JPS63944B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the formation direction of a pattern having tapered edges.

In integrated circuit elements, bubble memory elements, etc., the elements are formed by stacking patterns one after another, so if there is a sudden change in the thickness of the lower layer pattern, the upper layer pattern will break off at that portion. Therefore, a technique for flattening the pattern after it is formed or a technique for forming the edges of the pattern into a tapered shape is required. Conventional taper etching methods have been carried out by controlling the adhesion between the photoresist and the film to be etched and performing chemical etching. However, this method can only be applied to a limited number of materials and has a limited range of applications. Furthermore, this method has problems in controllability, and in particular, it is difficult to form a uniform taper angle of a fine pattern of several μm. On the other hand, planarization techniques include (1) resist lift-off method, (2) anodic oxidation method, (3)
Coating methods such as resin etc. have been devised, but
These methods also have problems in that the range of use is limited and the number of man-hours increases.

SUMMARY OF THE INVENTION An object of the present invention is to provide a taper etching method that can be used to form a fine pattern with good controllability and has a wide range of applications.

That is, the present invention provides a first method to be etched.
A second layer is provided on the layer to control the taper angle of the pattern to be etched, and a mask pattern is formed using photoresist or the like on this second layer to form a sample, and this sample is rotated within the plane while ions are etched. A taper etching method in which the taper angle produced in the first layer is controlled by the second layer by performing etching by irradiating the beam in a shower shape from a direction tilted at a certain angle from the normal direction of the sample. be.

Ion etching (ion milling) is a method in which ions generated in an ionization chamber are accelerated with an appropriate acceleration voltage and collided with a sample to perform etching. In this etching method, the moving directions of the ions can be aligned, and the ions can be incident on the sample as a parallel beam bundle. Therefore, oblique etching is possible by appropriately tilting the sample surface with respect to the direction of ion incidence. The etching mechanism of ion etching is primarily due to the physical interaction of substances. Therefore, since all materials can be etched in principle, the range of applications is widened. However, the etching speed varies greatly depending on the material. The present invention utilizes this ion etching method,
The principle will be explained below.

FIG. 1 is a schematic cross-sectional view illustrating a conventional ion etching method using oblique incidence. As shown in a, a mask pattern 3 with a thickness h is formed on a film 2 to be etched with a thickness d attached to a substrate 1. ing. Using this mask pattern 3 as a mask, accelerated ions are irradiated in a shower shape from a direction 4 inclined by Θ from the normal direction of the sample. At this time, the sample is rotated, which is equivalent to the ion beam rotating and entering the sample as shown in the figure. When performing ion beam etching with oblique incidence, the incidence of the ion beam is partially restricted, so that a pattern generally having a shape as shown in b is formed. That is, a steep wall 5 is formed at the end of the mask material, and a gradual taper angle 6 is created as the distance from the mask end increases. In the case of a line-shaped pattern, the etching depth at the end of the mask is 1/2 of the film thickness d because the incidence of the ion beam is halved. Therefore, in the present invention, as shown in FIG. 2a, an auxiliary layer 8 of a different material with a thickness of d ₂ is provided on the layer to be etched 7 with a thickness of d ₁ to be patterned, and the thickness is adjusted as described above. When etching is performed using the mask pattern 3 of h as an etching mask, the etching rates v ₁ (Θ) and v ₂ (Θ) at the ion beam incident angle Θ of the layer to be etched 7 and the auxiliary layer 8 are as follows.
If the relationship d ₁ /v ₁ (Θ)=d ₂ /v ₂ (Θ) is satisfied, then
A formation as shown in FIG. 2b can be obtained. Here, if the ratio of v ₂ (Θ)/v ₁ (Θ) is made small, d ₂ also becomes small, so the step difference produced at the end of the mask pattern becomes small, and a tapered pattern can be obtained. If a chemical etchant or plasma etching gas that can selectively remove the auxiliary layer with respect to the etching layer is available, the auxiliary layer can be removed and separated, so the ratio of v ₂ (Θ) / v ₁ (Θ) is necessary. There is no need to make it small. The taper angle obtained by such a method is determined by the geometry and the etching rate of each layer.
Its reproducibility and controllability are better compared to conventional methods.
It's far superior. For example, consider the case where obliquely incident ion beam etching is performed at an incident angle Θ using a pattern with a mask thickness h as shown in FIG. 3 as a mask. In this case, the length of the shadow l is l=h
It is tanΘ. The etching speed of the mask is v _M (Θ)
If the film thickness of the mask changes to h' while etching the layer to be etched 7 and the auxiliary layer 8, then h' = h-{d ₁ (Θ) / v ₁ (Θ) + d ₂ (Θ) / V ₂ (Θ)}v _M (Θ) ...(1). The length of the shadow l′ at this time is l′=(h′+d ₁ +d ₂ ) tanΘ ……(2). If the taper angle produced in the layer 7 to be etched is expressed by α, α can be approximately determined from α=tan ⁻¹ {d ₁ /Max [l, l′]} . . . (3). Here, Max [l, l'] is assumed to take the larger value of both l and l'. (3)
Substituting equations (1) and (2) into the equations, the taper angle α is determined by each film thickness h, d ₁ , d ₂ and each etching rate v _M
(Θ), v ₁ (Θ), and v ₂ (Θ), the reproducibility is much better than that of conventional chemical etching methods.

