JPH0551174B2 - - Google Patents

Description

[Detailed Description of the Invention] [Summary] This is a method for flattening a surface by etching back using ion beam milling, in which the incident angle of the ion beam is changed so that etching is performed in a direction parallel to the substrate at the stepped portion. The etching speed is set at an angle that is higher than the etching speed in the depth direction of the flat portion. Thereby, planarization can be easily achieved with fewer steps.

[Industrial application field]

The present invention relates to an etchback method using ion beam milling as a surface planarization technique in the manufacturing process of semiconductor devices.

[Conventional technology]

Currently, in multilayer wiring for increasing the density and speed of semiconductor devices, planarization of interlayer insulating films or wiring metals is considered to be an essential technique in order to prevent disconnections at stepped portions. The etch-back method and the sputter etch method, which are conventionally used as flattening methods, will be explained.

(1) Example of flattening using the etch-back method: Figure 4a
A metal wiring pattern 12 is formed on the insulating film 11 as shown in FIG.
For example, if there is a difference in level due to
SiO ₂ 13 is deposited by sputter deposition or plasma CVD, and then a resist 14 is applied, and the resist surface is flattened using the fluidity of the resist (FIG. 4b). Then, for example
Resist 14 and SiO ₂ are separated by CF ₄ /O ₂ plasma.
Etching is carried out under the condition that the etching speed of 13 is equal (FIG. 4c). Through the above process,
The surface can be flattened by filling the recessed region with an insulating film. However, when flattening a deep step, this method has problems such as the difficulty of flattening the surface with resist and the strict restriction that the etching speed of the resist and the material to be flattened must be equal. occurs.

(2) Example of flattening by sputter etching: 5th
As shown in figure a, a metal wiring pattern 2 is formed on the insulating film 21.
If there is a step due to 2, for example, as an insulating film
Sputter deposition or plasma CVDT of SiO ₂ 23
(FIG. 5b). After that, the surface is sputter etched using Ar plasma. Because of the angular dependence of sputtering efficiency, the corners of the stepped portion are selectively etched, making the step gentle (FIG. 5c). This method only selectively etches the corners of the stepped portion and does not result in sufficient flattening.

[Problem that the invention seeks to solve]

As mentioned above, with the conventional method, it is difficult to flatten deep steps, and the etching conditions are harsh.
Alternatively, the etching is still insufficient, such as selectively etching the corners of the stepped portions, and sufficient flattening cannot be achieved.

[Means for solving problems]

In order to solve the conventional problems, the present invention has been proposed to perform ion beam milling on the surface of a substrate having a step on the surface, which has a film thickness comparable to or greater than the step. a step of depositing a thin film of Au as a material whose etching rate in the depth direction monotonically decreases as the angle between the surface normal and the ion incident direction increases; and etching in a direction parallel to the substrate on the stepped slope. etching back the thin film by the ion beam milling, with the ion beam milling setting the ion incidence angle with respect to the normal to the substrate at an angle such that the etching speed is higher than the etching speed in the depth direction of the flat portion; Features.

[Effect]

According to the above, by utilizing the dependence of the etching rate on the ion beam incident angle, the convex portions of the surface can be selectively etched and the surface can be flattened.

If the ion incidence angle is defined as the angle θ with respect to the substrate normal, as shown in Figure 3a, then the dependence of the etching rate in ion beam milling on the beam incidence angle is generally determined by the normal incidence (θ=
0) (Fig. 3 b-31) and those such as Si, which reach a maximum at θ = 40° to 60° (Fig. 3 b-32). In any case, when the ion incidence angle θ is 60° or more, the etching rate decreases as the incidence angle increases and becomes zero at 90°. Therefore, when etching back a surface with steps at an ion incidence angle θ as shown in Figure 2, the incidence angle Θ on the step slope is Θ<θ, and the etching rate depends on the ion beam incidence angle. Depending on the nature and shape of the step, there is a value θ at which the etching rate R(Θ) on the stepped slope is greater than the etching rate R(θ) on the flat portion. Etching back at this angle of incidence makes it possible to selectively etch the thin film on the convex portion (hereinafter referred to as oblique ion beam milling).

〔Example〕

As an example of the present invention, a width of 1 μm and a thickness of 0.3 μm is shown.
For ion beam milling, which has a film thickness similar to or greater than the step only in the concave area of the surface of a substrate consisting of a SiO ₂ film pattern with a step on the surface, Figs. 2 and 3 show that As explained above, the first case is that the etching rate in the depth direction of a flat surface monotonically decreases as the angle between the surface normal and the ion incident direction increases, leaving Au as a material and flattening the surface. As shown in the figure. the above
Au5 is applied to the entire surface of the uneven surface consisting of the SiO ₂ film pattern 51.
2 is deposited to a thickness of 0.4 μm by sputter deposition, for example (FIG. 1a). Thereafter, etchback is performed by ion beam milling (ion beam 53) with an ion incidence angle of about 70°, for example. At this time, the etching rate on the stepped slope is about five times as high as the etching rate on the flat area, making it possible to selectively etch the Au on the convex area (FIG. 1b).
By performing the above etchback until the SiO ₂ film is exposed, Au is removed only in the concave areas of the SiO ₂ pattern.
, and the surface is flattened (Fig. 1c).

〔Effect of the invention〕

As explained above, by etchback using oblique ion beam milling, planarization can be easily achieved with fewer steps. This planarization etchback method is a method for flattening and
It has the advantage of having a wide range of applications, such as self-aligned pattern formation using concave patterns.

[Brief explanation of the drawing]

1A to 1C are cross-sectional views of main parts of the embodiment of the present invention, and FIG. 2 is a diagram for explaining the principle of the present invention.
Figures 3a and 3b are diagrams explaining the definition of the ion incidence angle and diagrams showing the relationship between the ion incidence angle and the etching rate, Figures 4 a to c, and Figures 5 a to c, respectively.
are process diagrams of the first conventional example and the second conventional example, respectively. 11... Insulating film, 12... Metal wiring, 13...
Interlayer insulating film, 21... Insulating film, 22... Metal wiring, 23... Interlayer insulating film, 51... SiO ₂ (pattern), 52... Au, 53... Ion beam.

Claims (1)

[Claims] 1. An ion film having a film thickness equal to or greater than the step on the surface of a substrate having a step on the surface.
For beam milling, depositing a thin film of Au as a material whose etching rate in the depth direction of a flat surface monotonically decreases as the angle between the surface normal and the ion incidence direction increases; The thin film is etched by the ion beam milling, in which the ion incidence angle with respect to the normal to the substrate is set at an angle such that the etching rate in the direction parallel to the substrate on the slope is greater than the etching rate in the depth direction on the flat part. A method for flattening a surface, comprising the step of etching back.