JPH02181974A - Semiconductor device and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve characteristics of a semiconductor device such as response speed, optical sensitivity or current value by adapting the semiconductor device such that electric charges migrate within a specific a-Si1-xCx:H thin film. CONSTITUTION:A semiconductor device includes, as one of its components, an amorphous thin film 304 containing at least hydrogen atoms and principally composed of silicon and carbon atoms (abbreviated as a-Si1-xCx:H thin film wherein 0<x<=0.4). The a-Si1-xCx:H thin film has, in infrared absorption spectrum, an absorption coefficient at 2090cm<-1> corresponding to three times or less of the absorption coefficient at 2000cm<-1>. ln a plasma CVD process using gaseous mixture consisting of a molecular gas containing Si and H atoms and a molecular gas containing carbon atoms, a luminous intensity SiH of plasma emission spectrum Halpha can be controlled in order to control the state of hydrogen bond alpha(2090)/alpha(2000) in the a-Si1-xCx:H film and thus the photoconductivity can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a semiconductor device that operates by moving charges in an aSi+-8Cx:H thin film.
Examples include a thin film transistor, a solar cell, an electrophotographic photoreceptor, and a light emitting diode of the image sensor 9.

BACKGROUND ART A-S L I-XCX: Because H thin films have excellent surface hardness and hydrophobicity, they are generally used as protective layers or surface layers of devices used in humid environments or environments where surfaces are abraded. Furthermore a-8tr-xCx:
Since H thin films also have excellent heat resistance, attempts are being made to apply them to functional devices that operate stably even at high temperatures. Also, a
Since the -Si1-xCx:H thin film has a larger forbidden band width than the a-8i:H thin film, attempts have been made to apply it to large-area visible light emitting diodes.

The above effect can be further improved by increasing the amount of carbon in the film, that is, X, but as X increases, the photoconductivity of the a-Si1-3C,:H thin film decreases significantly. has been reported. . For this reason, a
-8i, the photoconductivity of the C,:H thin film is
．． Even if it is smaller than 4, it is smaller than a-8i:H and deteriorates the electrical characteristics of a semiconductor device using a-S i+-xCx:H thin film, and a-S 11-XC
Applications of X:H thin films have been limited to thin films that do not significantly affect electrical characteristics, such as surface protective layers and carrier injection blocking layers of electrophotographic photoreceptors.

Recently, plasma CV in which a mixed gas of monosilane gas (hereinafter referred to as S r Ha) and CH4 is diluted with a large amount of hydrogen has been developed.
By method D, a S 1I-x Cx : H(x-
It has been reported that when a 0,1 [i) thin film is produced, the absorption coefficient near 2900 cm-' in the infrared absorption spectrum is small, that is, the number of CHe and CH3 bonds can be reduced, and the photoconductivity is improved. (Matsu 1) Akihisa et al.
Journal of Applied Physics, 198
13, Vol. 60, pp. 4025-4027 RoJ, App
I, Phys, GO (198B) pli 4025-4
027. Ko ).

Problems to be Solved by the Invention When we evaluated the a S s I-XCX:H film that we had produced, it was found that the infrared absorption spectrum was 2900c.
It has become clear that even if the absorption in the vicinity of m-' is reduced to suppress the generation of CH2 and CH3 bonds, a film with excellent photoconductivity cannot necessarily be obtained. Therefore, not only CH2 bonds and CHa bonds, which are higher-order hydrogen bonds, but also a-S
It is believed that there are parameters that enhance the photoconductivity of the i + -xCx:H thin film and further improve carrier mobility and carrier lifetime.

The present invention finds the above parameters and a-81+-x
Cx: Improves characteristics such as response speed, photosensitivity, or current value of a semiconductor device using an H film.

Means for Solving the Problems In order to achieve the above objects, the semiconductor device of the present invention comprises an amorphous thin film (a-S t + -x
Cx: Abbreviated as H thin film. However, 0<X≦0.
4) as a component, a S i +−xCx'
In the infrared absorption spectrum of H thin film, 2090 cm-
It is characterized by having an absorption coefficient of 2000cr' or less than 3 times that of 2000cr', and having a function of moving charges through the a-81+-xCx:H thin film.

