JPH07113772B2 - Fine pattern forming method - Google Patents

Description

The present invention relates to a fine pattern forming method, and more particularly to a VLSI,
The present invention relates to a method for forming a fine resist pattern on a submicron level in the production of ultra-high speed transistors, magnetic bubble memories and the like.

[Conventional technology]

In recent years, as the degree of integration of semiconductor elements and the like has been remarkably improved, a method for forming a pattern with a very small line width and a very small interval with high accuracy has been desired.

As the degree of integration is improved, a multilayer wiring structure is required more and more in semiconductor devices and the like, and unevenness that cannot be ignored in the photolithography process appears on the surface of the semiconductor substrate to be patterned. Such irregularities irregularly reflect the exposure light that has passed through the photoresist, causing a phenomenon in which a portion that should not be exposed is irradiated. In addition, a standing wave is generated based on the interference between the reflected light from the base substrate and the incident light.

Since any of these effects causes a reduction in resolution, it has become difficult to perform high-resolution fine processing on an actual element by the conventional method using a single-layer resist.

For the purpose of solving the above problems, various multilayer resist methods have been proposed, and recently, a first resist layer is formed on a substrate using a conventional photoresist to flatten the unevenness of the base. , A two-layer resist method, in which a second resist layer is formed of a photo- and radiation-sensitive polymer composed of an organosilicon polymer, has been actively studied. (For example, A. Tanaka
et.al.ACS Polymer Preprints Vol.25, No.1, p.301, St.
Louise, April. 1984) The outline of the lithography process using such a two-layer resist method is shown in the figure. First, a first resist layer 2 and a second resist layer 3 are provided on a semiconductor substrate 1 as shown in FIG.
After irradiating a predetermined portion of the second resist layer 3 with light or radiation, a pattern is formed as shown in FIG. 2B by development and then treated with oxygen plasma, so that the remaining portion of the second resist layer 3 remains. On the other hand, the surface of the first resist layer 2 is exposed to SiO ₂ and the etching does not proceed. On the other hand, the exposed first resist layer 2 is oxidatively removed by etching,
The state shown in FIG.

By doing so, the unevenness of the base substrate is flattened, and the second resist layer becomes thin and uniform, so ideal exposure conditions are obtained, and high-resolution pattern transfer is expected.

In order to achieve high resolution by using the above two-layer resist method, the following conditions are essential.

(1) The first resist layer sufficiently absorbs the light used for the exposure of the second resist layer, and the influence of reflection from the base and standing waves does not reach the second resist layer.

(2) The etching rate ratio by the oxygen plasma of the first resist layer and the second resist layer is sufficiently large.

(3) The first resist layer is a coating solvent for the second resist layer,
Do not be attacked by developing solvent and rinse solvent.

(4) The first resist layer must withstand dry etching of the substrate.

Various resist materials have been proposed to date as the material for the second resist layer for the purpose of realizing the two-layer resist method as described above. (For example, E. Reichmanis,
G. Smolinsky, CW Wilkins, Jr., Solid State Technology
(Japan version) 10 pp52-67 (1985)) All of these materials contain organosilicon polymer, and Si atoms in the material turn into SiO ₂ during oxygen plasma treatment to form an oxygen plasma resistant film on the resist surface. . Utilizing this property, the first resist layer is processed as shown in FIG. By the way, most of these organosilicon resists have been negative resists so far, and their photosensitive areas are limited to Deep UV. X-rays and electron beams, so that their applications are limited. Further, in the case of a negative type resist, the irradiated portion is generally highly crosslinked, so that there is a process problem in that peeling is difficult after the process is completed. On the other hand, several types of positive resists are known, but most of them are limited to the deep UV.X-rays and electron beams. In addition, O ₂ RIE from (b) to (c) in FIG.
In the process of (O ₂ reactive ion etching, that is, reactive ion etching by oxygen plasma),
In order to keep the pattern conversion difference from the second resist layer to the first resist layer as small as possible, extremely high oxygen plasma resistance is required for the second resist layer. Nothing to meet is accepted.

