JP3256946B2 - Contact formation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a contact for connecting an upper wiring layer and a lower wiring layer separated by an interlayer insulating layer in a multilayer structure. More specifically, the present invention relates to a method for forming a contact which can be applied to a fine design rule and electrically stably connects an upper wiring layer and a lower wiring layer.

[0002]

2. Description of the Related Art With the miniaturization and high integration of ULSI, a multilayer wiring structure in which a plurality of wiring layers are stacked with an interlayer insulating layer interposed therebetween has come to be used. In this case, the connection between the upper wiring layer and the lower wiring layer is conventionally made by forming an opening (contact hole) in the interlayer insulating layer,
This has been done by connecting the upper wiring layer to the lower wiring layer via the contact hole. For example, as a memory of a circuit element, a field effect transistor (FE)
ULS of a multilayer wiring structure having circuit layers in which T) are arranged
In I, each electrode or wiring of the FET is used as a lower first wiring layer, an interlayer insulating layer is formed thereon, a contact hole is formed in the interlayer insulating layer, and then a second wiring is formed on the interlayer insulating layer. Form a layer. At this time, a contact is formed by inserting the second wiring layer into the contact hole formed in the interlayer insulating layer, and electrically and mechanically connecting the upper second wiring layer and the lower first wiring layer. I do.

Incidentally, such an interlayer insulating layer needs to have a considerable thickness in order to obtain sufficient insulation and pressure resistance between the upper and lower wiring layers sandwiching the interlayer insulating layer. For this reason, it is inevitable that the contact hole formed in the interlayer insulating layer is made considerably deep. Also, as a contact hole formed in the interlayer insulating layer, ULSI
With the increase in integration density and the progress of large-scale integration, it has become necessary to reduce the opening diameter.

On the other hand, an upper second wiring layer is generally formed by aluminum sputtering or the like, but aluminum does not have good contact hole coverage.
For this reason, it is very difficult to allow aluminum to enter the contact hole having a small opening diameter and a considerable depth as described above, that is, a contact hole having a high aspect ratio as the second wiring layer with good coverage. Therefore, it is difficult to electrically and mechanically satisfactorily connect the upper second wiring layer to the lower first wiring layer, and the contact portion between the first wiring layer and the second wiring layer is difficult to contact. There has been a problem that the resistance between the two layers is increased due to the occurrence of a defect or the disconnection of the step, and the reliability of the product is reduced.

Therefore, in recent years, without forming the second wiring layer in the contact hole, prior to the formation of the second wiring layer, tungsten is formed in the contact hole by CVD (chemical vapor deposition). A method of burying and thereby forming a contact has been adopted. For example, as a method for forming a contact for connecting a diffusion layer of a semiconductor element formed in a Si substrate and a wiring layer formed above the diffusion layer with an interlayer insulating layer interposed therebetween, FIG.
As shown in FIG. 1, first, the Si substrate 2 on which the diffusion layer 1 is formed
An insulating layer 3 is formed thereon, and a contact hole 4 is formed in the insulating layer 3. Next, as shown in FIG.
A tungsten layer 5 is formed on the entire surface of the insulating layer 3 by the VD method and the contact hole 4 is buried.
Then, etching back is performed to leave the tungsten layer 5 in the contact hole 4, and an upper wiring layer 6 is formed as shown in FIG.

In the method of forming a contact by burying tungsten in the contact hole, electrical and mechanical connection between the upper wiring layer and tungsten in the contact hole is ensured, and the contact resistance is improved. When forming a contact hole in the interlayer insulating layer , the etching stopper layer
The resist mask is tapered and its shape is changed.
The contact hole is formed by applying a taper etching process to form a contact hole in which the upper opening area is uniformly widened, thereby reducing the contact area between the wiring layer 6 and the tungsten 5 in the contact hole 4 as shown in FIG. It has also been expanded.

