JPS5928156A - Manufacture of exposure mask - Google Patents

Abstract

PURPOSE:To improve etching speed and pattern accuracy by etching an amorphous semiconductor layer contg. hydrogen atoms in plasma generated by glow discharge in a gaseous mixture of gaseous fluorocarbon with gaseous oxygen. CONSTITUTION:An a-Si:H layer 3 is uniformly coated with a photoresist 6, a previously manufactured mask 7 for exposure is mounted, and exposure is carried out. The unexposed parts of the photoresist 6 (the exposed parts in case of positive type) are removed by development. The layer 3 is etched by plasma etching as a dry process using a gaseous etchant such as a gaseous mixture of CF4 with 10% O2. An SiO2 film 13 formed on one principal side of a silicon wafer 10 by known thermal oxidation technique is coated with a photoresist 14, and a mask 11 for exposure obtd. by said etching is mounted on the photoresist 14. Ultraviolet light 15 is irradiated from a superhigh voltage mercury lamp of about 200W to expose selectively parts of the photoresist 14 not covered with the mask layers 3. The photoresist 14 is developed, and using the developed photoresist 14 as a mask the ground SiO2 film 13 is etched with an aqueous soln. of hydrofluoric acid, ammonium fluoride or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION 1. Field of Industrial Application The present invention relates to a method of manufacturing an exposure mask, and particularly to a method of manufacturing a photomask called a hard mask used in the manufacture of semiconductor devices and the like.

2. Prior Art Conventionally, hard masks using inorganic thin film materials have been used for exposure processing, and are considered useful because they have high surface strength and can be used repeatedly.

For this type of hard mask, high vacuum (~1O-0T
It is known that the light-shielding film is made of amorphous silicon (hereinafter referred to as a-8l) formed by electron beam evaporation or the like. This A-8T film has good see-through properties, allowing the underlying pattern to be seen through during semiconductor processing (that is, it is transparent to some extent for visible light). It exhibits light shielding properties against exposure beams of 3800X and 4aooX. The degree of this light blocking property is determined by the following optical density.
y).

Optical density = log (Io / I) (However, ・Io
(is the amount of incident light, and is the scene of transmitted light) However, the optical density of the above-mentioned commonly used A-81 film is at most 1.
．． 2 to 1.4, and a certain amount of incident light is transmitted, so it cannot be a perfect exposure mask. Therefore,
In order to achieve sufficient light-shielding properties, it is possible to increase the thickness of the A-81 film, but in this case, when etching the A-8I film from the mask material into a predetermined mask pattern, the thickness If the value is increased, the etching accuracy will deteriorate, and side etching will proceed too much, especially during wet etching, resulting in a defective mask pattern.

On the other hand, when forming the a-8t film, oxygen (0,) remaining in the Pelger or the film-forming tank mixes into the a-81 film, which causes oxidation of the a-8l film, etc. The film quality deteriorates. As a result, it was found that the optical density of the a-81 film decreased and its light shielding properties as a photomask deteriorated. This phenomenon cannot be avoided at a practical production level with conventional systems because oxygen of about 10-IQ to 10-'' Torr inevitably remains even if the Pelger or film-forming tank is made to have a fairly high vacuum. It cannot be done.

In addition, when etching the mask pattern as described above, a photoresist is coated on the a-8L film formed on the support (substrate), and this is exposed and developed in a predetermined pattern to form the mask. A method is known in which the underlying A-8L film is plasma-etched into a mask pattern in CF4 gas plasma. However, this processing method has an etching rate of 0.1 to 02 μm thick A-81.
The membrane is slow, for example, 10 minutes/100 cJ, and productivity is poor. Furthermore, since etching takes a busy time, as a result of long etching, the photoresist is damaged by plasma and its pattern accuracy is degraded.

3. Purpose of the Invention The purpose of the present invention is to improve the etching speed during processing such as the above-mentioned plasma etching and to improve pattern accuracy.

Another object of the present invention is to obtain an exposure mask with high optical density.

4. Structure and effects of the invention In other words, the present invention provides a method for etching a hydrogen atom-containing amorphous semiconductor layer (e.g., a-81 layer) formed on a support into a predetermined mask pattern using fluorocarbon gas (e.g., CF The method of manufacturing an exposure mask is characterized in that the hydrogen atom-containing amorphous semiconductor layer is etched in a plasma generated by a glue discharge of a mixed gas of a gas (e.g., gas) and an oxygen gas.

