JPH04317357A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:With regard to the manufacture of a contact hole in a shallow impurity-doped region, to form a contact hole by processing a dielectric oxide film using the anisotropic ion etching technique without damaging the surface of a silicon substrate. CONSTITUTION:A contact hole 12 extended to a silicon substrate 1 is formed by processing a dielectric oxide film 10 deposited on the substrate 1 using the anisotropic ion etching technique. A stopper layer 11, which is greater than the oxide film in the etching ratio, is sandwiched between the surface of the substrate 1 and the electric oxide film 10. Holes to be used for contact holes 12 are formed, at one end thereof stopped with the stopper layer 11, on the dielectric oxide film, 10 by the anisotropic etching, and the stopper layer 11 is then removed by the isotropic etching, thereby completing the contact holes 12. Here, the stopper layer 11 is constituted of an oxide film 3 deposited on the substrate 1 and a polysilicon film 7A laid over the oxide film 3.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of forming a contact hole in a shallow doped region.

With the miniaturization of integrated circuits, it has become necessary to form electrodes in regions with extremely shallow diffusion layers or shallow junctions. When electrodes are formed in such thin doped regions, damage near the surface of the impurity doped regions causes deterioration of device characteristics.

[0003] Therefore, there is a need for a method of forming a contact hole that penetrates a thick insulating oxide film and reaches the surface of the base substrate precisely and without causing deep damage to the surface of the base substrate.

0004

2. Description of the Related Art Conventionally, anisotropic ion etching such as reactive ion etching has been used as a method for forming contact holes in an insulating oxide film on a silicon substrate.

[0005] Such anisotropic ion etching is usually performed by applying an electric field to ions generated by plasma formation to turn them into high-energy particles, and causing the particles to collide with an insulating oxide film, thereby performing anisotropic etching.

[0006] Therefore, the vicinity of the etched surface is damaged by collisions with high-energy particles. Furthermore, the surface is covered with a layer contaminated with carbon, fluorine, etc. Therefore, in order to remove the damaged layer that occurs at the bottom of the contact hole, it is necessary to remove several tens of nanometers from the surface of the silicon substrate by isotropic etching that does not cause such damage.

[0007]

[Problems to be Solved by the Invention] As mentioned above, in the conventional method of forming a contact hole, a damaged layer is formed at the bottom of the contact hole. It was necessary to perform etching to a depth of nm.

[0008] Therefore, in regions where a high impurity concentration layer is formed on the surface to make contact, such as a source or drain region, the high impurity concentration layer on the surface is etched away and the contact resistance increases. Ta. In addition, when contacting a shallow diffusion layer, the surface of the diffusion layer is etched and thinned, and the contact surface and p-n
There is a problem in that the junctions are brought close together, leading to an increase in junction leakage current.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a semiconductor device in which contact holes are formed by anisotropic ion etching of an insulating oxide film without causing damage to the silicon surface.

0010

[Means for Solving the Problems] FIGS. 1 and 2 are process diagrams of an embodiment of the present invention, in which the process of forming a contact hole is shown in cross section.

Referring to FIG. 1, the first configuration of the present invention for solving the above-mentioned problems is to perform anisotropic ion etching on an insulating oxide film 10 deposited on a silicon substrate 1 to separate the substrate 1 from the insulating oxide film 10. A method for forming a contact hole 12 includes the steps of providing a stopper layer 11 having a large selectivity to the oxide film in the anisotropic ion etching between the surface of the substrate 1 and the insulating oxide film 10; Stopper layer 1
1 as a stopper to form a hole to become the contact hole 12 in the insulating oxide film 10 by the anisotropic ion etching, and removing the stopper layer 11 at the bottom of the hole by isotropic etching to form the contact hole. 12, and a second configuration is the method for manufacturing a semiconductor device according to the first configuration, wherein the stopper layer 11 is formed on the silicon substrate 1. The structure is characterized by consisting of an oxide film 3 and a polysilicon film 7A or an aluminum oxide film 14 deposited on the oxide film 3.

0012

[Operation] In the present invention, referring to FIG.
Anisotropic ion etching is used for etching. Therefore, the thick insulating oxide film 10 can be processed precisely and at high speed.

On the other hand, the anisotropic ion etching is stopped at the stopper layer 11. Therefore, damage caused by anisotropic ion etching remains within the stopper layer 11 and is not introduced into the underlying silicon substrate 1.

Furthermore, in the present invention, the stopper layer 11 is removed by dry or wet isotropic etching to expose the silicon surface. This isotropic etching is
Since high-energy particles are not used, no damage is introduced to the exposed silicon surface. Therefore, unlike the conventional method, there is no need to etch the silicon surface after forming the contact hole 12, and an increase in contact resistance and junction leakage current does not occur.

In order to obtain such an effect, the stopper layer 11
is a layer that has a high selection ratio with respect to the insulating oxide film 10 in anisotropic ion etching and a high etch rate with respect to silicon in isotropic etching.

[0016] As the material of such a stopper layer 11,
For example, Si3 N4 or various metals can be used. Furthermore, the stopper layer 11 can be made of a two-layered layer, for example, a thin film of polysilicon or Si3 N4 formed on the thin oxide film 3. At this time, the stopper layer 11 is removed by etching the polysilicon or Si3 N4 and then etching the oxide film 3 in two steps.

By using these two stopper layers,
The property of acting as a stopper in anisotropic etching and the property of removing silicon while leaving it behind in isotropic etching can be uniquely shared by layers with different properties. Therefore, it is possible to easily increase the selectivity of the stopper layer 11 with respect to the insulating oxide film 10 and the selectivity with respect to the silicon substrate 1 at the same time.

