JPH06347996A - Dry etching method for photomask - Google Patents

Abstract

PURPOSE:To provide the etching method which makes it possible to obtain a photomask having high accuracy by using a dry etching device having rotating magnetic fields. CONSTITUTION:A photomask substrate 11 is mounted on an RF electrode 10 surface in an etching chamber 2 of the dry etching device 1 having the rotating magnetic fields by electromagnets 5 to 8 and a pattern material is etched by reactive ion etching under the conditions of 50 to 150 gauss magnetic field intensity of the electromagnets, 0.03 to 0.3Torr reactive gaseous pressure in the etching chamber and 0.20 to 0.32W/cm<2> RF electric power density of the electrodes. The controllability of plasma is good and selection ratios are improved. The pattern material of the photomask is subjected to the etching with small CD loss, good intra-surface uniformity and high accuracy by setting magnetic field intensity, reactive gaseous pressure and RF electric power density to the values described above.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching method applied to a photomask manufacturing process used for manufacturing semiconductor devices and the like.

[0002]

2. Description of the Related Art Conventionally, in dry etching of an IC substrate, a rotating magnetic field is formed by an electromagnetic coil in an etching chamber, and the IC substrate covered with a pattern material is etched therein. The IC board used for this is
A Si wafer, on which poly-Si and an oxide layer + poly-Si are formed in layers as pattern material (Kevin G. Donoho
e: “Si trench etching by Precision 5000 Etch”, Semiconductor World 7 (8) pp.97-103 (1988)).
In the case of a photomask, the substrate is a quartz substrate and the pattern material is a Cr film, a Cr film with an antireflection film, or an SiO ₂ film such as SOG (sol-gel SiO ₂ by spin coating). No etching method using an etching apparatus has been proposed. It goes without saying that different pattern materials generally have different etching conditions, but there are large differences in the optimal etching conditions due to differences in etching requirements and performance goals. It was impossible to estimate the etching method for photomasks using different pattern materials and photomask substrates.

When etching is performed using a dry etching apparatus having a rotating magnetic field by an electromagnetic coil, the ionization and dissociation efficiency of plasma is enhanced even at low pressure due to the magnetron discharge by the magnetic field, and the DC bias applied to the substrate is increased by increasing the magnetic field strength. It is known that the DC bias can be lowered even with a relatively high RF power, and etching with high etching rate and low damage can be performed. Further, by rotating the magnetic field, uniform etching can be expected over the entire substrate.

[0004]

The structure to be etched is conventionally one in which a pattern material such as a poly-Si layer, an oxide layer + a poly-Si layer is formed on a substrate of a Si wafer, and The requirements and performance targets are, for example, in the case of silicon trench etching, opening width ≧ 0.5 μm,
Opening depth ≧ 10 μm, selection ratio (Si vs. thermal oxide film) ≧ 20:
1. The uniformity is ≦ ± 3% in the wafer, CD loss (critical dimension loss) <0.1 μm, sidewall angle is 85 to 90 ° by shape control, but it is etched by photomask etching. The structure is Cr on the quartz substrate
Film, Cr film with Cr oxide antireflection film, or SiO such as SOG
_Two films, for example, the pattern is a linear pattern and the line width is 2 to 4
μm, in-plane uniformity is 120 mm x 120 mm, and the line width is 3
σ ≦ 0.06μm, CD loss 0.08μm, etching depth 0.1-0.4μm, selection ratio (Cr or SiO ₂ to resist) 1.4-3 or more, which is remarkable for Si wafers. The etching content is different from the example. Therefore, it is necessary to optimize the dry etching conditions unique to the photomask, and by analogy with the etching conditions of the conventional example,
It is difficult to find the desired dry etching conditions.

It is an object of the present invention to provide a photomask etching method capable of obtaining a highly accurate photomask by using a dry etching apparatus having a rotating magnetic field by an electromagnetic coil.

[0006]

According to the present invention, Cr and Cr with an antireflection film are formed on an RF electrode surface in an etching chamber of a dry etching apparatus having a reaction gas introduction port, a vacuum exhaust port, and a rotating magnetic field formed by two pairs of electromagnets. , A photomask substrate covered with a pattern material such as SiO ₂ and provided with a photoresist having a pattern formed thereon, the magnetic field strength of the electromagnet is 50 to 150 gauss, and the reaction gas pressure in the etching chamber is 0. The pattern material was etched by reactive ion etching under conditions of 03 to 0.3 Torr (4 to 40 Pa) and RF power density of the electrode of 0.20 to 0.32 W / cm ² .