A-8i two, C of this semiconductor device manufacturing method
,: In the process of forming an H thin film, a gas containing silicon atoms and hydrogen atoms in its molecules and a gas containing carbon atoms in its molecules are introduced into a vacuum container as source gases, and an electric field is applied to the source gases under reduced pressure. The a-Si1--Cx:H thin film was produced under conditions such that the emission intensity at wavelength Ei5G, 3 nm from the plasma was 0.8 times or more compared to the emission intensity at wavelength 414.2 nm. It is characterized by forming.

Effect a -S 1 + -xCx: In the infrared absorption spectrum of the H thin film, the absorption peak at 2000 cm-' is Si
The absorption peak of 2090c+r' is due to H bonding, and the absorption peak of 2090c+r' is S
It is known that this is due to iH2 binding. Below, the absorption coefficient of 2000cr' is expressed as (X (2000
), the absorption coefficient at 2090cm-1 is written as α(2090), and α(2090)/α is used as a parameter representing whether there are more hydrogen bonds, SiH bonds or SiH bonds, that is, the hydrogen bonding state of the film. (2000) is used.

a −S t +−xCx: Conventionally, the atomic bonds that reduce the density of the H thin film and deteriorate the photoconductivity are higher-order bonds such as CH2 bonds and CH3 bonds that do not form the skeleton of the atomic bond network. It was reported in the example. However, the present inventor found that in a state in which the generation of the above CH2 bonds and CH3 bonds was suppressed, a-3! +-xC: It has been found that the factor that reduces the photoconductivity of H thin films is SiH2 bonds. It was also found that this tendency is more pronounced when the carbon content X is 0.4 or less. Furthermore, S
iH2 bond is a Si+-,C,:H film is prepared by
-8i: Very easy to generate compared to H film <Na-8t:
Even under production conditions in which SiH2 bonding is difficult to occur in the H film, α(2090)/α(2000) is a-8t.
: It was confirmed that the amount was more than three times that of the case of the H film. Therefore, it is very important to clarify the manufacturing conditions that reduce α(2090)/α(2000).

Plasma C commonly used to create amorphous thin films
In the VD method, plasma emission spectroscopy has the disadvantage that only luminescent radicals can be observed, but it has the advantage that it is the simplest plasma diagnostic method and can be performed without affecting the plasma. The inventor has discovered that plasma C
In the VD method, an a S 11-X Cx : H film was prepared using a mixed gas of a gas containing Si atoms and hydrogen atoms in the molecule and a gas containing carbon atoms in the molecule, and the plasma emission spectrum and hydrogen The bonding state and photoconductivity were investigated in detail. As a result, the wavelength B5G, 3
The intensity ratio between the Balmer series emission intensity (abbreviated as Hα) of hydrogen at im and the emission intensity of active species SiH at wavelength 414.2 im and the hydrogen bond state of the film α(2090)/α(200
0), there is a strong correlation between Hα emission intensity and S
It has been found that if the discharge conditions are set so that the intensity is greater than the iH emission intensity, α(2090)/α(2000) becomes smaller and the photoconductivity improves.

Although the exact cause of the above results is not known, the emission intensity of the active species SiH is due to the Sin Hm radical (
However, since it is thought that ml n is an integer and the density of O≦m≦2n+2) and the emission intensity of Hα reflects the density of H radicals, the following is currently considered. A state in which the emission intensity of Hα is higher than that of SiH is a state in which the density of H radicals is high, and Si
The dissociation of atoms and molecules containing H atoms progresses, resulting in film formation using 5inH* radicals with fewer H atoms, or the H radicals promote the withdrawal reaction of H atoms bonded to the film growth surface. Due to phenomena such as
It seems that α(2090)/α(2000) is decreasing.

Therefore, using a mixed gas of a molecular gas containing Si atoms and H atoms and a molecular gas containing carbon atoms, Taplasma CV
In method D, by controlling the emission intensity of Hα in the plasma emission spectrum and the emission intensity of SiH, a-Si1
-xCx: Hydrogen bond state α(2090)/α of H film
(2000) can be controlled, and photoconductivity can be improved. Therefore, even in semiconductor devices where a-Si1-xCx:H film could not be used conventionally due to its low photoconductivity and carrier mobility, aS1
I-XCX: Enables use of H membrane.

EXAMPLE FIG. 1 shows an example of a typical infrared absorption spectrum of an a-S i+-wcx:H thin film. This sample is 2
Almost no absorption due to CH2 and CHa bonds at 900 cm-1 is observed. SiH2 bond at 2090cm-1, 2000c 'SiH bond Q at 1 and Iooocm-'
CH bond of , SiC bond of 7GOcm-1, G40
The absorption peak due to the SfH, SiH2°5iHa bond at cm-1 is clearly seen.

