JPS6365642A - Formation of connection hole - Google Patents

Abstract

PURPOSE:To open connection holes in a constant dimension with good accuracy without depending on the film thickness of an insulating film and also, to contrive to be able to form the connection holes comparatively favorably even to the covering property of the upper conductor by forming the connection holes with their lower parts having a vertical sidewall and their upper parts with a constant slant. CONSTITUTION:A polyimide high-molecular resin film 104 is spin coated as an interlayer insulating film on a substrate with first layer Al wirings 103 formed through an insulating film 102 on an Si wafer 101 having a step on its surface. A plasma CVD SiO film 105 is formed on the polymide high- molecular resin film 104 and the opening parts 106 and 106' of the plasma CVD SiO film 105 are formed at places where interlayer connection holes are provided by a reactive ion etching method wherein CF4 gas is used using a photoresist as a mask. Then, connection holes 107 and 107' having a vertical sidewall are formed in the polymide high-molecular resin film 104 by a reactive ion etching method using the SiO film 105 as a mask. After the SiO film 105 which is an etching mask is removed by CF4 plasma etching, the whole surface of a sample is etched.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for forming interlayer connection holes in multilayer wiring used in electronic circuit devices, etc., or contact holes in semiconductor substrates, etc. The present invention relates to a method for forming a connection hole suitable for forming a connection hole with a high .

[Traditional martial arts]

2. Description of the Related Art As semiconductor devices and the like become more highly integrated, interlayer connection holes and contact holes in multilayer interconnections are becoming finer. Reactive ion etching is often used in traps to create minute holes. However, when a contact hole with vertical sidewalls is formed by reactive ion etching, the coverage of the upper layer conductor at this portion becomes a problem. This can be a serious problem, especially when the upper layer conductor is a metal film formed by sputtering or vapor deposition. For a solution to this, see the Proclaiming of First V.L.N.I.
Multi-level interconnection conference 1
Page 06 (1984) (Proc.

1 st VLSI tVultilevel Int
erconnectionConference pp
106-14 (1984), it has been considered to make the connecting holes sloped. However, if the connection hole is sloped, the thickness of the insulating film where the connection hole should be formed increases depending on the location, as shown in Figure @2.
If they are different from 2, even if the same mask is used, the dimensions of the contact holes will differ from dI+G depending on the thickness of the insulating film, which is not practical.

Also, how do you make this connection hole slanted?

This method is easily affected by film thickness variations due to process variations, and from this point of view, it is not a very desirable method.

[Problem that the invention seeks to solve]

The above slanting method does not take into account the step structure of the actual integrated circuit, or the fact that the thickness of the insulating film varies depending on the location due to the flattening of the insulating film, and the dimensions of the contact hole are not considered. There is a problem in that it is difficult to maintain constant control for connection holes as small as 1%.

An object of the present invention is to achieve a method independent of the thickness of an insulating film.

The object of the present invention is to form a connection hole with high precision and a constant size, and to form the connection hole with relatively good coverage of the upper layer conductor.

[Means for solving problems]

For the above purpose, the lower part of the connecting hole has a vertical side wall.

This is achieved by forming a connecting hole with a constant slope in the upper part.

In principle, the above shape can also be achieved by a method in which when forming the connecting hole, first performs isotropic etching halfway, and then switches to anisotropic etching to complete the opening. However, with uniisotropic dry etching, it is difficult to ensure uniformity within the wafer, and there is also the problem that dependence on one dimension is likely to occur. In conformal wet etching,
When the processing dimensions of the connection hole are reduced, there is a problem in that the uniformity of the dimensions deteriorates due to the cleaning blade during cleaning after etching. From a practical point of view, achieving the above shape by isotropic and anisotropic etching is not suitable for microfabrication.

In order to stably achieve the above-mentioned shape even in a fine connection hole, first, a connection hole with perpendicular i+ia walls is formed to a predetermined size, and then a highly anisotropic etching process (e.g. reactive ion etching, reactive etching) is performed. using reactive ion beam etching, biased reactive micro-plasma etching, etc.).

