JP2003208998A - Sheath width detecting method between plasma and boundary - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sheath width detecting method between the plasma and a boundary which is produced when a substrate or the like is installed into the plasma by observations. <P>SOLUTION: To produce a disk type metal plate 10 of a flat plate probe, which is presented for measurement, a metal disk of such as gold, platinum, copper, stainless steel, aluminum, or the like, is installed into the plasma, and a conductive thin film, of which the material is different from the above disk material, is formed on the metal plate 10 of the flat plate probe. Next, creating A<SB>r</SB>plasma, which it is going to measure, installing the metal plate 10 in the inside of it, and impressing predetermined voltage to exposure it to the plasma during a predetermined time, corresponding to impressed voltage, as shown in Fig. 3, a bright ring can be observed inside the perimeter of the metal plate. The sheath width DCL is detected by measuring the distance (r<SB>p</SB>-r<SB>imp</SB>) from the perimeter of the metal plate to the bright ring, and inserting it in the formula (4). <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of detecting a sheath width generated at a boundary between a plasma and a substrate when the substrate or the like is placed in the plasma.

[0002]

2. Description of the Related Art Recently, low-voltage glow discharge (DC, AC, high frequency, microwave discharge) has been used for manufacturing electronic devices and thin films. Generally, these substrates are installed in plasma. To be done. At this time, plasma parameters (plasma voltage, plasma density, electron temperature, etc.) are measured by a Langmuir probe (probe).
Excited species, positive ions, negative ions, etc., which are important for the process on the substrate, are measured by a mass spectrometer, and the optimum values are obtained by controlling the plasma based on these measured values.

For an infinitely flat substrate or wall, FIG.
As shown in (A), since the electric charge is neutral in the plasma, the number of electrons and the number of positive ions are the same (when negative ions are included, electron density _ne + negative ion density = positive ion density _ni ).
become. However, since electrons are light near the substrate or the wall, the wall reaches the wall early and the wall becomes a negative potential. Further, the electrons reaching the wall early generate a region having very few electrons near the wall, and a sheath is formed between the plasma and the substrate (or the container wall). The shape of the sheath depends on the applied voltage, plasma parameters, and the shape of the substrate.

In the case of a finite flat disk-shaped substrate, as shown in FIG. 6B, when the substrate is placed in plasma and a negative potential is applied to the finite flat disk-shaped substrate. , A sheath having a size corresponding to the applied voltage and plasma parameters is formed as in the case of an infinitely flat substrate.

The presence of the sheath is important in the process because when the substrate is placed in a plasma to make an electron device, the ions have the most important motion in these processes and the sheath is the accelerating region for the positive ions. This is a problem, and accurate measurement of the sheath width has been required. Conventionally, many methods such as a method using electron beam reflection, a laser induction method, a probe method, an emissive probe method, and an ion acoustic wave time flight method are known for measuring the sheath width, but these are direct methods. It is also contact.

[0006]

However, in the conventional electron beam method and probe method, it is necessary to electrically insulate the probe from the substrate, and the presence of an insulator for that purpose causes the substrate or the like to be installed in the plasma. The potential distribution of the sheath generated at the boundary between the plasma and the substrate at that time is changed, which causes a change in the ion flux to the substrate. It also causes a large error in the detection of the sheath. As described above, since there is no suitable measuring method, a theoretical estimation has been made without actual measurement. Therefore, the spatial resolution of the above-mentioned conventional method is poor, and there are inconveniences such as inapplicability to a substrate having a small size (smaller than 2 to 30 mm). Therefore, an object of the present invention is to provide a highly accurate and simple detection method of the sheath width between the plasma and the boundary, which occurs when a substrate or the like is placed in the plasma by actual measurement.

