JPH07314162A - Film formation - Google Patents

Abstract

PURPOSE:To provide a film forming method capable of flattening films without allowing voids to remain in these flattening films for LSIs and optical waveguide elements. CONSTITUTION:Two kinds of a silicon oxidized film 2 and silicon oxidized film 3 varying in dopants are formed on this order on a substrate 1. In succession, core patterns 3 are formed by dry etching and the first flattening film is formed at a thickness larger than one-third the difference in level by these patterns. Next, the surfaces of the recessed parts of the first flattening film 4 are irradiated with a laser 6 of the wavelength suitable for the material of the flattening film to form apertures 7 by transpiration. The taper angle of the apertures 7 is sufficiently smaller than 90 deg. and, therefore, the second flattening film 8 is formed. The flattening free from voids is resultinguly executed.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an optical waveguide device, VLSI
The present invention relates to a surface flattening technology for devices and the like.

[0002]

2. Description of the Related Art As the density of VLSI is increased, the demand for multilayer wiring is rapidly increasing, and the planarization technique is very important. In this case, a silicon oxide film is widely used as a flattening film. The optical waveguide also needs to be flattened in order to have multiple layers. In the optical waveguide, two kinds of silicon oxide films into which different kinds of dopants are injected are used for the core layer and the clad layer, respectively. The flattening film is required to have a thickness of 4 μm or more. Since the angle formed by the protrusions (the taper angle of the step) is as steep as 90 degrees, it is difficult for the raw material gas for film formation to enter the recesses, and voids are easily generated in these portions.

Further, as VLSI and optical integrated circuits are highly integrated, a technique for flattening unevenness having an aspect ratio of 1 or more is essential. At this time, if there are voids in the flattening film, the characteristics of the element are deteriorated. Atmospheric pressure CV of silicon oxide film
It is known that the D (APCVD) technique has relatively good step coverage, but this characteristic depends on the type of the silicon oxide film and the annealing temperature, that is, the reflow temperature. For example, in the case of a silicon oxide film (BPSG) doped with boron and phosphine, a step with an aspect ratio of 1 or more is satisfactorily covered by a reflow at 850 ° C. for 30 minutes, and an optimal reflow temperature when BPSG is further doped with germanium. It is reported that the temperature decreases to 750 ° C. in the 40th Spring Applied Physics Association Conference Lecture No. 31p-ZV-15, Proceedings pp. 757. However, such a high reflow temperature is not desirable because it may damage the semiconductor device or the optical waveguide device. Particularly in an optical waveguide device, such high temperature treatment causes diffusion of dopant in the core layer and the cladding layer, and disturbs the preset dopant distribution.

A typical example of a conventional waveguide forming process is shown in FIG. After two kinds of silicon oxide films 2 and 3 having different dopants are sequentially formed on the substrate 1, a core layer 3 (a) is formed by dry etching, and the core layer 13 (a) is used as a clad layer PSG. Or BPSG
And the like are covered with a silicon oxide film 9. When the aspect ratio is 1 or more, voids 1 are generated even if the silicon oxide film 14 is formed by APCVD.
0 occurs between the core layers 13 (a). The void 5 can disappear by reflowing at 800 ° C. for 30 minutes or more in a nitrogen or oxygen atmosphere. However, due to this high temperature treatment, the dopant of the core layer diffuses into the upper and lower clad layers and changes the shape of the core layer 13 (b) different from the design. Since this shape deterioration affects the electrical characteristics of the device, it is necessary to perform the planarization at a low temperature.

In order to realize step coverage at low temperature, various techniques have been developed, and many patents and papers have reported on the planarization technique and the technique for pre-planarization treatment. Ceramoglu's Recent Report (Journal of Vacuum Science and Technology B9 (5), pages 2530, 1
991), if any step has a taper angle of 70 degrees or less, void-free planarization is possible without any heat treatment. However, to maintain this angle, VL designed by the rule of submicron order
It is difficult for devices such as SI. On the other hand, in the case of an optical waveguide device, the taper angle has an extremely large effect on the characteristics, and it is necessary to maintain the taper angle of 90 degrees in order to obtain the desired device characteristics. Therefore, this method cannot be applied. .

