JP3156774B2 - High frequency plasma processing equipment with electron energy control function - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for generating a process plasma used in a semiconductor manufacturing process or a flat panel display such as an LCD.

[0002]

2. Description of the Related Art In a process of manufacturing a semiconductor integrated circuit, especially an LSI, a plasma process is often used for etching and thin film CVD. In this plasma process, electrically excited plasma electrons decompose a reactive gas, and the neutral active species or ionic species generated thereby are used for material processes such as etching and thin film CVD. Therefore, plasma electrons play an essential role in the process plasma.

On the other hand, recent miniaturization and high density of LSIs have come to impose strict requirements on control of plasma electrons in a plasma process. For example, Si
In the O2 / Si selective etching, it is necessary to ensure the selectivity with Si in the fine pattern in the high-speed etching, but this has become difficult as the pattern size decreases. Such a decrease in etching selectivity is caused by
This is because plasma electrons have excessively high energy based on the high ion amount required for high-speed etching, and the amount of radicals directly related to selectivity decreases.

In the etching of polycrystalline silicon as a gate electrode, an abnormal shape called a notch appears at the interface with the underlying silicon oxide film, which causes a deterioration in quality. The notch phenomenon is a problem that has arisen with the miniaturization of gate dimensions, but the occurrence itself is due to the curvature of the ion trajectory in the fine pattern, and this trajectory curvature occurs due to the imbalance of the positive and negative charge distribution in the fine pattern. This is due to charge-up. That is, since the electron energy is usually large and the speed is spread in the horizontal direction as well as in the vertical direction of the substrate, it is difficult to reach the bottom of the fine pattern. For this reason, the bottom of the pattern is positively charged by the ions and the top is negatively charged by the electrons, and the electric field generated by the charge imbalance causes the ion orbit to be curved, resulting in an abnormal shape. The phenomenon in which the shape abnormality occurs is more remarkable as the pattern width is smaller and the electron energy is larger. From this viewpoint, reduction of the electron energy is required.

[0005]

As described above, control of electron energy, which plays an essential role in plasma generation, is an indispensable subject in the next-generation LSI process in which miniaturization is advanced. Accordingly, an object of the present invention is to provide a plasma generator capable of controlling the electron energy of process plasma over a wide range.

[0006]

SUMMARY OF THE INVENTION Therefore, the present invention provides a high-frequency plasma processing apparatus for generating high-frequency power by supplying high-frequency power to a circular antenna close to a plasma generation chamber. An antenna and matching device circuit assembly having both terminals and an intermediate tap for switching and selecting a directional mode in at least two stages, and having a changeover switch for selectively connecting the both terminals and the intermediate tap in a circuit. It is a thing. (Note that the modes of the circular antenna include the “circumferential mode” described above and the “radial mode” described later, but the present invention considers the difference in the influence on the plasma electrons due to the difference in the circumferential mode. Since the term "mode" is used hereafter, the term "mode" refers to the "circumferential mode".)

Considering the circumferential mode of the antenna in the above configuration with reference to FIG. 1, the current flowing on the circular antenna 1 does not change on the circumference as shown by the arrow, but "m = In the "0 mode" (FIG. 1A), electrons e in, for example, four directions (indicated by broken lines in FIG. 1) in the circumferential electric field in the opposite direction are all tangential by the tangential electric field E through their respective orbits. Direction and will have a relatively high electron energy. Next, in the “m = 1 mode” (FIG. 1B) in which the current flowing on the circular antenna 1 changes twice during one round as shown by four thick arrows, two of these four electrons are In the orbit, both the acceleration and the deceleration are performed, and as a result, the electron energy is significantly lower than in the m = 0 mode. Furthermore, circular antenna 1
In the "m = 2 mode" (FIG. 1C) in which the current flowing above changes four times during one round as shown by eight thick arrows, all of these four electrons accelerate and decelerate on this orbit. Due to both effects, the electron energy is consequently significantly lower than in the m = 1 mode.