[0007]

However, if the contact area between the upper wiring layer 6 and the tungsten 5 in the contact hole 4 is increased as shown in FIG. 5, the wiring pitch of the upper wiring layer must be increased. Therefore, there is a problem that it is not possible to form into fine design rules. That is, if the contact is formed without taper etching at the time of forming the contact hole, the upper wiring 7 can be formed at a fine pitch as shown in FIG. If the reliability of the connection is reduced, and the contact is formed by taper etching at the time of forming the contact hole in order to improve the connection state between the upper layer wiring and the contact, as shown in FIG. The wiring 7 must be formed widely, and fine design rules cannot be realized.

SUMMARY OF THE INVENTION The present invention is intended to solve the above-mentioned problems, and provides a method of forming a contact which improves the connection between the upper wiring layer and the contact and realizes a fine pattern rule. It is intended to provide.

[0009]

In order to achieve the above object, the present inventor, when enlarging the contact area between the upper wiring layer and the contact, has to increase the opening area above the contact hole as in the prior art. It is necessary to increase the opening area only in a region that does not affect the fine wiring pattern without uniformly expanding, and for that purpose, the opening can be performed without performing the conventional taper etching when forming the contact hole. The periphery of the portion is formed of two types of insulating layers having different heating fluidities, and only the insulating layer having the higher heating fluidity can be substantially fluidized and tapered by heating. The inventors have found that the present invention is effective because the area can be expanded only to a predetermined region, and have completed the present invention.

[0010] That is, the present invention relates to an insulating laminate.
In a contact hole forming method for forming a tapered opening , a first insulating layer exhibiting heat fluidity is provided.
Formed on the substrate and having a lower heating fluidity than the first insulating layer
An opening is formed in the stacked body composed of the second insulating layer, a portion of the second insulating layer forming the periphery of the <br/> opening, first
By etching until the insulating layer is exposed.
A single layer of the first insulating layer exposing the periphery of the opening;
Surrounded and exposed by a laminate of the first insulating layer and the second insulating layer.
A method for forming a contact hole, characterized in that only a single layer portion of the first insulating layer is substantially fluidized by heating and the portion is tapered .

The present invention also provides a contact forming method characterized by embedding a conductive material in the contact hole formed as described above.

Hereinafter, the present invention will be described in detail with reference to the drawings. In each of the drawings, the same reference numerals represent the same or equivalent components.

FIG. 1 is a process explanatory view in the case where a contact for connecting a diffusion layer of a semiconductor element formed in a Si substrate and a wiring layer formed thereon via an insulating layer is formed by the method of the present invention. is there. In this method, as shown in the cross-sectional view of FIG.
An insulating layer 8 made of a first insulating material having a heating fluidity is formed on the substrate 2, and an insulating layer 9 made of a second insulating material having a lower heating fluidity than the first insulating material is formed thereon. Then, a photoresist 10 is applied thereon, and exposure and development are performed to form an opening 11 above the diffusion layer 1.

Next, using the photoresist 10 in which the opening 11 is formed as an etching stopper, an opening 12 is formed in the insulating layer 8 and the insulating layer 9 by a reactive ion etching (RIE) method or the like, and thereafter, FIG. The photoresist 10 is removed as shown in FIG. Opening 1
The shape of the opening surface of 2 can be various shapes such as a rectangle and a circle as needed.

Next, the insulating layer 9 having low heating fluidity is removed according to the shape of the contact to be formed. For example, as shown in the plan view of FIG. 3C, the insulating layer 9 having low heat fluidity is removed along the longitudinal direction (hatched portion) of the wiring 7 to be formed later on the upper wiring layer. 8 is exposed so that the periphery of the opening 12 is surrounded by a single layer of the insulating layer 8 and a laminate of the insulating layer 8 and the insulating layer 9. Note that such removal of the insulating layer 9 can be performed by a reactive ion etching method using a photoresist or the like as in the case of forming the opening 12 in the insulating layer 8 and the insulating layer 9.

