JPH077001A - Plasma etching system and method - Google Patents

Abstract

PURPOSE:To suppress plasma polymerization reaction in a thin hole and prevent polymer from being adhered to the peripheral wall of the thin hole by controlling a gas supply means in a plasma etching system and speeding up the flow rate of gas through the thin hole of a shower electrode. CONSTITUTION:A wafer W is carried into a treatment chamber 1 and is sucked and retained on a chuck electrode 61. Ar gas, CF4 gas, and CHF3 gas are introduced into the treatment chamber 1 via the shower electrode 3 and at the same time the inside of the treatment chamber 1 is evacuated. Then, a high-frequency power is applied between a cathode plate 54 and the chuck electrode 61, thus generating discharge plasma, allowing gas plasma to react with the wafer W, and hence etching a wafer surface. In this case, since the flow rate of gas passing through a thin hole 55 is set to 100Km/hour or faster, gas is supplied to the thin hole 55 so that a mass flow rate is equal to or higher than 620Kg/m<2>/hour, thus preventing polymer from being adhered to the gas emission hole of the shower electrode 3 for a long-term continuous use.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma etching system and a plasma etching method for plasma etching a substrate such as a semiconductor wafer, and more particularly to improvement of a shower electrode used as an upper electrode of a parallel plate electrode type etcher.

[0002]

2. Description of the Related Art For etching a semiconductor wafer, there is, for example, a parallel plate electrode type plasma etching apparatus having a pair of electrodes facing each other. In the parallel plate electrode type etching apparatus, a wafer is placed on the lower electrode, and a gas for plasma generation (for example, halogen gas or Freon gas) is ejected toward the wafer from a large number of gas ejection holes of the upper electrode. Then, a high frequency voltage is applied between the upper electrode and the lower electrode to turn the gas into plasma, and the wafer is etched by this plasma.

[0003]

However, the conventional upper electrode (shower electrode) is designed only to uniformly generate plasma, and the gas flow rate is optimized in order to optimally etch the wafer. However, it cannot be said that the pitch of the gas ejection holes, the diameter of the gas ejection holes, and the like are sufficiently taken into consideration.

Recently, the pattern of semiconductor devices tends to become finer and finer, and anisotropic etching having a high aspect ratio is used as such ultrafine processing. By the way, in order to realize anisotropic etching with a high aspect ratio, it is necessary to lower the internal pressure of the process chamber. Therefore, the processing gas undergoes plasma polymerization, and the polymer containing C, O, and F adheres to the peripheral wall of the gas ejection hole of the upper electrode. Such an attached polymer gradually grows as the plasma discharge time becomes longer, and develops into a foreign substance having a thickness of several tens of μm. Finally, the polymer mass drops from the upper electrode onto the wafer, which causes contamination and reduces the yield of semiconductor devices.

In addition, the same shower electrode cannot be shared by such high aspect ratio anisotropic etching and normal etching, and a dedicated shower electrode must be prepared for each application.

The present invention has been made to solve the above problems, and it is an object of the present invention to provide a plasma etching system and a plasma etching method which can be stably and continuously used for a long time.

[0007]

A plasma etching system according to the present invention comprises a container for confining plasma, a means for exhausting the inside of the container, a chuck electrode for holding a substrate, and a large number of pores facing the chuck electrode. And a power supply for applying a plasma voltage between the showerhead electrode and the chuck electrode, and a gas for plasma generation in the container through the pores of the showerhead electrode. And a means for controlling the gas supply means so that the mass flow rate of the gas is 620 kg / m ² / hour or more.

In the plasma etching method according to the present invention, the substrate is held by the chuck electrode inside the container, the inside of the container is evacuated so that the inside of the container is in a depressurized state, and when passing through the pores of the shower electrode. A gas for plasma generation was introduced into the container so that the mass flow rate was 620 kg / m ² / hour or more, a voltage was applied between the shower electrode and the chuck electrode, plasma was generated between both electrodes, and the generated plasma was generated. It is characterized in that it acts on the substrate.

In the plasma etching system of the present invention, the gas supply means is controlled to increase the flow velocity of the gas when passing through the pores of the shower electrode. Particularly, the pitch of the pores is 6 mm or more, and / or the diameter of the pores is 0.8 mm.
When the amount is less than the above, it becomes easy to supply a gas having a mass flow rate of 620 kg / m ² / hour or more to the shower head electrode. Here, the "mass flow rate" refers to the mass of the fluid flowing through the pipeline per unit time.

