JPH07307327A - Method and apparatus for surface treatment - Google Patents

Abstract

PURPOSE:To increase etching rate and etching selectivity, and deposit a film having high step-difference coverage at a high speed, by setting the retention time of treatment gas in a process chamber, the time constant of dissociation of the treatment gas, and the time constant of radical extinction on the inner wall of the process chamber as specified values. CONSTITUTION:When amorphous silicon is deposited by using silane plasma, taup=V/Sp obtained by the volume V of a process chamber and the effective exhaust speed Sp is set lower than or equal to 2taud which is the time constant of dissociation of treatment gas. Thereby the step coverage of a formed film is remarkably improved. On the other hand, the SiH3 radical density shows the maximum value in the case of taup=taud. When the treatment is performed in the range of half width 6taud>taup>0.1taud of the maximum point, high speed deposition is realized. The change with time of the time onstant tauw of radical extinction on the inner wall surface of the treatment equipmant which change causes the change of etching with time is reduced by shortening the gas retention time taup and increasing the volume to the wall area of the treatment chamber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment apparatus and a surface treatment method, and more particularly, to etching of an object to be treated using gas plasma and plasma CVD (Chemical Vapor Deposition).
position; chemical vapor deposition method), and a surface treatment method using this surface treatment apparatus.

[0002]

2. Description of the Related Art As is well known, surface treatment techniques using gas plasma are various techniques for performing surface treatment of an object to be treated by utilizing radicals and ions generated by collision of treated gas molecules and electrons. It is widely used in the manufacturing process of semiconductor devices.

For example, in plasma etching, an object to be processed is etched by both the ions and radicals. In recent years, it has become necessary to form various patterns having extremely fine dimensions. A technique for preventing obstacles and increasing the directionality of ions to perform more precise machining has become indispensable. The most effective means is to lower the processing gas pressure to a level of 1 mTorr (higher vacuum) and perform etching, and to perform high-speed etching in such a high vacuum, etching is performed. The plasma used also has a density of 10 ⁹ / cm ² to 10 ¹⁰ / cm.
² of low-density plasma, is shifted to a high density plasma of 10 ¹¹ ~10 ¹² / cm ^2.

On the other hand, in the case of plasma CVD, the film is deposited by adsorption of radicals on the surface of the object to be processed, and the surface of the deposited film is flattened by the sputtering effect of ions. In recent years, since it has become necessary to form a film on a structure having a step on the surface, it has become essential to enhance the flattening action of the film surface by ions. Therefore, CV
Also in the case of D, high density plasma of 10 ¹¹ to 10 ¹² / cm ² has come to be used.

[0005]

As described above, high-density plasma has come to be used in both etching and CVD. However, in such high-density plasma, compared with low-density plasma, Since the collision between the electron and the neutral species becomes frequent, the proportion of the neutral species that undergoes the dissociation reaction twice or more due to the collision with the electron also increases. Therefore, in the etching using the high-density plasma, the adverse effect caused by the radicals generated by these multiple dissociation reactions also becomes large.

For example, using CHF ₃ plasma, SiO ₂
When etching is performed, CF ₂ radicals are generated by the reaction shown by the following equation (first-order dissociation reaction), and SiO ₂ is etched by the CF ₂ radicals and ions.

[0007]

CHF ₃ + e ⁻ → CF ₂ + HF However, in the etching by high-density plasma, as shown in the following equation, the collision dissociation reaction (secondary order) between the electrons and CF ₂ or HF formed in the above Chemical formula 1 A large amount of F radicals are generated by the dissociation reaction of.

[0008]

Embedded image CF ₂ + e ⁻ → CF + F + e ⁻

[0009]

Embedded image HF + e ⁻ → H + F + e ⁻ F radicals generated by these secondary dissociation reactions etch Si as the base and PR (photoresist) film as the mask. Sex is significantly reduced. In the manufacturing process of a semiconductor device, it is required to satisfy two conditions of an etching selection ratio of 50 or more and an etching rate of 1 μm / min or more, but etching using high density plasma cannot satisfy these two conditions at the same time. .

