JPH04151819A - Manufacture of semiconductor - Google Patents

Abstract

PURPOSE:To make it possible to crystallize thermally a non-single crystal semiconductor obtained by a sputtering method by a method wherein an amorphous semiconductor film is formed on a substrate in an atmosphere containing hydrogen alone or hydrogen and inert gas as its main component by the sputtering method and this semiconductor film is crystallized at a specified temperature. CONSTITUTION:A semiconductor target of an oxygen concentration of 5X10<18>cm<-3> or lower is made of sputter using an atmosphere containing hydrogen alone or hydrogen of an amount of 20% or higher and inert gas of an amount of 80% or lower as its main component, whereby an amorphous semiconductor film (an a-Si film) of an oxygen concentration of 7X10<19>cm<-3> or lower is formed and hydrogen is previously made to disperse uniformly and is made to mix in this a-Si film. Moreover, this a-Si film is thermally crystallized by an annealing at a temperature of 450 to 700 deg.C or lower. Thereby, a non-single crystal semiconductor obtained by an industrially useful sputtering method is thermally crystallized and a polycrystalline semiconductor can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for manufacturing a semiconductor having a microcrystal structure having lattice distortion.

[Summary of the invention]

The present invention uses hydrogen or hydrogen as a main component gas (the rest is an inert gas such as argon) at an impurity concentration of 5
By sputtering a semiconductor target of 10'8 cm-" or less, an amorphous semiconductor with an oxygen concentration of 7 X 10" cm-3 or less, preferably IXl019 cm-3 or less, is thermally crystallized.
The present invention relates to a method for forming a semiconductor having a microcrystal structure having a lattice strain with an oxygen concentration of 110l9' or less.

[Conventional technology]

Conventionally, polycrystalline semiconductor devices have a semiconductor film formed by low pressure CVD or plasma CVD with a thickness of 550 to 650 mm.
A polycrystalline semiconductor film has been obtained by thermally crystallizing it by heat treatment at a temperature of .degree.

[Problems with conventional technology]

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

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

Conventionally, a-
It is known that a thin film transistor is manufactured using a 3i (amorphous silicon) film, or that its electrical characteristics are low (electron mobility is 0.1 cm 2 /Vsec or less).

Therefore, an a-3i film is obtained by a sputtering method using Alcon gas to which hydrogen is not added.

Furthermore, it was considered impossible to form a film by sputtering using only hydrogen or a gas containing hydrogen as a main component.

One way to solve this problem is to use sputtering.

In particular, the magnetron sputtering method (a) confines electrons near the target using a magnetic field, which suppresses damage to the substrate surface caused by high-energy electrons.

Mouth) Capable of high-speed film formation over large areas at low temperatures.

c) High safety and industrial efficiency as no dangerous gas is used.

There are advantages such as. However, in the non-single crystal semiconductor film obtained by sputtering, the presence of silicon atoms is biased, and due to the presence of impurities such as argon atoms and oxygen, or because hydrogen is not mixed at the same time, it is difficult to heat at temperatures below 700°C. It is known that crystallization is impossible.

[Purpose of the invention]

An object of the present invention is to obtain a microcrystalline semiconductor having lattice strain by thermally crystallizing a non-single-crystalline semiconductor obtained by a sputtering method that is industrially suitable for mass production.

[Structure of the invention]

The present invention is directed to forming an amorphous (or very close to amorphous) semiconductor film (hereinafter referred to as a-3i) by sputtering hydrogen or hydrogen and an inert gas onto a substrate in an atmosphere containing hydrogen as a main component. A film forming process;
The amorphous semiconductor film obtained by the sputtering method was
This is a semiconductor manufacturing method characterized by having a step of crystallizing at a temperature of 0 to 700°C, typically 600°C.

The present inventor added 20% or more hydrogen as an atmospheric gas in the sputtering method (the oxygen concentration in the atmosphere was 0.01%).
% or less, and high purity hydrogen of 5N (99,999% or more) is used), hydrogen is uniformly dispersed and mixed into the aSi film to be formed in advance, and this a-3
It has been discovered that the i-film can be thermally crystallized by annealing at a temperature of 450-700°C, typically below 600°C. The present invention is based on this experimental fact.

