JPH07221043A - Ion implantation method - Google Patents

Abstract

PURPOSE:To activate an ion-implanted semiconductor thin film without roughening up a mask by implanting ions from an ion source to the semiconductor thin film formed on a substrate at an acceleration voltage within a specified range and by irradiation with an energy beam while the substrate is being heated. CONSTITUTION:An active silicon layer is formed on a glass substrate 1, which is patterned in an island shape. Then, a gate insulating film 3 and a gate silicon 4 are formed on the active silicon layer 2. Next, the gate insulating 3 and the gate silicon 4 are subjected to patterning. Ions 5 from an ion source are implanted at an acceleration voltage of 0.5 to 10kV, the glass substrate 1 is irradiated with and an ultraviolet ray while being heated to approx. 100 to 600 deg.C by a heater 6 to activate the implanted ions 5, thus forming a p type silicon of low resistance. This makes it possible to lower the electric resistance of the semiconductor thin film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion implantation method for doping impurities into a semiconductor thin film on a large glass substrate used for manufacturing a liquid crystal display or the like, and particularly applicable to a glass substrate, at low temperature, The present invention relates to an ion implantation method capable of doping impurities with high speed and without film roughness.

[0002]

2. Description of the Related Art As a method of forming a junction used in the manufacture of a liquid crystal display using a thin film transistor (TFT) as a switching element, an n-type film is formed by a vapor phase reaction in an amorphous silicon transistor. Further, in many cases, a polycrystalline silicon transistor adopts a coplanar structure similar to that of an LSI semiconductor element and is formed by using an ion implantation method.

FIG. 5 is a sectional view showing a manufacturing process of such a thin film transistor having a coplanar structure in the order of steps. First, as shown in FIG. 5A, an active silicon layer 2 is formed on a glass substrate 1 and patterned into islands. Then, as shown in FIG. 5B, a gate insulating film 3 and a gate silicon 4 are formed on the active silicon layer 2, and the gate silicon 4 is patterned. After that, as shown in FIG. 5C, for example, phosphorus (P) ions 5 are implanted at a voltage of about 100 kV by ion implantation. The ions 5 penetrate the gate insulating film 3 on the source S and the drain D and are implanted into the active silicon layer 3. By heating the substrate 1, the implanted (doped) ions 5 are activated, the active silicon layer 3 becomes n-type silicon having a low resistance, and the gate silicon 4 into which the ions 5 are implanted becomes the gate G and the active silicon is formed. The layer 1 has a source S and a drain D on both sides thereof. Then, as shown in FIG. 5D, the protective film 8, the source electrode 9 and the drain electrode 10 are formed to obtain a thin film transistor. If boron (B) is used as an ion, P
A mold silicon is formed.

By applying such a thin film transistor to a display portion and a circuit portion, an active liquid crystal display is manufactured. Recently, since a large display is formed or a large number of small displays are taken from the substrate, the substrate becomes large, and for example, a size of about 450 mm × 350 mm is used. Therefore, high-speed doping techniques have been developed for large substrates. For the conventional large area high voltage ion implantation method, for example, see M. Tanjo,
et al. by SID Japan Display'92 Abstracts, 1992
Years, p.345-348. Ion density is 0.0
Although it is ² mA / cm ^2, it is described that since the acceleration voltage is as high as 40 keV or higher, the temperature of the substrate rises and the resist mask cannot be used. An example of a non-mass separation type ion irradiation system using a bucket ion source is G. Kawachi, e.
T. al. J. Electrochem. Soc., Vol.137, No.11, 1
990, p.3522-3526. With this material, an ion density of 0.5 mA / cm ² can be realized, and the required concentration of doping can be achieved in 1 minute or less. However, activation of the implanted ions requires energy irradiation,
Laser activation is used. In this case, very thin 5
When a silicon film of about 00Å is doped with laser to activate the laser, the film may be roughened by the energy of the laser. In such a conventional technique, a technique of irradiating a large-sized substrate with ions at high speed and low temperature and activating the implanted ions in a stable state of the film is not known.