According to the method of the present invention, since an etchant gas (fluorocarbon gas) and oxygen gas are mixed during etching in the plasma, the concentration of atomic fluorine in the plasma is reduced for reasons explained in detail later. This can significantly increase the etching rate.
Moreover, since the amorphous semiconductor layer to be etched contains hydrogen atoms, the hydrogen effectively prevents the accumulation of fluorine-deficient carbon heptatonide (CFx) polymers that are generated during etching. In addition, the amorphous semiconductor layer itself can increase its optical density due to the hydrogen atoms contained therein, and exhibit desired light-shielding mask characteristics.

5. Examples Hereinafter, the present invention will be explained in detail with reference to the drawings.

1 to 6 illustrate various photomask materials that can be processed into photomasks according to the present invention.

The mask material 1 in FIG. 1 is an optically transparent quartz plate (si
o, plate) 2, a hydrogen atom-containing amorphous silicon (hereinafter referred to as a-81:H) layer 3 is provided. StO as a substrate, thickness of plate 2 is 0.5-3
mm (preferably 1 to 2.5 mm), and the pa thickness of the a-81:H layer 3 is 300 to 5000X (preferably 700 to 3000X). This mask material 1 is manufactured by a method described later and processed into a desired exposure mask.

In the example shown in FIG. 1, a non-quartz plate (e.g., soda lime, borosilicate) whose coefficient of thermal expansion is close to a-81 can be used as the substrate.

Figure 2 shows a non-quartz plate 12 made of soda lime, borosilicate, etc.
First, a sto film 4 is formed on top to a thickness of 100 to 5000x (preferably 100 to 3000x), and a-
8t: H layer 3 is provided. In this case S10. Membrane 4 extends from substrate 12 to a-8l: Hlti 3 to N
This prevents the a-8t:H layer 3 from being contaminated by contamination by impurities such as a.

None of the mask materials shown in FIGS. 1 and 2 are provided with an anti-reflection means, but when the semiconductor surface is processed, which will be described later, the light reflected from the same surface is further reflected by the mask surface and the surface of the semiconductor surface is reflected. It is preferable to provide an antireflection film to prevent the photoresist film from being accidentally exposed to light.

In FIG. 3, an antireflection film 5 made of asi containing oxygen atoms, H, or a-81 containing oxygen atoms is provided on the -a-81:H layer 3, and this antireflection film serves as a mask for reflected light. This example shows an example in which the light is guided into the layer to prevent it from being re-reflected on the mask surface.

The thickness of the antireflection film 5 is set to a value that minimizes one reflection depending on the wavelength used during exposure.

FIG. 4 shows the anti-reflection film 5 as described above in a-8l:H layer 3.
An example is shown in which it is also provided between the substrate 2 or 12.

The outer shape of the exposure mask material on each side (or the exposure mask described later) may be square as shown in FIG. 5, or square as shown in FIG. 6, depending on the size of the semiconductor wafer to be processed. It may have the same shape as the wafer. In addition, as another shape, as shown in FIGS. 7 and 8, one having a notch or a straight portion 1a for peripheral alignment can be used.

Alternatively, for the same purpose, each corner of a quadrilateral may be removed in a straight line or in an arc shape, a pair of opposing sides of a quadrilateral may be bent into an arc shape, or it may be simply circular.

The exposure mask material 1 exemplified above has a predetermined amount (special KO,
a-81:H containing 1 to 30 at%) hydrogen atoms
Because it includes Layer 3, the optical density at the wavelength used is significantly improved compared to the conventional A-8L see-through mask. That is, the data shown in FIG. 13 (the wavelength used is 4aooX, the thickness of the a-stsH layer is 100OX) VC
According to
．． It can be seen that in the range of 3 to 25 atoms, the optical density is higher than that of the conventional Sl mask (1.2 to 1.4), and in the range of 0.5 to 20 atoms, the optical density is improved by 2 to 4 times. It is noteworthy that the optical density increases rapidly in the range where the hydrogen content is low, which clearly shows the advantage of actively introducing hydrogen atoms into a-81 according to the present invention. There is.

The hydrogen content in the a-31:H layer was determined by forming a homogeneous film on a high-resistance Sl wafer and using the infrared absorption spectrum of the film (the wafer thickness in this case is, for example, ~500 μm-a- The film thickness of 8l:H is, for example, 1 to 5 μm.
). The a-8l:H layer itself was formed by the vapor deposition method described later (FIG. 11). An example of the above-mentioned infrared absorption spectrum is shown in FIG. 14.
Obtain by paying attention to the stretching vibration pressure.

The hydrogen concentration N(i-8) is estimated to be about 10 atoms in the illustrated example when determined from the N-KXI (K is a constant) relational expression. However, this is just an example, and the hydrogen concentration can also be determined based on other known methods. In this way, the a-8lCH layer exhibits a high optical density due to the predetermined amount of hydrogen content. Therefore, the film thickness can be reduced, and the processing accuracy or sharpness of etching, which will be described below, is greatly improved.

That is, for example, in the case of etching by wet processing,
As shown in FIG. 9A, a known photoresist 6 (for example, negative type photoresist) is uniformly coated on the a-81:H layer 3, and then, as shown in FIG. 9B, a previously prepared exposure mask 7 is placed. and expose.

The exposure beam 8 passes through the non-masked portion 9 of the mask 7 and exposes the underlying photoresist 6 in a predetermined pattern.

Next, for example, the unexposed portion of the photoresist 6 (the exposed portion in the case of a positive type) is removed by development, leaving a pattern as shown in FIG. 9C. Then, as shown in FIG. 9D, the photoresist 6
Using the mask as a mask, the underlying a-81:H layer 3 is plasma etched and patterned.

FIG. 9E shows the exposure mask 11 manufactured in this manner.

This mask 11 is made of a silicon wafer 10 formed by a known thermal oxidation technique on one main surface of a silicon wafer lO as shown in FIG. 9F.
A photoresist 14 is applied on the 102 film 13, and an exposure mask 11 is placed on the photoresist. At this time, since the a-8i:H layer 3 of the mask 11 is transparent to visible light, if some pattern (for example, element isolation field 810, film, etc.) already exists on the surface of the wafer 10, , the pattern can be observed and therefore mask alignment can be performed more accurately. Next, e.g.
Irradiate with an ultra-high pressure mercury lamp of about 0W, mask Ifff 3
The photoresist 14 under the non-masked portion where no mask exists is selectively exposed. The mask layer 3 made of a-81:H does not transmit the light 15 in the above-mentioned wavelength range and exhibits sufficient light-shielding properties. Furthermore, as shown in FIG. 9G, using the developed photoresist 14 as a mask, the underlying 5LO2 film 13 is etched with hydrofluoric acid, ammonium fluoride aqueous solution, etc., and a desired pattern is left on the wafer 10. In this way, contact holes 16 for covering electrodes or wiring, for example, can be formed in the 5-lot film 13.

In the above-mentioned exposure mask manufacturing process 9, especially
In the etching step shown in Figure D, a dry process is performed using plasma etching (the etchant gas is e.g. CF, +O,
A-8i:
It is extremely important to etch the H layer 3. This will be explained below.

For this dry etching, a plasma etching apparatus as shown in FIG. 10 is used, for example.
7 is a holder for holding the substrate 2, 18 is a mesh tube for shielding, 19 is a plasma generation chamber, 20 is a high frequency electrode, and 21 is a high frequency power source. For example, a mixed gas 22 of etchant gas such as CF4 and 02 is placed in the etching tank 2.
3, plasma radicals are generated by p-discharge using a high-frequency peep pressure trap, and these radicals are introduced into the substrate 2 in the reaction chamber 24 through the mesh of the mesh tube 18.

This causes the a-81:H layer on substrate 2 to be plasma etched as described above. Note that this plasma etching is not limited to the apparatus shown in the figure, and can be performed using a known parallel plate type plasma etching apparatus. In addition to plasma etching, other dry etching methods such as reactive sputter etching can also be applied. Ru.

During dry etching in such a plasma, for example, a mixed gas of CF and Ol is used.
Fluorine radicals involved in etching are generated from 0, while fluorine-deficient CFx generated at the same time reacts with 0, and additional fluorine radicals are generated during this reaction.

