JPS62145720A - Manufacture of single crystal thin film - Google Patents

Abstract

PURPOSE:To provide a method for recrystallization which has a high stability against fluctuation of a laser beam or the like and against delicate variation of a sample structure by a method wherein an energy beam or heat of a lamp, a heater or the like is applied to a belt-shape polycrystalline thin film covering the recessed part of a non-single crystal thin film. CONSTITUTION:Steps 16a and 16b for control of grain boundary are formed on the surface of a smoothened layer insulating film 15 at the positive which are the two edges of a region to be single-crystallized as protruded patterns with the distance of 10-100mum between the steps in the direction parallel to the beam scanning direction. It is to be noted that the height of the unevenness formed at that time is 0.1-2mum and, most preferrably, 0.4-0.5mum. A polycrystalline silicon film 17 which is to be an active layer and a silicon oxide layer 18 are formed successively on the whole surface and a laser beam 20 is applied and made to scan along the stripe-shape steps to melt, solidify and single-crystallize the polycrystalline silicon film 17 between the step protrusions 16a and 16b.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a method for forming a single crystal thin film used in the field of manufacturing semiconductor devices, and more specifically relates to a method for forming a single crystal thin film formed on an amorphous insulating base. This invention relates to improvements in methods for converting non-single-crystalline thin films into single crystals by irradiating them with an energy beam or heating them with heaters, lamps, etc.

<Prior art> Conventionally, an amorphous or polycrystalline non-single crystal thin film is formed on an insulating film that does not have crystallinity, and this non-single crystal thin film is irradiated with an energy beam, or a heater, lamp, etc. Various methods have been proposed for producing single-crystal thin films by melting and recrystallizing them by heating.

Some of the methods are shown in FIGS. 3 to 6.

FIG. 3 shows a method in which a bimodal temperature distribution is obtained by shaping the intensity of the beam 21 to single-crystallize a non-single-crystal thin film 22, and FIGS. 4 to 6 respectively show the island method ( Embedded molding), SiN selective anti-reflection coating method, and polysilicon cap multilayer melt recrystallization method. silicon layer, 26 is an insulating film, 27
6 is a recrystallized silicon layer, 28 is a SiN film, 29 is an insulating film, and 30 is a polycrystalline silicon cap layer. This fourth
The methods shown in Figures 6 to 6 are for obtaining a bimodal temperature distribution by locally changing the reflectance, heat conduction, etc. depending on the sample structure, and producing a single crystal. There is also a method of using it.

<Problems to be Solved by the Invention> The conventional methods shown in FIGS. 3 to 6 above can all perform ideal single crystallization when the base is flat. That is, for example, in a stacked semiconductor device, single crystal layers that become active layers are stacked with an insulating film interposed between them.
Currently, surface steps affect the crystal growth process and its crystallinity, and for this reason, it is customary to flatten the underlying surface and perform single crystallization.

However, if the underlying surface is not sufficiently flattened, or even when the underlying surface is flat, there may be beam fluctuations or subtle changes in the sample structure, making it difficult to obtain a good single crystal using any of the above methods. In many cases, it is difficult to achieve this, and there are problems such as the generation of grain boundaries and discontinuity in crystal growth, which reduces the crystallinity.

The present invention was created in view of the above points, and includes a laser,
The aim is to provide a recrystallization method that is highly stable against beam fluctuations and subtle changes in sample structure.

<Means for Solving the Problems> In order to achieve the above-mentioned object, the method for forming a single crystal thin film of the present invention includes forming grains in a single crystallized region on the surface of a substrate insulator or an insulating film coated on a substrate. For the purpose of field control, defect prevention, and stress mitigation, a concave band-like step parallel to the beam scanning direction with a width of 10 μm to 100 μm and a depth of 0.1 μm to 2 μm is formed in advance, and then an insulator having this band-like step is formed. A non-single crystal thin film to be made into a single crystal is formed on a substrate or an insulating film, and a belt-shaped polycrystalline thin film with a width of 15 μm to 110 μm is formed on this non-single crystal thin film so as to cover the recessed portion with a thin insulating film interposed therebetween. Next, energy beam irradiation or heating with a heater, lamp, etc. is performed from above this band-shaped polycrystalline thin film, so that the non-single crystalline thin film in the recessed portion is made into a single crystal.

<Function> With the above configuration, the generation of grain boundaries is localized only in the convex portions of the band-like step portions, and single crystal regions without grain boundaries are formed in the concave portions.

FIG. 1 is a plan view showing the state of the substrate surface when a single crystal is formed by providing parallel steps on both sides of a region to be single crystallized according to the present invention.

In FIG. 1, l is a single crystallized region, 2 is a stepped portion, and 3 is a grain boundary.As is clear from FIG. 1, according to the present invention, f+) convex portions and single crystallization The growth of grain boundaries generated outside the area is stopped at the stepped portion 2, as shown in (■) in FIG. 1, to prevent upward expansion.

(3) The stress in the single crystallized portion 1 is concentrated on the stepped portion 2, and defects are generated there as shown in (■) in FIG. 1, thereby relaxing the stress in the single crystallized portion 1.

Due to these effects, a single crystal region 1 without grain boundaries can be easily obtained.

In carrying out the present invention, the width of the concave band-like step is set to 1.
If it is smaller than 0 μm, it is not preferable because it becomes difficult to actually fabricate a practical element in the single crystal thin film formed in the recess.

Furthermore, if the width of the concave band-like step is larger than 100 μm, it becomes difficult to uniformly convert a non-single crystal thin film within the width into a single crystal by irradiation with laser light or the like, which is not preferable.

