JPH05182935A - Dry-etching method - Google Patents

Abstract

PURPOSE:To extend the selecting range of etching state by a method wherein the mixed gas containing the first gas containing bromine and the second gas containing halogen excluding bromine is fed to a processed body and then a polysilicon exposed layer is etched away using a plasma comprising the mixed gas turned into plasma state. CONSTITUTION:A silicon oxide film, a polysilicon film are laminated on a silicon substrate and then a wafer W formed on the polysilicon film as the processed body is mounted on a circular lower electrode 2B. Next, HBr gas as the first gas and HCl gas as the second gas are led into a vacuum chamber 1 through a gas leading-in pipe and gas diffused plates 13, 14 to be vacuumized through an exhaust pipe 15. Next, a plasma is produced by impressing the space between an upper electrode 2A and the lower electrode 2B with high-frequency power and simultaneously irradiating the space with ultraviolet rays to etch away the wafer W on the polysilicon film. Through these procedures, a high selection ratio is shown at high etching rate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching method for etching a semiconductor wafer, for example.

[0002]

2. Description of the Related Art In the process of processing a semiconductor wafer, dry etching is carried out, for example, for the purpose of separating capacitors and elements or forming contact holes.
In such etching, various requirements are made, such as a large selection ratio with respect to the resist film and the underlying film, smooth verticality (good anisotropy) of the side wall of the groove, a large etching rate, and a small residue. Required.

Therefore, conventionally, for example, a gas such as CCl ₄ is used, and an electric field is applied to the gas to generate plasma, and the film is removed by Cl contained in the plasma, while the organic component of the resist film and C are removed by C. Silicon (Si)
At the same time, a protective film is formed to secure anisotropy, and the conditions of obtaining a high etching rate and a high selection ratio are found by adjusting the gas flow rate and the electric power value to perform etching.

[0004]

However, in the conventional method, the anisotropic shape is obtained by providing the side wall protecting action and the film removing action in one kind of gas. When the protective action is strengthened, it is difficult to find conditions under which both actions are optimally exerted, for example, a part of the polymer adheres as a residue to an unexpected place.

Moreover, the degree of each action also changes depending on other conditions such as the magnitude of the electric power value, that is, the energy of the plasma, so that the optimum condition is to satisfy a large etching rate, a good anisotropy and a high selection ratio at the same time. It is very difficult to find out.

For example, in order to obtain a high etching rate, it is sufficient to increase the plasma energy, but in this case, the sputtering action is too strong and the selection ratio with respect to the underlying film cannot be obtained, resulting in overetching. When the energy of plasma is reduced, the selection ratio increases, but this time the etching rate also decreases, and if there is an oxidized portion on the surface of the film to be etched, the removal action weakens and it may remain as a column-shaped residue.

The present invention has been made under such a background, and an object thereof is to provide a method capable of achieving a good anisotropic etching while obtaining a high selection ratio and a large etching rate. ..

[0008]

According to a first aspect of the present invention, there is provided a step of placing an object to be processed including a polysilicon exposed layer on one of a pair of electrodes facing each other, and a first step including bromine. Gas and a second gas containing a halogen other than bromine are supplied onto the object to be processed, and a high frequency voltage is applied between the pair of electrodes to turn the mixed gas into plasma, Etching the exposed polysilicon layer with plasma.

According to a second aspect of the invention, the distance between the pair of electrodes is 6
~ 8mm, the surface temperature of the object to be treated is 60 ~ 100
It is characterized by being set at ℃.

[0010]

When, for example, a mixed gas of HBr gas and HCl gas is supplied to the object to be processed on the electrodes and a high-frequency voltage is applied between the electrodes to perform etching by plasma obtained,
It is presumed that r reacts with, for example, an organic component of the resist film or silicon (Si) to generate a polymer, whereby sidewall protection is performed, and Cl removes the polysilicon film, for example. Therefore, the side wall protecting action and the film removing action are respectively shared by the two kinds of gases, so that optimum etching can be performed by controlling the flow rate ratio of these two gases.

