JPS62144331A - Etching method - Google Patents

Abstract

PURPOSE:To etch a mask layer with excellent controllability, maintaining the size of an opening section in the mask layer as it is while improving the capacity of fine processing by forming the mask layer deformed by heat and thermally treating the mask layer at a temperature where only the surface is deformed. CONSTITUTION:A device in which a mask layer 2 with an opening section 3 is shaped onto a body to be etched 1 is thermally treated at a temperature where only the surface of the mask layer 2 is deformed, only the surface is brought to a temperature higher than a glass transition point, and the shape of the opening section 3 in the mask layer 2 is formed to a shape having a section 3a gradually narrowed from the exposed surface 1a of the body to be etched 1 through heat treatment. The form of the opening section 3 is controlled to a shape that the mask layer 2 is projected gradually from the size l3 of the exposed section 1a of the body to be etched 1. When the size l3 of the exposed section 1a takes a small value, a shape proper to etching is acquired.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an etching method used in the manufacturing process of semiconductor integrated circuits and the like.

[Summary of the invention]

The present invention is an etching method for finely processing a semiconductor substrate, an electrode pattern, a wiring pattern, etc., in which the surface of a mask layer that is deformed by heat is heat-treated to have a shape that has a narrow opening in the mask layer. By deforming only and forming it and then anisotropically etching it,
This realizes microfabrication with a taper.

[Conventional technology]

In the manufacturing technology of semiconductor integrated circuits, research and development of fine etching methods is progressing in order to respond to the trend toward miniaturization of devices.

For example, in connection between an impurity region formed on a semiconductor substrate and a wiring layer, or in connection between wiring layers in a multilayer structure, openings are formed in an interlayer insulating film etc. by etching. The demand for higher precision in etching processing technology has been increasing since the trend toward miniaturization and multilayer structures.

By the way, the pattern rule for semiconductor integrated circuits is 1.5.
Etching is progressing to micrometers, 1.2μm, 1.0μm, and even submicrometers, and the etching process is mainly done by so-called RIE.
(reactive ion etching method). Since this RIE etching is anisotropic etching, a substantially vertical step is formed in the opening, which may cause problems in coverage when a wiring layer is formed on the step in the opening. Problems such as cutting will occur.

Therefore, a technology that aims to improve step coverage by alleviating such a step difference in the opening is attracting attention.As a method for alleviating such a step difference, a mask layer such as a photoresist is coated at a temperature of approximately 200°C or higher. There is a method of smoothing out the step difference using a high-temperature hake and etch-hacking it by etching with a low selectivity ratio, a method of applying heat treatment to the oxide film into which impurities are introduced, and attempting to reduce the desired step difference.
Methods such as using side walls or using adhesive flow films such as PSG and As5G are known. [Problem to be solved by the invention] In the method of etchback using etching with a small selectivity, as shown in FIG. 3, by heating the mask layer 31 to a high temperature, a shape with gentle steps can be obtained on the object to be etched 32. Become.

However, the mask r having a gentle step 31a
When iW31 is etched back, a shape 33 as shown by the two-dot chain line in FIG.
The opening size il of the mask layer 31 tends to be larger than the original size il depending on the shape of the mask layer 31 . When the size 12 of the opening portion is formed to be large in this way, the size increases accordingly, making it difficult to achieve miniaturization and making it difficult to maintain dimensional accuracy.

These problems are similar to other conventional methods of reducing step differences, and methods using reflow films also have problems such as limitations on materials.

As described above, conventional etching methods are unable to cope with the trend toward miniaturization of devices, mainly due to limitations in dimensional controllability.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide an etching method that is compatible with the miniaturization of devices and realizes microfabrication with a taper with excellent dimensional accuracy.

Means for Solving Problem c] The present invention has a substantially perpendicular opening on the object to be etched,
and a step of forming a mask layer that deforms due to heat, and performing heat treatment at a temperature that only the surface of the mask layer deforms,
The step of changing the shape of the opening of the mask layer by the heat treatment to have a portion that gradually becomes narrower from the exposed surface of the object to be etched, and performing anisotropic etching using the mask layer to form a groove by tapering the object to be etched. The above-mentioned problems are solved by an etching method comprising a step of forming a .