[0006] In Japanese Patent Application Laid-Open No. 4-262533, Kitaoka et al. Filed a method using an etch-back technique to achieve step coverage at a low temperature. This technique stops the film formation before reaching the desired thin film in the formation of the thin film for planarization.
Etching back is performed by dry etching so that the taper angle of the side wall becomes approximately 75 degrees, and then film formation is restarted to obtain a desired film thickness. This method requires high controllability in the etchback process. Although this etchback technology is used in the LSI manufacturing process,
In an optical waveguide device in which both the main constituent material of the flattening film and the uneven portion is silicon oxide, it is difficult to obtain controllability because there is almost no difference in etching rate between the flattening film etching and the uneven portion etching.

In JP-A-3-237721, Shiotani announced a technique for flattening using spin-on-glass (SOG). A method of forming a triple structure of a CVD silicon oxide film / SOG film / CVD silicon oxide film as a flattening film is also used as a method for obtaining a flattening film without voids at a low temperature. However, in these methods, in the optical device, the SOG layer has a higher refractive index than the upper and lower clad layers, which deteriorates the device characteristics. Although it is used in a part of the manufacturing process of LSI, it is difficult to apply it because it is difficult for the SOG raw material to enter the fine pattern of the submicron order.

[0008] In Japanese Patent Application Laid-Open No. 2-312237, Hongo et al. Announced a method of selectively forming a silicon oxide film in a recess by laser CVD. However, in this method, since the laser beam is traversed over the entire concave portion to perform the CVD of the desired film thickness, the productivity is extremely low.

In Japanese Patent Application Laid-Open No. 57-162445, Sato announced that the thin film on the upper part of the void is softened by heating by laser irradiation and is flattened by pouring into the void. However, with this method alone, unevenness remains on the upper part and it is not possible to completely flatten it. If you try to completely fill the void,
Since it takes a considerable amount of time, productivity is low. Further, since heat diffusion also occurs while filling the voids, when applied to an optical device, dopant diffusion from the clad layer to the core layer occurs and the characteristics deteriorate.

[0010]

As described above, according to the conventional method, the device surface cannot be planarized at a low temperature without deteriorating the characteristics of the device and significantly lowering the productivity. There was a problem. An object of the present invention is to obtain a film forming method capable of flattening, which solves the problems of the conventional method.

[0011]

In order to solve the above-mentioned problems of the prior art, the present invention forms a first layer thin film on a substrate having an uneven structure on the surface thereof, and then applies laser light After irradiating the upper portion of the concave portion of the thin film to expose the hollow portion by evaporation on the surface, the second thin film was formed to a desired thickness.

[0012]

In laser ablation, the temperature rises only within the range of the absorption length of the irradiated substance, the thermal conductivity of the substance and the thermal diffusion length determined by the pulse width of the laser. for that reason,
It is possible to minimize the influence of heating on the surroundings as compared with the techniques such as annealing and reflow for heating the entire substance. In addition, laser ablation requires significantly shorter time than melting using laser heating. On the other hand, when a cavity is present in the thin film, the inside of the cavity is exposed by evaporating the thin film above the cavity, so that it is possible to fill the inside of the cavity by subsequent film formation. When this cavity exists in the thin film deposited in the concave portion of the thin film that covers the uneven surface, transpiration over a wider area than the cross-sectional area of the cavity causes
Since the uneven structure having a gentle taper angle can be obtained from the unevenness of the surface, it is possible to flatten the unevenness without forming cavities by subsequent film formation.

The present invention makes use of these facts in an LSI.
The surface of the optical waveguide element is flattened without leaving a void in the flattening film. As a specific process procedure, a flattening film is formed to a thickness corresponding to about one-third of the step, and then the recess is irradiated with a laser to ablate the inside of the void to start the film formation again. Then, the voids are filled and the film formation is continued until the required film thickness is finally obtained. At this time, when the area of the recess is wide, a laser beam is swept to cause ablation throughout the recess.

In the present invention, since the temperature rise is limited to the vicinity of the laser light irradiation portion, there is no fear of disturbing the dopant distribution of the optical waveguide. Further, in the present invention, since only one type of silicon oxide film is used as the planarizing material,
The refractive index of the cladding layer does not change in the optical waveguide. The number of pulses required for ablation is 10 or less, and the time required for one ablation is C
Compared to melting by VD or heating, it is very short and therefore does not significantly reduce productivity.

