JPH0555165A - Opening for wiring and method of forming the same - Google Patents

Abstract

PURPOSE:To improve the shape of tungsten plug to be formed in a contact hole and to prevent an increase in resistance of the plug. CONSTITUTION:Shapes of vertical surfaces of a contact hole formed in an interlayer insulating film 11 are asymmetrically formed, and a seam of a tungsten film 15 to be formed by a blanket WCVD in a later step is obliquely formed, thereby preventing enlarging of the seam by etching back. Thus, generation of voids in the tungsten plug can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wiring opening such as a contact hole in a semiconductor device and a method for forming the same.

[0002]

PRIOR ART AND PROBLEMS TO BE SOLVED BY THE INVENTION Recently, L
With the high integration of SI, it is becoming difficult to bury a metal in a contact hole that is miniaturized by a conventional sputtering method without a void. For example,
In the submicron design rule, the reflow technique of the interlayer film after opening the contact hole and the bias sputtering technique of Al have been dealt with. However, in the half-micron and sub-half-micron design rules, it is difficult to fill a contact hole having a high aspect with a conventional sputtering method.

A contact hole filling technique using a CVD method such as selective tungsten or blanket tungsten, which is excellent in filling ability with respect to the sputtering method, has been actively studied in recent years as a promising candidate for a hole filling technique for a next-generation LSI.

The hole-filling method by selective tungsten CVD is an attractive method in that the number of steps is small and the generation of particles is suppressed. However, the selective CVD basically utilizes the difference in the surface condition, and in order to keep the surface condition constant, it is necessary to develop a corresponding pretreatment technique. Is hard to selectively grow like titanium nitride (TiN), or TiS even if it grows like titanium silicide (TiSi _x ).
A non-conductor such as TiF ₃ is formed at the interface between i _x and tungsten, and when tungsten is directly grown on Si, heat resistance cannot be expected to be about 600 ° C. There are many problems that need to be resolved in order to achieve this.

Therefore, the general view is that the blanket tungsten filling technology is first put into practical use.

In this blanket tungsten filling technique, the tungsten film is deposited on the entire surface of the substrate while filling the contact hole with the CVD tungsten film having a very good step coverage, and then the etch back is performed to leave the tungsten only in the contact hole. Take the step of saying. At this time, a layer such as TiN used as an adhesion layer of tungsten has a function of preventing the reaction between the tungsten and the underlying Si, so that a certain degree of heat resistance can be obtained. Also, unlike selective tungsten, there is an advantage that holes having different depths can be embedded and planarized at the same time.

In the future, a method of directly patterning the tungsten film may be considered because tungsten is also used as the upper wiring layer, but in this case, a tungsten film having a good morphology and good morphology should be deposited. Of course, these are CVD conditions that are in conflict with each other, which makes it difficult to realize.

Therefore, in the current application of blanket tungsten technology, a tungsten etchback process must be performed.

22 to 27 show a conventional method using a tungsten etch-back process. In this method, first, as shown in FIG. 22, on a silicon substrate 1,
An interlayer insulating film 2 made of SiO ₂ is deposited, and then a contact hole 3 is opened. Next, as shown in FIG. 23, an adhesion layer 4 having a laminated structure of titanium nitride (TiN) and titanium (Ti) is formed on the entire surface. Then, FIG. 24 and FIG.
As shown in, the tungsten film 5 is grown by the blanket tungsten CVD method to fill the contact hole 3. Then, the tungsten film 5 is etched back to be as shown in FIG. 26, and then the aluminum-based alloy film 6 is deposited to form wiring.

However, this tungsten etch-back process has the following problems. That is, the grain boundary boundaries of polycrystalline tungsten that grow from the contact sidewalls and hit each other (this is called a tungsten seam and shown by a broken line in the figure) exist along the center line of the contact. As shown in FIG. 26, the seam expands during the etch back to form the hole 5a in the plug. The expansion of the seam during the etch back is not a serious problem when the aspect ratio is small. However, this is a serious problem because the proportion of seams increases for contacts with a large aspect ratio.

If the tungsten seam expands and becomes void-like, the following problems occur, for example.

(A) Since no current flows in the seam portion, the resistance of the tungsten plug itself increases, and the increase in contact resistance cannot be ignored especially when it is used as a via hole.

(B) When this is insufficient, although depending on the step coverage of the barrier metal of the wiring layer formed on the upper layer of tungsten, the alloying reaction between the upper layer wiring and tungsten occurs at a certain heating temperature. Will occur. In particular, when the upper layer wiring is an Al-based alloy, a high resistance material such as WAl ₁₂ is formed by the alloying reaction, and when Al solid-phase diffuses in tungsten and reaches the underlying Si, the bonding is performed. The leakage current will increase.