As a result, the etching speed is significantly improved, e.g.
．． 1 minute/10 for a□-St film with a thickness of 1 to 0.2 μm
It can even be 0 cd. Further, the fact that the above-mentioned CFx reacts with hydrogen atoms in the a-81 film to prevent its polymerization also contributes to improving the etching rate.

In addition, according to the above photomask, since a predetermined amount of hydrogen atoms are contained in the amorphous semiconductor (especially a-81) layer, the contamination of residual oxygen into the semiconductor layer during film formation is significantly reduced. As a result, the optical density of the 7 mol 7 as semiconductor layer as a mask layer is improved particularly in the ultraviolet region, and the light-shielding property during exposure processing can be partially improved.
Therefore, even if the film thickness is thinner than the conventional one, the photomask can have the desired optical density, so the etching precision (processing sharpness) of the amorphous semiconductor layer is improved during etching for processing into a photomask, and the desired optical density is achieved. It becomes possible to obtain pattern accuracy or fine patterns.

From the above, it has been found that the hydrogen atom content of the amorphous semiconductor layer is preferably 0.1 to 30 atomic % (ratio of the number of hydrogen atoms to the total number of atoms in the layer). Further, if a-81 is used as an example of the above amorphous semiconductor, dry etching (for example, plasma etching using a fluorine-on gas as an etchant gas) can be performed satisfactorily.
The results are further improved by the fact that the membrane can be made thinner. That is, since the film thickness of the a-8l:H layer 3 can be made as thin as, for example, about 100 OX, the etching accuracy is extremely high. Therefore, side etching, which could not be avoided in the past, can be prevented, and pattern accuracy as an exposure mask can be significantly improved. That is, the shift pattern (side etch amount) from the designed line width was conventionally 0.3±0.
2 μm, but in the present invention, it is 0.1±0.1 μm, which greatly improves accuracy.

``Therefore, this exposure mask is particularly useful for semiconductor ICs.

It is very useful for miniaturization process in LSI etc.

Next, an apparatus for manufacturing an exposure mask material to be processed into an exposure mask according to the present invention will be described.

FIG. 11 shows a vacuum evaporation apparatus for forming the a-8l:H layer 3 described above. That is, the exhaust path 3 has the Pelger 301C butterfly flaps 32 forming a vacuum chamber.
A vacuum pump (not shown) is connected through 8, whereby the inside of the Pelger 3o is preliminarily heated to η, for example, 10"" to 10
-' Torr (e.g. 5X 10-' Torr)
The substrate 2 is placed inside the Pelger 3o and heated to a temperature of 150~150℃ using the heater 34.
500°C, preferably 200-450”C (e.g. 30
0° C.) and introducing activated or ionized hydrogen gas into the Pel jar 30 at, for example, 5×10 −1 Torr using the gas introduction tube 36 equipped with a discharge tube 37 , the Pel jar 3o is heated to face the substrate 2 . Silicon is heated and evaporated from a silicon evaporation source 25 disposed at. This heating means may be an electron beam 27 using an electron gun heating device 26 or a resistance heating method. Also,
A negative bias voltage, for example -
A DC voltage 35 of 10 kV or less may be applied.

As shown in FIG. 12, the hydrogen gas discharge tube 37 surrounds a discharge space 43, which has one cylindrical electrode member 42 having a gas population 41 and this one electrode member 42 at one end. For example, it consists of a discharge space member 44 in the form of a cylindrical glass ring, and another ring-shaped electrode member 46 provided at the other end of this discharge space member 44 and having an outlet 45, and the one electrode member 42 and the other electrode By applying a DC or AC voltage between the member 46 and the hydrogen gas supplied through the gas population 41, a glue discharge is generated in the discharge space 43, whereby hydrogen atoms activated by electronic energy active hydrogen and ionized hydrogen ions are discharged from the outlet 45. The discharge space member 44 in this illustrated example has a double pipe structure and is configured to allow cooling water to flow therethrough, and numerals 47 and 48 indicate a cooling water inlet and an outlet. 49 is a cooling fin for one electrode member 42; The distance between the awakening electrodes in the hydrogen gas discharge tube 37 is 10 to 15 cTrL, and the applied voltage is 500 to 8
00V, and the pressure in the discharge space 43 is about 10-'' Torr.

In such a vapor deposition apparatus, hydrogen gas is activated by electric discharge and introduced, and a negative voltage for absorption is applied to the substrate 2 while heating the substrate 2. Therefore, the thickness deposited on the substrate 2 is reduced. For example, hydrogen atoms are effectively and sufficiently pressured into the a-8l membrane of about 1500X, and residual oxygen in the Pelger that attempts to enter the membrane is effectively expelled. Therefore, oxidation of the obtained a-8l:H film is prevented, its light-shielding properties are improved, and the above-mentioned plasma etching rate is improved. Further, the heating temperature of the substrate 2 may be lower than that in the case of a known CVD apparatus, or the substrate 2 may be operated at room temperature without being heated. In any case, by using this vapor deposition apparatus, a-81 containing a desired amount of hydrogen can be deposited at a high film forming rate.

Note that the above-mentioned oxygen-containing A-81 layer 5 or 810W layer 4
(See FIGS. 2, 3, etc.), it is sufficient to introduce O3 into the Pel jar shown in FIG. 13, but in this case, the supply of hydrogen gas is stopped or the supply amount is reduced. StO
, layer 4 may further be formed by evaporation of 5iO1810, under the introduction of oxygen. By using the above-mentioned apparatus, a film obtained by using germanium instead of silicon or by simultaneous vapor deposition of silicon and germanium can also be made to contain hydrogen and improve its optical density.

In the above-mentioned example, a fluorinated carbon gas other than CF may be used as the gas used in plasma etching, and the amount of oxygen to be mixed can also be varied. good.

In addition, when a mixture of silicon and germanium or pure germanium is used instead of the above-mentioned silicon as a light-shielding layer of a photomask and a film is formed by the method described above, a mixture of silicon and germanium containing hydrogen and having a high optical density can be formed. Alternatively, a germanium film can be obtained. Further, in addition to the above-mentioned vapor deposition method, sputtering method or the like can be applied to form the light shielding layer.

[Brief explanation of drawings]

The drawings are for illustrating the present invention; FIG. 1, FIG. 2, FIG. 3, and FIG. 4 are cross-sectional views of each side of the exposure mask material; FIG. 5, FIG. 6, FIG. FIG. 8 is a plan view showing the outline of each side of the exposure mask material or the exposure mask, and FIGS. 9A to 9
Figure E is a cross-sectional view showing the processing method for an exposure mask in the order of steps, Figures 9F and 9G are cross-sectional views of each main process when processing a semiconductor using an exposure mask, and Figure 1'O is a plasma etching diagram. A schematic cross-sectional view of the device. Fig. 11 is a schematic cross-sectional view of the vacuum evaporation device, Fig. 12 is a cross-sectional view of the gas discharge tube, Fig. 13 is a graph showing the relationship between the hydrogen atom content in a-8l and its optical density, and Fig. 14. is an infrared absorption spectrum diagram of the a-8i:H film. In addition, in the symbols shown in the drawings, 1......Exposure mask material 2...・Substrate 3・
・・・・・・・・・・・・・・・・・・ a-8i: H layer 4
．． 13...5ill membrane 5...
・・・・・・・・・・・・Anti-reflection film 11 ・・・・・・
・・・・・・Exposure mask 6.14 ・・・・・・
... Photoresist 8.15 ...... Exposure beam 20 ...... High frequency electrode 22 ...... ...cF4+on, Agent Patent Attorney Hiroshi Aisaka (1 other person) Figure 5 Figure 6 Figure 9A Figure 9B Figure 9C Figure 9D Figure 11/jl Figure 9E Figure 9F Figure 96

Claims (1)

[Claims] l. When etching a hydrogen atom-containing amorphous semiconductor layer formed on a support into a predetermined mask pattern,
1. A method for manufacturing an exposure mask, comprising etching the hydrogen atom-containing amorphous semiconductor layer in plasma generated by glue discharge of a mixed gas of fluorocarbon gas and oxygen gas. 2. The method according to claim 1, wherein the amorphous semiconductor layer is formed of amorphous silicon. 3. The method according to claim 1 or 2, characterized in that the fluorocarbon gas is CF.