JPS6021807A - Flash annealing method of hydrogenated amorphous silicon - Google Patents

Abstract

PURPOSE:To etch simultaneously the part wherein a polycrystal is not needed without incurring the deterioration of characteristics and the unevenness of the film thickness due to the desorption of hydrogen by carrying out simultaneously the partial polycrystallization of hydrogenated amorphous silicon and the etching. CONSTITUTION:A light transmissible film 3 of a substance such as SiO2, Si3N4, etc. for preventing the desorption of hydrogen is formed on the part of a hydrogenated amorphous silicon thin film 2 formed on a substrate 1. Then the light 4, having higher luminous intensity than that in an ordinary flash annealing method, is irradiated by a xenon flash lamp, etc. to polycrystallize the part of the film 2 covered with the film 3, and the etching of the part of the thin film 2 not covered with the film 3 is simultaneously carried out. In this way, an expensive shading can be dispensed with, and the precision of the position of the polycrystal part can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a flash annealing method, and more particularly to a flash annealing method for polycrystallizing hydrogenated amorphous silicon, which is a photoconductive material.

[Prior art]

Hydrogenated amorphous silicon (a-5t: H) is amorphous silicon in which silicon (Ss) atoms are arranged irregularly, and the bonds that are not bonded to other 8i atoms are filled with hydrogen, It is a material that can be treated as a semiconductor because it can control p-type and n-type, and it is possible to form thin film transistors. This is attracting attention as a photoconductive material that can be used to form highly sensitive semiconductors over large areas at low cost, and is being applied to life-size optical sensors and liquid crystal panels.

By the way, in hydrogenated amorphous silicon, the carrier mobility is 1/2 or less, which is half V@Sec.

When a conductive element is formed, the operating speed is slower than when ordinary single crystal silicon is used. Therefore, when forming an optical sensor and a peripheral circuit for transferring signals obtained from the optical sensor on the same substrate using hydrogenated amorphous silicon, it is necessary to increase the operating speed of the peripheral circuit section. There is. For this reason, the hydrogenated amorphous silicon in the peripheral circuit portion is partially polycrystallized to improve carrier mobility. This partial polycrystalization is carried out by a heating operation called annealing to make the crystal grain size i0.1 to 1 μm.
/y, or higher carrier mobility can be obtained. Known annealing methods include a laser annealing method in which a high-energy laser beam such as a ruby laser or an argon laser is scanned and irradiated, and a flash annealing method in which a xenon flash lamp is emitted to irradiate light. Among these methods, the flash annealing method is widely used because it has the advantage of polycrystallizing large-sized hydrogenated amorphous silicon in a short time.

When exposed to strong light, such as when performing a flash annealing method, the hydrogen incorporated into the hydrogenated amorphous film is released, resulting in deterioration of properties and non-uniform film quality. There is a problem.

Furthermore, conventionally, elements are formed after the entire surface of hydrogenated amorphous silicon has been annealed, resulting in wasteful annealing of unnecessary portions that will be removed by etching in the future.

Furthermore, in order to perform partial polycrystalization, conventional flash annealing methods require a light-shielding device using a light-shielding mask, which increases equipment costs and requires a flash light source with high light intensity. However, there is a problem in that power consumption is large.

Furthermore, in the conventional flash annealing method, there is a problem that the boundary between the polycrystallized portion and the non-polycrystalized portion becomes unclear due to the diffraction effect of light, resulting in poor precision.

In addition, when manufacturing semiconductor devices using hydrogenated amorphous silicon as described above, Keyaki forms each region that makes up the semiconductor element, polycrystallizes the hydrogenated amorphous silicon, and finally forms electrodes and wiring patterns. The process of forming it from metal is adopted, making it complicated.

〔the purpose〕

The first object of the present invention is to develop hydrogenated amorphous silicon that does not cause deterioration of properties or non-uniformity of film thickness due to desorption of hydrogen, and can simultaneously perform etching of areas that do not require polycrystalization. An object of the present invention is to provide a flash annealing method.

A second object of the present invention is to provide a flash annealing method for hydrogenated amorphous silicon that does not require an expensive light shielding device and can use a flash light source with low light intensity.

Furthermore, a third object of the present invention is to eliminate the need for an expensive light shielding device and to have good positional accuracy of the polycrystalline portion.
Moreover, it is an object of the present invention to provide a flash annealing method for hydrogenated amorphous silicon that simplifies the entire process of manufacturing a semiconductor device.

〔composition〕

Hereinafter, the configuration of the present invention will be explained based on illustrated embodiments.