[Effect]

After intensive research to solve the above-mentioned problems, the inventors of the present invention realized that a shape suitable for etching can be obtained by thermally deforming only the surface of the mask layer, and devised the present invention. This is what was put out.

That is, a mask layer that is deformed by heat is formed, and heat treatment is performed at a temperature at which only the surface is deformed, so that only the surface is heated to a temperature higher than the glass transition point of the mask layer, and the shape of the entrance part of the mask layer is changed to the shape of the mask layer to be etched. It should have a portion that gradually becomes narrower from the surface where the object is exposed.

At this time, since only the surface is thermally deformed, excessive flow of the material forming the mask layer is prevented, and the dimensions of the openings in the mask layer are maintained as they are, making it possible to perform etching with good controllability and to improve microfabrication capabilities. will improve.

In addition, the shape of the mask layer opening can be controlled so that it has a portion that gradually becomes narrower from the exposed surface of the object to be etched.
The narrowed portion selectively blocks ions of anisotropic etching incident on the opening, and therefore a groove having a desired taper can be easily formed.

It is not yet clear why the opening has a shape that gradually becomes narrower from the exposed surface of the object to be etched. However, the reason why such a shape is obtained is presumed to be due to the fluidity of the mask layer, the interaction between adjacent patterns, and the wettability with the underlying object to be etched.

〔Example〕

Preferred embodiments of the present invention will be described with reference to the drawings.

This embodiment is an etching method used in manufacturing semiconductor devices such as semiconductor integrated circuits, and is particularly used to realize fine processing such as forming openings and the like. below,
This embodiment will be explained step by step.

(a) As shown in FIG. 1a, a mask layer 2 is formed on the object to be etched 1 using a normal photolithography technique, and the size 13 of the exposed portion 1a of the object to be etched 1 at the bottom is formed. An opening 3 whose side wall is substantially perpendicular to the main surface of the object 1 to be etched is formed.

Here, the object to be etched 1 is, for example, a semiconductor substrate such as a silicon substrate, a compound semiconductor substrate such as GaAs, or an insulating film such as a silicon oxide layer or a silicon nitride layer formed on these substrates, an insulating film between the eyebrows, or a metal or This is a semiconductor wiring layer, etc.

The mask I'ii2 is a photoresist or the like,
For example, it is a resist material such as 0FPR800 (manufactured by Tokyo Ohka Kogyo Co., Ltd., trade name). In addition, without being limited to this, at a relatively low temperature, for example, about 130 to 150°C,
Any mask jti2 may be used as long as only the surface undergoes glass transition and is thermally deformed by heat treatment.

(b) As shown in FIG. 1, a mask layer 2 having openings 3 is formed on an object to be etched 1, and heat treatment is performed at a temperature at which only the surface of the mask Ft2 is deformed.
Only the surface is brought to a temperature above the glass transition point, and by this heat treatment, the shape of the opening 3 of the mask layer 2 is shaped to have a portion 3a that gradually becomes narrower from the exposed surface 1a of the object 1 to be etched.

The above heat treatment can be performed using, for example, a hot plate, and when the above photoresist is used, approximately 140
It can be heated at a temperature of c.

By this heat treatment, the object to be etched 1 can be formed into a shape having a portion 3a that gradually becomes narrower from the exposed surface 1a, so that the object to be etched 1 has a shape that gently protrudes from the size 13 of the exposed portion 1a of the object to be etched 1. Opening 3 in shape
The shape of is controlled.

For example, between the opening width 14 at the narrowest portion and the size ρ3 of the exposed portion 1a of the object to be etched 1, the opening width β4 has a smaller value, and the opening width β4 and the size β3 have a smaller value. The difference influences the size of the taber, which will be described later. An experimental result has been obtained that a shape suitable for the etching of the present invention can be obtained when the size β3 of the exposed portion 1a is a small value.

(c) As shown in FIG. 1C, etching is performed using the RIE method (reactive ion etching method). At this time, etching is performed under conditions that reduce the etching depth ratio of the material forming the mask layer 2 and the material forming the object to be etched 1. For example, using a normal RIE device, CH
Add oxygen to F3, 0.05m, Torr, 1.0~
Anisotropic etching may be performed under conditions of approximately 1.5 kW. As a result of the etching, only the groove portion 4 is initially formed with the opening width β4 at the narrowest portion.