[0007]

In order to solve the above-mentioned problems, the method of detecting the sheath width between the plasma and the boundary according to claim 1 of the present invention is such that a metal disk is installed in the plasma, and A conductive thin film different from the disk material in a gas is formed on a disk-shaped metal plate for a flat plate probe, and then the metal plate is placed in a plasma of a second gas to be measured, and a predetermined voltage is applied. By applying and exposing to plasma for a predetermined time, a bright ring is formed inside the outer periphery of the metal plate corresponding to the applied voltage, and the distance from the outer peripheral edge r _p of the metal plate to the outer edge r _{imp of the} bright ring. (R _p −r _imp ) is measured, and the sheath width D _LC is detected by an arithmetic expression.

A plasma and a boundary according to claim 2 of the present invention
A method of detecting the width of the sheath between plasma and metal disks.
Installed inside and different from the disk material in the first gas
A conductive thin film is formed on a disk-shaped metal plate for a flat plate probe.
Then, the gold plate is placed in the plasma of the second gas to be measured.
Installed, apply a predetermined voltage and expose it to plasma for a predetermined time.
The inner side of the outer periphery of the metal plate according to the applied voltage.
Forming a bright ring on the outer peripheral edge r of the metal plate_p From bright
Outer ring edge r_imp Distance to (r_p -R_{im p} ) Total
Measured, calculation formula D_CL≈ 10 (r_p -R_imp ) By sheath
Width D_CLIs configured to detect.

A plasma and a boundary according to claim 3 of the present invention
The method for detecting the sheath width between the two is gold, platinum, copper, stainless steel.
Plas a metal disc made of aluminum, aluminum, etc.
It is installed in the machine and is different from the disk material in the first gas.
A conductive thin film on a disc-shaped metal plate for a flat plate probe.
Create and then measure the gold in the plasma of the second gas to be measured
Place a plate, apply a predetermined voltage and plasma for a predetermined time.
By exposing it, the inside of the outer periphery of the metal plate can be changed according to the applied voltage.
Forming a bright ring on the side, and the outer peripheral edge r of the metal plate_pClear
Outer edge of rui ring r_imp Distance to (r_p -R_imp )
Measure and calculate formula D _CL≈ 10 (r_p -R_imp ) By sea
Width D_CLIs configured to detect.

As a result, gold, platinum,
By exposing a metal plate formed on a metal disk made of copper, stainless steel, aluminum, or the like, on which a conductive thin film having a different metal material is formed, to the applied voltage by exposing it to the plasma of the reaction gas to be measured. Correspondingly, by measuring the distance between the outer edge of the bright ring formed inside the outer periphery of the metal plate and the outer peripheral edge of the metal plate, the boundary with the plasma generated when the substrate or the like is installed in the plasma by actual measurement It is possible to obtain the sheath width between them by calculation, to improve the spatial resolution, and to adapt it to a substrate having a small size (less than 2 to 30 mm).

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention is shown in FIGS.
Will be described in detail below. First, the principle of the present invention will be described with reference to FIGS.

In FIG. 1A, a one-dimensional and infinite metal plate has an electron density n _e = positive ion density n _i and an electron temperature T _e.
Of the sheath width D _CL when a -V ₀ voltage is applied.

[Equation 1] Is given.

In the above equation, ε ₀ is the permittivity in vacuum, e is the charge, m _i is the mass of the ion, and k is the Boltzmann constant.
Therefore, if the positive ion density n _i and the electron temperature T _e are detected by a Langmuir probe or the like, the applied voltage V ₀ is known, so that the sheath width D _CL can be estimated (however, it cannot be measured).

If a finite disk metal plate having a radius r _p is placed in the plasma and only the surface is exposed to the plasma, as shown in FIG. 1 (B) depending on the applied voltage V ₀ . A sheath is formed.

At this time, in order to consider the incidence of ions on the metal plate of the disk, it is necessary to find the equipotential surface in the sheath and the lines of electric force. Now, assuming that the center of the disk is O, the distance in the radial direction is r, and the distance in the height direction from the disk plate is z, the voltages at points z and r are respectively given by the following equations.

