JP2001177108A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an insulated gate FET of microcrystal semiconductor structure with lattice distortion. SOLUTION: A silicon oxide film 12 is formed on a glass substrate 11, and an a-Si film 13 is formed thereon through an RF sputtering method and turned to microcrystal in a hydrogen atmosphere. The microcrystal semiconductor film 13 is of crystal structure and 5 to 400 Å in average grain diameter based on the half band width of a Raman spectrum, 5 cm2 to 300 cm2/Vsec in electron mobility, and 7×1019 cm-3 or below in oxygen concentration. A gate oxide film 15 and an aluminum electrode 16 are formed for formation of an FET. The Raman spectrum of the channel forming region 17 of the FET resides on a wave number side lower than the peak value 520 cm-1 of a single crystal silicon, and the crystal of the semiconductor film 13 is possessed of a lattice distortion and kept free from barriers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor having a microcrystal structure having lattice distortion.

[0002] SUMMARY OF THE INVENTION The present invention is mainly composed gaseous hydrogen or hydrogen (remainder inert gas such as argon) impurity concentration in the atmosphere than 5 × 10 ¹⁸ cm ^-3 in the semiconductor data - sputter the target Thus, by thermally crystallizing an amorphous semiconductor having an oxygen concentration of 7 × 10 ¹⁹ cm ⁻³ or less, preferably 1 × 10 ¹⁹ cm ⁻³ or less, lattice strain of an oxygen concentration of 7 × 10 ¹⁹ cm ⁻³ or less can be obtained. The present invention relates to a method for forming a semiconductor having a microcrystal structure.

[0003]

2. Description of the Related Art Conventionally, a polycrystalline semiconductor device has a semiconductor film formed by a low pressure
A polycrystalline semiconductor film is obtained by heat-treating at a temperature of up to 650 ° C. for several hours to several tens of hours to thermally crystallize, and has been manufactured using this polycrystalline semiconductor film.

[0004]

When a non-single-crystal semiconductor film is obtained by a low-pressure CVD method, there is a problem that it is difficult to form a film uniformly on a large-area substrate.

Further, when a non-single-crystal semiconductor film is obtained by the plasma CVD method, there is a problem that the film formation process takes a long time.

Conventionally, there has been known an example in which a thin film transistor is manufactured using an a-Si (amorphous silicon) film obtained by a sputtering method to which hydrogen is added, but its electric characteristics are low (electron mobility is 0.1%). cm ² / Vsec or less).

Therefore, an a-Si film is generally obtained by a sputtering method using an argon gas to which no hydrogen is added.

[0008] Further, it has been considered that film formation by sputtering using only hydrogen or a gas containing hydrogen as a main component is impossible.

[0009]

As means for solving such a problem, there is a method using a sputtering method. In particular, in the magnetron type sputtering method, a) electrons are confined near the target by a magnetic field, and damage to the substrate surface by high energy electrons is suppressed. B) High-speed film formation over a large area at low temperatures. C) Since no dangerous gas is used, safety and industrial efficiency are high. There are advantages such as. However, the non-single-crystal semiconductor film obtained by the sputtering method has a bias in the presence of silicon atoms, and heat at a temperature of 700 ° C. or lower due to the mixture of argon atoms and oxygen impurities or the absence of hydrogen at the same time. It is known that crystallization is not possible.

[Object of the Invention] It is an object of the present invention to obtain a microcrystalline semiconductor having lattice distortion by thermally crystallizing a non-single-crystal semiconductor obtained by an industrially mass-produced sputtering method. And

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [Constitution of the Invention] The present invention relates to a method for forming an amorphous layer by sputtering on a substrate in an atmosphere containing hydrogen or hydrogen and an inert gas containing hydrogen as a main component.
Forming a semiconductor film (hereinafter referred to as a-Si) with an amorphous semiconductor film obtained by the sputtering method at 450 to 700 ° C.
A method for producing a semiconductor, comprising a step of crystallizing at a temperature of 0 ° C.