For the circumferential mode of the circular antenna, at least two of the above-mentioned m = 0, m = 1 and m = 2
If the stage can be selected, the electron energy can be increased /
Although it is possible to switch between two low steps, it is also possible to control the electron energy intensity over a very wide range as these three or more modes as desired.

Further, when the circular antenna has a radial mode n =
A structure comprising a large circular portion, a small circular portion, and a radius portion connecting these circular portions so as to obtain a value of 1. In addition to the electron energy control function, the radial distribution of the plasma is made uniform, and the wafer processing characteristics are improved. Can be formed in a radial direction, and a plasma generating apparatus advantageous for increasing the diameter of a wafer can be formed.

[0010]

FIG. 2 shows a typical embodiment of the plasma generator of the present invention. The apparatus 2 is an inductively coupled plasma etching apparatus, 3 is a reaction chamber forming the apparatus main body, and 4 is a chamber upper lid made of a quartz plate. An antenna conductor 5 and a water-cooling pipe 6 for cooling the antenna conductor are arranged on the upper lid 4, and a matching device and a matching circuit 7 are mounted thereon to constitute an antenna and matching device assembly 8. A processing gas source connection port 9 and a vacuum suction port 10 are formed as a flow path system related to the reaction chamber 3, and a processing substrate electrode 12 is mounted on the chamber bottom plate 3 a via an insulating ring 11.
As necessary electrical connections, a ground wire 13 is connected to the side of the chamber, and a ground-side matcher 14 is connected to the electrode 12.

As a driving power source of the apparatus, a main RF power source 15 is connected to the matching unit and matching circuit 7, and a bias RF power source 16 is connected between the matching unit 14 and the ground potential. When these power supplies 15 and 16 are energized, the upper cover 5
RF power is supplied to the upper antenna and the reaction chamber 3
A combined high-density plasma is generated therein. In order to apply the high-density plasma to a processing substrate, typically a silicon wafer 17 placed on the processing substrate electrode 12, to achieve predetermined etching characteristics, the antenna and matching unit assembly 8 must be operated. Therefore, an appropriate number of circumferential modes in the antenna conductor 5 must be established.

FIG. 3 shows a structural model for each mode when the antenna conductor 5 has one turn (indicated by “5-1”). For the antenna 5-1A of mode “0”, an arbitrary Slit split type terminal node 18 provided at 0 ° position
a and 18b are the bipolar terminals for supplying the RF current, and the current flowing from one (in this case, 18a) makes one round around the circular antenna conductor 5-1A as it is (in this case, 18a).
Reflux in b).

In the antenna 5-1B of mode "1", the terminal node 19 provided at an arbitrary 0 ° position and the terminal node 20 provided at a position 180 ° from the 0 ° position are used as the bipolar terminals of the RF current supply. The current flowing from one (in this case, 19) is diverted to both sides of the circular antenna conductor 5-1B and reaches the other (in this case, 20), and has two positions of 0 ° position and 180 ° position. The direction of the current is reversed.

Further, in the antenna 5-1C of mode "2", the terminal nodes 21 and 22 provided at arbitrary 0 ° and 180 ° positions and 90 ° shifted from the 0 ° and 180 ° positions by 90 ° respectively. The terminal nodes 23 and 24 provided at the position and the 270 ° position are a pair of bipolar terminals for supplying the RF current, respectively, and a first pair of nodes (in this case, 21 and 2)
2) is diverted to both sides of each position of the antenna conductor 5-1C, and flows into the second pair of nodes (in this case, 23, 2
4), and the current direction is reversed at four positions of 0 °, 90 °, 180 ° and 270 °.

