JPH03116722A - Method of forming buried contact - Google Patents

Abstract

PURPOSE:To avoid the step cut of a foundation barrier layer and degradation of the coverage of electrode or wiring metal layers over conductor members buried in contact windows by a method wherein an upper layer insulating film is provided and, before the electrode or wiring metal layers are applied, the shoulder parts of the upper layer insulating film are smoothened by re-melting the film. CONSTITUTION:A lower layer insulating film 21 is formed on a semiconductor substrate 20 and a re-meltable upper layer insulating film 22 are formed on the film 21. Contact windows 23 are drilled through the whole thicknesses of the films 21 and 22 on first and second regions 31 and 32. A polycrystalline silicon layer 34 is formed over the whole surface so as to fill the contact windows 23. After that, conductor members 24 are selectively buried on the bottom parts of the contact windows 23. Then the upper layer insulating film 22 is re-melted to make its shoulder parts 22a on the inner circumferential edges of openings of the contact windows 23 smooth. If an electrode or wiring metal layer 35 is formed over the conductor members 24 with a barrier layer as a foundation layer, the step cut of the foundation barrier layer can be avoided and the metal layer 35 can be applied with asatisfactory coverage. After that, the metal layer 35 is patterned to form respective electrode or wiring metal layers 25.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for forming electrodes or wirings to a circuit element portion of a very large semiconductor integrated circuit (VLSI), etc., through an insulating layer formed on a semiconductor substrate. A buried type contact that is applied to contact parts that contact each other through a contact window formed between the eyebrows, or when electrodes or wires laminated through a glabella insulating layer are brought into contact with each other through a contact window (via hole) drilled in the glabella insulating layer. It concerns the method of forming the part.

[Summary of the invention]

The present invention relates to a method of forming a buried contact portion,
A re-meltable upper insulating film is formed on the lower insulating layer to a desired thickness, a contact window is formed through the upper insulating film and the lower insulating layer, and the contact window is formed almost exclusively by the lower insulating layer. A conductive material is embedded in a limited area in the bottom of the contact window to be formed, and then the upper insulating film is remelted to make the shoulder at the edge of the contact window gentle. In this method, an electrode or wiring metal layer having a barrier layer as an underlying layer is deposited on the electrode or wiring metal layer, and by doing so, contact of the electrode or wiring metal layer can be made reliably and with high reliability through the fine contact window. do it like this.

[Conventional technology]

In semiconductor integrated circuits, ultra-large semiconductor integrated circuits are increasingly required, and as a result, electrodes or wiring patterns are becoming denser and more multilayered. In contact areas between interconnects formed in multiple layers, contact windows for contacting electrodes or interconnects with the insulating layer formed on the surface of the semiconductor substrate or the insulating layer between the eyebrows of multilayer interconnects are also miniaturized, and their aspect ratio (contact window The depth (thickness) of the contact window/width (diameter) of the contact window is becoming larger and larger. Directly injecting the metal layer constituting the electrode or wiring into the contact window by evaporation, sputtering, etc. through a contact window with such a large aspect ratio and connecting it to the circuit element or the underlying electrode or wiring provides good coverage. is not obtained. Therefore, in this case, first, a conductive material such as low resistivity polycrystalline silicon is buried in the contact window by, for example, the CVO method (chemical vapor deposition method), and the electrodes of each upper layer are connected to the buried conductive material. Alternatively, there is a tendency to adopt a so-called buried contact structure in which contact is made at a predetermined portion by extending a wiring metal layer so as to make electrical contact.

An example of a method for forming such a buried contact portion will be explained with reference to FIG.
This is a case where an electrode or wiring is brought into contact with a predetermined circuit element portion on a semiconductor substrate (1) through a contact window (3) formed in an insulating layer (2) such as NG using a buried contact structure. In this case, as shown in FIG. 2A, by applying photolithography to the insulating layer (2) as described above, for example, by anisotropic RIE (reactive ion etching), electrodes or wiring of circuit elements of the semiconductor substrate (1) are formed. A contact window (3) is bored in the contact part of the contact part.