Next, the insulating layer 8 is heated to such a degree that the insulating layer 8 is fluidized but the insulating layer 9 is not fluidized, so that a portion of the insulating layer surrounding the opening 12 which is formed of a single layer of the insulating layer 8, Only the part where the layer 8 is exposed is substantially fluidized,
The portion is tapered, and the cross section of the opening along the longitudinal direction of the wiring in the upper layer is enlarged as shown in the cross-sectional view of FIG. 4D, but as shown in the cross-sectional view of FIG. Then, a contact hole 13 whose opening cross section along the width direction of the upper layer wiring is not enlarged is formed.

After that, a tansguten layer 5 is formed on the entire surface of the insulating layer 8 and the insulating layer 9 including the inside of the contact hole 13 by a conventional method, and is etched back as shown in the sectional view of FIG. The contact 14 of the present invention is formed while leaving the tansguten layer 5 only in the contact hole 13. Then, an upper wiring layer is formed thereon, and the wiring layer is patterned by an ordinary method to form the wiring 7.

The multilayer structure thus obtained is shown in FIG.
As shown in the cross-sectional view of 2), the contact area between the wiring 7 and the contact layer 5 of the contact 14 is enlarged in the longitudinal direction of the wiring 7, as shown in the cross-sectional view of FIG. In the width direction of the wiring 7, the contact area between the wiring 7 and the tansguten layer 5 is the same as the cross-sectional area of the opening 12 initially formed. Therefore, according to the contact 14,
As shown in FIG. 3, while making the pitch of the wiring 7 fine,
Since the contact area between the wiring 7 and the contact 14 can be increased, a good connection state can be reliably obtained.

The method of forming a contact according to the present invention is not limited to the formation of the contact for connecting the diffusion layer formed in the Si substrate and the wiring layer formed thereon, as described above. In such a multilayer wiring structure, the present invention can be suitably applied to the formation of a contact connecting the first wiring layer and the second wiring layer.

FIG. 2 is an explanatory view of a process for forming such a contact. That is, when forming the contact shown in FIG. 2, first, the sectional view shown in FIG.
As shown in the plan view of 2), a first wiring layer 16 having a predetermined pattern is formed on a substrate 15. In addition, as such a substrate 15, for example, as in a semiconductor element in which a memory cell having an FET or the like is formed, a SiO
A substrate on which a semiconductor element having a surface insulating layer such as No. ₂ is formed.

Next, in the same manner as in FIG. 1 described above, an insulating layer 8 exhibiting heat fluidity as an interlayer insulating layer so as to cover the first wiring layer 16 and an insulating material having a lower heat fluidity than the insulating layer 8. A layer 9 is formed, and a photoresist 10 is further formed thereon.
Is formed, and an opening 11 is formed in a portion of the photoresist 10 located on the wiring layer 16.

Then, the insulating layer 8 and the insulating layer 9 are etched by using the photoresist 10 in which the opening 11 is formed as an etching stopper to form an opening 12 in the insulating layer 8 and the insulating layer 9. The photoresist 10 is removed as shown in FIG.

Next, as shown in the plan view of FIG. 3C, the insulating layer 9 having low heat fluidity is removed along the longitudinal direction (hatched portion) of the wiring 7 to be formed later on the upper wiring layer. The insulating layer 8 is exposed.

Thereafter, a portion where the insulating layer 8 is exposed by the heat treatment is tapered to form a contact hole. Then, tungsten is buried in the contact hole to form a contact. Next, an upper wiring layer 6 is formed thereon, and the wiring layer 6 is patterned to form a wiring 7.

The multilayer wiring structure thus obtained also has an enlarged contact area between the wiring 7 and the tungsten layer 5 in the longitudinal direction of the wiring 7 as shown in the sectional view of FIG. As shown in the cross-sectional view of FIG. 2D, the contact area between the wiring 7 and the tungsten layer 5 in the width direction of the wiring 7 is the same as the cross-sectional area of the opening 12 initially formed.