The present inventor adds 20% or more of hydrogen as an atmospheric gas in the sputtering method (oxygen concentration in the atmosphere is 0.01% or less, and high-purity hydrogen of 5N (99.999% or more) is used for hydrogen). By this, hydrogen is uniformly dispersed and mixed in advance in the a-Si film to be formed, and this a-Si film is 450
It has been discovered that thermal crystallization can be achieved by annealing at temperatures up to 700 ° C, typically below 600 ° C. The present invention is based on the above experimental facts.

In this crystallization, the average crystal grain size is 5 to 5.
It is as small as 400% and has a hydrogen content of less than 5 atomic%. In particular, the feature is that oxygen as an impurity is set to 7 × 10 ¹⁹ cm ⁻³ or less, preferably 1 × 10 ¹⁹ cm ⁻³ or less. By giving each microcrystal a lattice strain, the crystal interfaces thereof are intensely close to each other microscopically, and the barrier for carriers at the crystal grain boundaries is eliminated. Therefore, at a polycrystalline grain boundary having no lattice distortion, oxygen and the like segregate there and form a barrier.
However, in the present invention, there is no barrier or negligible barrier due to such lattice distortion, and the electron mobility is also excellent at 5 to 300 cm ² / Vsec. I was sorry.

[0014]

(Embodiment 1) This embodiment is a magnetron type RF
(High frequency) The a-Si film produced by the sputtering device is thermally crystallized to have lattice distortion, the average crystal grain size is as small as 5 to 400 mm, and the content of hydrogen is 5 atomic% or less. And oxygen as impurities is 7 × 10 ¹⁹ cm
A polycrystalline silicon semiconductor layer of a quasi-crystal (also referred to as semi-amorphous Quasi-crystal or Semi-amrphas) of ^-3 or less, preferably 1 × 10 ¹⁹ cm ^-3 or less was formed. The electrical characteristics of carrier mobility, threshold voltage,
A thin film transistor was manufactured using this microcrystalline silicon semiconductor layer, which is the most effective means for knowing the electrical characteristics such as the interface state density.

FIG. 1 shows a manufacturing process of the thin film transistor manufactured in this embodiment. First, a silicon oxide film (12) was formed on a glass substrate (11) under the following conditions by magnetron type RF.
It was formed to a thickness of 200 nm by a sputtering method. O ₂ 100% atmosphere Deposition temperature 150 ° C RF (13.56 MHz) output 400W Pressure 0.5 Pa Single crystal silicon is used as a target. On top of that, a-Si film which becomes a channel formation region by high-purity magnetron type RF sputtering equipment ( 13) is deposited to a thickness of 100 nm.

In this sputtering method, the back pressure was set to 1 × 10 ⁻⁷ Pa or less, and exhaust was performed using a turbo molecular pump and a cryopump. The amount of the supplied gas had a purity of 5N (99.999%) or more, and the additional gas used was 4N or more of argon used as needed. Data - single crystal silicon be 5 × 10 ¹⁸ cm ^-3 or less in the oxygen concentration target, for example an oxygen concentration of 1 × 10 ¹⁸ cm ^-3, the oxygen as an impurity in the film formed was very small.

The film formation conditions were a hydrogen content ratio of 20 to 100% and an argon content ratio of 80 to 0%, for example, a hydrogen content of 100%. Under such an atmosphere, H ₂ / (H ₂ + Ar) = 100% (partial pressure ratio), deposition temperature 150 ° C. RF (13.56 MHz) output 400 W, total pressure 0.5 Pa, and a high-purity Si target as a target. Thereafter, a time of 10 hours is applied at a temperature of 450 to 700 ° C., for example, 600 ° C., and thermal crystallization of the a-Si film (13) is performed in hydrogen or an inert gas, in this embodiment, 100% hydrogen. Was done. It was so-called microcrystal (or semi-amorphous).