[0011]

EXAMPLE An example of the present invention will be described below with reference to FIG.
FIG. 3 is a diagram showing an example of an apparatus for performing an etching process.

A gas introducing pipe 11 for introducing a processing gas is connected to the vacuum chamber 1 shown in FIG. 1, and an outlet region of the gas introducing pipe 11 is provided with a gas for uniformly introducing the gas. An introduction chamber 12 is formed.

Between the gas introduction chamber 12 and the vacuum chamber 1, there are provided first and second gas diffusion plates 13 and 14 made of, for example, alumite, and the first gas diffusion plate on the preceding stage side. As shown in FIG. 2A, the hole 13 has a hole 13a having a diameter of 3 to 5 cm, for example, at the central portion and four peripheral portions thereof, and the second gas diffusion plate 14 on the rear stage side.
As shown in FIG. 2B, the holes 14a having a diameter of, for example, about 0.5 to 1 mm are radially formed. The gas diffusion plates 13 and 14 and the members surrounding them constitute the upper electrode 2A in this example.

Below the upper electrode 2A, a lower electrode 2B which also serves as a mounting portion for the semiconductor wafer W is arranged so as to face the upper electrode 2A, and the upper electrode 2A has a high frequency through a capacitor C. The lower electrode 2B is connected to the power supply RF and grounded. Inside the lower electrode 2B, the wafer W is cooled and its surface temperature is, for example, 70%.
A flow path (not shown) for the cooling fluid is formed to maintain the temperature in the range of 120 ° C.

Further, an ultraviolet lamp 3 is arranged on the side surface of the vacuum chamber 1 through a window portion 31, and ultraviolet rays from the lamp 3 are applied to the plasma discharge region. By using the energy of ultraviolet rays in this way, plasma can be generated with low power energy, and sputter damage of the active species to the wafer can be suppressed. In the figure, 15 is a gas exhaust pipe, 16 is a vacuum pump connected to the gas exhaust pipe, and 17 is an APC (au
tomatic pressure control
r).

Next, a specific example of etching using the above apparatus will be described. A silicon oxide (SiO ₂ ) film and a polysilicon film are stacked in this order on the silicon substrate, for example, with a thickness of 200 Å and 4000 Å, respectively, and further on the surface of the polysilicon film.
For example, a wafer W having a diameter of 15 cm on which a resist film having a thickness of 10000 angstrom is formed is mounted on a circular lower electrode 2B having a diameter of, for example, 18 cm as an object to be processed,
HBr gas that is the first gas and HC that is the second gas
l gas is introduced into the vacuum chamber 1 through the gas introduction pipe 11 and the gas diffusion plates 13 and 14 at a flow rate of 30 SCCM and 200 SCCM, respectively, and is evacuated through the exhaust pipe 15 so that the gas pressure is 600 m, for example.
Set to Torr.

Then, for example, a frequency of 1 is applied between the electrodes 2A and 2B.
The polysilicon film of the wafer W was etched by applying a high frequency power of 3.56 MHz and a power value of 200 W and irradiating the ultraviolet lamp 7 to generate plasma.
At this time, the surface temperature of the wafer W is about 100 ° C., and the upper electrode 2
The temperatures of A and the lower electrode 2B were 40 ° C. and 60 ° C., respectively. The surface temperature of the wafer W was measured using a thermo label.

The etching rate and the selection ratio in such etching were as follows. That is, the etching rate of polysilicon is 3549 angstroms / minute, respectively, and the selection ratio to silicon oxide (etching rate of polysilicon / etching rate of silicon oxide) and the selection ratio to resist (etching rate of polysilicon / etching rate of resist) ) Is 2 each
It was 0.8 and 6.5.

Further, in the above etching, when the power values were 150 W and 250 W, that is, the power values per unit area of the wafer were 0.85 to 1.41 W / cm ² , the same etching as that described above was carried out. The results of speed and selectivity were as shown in FIG. Figure 3
In addition, the above-mentioned results are also shown in the table, ◯ indicates the etching rate of polysilicon, Δ indicates the selection ratio for silicon oxide, and × indicates the selection ratio for resist.