By etching the entire surface of the insulating film, a contact hole having the shape described above is formed. Ar gas was used for the connection hole having this shape. It is also possible to form it by so-called reverse sputtering. However, in this case, slanting is a practical method.

The insulating material scraped at the top of the connection hole will adhere to the surface of the lower conductor below the reading hole, increasing connection resistance or, in extreme cases, causing non-conductivity, so use reactive ion etching, etc. is more effective.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

Example 1 An insulating film 10 is formed on a 3i wafer 101 having a step on its surface.
A polyimide polymer resin film 104 having a thickness of about 3.5 μm was spin-coated as an interlayer insulating film on the substrate on which the first layer of At wiring 103 was formed via 2 (FIG. 41a). After that, as shown in the figure, a 0.2 μm plasma CVD5iO film 105 is formed on the polyimide polymer resin film 104.
The openings 10 of the plasma CVD 5iO film 105 are etched by reactive ion etching using a CFA-based gas using a photoresist (not shown) as a mask.
6.106' was formed. Next, as shown in Figure C, using the SiO film 105 as a mask, an oxygen gas pressure of 1 mtorr was applied
, high frequency (1 & 56KHz) i [force density 0.2N/-
By reactive ion etching under the conditions of
07' was formed. Furthermore, after removing the SiO film 105 as an etching mask using CF''4 plasma etching, the entire surface of the sample was etched under the conditions of an oxygen pressure of 1 mtorr and a high frequency power density of 0.5'N/crd to form a polyimide polymer sphere. The thickness of the film was approximately 2 μm (Fig. d). Through this treatment, the diameter at the bottom of the connection hole did not change, and the diameter at the top of the connection hole was approximately 0.5 μm, measured from the normal to the substrate. Nine tapered portions with an inclination of about 30' are formed, and in the deep connection hole 107', a depth of about 1 μm is formed below.
The vertical portion of the shallow contact hole 107'' was 0.2 μm in depth. After performing Ar sputter cleaning treatment on this, an At thin film with a thickness of approximately 1 μm was deposited. Formed by sputtering.

The second layer of At metal 11 is etched using conventional photoetching techniques.
lljl (not shown). The contact resistance at the connecting hole of the thus prepared sample with a diameter of 1°0 μm and a thickness of 1.5 μm was 200 mΩ/ke, and from the beginning the interlayer film 4 was 2 μm.
Value of 400 mΩ/
It was reduced by about half compared to the previous year. This can be determined from the SF and M observations of the cross-section of the connection hole.The coverage factor of the second layer At in this connection hole (the thickness of the At film at the thinnest part of the connection hole relative to the thickness of the second layer At wiring in the flat area) ratio) is 0.05
It was found that this was due to the improvement from ~0.1 to 0.2.

Example 2 After forming vertical connection holes in the same manner as in Example 1.

The sample was subjected to microwave plasma etching using oxygen gas (μ wave power 100 W, bias voltage 4 sOV, &
At an elementary gas pressure of 5 x 10-' Torr).

For sample B, oxygen plasma ashing (oxygen gas pressure 1゛for
The polyimide polymer between the eyebrows was etched on the entire surface using a high frequency power of 200 W to a film thickness of 3.5 μm to approximately 2 μm. In addition, in sample C, Ar sputter etching (
Etching was performed using Ar gas pressure of 5 mtorr and high frequency power of 500 W) until the film thickness was from 28 μm to approximately 2 μmK, and a second layer of At wiring was formed in the same manner as in Example 1, and the contact resistance of the contact hole was measured. 1μmφ1.5μ due to design
m depth connection hole, 430 mΩ/piece for sample B, sample B
In sample C, a contact resistance of 80 mΩ/ke was obtained, and in sample C, a contact resistance of 1 Ω to 10 Ω/ke was obtained in some parts, but most of the contact resistance was non-conducting (>10 Ω/ke).
/ke). In addition, in samples A and C, the diameter of the bottom of the connecting hole did not change from the original value.