FIG. 4 is a circuit diagram showing a basic embodiment of the antenna and matching box assembly 8. One-turn antenna 5-1
Are the vacuum variable capacitors C1, C2 via the mode changeover switch Sm and the mode designating switches S1, S2, S3.
2 in a π-type matching circuit. M1 and M2 are C1 and C2 adjustment drive motors. Both shoulders of the π-type circuit are connected to the variable capacitor C2 by the switch m0.
Through the position, the antenna 5-1 (the antenna 5-1 in FIG. 3)
One of the four nodes in C (0 ° node formed in the same manner as the slit-split type node in the antenna 5-1A) is connected to both sides a and b of the slit of the 0 ° node. As long as the mode designating switch S1 inserted into the antenna and the other mode designating switches S2 and S3 are not closed, the antenna remains in the circumferential mode “0” in this state.
Becomes

Next, the rear shoulder of the π-type circuit is m of the switch Sm.
At the 1 position, the antenna 5-1 is connected to the 180 ° node c, and the front shoulder is collectively connected to both sides a and b of the 0 ° position slit by closing only the mode designation switch S1, so that the antenna is in this state. It becomes the circumferential mode “1”. Further, the rear shoulder of the π-type circuit is connected to the 90 ° node d of the antenna 5-1 at the position m2 of the switch Sm, and is closed by the mode designation switch S3 to 270.
° Also connected to node e. In this state, the front shoulder of the π-type circuit is collectively connected to both sides a and b of the 0 ° position slit and the 180 ° node c by closing the further mode designating switches S1 and S2. It becomes “2”.

FIG. 5 is a circuit diagram showing an antenna and matching box assembly 8 'according to the second embodiment. In this embodiment, a switch circuit including an antenna 5-1 connected to both of the π-type shoulders is replaced by an inverted L-type circuit including an inductance L instead of the π-type matching circuit in the basic embodiment of FIG. Is connected between the rear end of the inverted L-type (the rear end of the variable capacitor C2 ′) and the ground potential. The connection relationship between each switch and the antenna 5-1 is the same as in FIG.
The same reference numerals are given to the respective parts, and the description is omitted. In this embodiment, one end of the antenna conductor can be directly grounded, so that the safety and operability of the plasma device are improved.

FIG. 6 shows a structural model for each circumferential mode when the antenna conductor 5 is wound twice (indicated by "5-2") and the radial mode is n = 1. In the antenna 5-2A in the circumferential mode m = 0, the slit-divided terminal nodes 25a and 25b provided at arbitrary 0 ° positions in the outer peripheral coil are used as the bipolar terminals for supplying the RF current, and the outer peripheral coil and the inner peripheral 180 ° connection with coil
Slit-type relay conductors 26a, 26 provided at the positions
b. This allows terminal node 25
a, 25b flows into the antenna conductor 5
-2A outer coil and inner coil are connected to the relay conductor 26.
The circuit makes a round around the detour point at a and 26b and returns to the other node.

In the antenna 5-2B of mode m = 1, the terminal nodes 27 and 28 formed at arbitrary 0 ° positions in the outer coil and the inner coil are used as the bipolar terminals for supplying the RF current, respectively. In this case, the connection with the coil is also made by the slit-division-type relay conductor portions 26a and 26b provided at the 180 ° position. This allows
The current flowing from one of the terminal nodes 27 and 28 is diverted to both sides of the outer coil or the inner coil of the antenna conductor 5 # 2B, flows into and bypasses the relay conductors 26a and 26b, and is further divided to both sides of the other coil. The current flows to the other node, and the direction of the current is reversed at both the 0 ° position and the 180 ° position in both the inner and outer coils.

Further, in the antenna 5-2C of mode m = 2, the terminal nodes 29 and 30 formed at arbitrary 0 ° positions and 180 ° positions in the outer peripheral coil, and at the arbitrary 0 ° positions and 180 ° position in the inner peripheral coil. The terminal nodes 31 and 32 formed at the positions are collectively used as the pole terminals for supplying the RF current as indicated by broken lines, and the connection between the outer and inner coils is at the 90 ° position and the 270 ° position, respectively. The formed slit-division-type relay conductor portion 33
a, 33b and 34a, 34b.
Outer peripheral terminal nodes 29 and 30 or inner peripheral terminal nodes 31 and 3
2 flows into both sides of the outer coil or inner coil of the antenna conductor 5-2C, flows into and bypasses the slit-division-type relay conductors 33a, 33b and 34a, 34b, and flows into and out of the other coil. It is a structure that shunts each and reaches the other collective node.
The directions of the currents are reversed at four positions of 90 °, 180 °, and 270 °.