Such an infrared absorption spectrum and a-S L I-X
The relationship between CX:H film and photoconductivity was investigated. As a result, a
-S 1I-XCX: A semiconductor device, such as a solar cell, that functions by moving charges through an H film.

The condition that must be met for the hydrogen bonding state of a-Si1□C,:H thin film to be used in electrophotographic photoreceptors, image sensors, optical sensors, light emitting diodes, thin film transistors, thin film diodes, etc. is α(2090)/α( 2000)≦
3, the product of carrier mobility (μ) and carrier lifetime (τ) (hereinafter referred to as μτ product) is 10-"
(cm2/V) or more. Also, preferably α(2090)/α(200
0)≦2 and μτ≧10−” (c m2/V ), optimally α(209G)/α(2000)≦1.5 and μτ
≧10-7 (Cm'/V). However, a in Figure 1
(2090)/(x (2θ00) is 1.2.

a-Si1-xCx: The X value of the H thin film is 0.
If it exceeds 4, 2900cr' of CH2, CHa is present in the film.
Since the absorption coefficient due to bond increases rapidly and the carrier mobility and carrier lifetime decrease significantly, 0<X≦0.4 is desirable, preferably 0.01≦X≦0.35, and optimally 0°Ol: a×≦0.3.

FIG. 2 shows an example of plasma emission spectra of S i H4 diluted with H2 and C2H'2 in a parallel plate capacitively coupled plasma CVD apparatus. 288.2 nm active species Si, 414.2 nm active species S i H, 43
The emission intensity of active species CH of 1 and 2 nm and HJ of 658 and 3 nm is clearly observed.

a -S 11-XCX: S I Hat S 12H61S I as a source gas providing Si atoms of the H film
HaF+ S tH2F21 5iHFs+ 5
iHsC1+ 5iH2C12+5iHC1mu S
CHJ, C2H6, CIHI as a raw material gas that provides C atoms using i (CHa) a, etc.

C4H111+ C2H4, Ca Ha, Ct
Using Ha, C*Ha, etc., using various plasma CVD equipment, and under various discharge conditions,
a −S i+ −x Cx: Hydrogen bond state α of H film
The relationship between (2090)/α(2000) and the plasma emission spectrum was investigated. As a result, the emission intensity of HJ and Si
Ratio of luminescence intensity of H (this is ■.

α/Isl, expressed as l) is 0.8 or more and α (2090)
It was found that /α(2000)≦3. Preferably 1. α/Is+H≧1 and α(2090)/α(20
00)≦2, optimally, INα/111)1≧1.5 and α(2090)/α(2000)≦1.5. Furthermore, while satisfying the above condition of I++α/Isn+, the ratio of the Si emission intensity at 288.2 nm to the SiH emission intensity at 414.2 nm (hereinafter abbreviated as Is+/l51s) is set to 0.8 or more. By doing so, α(2
It was also confirmed that 090)/α(2000) can be made small.

Furthermore, when the above raw material gas was used, it was also confirmed that the above state of INα/Is+H could be easily obtained by diluting it with hydrogen or helium.

a S 11-XCX: The amount of hydrogen for the H thin film was 5.
In order to suppress the increase in the number of higher-order bonds such as iHa, CH2, CH3 bonds, etc., the content is preferably 1 atomic % or more and 50 atomic % or less, and in order to prevent hydrogen from leaving the film at the product temperature and improve heat resistance. Preferably, the content is preferably 1 atomic % or more and 40 atomic % or less, and most preferably 1 atomic % or more and 35 atomic % or less.

Further, impurities may be added to control the carrier conductivity of the a-8iC:H thin film. B+ A L, which belongs to Group 3 of the periodic table, is a p-type impurity that provides p-type conductivity.
G a, I n, etc., preferably B, A1.
Ga is used, and as an n-type impurity that provides n-type conductivity, there are P+As+sb, which belongs to Group 3 of the periodic table, and P*As is preferably used.

Specific examples will be described below.