At the top of the contact hole, there is an inclined part (angle of inclination 2) with a depth of approximately 0.5 μm.
5°), whereas in sample B, the diameter expanded to about 3.5 μmK, and it was found that this was the cause of the bottom contact resistance. In the non-conducting connection hole portion of sample B, a thin film mainly composed of carbon other than At was formed on the surface of the first layer wiring, and this was presumed to be the cause of the high resistance. Furthermore, since the main component of this coating is carbon, it is considered that a portion of the polymer + Ij resin that was scraped while the upper part of the contact hole was sloped was deposited at the bottom of the contact hole and formed a coating.

Example 3 After forming a polyimide polymer resin film 304 in a thickness of approximately 3.5 μm on a substrate having steps as in Example 1, using a plasma CVD silicon nitride film 305 as a mask,
Oxygen reactive ion etching (0,: 1 mtorr,
O, a w/i) and Z5. A hole 306 with a vertical side wall was formed at a depth of c+m (Fig. 3a) 2. After removing the silicon nitride film 305 as shown in the figure, oxygen reactive ion etching (02 gas pressure! The entire surface of the polyimide polymer resin film was etched to a thickness of about 1.5 μm at a high frequency energy density of 0.5 W/ca). Even with this method, it was possible to form a connecting hole having the same shape as in Example 1, except that the hole size at the bottom was expanded by about 0.1 μm from the initial value. In addition, the contact resistance of the connection hole measured after forming the second JΔ wiring was 180 mΩ.
It was a good value of /.

In the above examples, only examples were shown in which reactive and anisotropic etching using oxygen was used for etching the entire surface of polyimide resin, but the reactive gas is not necessarily limited to pure oxygen; for example, Ar may be used. If a gas mixed with 2% or more oxygen is used, the physical impact effect will be increased, so that the upper part of the connection hole can be easily sloped without greatly changing the etching rate of the flat part. As described above, the object of the present invention can be sufficiently achieved even if a gas containing oxygen as a component is used.

In addition, in the embodiment, only the case where it is used between two layers of KT-based wiring is described, but it is also applicable to the case where it is used between the layers of KT-based two-layer wiring, or between the layers of multi-layer wiring of more than two layers, or diffusion 4. poly8
This does not preclude application to the contact hole portion for i-wiring.

In addition, although we have only mentioned the use of polymer resin (polyimide) as an interlayer insulating film, if we use an anisotropic etching method with sufficiently high reactivity with the underlying layer, other 5i materials can be used.
It is clear that the present invention can be applied to inorganic insulating films such as 02 series.

〔Effect of the invention〕

According to the present invention, connection holes can be formed in an insulating film whose thickness varies depending on the location while keeping the diameter at the bottom of the connection hole constant, and the coverage of the four connection holes in the upper layer is improved and stable. This has the effect of ensuring good continuity.

[Brief explanation of drawings]

FIG. 1 is a process schematic diagram representing an embodiment of the present invention. Figure 2 is a diagram showing the connection point of a conventional inclined connection hole, Figure 3
The figure is a schematic representation of another embodiment of the invention. 101.301...Si substrate, 102,302...
Insulating film, 103, 303...81 layer At wiring, 104
゜304...Polyimide resin film, 105...Plasma CVDs io, a os-...Plasma CVD5
iN. 106.106'...Etching mask opening. 107.107'... Vertical connection hole, 107". 107", 307", 307"... Connection hole with a slope at the top, 307, 307'... Vertical connection hole formed halfway , d... Connection hole upper diameter * hl * hl
...No intermembrane thickness* dl! d2... Connection hole bottom diameter.・－゛、Representative Patent Attorney Tokaku Ogawa ゛Part / Figure 2 Figure 2 Figure 3

Claims (1)

[Claims] 1. When forming a connection hole in an insulating film to ensure electrical connection between an upper layer and a lower layer thereof, first, after forming a connection hole with a predetermined dimension and a substantially vertical side wall, 1. A method for forming a connection hole, which comprises etching the entire surface of the insulating film using reactive anisotropic etching, thereby tapering an upper portion of the connection hole. 2. The connection according to claim 1, wherein the insulating film is made of a polymer resin, and the reactive anisotropic etching is reactive etching using a gas containing oxygen as a component. How to form pores. 3. The method for forming a connecting hole according to claim 2, wherein the polymer resin is an aromatic polyimide-based polymer resin.