JP2001023964A - Dry etching method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain high selective ratio with a superior controllability without using any harmful CO gas by using C4F8, CHF3, and O2 gases and the mixed gas of a rare gas for etching. SOLUTION: A C4F8 gas is supplied to a gas supply source 42, a CHF3 gas is supplied to a gas supply source 43, an O2 or CF4 gas is supplied to a gas supply source 44, and an Ar gas is supplied to a gas supply source 45. Then, valves 34, 35, 36, 37, and 32 are opened, thus adjusting the flow rate of gas from each of the gas supply sources 42, 43, 44, and 45 for mixing by mass flow controllers 38, 39, 40, and 41 for supplying to wafers 6a, 6b, and 6c being installed in a treatment chamber 2. As stated above, the O2 gas is added to the mixed gas of C4F8 and CHF3 gases, thus balancing a CF+ ion of a deposition type and a CF3+ ion of an etching type, and hence obtaining high selective ratio with a superior controllability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a dry etching method which can be used for manufacturing a semiconductor integrated circuit, an acceleration sensor using a micromachine, an angular velocity sensor, and the like.

[0002]

2. Description of the Related Art With the recent increase in the degree of integration of semiconductor devices, an etching technique for forming a very narrow contact hole with a high aspect ratio has been required, and silicon, which is generally used as an interlayer insulating film, has been required. A technique of etching an oxide film (SiO ₂ ) with a high selectivity to silicon (Si) is regarded as important.

[0003] As for sensors using a micromachine, small and high-precision sensors such as an acceleration sensor and an angular velocity sensor have been actively developed. In processing a sensor, high accuracy is required for dimensional tolerances in order to suppress variations in its characteristics.

In these processes, a reactive ion etching (RIE) method is used in which an etching gas is introduced into a processing chamber and plasma is generated in order to etch a silicon oxide film. In this case, as an etching gas to be used, a C _X F _Y- based gas is generally used, and recently, a C ₄ F ₈ (octafluorocyclobutane) gas which can be expected to have a high selectivity and a high etch rate has been used. .

C ₄ F ₈ gas has a large C / F ratio and is easy to form a deposition on silicon, so that it has a feature that it is easy to secure a selectivity. However, C ₄ F ₈ gas alone is rarely used. The reason is that C ₄
The reason for this is that the etching rate of the F ₈ gas is lower than that of the F ₈ gas compared to the etching effect, and the F ₈ gas is sometimes not etched.

[0006] Therefore, C, which is an excessive depot species at the time of dissociation,
To reduce F ⁺ , CO (carbon monoxide) gas is usually added. In some cases, O ₂ gas is added without using CO gas (see JP-A-9-129611).

As another typical etching gas, CHF ₃ gas containing hydrogen atoms is used for the purpose of reducing excess fluorine radicals. However, this gas may not be used alone. It is used as a mixed gas with CF ₄ gas or Ar (argon) gas to increase the etch rate.

[0008]

In the above-described process of adding CO gas to C ₄ F ₈ gas, harmful CO is used, so care must be taken in handling gas and treating exhaust gas. In addition, in the case where O ₂ gas is added to C ₄ F ₈ gas, an effect of reducing CF ⁺ of excess depot species can be expected, but a small amount of O ₂ gas cannot be removed because fluorine radicals which cause deterioration of the selectivity cannot be removed. There are difficulties in controllability, such as the selection ratio sharply deteriorating due to the addition of _two gases.

On the other hand, in a process mainly using CHF ₃ gas, fluorine radicals can be effectively removed, but the amount of CF ⁺ as a deposition species is relatively small as compared with CF ₃ ^{+ as an} etching species. There was a limit to raising the ratio.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an etching method which can control a high selectivity without using a harmful CO gas.

[0011]

The present inventors have conducted research on the etching of a silicon oxide film which can ensure a high selectivity with respect to silicon, and have obtained the following findings.