First, flash annealing method 1f for hydrogenated amorphous silicon according to the first embodiment! :Explained with reference to FIG. As shown in Figure 1 (,), a hydrogenated amorphous silicon thin film 2 is formed on a substrate 1 made of glass or a silicon wafer by a high-frequency glow 6 discharge method, etc., and the polycrystalline portion is covered with a thin film 2 of hydrogenated amorphous silicon. For thin film 2-H, S10
A light semi-transparent film 3 made of a substance that prevents desorption of hydrogen, such as S'13N4, is formed in close contact. This light semi-transparent film has a light transmittance and a film thickness depending on the light source so that an appropriate light intensity for annealing can be obtained when the irradiation light is transmitted through the film.

In this state, a xenon flash lamp or the like is used to irradiate the light 4 with a higher intensity than in the normal flash annealing method, but the irradiation is performed for a longer time than in the normal flash annealing method using a lamp with the same light intensity.

The high-intensity light irradiated at this time has an intensity suitable for annealing after passing through the light semi-transparent film 3, and the hydrogenated amorphous silicon thin film 2a is polycrystallized by the heat generated by the energy, while the light is Since the hydrogenated amorphous silicon thin film 2b without the semi-permeable film 3 has high energy, evaporation occurs and is removed, resulting in simultaneous etching. Moreover, since the one-light semi-transmissive film 3 is formed in close contact with the hydrogenated amorphous silicon thin film, the detachment of hydrogen, which tends to occur during flash annealing, is suppressed.

Next, a flash annealing method for hydrogenated amorphous silicon according to a second embodiment of the present invention will be explained with reference to FIG. The state before flash annealing is as shown in FIG. 2(,), and the substrate 1 and hydrogenated amorphous silicon thin film 2 are the same as in the first embodiment shown in FIG. 1(,). be.

However, the structure of the light semi-transparent film 3 is different.
a portion 3a having an appropriate thickness for polycrystallization;
It consists of a portion 3b formed thicker than this.

When irradiated with flash light 4 times in this state, polycrystalization occurs normally in the light semi-transparent film portion 3a having an appropriate thickness, but in the thicker light semi-transparent film portion 3b, the energy of the flash light 4 is reduced by half. It is absorbed by the permeable membrane 3b, and the hydrogenated amorphous material 7 below is absorbed. The energy does not reach the silicon layer, or even if it does, the energy is very small, so the hydrogenated amorphous silicon layer evaporates in the exposed part, as shown in Figure 2 (b), and a light transmissive layer of an appropriate thickness is formed. The polycrystalline silicon film 5 becomes a polycrystalline silicon film 5 in the area where the transparent film was, and the hydrogenated amorphous silicon film 6 is formed without being polycrystalized in the area where the thick semi-transparent film existed.

In this example, the thickness of the semi-transparent film 3 is partially changed; this is because the thickness of the semi-transparent film 3 is different between the part to be polycrystallized and the part to be left in the hydrogenated amorphous silicon state without polycrystallization. It is also possible to form a light semi-transparent film on the entire surface to a suitable thickness for polycrystalization, and then layer it only on the areas where polycrystallization is not performed, to form a light semi-transparent film. It is also possible to form a thick layer and then remove the portion to be polycrystallized by etching or the like.

Next, a method for flash annealing amorphous silicon according to a third embodiment of the present invention will be explained with reference to FIG. As shown in FIG. 3(a), a hydrogenated amorphous silicon thin film 2 is formed on a substrate 1 made of glass or silicon wafer by a high frequency glow discharge method, etc., and polycrystallization is performed in areas where polycrystallization is required. A layer 7 made of a material with high light absorption, such as carbon granoate, is further formed on the amorphous silicon thin film 2. In this state, a xenon flash lamp or the like is used to emit light 4 having an intensity that is weaker than in normal flash annealing and cannot polycrystallize the hydrogenated amorphous silicon thin film 2 as it is.
irradiate. As a result, the irradiated light is well absorbed in the light absorption layer 7, and the energy of the light becomes heat, which increases the temperature of the hydrogenated amorphous silicon thin film 2 underneath, causing polycrystalization. In areas where there is no layer, the irradiated light hardly raises the total temperature of the hydrogenated amorphous silicon thin film 2 and does not cause it to become polycrystalline, so it remains in an amorphous state. Therefore, after completing the light irradiation,
If light absorption is removed by M7, as shown in FIG. 3(b), a polycrystalline portion 5 and an amorphous portion 61 are formed.
ft: A silicon thin film having the following properties will be formed.