In this crystallization, the average crystal grain size is as small as 5 to 400, and the hydrogen content therein is 5 at % or less. In particular, it is advantageous that oxygen as an impurity is 7 x 10190 m-3 or less, preferably I x 10"cm-" or less. By imparting lattice strain to each microcrystal, the crystal interfaces of the microcrystals are brought into close contact with each other, thereby eliminating the barrier for carriers at the grain boundaries.

Therefore, in the grain boundaries of polycrystals that simply have no lattice strain, oxygen etc. segregate there and act as a barrier or inhibit the movement of carriers, but in the present invention, due to such lattice strain,
Since there is no barrier or a negligible barrier, the electron mobility is 5 to 300 cm2/Vsec, which is an order of magnitude better.

〔Example〕

(Example 1) In this example, an a-3i film produced using a magnetron-type RF (radio frequency) sputtering device was thermally crystallized to have lattice strain, and the average crystal grain size was adjusted to 5 to 40 mm.
It is small with 0 people, and the amount of hydrogen contained is less than 5 at%, and the amount of oxygen as an impurity is less than 7X1019cF3.
Preferably a semi-amorphous quasi-crystal or S
A polycrystalline silicon semiconductor layer (also referred to as emi-amrphas) was formed. A thin film transistor was fabricated using this microcrystalline silicon semiconductor layer, which is the most effective means for determining its electrical properties such as carrier mobility, threshold voltage, and interface state density.

FIG. 1 shows the manufacturing process of the thin film transistor manufactured in this example.

First, a silicon oxide film (12) was formed to a thickness of 200 nm on a glass substrate (11) by magnetron RF sputtering under the following conditions.

02100% atmosphere Film forming temperature 150℃ RF (13,56MHz) output 400W Pressure 0.5
Pa single crystal silicon is used as a target.Secondly, a high-purity magnetron type RF sputtering device is used to sputter an a-3i film (13
) is formed to a thickness of 1100 nm.

In this sputtering method, the back pressure was set to I x 10-7 Pa or less, and a turbo molecular pump and a cryopump were used for exhaust. The amount of gas supplied is 5 N (99,999%)
It had a purity of 4N or more, and 4N or more of argon was used as the additive gas, if necessary. The single crystal silicon of Targera 1~ also had an oxygen concentration of 5.times.10.sup.18 cm.sup.-3 or less, for example, I.times.10.sup.18 cm.sup.-" to extremely reduce the amount of oxygen as an impurity in the formed film.

The film forming 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%. In such an atmosphere, H2/(H2+Ar) = 100% (partial pressure ratio) Film forming temperature 150°C RF (13,56MHz) output 400W Total pressure 0.
The pressure was 5 Pa, and a high purity Si target was used.

After this, 1 at a temperature of 450 to 700°C, for example 600°C.
The a-3i film (13) was thermally crystallized for 0 hours in a hydrogen or inert gas atmosphere, in this example a 100% hydrogen atmosphere. It was so-called microcrystalline (or semi-amorphous).

The impurity purity in the amorphous silicon film formed by this method and the film after crystallization by heat treatment is reduced to S[M
It was investigated by the S (secondary ion equivalent analysis) method. Then, among the impurity concentrations during film formation, oxygen was 8XIO18cF3 and carbon was 3XIO"cm-3. Hydrogen was 4XIO"cm-3.
020 cF3, and the density of silicon is 4 x 1022 cm-
3, the amount corresponds to 1 atom, 96.

Oxygen concentration IX of target single crystal silicon
The investigation was conducted using 10'8cF3 as a reference. Also this SI
In the MS analysis, the distribution in the depth direction (depth profile) of the film after film formation was investigated, and its minimum value was used as a reference. This is because the surface contains silicon oxide that has naturally oxidized with the atmosphere. These values did not change significantly even after the crystallization treatment, and the oxygen impurity concentration was 8×IO18 cm −3 . In this example, the amount of oxygen was increased just in case, for example, N20 was added at 0.1 cc/sec and 10 cc/sec. Then, the oxygen concentration after crystallization is I x 10
The amount increased to 20cm-3,4X 1020cm-3.