Generally, the etch rate of a silicon oxide film and silicon is correlated with the relative amount of fluorocarbon ions (CF ⁺ , CF ₂ ⁺ , CF ₃ ⁺ ) present in plasma,
The etch rate of the silicon oxide film increases as the number of CF ₃ ⁺ ions increases, and the deposition rate of silicon increases as the number of CF ⁺ ions increases, so that the etch rate decreases. That is, in order to increase the selectivity of the silicon oxide film with respect to silicon, it is necessary to increase both CF ₃ ⁺ ions and CF ⁺ ions. The partial pressure ratio of the fluorocarbon ion can be measured using a mass spectrometer (Q-mass).

Therefore, the conventional etching gas described above is used.
Among them, CHF, which has a problem in increasing the selectivity,_Threegas,
CF_FourGas and Ar gas mixture (CHF_Three/ CF
_Four/ Ar gas), CF_Three ⁺Ions and CF⁺ion
Was measured. CHF_Three/ CF_Four/ Ar gas in parallel
Introduced into a flat plate etching system,
CF is generated at the time⁺With ions
CF_Three ⁺The ratio of ions was measured. The condition at this time is C
HF_Three: 250 sccm, CF_Four12.5 sccm,
Ar: 250 sccm, gas pressure 0.1 Torr, RF power
And 900 W. As a result, the partial pressure of Ar ions is reduced to 1
CF assuming 00%⁺Ions and CF _Three ⁺Ion ratio
Was 3.26% and 7.63%, respectively.

[0014] Next, utilizing the respective advantages of C ₄ F ₈ gas and CHF ₃ gas, C ₄ F ₈ gas, the mixed gas of CHF ₃ gas and Ar gas _{(C 4 F 8 / CHF 3} / Ar gas) And the partial pressures of CF ₃ ⁺ ions and CF ⁺ ions were measured. C ₄ F ₈ / CHF ₃ / Ar gas is introduced into the parallel plate type etching apparatus in the same manner as above, and a high frequency is applied to generate plasma, and CF ⁺ generated at that time is generated.
The ratio of ions to CF ₃ ⁺ ions was measured. The conditions at this time are as follows: C ₄ F ₈ : 30 sccm, CHF ₃ : 100 sc
cm, Ar: 300 sccm, gas pressure 0.1 Torr,
The RF power was 900 W. As a result, when the partial pressure of Ar ions was 100%, the ratios of CF ⁺ ions and CF ₃ ⁺ ions were 6.08% and 11.61%, respectively. Therefore, CF ₃ ^{+ is} higher than the conventional etching gas.
The partial pressures of the ions and the CF ⁺ ions both increase, and the selectivity of the silicon oxide film to silicon can be increased.

Further, the above C ₄ F ₈ / CHF ₃ / Ar
A mixed gas in which O ₂ was added to the gas was studied.
The conditions at this time are: C ₄ F ₈ : 30 sccm, CH
F ₃ : 100 sccm, Ar: 300 sccm, O ₂ :
5 sccm, gas pressure 0.1 Torr, RF power 900
W. As a result, when the partial pressure of Ar ions was 100%, the ratios of CF ⁺ ions and CF ₃ ⁺ ions were 4.73% and 9.37%, respectively.

Further, a mixed gas obtained by adding CF ₄ to the above C ₄ F ₈ / CHF ₃ / Ar gas was examined.
The conditions at this time are as follows: C ₄ F ₈ : 15 sccm, CH
F ₃ : 100 sccm, Ar: 300 sccm, C
F ₄ : 50 sccm, gas pressure: 0.1 Torr, and RF power: 900 W. As a result, the partial pressure of Ar ions is reduced to 10
The ratios of CF ⁺ ions and CF ₃ ⁺ ions at 0% were 5.76% and 15.17%, respectively.

From these results, C ₄ F ₈ / CHF ₃ /
In an Ar gas and an etching gas to which O ₂ or CF ₄ is added, both CF ⁺ ions and CF ₃ ⁺ ions always exceed CHF ₃ / CF ₄ / Ar gas, so that etching with a high selectivity can be performed. . Note that C ₄ F
By adding O ₂ or CF ₄ to the ₈ / CHF ₃ / Ar gas, CF ⁺ ions of the deposition type and C ⁺ of the etching type are added.
F ₃ ⁺ ions can be kept in a well-balanced manner.