As described above, from the viewpoint of practicality, the known organosilicon-based resist is not yet sufficient as the upper layer resist (second resist layer in FIG. 1) of the two-layer resist method, and requires a great improvement. I am trying.

In the lithography process of the current semiconductor process, in principle, the alkali development positive resist excellent in resolution and dry etching resistance is mainstream, and it is considered that this tendency will continue in the future. Therefore, taking practicality into consideration, the most promising two-layer resist process is a process in which a positive resist which is excellent in resolution, sensitivity and oxygen plasma resistance and which is an alkali developing type is used as the upper layer resist.

[Problems to be solved by the invention]

As described above, none of the conventional two-layer resist methods satisfy all the conditions of resolution, sensitivity, photosensitive wavelength region, and pattern transfer accuracy from the upper layer to the lower layer.

An object of the present invention is to use an alkali-developable positive type organosilicon resist, which is extremely excellent in resolution / sensitivity and oxygen plasma resistance, as an upper layer resist, thereby satisfying each of the above conditions and being a very practical two-layer resist. To provide the law.

[Means for solving problems]

In order to achieve the above object, the inventors have studied various materials, and as a result, use a photosensitive resin composition containing an alkali-soluble organosilicon polymer and a photosensitive dissolution inhibitor as main components as the second resist layer. The method was found to be effective, and the present invention was devised.

In the two-layer resist method, it is necessary to use, as the second resist layer, a polymer material having both photosensitivity and oxygen plasma resistance. As such a material, an organometallic polymer containing a metal atom in the molecule can be used. This is because the organometallic polymer coating generally forms a metal oxide film derived from the metal element in the polymer on the surface by the oxygen plasma treatment, and this oxide film has a remarkable resistance to oxygen plasma. However, it has been difficult to impart photosensitivity to the organometallic polymer itself. Therefore, as a result of examining various possibilities, it was found that a method in which oxygen plasma resistance and photosensitivity are assigned to different substances and a composition obtained by mixing the two is used as the second resist layer is effective. I found it. That is, it was found that in a coating film composed of a mixture of an alkali-soluble organometallic polymer and a photosensitive dissolution inhibitor, only a light-irradiated portion was selectively solubilized in an alkali developing solution to obtain a positive resist pattern. Then, such a positive resist pattern is formed on the appropriate organic polymer material film in the same manner as above, and O ₂
It was confirmed that when the RIE process was performed, the lower layer of the organic polymer material film was etched and the pattern was accurately transferred from the upper layer to the lower layer as shown in (b) to (c) of the figure.

Next, the alkali-soluble organometallic polymer which is one of the main components of the photosensitive resin composition of the present invention will be described. Considering its role, the alkali-soluble organometallic polymer can be efficiently contacted with oxygen plasma. It is desirable that the metal element is contained in the polymer main chain rather than existing in the polymer side chain. Further, Si, Ge, Sn, Ti and the like can be considered as the metal element, but Si is most effective in consideration of availability of raw materials, easiness of synthesis, safety and the like. In order to impart alkali solubility to the organometallic polymer, an acidic group such as a phenolic hydroxyl group or a carboxyl group may be introduced into the side chain of the polymer.

From the above viewpoints, as a result of studying various organosilicon polymers as the alkali-soluble organometallic polymer, an alkali-soluble polysiloxane in which the unit represented by the following general formula (1) occupies at least 40% or more of the polymer skeleton It has been revealed that the organosilsesquiosane polymer is excellent in all properties.

[R ₁ —SiO _3/2 ] (1) In the general formula (1), R ₁ is an organic group having a phenolic hydroxyl group, for example, C _{1 to} C ₆ having a phenol group or a catechol group. Is an alkyl group. These alkali-soluble polyorganosilsesquioxane-based polymers are soluble in an alkaline aqueous solution, for example, an aqueous solution of tetramethylammonium hydroxide, an aqueous solution of sodium hydroxide, and the like, and a general organic solvent such as alcohols, ethers, and ketones. It easily dissolves in compounds, esters, cellosolves, amides, etc.

Further, these alkali-soluble polyorganosilsesquiosane-based polymers show almost no film reduction in oxygen plasma.