[0007]

When the dry etching apparatus having a rotating magnetic field is used to dry-etch the photomask substrate, the controllability of the plasma is good, the magnetic field strength on the surface of the photomask substrate is high, and thus the ionization and dissociation efficiency of the plasma is high. The effects expected from a dry etching device with a rotating magnetic field that can suppress the DC bias voltage applied to the photomask substrate even at low voltage can be obtained, but the magnetic field strength, reaction gas pressure, RF power density, and By setting the etching conditions of the reaction gas composition as described above, the selection ratio of the etching material to the resist is improved, the pattern processing accuracy is improved, and the in-plane uniformity of the photomask is improved. A photomask can be obtained.

[0008]

Embodiments of the present invention will be described with reference to the drawings.
In FIGS. 1 and 2, reference numeral 1 indicates a dry etching apparatus used for implementing the present invention. An etching chamber 2, a transfer chamber 3 and a substrate cassette stand 4 are housed in a panel 12 which constitutes the outer periphery of the dry etching apparatus 1, and electromagnets 5, 6, 7, 8 provided with the etching chamber 2 on the outer periphery thereof. I decided to set it inside. The electromagnet is a rectangular ring-shaped coil,
The electromagnets 5 and 6, and 7 and 8 are paired with each other, and low-frequency currents whose phases are shifted by 90 °, for example, are passed through these electromagnets. The coils of the electromagnets of each pair are wound in the same direction, and the combined magnetic field generated by the electromagnets 5 and 6 and the electromagnets 7 and 8 is parallel to the substrate, as indicated by the dotted arrows in FIGS. It is configured to rotate at the same frequency as the frequency of the low frequency current in the plane. In the etching chamber 2, a flat-plate RF connected to an RF power source 9 via a capacitor 13
The electrode 10 and the flat counter electrode 14 were provided so that the photomask substrate 11 was placed on the RF electrode 10 through the substrate delivery port 15 formed on the side of the etching chamber 2.

The photomask substrate 11 is shown in FIG.
As shown in one example, a transparent substrate 11a such as synthetic quartz is coated with Cr,
A photoresist 1 in which a pattern material 11b such as Cr or SiO ₂ with an antireflection film is thinly applied and a pattern is formed thereon.
1c is a common one. For the photoresist 11c, AZ-1350 (commercial item) similar to the IC substrate is used. The counter electrode 14 and the etching chamber 2 are kept at the ground potential. In order to supply a reaction gas for etching such as Cl ₂ + O ₂ into the etching chamber 2, a gas supply system 16 equipped with a gas cylinder or a mass flow controller is provided at the reaction gas inlet port 30. Exhaust system 1 equipped with a vacuum pump for controlling gas pressure
7 was connected to the vacuum exhaust port 18 of the etching chamber 2. As the reaction gas, CHF ₃ + O ₂ is used in addition to Cl ₂ + O ₂ .

A plurality of the photomask substrates 11 are housed in a cassette case 19, which is placed on the substrate cassette base 4, and is transferred from the cassette case 19 through a partition valve 20 by a transfer robot 21 during etching. Brought into chamber 3, then vacuum valve 22 and substrate transfer port 15
Is placed on the RF electrode 10 in the etching chamber 2 via. The transfer robot 21 is a known robot, which is a two-joint robot having a nodule 26 and a nodule 28, and has a motor shaft 24.
The reciprocating rotary motion of the tip portion of the transport arm 29 is performed by combining the rotary motions of the knot 26 and the knot 28. The movements of the first arm 25 and the second arm 27 are restricted in the horizontal plane. Movement of the tip of the transfer arm 29 between the cassette case 19 and the transfer chamber 3 via the partition valve 20, and the etching chamber 2 via the substrate transfer port 15.
The movement of the tip of the transfer arm 29 between the RF electrode 10 inside the transfer chamber 3 and the transfer chamber 3 is a rectilinear reciprocating motion due to the combination of the rotational movements of the robot arms 25, 27 and 29 at the motor shaft 24 and the nodes 26 and 28. Performed by. Substrate transfer between the vacuum valve 22 on the front surface of the substrate transfer port 15 and the partition valve 20 on the cassette case 19 side is performed by half-rotational movement of the transfer arm 29 of the transfer robot about the motor shaft 24 in the horizontal plane. . When the motor 23 provided outside the transfer chamber 3 is rotated, the plate-shaped transfer arm 29 mounts the photomask substrate 11 on the cassette case 19 and the RF electrode 1.
It rotates reciprocally to convey between 0.