Then, as shown in FIG. 2C, the contact window (3) is filled with a conductive material (4) having conductivity. Filling with the conductive material (4) is performed by, for example, depositing a polycrystalline silicon layer (4,) on the entire surface including the inside of the contact window (3) by LPGV (low pressure chemical vapor deposition) as shown in FIG. The polycrystalline silicon layer (4υ) on the upper surface of the insulating layer (2) is removed by etching it back from its surface by an anisotropic etching method such as RIB. (2) In order to avoid remaining the polycrystalline silicon layer (4I), that is, the polycrystalline silicon N (4I) that will become the conductive material (4) as described later, this etchback is performed as shown in Figure 2C. As shown, the insulating layer (2
) When the etching is carried out to a position recessed from the surface of the surface of the surface of the surface of the surface of the surface of the surface of the surface of the surface of the surface of the surface of the surface of the surface of the surface of the surface of the surface of the surface of the surface .lamda. After that, for example, impurity ions are implanted to form a contact window (3
) The polycrystalline silicon layer (4,) is made of a conductive material (4,) in which impurities are introduced into the polycrystalline silicon layer (4υ), and the polycrystalline silicon layer (4,) is made to have a low specific resistance by heat treatment and activation annealing treatment.
4), thereby embedding the contact window (3).

Next, as shown in the second diagram, a metal layer is formed over the entire surface of the conductive material (4) embedded in each contact window (3) by vapor deposition, sputtering, etc., and then photolithography is performed. Electrodes or wiring metals N (6) each having a desired pattern are deposited and formed by patterning using the applied etching.

According to such a configuration, since the contact window (3) is filled with the conductive material (4), for example, the semiconductor substrate (
1) It is said that electrical contact of the intended electrode or wiring metal N(6) can be made satisfactorily to the required part of the upper circuit element.

However, in reality, as mentioned above, the contact window (3
) The presence of the recess (5) on the conductive material (4) embedded in the contact portion causes a decrease in reliability, such as poor contact at the contact portion and occurrence of defective products. In other words, M is typically applied as a metal layer for electrodes or wiring in ordinary semiconductor devices, but the reaction between this M and the conductive material (4) in the contact window (3) and Si in the semiconductor substrate This may result in the formation of rectifying junctions in the contact portions, increase in contact resistance, destruction of shallow PN junctions in circuit elements due to the penetration of M into the semiconductor substrate, and especially as the area of contact portions becomes smaller. VLS where the components of circuit elements become shallower due to the reduction in area
Therefore, in VLSI and the like, a metal layer structure having a so-called barrier metal structure is used as an electrode or wiring (6). That is, for example, a stacked structure is adopted in which a Ti layer as a barrier metal and a TiN layer are sequentially formed as a lower layer, and an M or MSi layer is formed thereon. In this way, reaction between M forming the electrode or wiring metal layer and St of the conductive layer (4) and the substrate (1) is avoided by the base layer as a barrier metal.

However, when adopting such a barrier metal structure, a recess (
5) may cause a so-called step break in the underlying layer as a barrier metal, or a defect may occur due to insufficient coverage of the conductive material (4). In this case, the above-mentioned M and In addition, as shown in Fig. 3, which shows an enlarged view of the main part, M spikes (7) occur because the entry of M is not reliably blocked by the barrier underlayer, causing damage to the circuit elements. For example, it destroys the pn junction J and causes leakage current, resulting in unstable characteristics and the production of defective products. and,
The depth of this pn junction J tends to become shallower with the miniaturization of circuit elements in semiconductor integrated circuits, and is becoming more and more of a problem.

[Problem to be solved by the invention]

In the present invention, in the method for forming a buried contact portion described above, when filling the conductive material (4) into the contact window having a large aspect ratio, the conductive material (4)
Even when there is a recess on the top, the presence of the recess should prevent the electrode or wiring metal layer from breaking into the underlying layer as a barrier metal, thereby reducing the coverage, thereby preventing the characteristics of the contact portion from deteriorating. ,A1
To surely avoid occurrence of leakage current due to spikes, deterioration of characteristics, occurrence of defective products, etc.