Next, the photosensitive dissolution inhibitor which is another main component of the photosensitive resin composition of the present invention will be described. The role of the photosensitive dissolution inhibitor in the alkali-developable photosensitive resin composition acts to inhibit the alkali solubility of the alkali-soluble organosilicon polymer in the unexposed area, and on the other hand, in the exposed area, due to photolysis. That is, the exposed portion is changed to an alkali-soluble compound or loses the effect of inhibiting alkali dissolution to make the exposed portion alkali-soluble. As the photosensitive dissolution inhibitor relating to the present invention, o-nitrobenzyl ester, diazomeldrum acid, o-quinonediazide and the like can be used. Particularly, those which are sensitive to UV light of 300 nm or more include 1,2-naphtho Quinone diazides are effective. 1,2
Examples of the naphthoquinonediazides include the compounds (I) to (XXIV) shown below.

Next, a method for forming a fine pattern by the two-layer resist method using the photosensitive resin composition of the present invention will be described.

Alkali-soluble organosilicon polymers (these polymers may be used alone or in the form of a mixture).
70-95% by weight of base polymer containing 70-100% by weight of
(The alkali-soluble organosilicon polymer is mixed with a polymer such as a novolac resin, which is a film-forming auxiliary, in an amount of 0 to 30).
It is possible to mix in the range of% by weight. Exceeding this range is not preferable in terms of oxygen plasma resistance. ) And a photosensitive dissolution inhibitor 30 to 5% by weight (when a photosensitive dissolution inhibitor in an amount exceeding this range is used, it is not preferable in terms of sensitivity and oxygen plasma resistance. A single substance or a mixture of a plurality of substances may be used.) A photosensitive resin composition consisting of a substance dissolved in a general-purpose organic solvent such as ethyl cellosolve acetate is used as the second layer resist solution. .

Next, an outline of a two-layer resist method using the above photosensitive resin composition will be described. First, as the first resist layer of the two-layer resist method, a commercially available positive resist (for example, AZ manufactured by Shipley Co., Ltd.
1350J, Microposit 1300 series, Tokyo Ohka's OFPR
800 etc.) and a polyimide resin (for example, PIQ manufactured by Hitachi Chemical) can be used. These base leveling materials sufficiently level the irregularities of the substrate, sufficiently absorb the exposure light of the second resist layer, and are not attacked at the time of coating, developing or rinsing the second resist layer. .

The undercoat planarizing material is spin-coated and hard-baked under predetermined conditions to form a first resist layer. On top of this,
The second layer resist solution is spin-coated and prebaked under predetermined conditions to form a two-layer resist. (Corresponding to (a) in the figure.) Then, the upper layer (second resist layer) is exposed to a desired pattern, and an alkali developing solution such as an aqueous solution of tetramethylammonium hydroxide is used to selectively expose only the irradiated portion. To form a positive resist pattern in the upper layer. When this is processed by dry etching using oxygen plasma (referred to as O ₂ reactive ion etching or O ₂ RIE), the lower layer (first resist layer) can be processed using the upper layer resist pattern as a mask. At this time, depending on the purpose, the processed shape of the lower layer can be controlled by the oxygen gas pressure (Po ₂ ) in the O ₂ RIE. A relatively low oxygen gas pressure (Po ₂ <several mtorr) is desirable to obtain a high aspect ratio vertical shape, and a tapered etch shape is possible at a relatively high oxygen gas pressure (Po ₂ > several + mtorr). is there.

By the above two-layer resist process, submicron level fine processing can be easily performed with an aspect ratio of 3 or more.