Example 1 A gate electrode 301 made of Cr having a thickness of 0.1 μm was formed on a transparent insulating substrate by direct current sputtering, and the transparent insulating substrate 302 was placed on a ground electrode in a reaction vessel of a high-frequency plasma CVD apparatus. 5X IP'T inside the reaction vessel
After exhausting to below o r r, N2:IO~! 00SC
el+ S i H4: 10 to 50 sccm was introduced. Next, the pressure inside the reaction vessel was increased to 0.2 to 1. OT Or
After adjusting to r,! O ~ [00W, 13.56M
A high-frequency power of HZ is applied to start the discharge, and a 0.4 μm Si+-UN8 film 303 for the gate insulating film is deposited on the substrate.
After forming, the discharge was stopped. Next, the inside of the reaction vessel was
-” After exhausting to below T o r r, C2H2: 0
．． 5~5sec, S i Hi: 5~lO10
5c, H2: Introduce 50-200sccm, pressure crab 0.1-1.0T Or rl high frequency electric crab lO
0.08μm a-SI I-*CX at ~50W
:H film 304 was formed. At this time, I+4α/l5I
H was 0.8-3. Subsequently, PHa was added and n
Type a -81+-xCx: H film 305 is 0.02μ
m was formed and patterned. Next, the source electrode 30
6. A thin film transistor (A) as shown in the structural cross-sectional view of FIG. 3 was fabricated by depositing 27 μm of AIIO as a drain electrode 307 by electron beam evaporation.

In addition, apart from this, the above a S I I-XCX: H
The formation conditions during film formation were C2H2: 0.5 to 5 s.
ecm, S i HJ: 5~lO105c,
Pressure crab o, ai, o'r Or rt A thin film transistor CB) with a high frequency electric crab of 5 to 30 W was also manufactured. However, a-81I-XCX: IH during H film formation
a/Is++ was 0°6-0.8.

Also, under the same conditions as above, a −S i + −* CX
: When the H film was deposited on a single crystal Si wafer and the infrared absorption spectrum was measured, in the case of (A), α(
2090)/α(2000) is 1.0 to 2.8, whereas in the case of (B), α(2090)/α(200
0) was 3.0 to 4.0.

The drain current-gate voltage characteristics of thin film transistors (A) and (B) are that (B) is ON compared to (A).
The I current rise characteristics were poor, and the maximum ON current was also smaller by more than two orders of magnitude. This is (B) a-311-XC*:
Because there are many SiH2 bonds in the H film, the density of the film is low;
This is because, compared to the a-811-X Cx:H film in (A), the localized levels within the forbidden band that act as carrier traps increased, resulting in a decrease in carrier mobility and carrier lifetime.

Example 2 A transparent insulating substrate on which an ITO film was deposited was exposed to high-frequency plasma C.
Place in the VD device and add 50 ppml of 1 degree B diluted with H.
2He: 50-200sccmt CHa:
2~lO105c, SiH4:2~1Oscci
Introduced pressure crab 0.2~1. OT.

r rX High frequency crab 20~50W, p type a-S
11-XCx:H film is formed with a thickness of 0.05 to 0.3 μm,
Next, the above B2H6 was diluted with H2 and the B2H6 was diluted with H2.
e He: substituted with 2 to IOsccm, and C
I-type a-si by blocking Ha:) (0.3-0.7
μm was formed. Furthermore, the above B 2 Hs was replaced with 1 Oppm concentration of PHs: 2 to 10105c diluted with H2 to form an n-type a-8i:H film with a thickness of 0.07 to 0.3 μm.
A solar cell (A) was manufactured by laminating the layers and then forming an A1 electrode by direct current sputtering.

The above p-type a-S I I-x CX:H film was prepared using the same method as in Example 1 to prepare I, lα/Is++
: 1-3.2, α(2090)/α(2000):
It was confirmed that the value was 0.8 to 2.

In addition to (A), as a solar cell (B), Inα/
l5IH: 0. [i~0.8, α(2090)/α
(2000): p-type a S I+ which is 3-3.3
-xCx: A device using an H film was also manufactured.

When AM-1, 100 mW/cm2 light was irradiated from the ITO electrode side, the short circuit current and conversion efficiency of the solar cell of (A) were better than that of (B).

This is a p-type a-S i I-X used as a window layer.
This is because the cX:H film in (A) is denser than in (B) and the μτ product of carriers is larger.