In the method of forming a contact hole and a contact according to the present invention as described above, the first insulating material exhibiting heat fluidity includes silicon dioxide (BPSG) containing boron and phosphorus as impurities and phosphorus. Silicon dioxide (PSG), boron-containing silicon dioxide (BSG), arsenic-containing silicon dioxide (AsS
G) silicon dioxide containing boron, phosphorus and arsenic;
Silicon dioxide containing lead dioxide can be used. In particular, it is preferable to use silicon dioxide containing at least one of phosphorus, boron and arsenic from the viewpoint of versatility.

Further, the second insulating material having a lower heating fluidity than the first insulating material is silicon dioxide containing at least boron, phosphorus or arsenic as an impurity, and is higher than the first insulating material. Those with low concentration of these impurities, silicon dioxide (NSG), silicon nitride (Si ₃ N)
₄ , P-SiN), polysilicon (PolySi), and the like, and in particular, silicon dioxide or silicon nitride is preferably used from the viewpoint of insulating properties.

There is no particular limitation on the method of forming the insulating layer formed from these insulating materials, and the insulating layer can be formed by various methods.

In the example shown in FIGS. 1 and 2 described above, a predetermined portion around the opening 12 is formed by the insulating layer 8 exhibiting heat fluidity, and the remaining portion around the opening 12 is formed by the insulating layer 8. In order to obtain a structure in which the insulating layer 9 is formed of a laminated body of an insulating layer 9 having a lower heating fluidity than the insulating layer 8, the insulating layer 9 is first stacked over the entire surface of the insulating layer 8, and then the opening 12 is formed. Then, according to the process of partially removing the insulating layer 9, a predetermined portion around the opening 12 is formed by the insulating layer 8, and the remaining portion is formed by a laminate of the insulating layer 8 and the insulating layer 9. It is not always necessary to use the above-described steps as far as possible.

In the method of forming a contact according to the present invention, as the conductive material to be embedded in the contact hole, for example, Mo, Cu,
PolySi and silicide compounds such as WSi and MoSi can be used.

As the upper or lower wiring layer connected by the contact of the present invention, a conductive material forming these contacts can be used, or in addition to these, Al, Al-Si, Al-Si -Cu, T
A barrier metal structure in which a so-called barrier metal such as i, TiON or the like is laminated may be employed.

[0032]

According to the contact hole forming method of the present invention, a predetermined portion of the insulating layer forming the periphery of the opening is formed of the first insulating layer exhibiting heat fluidity, and the remaining portion is formed of the first insulating layer. Since the first insulating layer is formed of a second insulating layer having low heat fluidity, and only the first insulating layer is substantially fluidized by heating, only a portion of the periphery of the opening formed by the first insulating layer has a taper. It is possible to form a contact hole having an enlarged opening at that portion.

In forming the contact hole as described above, in particular, the second insulating layer is formed on the layer made of the first insulating material constituting the first insulating layer by heating and flowing more than the first insulating material. It is preferable that a layer made of a second insulating material having a low property is laminated because two kinds of insulating layers having different heating fluidities can be easily formed around the opening.

Further, in the contact forming method of the present invention, since the contact is formed by embedding a conductive material in such a contact hole, the contact area between the contact and the upper wiring layer is reduced. Of these, it is possible to enlarge the portion formed by the first insulating layer.

Therefore, when forming the contact hole, the portion of the insulating layer surrounding the opening to be formed by the first insulating layer is appropriately determined, and the portion for increasing the contact area between the contact and the upper wiring layer is defined as the contact area of the contact. By setting the area where the formation does not affect the wiring pitch of the upper wiring layer, it is possible to increase the contact area between the wiring and the contact while maintaining the pitch even for fine pitch wiring, It is possible to connect the wiring and the contact with high reliability.

[0036]

The present invention will be specifically described below with reference to examples.