Next, specific examples of the present invention will be shown.

Example 1 Alumina (Al ₂ O ₃ ) was deposited on a GGG bubble material substrate.
A three-layer film of titanium/gold/titanium (Ti/Au/Ti) was deposited at 100 Å each through a 5000 Å thick spacer.
Electron beam evaporation is performed to a thickness of 6000 Å and 1100 Å. Here, the lower Ti layer is a layer that strengthens the adhesion between alumina and Au, the Au layer is a layer to be etched, and the upper Ti layer is an auxiliary layer. AZ1350J (trade name, positive photoresist manufactured by Shipley) was patterned to a thickness of 1 μm, and then oblique incidence ion beam etching was performed at an ion beam incident angle Θ = 30°. The sample stage was rotated at approximately 3 rotations/min, and the etching conditions were an acceleration voltage of 500 V and an argon pressure of 2.0 × 10 ^-4 torr.
Perform etching for a minute. At this time, the taper angle generated in the Au pattern is approximately 40°. Since the upper Ti film as an auxiliary layer has a thickness of about 1100 Å, the step does not become a problem. Furthermore, when this Ti film is further laminated on top of it, it is advantageous not to remove it because it can be used as a layer for reinforcing adhesion to an insulating layer such as Al ₂ O ₃ . In addition, the partial pressure during oblique incidence ion beam etching is 3.0×10 ^-5 torr.
When etching is performed by mixing oxygen gas with argon gas, only the etching rate of Ti can be reduced, so the thickness of the upper Ti film can be made even thinner. In addition to Ti/Au/Ti, this method also uses molybdenum/gold/molybdenum (Mo/Au/Mo).
and tungsten/gold/tungsten (W/Au/
W) etc. can be similarly applied.

Example 2 Silicon dioxide (SiO ₂ ) on GGG bubble material substrate
4000 Å each of aluminum-copper (Al-Cu) (5% Cu) and Au via a 5000 Å spacer.
Electron beam evaporation is performed in this order to a thickness of 7400 Å. Here, Al--Cu is a layer to be etched, and Au is an auxiliary layer. On top of that, AZ1350J resist was patterned to a thickness of 1 μm, and then
Perform oblique incidence ion etching for minutes. The etching conditions were the same as in Example 1, with an acceleration voltage of 500 V and an argon pressure of 2.0×10 ^-4 torr. After etching is completed, the resist is removed using a plasma ashing method.
The peeling conditions were 0.5torr75W for 12 minutes. After resist removal, iodine/iodopotassium aqueous solution (KI: I ₂ :
Etching was performed for 1 minute with H ₂ O = 20 g: 10 g: 1000 c.c.) to remove Au. At this time, the taper angle created in Al-Cu is 20°.

Example 3 OMR ₈₃ (Tokyo Ohka's trade name, negative photoresist) was applied as an auxiliary layer to a thickness of 3200 Å, and a mask pattern with a thickness of 1.3 μm was formed using AZ1350J resist. The incident angle of the ion beam was 45°, the acceleration voltage was 500V, and the ion current density was
1.0mA/cm ² , argon pressure 2.0×10 ^-4 torr, 8
Perform oblique incidence ion etching for minutes.
OMR ₈₃ and AZ1350J resists are removed using OMR stripper. At this time, as the material to be etched,
The taper angle produced in the GaAs substrate is 20°.

As described in the three examples above, this method controls the taper angle of the pattern using a physical etching method called ion etching and the geometrical arrangement of each film thickness, so it has better controllability than conventional methods. It has excellent properties and the method is simple.

[Brief explanation of the drawing]

1A and 1B are schematic cross-sectional views of a sample for explaining the conventional oblique incident ion etching process, and FIGS. 2A and 2B are schematic cross-sectional views of a sample for explaining the process of the pattern forming method according to the present invention. 3 are schematic cross-sectional views of a sample for explaining the taper angle of the layer to be etched obtained by the present invention. 1... Substrate, 2, 7... Layer to be etched, 3...
...mask pattern, 4... direction of incidence of ion beam, 5... steep wall formed in pattern, 6...
...Taper angle generated in the layer to be etched, 8...Auxiliary layer.

Claims (1)

[Claims] 1. On a layer to be etched, having a thickness d ₁ and an etching rate V ₁ (θ) at an angle θ inclined from the normal direction of the film, that is, an ion beam incident angle θ,
Similarly, etching speed at ion beam incident angle θ
Form an auxiliary layer with V ₂ (θ) and a thickness selected as d ₂ ≧V ₂ (θ)/V ₁ (θ)・d ₁ , and form a mask pattern with resist on the auxiliary layer. The auxiliary layer and the layer to be etched are etched by irradiating the ion beam in a shower shape from a direction tilted at a certain angle from the normal direction of the sample while rotating the sample within the plane. A taper etching method characterized by continuously etching while creating a taper due to the shadow effect of a mask pattern, and then removing the auxiliary layer to obtain a pattern having tapered edges in the layer to be etched. .