JPH0638407B2 - Flattening method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for planarizing a substrate having irregularities.

[Prior Art] In a microminiature element such as a semiconductor integrated circuit element or a bubble memory element, it is necessary to sequentially form an insulating layer and a conductor layer. However, as the number of conductor layers increases to two or three, the level difference between the conductor layers becomes steeper, and disconnection or short circuit occurs at the intersection of the conductor layers, which makes it difficult to practically form a laminated structure.

In order to prevent such disconnection of the conductor layer, it is effective to flatten the surface of the insulating layer before forming the conductor layer, and various methods have been attempted conventionally. FIG. 1 shows one of the methods, which is called an etch back method. According to this method, first, as shown in FIG. 1 (a), the organic polymer film 3 is spin-coated on the insulating layer 2 formed on the conductor layer 1, and then the organic polymer film and the insulating layer are formed. The smoothness of the coated surface of the organic polymer film is transferred to the insulating layer by performing the etching under the condition that the dry etching rates are equal. It can be said that this method is a very promising method in device manufacturing because it can be flattened at a low temperature and the smoothness of the coated surface can be transferred to the insulating layer. However, in practice, when an organic substance such as a resist is spin-coated, the result is as shown in FIG. 1 (b), and generally there is a drawback that the irregularities of the substrate cannot be completely filled.

On the other hand, if a material having a low heat distortion temperature such as polystyrene having a molecular weight of about 100,000 is spin-coated and then heated to a temperature higher than the heat distortion temperature (for example, 200 ° C.) to flow,
It has been disclosed that the unevenness of the substrate can be remarkably improved as shown in FIG. (C) (JP-A-59-225526).

[Problems to be Solved by the Invention] Considering that patterns having various step widths are uniformly flattened, it is desirable that the molecular weight of the applied organic polymer is as small as possible. For example, when polystyrene with various molecular weights was applied to a substrate with steps and the difference in height after heating at a constant temperature was measured by the Taristep, it was found that when low molecular weight polystyrene was used, the conductor width was wide. However, it was found that an ideal flat surface with no height difference could be realized. This is because the melt viscosity of polystyrene has a remarkable molecular weight dependence. If the heating temperature is high, even a polymer having a relatively high molecular weight can be flattened, but it cannot be heated to such a high temperature that decomposition of the polymer occurs. Considering this, in the case of polystyrene, a polymer having a molecular weight of 10,000 or less is desirable.

However, when the molecular weight of the polymer is small, there is a problem that the molten polymer is condensed by the surface tension when the polymer is heated to a temperature higher than the heat distortion temperature in order to flow.

An object of the present invention is to provide a flattening method capable of preventing condensation of a polymer at the time of thermal deformation heating as described above and forming an excellent flat surface.

[Means for Solving Problems] That is, according to the present invention, a step of providing an insulating film on a substrate having a step, and an organic film having at least one amino group and at least one alkoxysilyl group on the insulating film. A step of forming an organic film made of a compound, a step of forming an organic polymer film made of an organic polymer having a molecular weight of 10,000 or less on the organic film, and reducing the melt viscosity of the organic polymer to a flat surface. And a step of dry-etching the organic polymer flat surface to transfer the flat surface to the insulating film, and a step of forming an insulating film on a substrate having a step. A step of providing, a step of forming an organic film made of an organic compound having at least one amino group and at least one alkoxysilyl group on the insulating film, and a molecule on the organic film. Is a step of forming an organic polymer film consisting of an organic polymer of less than 10,000 and a cross-linking agent, a heating step of forming a flat surface by significantly lowering the melt viscosity of the organic polymer, and irradiating ultraviolet rays to the organic layer. A planarization method comprising a step of crosslinking a polymer and a step of dry-etching the obtained organic polymer flat surface to transfer the flat surface to the insulator.