[Action]

First, in the photosensitive resin composition relating to the present invention, an alkali-soluble organosilicon polymer is a one component, to form a silicon oxide film in an oxygen plasma, O ₂ RIE
Functions as a resistant film. On the other hand, the other main component, the photosensitive dissolution inhibitor, inhibits the alkali solubilization of the alkali-soluble organosilicon polymer in the unexposed portion, and the inhibitor itself becomes alkali-soluble by photolysis in the exposed portion, It functions to dissolve the entire exposed area in an alkaline developer. Therefore, the photosensitive resin composition composed of these two main components can be used as the upper layer resist (second resist) of the two-layer resist method. That is, a first resist layer made of a suitable organic polymer material is formed on the surface of a semiconductor substrate, a second resist layer made of the above photosensitive resin composition is formed thereon, and the second resist layer is formed as described above. When this is patterned, the second resist layer has high O ₂ RIE resistance, so this pattern is used as a mask for the first resist layer.
Can be dry-etched by O ₂ RIE.

By the process described above, a submicron pattern having a high aspect ratio can be easily formed.

〔Example〕

 Hereinafter, the present invention will be specifically described with reference to Examples.

First, a synthesis example of the alkali-soluble organosilicon polymer used in the second resist layer of the present invention will be described.

Synthesis Example 1. Synthesis of poly (p-hydroxybenzylsilsesquioxane) and poly (p-methoxybenzylsilsesquioxane-co-p-hydroxybenzylcissesquioxane).

1.1 Synthesis of p-methoxybenzyltrichlorosilane 30g magnesium powder (1.2gatom) in a 2l three-necked flask equipped with a stirrer, reflux tube, dropping funnel and thermometer,
170 g (1.00 mol) of silicon tetrachloride and 5 diethyl ether
Add 00 ml. After cooling the flask to 10 ° C or lower, p-methoxybenzyl chloride 100 g (0.639mo) was added from the dropping funnel.
A mixture of l) and 200 ml of diethyl ether is added dropwise over 4 hours. After aging at room temperature for another hour, excess magnesium and magnesium chloride are removed by suction filtration.
44.0g (0.172mol) of the target product by distilling the solution
Obtained. Yield 26.9% Boiling point 117.5-119.5 ° C / 3.0 mmHg NMR spectrum (60 MHz, CCl ₄ , CH ₂ Cl ₂ δ5.33) δ2.91 (2H, S),
3.90 (3H, S), 6.91 (2H, d, J = 8Hz), 7.20 (2H, d, J = 8H
z) 1.2 Synthesis of poly (p-methoxybenzylsilsesquioxane) In a 100 ml three-necked flask equipped with a magnet bar, a dropping funnel and a reflux tube, 11 g (0.13 mmol) of sodium hydrogen carbonate and 40 ml of water are placed. From the dropping funnel, a mixture of 10.23 g (40.0 mmol) of p-methoxybenzyltrichlorosilane and 10 ml of diethyl ether was added dropwise over 30 minutes, followed by aging for 30 minutes. After completion of the reaction, the reaction mixture is extracted with ether and dried over sodium sulfate. Diethyl ether was distilled off under reduced pressure to obtain 5.10 g of a hydrolysis product. NMR spectrum (60MHz,
CDCl ₃ ,, CH ₂ Cl ₂ δ5.33) δ2.03 (2H, br.S), 3.80 (3H, b
rS), 6.80 (4H, br.S). IR spectrum (νcm ^-1 ) 3400,
2950,2850,1610,1510,1460,1300,1250,1180,1090,1035,
890,835,790,760. Weight average molecular weight 2,000. 4.80 g of the hydrolysis product obtained above and 1 of potassium hydroxide
Add 49 mg of 0 wt% methanol solution to a 25 ml eggplant flask. 2
Heat at 00 ° C for 2 hours. After completion of the reaction, the reaction mixture is dissolved in benzene and added dropwise to methanol to precipitate a solid. After filtration, it was dried under reduced pressure to obtain 4.00 g of the desired product. NMR spectrum (60MHz, CDCl ₃ , CH ₂ Cl ₂ δ5.33) δ
1.91 (2H, br.S), 3.78 (3H, br.S), 6.73 (4H, br.S), IR
Spectrum (ν cm ^-1 ) 2950,2850,1615,1515,1465,1305,
1250,1195,1120,1040,840,800,770. Weight average molecular weight 3,30
0.1.3 Synthesis of poly (p-methoxybenzylsilsesquioxane-co-p-hydroxybenzylsilsesquioxane) In a 100 ml round-bottomed flask equipped with a reflux tube, 3.73 g of poly (p-methoxybenzylsilsesquioxane) (MeOC ₆ H ₄ CH
₂ SiO _3/2 units (21.6 mmol), chloroform 20 ml and trimethylsilyliodine 6.92 g (34.6 mmol) were added, and the temperature was 70 ° C.
Stir for 72 hours with a magnetic rod at. After adding 20 ml of methanol at room temperature and further stirring for 30 minutes, low-boiling substances are distilled off under reduced pressure, and the residue is extracted with a mixed solvent of diethyl ether and tetrahydrofuran. The extract solution is washed with an aqueous solution of sodium hydrogen sulfite, an aqueous solution of sodium hydrogencarbonate and brine, and then the solvent is distilled off under reduced pressure. The obtained polymer was reprecipitated with acetone / hexane and dried by heating under reduced pressure to obtain 2.71 g of the desired product. Weight average molecular weight 4000. Hydroxyl content 100%, NMR spectrum (60MHz, DMSO-d ₆ , CH ₂ Cl ₂
δ5.68) δ1.75 (2H, br.S), 6.58 (4H, br.S), 8.88 (-
0H, br.S), IR spectrum (νcm ^-1 ) 3350,1620,1515,145
0,1240,1185,1120,1040,840,805,760. The hydroxyl group content can be controlled by the amount of trimethylsilyl iodide or the reaction time. For example, using 1.6 equivalents of trimethylsilyliodine, the reaction time was 39% at 4 hours and 54% at 7 hours.
%, Conversion rate was 75% at 12 hours, 85% at 22 hours, and 100% at 50 hours.

