JPS6249353B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION An object of the present invention is to provide an etching method that is effective in forming a metal thin film pattern formed on a support substrate, such as a hard mask often used in the manufacture of semiconductor devices.

As is well known, in the manufacturing process of semiconductor devices, hard masks have come to be used frequently in recent years to form predetermined impurity regions on semiconductor wafers by ion implantation or diffusion methods, or to provide metal wiring. Ta.

Conventionally, such hard masks have been made by forming a metal thin film of chromium and chromium oxide in this order on a quartz glass substrate, drawing a desired pattern using photoresist technology, and then coating the exposed metal thin film with cerium nitrate after development. It was made by removing the resist film using an etching solution such as an ammonium-based or ammonium-based etching solution, and finally removing the resist film.

However, since the etching end point of such a metal pattern was determined visually and by experience, it was extremely inaccurate and required many reworks.

The purpose of the present invention is to provide a chemical etching method that eliminates such inconveniences during pattern formation of metal thin films, automatically detects the end point of etching, and enables highly accurate etching. While injecting etching solution into a rotating thin film substrate, the amount of transmitted light or reflected light when irradiating light onto a specific pattern of the thin film is controlled under specific conditions, that is, synchronized with the rotation of the metal thin film substrate. Alternatively, the measurement is performed synchronously at a rate of an integral number of rotations, and the injection of the etching liquid is stopped when no temporal change in the amount of measured light is detected.

Next, one embodiment of the method of etching a metal thin film pattern according to the present invention will be described in detail using an example of a chromium-chromium oxide film-based hard mask.

Chrome over 25 square inches of low expansion glass
A mask pattern is formed using photoresist technology on an opaque film formed by stacking 550 Å and 250 Å of chromium oxide, and the photoresist is developed to expose the mask pattern using a cerium nitrate-based etching solution that is often used as an etching solution. liquid was used.

First, before placing the mask pattern on a light-transmitting support that rotates at approximately 300 revolutions per minute, the amount of light that passes through the support in this rotating state maximizes the scale of the synchroscope of the measuring instrument. After setting a constant light flux (point A in the figure), the rotation was stopped and the mask pattern was placed on the support. In order to obtain a constant luminous flux, a 20 watt halogen lamp turned on by a stabilized power source was used to illuminate the exposed area of the metal thin film through a lens through a lens. At this time, the light beam was circular with a diameter of about 6 mm, and as shown in the figure, the amount of transmitted light decreased to 5% of that before placement at the time the mask pattern was placed (point B in the figure).

Next, in this rotating state, a constant flow of cerium nitrate-based etching solution was injected from the center of the mask pattern, and after 32 seconds, the scale of the measuring device did not change.
As shown in the figure, it was determined that there was no longer any change in light intensity, so injection of the etching solution was stopped and cleaning was performed with deionized water.

By the way, in order to accurately measure the amount of transmitted light only in a specific part of a horizontally rotating mask pattern, the photocouplers are connected intermittently by small holes provided in a rotating plate attached to the rotating shaft of the mask pattern support. As a result, the amount of light transmitted through a specific part of the mask pattern is received by a phototransistor and measured by a synchroscope via a gate circuit that is set to open only during the period when an optical signal is generated.

In the above example, the amount of transmitted light in a specific part was measured at a rotation speed synchronized with the rotation of the mask pattern, but if the gate circuit is opened for the first time when the photocoupler is interrupted 30 times, Similar results were obtained even when the amount of transmitted light was measured for the first time after a specific part passed under the light beam 30 times.

The above etching operation was performed 10 times on a mask with a design standard pattern of 4 μm width, and the measurement accuracy was
When checked with a 0.05 μm micro-dimensional measuring device, data with a variation of 4±0.35 μm was obtained.

This value is considered to be a satisfactory value, since it is the sum total of errors in the photoresist exposure apparatus, errors in the development process, errors in the etching method of the present invention, and errors in etching uniformity. Conventionally, during chemical etching, only the etching liquid temperature and etching time were controlled, and in order to obtain proper etching results, it was cumbersome to perform several visual inspections after stopping etching. The etching method has the advantage that it is possible to obtain a proper etching result in one go, and that the finer the mask pattern, the higher the detection sensitivity to variations in pattern width. It has a great effect on improvement.

The cerium nitrate-based etching solution used for the chromium thin film was confirmed to have negligible absorption effects when measuring the amount of transmitted light. If there is, a wavelength band with less absorption may be used. That is, it is clear that, for example, a filter or a light emitting diode that emits a specific wavelength may be used.

By the way, to help understand the basic concept of the etching method of the present invention, an example of pattern etching control of a hard photomask for semiconductors has been explained. , e.g. thin film hybrid
In the case of an IC, a method may be adopted in which light is irradiated onto the mask pattern at a certain angle and the amount of reflected light is measured.

As described above, according to the method for etching a metal thin film according to the present invention, it is possible to effectively and accurately etch a metal thin film formed on any substrate, and it is also possible to perform highly accurate etching automation. This will make a major contribution.

[Brief explanation of the drawing]

The figure is a curve diagram showing the amount of transmitted light and etching time.

Claims (1)

[Claims] 1. When photoetching a metal thin film formed on a light-transmissive or light-reflective support substrate, a certain amount of light is incident on a specific area of the exposed pattern of the photoresist-treated thin film substrate, and the thin film substrate is rotated. In this state, the etching solution is injected, and the amount of transmitted or reflected light is measured in synchronization with the rotation of the thin film substrate or at a rate of one integer of the rotation speed, and the measured light amount is determined. A method for chemically etching a metal thin film, characterized in that the injection of the etching solution is stopped when a temporal change in etching is no longer detected.