[0005]

Therefore, an object of the present invention is to provide a method of implanting ions into a semiconductor thin film formed on a large-sized substrate at high speed and low temperature and activating the film without roughening it. To get.

[0006]

This problem is solved by implanting ions from an ion source into a semiconductor thin film formed on a substrate at an accelerating voltage of 0.5 to 10 kV, and then irradiating an energy beam while heating the substrate. It is solved by doing.
At this time, it is preferable that the ion source is a non-mass separated bucket type ion source, the energy beam is an excimer laser, the substrate is glass, and the heating temperature is preferably 100 to 600 ° C. .

[0007]

With this structure, the energy intensity for activating the implanted ions by the energy beam can be lowered,
Roughness of the semiconductor thin film can be suppressed. Further, by using the bucket type ion source, it is possible to implant ions at a high concentration in a short time while suppressing an increase in the substrate temperature. Furthermore, a glass substrate having poor heat resistance can be adopted.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a diagram showing an example of using the ion implantation method of the present invention for manufacturing a thin film transistor. First, as shown in FIG. 1A, a film thickness of 50 n is formed on a glass substrate 1.
m active silicon layer 2 is formed and patterned into an island shape. Then, as shown in FIG. 1B, a gate insulating film 3 having a film thickness of 100 nm and a gate silicon 4 having a film thickness of 100 nm are formed on the active silicon layer 2. Then, the gate insulating film 3 and the gate silicon 4 are patterned. After that, as shown in FIG. 1C, for example, boron ions 5 are implanted by ion implantation.
In this ion implantation, a non-mass separation type bucket type linear ion source is used as an ion source, and an acceleration voltage of 0.
5-10 kV, preferably 1-5 kV, ion density of 0.
05-1 mA / cm ² , preferably 0.1-0.5 mA
/ Cm ² conditions. Under the conditions of an accelerating voltage of 2 to 5 kV and an ion density of 0.5 mA / cm ² , the temperature rise of the glass substrate 1 is about 100 ° C., and a resist mask can be used. Boron ions 5 are implanted into both sides of the gate silicon 4 and the active silicon layer 2 which are not covered with the gate insulating film 3.

Next, as shown in FIG. 1D, the glass substrate 1 is heated by the heater 6 to about 100 to 600 ° C., preferably about 200 to 400 ° C., and the ultraviolet pulse laser energy beam 7 is applied to the substrate surface. To activate the implanted ions 5. The irradiation condition of this energy beam is that the energy density is 100 to 250 mJ /
It is preferably about cm ² . An excimer laser is suitable as the laser. By this activation, P-type silicon having low resistance is formed, and the gate G, the source S and the drain D are formed.
Is formed. Next, as shown in FIG. 1E, the protective film 8, the source electrode 9 and the drain electrode 10 are formed to obtain a thin film transistor.

According to such an ion implantation method, it is possible to prevent the film from being roughened by irradiation with an energy beam for activating the semiconductor thin film (active silicon layer 2 and gate silicon 4), and to reduce the electric resistance (sheet resistance) of the semiconductor thin film. ) Can be lowered. FIG. 2 shows the relationship between the substrate heating temperature, the laser activation energy and the sheet resistance in the example of implanting boron into the silicon thin film. The ion implantation conditions are as follows: acceleration voltage 5 kV, ion Density 0.125 mA / cm ² , implantation time 6 seconds, acceleration voltage 1 kV, ion density 0.5 mA / cm ² , implantation time 4
There are two types of 5 seconds.