Next, a method for manufacturing a semiconductor device including a flash annealing process for amorphous silicon according to a fourth embodiment of the present invention will be described with reference to FIGS. 4 to 7. As shown in FIG. 4, this manufacturing method includes a step of forming a hydrogenated amorphous silicon film on a substrate (block A), and a step of forming a metal thin film in a predetermined pattern (block B).
, flash annealing process (block C), gold M
The process includes a step (block D) of etching the thin film into the shape of an electrode or wiring. FIGS. 5 to 7 show the steps of constructing, for example, an MO8 transistor using this manufacturing method, in which (,) in each figure represents a plan view, and () represents a center sectional view. There is.

First, as shown in FIG. 5, a gate electrode 12 is formed of aluminum, for example, on a glass or silicon substrate 11, and a gate insulating film is formed on the sheet metal surface.
For example, is the film of trisilicon tetranitride (813N, i ), which is 3, positive? CVD (Chemical Vapov)
I) The hydrogenated amorphous silicon film 14 is formed to a thickness of approximately 0.3 μm by epos-ition (chemical vapor deposition) method, and the hydrogenated amorphous silicon film 14 is formed to a thickness of approximately 0.3 μm by, for example, a glow discharge method.
．． It is assumed that the thickness is 5μ.

Next, as shown in FIG. 6, a metal film 15 of aluminum or the like is formed in a predetermined pattern so that the hydrogenated amorphous silicon film 14 on the gate electrode 12 is exposed. This pattern is formed so that only the portions of the hydrogenated amorphous silicon that need to be polycrystallized are opened. Next, when the flash light 16 is irradiated using a xenon lamp or the like, the light directly hits the hydrogenated amorphous silicon film 14 at the opening 15a, so the energy of the flash light 16 is converted into heat within the hydrogenated amorphous silicon film 14. The crystal grains become finer and polycrystalline, and flash annealing is completed. On the other hand, since almost all of the flash light 16 is reflected in a certain portion of the metal film 15, the temperature does not increase in the hydrogenated amorphous silicon film 14 located thereunder, and polycrystallization does not occur.

Next, the metal film 15 is etched and used as an electrode or wiring. In FIG. 7, metal films left in a predetermined pattern on both sides of the polycrystalline portion 17 by flash annealing are used as the source electrode 18s1, the drain electrode 18D, and the wiring 18w. At this time, the polycrystalization of the polycrystalline portion 17 is caused by heat conduction, and the source electrode 18! Since it extends below the I and drain electrodes 18D, both electrodes 18s and 18D are in direct contact with the polycrystalline portion 17, allowing current to be delivered and received.

〔effect〕

As described above, according to the present invention, there is no deterioration of characteristics or non-uniformity of film thickness due to desorption of hydrogen, and moreover, it is possible to simultaneously etch portions that do not require polycrystallization.

Furthermore, by using a light-absorbing material, a flash light source with low light intensity can be used without using an expensive light shielding device.

Furthermore, by using a metal thin film, the positional accuracy of the polycrystalline portion can be ensured without using an expensive light shielding device, and the entire manufacturing process can be simplified.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are process diagrams of a flash annealing method for hydrogenated amorphous silicon according to a first embodiment of the present invention, and FIGS. 2(a) and (b) are process diagrams of a second embodiment of the present invention. FIGS. 3(a) and 3(b) are process diagrams of a flash annealing method for hydrogenated amorphous silicon according to a third embodiment of the present invention; FIG. Flowchart of a method for manufacturing a semiconductor device including a flash annealing method for hydrogenated amorphous silicon as one step according to a fourth embodiment of the present invention, FIGS. 5(a), (b), and FIG. 6(a) + (b) )
, FIGS. 7(a) and 7(b) are process diagrams of the same manufacturing method. 1... Substrate, 2... Hydrogenated amorphous silicon thin film, 3... Light semi-transparent film, 4... Flash light, 5
... Polycrystalline silicon thin film, 7... Light absorption layer, 11
... Substrate, 12... Gate electrode, 13... Gate insulating film, 14... Hydrogenated amorphous silicon film, 1
5... Metal film, 16... Flash light, 17...
Polycrystalline portion, 18s...source electrode, 18D...
drain electrode. Applicant's agent Kiyoshi Inomata - [A Figure 1 (0) Figure 2 (0) Figure 3 (0) (b)

Claims (1)

[Claims] A flash annealing method for hydrogenated amorphous silicon characterized by simultaneously performing partial polycrystalization and etching of the hydrogenated amorphous silicon.