In the present invention, before applying the organic polymer film on the insulating film, an organic thin film is formed on the insulating film to increase the surface energy of the substrate, so that the surface tension of the molten polymer during heat deformation heating is increased. The affinity between the substrate surface and the molten polymer is increased to prevent the molten polymer from condensing. The organic thin film between the insulating film and the organic polymer film has a functional group capable of forming a chemical bond with the insulating film and a functional group for increasing the surface energy. In the present invention, an alkoxysilyl group is used as a functional group capable of forming a chemical bond with an insulating film, and an organic compound having a primary, secondary or tertiary amino group is used as a functional group for increasing surface energy.

Such an organic thin film can be spin-coated,
It can also be formed by vapor phase growth.

Polystyrene is preferable as the organic polymer having a molecular weight of 10,000 or less. In this case, dry etching is preferably performed at a temperature of 20 ° C. or lower because the glass transition temperature (Tg) of polystyrene is low.

In the present invention, in addition to the above as an organic polymer having a molecular weight of 10,000 or less, those which can obtain an organic polymer film whose melt viscosity is remarkably reduced in the heating step, for example, siloxane, polystyrene derivatives (substituents are alkyl groups, acetyl groups, hydroxy groups) , Α-methyl group), polyvinyl pyridine, polyvinyl pyrrolidone, polyacrylonitrile, polymethacrylonitrile, novolac resin, and the like.

The present invention further includes a planarization method in which a crosslinkable organic polymer having a molecular weight of 10,000 or less as an organic polymer and a crosslinking agent are used in combination. Examples of the crosslinking agent include 2,6-bis (4 '
-Azidobenzal) 4-methylcyclohexanone.

[Operation] As the insulating film material, SiO ₂ is typically used, and other metal oxides are used. Hydroxyl groups are present on the surface of these oxides, and the alkoxysilyl group contained in the organic film formed on the insulating film is hydrolyzed and easily reacts with this hydroxyl group to form a chemical bond. As a result, the amino groups are arranged facing the side opposite to the substrate surface, so that the surface energy can be increased as compared with the case where no treatment is performed with the organic film. The surface of the substrate, which has a high surface energy, easily adheres to other substances, and even when the step difference is eliminated by using a low molecular weight organic polymer, the force to bond the substrate surface and the polymer is generated during thermal deformation heating. It overcomes the surface tension that tends to condense, thus preventing condensation.

The same effect can be expected by using a chlorosilyl group instead of an alkoxysilyl group, but considering that hydrogen chloride is generated as a result of hydrolysis with a chlorosilyl group, there is a risk of adverse effects such as substrate damage. Therefore, it is not preferable.

Further, in the dry etching step of applying polystyrene or the like and then transferring it to the insulating film of the lower layer, when polystyrene having a small molecular weight is used in order to particularly improve the planarization, the Tg of polystyrene is low, so It is necessary to prevent temperature rise. Normally, the temperature rise is prevented by cooling the polymer table during etching (20 ° C or less), but in order to remove the restriction on the temperature rise during etching, it is necessary to increase the Tg of polystyrene before etching. is necessary. Polystyrene is known to absorb far-ultraviolet light and crosslink, but its sensitivity is low. Crosslinking agents sensitive to far-ultraviolet light, eg 2,6 bis (4'-azidobenzal)
When 4-methylcyclohexanone was mixed and irradiated with far-ultraviolet light, improvement in heat resistance was recognized. At this time, no significant difference was observed in the coating characteristics and the melt viscosity characteristics due to the mixing of the crosslinking agent. Also, even when a cross-linking agent is mixed,
By carrying out the surface treatment step in the present invention,
It was possible to prevent condensation during deformation heating of the polymer.

[Examples] Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1 8000 Å SiO ₂ was deposited on a conductor pattern having a thickness of 6000 A, and vaporized with 3-aminopropyltrimethoxysilane.
Exposed for 20 minutes at room temperature. A polystyrene having a molecular weight of 2000 was applied to a thickness of 7,000Å using ethyl cellosolve acetate as a solvent. After coating, it was heated at 220 ° C. for 30 minutes in a nitrogen atmosphere. Next, in a DEM-451 (trade name of Anelva Co., Ltd.) reactive ion etching apparatus, a polymer table whose temperature was controlled at 20 ° C. was provided on the RF application side for etching. The etching gas is CF ₄ / O ₂ so that SiO ₂ and polystyrene are etched at a constant rate.
Was used. High frequency power 100W, chamber pressure 4.5Pa, C
Under conditions of an F ₄ flow rate of 30 sccm and an O ₂ flow rate of 2.5 sccm, the shape of the polystyrene coating film was directly transferred to the SiO ₂ film, and a nearly ideal flat surface was realized over a conductor width of 50 μm or more.

