JPH07106587A - Impurity implantation method for silicon thin film transistor - Google Patents

Abstract

PURPOSE:To prevent deterioration of semiconductor film quality, by implanting ions in a silicon thin film transistor, after an impurity ion beam is irradiated with laser light wherein the wavelength is smaller than or equal to a specified value and the energy density is larger than or equal to a specified value. CONSTITUTION:From a laser light source 1, laser light 2 wherein the wavelength is 351nm or shorter and the energy density is 150mJ.cm<-2> or larger is reflected by a mirror 3, and made to enter so as to intersect an ion beam 4. The ion beam 4 which contains PH ions, PH2 ions, etc., accelerated by an ion source is irradiated with the laser light 2 above a semiconductor substrate 5, and H ions are released. The ion beam 4 from which H ions are released collides against the semiconductor substrate 5 fixed on a substrate holder 6, and enters the semiconductor substrate in accordance with the kinetic energy of the ions. Hence P ions from which H ions are released are implanted in the semiconductor substarte 5, so that substrate heating and film quality deterioration of semiconductor are reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for ion-doping impurities into a semiconductor substrate, and particularly to prevent temperature rise and characteristic deterioration of the semiconductor substrate due to hydrogen ions.

[0002]

2. Description of the Related Art An ion implanter comprises an ion source, a mass spectrometer, an accelerating tube, an electrostatic scanning system and a Faraday cup.

An ion source is a portion where the kinetic energy of electrons given by an electric field is converted into the internal energy of injected molecules by inelastic collision between injected molecules and electrons.

The converted internal energy is consumed as excitation, dissociation, or ionization of injected molecules.

In this way, the gas containing the necessary dopants is ionized by electron beam bombardment or discharge to form a beam and is extracted from the ion source.

This ion beam is passed through a mass spectrometer using a magnet to select only desired ions.

After that, the ions are irradiated with 10 keV in the acceleration tube.
To 200 keV, and the accelerated ion beam having a diameter of several mm to several tens of cm is electrostatically scanned in the X and Y directions and injected into the substrate masked with the resist.

In the high-current type ion implantation apparatus, in order to avoid the temperature rise of the substrate during the ion implantation, a mechanical operation of rotating a disk in which a plurality of substrates are arranged is performed.

When the substrate to be implanted is single crystal silicon, when the ion implantation axis direction coincides with the crystal axis direction, there is a phenomenon that the implanted ions penetrate deep inside the crystal.

In order to prevent this phenomenon called channeling, the ion implantation direction and the direction normal to the substrate surface are 7
It is usual to be shifted only once.

Even in the case of amorphous silicon, the (111) plane grows at a growth temperature of 275 ° C. or higher (K. Morie).
t. al: Jpn. J. Appl. Phys. vol.
20 (1981), no. 12, p2431-243
2), and even in the case of polycrystalline silicon, the hydrogen concentration is 0.
0 to 1 atomic% (Japanese Patent Laid-Open No. 58-84464) or chlorine concentration of 0.01 to 5 atomic.
c% (JP-A-58-123771) or a fluorine concentration of 0.01-1 atomic% (JP-A-58-123771).
(-123772), from the (111) plane to (2
20) Since it is known that the surface develops, channeling should be noted, though not as much as single crystal silicon.

A liquid metal ion source of a type in which ions are taken out directly from the surface of the liquid metal by a strong electric field instead of the gas (Liquid Metal Ion Source)
Is also used.

When a liquid metal ion source is used, maskless microdoping which does not require a resist or the like can be performed, but there is a drawback that an injection layer having a stable composition cannot be obtained for a long time.

An ion doping method is one of the impurity doping methods which can be injected into a large area substrate without using a mass spectrometer.

Even within the ion doping apparatus, the H ⁺ contained in the ion beam is utilized by utilizing the mass difference by magnetic scanning.
There has been a method for manufacturing a semiconductor that reduces the number of ions (Japanese Patent Publication No. 3-49176).

In this conventional magnetic scanning, the magnetic field lines are passed from the front to the back with respect to the positive ion flow flowing from the upper side to the lower side, and the positive ion flow is moved from the left side to the right side according to the equation F = I × B. In addition, a positive ion flow is deflected from right to left by passing magnetic field lines from the back to the front, and light hydrogen ions are flowed out of the substrate for ion doping by utilizing the mass difference of F = mα. .

The reduction of H ⁺ ions in the ion beam by magnetic scanning not only requires an electromagnet for magnetic scanning, but is not useful for separating unseparated hydrogen such as PH ions and PH ₂ ions. There was a club where it was concentrated.