[Means for Solving the Problems] The present invention provides, for example, a lower insulating layer (2) as shown in FIG. 1A.
1), a step of forming a remeltable upper layer insulating film (22) to a required thickness t, and
2) and lower layer insulation 1! (21) to form a contact window (23) through the contact window (23), and as shown in FIG. The process of embedding a conductive material (24) in a limited manner in the bottom of the contact window (23) and smoothing the shoulder (22a) at the periphery of the contact window (23) of the upper layer insulating film (22) as shown in the first figure. The re-melting process for the upper insulating film (22) and the contact window (
23) An electrode or wiring metal layer (25) having a barrier layer as a base layer is applied over the conductive material (24) in the electrode or wiring metal layer (25) to form a buried contact portion of the electrode or wiring metal layer (25). Take the process.

[Effect]

According to the method of the present invention described above, the conductive material (24) provided with the upper insulating film (22) and embedded in the contact window (23)
Before depositing the electrode or wiring metal layer (25) on the upper insulating film (22), the shoulder (22a) of the upper insulating film (22) is
By remelting this, a smooth surface was created, so the electrode or wiring metal layer (25
), therefore, the underlying barrier layer is formed on a smooth adhesion surface, causing breakage and conductive material (24
), and the barrier layer is properly adhered to the contact window (2), thereby ensuring that it can function as a barrier metal layer.
3) It is possible to avoid reactions with the embedded conductive material (4) or the underlying Si of the semiconductor substrate, for example, and the occurrence of spikes as explained in FIG. 3, thereby causing breakdown of the bond.

It is possible to avoid the occurrence of leaks and other inconveniences that cause reliability and characteristic deterioration.

〔Example〕

Referring to FIG. 1, the method for forming a buried contact portion according to the present invention will be described in detail in each part of a circuit element formed on a silicon semiconductor substrate or, for example, a silicon semiconductor substrate (20) having a silicon semiconductor layer on an insulating substrate. On the other hand, a case where an electrode or a wiring metal layer is contacted will be exemplified. In this case, the silicon semiconductor substrate (21) is formed in a pnn junction furnace, and the first
This is a case where electrodes or wiring metal layers are to be contacted to the second regions (31) and (32), respectively.

In this case, a lower insulating layer (21) made of, for example, SiO□ is formed on the semiconductor substrate (20) to a required thickness, and on top of this a remeltable insulating layer (21) of, for example, phosphorus, has a required thickness t. Silicate glass (PSG), boron phosphorus silicate glass (BPSG), arsenic silicate glass (As
An upper layer insulating film (22) made of SG) or the like is formed.

These upper layer insulating film (22) and lower layer insulating film (21)
) over the entire thickness of the first and second regions (31) and (
32) A contact window (23) is formed thereon by photolithography and anisotropic etching perpendicular to the plane of the substrate (20), such as anisotropic RIE.

As shown in FIG. 1B, a polycrystalline silicon layer (34) is deposited over the entire surface of the contact window (23) by LPCVD or the like. In this case, the polycrystalline silicon layer (34) is formed to a thickness that makes the surface almost flat, or a photoresist layer (not shown) is coated on the polycrystalline silicon layer (34) to make the surface flat. Apply to.

Thereafter, as shown in FIG. 1C, a polycrystalline silicon layer (3
4) or the surface of the resist layer formed thereon by anisotropic etching in a direction perpendicular to the flat surface of the contact window (2).
3) Proceed etching, for example, anisotropic RIE, in the depth direction. In this case, the contact window (23) formed at least on the upper insulating film (22) and in the upper insulating film (22)
) by removing the polycrystalline silicon layer (34) over the thickness of the lower insulating layer (21) to form a contact window (
Polycrystalline silicon layer (34) limited to the bottom part of 23)
Etching is continued until . Thereafter, impurities are ion-implanted into the conductive material (34) at a high concentration by ion implantation, for example, to lower the resistivity of the conductive material (34).
24). The conductive material (24
) are formed independently and separately for each contact window (23), and a recess (26) is present on the conductive material (24). In this case, this recess (26
) is selected in advance so that the depth of the upper insulating film (22) substantially matches the thickness L of the upper insulating film (22).

