JPH02212841A - Photomask and photomask blank - Google Patents

Abstract

PURPOSE:To reduce an average grain size and to obtain a smooth film structure by using NiCr:N (nitrogen-added nichrome alloy) for a light shielding layer. CONSTITUTION:Three layers; a layer in which nickel is added to chromium, a layer in which nitrogen is added to a nickel-chromium alloy and a layer in which oxygen and nitrogen are added to chromium, are successively formed on a transparent substrate. Namely, the particles grow larger than Cr, Cr:N:C, etc., if only the NiCr is used but the particle size is drastically reduced if N is added to the NiCr alloy. For example, the average grain size decreases from 70Angstrom to about 15Angstrom and the film having no cracking structure is obtd. if about 10% N is added to 80 to 20% NiCr. The finer average grain sizes are obtd. in this way and the smooth film structure is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a photomask blank and a photomask for semiconductor manufacturing. More specifically, the present invention relates to a photomask blank and a photomask configured with layers having finer grain sizes.

[Prior art and its problems] Chromium or a layer in which carbon (hereinafter referred to as C), nitrogen (hereinafter referred to as N), etc. are added to chromium (hereinafter referred to as Or) is a light-shielding layer of a photomask blank. is used as. These films are usually produced using a magnetron sputtering method, and the particle size is usually on the order of several tens of nanometers. This can be determined by taking a transmission electron microscope or an X-ray diffraction pattern.

The particle state of the film is required to be finer in order to form a fine pattern as a photomask. As the pattern of the photomask becomes finer, the grain size of the film is also required to become finer.

The average particle diameter of photomask blanks currently in use is several dozen, but Cr:N, Cr:lI:C(N
When the total amount of 1Ct, etc. is about 20 atomic %), it is about 30λ. This is calculated by reading the half-value of the diffraction peak measured using the X41 diffractometer for thin films.
It can be calculated using Cherrer's formula. Observation of the thin film using a transmission electron microscope reveals that the particles are of approximately the same size.

By the way, a low surface reflection blank can be measured with a scanning electron microscope at approximately I
When observed at a magnification of about 0,000 times, a crack-like structure on the order of several hundred particles can be seen. The structure of the blank is 700~B
oo Cr or Cr:N layer on top of Cr:O:N
73 is attached to about 300 people, so it appears to reflect the surface structure of the Habo base. In the shape after etching, irregularities on the order of several hundred were observed, and this is thought to be a factor determining the limit of miniaturization.

[Means for Solving the Problems] The above problems are solved by the present invention, which provides a photomask and a photomask blank using old Cr:N (nitrogen-doped nichrome alloy) in the luminescent layer.

[Function] According to the photomask blank of the present invention, a smooth film structure with a finer average grain size can be obtained;
, Cr:? If l:C or the like is used, a crack-like structure on the order of several hundred cracks will be formed.

With NlCr alone, the particles are rather Cr, Cr:N:
Although the particle size is larger than that of C, etc., it has been found that when K is added to the old Cr alloy, the particle size becomes significantly smaller. For example 80
Adding about 1O% H to ~20% prior Cr reduces the average particle size from 70 to about 15. Cr:N(PH
(approximately 20%), it is approximately 30 people. In other words, compared to Cr:C or Cr:N:C, the particle size of old Cr:If is about 1/2. Moreover, it was found that a film without crack structure could be obtained.

The structure has a base layer of about 20OA of Cr:N and an upper layer of C.
It is maintained even if about 300 people are formed.

Furthermore, the etching rate of each layer when laminated is affected by the relative value of each electrochemical potential. for example,
In a ceric ammonium nitrate etchant, which is an etchant for Cr, the potential difference with the platinum electrode is taken as an electrochemical potential, and if platinum is set to zero potential, (:r, cr:ll, NlCr, etc. are all negative potentials. However, if you use the smaller potential as the base layer and etch it, both the upper and lower layers will have the same etching rate as a single layer, but if you use the higher potential as the base layer, the upper layer will etch faster and the lower layer will etch slower than the base layer. Indicates rate.

This phenomenon needs to be taken into consideration. The reason is that the dimensional accuracy of the pattern formed by etching decreases if the etching speed is too high. Also, the cross-sectional shape of the pattern will be more vertical if the underlying layer is etched faster than the upper layer. In the opposite case, a tapered cross section is obtained. Considering the above, and taking an optical density of 2.8 as an example, the photomask blank of the present invention has the following four-layer structure in order from the surface.

1st layer Cr:0:N 280A (Surface anti-reflection layer) 2nd layer Old Cr:M 1[16OA (L and optical layer) 3rd layer Cr:N 200 people (etching end point detection layer) 4th J
il Transparent substrate Here, the light absorption coefficient α of the transparent layer is 60 (1/im)
and the others are zero.

Here, the total etching time and cross-sectional shape are adjusted by keeping the N concentration constant through Cr:N and NiCr:N, or by changing the N concentration in old Cr:N as necessary. .

[Example code] Next, the present invention will be explained in detail with reference to Examples.

Through the support hole, as 4 plates, ll0YA LE-30 (product name)
5''X 5'X O,09''' was used for normal cleaning treatment. This substrate was sputtered using a high frequency (RF) magnetron sputtering device (Nippon Anelva ILC-70).
5), sequentially Cr:N → ! 1lcr:N4Cr:
A film of 0:N was formed.

The mixing ratio of argon and nitrogen gas was adjusted so that the N114 degree in the film was about 10% in l1lCrJ, Cr:N.

The residual gas pressure was 3X10-@Torr, and the total gas pressure during sputtering was 1 to 3XIO''QTorr.

A film was obtained by designing the discharge power to be 1.1 Kf (2.2 r/am2) and adjusting the tray speed (speed at which the substrate advances over the sputtering target).

The surface of the prepared film was examined using a 5EW (scanning electron microscope).
When observed at 0000-100000 times, several 100
No human-scale cracked structure was observed in the membrane, and the membrane was found to be uniform and dense.

After this blank was microfabricated using a normal photolithography process, in-plane dimensional variations were examined.

Regarding dimensional variations, 25 points with the same dimensions due to the design
As a result of measurement at several places, the standard deviation is ±3σ, which is ±0.
07 μ Otori was obtained.

Note that Cr:O:N, NlCr:N1C used here
For r:N, the etch rate in the film thickness direction measured in a single layer is ~70λ/sea, IEt person/sec, 3
0λ/sea, but with this laminated structure, ~15G
person/sec, reλ/sea 130 seconds/ssc (estimated from the electrochemical potential profile in the etching solution). The size of the potential is (
Cr:O:N) < (Cr:N) < (old Cr:N
), and it was confirmed that the etching rate of Cr:O:N was increased.

[Effects of the Invention] According to the configuration of the present invention, a photomask blank and a photomask having a finer average particle diameter and a smooth FA structure are provided. Patent applicant: Toppan Printing Co., Ltd.

Claims (2)

[Claims] (1) Three layers are sequentially formed on a transparent substrate: a layer made of chromium with nickel added, a layer made of a nickel-chromium alloy with nitrogen added, and a layer made of chromium with oxygen and nitrogen added. A photomask blank made of (2) Form a pattern on a transparent substrate in three layers: a layer made of chromium with nickel added, a layer made of nickel-chromium alloy with nitrogen added, and a layer made of chromium with oxygen and nitrogen added. A photomask made of