After the etching was completed under each condition, the surface of the wafer was observed with an SEM photograph. As a result, the polysilicon film was cut almost perpendicularly to the base film without overetching the base film. Almost no residue was attached to the part, and the cut was made with good right angle.

That is, according to this embodiment, the etching rate is as high as about 2400 angstroms / minute to 3500 angstroms / minute and about 16 times for silicon oxide.
Polysilicon can be etched with a high selection ratio of ~ 35,
It is understood that etching with good anisotropy can be achieved without overetching, and a high selection ratio can be obtained for the resist.

Next, using the apparatus of FIG. 1, Cl ₂ gas is introduced as a _second gas into the vacuum chamber 1 instead of HCl gas, and the flow rate ratio of HBr to the total flow rate is set to 2
Set to 5%, 50%, and 75%, respectively (Cl ₂ flow rate ratios are 75%, 50%, and 25%, respectively), and set the power value to 1
When the same wafer W as described above was etched at 75 W, the results of the etching rate and the selection ratio are shown in FIG.
It was as shown in. In FIG. 4, ◯ is the etching rate of polysilicon, Δ is the selection ratio for silicon oxide, and X is the selection ratio for resist.

As can be seen from these results, even when HBr gas and CL ₂ gas are used as a mixed gas, the selectivity is as high as about 25 to 50 for silicon oxide and 2
Polysilicon can be etched at a large rate of 000 to 3000 angstrom / min, and a large selection ratio can be obtained for resist.

[0024] However Observation of the surface of the wafer after each etched with SEM photograph, the flow rate of HBr gas is _{75% (HBr75 / CL 2 25} ) base film (silicon oxide as conditions those shown in FIG. 5 of the A large number of columnar residues 41 a were formed on the film 41. In FIG. 5, 42 is a polysilicon film and 43 is a resist film. Also HBr
Gas flow rate of 25% for (HBr25 / _CL 2 75) conditions things, the columnar residue was not observed at all, the flow rate of HBr gas is 50% (HBr50 / C
The slightly columnar residues those conditions L 2 ₅₀₎ were observed.

Next, such a phenomenon will be considered together with the fact that a high selection ratio can be obtained as described above. First, HBr
As the gas flow rate ratio increases, the amount of residue increases, so that Cl (chlorine) mainly removes polysilicon, while Br (bromine) forms a polymer together with silicon and the organic components in the resist film, It is considered that this adheres to the side wall of the polysilicon film and becomes a protective film, and that anisotropy is obtained by this.

When the flow rate ratio of HBr becomes considerably large, the amount of the polymer becomes excessive, and as a result, the polymer is presumed to be deposited and deposited on the portions other than the side wall and appear as columnar residues.

Since such a residue acts as an impurity on the device and impairs its characteristics, generation of the above residue is suppressed when etching is performed with a mixed gas of HBr gas and CL ₂ gas. For mixed gas (H
The flow rate ratio of HBr gas to Br + CL ₂ ) is preferably 50% or less. If the flow rate ratio of HBr gas is too small, the side wall protection function is deteriorated, and the side wall is scooped and undercut, so that the flow rate ratio of HBr gas is preferably in the range of 5 to 50%.

As described above, the side wall protection function of Br and C
In order to secure the anisotropic etching due to the interaction with the film removal function of l, it is important that the amount of Br relative to Cl does not exceed a certain limit value in order to suppress the formation of columnar residues. However, the limit value is considered to depend on the type of gas that produces Br and the type of gas that produces Cl. Experiments were conducted in advance to determine the flow rate ratio at which columnar residues are produced. It is necessary to keep it.

When the above-mentioned wafer was etched with a mixed gas of HBr gas and HCl gas, at least HBr gas of 10 to 50 SCCM, H
When the Cl gas is in the range of 150 to 300 SCCM,
Good etching with good corner right angle could be performed without generating columnar residues.