The present invention has been made based on the above study,
In the dry etching method according to the first aspect,
_The etching is performed using a mixed gas of ₄ F ₈ gas, CHF ₃ gas, O ₂ gas and rare gas.

By adding the O ₂ gas to the mixed gas of the C ₄ F ₈ gas and the CHF ₃ gas as described above, CF ⁺
The ions and the CF ₃ ⁺ ions of the etching species are kept in a well-balanced state, and the controllability and high selectivity can be obtained.

[0020] In this case, as in the second aspect of the present invention,
And C_FourF₈Gas and CHF_ThreeGas and O _Two3-1 gas
The ratio is 5:10 to 50: 1, and the flow rate of the rare gas is
Use a mixed gas that provides 60-80% of the gas flow rate
Is preferred.

Further, in the dry etching method according to the third aspect, C ₄ F ₈ gas, CHF ₃ gas, CF ₄
The etching is performed using a mixed gas of a gas and a rare gas.

Also in the present invention, CF ⁺ ions of the depot type and CF ₃ ⁺ ions of the etching type are maintained in a well-balanced state.
A high selectivity can be obtained with good controllability.

In this case, the C ₄ F ₈ gas, the CHF ₃ gas, and the CF ₄ gas are 1 to 1 as in the _{fourth aspect} of the present invention.
It is preferable to use a mixed gas having a ratio of 0: 2 to 20: 1 and a flow rate of the rare gas of 60 to 80% of the total gas flow rate.

As the rare gas, in addition to Ar gas, He (helium) gas, Xe (xenon) gas,
Kr (krypton) gas, Ne (neon) gas, or the like can be used.

[0025]

FIG. 1 shows a cross section of an etching apparatus 1 used for carrying out an etching method according to the present embodiment.

The processing chamber 2 in the etching apparatus 1
Is made of, for example, aluminum that has been subjected to anodized aluminum oxide, and the processing chamber 2 is grounded together with the counter electrode 4 via a ground wire. Further, a high frequency power of, for example, 13.56 MHz is applied from the high frequency power supply 5 to the processing chamber 2, and the lower electrode 3 on which the wafer is installed and the reaction gas parallel to the lower electrode 3 can be flowed at equal intervals in a shower shape. A counter electrode 4 having a gas supply hole is provided. The lower electrode 3 and the counter electrode 4 are structured to circulate cooling water or hot water whose temperature is controlled by a chiller or the like as necessary to prevent an unnecessary rise in temperature of the electrodes and to reduce adhesion of deposits. It has become.

Wafers 6a, 6b, 6 to be etched
“c” has a structure in which a plurality of sheets are simultaneously provided on the lower electrode 3.

The processing chamber 2 is provided with a gas inlet 31, and a gas inlet pipe 32 and a valve 33 are connected to the gas inlet 31. Gas supply sources 42, 43, 4
The gases from 4 and 45 are supplied to gas introduction pipes 32 via mass flow controllers 38, 39, 40 and 41 for flow control, and via valves 34, 35, 36 and 37, respectively.

In this embodiment, C _{4 is} supplied to the gas supply source 42.
An F ₈ gas is supplied, a CHF ₃ gas is supplied to a gas supply source 43, and an O ₂ gas (or CF ₄ gas) is supplied to a gas supply source 44.
Gas), and an Ar gas is supplied to the gas supply source 45.

On the other hand, an exhaust pipe 51 is connected to a lower portion of the processing chamber 2, and a vacuum pump 5 is connected through the exhaust pipe 51.
The pressure is reduced by evacuation means such as 2 and the gas supply sources 42 to
With the gas supplied from 45, the inside of the processing chamber 2 can be maintained at a degree of vacuum of, for example, several tens mTorr to 1 Torr.