In addition, for example, using SiH ₄ plasma, S
For a plasma CVD process for depositing the i layer, is generated SiH ₃ radicals by reaction (primary dissociation reaction) shown in the following equation, the deposited film of Si is generated on an object to be processed by the SiH ₃ radical .

[0011]

Embedded image SiH ₄ + e ⁻ → SiH ₃ + H + e ⁻ However, when high-density plasma is used, the SiH ₃ radicals formed in Chemical formula 4 have higher order (2 The secondary and tertiary dissociation reactions cause dissociation into SiH ₂ and SiH.

[0012]

Embedded image SiH ₃ + e ⁻ → SiH ₂ + H + e ⁻

[0013]

Embedded image SiH ₂ + e ⁻ → SiH + H + e ⁻ These SiH ₂ and SiH are also deposited on the object to be processed, but since they have a high adsorption coefficient, they are remarkably adsorbed on the upper surface and the upper end of the step, and the step However, there is a problem in that the film is poorly adsorbed on the side surface and the bottom of the film and a film having a low step coverage is formed.

An object of the present invention is to solve the above problems of the prior art, and to perform etching having a sufficient etching rate and etching selectivity and CVD capable of depositing a film having a high step coverage at a high rate. It is to provide a surface treatment apparatus and a surface treatment method that can be performed.

Another object of the present invention is to provide a surface treatment apparatus and a surface treatment method capable of suppressing the generation of radicals due to a higher order dissociation reaction and reducing obstacles due to the radicals formed due to a higher order dissociation reaction. Is to provide.

[0016]

To achieve the above object, the present invention is based on the novel finding that the composition of radicals in plasma can be controlled by controlling the residence time of gas in a processing chamber. Taking advantage of the fact that the time constant of the second-order dissociation reaction is longer than that of the first-order dissociation reaction, the gas residence time in the processing chamber is shortened, so that harmful reactions generated by the second- or higher-order dissociation reaction By reducing the ratio of radicals (for example, SiH _{2 in} the case of Chemical formula 5) and further reducing the surface area of the inside of the processing chamber with respect to the volume of the processing chamber, radicals useful for processing (for example, SiH 2 in the case of Chemical formula 5) are obtained. _It reduces the disappearance of ₃ ) and increases the amount of radicals needed.

[0017]

The function of the present invention will be described with reference to the deposition of amorphous silicon by CVD and the etching of SiO ₂ .

First, the case of depositing amorphous silicon using silane plasma will be described. Silane S
The relationship between the gas residence time τ _p and the radical density in the iH ₄ dissociation reaction will be described. SiH ₄ enters the processing chamber at time t = 0, and when the time t is between t ₁ and t ₁ + Δt ₁ , e ⁻ + S
The probability P ₁ of receiving the dissociation reaction of iH ₄ → e ⁻ + SiH ₃ + H is represented by the following equation.

[0019]

[Equation 1]

Here, τ _d1 is the time constant of the reaction in which SiH ₄ dissociates into SiH _3, and τ _p is the time constant of exhaust, which is given by the following equation.

[0021]

[Formula 2] τ _p = V / S _P V is the volume of the processing chamber S _P is the effective pumping speed in the processing chamber This SiH ₃ remains in the processing chamber without being dissociated between t = t _{1 and} t ₂ . The probability P ₁₂ is expressed by the following equation.

[0022]

[Equation 3]

Here, τ _d2 is the time constant of the reaction in which SiH ₃ is dissociated into SiH ₂ and is approximated by τ _{d1 to} τ _d2 = τ _d.
The probability PSi _H3 that iH ₄ exists in the processing chamber in the form of SiH ₃ after t hours is given by the following equation.

[0024]

[Equation 4]

[0025] Therefore, the density N _SiH3 of SiH ₃ existing in an arbitrary time is given by the following equation.

[0026]

[Equation 5]

[0027] Q is by using that there is relationship Q = Const · PV / τ _p between the flow rate and residence time, the density N _SiH3 of SiH ₃ existing in the arbitrary time is given by: Was confirmed.