Here, the halogen that performs the removing function is not limited to Cl, but may be, for example, F other than Br, and if the gas contains the halogen, various gases can be used as the second gas. it can.

Also, a first component containing Br that fulfills a side wall protection function.
The gas is not limited to HBr gas, and various gases such as Br ₂ gas can be used.

In the present invention, in addition to the gas directly involved in etching, an inert gas such as He may be introduced into the vacuum chamber in order to stabilize the plasma. Furthermore, as the first gas, at least Br
Any other halogen-containing compound may be used as long as it is a gas containing, and the second gas is a gas containing Br if it is a gas containing at least halogen other than Br. Good.

In FIG. 6, an object to be processed (semiconductor wafer) W is fixed by mechanical clamping means, and a gas as a heat transfer medium is introduced into the space between the back surface of the semiconductor wafer W and the upper surface of the lower electrode supporting the same. An example is shown in which polysilicon is etched using the apparatus to be introduced.

In the figure, reference numeral 5 denotes a reaction vessel in which the aluminum surface is anodized and the inside is kept airtight, and an electrode body 52 which can be raised and lowered by an elevating mechanism 51 is provided above the reaction vessel. The electrode body 52 is made of aluminum whose surface is anodized. A cooling means is combined with the electrode body 52, and the cooling means includes, for example, a flow path 53 circulating inside the electrode body 52,
The cooling device 55 is connected to this via a pipe 54, and has a structure in which, for example, water is controlled to a predetermined temperature and circulates.

An upper electrode 6A made of amorphous carbon having a large number of holes formed on the lower surface of the electrode body 52, for example.
Are electrically connected to the electrode body 52 and are provided via the space 60. In this space 60, the gas supply pipe 6
1 is connected, and this gas supply pipe 61 has a role of supplying a reaction gas from a gas supply source (not shown) outside the reaction container 5 to the space 60. This upper electrode 6A
An insulating ring 56 is provided around the electrode body 52. A shield ring 57 is arranged so as to extend from the lower surface of the insulating ring 56 to the peripheral portion of the lower surface of the upper electrode 6A. The shield ring 57 is made of an insulating material such as ethylene tetrafluoride resin so that plasma can be generated in the same diameter as the semiconductor wafer W to be etched. Further, an exhaust pipe 58 for exhausting the inside of the reaction container 5 to a predetermined vacuum state is provided below the reaction container 5. Further, the upper electrode 6A is connected to the high frequency power supply RF.

A flow switch 62 is provided in the middle of the pipe 61 to detect a cooling failure of the upper electrode 6A, and it is determined whether the flow rate of the cooling water flowing in the pipe 54 is within a set range or not. The presence or absence of a flow is detected, and when it deviates from the set value, plasma generation is stopped.

Below the upper electrode 6A, a lower electrode 6B serving as a mounting table for the semiconductor wafer W is provided so as to face the upper electrode 6A. An insulating elastic film 63 (polyimide resin) having a thickness of about 25 μm is attached to the upper surface of the lower electrode 6B with an acrylic adhesive. The elastic film 63 is provided to keep the impedance between the semiconductor wafer W and the lower electrode 6B constant. That is, the impedance between the semiconductor wafer W and the lower electrode 6B tends to be non-uniform because it depends on the distance between the two, but by interposing the insulating elastic film 63 between them, the impedance between them is Since it is dominated by the elastic film 63 rather than the distance between the two surfaces, it tends to be constant.

A clamp ring 65 which can be moved up and down by a drive mechanism 64 such as an air cylinder is arranged on the outer peripheral side of the lower electrode 6B.
The peripheral portion of the semiconductor wafer W is removed by the elastic film 63.
By pressing it to the side, the semiconductor wafer W is held on the upper surface of the lower electrode 6B with a predetermined clamp load.

On the upper surface of the lower electrode 6B, it is assumed that the clamp load applied to the peripheral edge of the semiconductor wafer W by the clamp ring 65 is applied as an evenly distributed load due to the fixing at the peripheral portion of the semiconductor wafer W. The semiconductor wafer W is formed in a convex shape with a curved surface that is substantially the same as the deformed curved surface (uniformly distributed load curved surface).

