JPH0154856B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor device, in which a portion of a polycrystalline semiconductor layer is selectively annealed and crystallized using a laser beam, and etching rates differ due to differences in the degree of crystallization. The present invention provides a method for manufacturing a semiconductor device that selectively leaves only regions with advanced crystallization.

Conventionally, polycrystalline silicon is annealed with laser light to increase _the grain _size or make it _a single crystal. The method used is to chemically grow crystalline silicon in a vapor phase and then irradiate it with laser light several times. At this time, when the entire surface of the polycrystalline silicon thin film is annealed, the entire surface of the thin film is crystallized, and at the same time, the area under this polycrystalline silicon thin film is
The base substrate of the Si ₃ N ₄ film or SiO ₂ film is also heated, which causes the inconvenience that a selective crystallized silicon film using a resist mask is required to selectively form a part of the crystallized silicon. Etching is required.

In view of these problems, it is conceivable to irradiate only a part of the sample with laser light to crystallize the sample locally, but this method requires the dimensional accuracy of the laser beam diameter that determines the annealing width, and the scanning It is necessary to improve the positional accuracy of the mechanical system and prevent the laser beam from irradiating outside the desired area. This has the disadvantage that the optical system and scanning system are complicated.

Incidentally, such crystallization technology by laser annealing is useful as a technology for dielectric separation and multilayering of circuit elements such as transistors built into semiconductor integrated circuits, and for this reason, some parts can be removed by annealing with laser light. What is desired is a simple method of crystallizing polycrystalline silicon in a region and selectively leaving only that region.

The present invention provides a manufacturing method that can solve the above-mentioned problems, and involves covering a polycrystalline semiconductor with a mask made of metal or the like, and then selectively removing the metal in the areas to be annealed. The laser beam was applied to this area, while the laser beam was reflected by a metal mask in other areas to prevent the annealing effect from occurring due to the laser beam entering the polycrystalline silicon. , laser light is irradiated to selectively anneal a part of the polycrystalline silicon sample, that is, the polycrystalline silicon part located in the area where metal has been removed, in order to crystallize the grain to a large size, and then a metal mask is applied. After the removal, the entire surface is etched, and by actively taking advantage of the fact that polycrystalline silicon with fine grain size is quickly etched away, the area where the grain size has become crystallized by annealing with laser light is self-aligned. The present invention is characterized in that it is formed as follows.

A method according to an embodiment of the present invention will be explained in detail below with reference to the drawings. FIG. 1 shows a cross-sectional view of a polycrystalline silicon sample for selective annealing before laser irradiation. In FIG. 1, after forming a SiO ₂ film or a Si ₃ N ₄ film 2 on a base substrate 1, a polycrystalline silicon film 3 is further formed by chemical vapor deposition or the like, and then this polycrystalline silicon film 3 is A metal mask 4 is placed directly on top. As a material for the metal mask, a metal that reflects laser light and has good adhesion to polycrystalline silicon or SiO ₂ film, such as gold, aluminum, chromium, etc., or a metal oxide or metal silicide is used. In addition, in FIG. 1, only one layer of metal mask is formed, but
A metal with good adhesion and a metal with good reflectivity for laser light may be laminated.

The laser beam 5 is irradiated continuously or in a pulsed manner from above the sample selectively covered by the metal mask 4 in this manner. Note that since the entire surface of the sample cannot be annealed at once, the beam diameter of the laser light source is narrowed down with a lens, and the sample is continuously two-dimensionally scanned with laser light 5 to irradiate the entire surface of the sample with the laser light.
Under the arrangement shown in Figure 1, the entire surface of the sample is illuminated with 5 laser beams.
When the laser beam is scanned once or many times, the laser beam is absorbed by the polycrystalline silicon in the window portion of the metal mask where there is no metal, and the temperature of the polycrystalline silicon rises.
The part shown by is crystallized. In other words, when the output of the laser beam is at an appropriate intensity, the temperature of polycrystalline silicon becomes close to its melting point, and the grain size increases through a solid phase reaction, or it becomes a liquid phase, and when the irradiation ends, it becomes a single crystal during the recrystallization process. Crystallization of etc. is promoted.

On the other hand, since most of the laser light is reflected in the area where the metal mask 4 is present, the temperature of the polycrystalline silicon 3 under the metal mask 4 does not increase much and the grain size does not change. Note that when the laser beam irradiation is repeated many times, the grain size of the polycrystalline silicon in the portion increases, and the grain size reaches several μm to several tens of μm or more.

FIG. 3 shows a cross-sectional view after removing the metal mask. The etching rate of polycrystalline silicon is determined by the crystal orientation and crystal grain size. The crystal orientation with the fastest etching rate is the (111) plane;
(100) plane order. In the region annealed with laser light, the (100) plane is selectively formed, and in the region not irradiated with laser light, the etching rate is a mixture of the three types of crystal orientations mentioned above and shows a value equivalent to that of the (110) plane. . Furthermore, the etching rate becomes faster as polycrystalline silicon has a smaller crystal grain size. Due to the synergistic effect of both crystal orientation and crystal grain size, the etching speed of polycrystalline silicon in the so-called laser beam-unexposed region where the crystal grain size is small is several times that of the portion 6 that has been annealed and crystallized by the laser beam. Faster than that.