Example 3 S i H41C2H21 on a mirror-polished AI drum
IHα/I sls: 1-2, Is+/I
s+H: 0.9-1.4, α(2090)/α(20
00): p-type a for charge transport layer which is 1.0-1.8
-S s + -xCx: H film of 15μIn is formed,
Further, a p-type a-3t:H film for a charge generation layer was laminated to a thickness of 1 to 3 μm to prepare an electrophotographic photoreceptor (A). In addition, the p-type a-S s I-X Cx:H film for the charge transport layer is Inα/I SIH: 0.4 to 0.8, Inα/l5
IH,l: 0. G=0.8, α(2090)/α(2
000): Electrophotographic photoreceptor (B
) were also prepared, and when these photoreceptors were corona charged at +6.3 kV, (A) obtained a surface potential of +600 to 900 V, and the residual potential was +50 V when exposed to 31x white light.
(B) has a surface potential of +700 to 1050
Although V was obtained, the residual potential was as large as +100 to 300V. The cause of the large residual potential in (B) is the carrier μ of the p-type a S 1 +-XCX:H film for the charge transport layer.
This is because the τ product is small.

Example 4 On a mirror-polished A1 drum, by plasma CVD method,
A p-type a-8i:H film was used as a charge injection blocking layer at 0.1-1
．． 0μs, i type a-si:H film 15-20μm1
As a surface protective layer, an a-SL-X Cx:H film having an infrared absorption spectrum shown in FIG. 1 was used at a concentration of 0.05
An electrophotographic photoreceptor (A) was manufactured by sequentially laminating layers for ~0.2 μs. Also, similar to (A), a (2090)/(! (
2000): aS 11--CX which is 3.15:
An electrophotographic photoreceptor (B) using H film as a surface protective layer was also produced.

When these photoreceptors were installed in a commercially available copying machine and repeatedly charged and exposed to light, an increase in residual potential was observed in (B) with repeated charging and exposure, but no change was observed in (A). . This is a − of the surface protective layer in (B).
This is because the μτ product of carriers in the S r +−x Cx :H film is small.

Effects of the Invention According to the present invention, operating characteristics such as response speed, photosensitivity, and operating current of a semiconductor device are improved.

[Brief explanation of the drawing]

FIG. 1 shows a-Si prepared in one embodiment of the present invention.
1 to C,: A diagram showing an infrared absorption spectrum of a H thin film, FIG. 2 is a diagram showing an example of a plasma emission spectrum obtained in an example of the present invention, and FIG. 3 is a diagram showing an example of a plasma emission spectrum obtained in an example of the present invention. 1 is a cross-sectional view showing the structure of a thin film transistor. 304”・a −S 1 +−x Cx: H film,
305・n-type a-3i+-xCx: H film. Agent's name: Patent attorney Shigetaka Awano Haka 18, Mitsutsuki Yukuni 3rd figure 0 and q sentence section defeated prisoner X1l-・? 04! o5 I heat the stone i @ TdA Ito board 511-χNχ order Q-51r-x Cz: HH n% Q-5N-xCx: Hm source to extreme Int No.

Claims (5)

[Claims] (1) An amorphous thin film containing at least hydrogen atoms and mainly composed of silicon atoms and carbon atoms (hereinafter referred to as a-
Si_1_-_xC_x: Abbreviated as H thin film. However, 0<X≦0.4), and the a-Si_1_-
_xC_x: 20 in the infrared absorption spectrum of the H thin film
The absorption coefficient at 90 cm^-^1 is 3 times or less than the absorption coefficient at 2000 cm^-^1, and the a-Si_1_-_x
C_x: A semiconductor device characterized in that it is configured to move charges in a H thin film. (2) The semiconductor device according to claim 1, wherein the a-Si_1_-_xC_x:H thin film has a hydrogen content of 1 atomic % or more and 50 atomic % or less. (3) The method for manufacturing a semiconductor device according to claim 1, wherein a gas containing silicon atoms and hydrogen atoms in its molecules and a gas containing carbon atoms in its molecules are introduced into a vacuum container as source gases, and the Conditions in which an electric field is applied to the raw material gas under reduced pressure to generate plasma by discharge, and the emission intensity at a wavelength of 656.3 nm from the emission of the plasma is 0.8 times or more compared to the emission intensity at a wavelength of 414.2 nm. a-Si below
_1_-_xC_x: A method for manufacturing a semiconductor device, characterized by forming an H thin film. (4) The emission intensity at a wavelength of 288.2 nm from plasma emission is 0.8 compared to the emission intensity at a wavelength of 414.2 nm.
4. The method of manufacturing a semiconductor device according to claim 3, wherein the manufacturing method is twice as large. (5) The method for manufacturing a semiconductor device according to claim 3, wherein at least hydrogen gas or helium gas is mixed with the raw material gas.