In the above-described etching apparatus 1, by opening the valves 34, 35, 36, 37 and 32, the gases from the gas supply sources 42, 43, 44 and 45 are supplied to the mass flow controllers 38 and 39, respectively. , 4
The flow rate is adjusted by 0 and 41, and the mixed gas is supplied to the gas introduction pipe 32. This mixed gas is supplied from the counter electrode 4 to the wafers 6a, 6b, 6c placed on the lower electrode 3 in a shower shape. Further, the inside of the processing chamber 2 is a vacuum pump 5.
Due to 2, the vacuum degree is maintained at several tens mTorr to about 1 Torr. Then, by applying high-frequency power to the lower electrode 3, plasma is generated between the lower electrode 3 and the counter electrode 4, and the wafers 6a, 6b, 6c are etched. The wafers 6a, 6b, and 6c have a silicon oxide film formed on silicon, and the silicon oxide film is selectively etched by the above-described etching.

Next, experimental results for setting the flow rates of the respective gases used for the above-described etching will be described.

[0033]

(Embodiment 1) Using the etching apparatus 1 described above, the gas used for the etching process was C ₄ F ₈ / C
Using a mixed gas of HF ₃ / O ₂ / Ar, the flow rate of C ₄ F ₈ gas is 30 sccm, and the flow rate of CHF ₃ gas is 100 s
An etch rate (silicon oxide) when the flow rate of the O ₂ gas was changed by applying high-frequency power of 900 W while maintaining the processing chamber 2 at a vacuum of 0.1 Torr while the flow rate of the Ar gas was 300 sccm and the flow rate of the Ar gas was 300 cm. Film etch rate)
And the selectivity (selectivity between silicon oxide film and silicon) were examined. The results are shown in the graph of FIG. According to FIG. 2, the etch rate increases with the increase of the flow rate of O ₂ gas, the selection ratio between the flow rate is 2~5sccm of O ₂ gas is ∞
It turns out that it becomes.

The flow rate of the CHF ₃ gas is set to 100 scc.
m, the flow rate of O ₂ gas is 5 sccm, and the flow rate of Ar gas is 3
00 sccm, and the degree of vacuum in the processing chamber 2 is 0.1 Torr.
r, 900 W of high frequency power is applied, and C
₄ F ₈ was examined Engineering Tchireto the selection ratio when changing the flow rate of the gas. The results are shown in the graph of FIG. According to FIG. 3, the flow rate of the C ₄ F ₈ gas is 15 to 30 sccm.
It can be seen that the selection ratio becomes Δ between.

Next, the flow rate of the C ₄ F ₈ gas is set to 30 scc.
m, the flow rate of O ₂ gas is 5 sccm, and the flow rate of Ar gas is 3
00 sccm, and the degree of vacuum in the processing chamber 2 is 0.1 Torr.
r, 900 W of high frequency power is applied, and C
The etch rate and the selectivity when the flow rate of the HF ₃ gas was changed were examined. The results are shown in the graph of FIG. According to FIG. 4, the selectivity is initially low when the flow rate of the CHF ₃ gas is increased, but rapidly increases when the flow rate exceeds 50 sccm, and becomes 急 激 at 100 sccm.

According to the study of the present inventors based on the above experimental results, the ratio of C ₄ F ₈ gas, CHF ₃ gas and O ₂ gas is 3-15: 10-10: 1, and When a mixed gas in which the flow rate of the Ar gas is 60 to 80% of the total gas flow rate is used, the silicon oxide film can be etched with good control while securing a very high selectivity to the underlying silicon. . (Embodiment 2) Using the etching apparatus 1 described above, the gas used in the etching process was C ₄ F ₈ / CHF ₃ / C
Using a mixed gas of F ₄ / Ar, the flow rate of C ₄ F ₈ gas is 30 sccm, the flow rate of CHF ₃ gas is 100 sccm,
With the flow rate of Ar gas set to 300 sccm and the degree of vacuum in the processing chamber 2 kept at 0.1 Torr, high-frequency power was applied at 900 W, and the etch rate and selectivity when the flow rate of CF ₄ gas was changed were examined. Was. The results are shown in the graph of FIG. According to FIG. 5, the etch rate increases as the flow rate of the CF ₄ gas increases, and the CF ₄ flow rate becomes 50 sc.
It can be seen that the selectivity becomes Δ in cm.