[0028]

[Equation 6]

P was determined in the same manner as the pressure in the processing chamber, and the densities NSiH ₂ and NSiH of SiH ₃ and SiH existing at the above arbitrary times were obtained, and the results shown by the following equations were obtained.

[0030]

[Equation 7]

[0031]

[Equation 8]

The results are shown in FIG. As is apparent from FIG. 1, when τ _p is lowered to 2τ _d or less, the radical density of SiH ₂ having a large adsorption coefficient is lowered, and thus the step coverage of the obtained film is significantly improved.

On the other hand, radical density of SiH ₃ is the deposition species, was found to take the maximum value in the τ _p = τ _d as shown in FIG. Therefore, the half-value width 6τ _d of this maximum point
High-speed deposition can be realized by performing the treatment within the range of> τ _p > 0.1τ _d . That is, 2τ _d ＞ τ _p ＞
If the deposition is performed within the range of 0.17τ _d , a film with high step coverage can be deposited at high speed.

Next, the value of τ _d will be described. The time constant τ _d for the neutral particles to collide and dissociate with the electrons is expressed by the following equation.

[0035]

[Equation 9]

E is the electron energy n _e is the electron density f (E) is the electron energy distribution function σ (E) is the collision dissociation cross section v (E) is the electron velocity.

FIG. 2 shows the electron energy E (eV) dependence of the distribution function f (E) of electron energy and the dissociation cross section σ (E) obtained from these results. Threshold energy E
_th is about 10 eV and maximum cross-sectional area σ _max is about 0.2 × 10 ¹⁶
cm ² and using the value of dissociation cross section σ (E) shown in FIG. 2, assuming f (E) to be Boltzmann distribution, the dissociation time constant τ _d was obtained, and the result shown in the following equation was obtained. It was

[0038]

[Equation 10]

Te is an electron temperature. The results are shown in FIG. As apparent from FIG. 3, for example, T _e ~5eV, when using high-density plasma of N _e ~10 ¹¹ / cm ^2, constant tau _d time dissociation of about 100msec
Is. Therefore, if τ _p <200 msec, it becomes clear that the condition of τ _p <2τ _d is satisfied, the radical density of SiH ₂ is reduced, and the step coverage is improved. If τ _p > 10 msec, It has been clarified that the above condition τ _p > 0.1τ _d is satisfied, the radical density of SiH ₃ is increased, and the deposition rate is increased.

Next, etching of SiO _{2 with} CHF ₃ will be described. Similarly to the case of depositing amorphous silicon by CVD, the densities N _CF2 and N _F of CF ₂ and F radicals in the processing chamber were obtained, respectively, as shown in the following equations.

[0041]

[Equation 11]

[0042]

[Equation 12]

Further, considering the influence of CF ₂ disappearing on the wall surface of the processing chamber, the following equation is obtained.

If the etching is radical-controlled, S
The etching rate of iO ₂ is approximately proportional to the density of CF ₂ , and the etching rate of Si is approximately proportional to the density of F. Therefore, SiO
Etch rate and SiO ₂ / Si selectivity of ₂ are respectively given by the following Expression 13 and Expression 14.

[0045]

[Equation 13]

C ₁ is a proportional constant

[0047]

[Equation 14]

C ₂ is a constant of proportionality When the value of the above-mentioned proportionality constant is obtained from an experiment, c ₁ =
47, c ₂ = 6.6, and it was found that the condition for making the selection ratio γ or more is represented by the following equation.

[0049]

Equation 15] Therefore _{τ p / τ d <47 /} γ, for example, using high-density plasma of tau _d = 30 msec, in order to obtain a higher etching selection ratio 50,
The gas residence time τ _p may be set to 30 msec or less.

On the other hand, the conditions for making the etching rate R or higher were obtained, and the results shown in the following equation were obtained.

[0051]

[Equation 16]

Where β = 3.3 P / R

[0053]

[Equation 15] and

In order for [Equation 16] to have a common solution, the time constant τ _w of the above radical annihilation must satisfy the following equation.