Further, the depth of the concave band-like step is less than 0.1 .mu.m, which is not preferable because step breakage occurs in the single crystal thin film, etc., making it difficult to form a high-quality single crystal.

In addition, by forming the polycrystalline thin film formed at the top to be wider than the width of the concave band-like step by about 5 μm to 10 μm, a good bimodal temperature distribution necessary for single crystallization can be obtained. .

<Example> Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIGS. 2(a) to 2(e) are cross-sectional views for explaining each step when the present invention is applied to a multilayer melt recrystallization method.

First, as shown in FIG. 2(a), required circuit elements such as MOS transistors are placed on a semiconductor substrate 11 with an oxide film 12 for element isolation. A conductor 14 such as polysilicon or high melting point metal is formed between each circuit element.
The surface is covered with an interlayer insulating film 15. In the state shown in FIG. 2(a), the underlying semiconductor substrate II is on the surface of the insulating film 5.
Since the unevenness is caused by the 4th grade, corresponding unevenness is generated.

Next, as shown in FIG. 2(l), the surface of the semiconductor substrate covered with the insulating film 15 is planarized by a known planarization method, such as an etch-back method.

Note that the etch-back method is a method in which an organic film such as a photoresist is applied to the uneven surface of a semiconductor substrate, and the planar shape of the organic film is transferred to the base.

Next, as shown in FIG. 2(c), steps +6a and 16b are formed on the surface of the planarized interlayer insulating film 15 for grain boundary control.

. . . At the positions at both ends of the part to be single-crystalized, the interval between strip-like steps parallel to the beam scanning direction is 10 μm to 100 μm wide (for example, 40 μm wide).
It is formed as a convex pattern. Note that the amount of unevenness formed at this time is 0.1 μm to 2 μm, and 0.4 to 0.5 μm.
is optimal.

Next, as shown in FIG. 2(d), a structure for single crystallization is formed. Here, a multilayer melt recrystallization method using a polysilicon cap was used. That is, the first level difference in the tube +6a
, 16b, . . . are formed on the entire surface of the interlayer insulating film 15, a polycrystalline silicon 17 and a silicon oxide film 18, which will become an active layer, are deposited in this order by, for example, a chemical vapor deposition method (CVD method). Deposition, and then the silicon oxide film 1
Form a polycrystalline silicon cap layer 19 with a width of 15 μm to 110 μm (for example, 50 μm width) in the region including the step portion of No. 8 (single-crystalline region including the step portion at both ends) by, for example, chemical vapor deposition (CVD method). to form a structure for single crystallization.

After forming the above structure, as shown in FIG. 2(e), the laser beam 20 is irradiated and scanned along the band-shaped step, thereby increasing the area sandwiched between the step protrusions 16a and 16b. The crystalline silicon 17 is melted and solidified to become a single crystal.

Through each of the above steps, a step is placed outside the desired single crystal region, and this step is used as a sacrificial region to concentrate grain boundaries and defects, thereby preventing grain boundaries and defects from occurring within the single crystal region. prevent and obtain a good quality single crystallized layer.

<Effects of the Invention> As described above, according to the present invention, the following effects can be obtained.

(1) Growth of grain boundaries generated outside the convex portion or the single crystal region is stopped at the stepped portion and prevented from penetrating into the single crystal region, so that a uniform and high quality single crystal can be obtained in the concave portion.

(2) Grain boundaries generated in the recesses in the single crystal region can be guided outside the single crystal region at the stepped portion and can be prevented from further expansion, so that a uniform and high quality single crystal can be obtained.

(3) By concentrating the stress in the single crystallized part on the stepped part and intentionally creating defects there, the stress in the single crystallized part can be relaxed.

(4) Since the cross-sectional temperature profile becomes bimodal due to the bimodal insulating film step, a single crystal can be obtained over a wider area.

[Brief explanation of drawings]

FIG. 1 is a plan view showing the state of the surface of a single crystallized substrate formed according to the present invention, and FIGS. 2(a) to (e) are sectional views for explaining the steps of an embodiment of the present invention, respectively. FIGS. 3 to 6 are sectional views for explaining the prior art, respectively. l... Single crystallized region, 2... Step portion, 3... Crystal grain boundary, 11... Semiconductor substrate, 15... Interlayer insulating layer, 1
6a, 16b... Stepped convex portion, 17... Polycrystalline silicon serving as an active layer, 18 Silicon oxide film, 19... Polycrystalline silicon cap layer, 20... Laser beam.

Claims (1)

[Claims] 1. Irradiating an energy beam to a non-single crystal thin film formed on the surface of an insulating substrate or a substrate covered with an insulating film;
Alternatively, in a method for forming a single crystal thin film in which the single crystal thin film is made into a single crystal by heating with a heater, a lamp, etc., the surface of the substrate insulator or the insulating film coated on the substrate is preliminarily coated with a width of 10 μm to 100 μm and a width of 0.1 μm to 2 μm. forming a concave belt-like step in depth, forming a non-single crystal thin film to be made into a single crystal on the insulating substrate or insulating film having the step in the step formed by the above process; A thin insulating film is formed on the non-monocrystalline thin film, and a strip-shaped polycrystalline thin film with a width of 15 μm to 110 μm is formed on the thin insulating film formed by the above process so as to cover the recessed part, and the strip-like polycrystalline film formed by the above process is A method for forming a single crystal thin film, which comprises irradiating the polycrystalline thin film with an energy beam or heating it with a heater, lamp, etc. to convert the non-single crystal thin film in the recess into a single crystal. 2. The method for forming a single crystal thin film according to claim 1, wherein the non-single crystal thin film to be single crystallized is a silicon thin film.