[0010]

[Function] The plasma polymerization reaction in the pores is greatly affected by the gas flow rate. When the pitch of the pores is narrow or when the diameter of the pores is large, the gas flow velocity becomes slow, so that the weakly charged plasma in the pores is polymerized and the polymer is deposited on the peripheral wall of the pores. Therefore, a gas having a mass flow rate of 620 kg / m ² / hour or more is supplied to the shower electrode. In such a gas supply system, the plasma polymerization reaction in the pores is suppressed, and it becomes difficult for the polymer to adhere to the peripheral wall of the pores. Even if a polymer is generated, the polymer is blown away by the high-velocity gas flow and does not grow and develop until it becomes a large lump.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Various embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an overall schematic diagram showing a plasma etching system according to an embodiment of the present invention. The processing chamber 1 is composed of an aluminum wall, and the inside is kept airtight. An electrode unit 2 is provided above the processing chamber 1.
Is provided. The electrode unit 2 is a lifting cylinder 21.
It is supported so that it can move up and down.

A shield ring 25 is mounted on the electrode unit 2, and a cooling block 23 is provided inside the shield ring 25.
Is stored. The shield ring 25 is made of an insulating material. An internal passage 42 is formed in the cooling block 23 so that the refrigerant flows from the cooling device 41 to the internal passage 42.

Further, baffle plates 51 and 52 are provided in the recess of the cooling block 23. Cooling block 23
A shower electrode 3 is detachably attached to the lower end of the with screws 58. The peripheral portion of the shower electrode 3 is pressed against the cooling block 23 by the insulating ring 24.

The shower head electrode 3 is formed by combining a cathode plate 54 and a cooling plate 53, and the plates 53 and 54 are adhered to each other. The cathode plate 54 is made of amorphous carbon, and the cooling plate 53 is made of aluminum or aluminum alloy. Shower electrode 3 has a frequency of 400 KH
z, and the chuck electrode 61 is electrically connected to the high frequency power source 12 having a power value of 1300 W, while the chuck electrode 61 is grounded. As a result, the shower electrode 3 and the chuck electrode 61 below form a plasma generation circuit.

The second baffle plate 52 is located directly above the shower electrode 3, and the first baffle plate 51 is the second baffle plate 52.
And the gas supply port of the pipe 26 is located directly above the first baffle plate 51. The shower head electrode 3 and the first and second baffle plates 51 and 52 are provided substantially horizontally and in parallel with each other. The gas introduction chamber 22 is formed by the first baffle plate 51 and the cooling block 23. Vent holes 51 a, 52 a, 55 are formed in the first and second baffle plates 51, 52 and the shower electrode 3, respectively. The diameters of the ventilation holes 51a, 52a, 55 are larger in this order. A cooling plate 53 is in close contact with the back surface of the cathode plate 54 of the shower electrode 3, and the cooling plate 53 has a temperature of about 20 ° C.
The cathode plate 54 is cooled by being maintained at. The cooling block 23 and the first and second baffle plates 51 and 52 are made of aluminum or aluminum alloy.

An opening at one end of a gas supply pipe 26 communicates with the center of the upper portion of the gas introduction chamber 22. The base end side of the gas supply pipe 26 is branched into three, and each branch pipe communicates with a gas supply source 71a, 71b, 71c via a mass flow controller (MFC) 72a, 72b, 72c, respectively. The gas supply source 71a contains Ar gas, the gas supply source 71b contains CF ₄ gas, and the gas supply source 7a.
CHc ₃ gas is contained in 1c. Each of the gas supply sources 71a, 71b, 71c is equipped with a pressure adjusting valve, and the movable part power source of the pressure adjusting valve is connected to the output part of the controller 70. Further, the power supplies of the movable parts of the MFCs 72a, 72b, 72c are also connected to the output part of the controller 70. The MFCs 72a, 72b, 72c are the controller 7
0 is controlled independently of the gas supply sources 71a, 71b, 71c. That is, each gas supply source 71a, 71b, 71c is controlled to have a constant pressure, but each MFC 72a, 72b, 72c is controlled to have a constant flow rate.

A wafer holder 6 having a chuck electrode 61 is provided below the processing chamber 1, and a wafer W is placed on the chuck electrode 61. The chuck electrode 61 contains an electrostatic chuck 64 to which DC power is supplied from an external DC power source E. The chuck electrode 61 is made of aluminum or aluminum alloy. In addition,
The distance between the showerhead electrode 3 and the chuck electrode 61 is about 1
It is placed at a height position such that it becomes cm. The lower surface of the chuck electrode 61 is in close contact with the cooling block 63. The cooling block 63 has an internal passage 62, and the refrigerant is supplied to the internal passage 62 from a refrigerant supply source (not shown).