When etching the pattern material of the photomask substrate 11 on the RF electrode 10, the etching chamber 2 is used.
A process of exhausting the inside by an exhaust system 17, introducing a reaction gas from a reaction gas introducing port 30, exciting two pairs of electromagnets 5, 6, 7, 8 and applying RF power to the RF electrode 10 to excite plasma. Go through. The same low-frequency alternating current is applied to the two pairs of electromagnets 5 and 6 and 7 and 8 in the same direction, and the electromagnet 5
By shifting the phases of the currents applied to the electrodes 6 and 7 and 7 and 8 by 90 °, a rotating magnetic field is formed in a plane parallel to the photomask substrate 11. Plasma generated between the RF electrode 10 and the counter electrode 14 is generated by the rotating magnetic field in the photomask substrate 11
Collected on the surface of the substrate, its density increases, the introduced reaction gas is efficiently dissociated, and a slight DC
Reactive ion etching is performed in a state where only a bias voltage is generated. In this case, the photomask substrate 11
Unlike IC substrates, it is synthetic quartz, not silicon,
The pattern material applied to the substrate is made of poly-S like the IC substrate.
i, oxide layer + polySi, not Cr, antireflection film Cr, S
Since it is iO ₂ etc., even if the reaction gas is introduced under the same conditions as the dry etching for the IC substrate, the selectivity of the etching material to the resist and the in-plane uniformity of the photomask are poor, but the magnetic field strength 50 to 150 gauss, and the reaction gas pressure in the etching chamber 2 is 0.03 to
By setting the RF power density of the electrode 10 to 0.3 Torr (4 to 40 Pa) and 0.20 to 0.32 W / cm ² , the selection ratio and the in-plane uniformity of dimensions are improved, and high precision is achieved. The photomask of is obtained.

A specific embodiment of the present invention is as follows.

Example 1 As a photomask substrate 11, a thickness of 6.35 mm, 152
On the surface of a synthetic quartz substrate having a size of × 152 mm, one Cr layer having a film thickness of about 750 Å is provided as a pattern material, or a Cr layer with a Cr oxide-based antireflection film having a film thickness of about 300 Å is further formed thereon. Layer or two layers,
A layer of this pattern material coated with AZ-1350 photoresist was used. A linear pattern having a line width of 2 to 4 μm was formed on the photoresist. The etching conditions were set as shown in Table 1 and the photomask substrate 11 was subjected to reactive ion etching.

[0014]

[Table 1]

This photomask substrate 11 is attached to the surface of the RF electrode 10 in the etching chamber 2 shown in FIGS. 1 and 2, and Cl ₂ + O ₂ is introduced as a reaction gas from the reaction gas inlet 30. The composition ratio O ₂ / (Cl ₂ + O ₂ ) is 10
-25%, the reaction gas pressure is 0.05-0.3 Torr (6.
7-40 Pa), magnetic field strength (amplitude of rotating magnetic field) 57-1
Reactive ion etching was performed on the photomask substrate 11 while changing the magnetic field rotation speed to 10 Hz and the power density of the RF electrode 10 to 0.2 to 0.32 W / cm ² . In this case, the magnetic field dependence of the etching rate and the selection ratio of the pattern material and the photoresist is shown in FIG. 4, the reaction gas composition ratio dependence is shown in FIG. 5, the reaction gas pressure dependence is shown in FIG. The power density dependence is shown in FIG. 7, respectively. Also,
The magnetic field dependence of the DC self-bias and plasma electron density is shown in FIG. 8, the reaction gas composition ratio dependence is shown in FIG. 9, the reaction gas pressure dependence is shown in FIG. 10, and the power density dependence of the RF electrode 10 is shown. 11 respectively. FIG. 12 shows the magnetic field strength dependence of the in-plane uniformity 3σ, and FIG. 13 shows the CD gain (CD loss with a negative sign) and the pressure dependence of the in-plane uniformity 3σ.
The RF power density dependency is shown in FIG. 14, and the electrode spacing dependency is shown in FIG.

In this case, the etching rates of the pattern material and the photoresist (AZ-1350) are 22 to 3 respectively.
At 5 mn / min and 6 to 27 nm / min, the selection ratio of the pattern material and the photoresist becomes 1.3 to 1.8 or more by observing the pattern cross section of the etching (FIGS. 4 to 7), and the pattern line width The in-plane uniformity 3σ (measured value of line width-three times the variance of average value of line width) was 0.06 μm or less. Furthermore, CD loss (critical dimension loss = design dimension-measured dimension) is smaller than 0.08 μm (Figs. 13 to 14), and DC
Bias voltage is 15 to 150 V, electron density is (2.8 to
8) × 10 ⁹ / cm ³ (FIGS. 8 to 10), the pattern shape was good.