The sample in which single crystallized portions have been selectively formed as shown in FIG. 3 through the above processing is then subjected to an etching process using a nitric acid-hydrofluoric acid based etching solution. As already explained, the etching rate is fast in the portion of the polycrystalline silicon 3 with fine crystal grain size that remains in the sample without being annealed, while on the other hand, the crystal grain size becomes larger after being annealed with laser light, and the crystal grain size increases. The etching speed is slow in the hardened areas. Therefore, when the etching process is performed for a certain period of time, all of the polycrystalline silicon 3 with fine crystal grain sizes is etched away, while the crystallized portions where the crystal grain size has become larger due to annealing with laser light are selectively left behind. The structure shown in FIG. 4 is obtained.

Next, other embodiments will be described. FIG. 5 shows that a SiO 2 film 7 is formed between the polycrystalline silicon 3 by thermal oxidation or chemical vapor deposition without directly providing a metal mask 4 on the polycrystalline silicon ₃ .
FIG. 2 is a cross-sectional view of a sample for selective annealing in which
The other parts are the same as those in FIG. When the sample shown in FIG. 5 is annealed with laser light in the same manner as above, the laser light is transmitted through the window portion of the metal mask without being absorbed by the SiO ₂ layer 7. It is absorbed by the polycrystalline silicon 3 below.

FIG. 6 is a diagram showing the state after such laser light irradiation, and similarly to the state shown in FIG. In the process, it becomes a single crystal and a crystallized portion is generated. After that, the metal mask 4 and the SiO ₂ film 7 are removed from the top of the sample, resulting in the same structure as shown in FIG. 3, and the crystallized portion 6 with increased crystal grain size is left in the same manner as described above. Etching treatment can be performed for this purpose.

As described above, according to this example, it is extremely easy to crystallize part of the polycrystalline silicon on the sample by laser annealing and selectively leave this crystallized part. During laser annealing, a metal mask is provided on top of the polycrystalline silicon, so the positional and dimensional accuracy of the annealed area is determined mostly by the pattern positional and dimensional accuracy of the metal mask, and the accuracy is extremely high. becomes. Therefore, dielectric separation and multilayering of circuit elements built into a semiconductor integrated circuit become possible by making full use of laser annealing using a mask. In addition, the accuracy of the mechanical scanning part of the laser beam that determines the annealing position is
Approximately 100 μm is sufficient, and this mechanical scanning section becomes simple without requiring particularly high precision. Furthermore, the diameter of the laser beam only needs to have sufficient energy for annealing, and is not limited by the dimensions of the annealing region. Therefore, a sufficiently thick beam can be used, and the optical system for focusing the laser beam can therefore be simplified. In addition, we selectively leave crystallized portions where the crystal grain size has increased due to annealing,
The process of removing polycrystalline silicon with other small grain sizes takes advantage of the difference in etching speed based on the size of the crystal grains, so laser light is irradiated without using a resist mask etc. during etching. It also has the advantage of being able to form areas in a self-aligned manner.

[Brief explanation of drawings]

1 and 5 are cross-sectional views of the sample before laser annealing in the method of the embodiment of the present invention, FIGS. 2 and 6 are cross-sectional views of the sample after laser annealing in the same method, and FIG. 3 is the same. Cross-sectional view of the sample before etching polycrystalline silicon in the method,
FIG. 4 is a cross-sectional view of a sample after etching polycrystalline silicon in the same method. 1... Base substrate, 2... SiO ₂ film or Si ₃ N ₄
Film, 3... Polycrystalline silicon film, 4... Metal mask, 5... Laser light, 6... Portion with increased crystal grain size or single crystal, 7... SiO ₂ film.

Claims (1)

[Claims] 1. After selectively covering a polycrystalline semiconductor layer formed on a base substrate with a mask made of a material that blocks transmission of laser light, irradiating the polycrystalline semiconductor layer with the laser light,
After annealing the portion of the polycrystalline semiconductor layer that is not covered by the mask to increase the crystal grain size or convert it into a single crystallized portion, the mask is removed to expose the entire surface, and then the mask is removed to expose the entire surface. 1. A method of manufacturing a semiconductor device, characterized by etching the entire surface and selectively removing amorphous portions. 2 The material of the mask is gold, aluminum, chrome,
2. The method of manufacturing a semiconductor device according to claim 1, wherein the semiconductor device is made of either a metal oxide or a metal silicide. 3. The method of manufacturing a semiconductor device according to claim 1, wherein a coating that transmits laser light is provided between the polycrystalline semiconductor layer and the mask.