Note that the stopper layer 11 may be much thinner than the insulating oxide film 10, and deterioration in processing accuracy due to isotropic etching is usually within a negligible range.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained based on an embodiment with reference to FIG. First, referring to FIG. 1(a), a silicon substrate 1 is formed with an oxide isolation band 2, source and drain regions 4 and 5 with high concentration on the surface, using a normal MOS transistor manufacturing process.
, a gate oxide film 3 with a thickness of 8 nm, and a gate electrode 6 are formed.

Next, referring to FIG. 1(b), a thickness of 20
A polysilicon film 7 having a thickness of 7 nm is deposited by CVD or sputtering. Next, referring to FIG. 1(c), the polysilicon film 7 is removed by dry etching using the resist pattern 8 as a mask, leaving only the polysilicon film 7A where the contact hole 12 is to be formed.
After forming the stopper layer 11 consisting of the oxide film 3 and the oxide film 3, the resist is removed.

Next, referring to FIG. 1(d), an insulating oxide film 10 with a thickness of 600 nm is deposited by phosphor glass flow, a resist 9 is applied thereon, and a contact hole pattern 12A is opened by photolithography. .

Next, referring to FIG. 1(e), CF4
Contact hole pattern 12A was formed by parallel plate reactive ion etching using a mixed gas of
The insulating oxide film 10 is anisotropically etched until it reaches the polysilicon 7A. At this time, the polysilicon film 7A functions as a stopper for anisotropic etching.

Next, referring to FIG. 1(f), the bottom portion of the contact hole pattern 12A of the polysilicon layer 7A is etched by isotropic etching, for example, ion etching using a mixed gas of CF4 and O2, or It is removed by wet etching using fluoronitric acid.

Note that by removing a portion of the surface side of the polysilicon layer 7A using anisotropic ion etching in advance, deterioration in processing accuracy due to isotropic etching can be reduced.

Next, referring to FIG. 1(g), the oxide film 3
The bottom portion of the contact hole pattern 12A is removed by isotropic etching, for example, isotropic plasma etching using a mixed gas of CF4 and H2, or wet etching using buffered hydrofluoric acid to expose the silicon surface.

Next, referring to FIG. 1H, after removing the resist 9, a wiring material is deposited to form a contact, and then a wiring 13 is formed by patterning. FIG. 2 is a process diagram of another embodiment of the present invention, showing an example in which an aluminum oxide film is used in place of the polysilicon film 7.

Referring to FIGS. 2(a) and 2(b), aluminum oxide film 14 is used instead of polysilicon film 7 with IAD (IAD).
The film is deposited to a thickness of, for example, 10 nm by an on-Assisted Deposition method.

In the IAD method, oxygen ions are applied to the substrate during vapor deposition to improve the properties of the aluminum oxide film. Next, referring to Figures 2(c) and (d), CF4 and C
A hole that will become a contact hole 12 is made in the insulating oxide film 10 by parallel plate type reactive ion etching using a mixed gas of HF3.

The selectivity in this etching is Al2O
3 Film: SiO2 film = 1:200 and is very large, so it is possible to process a precise cross-sectional shape. Next, the aluminum oxide film 14 at the bottom of the hole is removed by immersing it in, for example, a buffered hydrofluoric acid solution.

Next, the oxide film 3 is removed by immersing it in, for example, a buffered hydrofluoric acid solution. At this time, while removing the 10 nm thick aluminum oxide film 14, the amount of the insulating oxide film 10 that is etched is only about 25 nm. Therefore,
Shape deformation can be reduced.

According to this embodiment, unlike polysilicon, aluminum oxide is an insulator, so there is no need to separate the aluminum oxide film 14 for each contact. Therefore, it is possible to omit the step of patterning the polysilicon film 7 as shown in FIG. 1(c).

[0032]

[Effects of the Invention] According to the present invention, even if a contact hole is formed using anisotropic etching of an insulating oxide film, no damage layer is formed on the silicon surface, and there is no need to etch the silicon surface. Since it is possible to form contact holes with high precision that allow contact with low contact resistance and low leakage current, it greatly contributes to improving the performance of semiconductor devices.

[Brief explanation of drawings]

[Figure 1] Example process diagram of the present invention

[Figure 2] Process diagram of another embodiment of the present invention

[Explanation of symbols]

1 Board 2 Separation strip 3 Oxide film 4 Drain region 5 Source area 6 Gate 7,7A Polysilicon film 8,9 Resist 10 Insulating oxide film 11 Stopper layer 12 Contact hole 12A Contact hole pattern 13 Wiring 14 Aluminum oxide film

Claims (2)

[Claims] 1. An insulating oxide film (10) deposited on a silicon substrate (1) is anisotropically etched to remove the silicon substrate (1).
In the method of forming a contact hole (12) with the substrate (1), the anisotropic ion etching has a large selectivity to the oxide film between the surface of the substrate (1) and the insulating oxide film (10). A step of providing a stopper layer (11) and a step of forming the contact hole (12) in the insulating oxide film (10).
) by the above-mentioned anisotropic ion etching using the stopper layer (11) as a stopper, and removing the stopper layer (11) at the bottom of the hole by isotropic etching to form the contact hole ( 12) A method for manufacturing a semiconductor device, comprising the step of forming. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the stopper layer (11) includes an oxide film (3) formed on the silicon substrate (1) and an oxide film (3) formed on the silicon substrate (1).
) a polysilicon film (7A) or an aluminum oxide film (14) deposited thereon.