An exhaust pipe 11 is connected to the lower side wall of the processing chamber 1. The exhaust pipe 11 communicates with the suction port of the vacuum pump 83. A valve 82 and a pressure sensor 84 are attached in the middle of the exhaust pipe 11. The pressure sensor 84 is connected to the input part of the controller 70, and the operation of both the valve 82 and the vacuum pump 83 is controlled based on the detected pressure.

As shown in FIG. 2, the cathode plate 54 of the shower electrode 3 is made of a disc having a thickness of 4 mm, and a large number of fine holes 55 are formed in the region backed up by the cooling plate 53. As shown in FIG. 3, the pores 55 have equal pitch intervals P.
Are arranged in a grid. The pore 55 has a diameter d
Is 0.6 mm and the pitch interval P is 7 mm. 8
The cathode plate 54 for an inch wafer has a diameter of 285 mm, and in this case, it is preferable that the diameter of the gas ejection region in which the pores 55 are present is 180 mm or more. Further, the cathode plate 54 for a 6-inch wafer has a diameter of 200 mm, and in this case, it is preferable that the diameter of the gas ejection region in which the pores 55 exist is 120 mm or more. Note that, as shown in FIGS. 5 and 6, the shower electrodes 3 may be radially arranged at equal pitch intervals P.

As shown in FIG. 4, the pores 5 on the cathode plate side
The diameter of 5b is smaller than that of the pores 55a on the cooling plate side. Therefore, if the gas flow velocity passing through the pores 55a and 55b is small, the polymer may be deposited at the step 56, and the gas may be difficult to flow into the pores 55b on the cathode plate side.

Next, the case of plasma etching the silicon wafer W will be described. The wafer W is loaded into the processing chamber 1 and held on the chuck electrode 61 by suction. Ar gas, CF ₄ gas, and CHF ₃ gas are introduced into the processing chamber 1 through the shower electrode 3, and the inside of the processing chamber 1 is evacuated to an internal pressure of 0.5 Torr or less. Then, 400 KHz between the cathode plate 54 and the chuck electrode 61,
A high frequency voltage having a power value of 1300 W is applied. As a result, discharge plasma is generated and the gas plasma reacts with the wafer W, so that the wafer surface is etched.

At that time, the gas flow rate is 100 K as in the conventional case.
When it is slower than m / hour, the processing gas is plasma-polymerized in the pores 55 and adheres to the peripheral wall of the pores 55 as a polymer. On the other hand, in this embodiment, in order to set the flow rate of the gas passing through the pores 55 to 100 km / hour or more, the gas is supplied to the pores 55 at a mass flow rate of 620 kg / m ² / hour or more.

FIG. 7 is a characteristic diagram showing the results of investigating wafer contamination by taking the plasma discharge time on the horizontal axis and the number of discharged foreign substances (polymers) attached to one wafer on the vertical axis. When the number of the wafer-adhering polymers exceeded 45, it was judged as a failure. As is clear from the figure, according to this example, the number of wafer-adhering polymers was small, and it was judged as acceptable.

When the gas flow velocity is increased in this way,
Plasma is generated uniformly and the stable discharge region is 0.15To
Spread from rr to 3.0 Torr. As a result, etching with a high aspect ratio to low etching can be realized.

FIG. 8 is a cross-sectional view of a high aspect ratio etched wafer. The wafer is uniformly etched both in the central portion and the peripheral portion. Next, the gas velocity distribution directly above the wafer will be examined using computer simulation. Here, in order to simplify the problem, it is assumed that the gas is uniformly supplied from the entire shower head surface as shown in FIGS. 9 and 15. Simulation was performed under the following conditions. [Simulation conditions] Model shape Cathode plate pore diameter (mm) d = 0.
6,0.8 Diameter of gas injection area of shower electrode φ = 2r ₀ (shower diameter (mm)) = 16
0,180,210 Process conditions Gas composition: CF ₄ 30 (SCCM): CHF ₃ 30 (SCCM): Ar 600 (SCCM) Gas physical properties: Average physical properties of a mixed gas obtained by mixing the above three kinds of gases with the third temperature Gas flow state obtained by approximation using a formula: Compressed flow (However, consider that the density changes depending on the internal pressure of the reaction vessel.

Pressure: P ₈ = 0.6 (Torr) where the central point on the upper surface of the wafer is the reference point pressure P _8, and ΔP = 10.9 (Torr) temperature when the pressure difference ΔP between the reference point and the gas inlet is : In the case of gas flow rate calculation, a constant temperature T = 100 ° C. in the calculation area.