The lower electrode 6B has a built-in cooling jacket 67 communicating with the cooling water pipe 66 so as to cool the semiconductor wafer W.

Here, a microscopic space is inevitably formed between the elastic film 63 disposed on the upper surface of the lower electrode 6B and the semiconductor wafer W due to the surface roughness of the back surface of the semiconductor wafer W when viewed microscopically. It is formed. Therefore, inside the lower electrode 6B, a gas introduction pipe 7 for introducing a gas serving as a medium for assisting heat transfer between the elastic film 63 and the semiconductor wafer W into the minute space is provided so as to penetrate the central portion. Has been.
The gas introduction pipe 7 is connected to a gas supply source 71 via a pressure adjusting mechanism 70 arranged outside the reaction vessel 5.

The gas introduction pipe 7 is branched in the pressure adjusting mechanism 70, and one branch pipe is sequentially arranged from the gas supply source 71 side.
Flow rate regulator 72 for adjusting the flow rate of the introduced gas, main on-off valve 7
3 and a pressure gauge 74 are provided. The other branch pipe is connected to a vacuum pump 77 via a sub opening / closing valve 75 and a pressure adjusting valve 76. Pressure control valve 76
Is the elastic film 63 measured by the pressure gauge 74.
The computer 78 is automatically controlled by a controller 78 according to a control program stored in advance in accordance with the pressure in the minute space between the semiconductor wafer W and the semiconductor wafer W, and the main opening / closing valve 73 and the auxiliary opening / closing valve 75 are interlocked. Is configured.

As the heat transfer medium gas, an inert gas such as nitrogen gas, helium or argon is used, but it is also possible to use a reaction gas used for processing a semiconductor wafer. Not limited.

In addition to the method of fixing the semiconductor wafer W by the mechanical clamp as described above, the semiconductor wafer W may be fixed by an electrostatic chuck as shown in FIG.

FIG. 7 shows only the lower electrode portion, and the other structure can be exactly the same as that shown in FIG.

Explaining the apparatus of FIG. 7, a table 83 is provided on the lower component member 81 via an insulating portion 82. The table 83 is provided with an electrostatic chuck 84 for fixing and holding the semiconductor wafer W, and a temperature adjusting section 85 for adjusting the temperature of the semiconductor wafer W. The temperature adjusting section 85 has a fluid passage for circulating a cooling fluid. 86 is formed.

Further, a heat transfer gas supply hole 87 is formed penetrating the lower component 81, the insulating part 82 and the table 83, and a heat transfer gas unit is formed at the base end of the heat transfer gas supply hole 87. 88 is connected, and a heat transfer gas such as helium is transferred between the electrostatic chuck 84 and the semiconductor wafer W from the heat transfer gas unit 88 via the gas supply hole 87 at a pressure of, for example, 10 Torr per second 1c.
By supplying c, the temperature difference between the semiconductor wafer W and the electrostatic chuck 87 can be suppressed to 10 ° C. or less.

The electrostatic chuck 84 includes a chuck body 91 which constitutes a lower electrode, a flexible electrostatic attraction sheet 92 which is arranged on the upper surface of the chuck body 91, and a power source for supplying power to the electrostatic attraction sheet 92. And a power feeding sheet 93. The chuck body 91 is made of, for example, aluminum and has a rectangular hole (not shown) that penetrates to the back surface.

The electrostatic attraction sheet 92 includes two insulating polyimide sheets 92a and these polyimide sheets 92a.
Conductive sheet 92b as a dielectric layer interposed between a and
And has a circular shape according to the surface shape of the chuck body 91. The peripheral edges of the two polyimide sheets 92a are fused so as to cover the peripheral edges of the conductive sheet 92b. The conductive sheet 92b is made of a conductor such as copper and has a thickness of about 20 microns, and each polyimide sheet 92a has a thickness of about 50 microns.