[0015]

Embodiments of the present invention applied to the formation of an optical waveguide will be described in detail below with reference to the drawings.

FIG. 1 is a schematic view showing each step of the present invention.

Two kinds of silicon oxide film 2 and silicon oxide film 3 having different dopants are formed in this order on the substrate 1 by 2 μm.
The film is formed to the above film thickness. Subsequently, the silicon oxide 3 is etched by dry etching to form a core pattern 3 (a) having an aspect ratio of 2. This core pattern 3
The first flattening film 4 is formed to have a thickness of one third or more of the step due to (a). Although the void 5 exists inside the flattening film 4, the recess is filled after the formation of the first flattening film 4. This is because the deposition rate of the silicon oxide film is high on the side surface of the convex portion and low on the upper surface of the convex portion. Next, a laser 6 having a wavelength suitable for the material of the flattening film is irradiated onto the concave portion of the first flattening film 4, and the opening 7 is formed by evaporation.

FIG. 2 shows an example of CV by ArF laser.
The ablation characteristics of the D silicon oxide film are shown. An example of this is a silicon dioxide film with no dopant, but if any dopant is included, the required irradiation intensity is much lower. Since the ablation depth can be controlled by the irradiation pulse number and the laser light intensity, the opening 7 having a desired depth can be formed in a short time by selecting the optimum irradiation pulse number and the laser light intensity according to the flattening film thickness. It becomes possible to obtain. For example, when a CVD SiO ₂ film without a dopant is used as a flattening film, it is possible to obtain an ablation depth of 3.5 μm in only ²⁰⁰ mS under irradiation conditions of 50 Hz and 8 GW / cm ² . In addition, since the laser beam can be focused to a minimum diameter of 0.2 μm, the LS designed with the submicron rule
It can also be applied to I. Since the taper angle of the opening 7 is sufficiently smaller than 90 degrees, void-free planarization can be performed by subsequently forming the second planarizing film 8. Plasma CV is used as a method for forming the silicon oxide film.
D, or atmospheric pressure CVD can be used. In the present invention, the temperature rise caused by the evaporation or melting by the laser is limited to the vicinity of the irradiation part, and therefore there is no fear that the device characteristics will be deteriorated. Further, since the time required for evaporation is much shorter than that of CVD, the productivity does not significantly decrease. The material of the flattening film is not limited to the silicon oxide film, but a SiON film, a silicon nitride film or the like can be used.

The film forming method of the present invention can be applied not only to the flattening of the optical waveguide device but also to any flattening technique having a possibility of void generation. For example, it can be applied to flattening VLSI devices on the order of submicrons.

[0020]

As described above, according to the method of the present invention, the device surface can be flattened at a low temperature without deteriorating the device characteristics and significantly reducing the productivity. .

[Brief description of drawings]

FIG. 1 is a process schematic diagram showing an example to which the present invention is applied.

FIG. 2 CV according to the number of ArF laser light irradiation pulses and intensity
The figure which shows the ablation depth characteristic of a D silicon oxide film.

FIG. 3 is a process schematic diagram showing a conventional example.

[Explanation of symbols]

 1 Substrate 2 Silicon Oxide Film 3 Silicon Oxide Film 3 (a) Core Pattern 4 First Flattening Film 5 Void 6 Laser Light 7 Opening 8 Second Flattening Film 13 (a) Core Layer 13 (b) Core Layer 14 Silicon Oxide film

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H01L 21/316 M 21/318 M 21/3205 21/768 H01L 21/88 K 21/90 P

Claims (3)

[Claims] 1. After forming a first-layer thin film on a substrate having an uneven structure on the surface, laser light is applied to the upper part of the concave portion of the thin film to expose a cavity portion by evaporation on the surface, and Two
A film forming method comprising forming a thin film of a layer to a desired film thickness. 2. The first thin film is a SiO ₂ film or S
The film forming method according to claim 1, which is an iON film or a silicon nitride film. 3. The second thin film is a SiO ₂ film or S
The film forming method according to claim 1, which is an iON film or a silicon nitride film.