[Equation 2]

As an example, the radius r _P = 5 mm, the electron temperature T _e = 1 eV, the positive ion density n _i = 5 × 10 ¹⁴ m ^-3 and the applied voltage V ₀ = -300 V, the equipotential surface and the electric force lines. An example of calculation of is shown in FIG. From the figure, the trajectory of the ions (initial velocity = 0) placed on the edge (1) of the disk plate can be calculated using the momentum conservation and energy conservation equations.

The result is the locus of the solid line (1) in the figure.
It The arrival point on the radius of the disk of the ion at this time is r
_imp And Ions between (1) and (2) are shown
As described above, a narrow range of the disc position in the r direction (r_imp When
r₂ During). On the other hand, r _p-R_imp Ion between
It is an area that does not reach. Also, r₂ > When r ≧ o, comparison
Ions reach the mean.

Therefore, a thin thin film is deposited in advance on the disk plate surface, and this is placed in the vicinity of the plasma on which a predetermined substrate or the like is installed. At this time, upon exposure to appropriate time (several minutes) predetermined plasma, between r _p -r _imp until intact, membrane between r _imp -r ₂ is etched by ion bombardment. At this time, although ion collision occurs during r ₂ >r> o, it becomes smaller than that between r _{imp and} r ₂ .

[0019] Consequently, as shown in FIG. 3, toward the center from the outer periphery of the disc plate surface, r _p -r original thin film region between the _imp, r _imp -r bright ring area between _2, r _2> r
Some etched areas between> o are formed.

Next, the distance r _p -r _imp from the outer circumference of the disk plate surface to the bright ring is measured, and the sheath width D _exp
A method for obtaining is described. The applied voltage V ₀ is a known value because it is set from the outside. On the other hand, the ion density n
_{Although i} and the electron temperature T _e can be measured by a Langmuir probe or the like, it is assumed that the Langmuir probe or the like is not installed here.

Therefore, the ion density n_i , Electron temperature T_e Is
Since it is unknown, by using equation (1),
Width D_CL(≒ D_exp ) Can not be asked. There
And n _i , T_e Calculation diagram as shown in Fig. 2
To get From the calculation diagram of FIG. 2, the outer peripheral edge r of the disc plate_p so
The ion trajectory of_imp Ask for. Repeat this process
Returned and measured r_imp Calculated as r_imp Match
Ion density n_i , Electron temperature T_e To decide.

As a result, the sheath width D _CL (≈D _exp ) is obtained. D _exp and r _p found in actual plasma
The relationship of −r _imp is shown in FIG. By referring to this figure, it can be understood that D _exp ≈10 (r _p −r _imp ). That is, the sheath width D _CL is

[Equation 3] Can be found at.

The embodiment using the principle of the present invention is achieved by using a commonly used plasma device as the main plasma device and adding some improvements thereto. An example thereof will be described with reference to the schematic view of the plasma device of the present invention in FIG. In the figure, 1 is a wall made of stainless steel which constitutes a container of a plasma device, 2 is a cathode made of a tungsten wire, 3 is a DC power supply (DC 100V, 10A), 4
Is a variable power source for discharge (DC 200 V, 200 mA), which constitutes the plasma generator 5 and is arranged on one side surface of the container.

6 is a Langmuir probe probe,
Reference numeral 7 is a variable power source for applying a probe voltage, and 8 is a resistance for current detection, which constitutes a Langmuir probe unit 9 and is arranged on the other side surface of the container. Reference numeral 10 is a disk plate made of metal for a flat plate probe, and 11 is a variable power source for applying a probe voltage (DC 400V, 50 mA), which constitutes a flat plate probe portion 12 for sheath width detection and is arranged on the bottom surface of the container. The applied voltage V is sent to a computing personal computer (not shown). Further, although not shown, a valve or other means for supplying / discharging the reaction gas is naturally provided.