The power feeding sheet 93 is an electrostatic attraction sheet 92.
Similarly, it is composed of two polyimide sheets 93a and a conductive sheet 93b interposed between them. The power feeding sheet 93 and the electrostatic attraction sheet 92 need only be made of materials having substantially the same thermal expansion coefficient, and are not necessarily formed of the same material.

A contact is formed at one end of the power feeding sheet 93, and is electrically connected to a contact formed on the back surface of the electrostatic attraction sheet 92. A contact is also formed on the other end of the power feeding sheet 93, and this contact is electrically connected to the lead wire 94. The lead wire 94 is connected to a DC power supply 96 via a switch 95. Therefore, switch 9
5 is turned on, and a DC voltage of, for example, 2 KV can be applied from the DC power supply 96 to the electrostatic attraction sheet 92 via the power feeding sheet 93. The vicinity of the contact at the other end of the power feeding sheet 93 is hermetically sealed by an O-ring (not shown).

In the electrostatic chuck 84, a high voltage (2 KV) is applied by the DC power supply 96 between the semiconductor wafer W and the conductive sheet 92b of the electrostatic attraction sheet 92, and the conductive sheet 92b and the semiconductor wafer W are applied. Positive and negative charges are generated in and, and the semiconductor wafer W can be adsorbed and held by the Coulomb force that acts between them. Adsorption force F at this time
Is theoretically represented by the following equation, where S is the area of the conductive sheet 252, ε is the dielectric constant of the insulating film, V is the voltage, and d is the thickness of the insulating film.

F = (1/2) Sε (V / d) ^{2 The} above adsorption force F is F = 50 g / cm ² when a polyimide sheet is used for the insulating film, and when the ceramic is used. It becomes 200-500 g / cm ² .

In this embodiment, the electrostatic attraction sheet 92 and the chuck body 9 are used as a power feeding means for obtaining the attraction force F.
The sheet for power feeding 93 covered with 1 is used. Therefore, when the electrostatic chuck is used as the chuck of the plasma etching apparatus, since the power feeding sheet 93 is not exposed to the plasma generation space, the life of the sheet can be greatly extended without being damaged by the plasma. ..

Further, in this embodiment, the temperature of the semiconductor wafer W is adjusted, for example, cooled by the temperature adjusting unit 85 when performing the plasma etching. In order to perform such cooling, the semiconductor wafer W and the electrostatic attraction sheet 92
It is indispensable to fill a gas for increasing the heat transfer coefficient between the and (for example, via the device shown in FIG. 6). In other words, heat transfer is not satisfactorily performed with the above-mentioned adsorption force F. Therefore, the attraction force F also has a sealing action for increasing the pressure of the heat conductive gas introduced between the semiconductor wafer W and the electrostatic attraction sheet 92.

Electrostatic attraction sheet 92 and power feeding sheet 9
The insulating material and the conductive material forming the insulating layer and the conductive layer of No. 3 are not limited to polyimide and copper, and a ceramic sheet can be used as the insulating layer. Any material may be used as the material for the electrostatic attraction sheet 92 and the power feeding sheet 93 as long as they have substantially the same thermal expansion coefficient so that thermal deformation of both does not hinder the electrical connection between the contacts.

When the above electrostatic chuck is applied to a plasma etching apparatus, when plasma is generated between the upper electrode and the lower electrode, the semiconductor wafer arranged between these electrodes is affected by the generated plasma. It conducts with the upper electrode, and negative charges are accumulated in the semiconductor wafer. Therefore, the Coulomb force between the electrostatic attraction sheet on which positive charges are accumulated and the semiconductor wafer is increased, and the attraction force of the electrostatic chuck is enhanced.

Next, an example in which the influence of the temperature change of the lower electrode on the etching rate, the etching selection ratio, the etching shape and the like is investigated by using the apparatus shown in FIG. 6 will be described.