The value of the hydroxyl group content of these polymers was determined by carrying out the reaction in deuterated chloroform and tracing the process of conversion of methoxy groups to trimethylsiloxy groups by NMR spectrum.

Regarding the solubility of the above polymer, as a result of examination with a typical general-purpose organic solvent, a polymer having a hydroxyl group content of 40% or more was found to be methanol, tetrahydrofuran, N, N-dimethylacetamide, 2-methylcyclohexanone, isoamyl acetate, methyl Although dissolved in cellosolve and dimethyl sulfoxide,
It was insoluble in toluene, hexane, and carbon tetrachloride. On the other hand, the aqueous solution was dissolved in a tetramethylammonium hydroxide aqueous solution and a sodium hydroxide aqueous solution.

The oxygen plasma resistance was examined as follows. That is, a 10 wt% ethyl cellosolve solution of each polymer was applied on a silicon substrate by spin coating, and prebaked at 100 ° C for 30 minutes to obtain a film thickness of about 0.2.
A μm polymer coating was formed. Then, using a barrel type asher, oxygen plasma (condition: oxygen pressure 0.5 torr,
When exposed to RF300W) for 20 minutes, the above polymer did not cause any film sticking. However, when a parallel plate type O ₂ RIE system (conditions: oxygen pressure 20 mtorr, RF200 W (14 MHz), cathode bias voltage −130 V) was used, the polymer XXV had a film slip velocity of 23 Å / min. At this time, organic substances that are generally considered to have relatively high oxygen plasma resistance, for example, PIQ (manufactured by Hitachi Chemical),
OFPR-800 (manufactured by Tokyo Ohka), AZ1350J (manufactured by Hoechst), etc. had a film slip rate of about 1220Å / min. Further, the film slip rate of the polymer was hardly affected by the hydroxyl group content.

Next, an example of the two-layer resist method will be described in detail.