In the case of the reaction calculation, the constant temperature T ₈ = 60 ° C. on the wafer and the constant temperature T ₉ = 250 ° C. with the shower head.

The relationship between the velocity distribution near the wafer and the etching characteristics was obtained by computer simulation to find the gas flow state in the reaction vessel when the shower diameter (the diameter of the gas ejection area in the electrode) was changed to 160 mm, 180 mm and 210 mm. Consider. Here, in order to simplify the problem, changes in the flow state due to consumption of raw material gas and generation of by-product gas are ignored.

10 to 12 show a shower diameter of 16
It is a gas flow velocity distribution chart which shows the result of having respectively investigated about the gas flow state variously changed to 0 mm, 180 mm, and 210 mm. In this case, an 8-inch diameter silicon wafer was examined using a shower electrode having a pore diameter of 0.6 mm. As is clear from these figures, while the gas reaches the shower head 3 from the baffle 51, the gas is dispersed in the horizontal direction, but the gas flow velocity varies widely. This means that the baffles 51 and 52 have the function of dispersing the gas, but do not have the function of adjusting the flow velocity to make them uniform.
On the other hand, between the shower head 3 and the wafer W, the gas flow velocity increases almost uniformly from the central portion toward the peripheral portion. This means that the shower head 3 has a function of making the gas flow velocity uniform.

The uppermost baffle 50 shown in FIG. 9 is a member for adjusting the pressure of the introduced gas. In the figure, the distance L ₁ is 16 mm, the distance L ₂ is 16.5 mm, the distance L ₃ is 24 mm (= 20 mm + 4 mm), the distance L ₄ is 10 mm, and the radius r.
₀ is 110.5 mm and radius r ₁ is 160 mm (or 180 m)
m or 210 mm).

As is apparent from FIG. 10, when the shower diameter is 160 mm, the gas flow velocity rapidly increases from the central portion of the wafer toward the peripheral portion. Moreover, the maximum value of the gas flow velocity is the highest among the three. On the other hand, as is apparent from FIGS. 11 and 12, when the shower diameter is 180 mm and 210 mm, the gas flow velocity is almost constant from the wafer central portion to the peripheral portion, and the fluctuation is small.

Next, the distribution characteristics of the gas velocity will be described with reference to FIGS. 13 and 14. In FIG. 13, the horizontal axis indicates the distance r (mm) from the wafer center, and the vertical axis indicates the gas velocity v.
(M / sec) is shown, and the result of examination for a shower electrode having a pore diameter of 0.6 mm is shown. In FIG. 14, the horizontal axis represents the distance r (mm) from the wafer center, and the vertical axis represents the gas velocity v (m /
Second), the results obtained by investigating a shower electrode having a pore diameter of 0.8 mm are shown. In the figure, the black circle has a shower diameter of 16
The results for 0 mm, the white circles for the shower diameter of 180 mm, and the black triangles for the shower diameter of 210 mm are shown.

As is clear from both figures, the gas velocity distribution just above the wafer does not depend on the pore diameter d. Further, the gas velocity increases linearly from the center of the wafer and becomes maximum at the peripheral portion of the wafer. If the shower diameter is 160 mm, the distance r is 80
A maximum gas velocity of 1.32 m / sec was obtained at the mm position. When the shower diameter was 180 mm, the maximum gas velocity of 1.10 m / sec was obtained at the position where the distance r was 95 mm. When the shower diameter was 210 mm, the maximum gas velocity of 0.98 m / sec was obtained at the position where the distance r was 105 mm.

Next, the distribution of gas velocity just above the wafer will be examined. As shown in FIGS. 13 and 14, the gas velocity in the wafer radial direction had the maximum distribution in the vicinity of the wafer peripheral portion. Consider the reason for this.

Here, in order to simplify the problem, FIG.
In the model shown in (1), the gas is uniformly supplied from the entire shower head. The case where the distance r (distance from the wafer center) is smaller than the radius r ₀ of the shower gas injection region (r ≦ r ₀ ) and the case where the distance r is larger than the diameter r ₀ (r> r ₀ ) are classified into cases. Each will be explained. (A) In the case of r ≦ r _{0 In} this region (region where the shower gas is jetted), the gas flow rate f per unit area of the shower head is given by the following equation (1). However, r ₀ represents the diameter of the gas injection region in the shower electrode, and V ₀ represents the introduced gas flow rate.

F = V ₀ / πr ₀ ² (1) The gas flow rate F at the position of the distance r is given by the following equation (2). F = πr ² f = (r ² V ₀ ) / (r ₀ ² ) ... (2) The cross-sectional area S of the flow path through which the gas having the flow rate F passes is given by the following formula (3). However, L ₅ is the distance from the gas ejection port to the upper surface of the wafer.

S = 2πrL ₅ (3) Therefore, the gas velocity v is given by the following equation (4). v = F / S 2 = (V ₀ / 2πL ₅ r ₀ ² ) · r (4) As is apparent from this, the gas velocity v increases in proportion to the distance r. Since the gas velocity v is inversely proportional to r ₀ ² , the smaller the shower radius r _{0, the} greater the gas velocity v. (B) In the case of r> r _{0 In} this region (region outside the shower gas injection region), the gas is supplied only within the range of the radius r ₀ from the center, so the gas flow rate F is expressed by the following equation (5). It becomes equal to V ₀ as shown in.

F = V ₀ (5) Then, the gas velocity v is obtained by the following equation (6). v = F / S 2 = (V ₀ / 2πL ₅ ) · (1 / r) (6) As is clear from this, the gas velocity v becomes smaller as the radius r becomes larger, and does not depend on r ₀ .

Table 1 shows the results of an experimental examination of the relationship between the gas velocity and the etch rate. Each gas velocity and etch rate were measured at a distance of 90 mm from the center of the wafer. As is clear from this table, shower diameter 2r
_The larger the _{value of 0 and the} smaller the gas velocity, the lower the etch rate. This is because as the gas velocity is smaller, the by-product gas generated by the etching reaction is less likely to be discharged,
It is caused by staying near the wafer surface.

Table 1 2r ₀ gas speed Etch rate (mm) (m / sec) (A / min) 160 1.150 5024 180 1.033 5023 210 0.7605 4770 Table 2 and Table 3 show experiments on the relationship between gas concentration and contact hole shape. The results of the examination are shown below. Table 2 shows the results measured at 10 mm away from the wafer center, and Table 3 shows the results measured at 90 mm away from the wafer center. Here, the "taper angle" refers to the inclination angle of the peripheral wall of the contact hole 94 shown in FIG.

Shower diameter 2r at any position
_{As 0} increases, the taper angle decreases as the gas velocity decreases. This is because as the gas velocity is smaller, the by-product gas generated by the etching reaction is less likely to be discharged,
It is caused by staying near the wafer surface.

[0042] Next, the results of studying the etching reaction using computer simulation will be described.

16 to 18 are simulation model diagrams showing the SiF ₄ gas concentration distribution in the plasma generation region modeled by the reaction simulation. In the figure, the wafer end is located at the reference numeral WE, and gas is supplied from above the wafer and exhausted to the right.

In the plasma generation region, the reaction represented by the following formula (7) proceeds and SiF ₄ is produced as a by-product gas. SiO ₂ + CF ₄ → SiF ₄ + CO ₂ (7) In the vicinity of the wafer, not only the raw material gas but also the by-product gas participates in the reaction. The etch rate is CF ₄ gas concentration and S
It is governed by the iF ₄ gas concentration. On the other hand, the shape of the contact hole is governed by the CHF ₃ gas concentration and the SiF ₄ gas concentration. Therefore, the source gases CF ₄ and CHF ₃
In addition, it is necessary to know the concentration distribution of SiF ₄ , which is a by-product gas.

As shown in FIGS. 19 and 20, the concentrations of the raw material gas and the by-product gas immediately above the wafer were uniform near the center of the wafer and varied in the vicinity of the wafer edge.

Table 4 shows the results of an examination of the relationship between the shower diameter 2r ₀ and the CF ₄ concentration distribution. The% value in parentheses in the table is the initial concentration value 4.5454 on the gas supply side.
It represents the rate of decrease of the CF ₄ concentration directly on the wafer with respect to × 10 ^-2 (mol / mol). The gas concentration was examined at a position directly above the wafer.

When the shower diameter 2r ₀ is 160 mm,
The difference between the concentration just above the wafer and the initial concentration is 3.6%.
Further, the CF ₄ concentration difference within the wafer surface is only 1%. When the shower diameter 2r ₀ is 180 mm, the difference between the concentration just above the wafer and the initial concentration is 3.6%. Further, the difference in CF ₄ concentration within the wafer surface is only 0.1%.

When the shower diameter 2r ₀ is 210 mm,
The difference between the concentration just above the wafer and the initial concentration is 4.6%.
This density difference is larger than the former two and is a value that cannot be ignored. On the other hand, the difference in CF ₄ concentration within the wafer surface is only 0.2%.

Shower diameter 160 mm (gas supply rate 1
In the case of 0.6 m / sec), the gas concentration is maximum, and in the case of a shower diameter of 210 mm (gas supply speed 5.70 m / sec), the gas concentration is minimum. However, the difference between the two concentrations is 1.
Only 5%. Further, the CF ₄ concentration difference within the wafer surface is also less than 1%. Therefore, it can be said that the difference in CF ₄ gas (raw material gas) concentration on the wafer surface due to the difference in shower diameter is small.

Table 4 2r ₀ CF ₄ concentration (mol / mol) (mm) Wafer center part Wafer peripheral part 160 4.4211 × 10 ^-2 (2.8%) 4.3744 × 10 ^-2 (3.8%) 180 4.3818 × 10 ^-2 ( 3.6%) 4.3755 × 10 ^-2 (3.7%) 210 4.3386 × 10 ^-2 (4.6%) 4.3471 × 10 ^-2 (4.4%) Table 5 shows the results of an examination of the relationship between shower diameter 2r ₀ and SiF ₄ concentration distribution. Indicates. The gas concentration was examined at a position directly above the wafer.

When the shower diameter 2r ₀ is 160 mm,
The peripheral portion has a higher SiF ₄ concentration than the central portion of the wafer.
The difference in SiF ₄ concentration between the central part of the wafer and the intermediate part is 1%, whereas the difference in concentration between the central part of the wafer and the peripheral part is 36%.
Extends to It can be said that the difference in SiF ₄ concentration within the wafer surface is particularly large.

When the shower diameter 2r ₀ is 180 mm,
The difference in concentration between the central portion of the wafer and the intermediate portion is 1%, and the difference in concentration between the central portion of the wafer and the peripheral portion is 3%. It can be said that the difference in SiF ₄ concentration within the wafer surface is small.

When the shower diameter 2r ₀ is 210 mm,
The difference in concentration between the central portion of the wafer and the intermediate portion is 1%, and the difference in concentration between the central portion of the wafer and the peripheral portion is 3.2%. It can be said that the difference in SiF ₄ concentration within the wafer surface is small.

160 mm shower diameter 2r ₀ and 2
Comparing with the case of 10mm shower diameter 2r ₀ ,
The latter is about 40% higher than the former at the center of the wafer. Further, the difference in the in-plane concentration of the wafer is significantly larger in the former than in the latter.

Table 5 2r ₀ SiF ₄ concentration (mol / mol) (mm) Wafer center part Wafer middle part Wafer peripheral part 160 1.4168 × 10 ^-3 1.4299 × 10 ^-3 1.9257 × 10 ^-3 180 1.8512 × 10 ^-3 1.8700 × 10 ^-3 1.9145 × 10 ^-3 210 2.3299 × 10 ^-3 2.3583 × 10 ^-3 2.2573 × 10 ^-3 Based on such knowledge, let us consider the SiF ₄ gas concentration distribution. Again, in order to simplify the problem, Figure 1
As shown in FIG. 5, it is assumed that the gas is uniformly supplied from the entire shower head surface. Si per unit area of wafer
When the F ₄ generation amount is b, the SiF ₄ total amount B at a distance r from the wafer center is given by the following equation (8).

B = πr ² · b (8) Below, the radius of the gas injection region in the shower electrode (shower radius) r ₀ and the wafer radius r ₈ and the arbitrary distance r from the wafer center are classified according to the size. Explain. (C) Case of r ≦ r _{0 In} this region (shower gas injection region), the SiF ₄ concentration C is given by the following equation (9). The raw material gas flow rate F is given by the above equation (2).

C = B / F 2 = (πb / V ₀ ) r ₀ ² (9) In this region, the concentration C increases as the radius r ₀ increases. (D) In the case of r ₀ ≦ r ≦ r _{8 In} this region, the raw material gas flow rate F is given by the above equation (5). On the other hand, since it is a region where the shower gas is jetted toward the wafer, SiF ₄ is generated. Therefore SiF
The concentration C of ₄ is given by the following equation (10).

C = B / F 2 = (πb / V ₀ ) r ² (10) In this region, the concentration C does not depend on the radius r ₀ but the radius r
The higher the, the higher. (E) In the case of r ₈ ≦ r In this region (region far from the wafer), SiF ₄
The total amount B is given by the following equation (11).

B = πr ₈ ² · b (11) Therefore, the SiF ₄ concentration C is given by the following equation (12).
The raw material gas flow rate F is given by the above equation (2).

C = B / F = (πr ₈ ² r ₀ ² b / V ₀ ) · (1 / r ² ) ... (12) In this region, the concentration C increases as the radius r ₀ increases, and the distance r Becomes larger, becomes lower.