Silicon oxide (Si
The O ₂ ) film and the polysilicon film each have a thickness of 200, for example.
For example, a semiconductor wafer W having a diameter of 15 cm and having a resist film having a thickness of 10000 angstroms, which is stacked in this order at a thickness of 4000 angstroms and is formed on the surface of a polysilicon film, is used as a processing object and has a circular lower portion having a diameter of 18 cm, for example. It is placed on the electrode 114, and HBr gas which is the first gas and HCl gas which is the second gas are, for example, 30 sccm and 200 s, respectively.
The gas pressure is set to 500 mTorr by introducing the gas into the reaction vessel 5 through the gas supply pipe 61 at a flow rate of ccm and evacuating through the exhaust pipe 58.

Further, the distance between the electrodes 6A and 6B was set to 8 mm, the clamping pressure was set to 5 Kg / cm ^2, and helium as a cooling gas medium was caused to flow at 5 sccm through the gas introduction pipe 7 with a back pressure of 3 Torr.

Then, for example, a frequency of 1 is applied between the electrodes 6A and 6B.
A high frequency power having a power value of 200 W at 3.56 MHz was applied to generate plasma to etch the polysilicon film of the semiconductor wafer W. At this time, the temperature of the upper electrode 6A is set to 40 ° C., and the temperature of the lower electrode 6B is set to 20 ° C. to 8 ° C.
The temperature was changed to 0 ° C. At this time, the surface temperature of the semiconductor wafer W changed from about 60 ° C to about 120 ° C. The surface temperature of the semiconductor wafer W was measured using a thermo label.

The results are shown in FIGS. 8 and 9 (A)-(D).
Shown in. The temperature in the parentheses on the horizontal axis of the characteristic diagram shown in FIG. 8 is the surface temperature of the wafer. 9A shows the case where the temperature of the lower electrode 6B is 20 ° C., FIG. 9B shows the case where the temperature of the lower electrode 6B is 40 ° C., and FIG. 9C shows the case where the temperature of the lower electrode 6B is 60 ° C. 9C shows the case where the temperature of the lower electrode 6B is 80.degree. In the figure, 97 is a silicon substrate, 98 is a silicon oxide film, 99 is polysilicon, 1
00 is a resist film.

That is, the polysilicon etching rate increased when the temperature of the lower electrode 6B was 80 ° C., but no significant difference was observed at temperatures lower than that. The etching rate for SiO ₂ is lower electrode 6B.
Increased with increasing temperature. The selection ratio of polysilicon to silicon oxide (polysilicon etching rate / silicon oxide etching rate) depends on the lower electrode 6.
It significantly decreased as the temperature of B increased. The selection ratio of polysilicon to resist (polysilicon etching rate / resist etching rate) depends on the lower electrode 6
It increased slightly as the temperature of B increased. Further, when the temperature of the lower electrode 6B was 80 ° C., the side etching became large as shown in FIG. 9 (D).

From the above, it was confirmed that the temperature of the lower electrode 6B is appropriately in the range of 20 ° C to 60 ° C. If the temperature of the lower electrode 6B is lower than 20 ° C,
This is not preferable because there are problems that the etching rate of polysilicon is lowered, etching takes a long time, and foreign matter is likely to remain on the wafer.

Next, an example in which the change in the distance between the lower electrode and the upper electrode affects the etching rate, the etching selection ratio, the etching shape, etc., using the apparatus shown in FIG. 6 will be described.

Silicon oxide (Si
The O ₂ ) film and the polysilicon film each have a thickness of 200, for example.
For example, a semiconductor wafer W having a diameter of 15 cm and having a resist film having a thickness of 10000 angstroms, which is stacked in this order at a thickness of 4000 angstroms and is formed on the surface of a polysilicon film, is used as a processing object and has a circular lower portion having a diameter of 18 cm, for example. Place it on the electrode 6B,
HBr gas that is the first gas and H that is the second gas
Cl gas is, for example, 30 sccm and 200 sccc, respectively.
The gas pressure is set to 500 mTorr by introducing the gas into the reaction vessel 5 through the gas supply pipe 61 at a flow rate of m and evacuating through the exhaust pipe 58.