Next, as shown in the first diagram, the upper insulating film (22) is heated and remelted (including softening), that is, reflowed, and the shoulder (22) at the inner peripheral edge of the opening end of the contact window (23) is
A) is a surface with a gentle roundness.

As shown in FIG. 1E, an electrode or wiring metal layer (35) is formed over the conductive material (24) within the contact window (23). This metal J'! (35), for example, a barrier metal underlayer formed by laminating a Ti layer and a TiN layer;
A MSi layer is sequentially formed by vapor deposition or sputtering. In this case, since the shoulder portion (22a) of the upper layer insulating film (22) is a gentle surface, no breakage occurs in the underlying barrier layer, and the contact window (23) has good coverage. conductive material (24
) into the recess (26) and is formed in a dense manner.

Thereafter, as shown in FIG. 1F, the metal layer (35) is patterned by pattern etching, for example, by photolithography, and a desired pattern of the electrode or wiring metal layer (2) is formed on each contact window (23).
5) Form. In this way, each electrode or wiring metal layer (25) is connected to the first and second regions (
31) and (32). According to such a configuration, even within the contact window (23) having a large aspect ratio, the conductive material (24) made of, for example, a low resistivity polycrystalline silicon layer is embedded by, for example, LPGVD, so that the contact window (23) can be reliably Contact is made to each region (31) and (32) of the electrode or wiring metal layer.

In addition, in the above-mentioned example, the first
This is a case where the method of the present invention is applied when contacting the electrode or wiring metal layer (25) to the second regions (31) and (32).
0) A contact window is formed in the interlayer insulating layer in the electrode or wiring metal layer having a multilayer structure via the interlayer insulating layer formed above, so that contact between the electrodes or the wiring metal layers is made so-called via-hole contact. The present invention can also be applied in such cases.

Further, in the above-mentioned example, the conductive material (24) is composed of a low resistivity polycrystalline silicon layer, but this can be replaced by silicide or polycrystalline silicon compound formed by depositing a metal layer on polycrystalline silicon. It can also be composed of layers.

〔Effect of the invention〕

According to the method of the present invention described above, the upper insulating film (22) is provided and the electrode or wiring metal layer (25) is formed on the conductive material (24) embedded in the contact window (23). The shoulder portion (22a) of the upper insulating film (22) was previously remelted to give it a smooth surface, so that the electrode or wiring metal layer (25) formed thereon
Therefore, the underlying barrier layer is formed on a smooth adhesion surface, causing breakage and conductive material (24).
By avoiding a decrease in coverage and ensuring good adhesion, it can reliably function as a barrier metal layer, and the buried conductive material (4) in the contact window (23) or underneath it can be reliably performed. For example, reactions with Si in the semiconductor substrate and the occurrence of spikes as explained in Fig. 3 can be avoided, thereby preventing junction breakdown, cracking, other reliability and characteristic deterioration, and the production of defective products. It can be avoided.

[Brief explanation of drawings]

FIGS. 1A-F are enlarged sectional views of essential parts in each step of an example of the method for forming a buried contact portion according to the present invention, and FIGS. 2A-D are enlarged sectional views of main parts in each step of a conventional method. , FIG. 3 is an explanatory diagram of M spike. (20) is a semiconductor substrate, (21) is a lower insulating layer, (22)
) is the upper insulating film, (23) is the contact window, (24) is the conductive material, (26) is the recess, (22a) is the shoulder, (25)
is an electrode or a wiring metal layer. Agent Hidemori Matsukuma Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] A step of forming a remeltable upper insulating film to a desired thickness on the lower insulating layer, and forming a contact window through the upper insulating film and the lower insulating layer. a step of embedding a conductive material in a limited manner into the bottom of the contact window formed almost only by the lower insulating layer of the contact window; a remelting step; and a step of depositing an electrode or wiring metal layer having a barrier layer as a base layer over the conductive material in the contact window to form a contact portion of the electrode or wiring metal layer. A method for forming a buried contact portion, characterized in that: