JP5434825B2 - Dry etching method - Google Patents

Description

  The present invention is for processing a photomask blank, which is a material of a photomask used for fine processing, such as a semiconductor integrated circuit, a CCD (charge coupled device), a color filter for an LCD (liquid crystal display device), a magnetic head, etc. into a photomask. The present invention relates to a suitable dry etching method.

  In recent years, in semiconductor processing, circuit pattern miniaturization has become more and more necessary, especially due to high integration of large-scale integrated circuits. There is an increasing demand for miniaturization technology of contact hole patterns for wiring. For this reason, even in the manufacture of photomasks with circuit patterns written thereon, which are used in photolithography to form these wiring patterns and contact hole patterns, a technique capable of writing circuit patterns more finely and accurately along with the above-mentioned miniaturization. Is required.

  In order to form a photomask pattern with higher accuracy on the photomask substrate, it is first necessary to form a high-precision resist pattern on the photomask blank. Photolithography when processing an actual semiconductor substrate performs reduction projection, so the photomask pattern is about four times as large as the actually required pattern size, but that does not mean that the accuracy is reduced. Rather, the original photomask is required to have higher accuracy than that required for the pattern accuracy after exposure.

  Furthermore, in the lithography that is currently being performed, the circuit pattern to be drawn is a size that is considerably smaller than the wavelength of the light to be used. If a photomask pattern in which the circuit shape is four times as it is is used, Due to the influence of light interference or the like that occurs during photolithography, the shape as in the photomask pattern is not transferred to the resist film. Therefore, in order to reduce these influences, it may be necessary to process the photomask pattern into a more complicated shape than an actual circuit pattern (a shape to which so-called OPC: Optical Proximity Correction (optical proximity effect correction) or the like is applied). Therefore, even in lithography technology for obtaining a photomask pattern, a highly accurate processing method is currently required. Lithographic performance may be expressed with a limit resolution, but this resolution limit is equivalent to or higher than the resolution limit required for optical lithography used in semiconductor processing processes using photomasks. Limiting resolution accuracy is required for the lithography technique in the photomask processing process.

  In the formation of a photomask pattern, a photoresist film is usually formed on a photomask blank having a light shielding film on a transparent substrate, a pattern is drawn with an electron beam, a resist pattern is obtained through development, and Using the resist pattern as an etching mask, the light-shielding film is etched to be processed into a light-shielding pattern. However, when miniaturizing the light-shielding pattern, keep the film thickness of the resist film as it was before miniaturization. If so, the ratio of film thickness to the pattern, the so-called aspect ratio, becomes large, the pattern shape of the resist deteriorates, and pattern transfer does not work well, and in some cases the resist pattern collapses or peels off. . Therefore, it is necessary to reduce the resist film thickness with miniaturization.

  On the other hand, as a light-shielding film material, silicon-based materials such as silicon-containing materials and silicon-and-transition metal-containing materials have superior light-shielding properties against exposure light of 200 nm or less, compared to conventionally used chromium-based materials. In addition, it can be processed by fluorine-based dry etching that hardly damages the resist pattern, and higher-precision processing can be performed (Patent Document 1: Japanese Patent Application Laid-Open No. 2007-244105). In addition, even when combined with technology that uses an etching mask to perform higher-precision processing, it is better to process a silicon-based light-shielding film using a chromium-based material as an etching mask. As a result, it has been found that pattern errors and processing errors due to side etching are smaller than when processing a chromium-based material (Patent Document 2: Japanese Patent Application Laid-Open No. 2007-24410). For this reason, as a next-generation light-shielding film material, a light-shielding film using a film made of a silicon-based material is considered promising.

  A method using a hard mask technique using a chromium-based material for a light-shielding film made of a silicon-based material described in Japanese Patent Application Laid-Open Publication No. 2007-244102 (Patent Document 2) is an advantageous method for performing high-precision fine processing. However, when manufacturing a photomask blank, a light-shielding film made of a silicon-based material must be formed, and then transferred to a different chamber to form a film made of a chromium-based material. For this reason, in the manufacturing process, the risk of occurrence of foreign object defects increases. In addition, after the formation of the light shielding film pattern, a process of removing the hard mask film made of a chromium-based material must be added. Therefore, a technique is expected in which a hard mask effect can be obtained by a more simplified photomask blank configuration and the number of overall steps can be reduced.

JP 2007-2441065 A JP 2007-2441060 A Japanese Patent Laid-Open No. 2001-27799 JP 2004-333653 A JP-A 63-85553 JP-A-7-140635 JP 2006-317665 A

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an etching method capable of selectively etching one of two layers made of a silicon-based material.

The present inventor paid attention to chlorine-based dry etching in examining the possibility of selective etching of the same series of silicon-based materials. A method for selectively etching one of the two layers containing silicon in contact with each other is disclosed in, for example, Japanese Patent Laid-Open No. 63-85553 (Patent Document 5), and contains a transition metal formed on a quartz substrate. When a silicon film is etched under chlorine-based dry etching conditions containing oxygen using silicon oxide (Si _m O _n ) as an etching mask, the silicon oxide etching mask and the quartz substrate are not damaged and contain a transition metal. It has been shown that silicon films can be selectively etched. However, a specific method for selectively removing silicon oxide is not shown, and silicon oxide is not always convenient because it is a material that easily generates foreign matter during sputtering film formation.

  Japanese Patent Laid-Open No. 2001-27799 (Patent Document 3) shows that the MoSiON film can be etched under chlorine-containing dry etching conditions containing oxygen. From a specific example, the oxygen content is about 20%. Until now, it has been shown that the etching rate is effective, and the etching rate gradually decreases as the amount of oxygen increases. However, in this case, since the etching rate does not change rapidly, it has been considered that selective etching is difficult even if the oxygen content is adjusted.

  As a result of intensive studies to solve the above-mentioned problems and pursuing the possibility of selective etching, even when silicon-based materials containing molybdenum, silicon, oxygen and / or nitrogen are used, molybdenum and silicon As a result, it was found that selective etching is possible by adjusting the amount of oxygen added to the etching gas by chlorine-based dry etching containing oxygen, thereby achieving the present invention. .

Accordingly, the present invention provides the following dry etching method.
Claim 1:
A first silicon-based material layer containing molybdenum, silicon, and oxygen and / or nitrogen;
Molybdenum, silicon, oxygen and / or nitrogen are contained, the total content (atomic%) of oxygen and nitrogen is equal to or less than the first silicon-based material layer, and the composition ratio of molybdenum and silicon (Mo / Si (atomic ratio)) is higher than the first silicon-based material layer, the second silicon-based material layer is the second silicon-based material layer, the first silicon-based material layer is It is a method of selectively removing by etching,
Using a chlorine-based dry etching gas containing oxygen, the ratio of the chlorine-based gas to the oxygen gas is set so that the etching rate of the second silicon-based material layer with respect to the etching rate of the first silicon-based material layer is increased. A dry etching method comprising: setting and selectively removing the second silicon-based material layer by etching.
Claim 2:
The composition ratio of molybdenum and silicon in the second silicon-based material layer (Mo / Si (atom)) with respect to the composition ratio (Mo / Si (atomic ratio)) of molybdenum and silicon in the first silicon-based material layer. 2. The dry etching method according to claim 1, wherein the ratio)) is 1.5 times or more.
Claim 3:
3. The dry etching according to claim 1, wherein the ratio of chlorine gas to oxygen gas (oxygen gas / chlorine gas (molar ratio)) is 0.0001 to 1 in the chlorine dry etching. Method.
Claim 4:
Chlorine containing oxygen while changing the ratio of chlorine gas to oxygen gas (oxygen gas / chlorine gas (molar ratio)) for the first silicon material layer and the second silicon material layer. Dry etching is performed to obtain an etching rate of each of the first silicon-based material layer and the second silicon-based material layer, and by comparing these, the second silicon-based material layer is converted into the first silicon-based material layer. The ratio of a chlorine-based gas and an oxygen gas that can be selectively removed by etching while leaving the system material layer is determined, and dry etching is performed under the condition in which the ratio is set. The dry etching method according to any one of claims.
Claim 5:
Etching the photomask blank or photomask manufacturing intermediate in which the first silicon-based material layer is formed on the substrate as the upper layer of the light-shielding film, and the second silicon-based material layer is formed as the lower layer of the light-shielding film. The dry etching method according to any one of claims 1 to 4.
Claim 6:
After the first silicon-based material layer is dry-etched with a chlorine-based gas that may contain oxygen, the first silicon-based material layer is dried without removing the photomask production intermediate from the dry etching chamber. Select the second silicon-based material layer, leaving the first silicon-based material layer, using an oxygen-containing chlorine-based gas whose oxygen content is higher than the etching gas used in the etching. 6. The dry etching method according to claim 5, wherein the etching is removed by etching.

  According to the present invention, one of the two layers made of a silicon-based material can be selectively etched. For example, in processing of a light-shielding film containing molybdenum and silicon, the light-shielding film is configured to include an upper layer and a lower layer, the lower layer has a higher composition ratio of molybdenum and silicon to the upper layer, and the total of oxygen and nitrogen If the light shielding film that constitutes each layer is formed with the content ratio (atomic%) of the upper layer being lower than the upper layer, the lower layer is processed using the upper layer pattern as a hard mask by adjusting the amount of oxygen in chlorine-based dry etching Can do. In the processing of the light shielding film having such a configuration, the light shielding film pattern can be processed in a continuous process while utilizing the hard mask effect in one dry etching chamber, thereby further simplifying the process. can do.

6 is a graph showing a change in reflectance of a film with respect to etching time, measured by changing an O ₂ flow rate in Experimental Example 1. 6 is a graph showing a change in reflectance of a film with respect to etching time, measured by changing an O ₂ flow rate in Experimental Example 2. It is the schematic which shows the dry etching apparatus used by the experiment example and the Example.

Hereinafter, the present invention will be described in more detail.
In the dry etching method of the present invention, the first silicon-based material layer containing molybdenum, silicon, oxygen and / or nitrogen, the second containing molybdenum, silicon, oxygen and / or nitrogen. The second silicon-based material layer is selectively etched away from the silicon-based material layer by dry etching, leaving the first silicon-based material layer.

  As the second silicon-based material layer, one having a total content (atomic%) of oxygen and nitrogen equal to or lower than that of the first silicon-based material layer is applied. In addition, the second silicon-based material layer has a composition ratio (Mo / Si (atomic ratio)) between molybdenum and silicon higher than that of the first silicon-based material layer.

The chlorine-based dry etching used here uses chlorine gas (Cl ₂ ) or the like, and oxygen is added under typical dry etching conditions typically used for etching a chromium-based material film of a photomask blank. The amount can be adjusted (by adjusting the ratio of oxygen gas and chlorine gas).

  Specifically, the ratio of chlorine gas to oxygen gas (oxygen gas / chlorine gas (molar ratio)) is preferably 0.0001 to 1, more preferably 0.0003 to 0.5, and particularly preferably 0. .0005 to 0.3. The flow rates of chlorine gas and oxygen gas may be, for example, 100 to 300 sccm for chlorine gas, 0.1 to 100 sccm for oxygen gas, or 1 to 20 sccm for helium gas. The gas pressure is preferably 1 to 10 mtorr.

  In this dry etching, a chlorine-based gas and an oxygen gas are used so that the etching rate of the second silicon-based material layer is increased relative to the etching rate of the first silicon-based material layer using a chlorine-based dry etching gas containing oxygen. The ratio is set. The selective etching condition for the second silicon-based material layer is that the ratio of chlorine-based gas to oxygen gas (oxygen gas / chlorine-based gas (molar ratio) for the first silicon-based material layer and the second silicon-based material layer. )) Is changed, and chlorine-containing dry etching containing oxygen is performed to obtain the etching rates of the first silicon-based material layer and the second silicon-based material layer. The ratio of the chlorine-based gas and the oxygen gas that can selectively etch away the silicon-based material layer leaving the first silicon-based material layer can be determined. If dry etching is performed under the condition in which this ratio is set, the second silicon-based material layer can be selectively etched.

  More specifically, for example, it can be determined by the following method. First, a film of a silicon-based material is formed on a substrate such as a quartz substrate used as a photomask substrate, and the oxygen gas content of the silicon-based material film is predetermined (oxygen gas and chlorine-based gas). Oxygen by performing multiple dry etchings with chlorine-based gas (with a predetermined ratio) by changing the oxygen gas content (changing the ratio of oxygen gas to chlorine-based gas) and obtaining their etching clear time. The etching rate of the silicon-based material film with respect to the added amount can be obtained.

  This etching clear time can be obtained by measuring the reflectance of the silicon-based material film during etching. In addition, when the silicon-based material film can be observed during etching, a visual method is used, and the plasma in the etching chamber is measured. A method based on analysis of ions or elements in plasma by analysis of emission spectrum or the like may be used. Also, instead of etching clear time, a part of the silicon-based material is masked, and after etching for a predetermined time, it is etched away by optical methods such as stylus type film thickness meter and transmittance, and ellipsometry. The etching rate can also be obtained by a method of measuring the film thickness, which may be applied in combination.

  In the chlorine-based dry etching containing oxygen with respect to the silicon-containing material containing molybdenum, the total content of oxygen and nitrogen is the same between the first silicon-based material layer and the second silicon-based material layer. Even if the composition ratio of molybdenum to silicon is different, an etching rate difference capable of selective etching can be obtained by controlling the amount of oxygen when performing chlorine-based dry etching. In particular, the composition ratio of molybdenum to silicon (Mo / Si (atomic ratio)) of the second silicon-based material is larger than the composition ratio of molybdenum to silicon (Mo / Si (atomic ratio)) of the first silicon-based material. If it is 1.5 times or more, an etching rate difference of 10 times or more can be obtained. In addition, although the upper limit of the ratio of these composition ratios is not specifically limited, Usually, it is 20 times or less.

Furthermore, if the total content of oxygen and nitrogen in the first silicon-based material layer is higher than that in the second silicon-based material layer (the total content of oxygen and nitrogen in the second silicon-based material layer is If it is lower than one silicon-based material layer, a higher etching selectivity can be obtained. For example, when there is a difference in the total content of oxygen and nitrogen between the first silicon-based material layer and the second silicon-based material layer, the total content of nitrogen and oxygen in the first silicon-based material layer If the difference (C ₁ -C ₂ ) between the rate C ₁ (mol%) and the total content C ₂ (mol%) of nitrogen and oxygen in the second silicon-based material layer is 5 or more By adjusting to an appropriate oxygen addition amount using the method as described above, the etching rate of the second silicon-based material layer is made larger than the etching rate of the first silicon-based material layer, particularly 10 times or more. Thus, an etching rate difference sufficient for obtaining selectivity can be obtained. Therefore, the second silicon-based material layer has a total content (atomic%) of oxygen and nitrogen equal to or lower than that of the first silicon-based material layer, and a composition ratio (Mo / Si (atomic ratio) of molybdenum and silicon). If it is higher than the first silicon-based material layer, selective etching with further margin becomes possible.

  Next, an embodiment for carrying out the present invention will be described in more detail by taking as an example the processing of a photomask blank for producing a binary mask, which is a preferred application example of the dry etching method of the present invention.

  The light shielding film of the binary mask blank used in the photomask blank processing method has an optical characteristic that the optical density with respect to the exposure light when using the photomask is preferably 2.5 or more and 4 or less as a whole. Used. When the etching method of the present invention is applied to a photomask blank having such a light shielding film or a photomask manufacturing intermediate, a light shielding film including an upper layer and a lower layer is formed on a transparent substrate such as a quartz substrate, and an upper layer is formed. Is the first silicon-based material layer and the lower layer is the second silicon-based material layer.

  Further, as an intermediate layer between the upper layer and the lower layer, a content ratio of molybdenum to the upper layer and silicon may be the same, but a layer in which the total content of oxygen and nitrogen is smaller than that of the upper layer may be provided. Each layer may be composed of multiple layers.

  The upper layer of the light shielding film of the photomask blank is preferably a layer having an antireflection function as well as a layer for obtaining a hard mask effect. Specific examples of silicon-based materials containing molybdenum, silicon, and oxygen and / or nitrogen constituting the upper layer include molybdenum silicon oxide, molybdenum silicon nitride, molybdenum silicon oxynitride, and molybdenum silicon oxycarbide. , Molybdenum silicon nitride carbide, and molybdenum silicon oxynitride carbide.

  The composition of the upper layer is 10 atomic percent to 95 atomic percent of silicon, particularly 30 atomic percent to 90 atomic percent, oxygen is 0 atomic percent to 50 atomic percent, particularly 0 atomic percent to 30 atomic percent, and nitrogen is 0 atomic percent. Atomic% to 40 atomic%, especially 1 atomic% to 20 atomic%, carbon is 0 atomic% to 20 atomic%, particularly 0 atomic% to 5 atomic%, molybdenum is more than 0 atomic% to 35 atomic% In particular, it is preferably 1 atomic% or more and 20 atomic% or less. In particular, the total amount of nitrogen and oxygen is 0 atomic percent to 60 atomic percent, particularly 0 atomic percent to 50 atomic percent, particularly 1 atomic percent to 40 atomic percent, and more preferably 1 atomic percent to 30 atomic percent. It is preferable.

  Specific examples of silicon-based materials containing molybdenum, silicon, and oxygen and / or nitrogen constituting the lower layer include molybdenum silicon, molybdenum silicon oxide, molybdenum silicon nitride, and molybdenum silicon oxynitride. , Molybdenum silicon oxycarbide, molybdenum silicon oxycarbide, and molybdenum silicon oxynitride carbide.

  In this case, the composition of the upper layer, which is the first silicon-based material layer, and the lower layer, which is the second silicon-based material layer, are each composed of molybdenum and silicon (Mo / Si (atomic ratio)), The first silicon material layer and the second silicon material layer are set so as to satisfy the total content (atomic%) of oxygen and nitrogen.

  For the light shielding film, the first silicon-based material and the second silicon-based material are selected according to the required optical density and reflectance, and the upper layer and the lower layer are appropriately selected depending on the absorption coefficient of these materials. The thickness of the intermediate layer is designed in the case of having a thickness and further an intermediate layer. However, in carrying out the dry etching method of the present invention, the upper layer is preferably 1 to 30 nm, more preferably 2 to 10 nm. It is preferable to have a thickness. The thickness of the lower layer and the intermediate layer is not particularly limited, but the effect of the present invention is particularly remarkable when the thickness of the lower layer is 20 nm or more.

  Furthermore, the light-shielding film to which the dry etching method of the present invention can be suitably applied has the required optical density and reflectivity for 193 nm exposure light even when the film thickness is 100 nm or less, and even 70 nm or less. It becomes the light shielding film which has.

  A method of processing the light shielding film of the photomask blank into a photomask by dry etching is performed, for example, in the following steps.

  As the first step, first, a resist pattern for protecting a region where the light shielding film is left is formed. Specifically, a resist film is formed on the light-shielding film of the photomask blank, pattern exposure is performed with a high energy beam such as an electron beam, a short wavelength light beam, EUV, etc., and a predetermined exposure is performed according to the type of the resist film. A resist pattern is obtained by developing after processing. The resist film used here may be either a negative type or a positive type as long as it can resolve the required pattern rule, and the material is not particularly limited, but basically a high resolution can be expected. It is preferable to use a chemically amplified resist. In order to prevent pattern collapse during development, the film thickness is preferably from 50 nm to 250 nm, particularly from 50 nm to 150 nm.

Next, the resist pattern is transferred onto the light shielding film by dry etching using a chlorine-based gas that may contain oxygen. Here, dry etching using a chlorine-based gas that may contain oxygen is an effective etching rate for the first silicon-based material in a test for confirming the above-described etching selectivity performed prior to actual processing. The etching gas composition is obtained to obtain Usually, the mixing ratio of chlorine gas and oxygen gas (Cl ₂ gas: O ₂ gas) that gives this effective etching rate is found in the range of 1: 2 to 20: 0 by volume, and if necessary An inert gas such as helium may be mixed and used. The flow rates of chlorine gas and oxygen gas can be, for example, 100 to 300 sccm for chlorine gas, 0 to 100 sccm for oxygen gas, or 1 to 20 sccm for helium gas. The gas pressure is preferably 1 to 10 mtorr.

  The upper layer etching may be performed under fluorine-based dry etching conditions, but in order to perform the lower layer dry etching to which the dry etching method of the present invention is applied, the film to be processed is once taken out from the dry etching apparatus. When the operation is performed, the risk of defect generation increases. Therefore, it is preferable to transfer the pattern by the same type of chlorine-based dry etching as the lower layer etching so that the next process can be performed by the same dry etching apparatus.

Next, using the upper layer pattern of the light-shielding film patterned by the above-described chlorine-based dry etching as an etching mask (hard mask), pattern transfer is performed by chlorine-based dry etching on the lower layer, the intermediate layer, and the lower layer of the light-shielding film. The dry etching conditions are such that in the above-described test for confirming the etching selectivity, the first silicon-based material is hardly etched and an effective etching rate is given to the second silicon-based material. Usually, this condition is that the mixing ratio of chlorine gas and oxygen gas (Cl ₂ gas: O ₂ gas) is found to be 1: 2 to 20: 1 by volume flow ratio, and if necessary, inert such as helium. You may mix and use gas. The flow rates of chlorine gas and oxygen gas can be, for example, 100 to 300 sccm for chlorine gas, 0.1 to 100 sccm for oxygen gas, or 1 to 20 sccm for helium gas. The gas pressure is preferably 1 to 10 mtorr.

  Thus, by using the first silicon-based material layer as a hard mask and dry etching using a chlorine-based etching gas with an adjusted oxygen gas ratio, the hard mask effect of the first silicon-based material layer pattern is utilized. Thus, the second silicon-based material layer can be etched, thereby achieving highly accurate pattern processing of the light shielding film.

  When the dry etching process for the upper layer of the first silicon-based material is performed by chlorine-based dry etching, the dry ratio of the first silicon-based material is changed by changing the oxygen mixing ratio among the etching gas conditions. The etching process and the second silicon material dry etching process can be performed continuously.

  Specifically, after the first silicon-based material layer is dry-etched with a chlorine-based gas that may contain oxygen, the photomask manufacturing intermediate having a film to be processed is not taken out from the dry-etching chamber. What is necessary is just to dry-etch using the chlorine-type gas containing oxygen which increased oxygen content rather than the etching gas used in the case of the dry etching of 1 silicon-type material layer.

  In this case, after the dry etching of the first silicon-based material is performed for about 1 to 2 times the necessary etching time obtained from the etching rate obtained in the test for confirming the etching selectivity, the second etching is performed. It is preferable to switch to gas conditions for etching the silicon-based material.