In FIG. 24, the magnetic field strength is 100 gauss, the magnetic field rotation speed is 1 Hz, the gas composition ratio O ₂ / (Cl ₂ + O ₂ ) is 20%,
The reaction gas pressure is 0.10 Torr (13 Pa), the RF power density is 0.22 W / cm ² , and only one Cr layer having a thickness of about 750 Å is provided as a pattern material on the surface of the quartz substrate 11. An example of a cross-sectional shape of a SEM (scanning electron microscope) photograph of a product obtained by applying a photoresist of AZ-1350 to form a pattern and performing reactive ion etching is shown. In addition, FIG.
An example of a cross-sectional shape by an SEM photograph of a product obtained by applying a ZEP 810 electron beam resist instead of the above photoresist to form a pattern and performing reactive ion etching under the same conditions as above is shown in FIG.

On the other hand, the reaction gas is Cl ₂ + O ₂ , and the reaction gas pressure is 0.05 to 0.3 Torr as in the above case.
(6.7 to 40 Pa), the gas composition ratio O ₂ / (Cl ₂ + O ₂ ) is 10% or less or 2 even when the magnetic field rotation speed is 1 Hz.
5% or more and magnetic field strength of 57 gauss or less or 11
0 gauss, when the RF power density 0.20 W / cm ² or less, or 0.32 W / cm ² or more, the selectivity of 0.8 to 2.
8. The in-plane uniformity is 0.05 to 0.13, but one of them is worse than the above case, the CD loss is 1 μm or more, DC
The bias voltage is 40 to 300 V, and the electron density is (3 to 7.
7) × 10 ⁹ / cm ³ , and these numerical values were inferior to those in the above case, and the pattern shape was also inferior.

In Example 1, the distance between the RF electrode 10 and the counter electrode 14 was changed in the range of 40 to 80 mm, and the increase and decrease of the CD loss of this distance and in-plane uniformity were examined. It has been found that this gap is suitably 40 to 60 mm (Fig. 15).

Example 2 The material and shape of the photomask substrate 11 are the same as those of Example 1.
The same material as that of No. 1 was used, a SnO ₂ layer with a thickness of 150 Å was provided as an etching stopper layer on the surface of the substrate, and SOG (sol-gel SiO ₂ by spin coating) as a second pattern material had a thickness of 4000 on the surface.
It was applied to Angstrom. Next, a pattern of Cr, which is the first pattern material, was formed under the conditions of Example 1. A photoresist of AZ-1350 was applied on the second pattern material, and a linear pattern having a line width of 2 to 4 μm was previously formed thereon. Then, the reactive ion etching was performed by setting the etching conditions as shown in Table 2.

[0021]

[Table 2]

This photomask substrate 11 is attached to the surface of the RF electrode 10 in the etching chamber 2 shown in FIGS. 1 and 2 as in the case of the first embodiment, and CHF ₃ + O ₂ as a reaction gas is introduced from the reaction gas inlet 30. The gas composition ratio O ₂ / (CHF ₃ + O ₂ ) is 5 to 8%, and the reaction gas pressure is 0.0
3 to 0.05 Torr (4 to 7 Pa), magnetic field strength (amplitude of rotating magnetic field) 50 to 150 gauss, magnetic field rotation speed 1 Hz, power density of RF electrode 10 changed to 0.2 to 0.30 W / cm ² . Then, the reactive ion etching of the photomask substrate 11 was performed. In this case, the etching rate of the pattern material and the photoresist (AZ-1350) is 23 to 4 respectively.
At 8 nm / min and 0.8-15 nm / min, the selection ratio between the pattern material and the photoresist became 3 or more. DC bias voltage is 70-220V, electron density is (7-11) × 10 ⁹
/ Cm ³ , the pattern shape was good.