[0025] In thus constructed plasma apparatus, under _{A r} gas pressure of about 1～10MT _orr,
A voltage is applied to the cathode 2 made of tungsten wire by using the stainless steel container 1 as an anode (voltage 150 V, current 100-).
About 200 mA) to heat and discharge.

Since rows of permanent magnets (not shown) are alternately installed on the outer wall of the stainless steel container 1 for each NS row, the closer the outer wall of the stainless steel container 1 is to the stronger magnetic field, the lower the plasma pressure. It is maintained even at (1 _{mT orr} or less). Further, the plasma is uniformly maintained in the stainless steel container. At this time, plasma parameters (potential,
(Density, electron temperature, etc.) is measured by the probe 6 of the Langmuir probe of the Langmuir probe unit 9, and the obtained voltage v and current I are sent to a computing personal computer (not shown).

In order to prepare the disk-shaped metal plate 10 of the flat plate probe for measurement, gold, platinum, copper, stainless steel,
A metal disk such as aluminum is installed in the plasma. At this time, in order to form a thin film on the surface of the disk in advance, O ₂
Plasma is generated using gas to form a conductive thin film such as tungsten on the disk-shaped metal plate 10 for the flat plate probe.

Next, an _Ar plasma to be measured is created, the gold plate 10 is placed in the plasma, and a predetermined voltage is applied and exposed to the plasma for a predetermined time. As shown in FIG. 3, a bright ring can be observed inside the outer periphery of the metal plate. By measuring the distance (r _p −r _imp ) from the outer peripheral edge of the gold plate to the outer edge of the bright ring and inserting it into the above equation (4), the sheath width D _CL
Can be measured.

[0029]

As described above, according to the method of detecting the sheath width between the plasma and the boundary of the present invention, the sheath width of the target surface, which is the most important parameter in the plasma surface treatment technology by the impact of positive ions, is set to the passive surface. Detecting from a model that is simpler than the dimension of allows for easy optimization of plasma parameters and target bias to improve target surface uniformity. Further, the present invention is a method for directly controlling the interaction between the plasma and the target, and is effective in many plasma surface treatment fields.

[Brief description of drawings]

FIG. 1 is a diagram showing a state where a sheath is formed by a plasma device of the present invention.

FIG. 2 is a calculation diagram of equipotential surfaces and lines of electric force.

FIG. 3 is a thin film area diagram of a disk plate surface.

FIG. 4 is a correlation diagram of the sheath width and the distance on the disk plate surface.

FIG. 5 is a schematic view of a plasma device of the present invention.

FIG. 6 is a diagram showing a state in which a sheath is formed by a normal plasma device.

[Explanation of symbols]

1 stainless steel wall 2 cathode 3 DC power supply 4 Variable power supply for discharge 5 Plasma generator 6 Langmuir probe tips 7 Variable power supply for probe voltage application 8 Current detection resistor 9 Langmuir probe part 10 Disc probe plate 11 Variable power supply for probe voltage application 12 Flat plate probe for sheath width detection

Claims (3)

[Claims] 1. A metal disk is placed in the plasma,
Conductive thin film different from the disk material in the first gas
On a disk-shaped metal plate for a flat plate probe, and then
Place the metal plate in the plasma of the second gas to be measured,
By applying a constant voltage and exposing it to plasma for a predetermined time
Depending on the applied voltage, a bright
Forming a ring and the outer peripheral edge r of the metal plate._p From a bright ring
Outer edge r_{im p} Distance to (r_p -R_imp ) Is measured and calculated
Sheath width D according to the formula_CLIs characterized by detecting
A method for detecting the sheath width between the tsuma and the boundary. 2. The equation for calculating the sheath width is D _CL ≈10 (r
_p- r _imp ). The method for detecting the sheath width between the plasma and the boundary according to claim 1. 3. The sheath width detecting method between the plasma and the boundary according to claim 1, wherein the metal disk is made of gold, platinum, copper, stainless steel, aluminum or the like.