The impurity purity in the amorphous silicon film formed by the above method and the film crystallized by the heat treatment was examined by SIMS (secondary ion mass spectrometry). Then, among the impurity concentrations during the film formation, oxygen was 8 × 10 ¹⁸ cm ⁻³ and carbon was 3 × 10 ¹⁶ cm ⁻³ . Hydrogen had a concentration of 4 × 10 ²⁰ cm ⁻³ , which was equivalent to 1 atomic% when the density of silicon was 4 × 10 ²² cm ⁻³ . These were examined on the basis of the oxygen concentration of the target single crystal silicon of 1 × 10 ¹⁸ cm ⁻³ . In this SIMS analysis, the distribution in the depth direction (depth profile) of the film after film formation was examined, and the minimum value was used as a reference. This is because the surface has silicon oxide naturally oxidized with the atmosphere.
These values did not change significantly even after the crystallization treatment, and the oxygen impurity concentration was 8 × 10 ¹⁸ cm ⁻³ . In this embodiment, the oxygen is increased just in case, for example N ₂ O
Was added at 0.1 cc / sec and 10 cc / sec. Then, the oxygen concentration after crystallization increased to 1 × 10 ²⁰ cm ⁻³ and 4 × 10 ²⁰ cm ⁻³ . However, when such a coating was used, at the same time, crystallization could be achieved only by increasing the temperature required for crystallization to 700 ° C. or more, or increasing the crystallization time by at least five times. That is, considering industrially the softening temperature of the glass of the substrate, the treatment at 700 ° C. or lower, preferably 600 ° C. or lower is important, and it is also important to reduce the time required for crystallization. However, no matter how much impurities such as oxygen concentration are reduced, it is experimentally impossible to crystallize an a-Si semiconductor by thermal annealing at 450 ° C. or lower.

In the present invention, as a result of using such a high-quality sputtering apparatus, the oxygen concentration during film formation was 1 × 10 ²⁰ cm ⁻³ or more due to leakage from the apparatus. In such a case, such characteristics of the present invention cannot be expected.

[0020] It is the oxygen concentration of 7 × 10 ¹⁹ cm ^-3 or less in the as of nuclear, and the heat treatment temperature was determined to be 450 to 700 ° C..

Of course, in the case of germanium, or in the case of a compound semiconductor of silicon and germanium, the annealing temperature could be lowered by about 100 ° C.

This microcrystalline semiconductor has lattice distortion, and as shown in the laser Raman analysis data shown in FIG. 4, it has shifted to the lower wave number side as compared with single crystal silicon. A method for manufacturing an insulated gate field effect transistor will be described below in order to examine electric characteristics. That is, device isolation patterning was performed on the thermally crystallized microcrystalline silicon semiconductor obtained by the method of the present invention to obtain the shape shown in FIG. 1 (a).

Next, an n ⁺ a-Si film (14) was formed to a thickness of 50 nm by a magnetron type RF sputtering method under the following conditions.

The film formation conditions, the hydrogen partial pressure ratio from 20 to 99% or more (80% in this embodiment), argon partial pressure ratio from 80 to 0% (19% in this embodiment), PH ₃ min ratio of 0.1% to 10% In an atmosphere of 1% in this example, the film formation temperature was 150 ° C, RF (13.56 MHz) output was 400 W, total pressure was 0.5 Pa, and a single crystal (oxygen concentration 1 × 10 ¹⁸ cm
^-3 ) Si was used as a target.

In order to manufacture a semiconductor layer having one conductivity type, a PCVD method may be used. Further, after forming the active layer, impurities (for example, B (boron), P (phosphorus), As (arsenic)) may be added by ion implantation to form a source and a drain.

Thereafter, gate region patterning is performed to
The shape of (b) was obtained.

Next, a gate silicon oxide film (15) was formed to a thickness of 100 nm by magnetron RF sputtering under the following conditions to obtain the shape shown in FIG. 1 (c). Oxygen atmosphere 100% pressure 0.5pa, film formation temperature 100 ° C RF (13.56MHz) output 400W Single crystal silicon target or synthetic quartz target was used.

Next, contact hole opening and patterning were performed to obtain the shape shown in FIG.