The antenna and matching device assembly using the two-turn antenna described above can also be configured in accordance with the circuits 8 and 8 'shown in FIGS. However,
Although the number of relay conductors in the antennas in the radial mode m = 0 and m = 1 is one pair, the number of relay conductors in the antenna in the radial mode m = 2 is two, so that the antenna is replaced or the pair of relay conductors is replaced. It is necessary to provide a fixed structure and a switch structure for electrically forming and removing the other pair.

Experiments and Discussion In the basic embodiment of the antenna and Π-type matching box assembly shown in FIG. 4, the case where the number of antenna modes is m = 0,
The plasma electron energy generated when m = 1 was compared and measured as follows. The plasma generator (not shown) used in the experiment was provided with a SUS chamber having an inner diameter of 27 cm, and the plasma electron energy in the chamber was measured by an electrostatic probe method. Antenna 5-1 in radial mode m = 0 and m = 1
3A and 3B, the inner diameter of the annular main body is 11 cm, the outer diameter is 16 cm (the conductor width is 2.5 cm), the node width is 2.5 cm, and The inter-node slit width of -1A was 1 mm.

An argon plasma was generated in the chamber, and an electron temperature and an electron density representing the electron energy were measured by an electrostatic probe. FIG. 7 shows the radial dependence of the electron temperature, and FIG. 8 shows the radial dependence of the electron density in each of the modes m = 0 and m = 1. A)
And the case of 900 W (B). According to these results, in the electron density graph of FIG. 8, there is almost no difference between m = 0 and m = 1,
In the graph of FIG. 7, the electron temperature in the case of m = 1 drops to about half of that in the case of m = 0. This result clearly shows that electron energy control by the number of modes is possible.

FIGS. 9 and 10 show the measured values of the electron energy distribution in this case in comparison between the antenna modes. 9 (RF power 900 W) and FIG. 10 (RF power 7
00W), it is clear that the electron energy in the case of the mode number m = 1 is small and the half width is only about half that in the case of m = 0, so that the mode number is m = 0,
It can be seen that by switching between m = 1, electron energy control can be performed reliably. In these figures, Teq is an equivalent temperature obtained when the measured value is fitted to a Maxwell distribution function, and Vs is a plasma space potential. In addition, Maxwell as a graph name (label) represents a theoretical curve of a Maxwell distribution function that best fits an actually measured value, and Druyvesteyn represents a theoretical curve of a Druyvesteyn distribution function, which is a theoretical function under thermodynamic equilibrium conditions. While this is a Maxwell distribution function, it is a theoretical function that takes into account the influence of an electric field. This Druyvesteyn distribution function is a theoretical curve with the larger peak energy on the data. Experiment shows an actually measured curve and is a noisy curve, so it can be easily identified from other curves. Note that these curves are displayed in color on the measuring instrument and can be easily distinguished.

Next, the difference in electron energy between modes m = 1 and m = 2 will be considered theoretically. This electron energy evaluation was performed on a flat plate plasma. In the plasma plane shown in FIG. 11, L is the distance of electric field mode change due to antenna mode change, and y = 0 and y
= 2L is considered to be the same place (repetition at a period of 2L).
Here, when Ey is the intensity of the induced charge and λ is the mean free path of the electron, the electron energy per one mean free path is y =
The amount U accumulated between 0 and y = L is

[0026]

(Equation 1)

When the above equation is divided by its integral path length to obtain an average electric field,

[0028]

(Equation 2)

The first term (2E _y / π) on the right side of this equation is the average electric field in the case of mode 0, and L / λ in the second term is L
If / λ = X, then mode 1 at X = 4 and mode 2 at X = 2, the second term (X−π / 2) / X is X ≧ π / 2
Is less than or equal to 1 and 0.61 in the case of mode 1 and 0.21 in the case of mode 2, which is about 35% of the former.
? It is considered that the electron acceleration is reduced by about 40%.
It is considered that the sign (electric field direction) of the second term (X−π / 2) / X may be inverted to 1 or more when X ≦ π / 2, but actually θ = π / Integrating up to 2 itself is an overestimation of the reversal electric field, and it is possible to make it 1 or less in all the positive regions of X if θ is appropriately limited.