Example 1. First, OFPR-8 was used as a first resist layer on a silicon wafer.
00 (manufactured by Tokyo Ohka Co., Ltd.) is spin-coated to a thickness of 2 μm, and it is 30
Bake for 30 minutes at 200 ° C. for 30 minutes. (Hereinafter, this is abbreviated as "hard bake OFPR-800".) Next, the alkali-soluble polyorganosilsesquioxane-based polymer synthesized in 1.3 of Synthesis Example 1 (hereinafter abbreviated as "alkali-soluble base polymer") Is a poly (p-methoxybenzylsilsesquioxane-co-p-hydroxybenzylcissesquioxane) (provided that it has the general formula XXV
, N / (m + n) = 1.0, that is, one having an OH conversion rate of 100%) and the 1,2-naphthoquinonediazide derivative (X
II) (20 wt% of alkali-soluble base polymer) was dissolved in ethyl cellosolve acetate to obtain a second resist solution. (However, the resist solid content was 27% by weight.) Next, the second resist solution was spin-coated on the first resist and prebaked at 80 to 90 ° C. for 30 minutes. At this time, the film thickness of the second resist layer was 1.0 μm. With the resist structure as described above, first, the exposure / development characteristics of the second resist layer were examined. The conditions are shown below.

Exposure condition: Contact exposure with COBILT AF2800H.

Development conditions: Tokyo Ohka's developer NMD-3 (2.38% tetramethylammonium hydroxide aqueous solution) diluted to 0.48% is used as a developer and immersed in this for 3 minutes and then in pure water for 1 minute.

Using the above exposure and development conditions, shaking only the exposure amount,
The residual resist film thickness (normalization) after development at each exposure dose is plotted against the exposure dose, and the minimum exposure dose at which the residual film is zero (this value is defined as resist sensitivity) is calculated to be about 30 mJ. It was / cm ² .

Next, the second resist layer was patterned under the above exposure and development conditions. Here, when pattern transfer is performed using the same photomask, the transfer dimension to the second resist layer changes depending on the exposure amount. Therefore, for convenience, 1 μm lines & s
The exposure amount transferred at a paces of 1: 1 was taken as the optimum exposure amount. In this embodiment, the optimum exposure dose is 80 mJ / cm ² (however, 36 m
(Measured at 5 nm).

Therefore, after patterning the second resist layer under the above conditions, the parallel plate type RIE device was used to perform 20 to 20% by O ₂ RIE (conditions: O ₂ pressure = 3 mtorr, RFPWR = 0.64 mW / cm ² (7 MHz)). 30
After that, the first resist layer was patterned using the second resist layer as a pattern mask. As a result, a resist pattern having a vertical step shape with a pattern dimension of submicron level and an aspect ratio of 3 or more was accurately obtained. At this time, the dimensional conversion difference from the second resist pattern to the first resist pattern is 0.1 μm.
It was below.

In the same manner as in Example 2 to Example 1, the two-layer resist method was tried under various conditions shown in Table 1.
It was possible to obtain a fine resist pattern having a vertical step shape with an aspect ratio of 3 or more with a pattern dimension of the submicron level.

[Advantages of the Invention] As described above, according to the present invention, a fine resist pattern having a pattern dimension of submicron level and a high aspect ratio can be obtained with high accuracy. Moreover, since the alkali developing process, which is currently the mainstream in the semiconductor process, can be applied as it is, it is extremely advantageous in practical use and is a very effective technique for the manufacturing process of semiconductor elements and the like.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a lithography process using the two-layer resist method. 1 ... Semiconductor substrate, 2 ... Organic polymer material film (first resist layer), 3 ... Light and radiation sensitive polymer film (second resist layer).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Kazuo, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Inside the Institute of Industrial Science, Hitachi, Ltd. (56) References JP-A-61-3139 (JP, A) Kai 57-168247 (JP, A) JP 57-168248 (JP, A) JP 61-188539 (JP, A)

Claims (1)

[Claims] 1. A first resist layer is provided on a substrate, a second resist layer is provided on the first resist layer, and a desired portion of the second resist layer is exposed to light or radiation and developed to develop the first resist layer. In the method of forming a fine pattern in which a desired portion is exposed and a portion of the exposed first resist layer is removed by reactive ion etching using oxygen plasma, the second resist layer is represented by the following general formula (1). A method for forming a fine pattern, which is a photosensitive resin composition comprising an alkali-soluble polyorganosilsesquioxane polymer composed of units and a photosensitive dissolution inhibitor. [R ₁ -SiO _3/2 ] (1) (However, R ₁ in the general formula (1) is an organic group having at least one phenolic hydroxyl group.)