On the other hand, the general ion doping method does not have a mass analyzer as in the ion implantation method, and PH ions and PH
_Since ions containing H such as ₂ ions and H ions are implanted, the temperature of the semiconductor substrate is greatly increased, and there is a problem that a resist that can be easily peeled off after ion doping is not usable as compared with an inorganic insulating film.

Further, ions other than impurities that control the conductivity of the semiconductor, such as H ions, are implanted in the film,
There is a problem that the film quality of the semiconductor is deteriorated.

This is SiH covalently bonded_Four, B
H₃, CH_Four, AlH₃, PH₃, Ga₂H ₆, GeH_Four, A
sH₃, SnH_Four, SbH₃, PbH_FourAre all volatile
Known as a compound, the reaction of desorbing from the substrate generates heat.
This is probably because it is a reaction.

[0021] Si (c) + 4H (g ) → SiH 4 (g) ΔH = 34- {0 + 4 (217)} = - 837.8kJ · mol This behavior of the silane compound represented by Si _m H _{2m + 2} It also appears in the boiling point.

That is, two H for one Si in the limit.
For ({2m + 2} / m≈2) silane compound, tetrasilane Si ₄ H ₁₀ (10/4 = 2.5) gives 1
53 ° C. at 93 ° C. with trisilane Si ₃ H ₈ (8/3 = 2.7)
C, disilane Si ₂ H ₆ (6/2 = 3) is -15 ° C., monosilane SiH ₄ (4/1 = 4) is -112 ° C., and the boiling point decreases as the number of H increases with respect to Si. Has become unstable.

FIG. 3 shows a cross-sectional view of a polycrystalline silicon thin film transistor using the conventional ion doping method.

In FIG. 3, polycrystalline silicon 13 having a (311) plane, which is crystal-grown at 675 ° C., and a thermal oxide film 14 obtained by thermally oxidizing polycrystalline silicon are formed on a quartz substrate 12.

A gate 15 made of polycrystalline silicon is applied to a part of the thermal oxide film 14, and a conductive resist 16 extending to the quartz substrate is applied to the other part of the thermal oxide film.

In this case, the resist may be burned by the ion beam 4 from above and may not be removed from the quartz substrate.

FIG. 4 is a plan view of the burn-in portion of the resist.

As shown by the hatched portion in FIG. 4, the resist 14 remains around the gate line 17, the gate 15, the source 18 and the drain 19 after the ion doping. Further, there is a phenomenon that the mobility of polycrystalline silicon is lowered.

The H thus injected into the substrate in vacuum.
Since (hydrogen) combines with Si (silicon) to generate an exothermic reaction, in ion doping suitable for a large-area substrate, the phenomenon of resist sticking to the substrate occurs and S
There is a drawback that the crystallinity of the semiconductor is lost due to the elimination of i.

[0030]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the problems that the temperature of the semiconductor substrate is so high that the resist cannot be used and that the film quality of the semiconductor is deteriorated.

[0031]

The present invention provides a semiconductor impurity doping method for doping a semiconductor substrate made of polycrystalline Si or the like with an impurity for controlling semiconductor conductivity such as P or B by using an ion doping method. , PH ₂ ions, H ions, etc., which are not mass-separated, are irradiated with laser light having a frequency higher than the H desorption energy of each ion to separate the H ions from the ion beam. A method of implanting impurities into a silicon thin film transistor, in which ions other than H are implanted into a semiconductor substrate.

[0032]

First, the moving distance in the laser light flux will be calculated when the reaction time for the PH ions containing hydrogen to be separated into P ⁺ and H by the laser light proceeds in 1 ns.

The speed of the ions than eV = mv ^2/2 v =
√ (2 eV / m), and the ion migration distance s is represented by s = vt, so the electron's electric quantity e = 1.6 × 10
^-19 [C], acceleration voltage V = 2 × 10 ⁵ V, mass of PH ion m = (31 + 1) / 6 × 10 ²³ = 5.31 × 10 ^-26
[Kg], using reaction time t = 1 × 10 ⁻⁹ [s], s
= 1 × 10 ^-9 × √ (2 × 1.6 × 10 ^-19 × 2 × 10 ⁵ /
5.31 × 10 ⁻²⁶ ) = 1.1 × 10 ⁻³ [m].

Since it is estimated that the lighter injected molecule has a larger migration distance, the migration distance for borane (BH ₃ ) is shown in Table 1.

Table 1 Travel distance of fragment of borane in the case of accelerating voltage of 200 kV / mm Ion species B BH BH ₂ BH ₃ Travel distance 1.889 1.807 1.734 1.670 Relative value 1 0.96 0. 92 0.88 From Table 1, it is presumed that the more hydrogen injected molecules, the slower it becomes, and the higher the probability of collision with photons.

Next, since it is considered that hydrogen is desorbed from hydrogen-containing ions in proportion to the product of the number of photons and the injected molecules, the number of injected molecules in a vacuum of 10 ⁻² Torr and a volume of 10 mm × 10 mm × 50 mm is set. Approximate.

As the number of injected molecules n, pressure P, volume V, gas constant R, temperature T and Avogadro's number Na, P = 10 ^-2 To
rr = 10 ⁻² × 1.013 × 10 ⁵ /760=1.33
[Pa], V = 10 mm × 10 mm × 50 mm = 5 × 1
0 ^-6 [m], R = 8.31 [Jmol ^-1 K ^-1 ], T = 2
73.15 + 25 = 298.15 [K], Na = 6 × 1
0 ²³ into n = PV / (RT / Na), n = 1.
It becomes 62 × 10 ¹⁵ .

It is estimated that the probability of collision with photons decreases as the pressure decreases, but the relationship between the output energy of the laser beam and the number of hydrogens injected into the substrate was not clear, but it became clear in the present invention. .

It is summarized as follows.

PH ions, P extracted from the ion source
When H ₂ ions or the like are irradiated with laser light, hydrogen bonded to P is separated.

By implanting P ions into which hydrogen has been separated into the semiconductor substrate, the rise in substrate temperature becomes smaller than in the prior art.

Further, the H ions separated by the laser beam are combined with other hydrogen ions to become H ₂ gas, and the ratio of being exhausted without being injected into the substrate increases, so that the amount of hydrogen injected into the semiconductor substrate decreases. .

Therefore, the deterioration of the semiconductor film quality due to hydrogen ions can be reduced.

[0044]

EXAMPLE FIG. 1 shows a schematic view of an ion doping apparatus used in the semiconductor impurity doping method of the present invention.

In this embodiment, PH ₃ gas (gas concentration: 0.
The figure shows a case where the present invention is applied to an ion doping apparatus in the case of using (01 to 5% H ₂ dilution).

As shown in FIG. 1, the pressure 10 in the center of the figure
^-2 wavelength 193 in the ion doping chamber of Torr
A laser light source 1 of 10 nm ArF excimer laser has a laser beam 2 of 10 mm × 10 mm vertically and horizontally reflected by a mirror 3 and passes through a quartz window and has an ion beam 4 and a length of 50 m.
The light enters so as to cross over m.

The laser light 2 is emitted from the upper part of the semiconductor substrate 5 by the ion beam.
PH ions accelerated by a hydrogen source, PH ₂Ions such as ions
To remove H ions by irradiating the ion beam 4 containing
Let

The ion beam 4 from which the H ions have separated collides with the semiconductor substrate 5 fixed on the substrate holder 6 and sunk into the semiconductor substrate according to the kinetic energy of the ions.

In this way, P ions from which H ions have been released are implanted into the semiconductor substrate 5.

Further, the H ions released by the laser light irradiation combine with other hydrogen ions to become H ₂ gas, and the ratio of being exhausted without being injected into the semiconductor substrate increases.

As a peripheral device, a doping gas 7 is introduced into the device from above the ion doping processing chamber, and R
It is ionized by the F power source 8 to generate various ion species called a fragment in the device.

In the ion doping method of this embodiment, positively charged ionic species are extracted by the extraction power source 9 as the ionic species.

Ions having a quantity of electricity of ne are obtained by adding the voltage Vo of the extraction power supply 9 and the voltage Va of the acceleration power supply 10 (V
o + Va) and kinetic energy proportional to the number of electric charges of the ions are received and implanted into the semiconductor substrate.

The amount of H ions implanted into the semiconductor substrate by laser light irradiation is shown in semi-logarithmic display in FIG.

FIG. 2 shows an acceleration voltage of 30 kV and a P dose of 1 × 1 using a doping gas diluted with PH _{3 at a} concentration of 5% H _2.
It shows the laser energy density dependence of the H concentration in the Si substrate when the N-type <111> direction Si wafer is doped under the condition of 0 ¹⁶ dose / cm ² .

As the laser, an ArF (193 nm) excimer laser is used.

From FIG. 2, it can be seen that the amount of H ions implanted into the semiconductor substrate can be reduced by increasing the laser energy density applied to the ion beam.

It is considered that the collision probability between the ion species and the laser light in the low pressure gas increases as the laser energy density increases.

Laser energy density is 150 mJ / c
In the case of m ² or more, the PMMA-based resist and the novolac-based resist were not burnt on the substrate.

It was also found that the decrease in the intensity of the crystal plane near the surface observed by electron diffraction after ion doping was suppressed by about 50% as compared with the condition without laser light, and the damage to the crystal was small.

Similar results were obtained with a polycrystalline silicon substrate in which the (111) plane was mainly grown at a substrate temperature in the range of 350 ° C to 400 ° C.

The excimer laser light source used in the present invention is NeF (108 nm)> ArCl (175 nm).
> ArF (193 nm)> KrCl (222 nm)> K
rF (249 nm)> XeBr (282 nm)> XeC
In the order of 1 (308 nm)> XeF (351 nm), the desorption effect of H ions is large.

[0063] In the case of PH _3, of 0 ℃, which is in a stable state PH ₃
Has a hydrogen binding energy of 316 kJ / mol (Chemical Handbook Basic Edition revised third edition, II-322, 1991), and when converted to a wavelength, λ = Na × h × c / E = 6.0 ×.
^{10 23 × 6.6 × 10 -34 ×} 3 × 10 8/316 × 10 3
= 376 × 10 ⁻⁹ m = 376 nm.

[0064] Therefore, for simplicity, flag placement in the higher energy _{^{(PH 3 +, PH 2 +}} , PH + , etc.) if Shimese with PH _3, it is irradiated with laser light of a wavelength 376nm to PH ₃ For example, it is presumed that hydrogen is released from PH ₃ and a part of it becomes kinetic energy that intersects the ion beam of hydrogen molecules.

As described above, according to the present invention, the hydrogen concentration in the substrate changes depending on the collision characteristics of hydrogen-containing implanted molecules and photons in a vacuum, which makes it possible to use a resist in the ion doping method and to improve the crystal structure of the substrate. The disturbance is small.

The injection molecule used in the present invention is a hydrogen compound, and Si that forms a volatile compound by covalently bonding with hydrogen.
_{H 4, BH 3, CH 4} , AlH 3, PH 3, Ga 2 H 6, Ge
H _4, is _{AsH 3, SnH 4, SbH 3} , PbH 4, BiH 3 like.

[0067]

In the ion doping apparatus, since the ions generated by the ion source are doped into the semiconductor substrate without mass separation, the problem that the substrate is heated by H ions is large and a large amount of H ions are injected into the film. Therefore, there is a problem that the film quality of the semiconductor is deteriorated, but in the present invention, H ions bonded to P ions and B ions can be released by irradiating the ion beam with laser light.

Therefore, the amount of H ions implanted into the semiconductor substrate can be greatly reduced as compared with the conventional case, so that the substrate heating and the deterioration of the semiconductor film quality due to the above H ions can be made much smaller than in the conventional case.

Further, since the resist mask which cannot be used in the conventional ion doping can be used, there is an advantage that the conventional semiconductor ion implantation process can be applied as it is.

[Brief description of drawings]

FIG. 1 is a diagram of a doping apparatus for irradiating an ion beam with laser light according to the present invention.

FIG. 2 is a laser energy density characteristic diagram of H concentration in a Si substrate using the present invention.

FIG. 3 is a cross-sectional view of a thin film transistor using a conventional ion doping method.

FIG. 4 is a plan view of a thin film transistor using a conventional ion doping method.

[Explanation of symbols]

 1 Laser Light Source 2 Laser Light 3 Mirror 4 Ion Beam 5 Semiconductor Substrate 6 Substrate Holder 7 Doping Gas 8 RF Power Supply 9 Extraction Power Supply 10 Acceleration Power Supply 11 Deceleration Power Supply 12 Quartz Substrate 13 Polycrystalline Silicon 14 Thermal Oxide Film 15 Gate 16 Resist 17 Gate Line 18 source 19 drain

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H01L 21/265 21/268 B

Claims (5)

[Claims] 1. An ion beam of an impurity formed by discharge of a hydride of an impurity is irradiated with laser light having a wavelength of 351 nm or less and an energy density of 150 mJ · cm ⁻² or more, and then the silicon thin film transistor is ionized by the ion beam. A method for implanting impurities into a silicon thin film transistor, which comprises implanting. 2. The method of implanting impurities into a silicon thin film transistor according to claim 1, wherein the discharging is performed in a mixed gas of an inert gas, hydrogen and a hydride of impurities at a pressure of 10 ⁻² Torr or less. 3. An ion beam without mass separation,
The method of implanting impurities into a silicon thin film transistor according to claim 1, wherein laser light irradiation is performed. 4. The ion beam, which is not mass-separated, contains hydrogen-bonded ions.
Method for implanting impurities into silicon thin film transistor. 5. The method of implanting impurities into a silicon thin film transistor according to claim 1, wherein the laser light has an energy higher than the desorption energy of hydrogen in the ion beam.