From FIG. 2, when the accelerating voltage is 1 kV, when the substrate temperature is set to 300 ° C. and laser irradiation is performed,
It can be seen that the sheet resistance becomes higher than that when activated by laser irradiation at a substrate temperature of 25 ° C. On the other hand, when the accelerating voltage is 5 kV, when the substrate temperature is set to 300 ° C. and laser irradiation is performed, the sheet resistance is lower than that when activated by laser irradiation at the substrate temperature 25 ° C. Become. Accordingly, the acceleration voltage is constant value or more, 2 kV or more in the case of boron, preferably by a least 3 kV, and those activated with even 25 ° C. to lower the laser energy, for example, from 200 mJ / cm ² to 150 mJ / cm ² The same sheet resistance is obtained.
Further, since the laser energy can be lowered and activated, the film roughness can be reduced. Further, even if the ion implantation amount is reduced, a low sheet resistance can be obtained, and high-speed doping can be performed.
The acceleration voltage is slightly higher when the ions are phosphorus,
It is desirable to set it to 3 kV or more. When the voltage exceeds 10 kV, the substrate temperature rises and the resist mask cannot be used.

FIGS. 3 and 4 are for explaining the above-mentioned operation. In FIG. 3, the acceleration voltage at the time of ion implantation is 1 kV.
(A) shows the surface of the silicon thin film after ion doping, and (b) shows that after laser activation. After the ion doping, a natural oxide film (SiOx) of silicon and a deposited layer of boron are formed on the surface of the silicon thin film, and part of the boron is oxidized. Moreover, since the acceleration voltage is low, a considerable amount of boron exists on the surface of the silicon thin film or immediately below the surface. When laser activation is performed while heating this, part of the boron on the surface diffuses into the silicon thin film as shown in FIG. 3B, but since the substrate temperature is high,
The loss of boron due to volatilization is large, the total amount of boron taken into the silicon thin film is reduced, and the sheet resistance is increased.

FIG. 4 shows that the acceleration voltage during ion implantation is 5 kV.
(A) shows the surface of the silicon thin film after ion doping, and (b) shows that after laser activation. In this case, since the ion accelerating voltage is high, most of the boron after the ion doping is taken into the silicon thin film. When laser activation is performed by raising the substrate temperature and activating, there is almost no loss due to volatilization of boron as shown in (b), boron is effectively taken in, and the activation effect by heating is added, The activation is fully performed and the sheet resistance is reduced. An electron beam, lamp annealing, etc. can be used for heating the substrate. The heating temperature is about 100 ℃.
From the above, it is preferable that the temperature is 600 ° C. or lower at which the glass is deformed in the case of a glass substrate.

[0014]

As described above, according to the present invention,
When activating with the energy beam after ion implantation, by irradiating the energy beam while heating the substrate, sufficient activation can be achieved even if the energy intensity of the energy beam is reduced, and film roughness can be prevented. Moreover, an effect such as low resistance can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a process of an example in which the ion implantation method of the present invention is applied to manufacturing a thin film transistor.

FIG. 2 is a graph showing the operation of the present invention.

FIG. 3 is a model diagram showing an operation of a comparative example.

FIG. 4 is a model diagram showing the operation of the embodiment of the present invention.

FIG. 5 is a cross-sectional view showing a process of an example in which a conventional ion implantation method is applied to manufacturing a thin film transistor.

[Explanation of Codes] 1 glass substrate 2 active silicon layer 4 gate silicon 5 ion 6 heater

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H01L 21/336 9056-4M H01L 29/78 311 P

Claims (3)

[Claims] 1. Ions characterized by implanting ions from an ion source into a semiconductor thin film formed on a substrate at an accelerating voltage of 0.5 to 10 kV, and then irradiating an energy beam while heating the substrate. Injection method. 2. The ion source according to claim 1, wherein the ion source is a non-mass separated bucket type ion source, the energy beam is an excimer laser, and the semiconductor thin film is silicon.
An ion implantation method, wherein the substrate is glass. 3. The ion implantation method according to claim 1, wherein the heating temperature is 100 to 600 ° C.