Therefore, there is a need for a method of suppressing or preventing the expansion of this tungsten seam.

The tungsten seam expands particularly greatly along the center line of the contact, but the seam extending from the bottom edge of the contact does not expand significantly even if the tungsten over-etch is increased. The possible causes are as follows. That is, the seam extending from the bottom edge of the contact is generated while the growth point of the seam is moving with respect to the growth of tungsten, whereas the seam extending along the center line of the contact is
It is formed instantly at the moment the contact hole is completely filled. It is considered that in the seam portion extending along the center line of the contact thus formed, a large amount of reaction by-products such as F are taken in and tungsten having a very porous film quality is formed. On the contrary, since the seam extending from the edge of the bottom of the contact is generated while the growth point of the seam moves with respect to the growth of tungsten, the incorporation of the reaction by-product is not so remarkable and the film quality is not so bad.

The present invention provides a contact hole and a method for forming the contact hole, which prevents the tungsten seam from expanding as described above, prevents the resistance of the tungsten plug from rising, and prevents defective wiring patterning. To do.

[0017]

Therefore, in the invention according to claim 1, the shape of the longitudinal section is formed asymmetrically in the wiring opening in which the conductor is embedded by the blanket CVD and the subsequent etchback. Is the solution.

The invention according to claim 2 is a blanket CV.
In the wiring opening in which the conductor is embedded by D and the subsequent etch back, the opening area is asymmetrically increased from the center line of the opening toward the upper part of the opening, which is a means for solving the problem.

The invention according to claim 3 is a blanket CV.
In the method of forming an opening for wiring in which a conductor is embedded by D and subsequent etch back, the upper part of the opening is formed by oblique ion implantation and isotropic etching, and the lower part is formed by anisotropic etching. The solution is.

The invention according to claim 4 is the blanket CV.
In the method of forming an opening for wiring in which a conductor is embedded by D and subsequent etch back, after forming the opening, an anisotropic conductive deposited thin film is formed obliquely at least in the opening, Forming the shape of the longitudinal section asymmetrically is the solution.

The invention according to claim 5 is a blanket CV.
In the method of forming an opening for wiring in which a conductor is embedded by D and subsequent etch back, forming asymmetrical vertical cross-sections by a plurality of mask aligning steps and patterning is a solution.

[0022]

According to the first aspect of the invention, since the shape of the vertical cross section of the opening is formed asymmetrically, the seam of the conductor layer formed by blanket CVD in the opening for wiring becomes non-linear. Therefore, the seam is less likely to be exposed to the etchant during the etch back, and has the effect of preventing the expansion of the seam (generation of holes) accompanying the etch back.

According to the second aspect of the present invention, the opening area increases toward the upper part of the opening to improve the step coverage, and the opening area increases asymmetrically from the center line of the opening. The seam of the conductor embedded in the wiring opening has a large number of portions oblique to the depth direction of the wiring opening, and the seam is less likely to expand due to the etch back.

According to the third aspect of the invention, since the upper portion of the opening is formed by oblique ion implantation and isotropic etching,
The center line is inclined with respect to the lower center line formed by anisotropic etching, and the blanket C in the subsequent process is used.
Since the seam of the conductor formed by VD is inclined, it is difficult for the seam to expand due to etch back.

According to the fourth aspect of the present invention, an obliquely anisotropic conductive deposited thin film is formed in the opening that is temporarily opened, so that the longitudinal section of the opening is made asymmetric. ..

In the invention described in claim 5, as in the invention described in claims 3 and 4, there is an effect that the longitudinal section of the opening is asymmetric.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on each embodiment shown in the drawings.

(First Embodiment) FIGS. 1 to 8 are sectional views showing the steps of the first embodiment.

In this embodiment, as shown in FIG. 1, an interlayer insulating film 11 made of SiO ₂ is formed on a silicon substrate 10, for example, 8 times.
After forming the film to a film thickness of 00 nm, a photoresist is applied and patterning is performed.
A resist pattern 12 set to m is formed (FIG. 2).

Next, as shown in FIG. 3, after forming a contact hole 13 for anisotropic etching, for example, phosphorus (P) is ion-implanted by oblique ion implantation. The injection conditions are as follows, for example.

Phos ⁺ , 2 KeV, IE 14 cm ^-2 Next, dry or wet isotropic etching is performed. Then, the etching rate of the portion of the interlayer insulating film 11 into which phosphorus (P) is injected is increased, so that the shape of the contact hole 13 is processed to have an asymmetric vertical cross section, as shown in FIG. It Note that FIG. 4 shows a state in which the resist pattern 12 is removed.

