JPH01293346A - Mask for transferring pattern - Google Patents

Abstract

PURPOSE:To maintain the gap between a mask and wafer at a prescribed value by providing at least three conductive patterns, which measure electrostatic capacity, around an exposure area having a transfer pattern formed on a transfer mask. CONSTITUTION:Around the transfer pattern formed in the exposure area 12 of the transfer mask 1, at least three conductive patterns 4 for measuring electrostatic capacity are provided, and the patterns 4 are made of the same heat energy linear absorber with the transfer pattern. Two electrodes are imparted to the conductive patterns 4 and wafer 2 each; by measuring the electrostatic capacity of the capacitance whose dielectric is the air between the conductive patterns 4 and wafer 2, the gap between the mask 1 and wafer 2 is measured, and its value is fed back to an exposure device in real time. Thus, the gap between the mask and wafer is maintained at the prescribed value.

Description

[Detailed Description of the Invention] [Summary] Regarding a pattern transfer mask for photolithography used in a semiconductor device manufacturing process, the gap between the mask and a wafer can be measured accurately and in an extremely short time.
Our goal is to provide a pattern transfer mask that feeds back this value in real time to the moving device of the stage on which the wafer is placed, making it possible to always maintain the gap between the mask and the wafer at a predetermined value. At least three conductive patterns for capacitance measurement are provided around the pattern to be measured.

[Industrial application field]

The present invention relates to a pattern transfer mask for semiconductor devices. In particular, the present invention relates to improvements to facilitate measurement of the gap between a pattern transfer mask and a wafer.

[Conventional technology]

Conventionally, the following method has been used to measure the gap between a pattern transfer mask and a wafer. A laser beam or the like is irradiated obliquely to the mask surface, and interference fringes are generated by interference between the reflected light from the mask surface and the reflected light transmitted through the mask and reflected at the wafer surface. Detected using an image sensor,
From this, the wavelength of the interference wave is calculated using a fast Fourier transform method or the like. The gap between the mask and the wafer is determined using the relationship in which the interval between interference fringes is determined based on the gap between the mask and the wafer.

[Problem to be solved by the invention]

However, since the mask has a thickness, the laser beam is reflected by the upper and lower surfaces of the mask, and an interference wave of three laser beams is formed: these two reflected lights and the reflected light from the wafer surface. It is difficult to measure the gap accurately.

In particular, in the case of an X-ray exposure mask, the thickness of the mask is as thin as 2 to 6 μm to reduce absorption of X-rays, and the gap between the mask and the wafer is several 107 nm, which is about the same as the thickness of the mask. Therefore, it is possible to distinguish between interference waves formed by three reflected beams from the top surface of the mask, from the bottom surface of the mask, and from the wafer surface, and interference waves formed by two reflected beams from the bottom surface of the mask and from the wafer surface. That is difficult. In addition, calculating the wavelength from interference fringes requires complex calculation work and long calculation time. For example, when calculating using the fast Fourier transform method, it requires as many as 1.5 million calculations. It takes several seconds. When transferring a mask pattern onto a wafer, the position of the stage on which the wafer is placed may shift due to vibrations, etc., and the mask may be deformed due to temperature changes, so please keep the gap between the mask and wafer small. It is desirable to constantly adjust the gap between the mask and wafer by measuring it in real time and feeding it back to the moving device of the stage on which the wafer is placed, but if it takes more than 10 seconds to measure the gap, real-time control is necessary. is not possible.

The present invention aims to eliminate this drawback by measuring the gap between the mask and the wafer accurately and in an extremely short time, and feeding this value back in real time to the moving device of the stage on which the wafer is placed. An object of the present invention is to provide a pattern transfer mask that can always maintain a gap between the mask and a wafer at a predetermined value.

[Means to solve the problem]

The above purpose is to form at least three conductive patterns (4) for capacitance measurement around the exposure area (12) where the transfer pattern is formed on the transfer mask (1). This is achieved by using a transfer mask.

[Effect]

Refer to FIG. 3. The conductive pattern 4 for capacitance measurement formed with the same thermal energy ray absorber as the transfer pattern formed in the exposure area 12 of the transfer mask 1 is used as one electrode, and the wafer 2 is used as the other electrode. A capacitor is formed using air sandwiched between the picture electrodes as an electrode and a dielectric material. If an alternating current voltage E with an angular velocity of ω is applied between the conductive pattern 4 and the wafer 2, the current I flowing through the capacitor becomes I-ωCE.