[0030]

As described above, the present invention controls the electron energy of the plasma by switching the circumferential mode of the antenna in the high-frequency plasma generator, thereby increasing the amount of high ions necessary for processing fine patterns in high-speed etching. / Electron energy control according to process requirements, such as establishment of a low electron energy state.

[Brief description of the drawings]

FIG. 1 shows the principle of electron energy control of the present invention in (A) radial mode m = 0, (B) m = 1, and (C) m =
It is a schematic diagram shown with 2 antenna models.

FIG. 2 is a schematic structural view showing an embodiment of a high-frequency plasma generator of the present invention.

FIG. 3 is a schematic diagram showing a structural model of (A) a radial mode m = 0, (B) m = 1, and (C) m = 2 in a single-turn antenna used in the device embodiment of the present invention. .

FIG. 4 is a circuit diagram showing a first embodiment of an antenna and matching box assembly including an antenna according to the structural model of FIG. 3;

FIG. 5 is a circuit diagram showing a second embodiment of the antenna and matching box assembly including the antenna according to the structural model of FIG. 3;

FIG. 6 shows (A) a radial mode m = 0 and (B) in a two-turn antenna for use in the plasma generator of the present invention.
It is a schematic diagram which shows the structural model of the same m = 1 and (C) m = 2.

FIG. 7 shows the difference in electron temperature between antenna modes by using RF
It is a graph divided into the case (A) of electric power 700W and the case (B) of 900W.

FIG. 8 shows the difference in electron density depending on the antenna mode,
It is a graph divided into the case (A) of electric power 700W and the case (B) of 900W.

FIG. 9 is a graph showing the difference in electron energy distribution depending on the antenna mode in the case of RF power of 700 W (A) and in the case of 900 W of RF power (B).

FIG. 10 is a graph showing a difference in electron energy distribution depending on an antenna mode in a case of RF power of 700 W (A) and a case of RF power of 900 W (B).

FIG. 11 is a diagram showing plasma plane coordinates of a plate-like plasma for describing a difference in electron energy between antenna modes m = 1 and m = 2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Circular antenna 2 Plasma etching apparatus 3 Reaction chamber 4 Quartz upper lid 4 5 Antenna conductor 6 Water cooling pipe 6 7 Matching device and matching circuit 8 Antenna and matching device assembly 9 Processing gas source connection port 10 Vacuum suction port 10 11 Insulation ring 12 Processing substrate electrode 13 Ground wire 14 Ground side matcher 15 Main RF power supply 15 16 RF power supply for bias 17 Silicon wafer 17

Claims (3)

(57) [Claims] 1. A high-frequency plasma processing apparatus in which high-frequency power is supplied to a circular antenna close to a plasma generation chamber to generate plasma, wherein the circular antenna switches and selects a circumferential mode in at least two stages. An electronic energy control function, comprising an antenna and a matching circuit circuit assembly having both terminals and an intermediate tap for performing the connection, and a changeover switch for selectively connecting the both terminals and the intermediate tap in a circuit. A high-frequency plasma processing apparatus having: 2. The method according to claim 1, wherein the circular antenna has a circumferential mode of m.
2. The high-frequency plasma processing apparatus according to claim 1, further comprising a double terminal and an intermediate tap structure which can select three stages of = 0, m = 1 and m = 2. 3. The circular antenna according to claim 2, wherein the circular antenna includes a large circular portion, a small circular portion, and a radius portion connecting these circular portions so that a radial mode n = 1.
The high-frequency plasma processing apparatus according to the above.