Next, as shown in FIG.
After depositing the adhesion layer 14 having the i / TiN structure, as shown in FIGS. 6 and 7, the blanket W is subjected to CVD, for example, under the following conditions to fill the contact hole 13 with the tungsten film 15. The CV of this blanket W
D is carried out in two steps, a nucleation step that promotes initial growth, that is, nucleation, and a subsequent deposition step. Further, in this embodiment, the film thickness of the tungsten film 15 is 0.5 μm.

(Nucleation step) ○ Gas and its flow rate Silane (SiH ₄ ) ... 5 _SCCM Tungsten hexafluoride (WF ₆ ) ... 7 _SCCM ○ Pressure ... 4 Torr ○ Temperature ... 450 ° C. ○ Time ... 60 seconds (deposition step) ○ Gas and its flow rate Tungsten hexafluoride (WF ₆ ) ... 95 _SCCM Hydrogen (H ₂ ) ... 550 _SCCM ○ Pressure ... 80 Torr ○ Temperature ... 450 ° C. ○ Time ... 80 seconds Next, the tungsten film 15 is etched back. As shown in FIG. 8, a plug made of a tungsten film 15 is formed in the contact hole 13.

During the growth of the blanket W, the seam 15a of the tungsten film 15 is formed in the upper opening of the contact hole 13 while the surface on which it is formed moves, so the quality of the tungsten film depends on the edge of the bottom of the contact hole. It is equivalent to that of the seam part that extends from the part, and the seam does not expand even if exposed to the etchant during etch back.

(Second Embodiment) FIGS. 9 to 12 show the steps of the second embodiment.

In this embodiment, as shown in FIG. 9, after the resist pattern 12 is formed on the interlayer insulating film 11, before the interlayer insulating film 11 is processed, oblique ion implantation using phosphorus (P) is performed. To do. Then, dry or wet isotropic etching is performed (FIG. 10), followed by anisotropic mode reactive ion etching (RIE), and as shown in FIG. 13 is formed. A plan view of the contact hole 13 is as shown in FIG. Also in this embodiment, when the plug is formed by the blanket W, the same action and
The effect is obtained.

(Third Embodiment) FIGS. 13 to 15 show the steps of the third embodiment.

In this embodiment, first, the inter-layer insulating film 11 is formed on the silicon substrate 10, and the well-known method is used to form the interlayer insulating film 11 as shown in FIG.
As shown in FIG. 5, a tapered contact hole 13 is formed.

Next, as shown in FIG. 14, a contact hole 13 having an asymmetric taper angle is formed by forming, for example, TiN of the adhesion layer 14 by an anisotropic deposition method such as ECR CVD. .. At this time, ECR
The conditions of CVD are as follows, for example.

○ Gas and its flow rate Titanium tetrachloride (TiCl ₄ ) ... 10 _SCCM nitrogen (N ₂ ) ... 15 _SCCM hydrogen (H ₂ ) ... 50 _SCCM argon (Ar) ... 43 _SCCM ○ Microwave power ... 2.8 KW ○ Temperature: 650 ° C. Pressure: 1 mTorr After that, C of the blanket W under the same conditions as in the first embodiment.
If VD is performed and the tungsten film 15 is formed, the seam 15a becomes inclined with respect to the depth direction of the contact hole 13, and the seam 15a is formed in the same manner as in each of the above embodiments.
Can be prevented from expanding.

(Fourth Embodiment) FIGS. 16 and 17 show a fourth embodiment.
The process of the embodiment is shown, and this embodiment is intended to obtain an asymmetric contact hole by utilizing partial receding of the resist mask.

First, as shown in FIG. 16, a resist pattern 12 is formed on an interlayer insulating film 11 formed on a silicon substrate 10 and is obliquely ion-implanted so that only one side wall of the opening of the resist pattern 12 is formed. Impurities such as As are implanted. The As ion implantation conditions are, for example, as shown below.

As ⁺ 50 KeV 5E15 cm ^-2 By thus implanting ions only into one side wall of the opening of the resist pattern 12, the retreat speed of the resist can be made asymmetric.

Then, such a resist pattern 12 is formed.
Using the mask as a mask, a contact hole 13 is formed in the interlayer insulating film 11.
When dry etching is carried out, the opening area is asymmetrically increased from the center line of the opening toward the upper part of the opening as shown in FIG. Therefore, by forming a tungsten film by the same method as in the first embodiment and performing etch back, it becomes possible to form a tungsten plug in which the seam does not expand.

(Fifth Embodiment) FIGS. 18 to 21 show each step of the fifth embodiment.