Here, C is the capacitance of the capacitor. If we measure the current ■ flowing through the capacitor, we can find the capacitance C from the relationship I-ωCH, and if we find the capacitance C, we can change G- to -A.
The gap G can be found from the relationship: /C. Here, K is the dielectric constant of air, and A is the area of the conductive pattern 4.

The above calculation is simple, and gap measurements made using this formula can be made in an extremely short time, so the measurement results are fed back in real time to the moving device of the stage on which wafer 2 is placed to determine the position of the stage. The gap G between the mask 1 and the wafer 2 can be maintained at a predetermined value at all times.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS A pattern transfer mask according to an embodiment of the present invention will be described below with reference to the drawings.

See FIGS. 1(a) and (b) FIG. 1(a) is a plan view of a pattern transfer mask,
FIG. 1(b) is a sectional view taken along the line AA.

Reference numeral 1 denotes a mask made of silicon, silicon carbide, etc., with a thickness of 2 to 6 nm, around which a silicon ring 3 with a thickness of about 500 μm is formed, which is in turn formed into a reinforcing ring 11 made of quartz, ceramic, etc. with a thickness of about 5 m. It is glued. The mask 1 has an exposure area 12 on which a transfer pattern is formed, and a light-shielding frame 13 made of an energy ray absorber that blocks ultraviolet rays, X-rays, etc. is provided around the outer periphery of the exposure area 12 to enable attachment to a stepper or the like. ing. At least three conductive patterns 4 for capacitance measurement are formed on the outside of the light-shielding frame 13 and are made of substantially the same material as the energy ray absorber used for the transfer pattern of the mask.

The formation method is to deposit an energy ray absorber made of gold, tungsten, tantalum, etc. on a mask 1 made of silicon, silicon carbide, etc. using a sputtering method, etc., and then pattern it to form a layer in the exposed area 12. transfer pattern, shielding frame 13, and conductive pattern 4 for capacitance measurement
and the external drawer door 14 are formed at the same time. In addition,
At least three conductive patterns 4 for capacitance measurement are provided, and the gaps at at least three locations are made equal, thereby making it possible to arrange the mask and the wafer in parallel.

The diagram shown in FIG. 2 is an example of the conductive pattern 4 for capacitance measurement,
It consists of a circular pattern 4 with a diameter of about 2 cm and leads 14 led out from this, and a shielding layer 15 for shielding noise from the outside is formed on the outside of these. It goes without saying that the shape of the conductive pattern 4 for capacitance measurement is not limited to the shape shown in the figure, and can be freely selected as long as the required area is obtained.

〔Effect of the invention〕

As explained above, in the pattern transfer mask according to the present invention, at least three conductive patterns for capacitance measurement are formed around the pattern to be transferred, and the conductive patterns and the wafer are used as picture electrodes. Since the gap between the mask and the wafer is measured by measuring the capacitance of a capacitor that uses air as a dielectric between the conductive pattern and the wafer, the gap can be measured in a short time of 10 Ims or less. The measurement results can be fed back to the exposure apparatus in real time, so that the gap between the mask and the wafer can always be maintained at a predetermined value. Furthermore, the measurement accuracy has also been improved, and the accuracy has decreased from about ±0.2za in the prior art to about ±0.025n. Furthermore, since the conductive pattern for capacitance measurement is formed at the same time as the patterning of the transfer pattern, manufacturing is extremely simple.

[Brief explanation of the drawing]

FIG. 1(a) is a plan view of a pattern transfer mask according to an embodiment of the present invention. FIG. 1(b) is a sectional view taken along line AA of a pattern transfer mask according to an embodiment of the present invention. FIG. 2 is an example of a conductive pattern for capacitance measurement. FIG. 3 is a diagram illustrating the principle of gap measurement. DESCRIPTION OF SYMBOLS 1... Mask, 2... Wafer, 3... Silicon ring, 4... Conductive pattern for capacitance measurement, 11... Reinforcement ring, 12... Exposure area, 13... Light shielding frame, 14... External drawer lead, 15... Noise shielding layer.

Claims (1)

[Claims] A pattern transfer mask characterized by having at least three conductive patterns (4) for capacitance measurement around a pattern to be transferred.