However, when such a film was used, crystallization could only be achieved by raising the temperature required for crystallization to 700° C. or higher, or increasing the crystallization time by at least 5 times. That is, considering the softening temperature of the glass of the substrate from an industrial perspective, it is important to process at a temperature of 700° C. or lower, preferably 600° C. or lower, and it is also important to further reduce the time required for crystallization.

However, no matter how you reduce impurities such as oxygen concentration,
It has been experimentally impossible to crystallize the a-3i semiconductor by thermal annealing at temperatures below 450°C.

In addition, in the present invention, if as a result of using such a high quality sputtering apparatus, the oxygen concentration during film formation becomes I x 102102 O" or more due to leakage from the apparatus, the characteristics of the present invention I can't really hope for that.

As such, the oxygen concentration is 7 x 1019 cm-3 or less, and the heat treatment temperature is 450 to 700°C.
It was decided that.

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

This microcrystalline semiconductor has lattice strain, and as is clear from the laser Raman analysis data shown in FIG. 4 below, it was shifted to the lower wave number side compared to single crystal silicon.

In order to investigate the electrical characteristics, the insulated gate type electrolytic effect l
・Describe the method for manufacturing transistors. That is, the thermally crystallized microcrystalline silicon semiconductor obtained by the method of the present invention was subjected to device separation patterning to obtain the shape shown in FIG. 1(a).

Next, an n+a-8i film (14) was formed to a thickness of 50 nm by magnetron RF sputtering under the conditions shown below.

The film forming conditions were a hydrogen partial pressure ratio of 20 to 99% or more (80% in this example), an argon partial pressure ratio of 80 to 0% (19% in this example), and a PH3 partial pressure ratio of 0.1% to 10% (in this example, 19%). In the example, 1%), film formation temperature: 150°C, RF (13,56MHz) output: 400W, total pressure: 0.
5 Pa, and the target was a single crystal (oxygen concentration 1 x 10"
cm-')Si was used as a target.

Furthermore, a PCVD method may be used to fabricate the semiconductor layer having the negative conductivity type. Furthermore, after forming the active layer, impurities (e.g. B (boron), P (phosphorus), As (arsenic)) are added to form the source and drain.
may be added by ion implantation.

Thereafter, gate region patterning was performed to obtain the shape shown in FIG. 1(b).

Next, a gate silicon oxide film (15) was formed to a thickness of 1100 nm by magnetron RF sputtering under the following conditions to obtain the shape shown in FIG. 1(C).

100% oxygen atmosphere Pressure 0.5pa.

Film formation temperature: 100° C. RF (13.56 MHz) output: 400 W Single crystal silicon target or synthetic quartz target was used.

Next, patterning is performed to open the contact hole, and the first
The shape shown in figure (d) was obtained.

Finally, 30% aluminum electrode (16) was applied by vacuum evaporation.
The shape as shown in FIG.
A thin film transistor was completed by performing 30 m1n at a temperature of 375° C. in a 0.00% atmosphere.

The purpose of this hydrogen thermal annealing is to reduce the interface state between the polycrystalline silicon semiconductor and the silicon oxide insulating film and improve device characteristics.

Note that 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.

Furthermore, the size of the channel portion (17) in FIG. 1(e) of the thin film transistor manufactured in this example is 100×10
The size is 0 μm.

The above is the method for manufacturing a thin film transistor using the polycrystalline silicon semiconductor layer manufactured in this example. In order to demonstrate the effects of the present invention, the channel forming region is shown in FIG.
We prepared five examples in which the hydrogen concentration and the unintentionally mixed oxygen concentration, which are the conditions when forming the a-3i layer (13), by magnetron-type RF sputtering were changed. The manufacturing method is shown.

(Example 2) In this example, in the manufacturing method of Example 1, the partial pressure ratio of the atmosphere during sputtering when manufacturing the channel forming region (13) in FIG. 0% (partial pressure ratio), and was produced in the same manner as in Example 1 except for the following.