  According to the dry etching method of the present invention, the second silicon-based material layer (lower layer) can be etched without almost etching the first silicon-based material layer (upper layer). In this case, even when the second silicon-based material layer (lower layer) is etched, even if the edge of the resist pattern is damaged during dry etching and a part of the upper layer is exposed, When etching the silicon material layer 2 (lower layer), the etching conditions under which the first silicon material layer (upper layer) functions as a hard mask are applied, so that the first silicon material layer (upper layer) is damaged. I do not receive it. Therefore, in the dry etching method of the present invention, a resist film having a thickness necessary for etching the first silicon-based material layer (upper layer) may be used. Thus, a film pattern can be formed.

  EXAMPLES Hereinafter, although an experiment example and an Example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example.

[Experimental Example 1]
(Mo: Si: N = 2: 60: 18 (atomic ratio), Mo / Si = 0.37, total content of oxygen and nitrogen = 18 atomic%) with a thickness of 21 nm formed on a quartz substrate. In order to evaluate the oxygen amount and etching rate in the etching gas under chlorine-based dry etching conditions using a film of silicon-based material containing molybdenum, the oxygen amount was changed between 1 to 4 sccm according to the following conditions, and the wavelength The change in reflectance with respect to 675 nm inspection light was measured over time. The obtained results are shown in FIG. FIG. 3 shows an outline of the etching apparatus used. In FIG. 3, 1 is a chamber, 2 is a ground, 3 is a lower electrode, 4 is an antenna coil, 5 is a substrate to be processed, and RF1 and RF2 are high-frequency power supplies.
RF1 (RIE: reactive ion etching): Pulse 700V
RF2 (ICP: inductively coupled plasma): CW (continuous discharge) 400W
Pressure: 6mTorr
Cl ₂ : 185 sccm
O ₂ : 1 to 4 sccm
He: 9.25 sccm

  From the change in reflectivity with respect to the dry etching time shown in FIG. 1, the reflectivity of the film surface before etching is about 25, whereas the reflectivity decreases as etching progresses, and the etching of the film ends. It can be seen that the reflectance is about 15. Further, it can be seen that the MoSiN film used here is hardly etched if the oxygen amount of the atmospheric gas in dry etching is 4 sccm or more (oxygen gas / chlorine gas (molar ratio) is 4/185 or more).

[Experiment 2]
The film is made of MoSiN having a thickness of 33 nm (Mo: Si: N = 16: 66: 18 (atomic ratio): Mo / Si = 0.24, total content of oxygen and nitrogen = 18 atomic%). As a film of the silicon-based material contained, the reflectance change was measured over time in the same manner as in Experimental Example 1. The obtained results are shown in FIG.

  As shown in FIG. 2, when the oxygen amount is 1 sccm (oxygen gas / chlorine gas (molar ratio) is 1/185), etching is performed at about 10 nm / min, and 2 sccm (oxygen gas / chlorine gas ( When the molar ratio was 2/185), it was confirmed that etching did not proceed at all.

[Experiment 3]
Three types of MoSiN films having a nitrogen content of 0, 18, and 28 atomic% and a composition ratio of molybdenum to silicon (Mo / Si) of 0.33 were formed on the substrate. Of the indicated conditions, the etching rate of each film was measured with an oxygen amount of 0 sccm, and was 4.90, 2.41, and 0.83 (０．８ / sec), respectively. As a result, it was confirmed that the etching rate when chlorine-based dry etching is performed decreases as the degree of oxidation (total content of oxygen and nitrogen) of the silicon-based material film containing molybdenum increases. It was. In this example, the etching was performed under conditions that do not contain oxygen as a condition for obtaining an effective rate for all the films. Can be obtained.

[Example 1]
On the quartz substrate, a lower layer made of MoSiN (Mo: Si: N = 22: 60: 18 (atomic ratio)) with a thickness of 50 nm, and a MoSiN (Mo: Si: N = 16: thickness) with a thickness of 10 nm thereon. A photomask blank having a light-shielding film having an upper layer of 66:18 (atomic ratio) was prepared, and a 150 nm thick chemically amplified resist film for EB exposure was formed thereon using a spin coater. On this resist film, a resist pattern was formed after pattern drawing with an EB exposure apparatus and developed to protect the portion where the light shielding film remains.