In the case of the substrate not subjected to the 3-aminopropyltrimethoxysilane treatment, the polystyrene was condensed in the center of the substrate due to the heating after the application of polystyrene, and the planarization could not be performed.

Example 2 8000 Å SiO ₂ was deposited on a conductor pattern having a thickness of 6000 Å and exposed to vapor of 3-aminopropyltrimethoxysilane at room temperature for 20 minutes. 2,6-bis (4'-azidobenzal) 4-methylcyclohexanone was mixed with polystyrene having a molecular weight of 2000 at a ratio of 10 wt% and xylene was used as a solvent to apply a thickness of 7,000 Å. After application 220 ° C in nitrogen atmosphere
The mixture was heated for 1 hour at 60 ° C., followed by irradiation with far-ultraviolet light for 60 minutes in a nitrogen atmosphere for crosslinking. Next, in a DEM-451 reactive ion etching apparatus, etching was performed under conditions of a high frequency power of 100 W, a chamber pressure of 4.5 Pa, a CF ₄ flow rate of 30 sccm, and an O ₂ flow rate of 2.5 sccm. After etching, almost the coating film shape of the organic film was transferred to the SiO ₂ film as it was, and a substantially ideal flat surface was realized over a conductor width of 50 μm or more.

In addition, as in the case of Example 1, in the substrate which was not subjected to the 3-aminopropyltrimethoxysilane treatment, the polystyrene was condensed in the center of the substrate due to the heating after coating the polystyrene, and the planarization could be performed. could not.

Example 3 An experiment was performed in the same manner as in Example 1 except that N- (β-aminoethyl) -γ-aminopropyltrimethoxysilane was used instead of 3-aminopropyltrimethoxysilane in Example 1. As a result, the same result as in Example 1 was obtained and the substrate could be planarized.

Example 4 An experiment was performed in the same manner as in Example 2 except that N- (β-aminoethyl) -γ-aminopropyltrimethoxysilane was used instead of 3-aminopropyltrimethoxysilane in Example 2. As a result, the same result as in Example 2 was obtained and the substrate could be planarized.

[Effects of the Invention] As described above, it is understood that the flattening method according to the present invention has no pattern width dependency and an ideal flat surface can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic sectional view on a substrate for explaining the etch back method. 1 ... Conductor layer, 2 ... Insulating layer, 3 ... Organic polymer film

Claims (4)

[Claims] 1. A step of providing an insulating film on a substrate having a step, and a step of forming an organic film made of an organic compound having at least one amino group and at least one alkoxysilyl group on the insulating film. , The molecular weight on this organic film
A step of forming an organic polymer film made of an organic polymer of 10,000 or less, a heating step of significantly reducing the melt viscosity of this organic polymer to form a flat surface, and a dry etching of the organic polymer flat surface. And a step of transferring a flat surface to the insulating film. 2. The planarization method according to claim 1, wherein the organic polymer is polystyrene, and the dry etching is performed at a low temperature of 20 ° C. or lower. 3. A step of providing an insulating film on a substrate having a step, and a step of forming an organic film made of an organic compound having at least one amino group and at least one alkoxysilyl group on the insulating film. , The molecular weight on this organic film
A step of forming an organic polymer film composed of an organic polymer of 10000 or less and a cross-linking agent, a heating step of significantly reducing the melt viscosity of the organic polymer to form a flat surface, and irradiating ultraviolet rays to the organic polymer film. A planarization method comprising a step of crosslinking molecules and a step of dry-etching the obtained organic polymer flat surface to transfer the flat surface to the insulating film. 4. The planarization method according to claim 3, wherein the organic polymer is polystyrene and the crosslinking agent is 2,6-bis (4'-azidobenzal) 4-methylcyclohexanone.