The oxygen concentration had 2×1020 cm−3.

(Example 3) In this example, in the manufacturing method of Example 1, the partial pressure ratio of the atmosphere during sputtering when manufacturing (13) in FIG. 20% (partial pressure ratio), and was otherwise produced in the same manner as in Example 1. The oxygen concentration during film formation was 7×10 19 cm −3 .

(Example 4) In this example, in the manufacturing method of Example 1, the partial pressure ratio of the atmosphere during sputtering when manufacturing the channel forming region (13) in FIG. 50% (partial pressure ratio), and was otherwise produced in the same manner as in Example 1.

The oxygen concentration during film formation was 3 x 10'' cm-3.

(Example 5) In this example, in the manufacturing method of Example 1, the partial pressure ratio of the atmosphere during sputtering when manufacturing the channel forming region (13) in FIG. 80% (partial pressure ratio),
The other parts were manufactured by the same method as in Example 1. The oxygen concentration during film formation was IXl019cm-3.

The results of comparing the electrical characteristics of the above examples will be shown below.

FIG. 2 shows the carrier mobility μ (FIEL
This is a graph showing the relationship between D MOBILITY) and hydrogen partial pressure ratio (PH/Ptot*=H2/(H2+Ar)) during sputtering.

The correspondence between the plot points in FIG. 2 and the examples is shown in Table 1 below.

Table 1 PH/PTOTAL% Example number According to Figure 2, when hydrogen partial pressure is 0%, oxygen concentration is 2X1
Since there is also 0"cF3, 3 xlO-'cm2V/se
On the other hand, as in the present invention, the mobility is extremely high at 2 cm2/Vsec or more at <20% or more and at an oxygen concentration of 7 Xl01 gcm-3 or less (FIE
LD MOBILITY) is obtained.

This is presumed to be because when hydrogen was added, oxygen in the chamber within the sputtering was converted to water, which could be actively removed by the cryopump.

FIG. 3 is a graph showing the relationship between threshold voltage and hydrogen partial pressure ratio (PH/PtoTAL=H2/(H2+Ar)) during sputtering.

Hydrogen partial pressure ratio (P++/ProtAL-H2/(H2+A
The correspondence between r)) and the example numbers is the same as in Table 1.

Considering that the lower the threshold voltage is, the lower the operating voltage for operating the thin film transistor, that is, the lower the gate voltage, and the better the characteristics of the device, the results shown in Figure 3 indicate that the partial pressure ratio of hydrogen is A threshold voltage of 8V is achieved by sputtering with a high 20% or higher condition.
The following normally off states can be obtained. That is,
A device using a microcrystalline silicon semiconductor layer ( It can be seen that the thin film transistor (in this example) exhibits good electrical characteristics.

This figure shows a laser Raman spectrum of a polycrystalline silicon semiconductor layer obtained by thermally crystallizing an a-3i film. Table 2 shows the relationship between the display symbols shown in FIG. 4, the example numbers, and the hydrogen partial pressure ratio during sputtering.

Table 2 Indication symbol Example number Hydrogen partial pressure (41) 2 0% (42) 3 20% (43) 4 50% (44) 1 100% Looking at Figure 4, the curve compared to curve (42) (43), that is, a-3i which becomes the channel forming region ((17) in FIG. 1(e))
Comparing cases where the partial pressure ratio of hydrogen during sputtering when producing a semiconductor layer is 0% and 100%, when crystallization is performed by thermal annealing, when the partial pressure ratio of hydrogen during sputtering is 100%. The Raman spectrum of has remarkable crystallinity, and its average crystal grain size is 5 to 400, typically 100 to 200, larger than the half width.

The wave number is shifted to a lower wave number than the peak value of 520 cm −' of single crystal silicon, and there is clearly lattice distortion. This clearly shows the feature of the present invention. In other words, the effect of producing the a-3i film by sputtering with hydrogen added is as follows:
This phenomenon appears only after the a-3i film is thermally crystallized.