[0054]

[Equation 17]

Here, α = γ / 47.

Therefore, it was found that the condition necessary to realize the etching at the etching rate of 1 μm / min or more and the selection ratio of 50 or more is given by the following equation by the formula 24.

[0057]

[Equation 18]

Τ _w is peculiar to the apparatus structure, the adsorption coefficient of CF _{2 on} the inner wall of the processing chamber is about 0.02, the temperature of neutral radicals is about 300 K, the processing chamber volume is V, and the area of the processing chamber wall is And A respectively, τ _w is expressed by the following equation.

[0059]

Τ _w = 5.5 × 10 −3 V / A.

It was found that the condition of the above equation 18 is as follows when the high density plasma of τd to 30 msec is used.

[0061]

[Equation 20]

The obtained results are shown in FIG. As is clear from FIG. 4, when the degree of vacuum is 1 mTorr, τ
Using a high density plasma of _d ~ 30 msec, a selection ratio of 50
It has been found that the gas residence time τ _p is set to 28 msec or less and the V / A is set to 8 cm or more in order to perform the etching at the etching rate of 1 μm / min or more. In the past, the value of V / A was about 4 to 6 cm at maximum, and it was difficult to make it larger than this.
Although good results were not obtained, the present invention provided a practically sufficient etching rate and etching selectivity.

Next, the change with time of etching will be described. Since the change over time in etching occurs due to the change in the time constant τ _w of radical annihilation on the inner wall surface of the processing apparatus, it has been clarified that the value of the following equation can be used as an index of change over time.

[0064]

[Equation 21]

When τ _d and τ _p decrease, or when τ _w increases due to the increase of V / A, the value of the above equation 21 becomes small. Therefore, as described above, the gas residence time τ
It was found that shortening _p and increasing V / A are also effective in reducing the change over time.

[0066]

【Example】

<Example 1> Using a high density plasma formed from CHF ₃ gas and using the photoresist film as a mask, polyS
The SiO ₂ film formed on i was etched. ECR and TC are the discharge methods that generate high-density plasma.
There are P, ICP, helicon, magnetron, and the like, and the same effect can be obtained by using any method, but in this embodiment, it is easy to take a large V / A.
CP discharge was used. As the processing chamber, two types of processing chambers having V / A of 5 cm and 10 cm were used.

Both devices can control the exhaust speed by controlling the opening of the valve and change the gas residence time in the processing chamber to a desired value. The pressure in the processing chamber was set to 1 mTorr, the plasma density was set to 3 × 10 ¹¹ / cm ² , and the electron temperature was set to 5 eV. Therefore, the dissociation time constant τ _d in this case is about 30 msec.

SiO ₂ for photoresist and Si
The etching selectivity and the gas residence time τ _p dependence of the SiO ₂ etch rate were measured, and the obtained results are shown in FIG.

As is clear from FIG. 5, the etching selectivity increased in inverse proportion to the decrease in residence time τ _p . It was confirmed that a high etching selection ratio of 50 or more can be obtained when the residence time τ _p is 28 msec or less, that is, τ _p / τ _d is 1 or less.

On the other hand, according to the above equation 20, V / A is 8
An etching rate of 1 μm / min or more can be obtained if the thickness is at least cm, but V / A is 8 cm and 1 in this embodiment.
In all cases, the gas residence time τ _p is 10 m
In the range from sec to 30 msec, 1 μm /
It was confirmed that an etch rate of min or more could be obtained.
However, when V / A = 5 cm, an etching rate of 1 μm / min or more was not obtained.

It was confirmed that the same effect can be obtained even when the same measurement is performed by changing the discharge method, the type of gas system, the type of material to be etched, the type of mask or the base.

Example 2 In this example, high density plasma formed from silane gas was used to deposit amorphous silicon on an object to be processed (quartz glass) having a step structure shown in FIG.

As a method of generating high density plasma, EC
R discharge was used. The pressure in the processing chamber was 10 mTorr, the plasma density was 10 ¹¹ / cm ² , and the electron temperature was 5 eV.
Therefore, the dissociation time constant at this time is about 100 msec.

The relationship between the step coverage and deposition rate of the amorphous silicon layer formed under these conditions and the gas residence time τ _p in the processing chamber was measured. Here, as the index of the step coverage, the ratio a / b of the film thickness a of the amorphous silicon layer at the upper part of the step and the film thickness b at the bottom of the step shown in FIG. 6 was used.

The obtained results are shown in FIG. As is clear from FIG. 7, when the residence time τ _{p of the} gas is shortened, the step coverage is improved, and when τ _p is 100 msec or less, the step coverage a / b is 0.9 or more, which is a practically sufficient step. It was confirmed that coatability could be obtained.

On the other hand, regarding the deposition rate, when the residence time τ _p is 100 msec, the deposition rate reaches a maximum value (10
0 nm / min), and if τ _p is 10 msec or more, half or more of the maximum value is obtained, and it was confirmed that amorphous silicon can be deposited at a rate practically sufficient.
Therefore, if the stay time τ _p is 100 msec or less, 10 ms
It was confirmed that if it is cc or more, a practically sufficient deposition rate and step coverage can be obtained at the same time.

In the present embodiment, the case of depositing amorphous silicon by using silane plasma is shown, but the present invention is not limited to this embodiment, and other gases such as silicon oxide and The same applies to depositing other materials such as silicon nitride. Furthermore, regarding the discharge method, not only ECR but TC
It was found that similar effects can be obtained by using other methods such as P, ICP, helicon, and magnetron.

[0078]

As is apparent from the above description, according to the present invention, the composition of the plasma in the processing chamber can be easily controlled to realize high-speed etching with a high selection ratio, and at the same time, the change over time can be reduced. And stable etching can be performed.

When the present invention is applied to CVD,
By easily controlling the composition of plasma in the processing chamber, a film having excellent flatness and step coverage can be formed at high speed.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a dissociation time constant and a gas residence time, and a radical density.

FIG. 2 is a diagram showing electron energy dependence of dissociation cross section and electron energy distribution function.

FIG. 3 is a graph showing the relationship between electron temperature and dissociation time constant.

FIG. 4 is a diagram showing a range in which a predetermined etching rate and selectivity are obtained.

FIG. 5 is a diagram showing gas residence time, etching rate, and gas residence time dependence of etching selectivity.

FIG. 6 is a sectional view showing a step structure and an amorphous silicon layer formed thereon.

FIG. 7 is a diagram showing a relationship between a gas residence time, a deposition rate, and step coverage.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H01L 21/31 C

Claims (22)