Finally, aluminum electrode (1
6) is formed to a thickness of 300 nm and patterned to obtain the shape shown in FIG. 1 (e).
In a 0% atmosphere at 375 ° C. for 30 minutes, a thin film transistor was completed. This hydrogen thermal annealing reduces the interface level between the polycrystalline silicon semiconductor and the silicon oxide insulating film,
This is for improving device characteristics.

In the thin film transistor shown in FIG. 1 (e), S is a source electrode, G is a gate electrode, and D is a drain electrode.

The size of the channel portion (17) in the thin film transistor shown in FIG. 1 (e) manufactured in this embodiment is 100 × 100.
It has a size of μm.

The above is the method for manufacturing a thin film transistor using the polycrystalline silicon semiconductor layer manufactured in this embodiment. In order to show the effect of the present invention, the a-Si layer shown in FIG. Five examples were prepared in which the concentration of hydrogen and the concentration of oxygen mixed involuntarily were changed as conditions for forming (13) by a magnetron type RF sputtering method. Five examples of the method are described below.

[0033] (Example 2) This example of a channel forming region in the production process FIGS. 1 (a) the partial pressure ratio of the atmosphere during sputtering of making the (13) H ₂ / Example 1 ( (H ₂ + Ar) = 0% (partial pressure ratio), and the others were produced in the same manner as in Example 1. The oxygen concentration had 2 × 10 ²⁰ cm ⁻³ .

[0034] (Example 3) the partial pressure ratio of the atmosphere during sputtering of making the (13) of this embodiment serves as a channel formation region in the fabrication method in the Embodiment 1 FIG. 1 (a) H ₂ / ( (H ₂ + Ar) = 20% (partial pressure ratio), and the others were produced in the same manner as in Example 1. The oxygen concentration during the film formation was 7 × 10 ¹⁹ cm ⁻³ .

[0035] (Example 4) The partial pressure ratio of the atmosphere during sputtering of making the (13) of this embodiment serves as a channel formation region in the fabrication method in the Embodiment 1 FIG. 1 (a) H ₂ / ( (H ₂ + Ar) = 50% (partial pressure ratio), and the others were produced in the same manner as in Example 1. The oxygen concentration during the film formation was 3 × 10 ¹⁹ cm ⁻³ .

[0036] (Example 5) the partial pressure ratio of the atmosphere during sputtering of making the (13) of this embodiment serves as a channel formation region in the fabrication method in the Embodiment 1 FIG. 1 (a) H ₂ / ( (H ₂ + Ar) = 80% (partial pressure ratio), and the others were produced in the same manner as in Example 1. The oxygen concentration during the film formation was 1 × 10 ¹⁹ cm ⁻³ .

Hereinafter, the results of comparison of the electrical characteristics of the above embodiments are shown.

FIG. 2 shows the carrier mobility μ (FIELD) in the channel portion ((17) in FIG. 1E) of the completed Examples 1 to 5.
MOBILITY) and the hydrogen partial pressure ratio during sputtering (P _H / P
_{TOTA L = H 2 / (H} 2 + Ar)) is a graph of the relationship _{2 / (H 2 + Ar)} ). Table 1 below shows the correspondence between the plot points in FIG. 2 and the examples.

[0039]

[Table 1]

According to FIG. 2, when the hydrogen partial pressure is 0%, the oxygen concentration
Is 2 × 10²⁰cm^-33 × 10 ^-1cm^TwoV / sec
And, on the other hand, more than 20% and oxygen concentration as in the present invention.
Degree 7 × 10¹⁹cm^-3Significantly higher mobility 2 cm below^Two/ Vs
It can be seen that μ (FIELD MOBILITY) is obtained more than ec
You.

This is presumably because, when hydrogen was added, oxygen in the chamber in the sputter was converted to water, which could be positively removed by a cryopump.

FIG. 3 shows the threshold voltage and the hydrogen partial pressure ratio during sputtering (P _H / P _TOTAL = H ₂ / (H ₂ + Ar)).
Is a graph of the relationship.