Table 6 shows the results of an experimental examination of the relationship between the gas concentration and the etch rate. Each gas concentration and etch rate were measured at a distance of 90 mm from the center of the wafer. As is clear from this table, shower diameter 2r
_{When 0} is 210 mm, the etch rate is 2r ₀ is 160 mm
It is 5% (4770/5024 = 0.95) more than that at the time of. Since both have almost the same CF ₄ mole fraction, S
The difference in the iF ₄ mole fraction appears as the difference in the etch rate. From this, it is clear that the etch rate strongly depends on the concentration of SiF ₄ , which is a byproduct gas.

Assuming that SiF ₄ is adsorbed on the surface of the silicon wafer, the higher the concentration of SiF ₄ , the greater the amount adsorbed on the surface of the wafer and the more the etching reaction is hindered.
In this case, it is desirable to adopt the Langmuir adsorption isotherm as the reaction rate equation. Also, the shower diameter is 2r _0.
Becomes larger, the etching uniformity improves.

Table 6 2r ₀ CF ₄ mole fraction SiF ₄ mole fraction Etch rate (mm) (A / min) 160 4.384 × 10 ^-2 1.814 × 10 ^-3 5024 (6.9%) 180 4.379 × 10 ^-2 1.873 × 10 ^-3 5023 (6.4%) 210 4.343 × 10 ^-2 2.294 × 10 ^-3 4770 (5.2%) Tables 7 and 8 show the results of an experimental study on the relationship between gas concentration and contact hole shape. Table 7 shows the results measured at a distance of 10 mm from the wafer center, and Table 8 shows the results measured at a distance of 90 mm from the wafer center. Here, the "taper angle" refers to the inclination angle of the peripheral wall of the contact hole 94 shown in FIG.

Shower diameter 2r at any position
_The taper angle becomes smaller as ₀ becomes larger and as the CF ₄ concentration becomes lower. On the other hand, the taper angle increases as the SiF ₄ concentration decreases.

Table 7 2r ₀ CF ₄ mole fraction SiF ₄ mole fraction Tapered angle (mm) (°) 160 4.421 × 10 ^-2 1.417 × 10 ^-3 88.0 180 4.382 × 10 ^-2 1.851 × 10 ^-3 86.8 210 ^{4.339 × 10 -2 2.330 × 10 -3} 85.8 table 8 2r ₀ CF ₄ mole fraction SiF ₄ mole fraction taper angle (mm) (°) 160 4.384 × 10 -2 1.814 × 10 -3 87.6 180 4.379 × 10 - ² 1.873 × 10 ^-3 87.0 210 4.343 × 10 ^-2 2.294 × 10 ^-3 86.0 In the above embodiment, the high frequency application method employs the plasma etching (PE) mode, but the power split mode or the reactive ion is used. An etching (RIE) mode may be adopted.

[0066]

According to the plasma etching system of the present invention, the polymer does not adhere to the gas ejection holes of the shower electrode and can be continuously and stably used for a long time. Therefore, the wafer is not contaminated by the generated polymer, and the yield of semiconductor devices is dramatically improved.

Further, since the flow velocity of the gas passing through the pores of the shower electrode is made high, etching in a wide range from a high aspect ratio to a low aspect ratio can be realized. Furthermore, by increasing the flow velocity of the gas passing through the pores of the shower electrode, the uniformity of plasma is improved,
The stable region of plasma discharge expands to 0.15 to 3.0 Torr, and etching with a high aspect ratio (up to aspect ratio 3) becomes possible.

[Brief description of drawings]

FIG. 1 is a sectional block diagram showing an overall outline of a plasma etching system according to an embodiment of the present invention.

FIG. 2 is a plan view showing a shower electrode.

FIG. 3 is a partially enlarged plan view showing an enlarged part of a shower electrode.

FIG. 4 is a vertical cross-sectional view showing a part of pores of a shower electrode.

FIG. 5 is a plan view showing another shower electrode.

FIG. 6 is a partially enlarged plan view showing an enlarged part of another shower electrode.

FIG. 7 is a characteristic diagram showing the effect of the present invention.

FIG. 8 is an enlarged vertical cross-sectional view showing a part of a wafer having a high aspect ratio etched.

FIG. 9 is a sectional model view schematically showing the upper electrode unit.

FIG. 10 is a simulation model diagram showing a gas flow velocity distribution.

FIG. 11 is a simulation model diagram showing a gas flow velocity distribution.

FIG. 12 is a simulation model diagram showing a gas flow velocity distribution.