As shown in FIG. 1, a contact for connecting a diffusion layer of a semiconductor element formed in a Si substrate to a wiring layer thereover was formed. In this case, as the insulating layer 8 exhibiting heat fluidity, an insulating film made of silicon dioxide containing boron and phosphorus (BPSG) is formed at 6000 Å, and as the insulating layer 9 having lower heat fluidity than the insulating layer 8, An insulating film made of silicon dioxide containing no impurity was formed to a thickness of 500 Å. Then, a photoresist 10 is formed on the laminated body of the insulating layer 8 and the insulating layer 9 by an ordinary method, the photoresist 10 is patterned to form an opening 11, and then an RIE device (O ₂ / CH
F ₃ = 8/75 sccm, 50 mtorr, 1000
An opening 12 was formed in the insulating layers 8 and 9 by performing anisotropic etching in W). Next, after the insulating layer 9 around the opening 12 is partially removed, the insulating layer 9 is removed under N ₂ atmosphere.
Heat treatment was performed at 0 ° C. for 30 minutes. By this heat treatment, the portion where the insulating layer 9 was removed and the surface became the insulating layer 8 exhibited fluidity, and the opening 12 in that portion was tapered, but the portion where the surface was the insulating layer 9 was almost removed. It did not show fluidity. Thus, the contact hole of the present invention was formed.

Next, a W layer 5 is formed on the entire surface by a so-called blanket WCVD method and etched back to leave the W layer 5 only in the contact hole.
Was formed. Thereafter, an Al layer was formed as an upper wiring layer, and a wiring 7 was formed by photolithography.

As a result, the wiring 7 and the contact 14
In the width direction of the wiring 7, the wiring 7 was in contact with the same width as the wiring 7,
The wires 7 were in wide contact in the longitudinal direction, and the electrical connection between them was good.

[0040]

According to the contact forming method of the present invention, even when the upper wiring layer is formed according to a fine design rule, it is possible to improve the connection between the wiring layer and the contact.

[Brief description of the drawings]

FIG. 1 is a process explanatory view of a contact forming method of the present invention.

FIG. 2 is a process explanatory view of another contact forming method of the present invention.

FIG. 3 is a plan view of a multilayer structure in which contacts are formed by the method of the present invention.

FIG. 4 is a process explanatory view of a conventional contact forming method.

FIG. 5 is a sectional view of a contact formed by a conventional method.

FIG. 6 is a plan view of a multilayer structure in which contacts are formed by a conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Diffusion layer 2 Si substrate 3 Insulating layer 4 Opening 5 Tungsten layer 6 Wiring layer 7 Wiring 8 Insulating layer showing heating fluidity 9 Insulating layer with lower heating fluidity than insulating layer 8 10 Photoresist 11 Opening 12 Opening 13 Contact hole 14 contact 15 substrate 16 wiring layer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/3205 H01L 21/321 H01L 21/3213 H01L 21/28-21/288 H01L 21/44-21 / 445 H01L 21/768

Claims (3)

(57) [Claims] 1. A contact hole forming method for forming a tapered opening in an insulating laminated body, comprising: a first insulating layer exhibiting heat fluidity;
A second insulating layer having a lower heating fluidity than the first insulating layer;
The opening is formed in Ranaru laminate, a portion of the second insulating layer forming the periphery of the opening, the
To remove by etching until the first insulating layer is exposed
A single layer of the first insulating layer exposing the periphery of the opening;
The method is characterized in that only the exposed single-layer portion of the first insulating layer is substantially fluidized by heating and is tapered at the portion surrounded by the stacked body of the first insulating layer and the second insulating layer. Contact hole forming method. 2. The method according to claim 1, wherein the first insulating material constituting the first insulating layer comprises at least one of phosphorus, boron and arsenic as impurities.
Containing silicon dioxide , forming a second insulating layer
A second insulating material, a contact hole forming method according to claim 1, wherein a lower silicon dioxide impurity concentration than the first insulating material. 3. A method for forming a contact, comprising: burying a conductive material in a contact hole formed by the method according to claim 1.