In this embodiment, a contact hole having an asymmetric cross section is obtained by a plurality of mask aligning processes and patterning. First, as shown in FIG. 18, a resist pattern 12A having a large opening diameter is formed on the interlayer insulating film 11
Then, using the resist pattern 12A as a mask, the interlayer insulating film 11 is anisotropically etched to a depth of, for example, about 1/4 of the hole 13A.

Then, after removing the resist pattern 12A, a resist pattern 12B having a center of the hole 13A and an opening deviated from the center is patterned (FIG. 19).

In this embodiment, the resist pattern 1
The opening diameter of 2B is set smaller than the opening diameter of the resist pattern 12A.

Then, using the resist pattern 12B as a mask, anisotropic etching is performed to form a hole 13B, and the hole 13A and the hole 13B form a contact hole 13 (FIG. 20).

Next, a tungsten film 15 as shown in FIG. 21 is formed by a method similar to that of the first embodiment, and then etched back to form a tungsten plug without expansion of the seam 15a. Becomes In this example, the resist pattern 1 used first was used.
Of course, the interlayer insulating film 11 may have a multi-layered structure in order to facilitate detection of the end point during processing when patterning with 2A.

Although the respective embodiments have been described above, the present invention is not limited to these, and various design changes can be made.

For example, although the present invention has been described with reference to the contact hole in each of the above-described embodiments, the present invention is of course applicable to a wiring opening such as a via hole.

[0053]

As is apparent from the above description, according to the present invention, there is an effect that the resistance of the tungsten plug can be prevented from increasing without the tungsten seam expanding during the etch back process. Further, the barrier metal layer formed on the tungsten plug does not have step breakage, and the flatness of the aluminum-based alloy formed on the barrier metal layer becomes good. Therefore, there is an effect that an increase in junction leak current due to the penetration of aluminum (Al) into silicon (Si) and a defective wiring patterning can be prevented.

[Brief description of drawings]

FIG. 1 is a process drawing of a first embodiment.

FIG. 2 is a process drawing of the first embodiment.

FIG. 3 is a process drawing of the first embodiment.

FIG. 4 is a process drawing of the first embodiment.

FIG. 5 is a process drawing of the first embodiment.

FIG. 6 is a process drawing of the first embodiment.

FIG. 7 is a process drawing of the first embodiment.

FIG. 8 is a process drawing of the first embodiment.

FIG. 9 is a process drawing of the second embodiment.

FIG. 10 is a process drawing of the second embodiment.

FIG. 11 is a process drawing of the second embodiment.

FIG. 12 is a process drawing of the second embodiment.

FIG. 13 is a process drawing of the third embodiment.

FIG. 14 is a process drawing of the third embodiment.

FIG. 15 is a process drawing of the third embodiment.

FIG. 16 is a process drawing of the fourth embodiment.

FIG. 17 is a process drawing of the fourth embodiment.

FIG. 18 is a process drawing of the fifth embodiment.

FIG. 19 is a process drawing of the fifth embodiment.

FIG. 20 is a process drawing of the fifth embodiment.

FIG. 21 is a process drawing of the fifth embodiment.

FIG. 22 is a process diagram of a conventional example.

FIG. 23 is a process drawing of a conventional example.

FIG. 24 is a process drawing of a conventional example.

FIG. 25 is a process diagram of a conventional example.

FIG. 26 is a process drawing of a conventional example.

FIG. 27 is a process drawing of a conventional example.

[Explanation of symbols]

10 ... Silicon substrate, 11 ... Interlayer insulating film, 12 ... Resist pattern, 13 ... Contact hole, 15 ... Tungsten film.

Claims (5)

[Claims] 1. A wiring opening in which a conductor is embedded by blanket CVD and subsequent etch back, wherein a vertical cross-sectional shape is formed asymmetrically. 2. In a wiring opening in which a conductor is embedded by blanket CVD and subsequent etch back, the opening area increases asymmetrically from the center line of the opening toward the upper part of the opening. Aperture. 3. A method for forming a wiring opening in which a conductor is embedded by blanket CVD and subsequent etch back, wherein an upper portion of the opening is formed by oblique ion implantation and isotropic etching, and a lower portion is anisotropically etched. A method for forming a wiring opening, which is characterized in that 4. A method for forming a wiring opening in which a conductor is embedded by blanket CVD and subsequent etchback, wherein anisotropic conductivity is provided at least in the opening after forming the opening. A method of forming a wiring opening, comprising forming a deposited thin film to form the shape of a vertical cross section asymmetrically. 5. A method for forming an opening for wiring in which a conductor is embedded by blanket CVD and subsequent etch back, wherein a vertical cross-sectional shape is formed asymmetrically by a plurality of mask aligning steps and patterning. And a method for forming a wiring opening.