FIG. 13 is a characteristic diagram showing gas velocity immediately above a wafer.

FIG. 14 is a characteristic diagram showing gas velocity immediately above a wafer.

FIG. 15 is a model diagram schematically showing a gas shower between an electrode and a wafer.

FIG. 16 is a simulation model diagram showing the SiF ₄ gas concentration distribution.

FIG. 17 is a simulation model diagram showing a SiF ₄ gas concentration distribution.

FIG. 18 is a simulation model diagram showing the SiF ₄ gas concentration distribution.

FIG. 19 is a characteristic diagram showing CF ₄ gas concentration immediately above a wafer.

FIG. 20 is a characteristic diagram showing SiF ₄ gas concentration immediately above a wafer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Processing chamber, 2 ... Upper electrode unit, 3 ... Shower electrode, 6 ... Wafer holding stand, 11 ... Exhaust pipe, 12 ... High frequency power supply, 51, 52 ... Baffle plate, 53 ... Cooling plate, 54 ... Cathode plate, 55 ... Pores, 61 ... Chuck electrode, 70 ... Controller, 71a, 71b, 71c ... Gas supply source, 7
2a, 72b, 72c ... Mass flow controller

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Giichi Ito Nishihachiman, Ryuo-cho, Nakakoma-gun, Yamanashi Prefecture (No address) Inside Kofu Factory, Hitachi, Ltd. (72) Inventor Motohiro Hirano 3-3 Fujibashi, Ome City, Tokyo 2 Hitachi Tokyo Electronics Co., Ltd. (72) Inventor Hikaru Nozawa 3-3 Fujibashi, Ome City, Tokyo 2 Hitachi 3rd Tokyo Electronics Co., Ltd. (72) Hiromitsu Matsuo 3-3 Fujibashi, Ome City, Tokyo 2 Hitachi Inside the Tokyo Electronics Co., Ltd. (72) Inventor Shunichi Imuro 2381-1 Kitashitajo, Fujii-cho, Nirasaki-shi, Yamanashi Tokyo Electron Yamanashi Corporation Inside (72) Inventor Shigeki Tozawa 2381 Kita-Shijojo, Fujii-cho, Narasaki-shi, Yamanashi Kyo Electron Yamanashi Co., Ltd. (72) Inventor Toyo Miura Hosaka Town, Nirasaki City, Yamanashi Prefecture Tsu Sawa 650 Tokyo Electron Kutoron within Co., Ltd.

Claims (10)

[Claims] 1. A container for confining plasma, a means for exhausting the inside of the container, a chuck electrode for holding a substrate,
A showerhead electrode having a large number of pores facing the chuck electrode, a power supply for applying a plasma voltage between the showerhead electrode and the chuck electrode, and a container communicating through the pores of the showerhead electrode through the pores. A means for supplying a gas for plasma generation therein, and a means for controlling the gas supply means such that the gas passing through the pores has a mass flow rate of 620 kg / m ² / hour or more. Characteristic plasma etching system. 2. The plasma etching system according to claim 1, wherein the region where the gas is ejected from the pores extends over a range of 180 mm or more from the center of the shower electrode. 3. The plasma etching system according to claim 1, wherein the region where the gas is ejected from the pores extends over a range of 120 mm or more within a range of 180 mm from the center of the shower electrode. 4. The plasma etching system according to claim 1, further comprising a shower electrode having pores formed at a pitch interval of 6 mm or more. 5. The plasma etching system according to claim 1, further comprising a shower electrode having pores having a gas ejection port diameter of less than 0.8 mm. 6. The total opening area of the pores is 100 to 120 mm.
The plasma etching system according to claim 1, wherein the plasma etching system is in the range of ² . 7. The plasma etching system according to claim 1, wherein a cooling member cooled by a cooling medium is attached to the shower electrode. 8. The plasma etching system according to claim 1, wherein the shower head electrode has a disk shape, and the fine holes are formed in the shower head electrode so as to be arranged in a grid pattern with an equal interval pitch. 9. The plasma etching system, wherein the shower head electrode has a disk shape, and the fine holes are formed in the shower head electrode so as to form a concentric circle array with an equal pitch. 10. The substrate is held by a chuck electrode inside the container, the inside of the container is evacuated so that the inside of the container is in a reduced pressure state, and the mass flow rate is 620 k when passing through the pores of the shower electrode.
A gas for plasma generation is introduced into the container at a rate of at least g / m ² / hour, a voltage is applied between the shower electrode and the chuck electrode, plasma is generated between both electrodes, and the generated plasma acts on the substrate. A plasma etching method comprising: