. 1B, an adhesive layer 15 of TiN or the like is deposited on the insulating film 13 including the inside of the connection hole 14 by sputtering or the like. As sputtering conditions, reactive sputtering using a normal Ti target and N2 gas can be used.

Next, as shown in FIG. 1C, the shoulder portion 20 of the adhesion layer 15 is selectively etched away by so-called horizontal return etching using, for example, a bias ECRCVD method, and the overhang of the adhesion layer 15 is shaped. That is, at the same time as shaping, the adhesive layer 15a in the connection hole 14 and the insulating film 13 are
The upper adhesive layer 15b is separated from each other. In horizontal return etching, the etching rate and the deposition rate are equal for flat surfaces (horizontal surfaces) (that is, the overall etching rate is 0), and the etching rate is larger than the deposition rate for oblique surfaces ( That is, the etching is performed by bias ECRCVD under conditions in which the overall etching rate is greater than 0. This is called horizontal return etching because it allows etching to recede horizontally an angled surface without etching a flat surface. 27792
Various proposals are being made through issues such as No. 9.

The conditions for this horizontal return etching are as follows:
Supply gas SiH4 (25SCCM)/N2O (35
SCCM), pressure is 7 x 10-4 Torr, microwave power is 800W, bias RF power is 500W.
It is W. At this time, the overhang of the adhesive layer 15 is removed as shown in the figure.

Next, as shown in FIG. 2D, a blanket tungsten layer 16 made of a high melting point metal, for example, is formed by CVD. This CVD condition is, for example, a supply gas W
F6:H2 = 1:6, temperature 475℃, pressure 80To
This can be done by setting it to rr.

Next, as shown in FIG. 2E, blanket tungsten layer 16 is etched back. This is RIE
(reactive ion etching). As the RIE conditions, for example, the supply gas SF6 is
SCCM supplied, pressure 50mTorr, power 0.08
This can be done by setting it to W/cm2. At this time, it is desirable to stop the tungsten etchback at the position shown in FIG. 2E.

Next, as shown in FIG. 2F, the adhesive layer 15 on the insulating film 13 is removed by etching. The etching conditions at this time are, when the adhesion layer 15 is a TiN film, the supply gas Cl2 (30SCCM)/Ar (20SCCM),
Pressure 0.015mTorr, power 0.23W/cm2
This can be done by setting it to . When etching the adhesive layer 15, since the adhesive layer 15a inside the contact hole 14 and the adhesive layer 15b on the insulating film 13 are separated, only the adhesive layer 15b on the insulating film 13 is etched away, and the adhesive layer 15b inside the contact hole 14 is etched away. The adhesive layer 15a is not over-etched. In this way, the metal plug 16A is inserted into the connection hole 14.
is formed.

After that, as shown in FIG. 3G, the insulating film 1
The upper layer wiring 17 connected to the metal plug 16A is formed on the upper layer 3 to complete the desired multilayer wiring. It goes without saying that the above conditions are not limited to the above examples. For example, if there is a concern that deposition will occur on the horizontal surface due to variations in the conditions of horizontal return etching, a gas such as SiH4/Ar may be used.

According to this embodiment, after the connection hole 14 is formed, the adhesive layer 15 is formed, and then the adhesive layer 15 corresponding to the shoulder of the connection hole 14 is selectively removed by horizontal return etching. As a result, overhang of the adhesive layer 15 is suppressed, and the adhesive layer 15a inside the connection hole 14 and the adhesive layer 15b on the insulating film 13 are separated. Therefore, when the blanket tungsten layer 16 is then formed and the blanket tungsten layer 16 and the adhesive layer 15 below it are etched away, only the adhesive layer 15b on the insulating film 13 is removed in the adhesive layer 15. The adhesive layer 15a in the connection hole 14 is not over-etched. Therefore, a highly reliable metal plug 16A can be formed, and the reliability of the subsequent process for forming the upper layer wiring 17 is improved. In the above example, a diffusion layer is used as the lower layer wiring 12, but it goes without saying that the present invention can also be applied to other types of lower layer wiring. Further, the metal plug forming method of the present invention can be applied to via holes and contact holes.

[0018]

According to the method for forming a metal plug of the present invention, after forming an adhesion layer including the inside of the connection hole of the insulating film, the adhesion layer at the shoulder of the connection hole is selectively removed. Overhang of the adhesion layer is suppressed, making subsequent embedding of the metal layer advantageous. In addition, by selectively removing the adhesive layer, the adhesive layer inside the contact hole and the adhesive layer on the insulating film are separated, so that when the metal layer and adhesive layer are etched back,
Only the adhesive layer on the insulating film is removed, and over-etching of the adhesive layer in the connection hole is avoided. Therefore, it is possible to form a good and highly reliable metal plug, and it is also possible to improve the reliability of the subsequent process for forming upper layer wiring.

[Brief explanation of drawings]

FIG. 1 is a manufacturing process diagram (Part 1) showing an example of the method for forming a metal plug of the present invention.

FIG. 2 is a manufacturing process diagram (part 2) showing an example of the method for forming a metal plug of the present invention.

FIG. 3 is a manufacturing process diagram (Part 3) showing an example of the method for forming a metal plug of the present invention.

FIG. 4 is a manufacturing process diagram showing an example of a conventional metal plug forming method.

FIG. 5 is an explanatory diagram of a conventional example.

[Explanation of symbols]

11 Semiconductor substrate 12 Lower layer wiring 13 Insulating film 14 Connection hole 15, 15a, 15b Adhesive layer 16 Blanket tungsten layer 16A metal plug 17 Upper layer wiring

Claims (1)

[Claims] 1. A method for forming a metal plug in a contact hole of an insulating film, comprising the steps of: forming an adhesive layer on the insulating film including inside the contact hole; and selectively forming an adhesive layer on the shoulder of the contact hole. a step of separating the adhesive layer between the inside of the connection hole and the top of the insulating film; and a step of etching back the metal layer after forming the metal layer to form a metal plug in the connection hole. How to form a metal plug.