Then, the etching progresses, and after the narrowest portion 3a is removed by etching, the formation of the taper begins.

Incidentally, FIG. 1C shows the cross-sectional shape of the groove portion 4 before the taper is formed.

During the etching, the etching may be stopped when 10% of the total amount removed by etching remains. This is 1 of the total amount removed by ethoching.
By the time 0% is left, a taper has already been formed in the groove, and by etching under conditions with a high selectivity, the object to be etched 1 is not etched off excessively, and the dimensional accuracy 7 reproducibility is improved. This is because excellent etching can be achieved. Machining and notching using such a method is particularly effective when opening a silicon oxide film or a silicon nitride film on a silicon substrate. In this case,
It is best to set the conditions in advance and proceed with etching while monitoring with a laser interference monitor or the like.

(d) After the narrowest portion 3a is removed by etching, the formation of the taper 5 begins, but at the same time, the opening 3 of the mask layer 2 also begins to retreat. For this purpose, the openings 3 of the mask layer 2 are etched, as shown in FIG. 1d.
The upper end is overcut and has a taper of 5
This means that the groove portion 4 having the shape can be easily formed. The shape of the taper 5 depends on the opening width 14 at the narrowest part and the amount of retraction of the mask J''f2, but these can be easily controlled by setting conditions, and therefore, it is possible to The shape can be adjusted.

The groove portion 4 having the taper 5 obtained through the above steps has a width 14 of the groove portion 4 which is the opening width 14 at the narrowest portion.
The value is approximately equal to . Therefore, it can be said that by using the etching method of this embodiment, the dimensional accuracy of the opening is good and etching can be performed with good controllability.

In addition, since the shape of the mask layer 2 is utilized during etching, problems such as the opening of the groove 4 being enlarged are eliminated, and grooves can be formed with excellent reproducibility.

Here, the experimental results will be explained with reference to FIG.

The experiment was carried out using the above-mentioned photoresist, 0F as mask layer 2.
PR800 (manufactured by Tokyo Ohka Kogyo Co., Ltd., trade name) is used, and a silicon oxide film is used as the object 1 to be etched. As a result of heat treatment and etching under the conditions described above, a groove 4 having a taper 5 as shown in FIG. 2 could be obtained. The spacing 6i between adjacent grooves 14 is finer than the spacing obtained by a conventional etching method, such as a method in which the step is made gentle and etched back by etching with a small selectivity. It has become.

The temperature for thermally deforming only the surface in the etching method of the present invention depends on the material of the mask layer 2 used, and can take a value specific to the material.

[Effects of the Invention] Since the etching method of the present invention performs heat treatment at a temperature at which only the surface is deformed by heat, excessive flow of the material forming the mask layer is prevented, and therefore the dimensions of the openings in the mask layer remain unchanged. can be etched with good controllability, and microfabrication is easy.

Therefore, by applying the present invention to the manufacturing process of semiconductor devices, it becomes possible to easily manufacture highly integrated devices.

Further, since the shape of the predetermined mask layer opening of the present invention can be controlled, a groove having a desired taper can be easily formed, and the shape of the taper has excellent reproducibility. Therefore, by applying the present invention, it is possible to form a wiring layer with high dimensional accuracy, and it is possible to prevent breakage and the like.

[Brief explanation of drawings]

FIGS. 1a to 1d are cross-sectional views for explaining the etching method of the present invention step by step. Further, FIG. 2 is a perspective view based on an experimental example for explaining the results of an experiment using the etching method of the present invention, and FIG. 3 is a sectional view for explaining problems with the conventional example. be. ■...Object to be etched 2...Mask layer 3...Opening 4...Groove 5...Taber

Claims (1)

[Claims] A process of forming a mask layer having a substantially perpendicular opening on an object to be etched and deformed by heat, and performing heat treatment at a temperature at which only the surface of the mask layer deforms. A step of changing the shape of the opening of the mask layer by heat treatment so that it has a part that gradually becomes narrower from the exposed surface of the object to be etched, and performing anisotropic etching using the mask layer to form a groove in the object to be etched by tapering the object. An etching method consisting of a step of forming.