The flow rate of CHF ₃ gas is set to 100 scc.
m, CF ₄ flow rate 50 sccm, Ar gas flow rate 30
0 sccm, and the degree of vacuum in the processing chamber 2 is 0.1 Torr.
, While supplying 900 W of high frequency power, and C ₄
F ₈ was examined Engineering Tchireto the selection ratio when changing the flow rate of the gas. The results are shown in the graph of FIG. This figure 6
According to the graph, the selectivity becomes ∞ when the flow rate of the C ₄ F ₈ gas is between 15 and 30 sccm.

According to the study of the present inventors based on the above experimental results, C ₄ F ₈ gas, CHF ₃ gas and CF ₄
If the gas is mixed at a ratio of 1 to 10: 2 to 20: 1 and the flow rate of the Ar gas is 60 to 80% of the total gas flow rate, a very high selectivity to the underlying silicon is obtained. , The silicon oxide film can be etched with good control.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view of an etching apparatus used in an embodiment of the present invention.

FIG. 2 shows C ₄ F as a gas used in the etching process.
₉ is a graph showing an etch rate and a selectivity when an O ₂ gas flow rate is changed using a mixed gas of ₈ / CHF ₃ / O ₂ / Ar.

FIG. 3 shows C ₄ F as a gas used in the etching process.
₈ / CHF ₃ / O ₂ / Ar mixed gas and C ₄ F
₈ is a graph showing an etch rate and a selectivity when changing a gas flow rate.

FIG. 4 shows C ₄ F as a gas used in the etching process.
₈ / CHF ₃ / O ₂ / Ar mixed gas
₃ is a graph showing an etch rate and a selectivity when changing a gas flow rate.

FIG. 5 shows C ₄ F as a gas used in the etching process.
₈ / CHF ₃ / CF ₄ / Ar mixed gas
₄ is a graph showing an etch rate and a selectivity when changing a gas flow rate.

FIG. 6 shows C ₄ F as a gas used in the etching process.
₈ / CHF ₃ / CF ₄ / Ar mixed gas and C ₄
5 is a graph showing an etch rate and a selectivity when the F ₈ gas flow rate is changed.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Etching apparatus, 2 ... Processing chamber, 3 ... Lower electrode, 4 ...
Upper electrode, 5 ... High frequency power supply, 6 ... Wafer, 31 ... Gas inlet, 32 ... Gas inlet pipe, 33,34,35,36,3
7 valves, 38, 39, 40, 41 ... mass flow controllers, 42, 43, 44, 45 ... gas supply sources, 51
... exhaust pipe, 52 ... vacuum pump.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Muneo Yorinaga, 14, Iwatani, Shimowakaku-cho, Nishio-shi, Aichi Prefecture Inside Japan Automotive Parts Research Institute (72) Inventor, Takeshi Fukada 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture F-term in DENSO Corporation (reference) 4K057 DA13 DB06 DD01 DE06 DE08 DE14 DE20 DG07 DM02 DN01 5F004 AA05 BA04 BB13 BB25 BC03 CB04 DA00 DA01 DA16 DA22 DA23 DA26 DB03 EB01 EB03

Claims (4)

[Claims] 1. A dry etching method, wherein etching is performed using a mixed gas of a C ₄ F ₈ gas, a CHF ₃ gas, an O ₂ gas and a rare gas. 2. The method according to claim 1, wherein the C ₄ F ₈ gas, the CHF ₃ gas, and the O ₂ gas are in a ratio of ₃ to 15:10 to 50: 1.
The dry etching method according to claim 1, wherein a mixed gas is used such that the flow rate of the rare gas is 60 to 80% of the total gas flow rate. 3. A dry etching method, wherein etching is performed using a mixed gas of C ₄ F ₈ gas, CHF ₃ gas, CF ₄ gas and a rare gas. 4. A method according to claim 1, wherein said C ₄ F ₈ gas, said CHF ₃ gas, and said CF ₄ gas are in a ratio of 1-10: 2-20: 1,
The dry etching method according to claim 3, wherein a mixed gas is used such that the flow rate of the rare gas is 60 to 80% of the total gas flow rate.