Next, etching was performed by chlorine-based dry etching under the following etching condition 1 in which the upper layer obtained in the above experimental example was etched using the resist pattern as an etching mask.
[Etching condition 1]
RF1 (RIE): Pulse 700V
RF2 (ICP): CW 400W
Pressure: 6mTorr
Cl ₂ : 185 sccm
O ₂ : 1 sccm
He: 9.25 sccm

After etching for 1 minute and 30 seconds under the etching condition 1, further, 1 sccm of oxygen is added so that the lower layer can be etched without etching the upper layer, and further dry etching is performed under the following etching condition 2 After continuing for 8 minutes, the light-shielding film could be formed in a predetermined pattern shape by one etching.
[Etching condition 2]
RF1 (RIE): Pulse 700V
RF2 (ICP): CW 400W
Pressure: 6mTorr
Cl ₂ : 185 sccm
O ₂ : ₂ sccm
He: 9.25 sccm

1 Chamber 2 Ground 3 Lower electrode 4 Antenna coil 5 Substrate RF1 and RF2 High frequency power supply

Claims (6)

A first silicon-based material layer containing molybdenum, silicon, and oxygen and / or nitrogen;
Molybdenum, silicon, oxygen and / or nitrogen are contained, the total content (atomic%) of oxygen and nitrogen is equal to or less than the first silicon-based material layer, and the composition ratio of molybdenum and silicon (Mo / Si (atomic ratio)) is higher than the first silicon-based material layer, the second silicon-based material layer is the second silicon-based material layer, the first silicon-based material layer is It is a method of selectively removing by etching,
Using a chlorine-based dry etching gas containing oxygen, the ratio of the chlorine-based gas to the oxygen gas is set so that the etching rate of the second silicon-based material layer with respect to the etching rate of the first silicon-based material layer is increased. A dry etching method comprising: setting and selectively removing the second silicon-based material layer by etching.   The composition ratio of molybdenum and silicon in the second silicon-based material layer (Mo / Si (atom)) with respect to the composition ratio (Mo / Si (atomic ratio)) of molybdenum and silicon in the first silicon-based material layer. 2. The dry etching method according to claim 1, wherein the ratio)) is 1.5 times or more.   3. The dry etching according to claim 1, wherein the ratio of chlorine gas to oxygen gas (oxygen gas / chlorine gas (molar ratio)) is 0.0001 to 1 in the chlorine dry etching. Method.   Chlorine containing oxygen while changing the ratio of chlorine gas to oxygen gas (oxygen gas / chlorine gas (molar ratio)) for the first silicon material layer and the second silicon material layer. Dry etching is performed to obtain an etching rate of each of the first silicon-based material layer and the second silicon-based material layer, and by comparing these, the second silicon-based material layer is converted into the first silicon-based material layer. The ratio of a chlorine-based gas and an oxygen gas that can be selectively removed by etching while leaving the system material layer is determined, and dry etching is performed under the condition in which the ratio is set. The dry etching method according to any one of claims.   Etching the photomask blank or photomask manufacturing intermediate in which the first silicon-based material layer is formed on the substrate as the upper layer of the light-shielding film, and the second silicon-based material layer is formed as the lower layer of the light-shielding film. The dry etching method according to any one of claims 1 to 4.   After the first silicon-based material layer is dry-etched with a chlorine-based gas that may contain oxygen, the first silicon-based material layer is dried without removing the photomask production intermediate from the dry etching chamber. Select the second silicon-based material layer, leaving the first silicon-based material layer, using an oxygen-containing chlorine-based gas whose oxygen content is higher than the etching gas used in the etching. 6. The dry etching method according to claim 5, wherein the etching is removed by etching.

Images