Further, the clamp pressure was set to 5 kg / cm ^2, and helium as a cooling gas medium was caused to flow at a back pressure of 3 Torr through the gas introduction pipe 122 at 5 sccm.

Then, for example, a frequency of 1 is applied between the electrodes 6A and 6B.
A high frequency power having a power value of 200 W at 3.56 MHz was applied to generate plasma to etch the polysilicon film of the semiconductor wafer W. At this time, the temperature of the upper electrode 6A was 40 ° C., the temperature of the lower electrode 6B was 60 ° C., and the distance between the lower electrode and the upper electrode was changed to 6 mm to 8 mm. The result is shown in FIG.

That is, the etching rate of polysilicon decreases as the distance between the lower electrode and the upper electrode increases, and the etching rate for SiO ₂ slightly decreases when the distance between the lower electrode and the upper electrode is 8 mm. did.
The selection ratio of polysilicon to silicon oxide (polysilicon etching rate / silicon oxide etching rate) showed the maximum value when the distance between the lower electrode and the upper electrode was 8 mm. Further, the etching uniformity of polysilicon is reduced as the distance between the lower electrode and the upper electrode is increased, and when the distance is 10 mm, the in-plane variation of the etching rate is close to 20%. Therefore, the distance between the lower electrode and the upper electrode is 6 mm.
It has been found that a range of up to 8 mm is suitable.

[0070]

According to the present invention, etching is performed using halogen such as Cl and Br, and as can be seen from the experimental examples, Br has a side wall protecting effect and another halogen has a function of removing a film. since the anisotropic etching is presumed that achievable I but coupled with, it is possible to select the state of etching by respectively control the amount of Br and other halogen, therefore, such a conventional example CCL ₄ As compared with the case where one type of gas is used to provide anisotropy, the selection range of the etching state becomes wider. As a result, the etching rate is high with a high selection ratio, moreover there are few residues, and a good right angle cut can be obtained, and good anisotropic etching can be achieved, which is suitable for the etching of fine patterns accompanying the high integration of devices. This is an extremely effective method.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of an apparatus used in an example of the present invention.

FIG. 2 is a plan view showing an example of a gas diffusion plate used in the apparatus of FIG.

FIG. 3 is a characteristic diagram showing the relationship between power supply power, etching rate, and selection ratio.

FIG. 4 is a characteristic diagram showing a relationship between a flow rate ratio of HBr, an etching rate, and a selection ratio.

FIG. 5 is an explanatory diagram showing an enlarged part of the wafer surface.

FIG. 6 is an explanatory diagram showing another example of the apparatus used in the examples of the present invention.

FIG. 7 is an explanatory diagram showing still another example of the apparatus used in the examples of the present invention.

FIG. 8 is a characteristic diagram showing a relationship between an electrode temperature, an etching rate, and a selection ratio.

FIG. 9 is an explanatory diagram showing a state of etching for each electrode temperature.

FIG. 10 is a characteristic diagram showing a relationship between an electrode interval, an etching rate, a selection ratio, and etching uniformity.

[Explanation of symbols]

 1, 5 Vacuum chamber 13, 14 Gas diffusion plate 2A, 6A Upper electrode 2B, 6B Lower electrode 3 Ultraviolet lamp 11, 61 Gas supply pipe 65 Clamp ring 70 Pressure adjusting mechanism 84 Electrostatic chuck 92 Electrostatic adsorption sheet 93 Power feeding sheet

Claims (2)

[Claims] 1. A step of placing an object to be processed including a polysilicon exposed layer on one electrode of a pair of electrodes facing each other, a first gas containing bromine, and a first gas containing halogen other than bromine. Supplying a mixed gas containing the second gas onto the object to be processed, applying a high frequency voltage between the pair of electrodes to turn the mixed gas into plasma, and etching the exposed polysilicon layer with the plasma. And a dry etching method comprising: 2. The dry etching method according to claim 1, wherein the distance between the pair of electrodes is set to 6 to 8 mm, and the surface temperature of the object to be processed is set to 60 to 100 ° C.