The hydrogen partial pressure ratio (P _H / P _TOTAL = H ₂ / (H
₂ + Ar)) and the example numbers are the same as in Table 1.

Considering that the lower the threshold voltage, the lower the operating voltage for operating the thin film transistor, that is, the lower the gate voltage, the better the characteristics of the device can be obtained. High partial pressure ratio 20
%, A normally-off state with a threshold voltage of 8 V or less can be obtained. That is, a device using a microcrystalline silicon semiconductor layer obtained by obtaining an a-Si film shown in (13) of FIG. 1 (a) to be a channel formation region and recrystallizing the a-Si film. It can be seen that (the thin film transistor in this example) shows good electrical characteristics.

FIG. 4 shows a laser Raman spectrum of a polycrystalline silicon semiconductor layer obtained by thermally crystallizing an a-Si film. FIG.
Table 2 shows the relationship between the symbols shown in Table 1 and the example numbers and the hydrogen partial pressure ratio during sputtering.

[0046]

[Table 2]

Referring to FIG. 4, the curve (4) is compared with the curve (42).
3), that is, the channel formation region ((17) in Fig. 1 (e))
Comparing the case where the partial pressure ratio of hydrogen at the time of sputtering at the time of forming an a-Si semiconductor layer is 0% and the case of 100%, the partial pressure ratio of hydrogen at the time of sputtering when crystallized by thermal annealing. Is 100%, the Raman spectrum has remarkable crystallinity, and the average crystal grain size is 5 to 400 °, typically 100 to 200 °, from the half width. Then, it shifts to a lower wave number side than the peak value of 520 cm ^{-1 of} single crystal silicon, and clearly has lattice distortion. This clearly shows the features of the present invention. In other words, the effect of producing an a-Si film by a sputtering method to which hydrogen is added appears only when the a-Si film is thermally crystallized.

With such lattice strain, the fine crystal grains are forcibly shrunk to each other, so that the close contact at the crystal grain boundaries becomes stronger, and the energy barrier for carriers at the crystal grain boundaries also increases. Segregation of impurities such as oxygen hardly occurs. As a result, high carrier mobility can be expected.

In general, when the drain voltage VD is low in a thin film transistor which is a field effect transistor, the relationship between the drain current ID and the drain voltage VD is expressed by the following equation. ID = (W / L) μC (VG-VT) VD (Solid.State electronics.Vol.24.No.11.pp.1059.198
1.Printed in Britain)

In the above equation, W is the channel width, L is the channel length, μ is the carrier mobility, C is the capacitance of the gate oxide film, VG is the gate voltage, and VT is the threshold voltage. .

Although Ar was used as the inert gas at the time of the above sputtering, other inert gas such as He, or a reactive gas such as SiH ₄ or Si ₂ H ₆ which was turned into plasma was used as an atmosphere gas. May be used by adding to some of them. In forming the a-Si film by the magnetron type RF sputtering method of this embodiment, the hydrogen concentration is 5 to 100%, and the film formation temperature is room temperature to 500 ° C.
RF output in the range of 500 Hz to 100 GHz
It can be arbitrarily selected within a range of 100 W to 10 MW, and may be combined with a pulse energy source. Further, light sputtering (wavelength: 100 to 500 nm or less) may be performed by applying more powerful light irradiation energy.

This is because the light atoms of hydrogen are turned into plasma, the positive ions required for sputtering are efficiently generated, and hydrogen or hydrogen atoms are uniformly added to the film formed by sputtering. As a result, This is for the purpose of forming a semiconductor film in which oxygen is mixed at a concentration of 7 × 10 ¹⁹ cm ⁻³ or less, preferably 1 × 10 ¹⁹ cm ⁻³ or less. In the present specification, the amorphous semiconductor film is simply abbreviated as an a-Si film in the specification. However, this is mainly made of a silicon semiconductor, but may be germanium or SixGe _1-x (0 <x <1).

This may be not only an intrinsic semiconductor but also a P or N type semiconductor. Further, the other reactive gas may be applied to the above means.

[0054]

According to the constitution of the present invention, in the step of thermally crystallizing a non-single-crystal semiconductor obtained by an industrially useful sputtering method to obtain a polycrystalline semiconductor, it becomes difficult to perform thermal crystallization which is a problem. The problem could be solved, and a high-performance thin film transistor could be manufactured using this polycrystalline semiconductor layer.

[Brief description of the drawings]

FIG. 1 shows manufacturing steps of Examples 1 to 6.

FIG. 2 shows the relationship between the partial pressure ratio of hydrogen added when an a-Si film serving as a channel formation region is formed and the mobility of carriers in the thin film transistor manufactured in this example in the manufacturing process of the thin film transistor manufactured in this example. It is shown.

FIG. 3 shows a relationship between a partial pressure ratio of hydrogen added when an a-Si film serving as a channel formation region is manufactured and a threshold value of a thin film transistor manufactured in the present embodiment in a manufacturing process of the thin film transistor manufactured in this embodiment. It shows the relationship.

FIG. 4 shows a Raman spectrum of a polycrystalline silicon semiconductor manufactured in this example. (11) ・ ・ ・ Glass substrate (12) ・ ・ ・ Silicon oxide film (13) ・ ・ ・ Active layer of microcrystalline semiconductor (14) ・ ・ ・ n ⁺ a-Si film (15) ・ ・
・ Gate oxide film (16) ・ ・ ・ Aluminum electrode (17) ・ ・ ・ Channel formation region (S) ・ ・ ・ Source electrode (G) ・ ・ ・ Gate electrode (D) ・ ・ ・ Drain electrode

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[Procedure amendment]

[Submission date] November 14, 2000 (200.11.
14)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

Claims (10)

[Claims] 1. An insulated gate field effect semiconductor device comprising: a semiconductor layer containing silicon formed on a substrate; and a gate electrode provided above the semiconductor layer with an insulating film interposed therebetween. A semiconductor layer having a source, a drain, and a channel formation region, wherein the semiconductor layer has a crystal structure in which an average grain size of crystal grains is calculated to be 5 to 400 degrees from a half-value width of a Raman spectrum, and the electron mobility of the semiconductor layer is 5 cm
² / Vsec to 300 cm ² / Vsec, the oxygen concentration of the semiconductor layer is 7 × 10 ¹⁹ cm ⁻³ or less, and the peak of the Raman spectrum of the channel formation region is 520
An insulating gate type field effect semiconductor device, which is on the lower wave number side than cm ^-1 , wherein the insulating film extends beyond an end of the semiconductor layer. 2. The insulated gate field effect semiconductor device according to claim 1, wherein said semiconductor layer is made of silicon. 3. The method of claim 1, wherein the semiconductor layer is Si _x
An insulated gate field effect semiconductor device comprising Ge _1-x (0 <x <1). 4. The insulated gate field effect semiconductor device according to claim 1, wherein said semiconductor layer contains 5 atom% or less of hydrogen. 5. The insulated gate field effect semiconductor device according to claim 1, wherein said semiconductor layer comprises a semiconductor selected from an n-type semiconductor, a p-type semiconductor and an intrinsic semiconductor. . 6. The insulated gate field effect semiconductor device according to claim 1, wherein the semiconductor layer has no barrier because the crystal has lattice distortion. 7. The insulated gate field effect semiconductor device according to claim 1, wherein said insulating film is a gate insulating film of said semiconductor device. 8. The insulated gate field effect semiconductor device according to claim 1, wherein said insulating film extends to a position where said semiconductor layer does not exist. 9. The insulated gate field effect semiconductor device according to claim 1, wherein said gate electrode contains aluminum. 10. The method according to claim 1, wherein
The source electrode and the drain electrode are connected to the semiconductor layer via an opening formed in the insulating film, and the insulating film is in contact with the entire surface of the semiconductor layer except for the opening. An insulated gate field effect semiconductor device.