Further, the surface of the photomask substrate 11 has a thickness of 150 Å as an etching stopper.
An SnO ₂ layer is provided, and a second pattern material 40 is formed on the layer.
A 60 Å thick SOG layer is applied, and a 1000 Å thick Cr layer is further provided as a first pattern material on this, and a AZ-1350 photoresist (resist A) is applied to form a line having a line width of 2 to 4 μm. Pattern was formed. Next, under the conditions of Example 1, a photoresist (resist B) of AZ-1350 was applied on the pattern of Cr, which is the first pattern material, to form a linear pattern having a line width of 2 to 4 μm. Reactive etching was performed. The etching conditions are a magnetic field of 100 gauss and a reaction gas composition ratio O.
₂ / (CHF ₃ + O ₂ ) = 7%, reaction gas pressure 0.10 Torr
(13 Pa) and RF power density was 0.22 W / cm ² . FIG. 26 shows an example of the pattern shape of this SEM photograph.

On the other hand, even if the reaction gas pressure of CHF ₃ + O ₂ is 0.03 to 0.05 Torr and the magnetic field rotation speed is 1 Hz, the gas composition ratio O ₂ / (Cl ₂ + O ₂ )
Of less than 5% or more than 8%, magnetic field strength of less than 50 gauss or more than 150 gauss, RF power density of 0.2
When the 0 W / cm ² or less, or 0.30 W / cm ² or more, selectivity ratio becomes 0.6 to 3, both worse than for the, DC bias voltage 20～450V, electron density (5
To 11) in × 10 ⁹ / cm ³ even these numbers worse overall than in the case of the pattern shape was also poor.

In all of these examples, when the magnetic field strength was increased, the electron density monotonically increased and the DC bias voltage monotonically decreased. This shows that the ionization and dissociation efficiency of plasma is improved by the increase of the magnetic field strength (FIGS. 8 and 20). Further, when the magnetic field strength was increased, the Cr etching rate of Example 1 showed one maximum value in the magnetic field strength range of 0 to 150 Gauss (FIG. 4), and the SOG etching rate of Example 2 monotonically decreased. (Fig. 1
6). This is a behavior which cannot be predicted at all from the tendency of the etching rate of silicon monotonically increasing with increasing magnetic field strength in the above-mentioned material of Kevin G. Donohoe. Furthermore, in each of these Examples 1 and 2, the electron density and the
The DC bias voltage does not change significantly (Figs. 9 and 2).
1), the etching rate and the selection ratio of Cr and the photoresist in Example 1 change relatively slowly (FIG. 5), and the etching rate and the selection ratio of SOG and the photoresist in Example 2 change greatly and the selection ratio The range of the gas composition ratio in which the ratio is 3 or more is 5 to 8%, which is extremely narrow (FIG. 17).

In the above embodiments, C is used as the pattern material.
Although Cr with an oxide type antireflection film of r, Cr is used, other known pattern materials with an antireflection film such as Cr with a nitride type antireflection film of Cr may be used. Further, a SiO ₂ film formed by sputtering or vapor deposition may be used instead of the SOG pattern material used in the above-mentioned embodiment. AZ- for photoresist
Photoresists other than 1350 or electron beam resists other than ZEP810 can be used. Furthermore, in the above-described embodiment, the example in which the linear pattern is formed on the photoresist has been described, but the method of the present invention can be applied to a pattern other than the linear pattern in which a contact hole is formed.

[0027]

As described above, according to the present invention, since the dry etching apparatus having the rotating magnetic field by the electromagnet is used for the dry etching of the photomask substrate, the controllability of the plasma is good and the DC bias is applied even at the low pressure. Since the voltage is low and the damage to the photoresist is small,
Improved selection ratio, magnetic field strength of 50 to 150 gauss, reaction gas pressure of 0.03 to 0.3 Torr, RF power density of 0.2
By setting it to 0 to 0.32 W / cm ^{2, there} is an effect that the CD loss is small in the pattern material of the photomask and highly accurate etching with good in-plane uniformity can be performed to obtain a highly accurate photomask. .

[Brief description of drawings]

FIG. 1 is a plan view in which a part of a dry etching apparatus used for implementing the present invention is cut away.

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is a cross-sectional view of a photomask substrate

FIG. 4 is a characteristic diagram showing a relationship between an etching rate and a selection ratio and a magnetic field.

FIG. 5 is a characteristic diagram showing a relationship between an etching rate and a selection ratio, and a reaction gas composition ratio.

FIG. 6 is a characteristic diagram showing the relationship between the etching rate and the selection ratio and the reaction gas pressure.

FIG. 7 is a characteristic diagram showing the relationship between the etching rate and the selection ratio and the RF power density.

FIG. 8 is a characteristic diagram showing the relationship between electron density and self-bias voltage.

FIG. 9 is a characteristic diagram showing the relationship between electron density, self-bias voltage, and composition ratio of reactive gas.

FIG. 10 is a characteristic diagram showing the relationship between electron density, self-bias voltage, and reaction gas pressure.

FIG. 11 is a characteristic diagram showing the relationship between electron density, self-bias voltage and RF power density.

FIG. 12 is a characteristic diagram showing the relationship between in-plane uniformity and magnetic field strength.

FIG. 13 is a characteristic diagram showing the relationship between in-plane uniformity and CD gain and pressure.

FIG. 14 is a characteristic diagram showing the relationship between in-plane uniformity and CD gain and RF power density.

FIG. 15 is a characteristic diagram showing the relationship between in-plane uniformity, CD gain, and electrode spacing.

FIG. 16 is a characteristic diagram showing the relationship between the etching rate, the selection ratio, and the magnetic field.

FIG. 17 is a characteristic diagram showing a relationship between an etching rate, a selection ratio, and a reaction gas composition ratio.

FIG. 18 is a characteristic diagram showing the relationship between the etching rate, the selection ratio, and the reaction gas pressure.

FIG. 19 is a characteristic diagram showing the relationship between etching rate, selectivity and RF power density.

FIG. 20 is a characteristic diagram showing the relationship between electron density, self-bias voltage, and magnetic field.

FIG. 21 is a characteristic diagram showing the relationship between electron density, self-bias voltage, and composition ratio of reactive gas.

FIG. 22 is a characteristic diagram showing the relationship between electron density, self-bias voltage, and reaction gas pressure.

FIG. 23 is a characteristic diagram showing the relationship between electron density, self-bias voltage, and RF power density.

FIG. 24: SEM of photomask substrate after etching
Cross-section photo sketch

FIG. 25: SEM of photomask substrate after etching
Cross-section photo sketch

FIG. 26: SEM of photomask substrate after etching
Cross-section photo sketch

[Explanation of symbols]

1 Dry Etching Device 2 Etching Chamber 5, 6, 7, 8 Electromagnet 9
RF electrode 11 Photomask substrate 11b Pattern material 11c Photoresist 18 Vacuum exhaust port 30 Reactive gas inlet

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yaichiro Watakabe 4-Chome, Mizuhara, Itami City, Hyogo Prefecture Mitsubishi Electric Co., Ltd. LSE Research Laboratories (72) Inventor Akihiko Ueno 2562 Terao, Chichibu, Saitama Prefecture 3 (72) Inventor Kosei, 6474-3 Yokose, Yokose-cho, Chichibu-gun, Saitama Prefecture (72) Atsushi Hayashi 2129-7 Yokose, Yokose-cho, Chichibu-gun, Saitama Prefecture Palace Heim 202

Claims (4)

[Claims] 1. A photoresist in which a pattern material is covered and a pattern is formed on an RF electrode surface in an etching chamber of a dry etching apparatus having a reaction gas introduction port, a vacuum exhaust port, and a rotating magnetic field of two pairs of electromagnets. The photomask substrate provided with is attached, and the magnetic field strength of the electromagnet is set to 50
˜150 gauss, reactive gas pressure in the etching chamber is 0.03 to 0.3 Torr (4 to 40 Pa), and RF power density of the electrode is 0.20 to 0.32 W / cm ² by reactive ion etching. A method for dry etching a photomask, characterized in that the pattern material is etched by means of: 2. The two pairs of electromagnets are provided outside the etching chamber, and one pair of electromagnets and the other pair of electromagnets are provided orthogonally to each other.
A method for dry etching a photomask according to. 3. The pattern material of the photomask substrate is a Cr film or a Cr film with an antireflection film, the magnetic field strength is 57 to 110 gauss, the reaction gas is Cl ₂ + O ₂ , and the gas composition ratio O thereof. ₂ / (Cl ₂ + O ₂ ) is 10 to 25%, the gas pressure is 0.05 to 0.3 Torr (6.7 to 40 Pa), and the RF power density is 0.20 to 0.32 W / cm ² 2. The method of dry etching a photomask according to claim 1, wherein the dry etching is performed by using. 4. The pattern material of the photomask substrate is
SiO ₂ film, the magnetic field strength is 50 to 150 gauss, the reaction gas is CHF ₃ + O ₂ , and the gas composition ratio is O ₂ / (CHF ₃
+ O ₂ ) at 5 to 8% and its gas pressure at 0.03 to 0.0
5 Torr (4 to 7 Pa), the RF power density is 0.20 to 0.
^2. The photomask dry etching method according to claim 1, wherein the etching is performed under a condition of 32 W / cm ² .