When there is lattice strain in this way, the microcrystalline grains are forcibly shrunk together, so the close contact between each other at the grain boundaries becomes strong,
Energy barriers for carriers at grain boundaries and segregation of impurities such as oxygen are less likely to occur there. As a result, high carrier mobility can be expected.

In general, in a thin film transistor which is a field effect transistor, when the drain voltage VD is low, the drain current ID
The relationship between VD and drain voltage VD is expressed by the following equation.

ID-(W/L) μC(VG-VT)VD(Soli
d, 5tate electronics, Vol.
, 24. No, 11. pp, 1059.19
81. 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, VC is the gate voltage, and VT is the threshold voltage. There is.

Ar is used as the inert gas during the above sputtering, or other inert gas such as He, or reactive gas such as SjH, 512Hs, etc., which is made into plasma, is used as part of the atmospheric gas. It may be added and used. In the formation of the a-3i film by the Magnetoron type RF sputtering method in this example, the hydrogen concentration was 5 to 100%,
The film forming temperature ranges from room temperature to 500'C, and the RF output is 500°C.
1] In the range of z~100GH7, output 100W~
It can be arbitrarily selected within the range of 10 MW, and may be combined with a pulse energy source. Optical sputtering may be performed by applying more powerful light irradiation (wavelength: 100 to 500 nm or less) energy.

This turns light atoms called hydrogen into plasma and efficiently generates the positive ions needed for sputtering.
Hydrogen or hydrogen atoms are uniformly added to the film formed by sputtering, and as a result, oxygen contamination is reduced to 7X10I9.
This is for forming a semiconductor film with a concentration of cF3 or less, preferably lXl019cm-3 or less.

In the specification of the present invention, an amorphous semiconductor film is simply referred to as a-
It is abbreviated as 3i film. However, this mainly uses silicon semiconductors, but germanium, 5ixGe+-,
(Q<x<1).

This may be not only an intrinsic semiconductor but also a P or N type semiconductor.

Further, the other reactive gases described above may be applied to the above means.

〔Effect of the invention〕

By adopting the structure of the present invention, it is possible to solve the problem of difficulty in thermal crystallization in the process of thermally crystallizing a non-single crystal semiconductor obtained by an industrially useful sputtering method to obtain a polycrystalline semiconductor. Furthermore, it was possible to fabricate a high-performance thin film transistor using this polycrystalline semiconductor layer.

[Brief explanation of the drawing]

FIG. 1 shows the manufacturing steps of Examples 1 to 6. Figure 2 shows the relationship between the partial pressure ratio of hydrogen added during the fabrication of the aSi film that will become the channel formation region and the carrier mobility in the thin film transistor fabricated in this example in the fabrication process of the thin film transistor fabricated in this example. It is something that Figure 3 shows the relationship between the partial pressure ratio of hydrogen added during the fabrication of the aSi film that will become the channel formation region and the threshold value in the thin film transistor fabricated in this example in the fabrication process of the thin film transistor fabricated in this example. This is what is shown. FIG. 4 shows the Raman spectrum of the polycrystalline silicon semiconductor produced in this example. (11), (12), (13), (14), (15), (16), (17), (S), (G), (D), activity of microcrystalline semiconductor with silicon oxide film on glass substrate Layer n''a-3i film Gate oxide film Aluminum electrode Channel formation region Source electrode Gate electrode Drain electrode

Claims (2)

[Claims] (1) Using an atmosphere of hydrogen or an inert gas containing hydrogen in an amount of 20% or more and 80% or less, and an oxygen concentration of 5 × 1
The oxygen concentration is 7x10 by sputtering onto the substrate using a semiconductor target with a concentration of 0^1^8cm^-^3 or less.
A step of forming an amorphous semiconductor film containing an amount of ^1^9cm^-^3 or less, and a step of recrystallizing the amorphous semiconductor film obtained by the sputtering method at a temperature of 450 to 700°C or less. A semiconductor manufacturing method characterized by: (2) In claim 1, the recrystallized semiconductor has lattice strain and has an average crystal grain size of 5 to 4.
A method for manufacturing a semiconductor characterized by having a thickness of 00 Å.