[Claims] 1. A processing chamber for processing an object to be processed, means for introducing a processing gas into the processing chamber, means for forming plasma of the processing gas, and the surface of the object to be processed using the plasma. And a means for exhausting the inside of the processing chamber, wherein the surface treatment apparatus has a volume V (cm ³ ) of the processing chamber and an exhaust speed S _{p of the} processing chamber.
(Cm ³ / sec) is used to define τ _p = V / S _p , the residence time τ _{p of} the processing gas in the processing chamber, the time constant τ _d of dissociation of the processing gas, and the inside wall of the processing chamber. A surface treatment apparatus further comprising means for controlling the composition of the radical to a desired composition by setting a time constant τ _w for extinguishing the radical to a predetermined value. 2. The processing gas is a gas for etching the object to be processed, and has a volume V (c) of the processing chamber.
m ³ ) and the pumping speed S _p (cm ³ / se of the processing chamber)
c) is used to define τ _p = V / S _p , the residence time of the processing gas in the processing chamber is τ _p , the dissociation time constant of the processing gas is τ _d , and radicals on the inner wall of the processing chamber are The disappearance time constant is τ _w , and the pressure in the processing chamber is P (m
Torr), the above τ _p is below the above τ _d ,
The surface treatment apparatus according to claim 1, wherein the τ _w is (3P-2) ^-1 times or more of the τ _d . 3. The electron density n _e in the discharge chamber is 10
^When the value of τp is ¹¹ m / cm ² or more, the value of τp is 30 msec or less, the volume of the processing chamber is V (cm ³ ), and the surface area of the inner wall of the processing chamber is A (cm ² ), The surface treatment apparatus according to claim 2, wherein the ratio V / A of A is (0.6P-0.4) ^-1 cm or more. 4. The processing gas is discharged by using ECR discharge, TCP discharge, ICP discharge, helicon discharge, or magnetron, the value of τp is 30 msec or less, and the volume of the processing chamber is V ( cm ³ ), and when the surface area of the inner wall of the processing chamber is A (cm ² ), the ratio V / A of V and A is (0.6P-0.4) ^-1 cm or more. The surface treatment apparatus according to claim 2. 5. The surface treatment apparatus according to claim 3, wherein the pressure P is 1 mTorr or less and the V / A is 8 cm or more. 6. The processing gas is a gas for depositing a desired substance on the object to be processed, and has a volume V (c) of the processing chamber.
m ³ ) and the pumping speed S _p (cm ³ / se of the processing chamber)
The residence time τ _p of the processing gas in the processing chamber defined as τ _p = V / S _p using c) is less than twice the time constant τ _d of dissociation of the processing gas. The surface treatment apparatus according to claim 1. 7. The surface treatment apparatus according to claim 6, wherein a residence time τ _p of the processing gas is 0.1 times or more a time constant τ _d of dissociation of the processing gas. 8. The processing gas is discharged using ECR discharge, TCP discharge, ICP discharge, helicon discharge, or magnetron, and the value of τ _p is 10 msec or more 20
8. The surface treatment apparatus according to claim 6, which is 0 msec or less. 9. The electron density n _e in the processing chamber is 10
¹¹ / cm ² or more, and the value of τ _p is 10 mse
The surface treatment device according to claim 6 or 7, wherein the surface treatment device is c or more and 200 msec or less. 10. The surface treatment apparatus according to claim 8 or 9, wherein the value of τ _p is 100 msec or less. 11. A surface of an object to be processed placed in a processing chamber,
In the etching method using plasma of the processing gas, τ _p = V / S _p is defined by using the volume V (cm ³ ) of the processing chamber and the exhaust speed S _p (cm ³ / sec) of the processing chamber. _D) the residence time τ _{p of} the processing gas in the processing chamber, τ _d the dissociation time constant of the processing gas, τ _w the radical annihilation time constant on the inner wall of the processing chamber, and P the processing chamber pressure.
(MTorr), τ _p is τ _d or less and τ _w is (3P-2) ^-1 times or more τ _d . 12. The plasma is an ECR of the processing gas.
The dry etching method according to claim 11, wherein the dry etching method is performed by discharge, TCP discharge, ICP discharge, helicon discharge, or discharge using a magnetron. 13. The electronic density in the processing chamber 10 ¹¹
The dry etching method according to claim 11, wherein the dry etching method is maintained at a value of not less than cm ² . 14. The value of τ _p is not less than 10 msec and not more than 200.
14. The dry etching method according to claim 12, wherein the dry etching time is msec or less. 15. The pressure P is 1 mTorr or less, and
15. The dry etching method according to claim 11, wherein the V / A is 8 cm or more. 16. The dry etching method according to claim 11, wherein the processing gas contains F as a component element, and the object to be processed is silicon oxide or silicon nitride. 17. A surface of an object to be processed placed in the processing chamber,
In a method of depositing a desired substance using plasma of a processing gas, τ _p = V using a volume V (cm ³ ) of the processing chamber and an exhaust speed S _p (cm ³ / sec) of the processing chamber.
/ S _p , the residence time of the processing gas in the processing chamber is τ _p , the time constant of dissociation of the processing gas is τ _d , and the time constant of radical annihilation on the inner wall of the processing chamber is τ _w . When the pressure of the processing chamber is P (mTorr), the volume V (cm ³ ) of the processing chamber and the exhaust speed S _p (cm) of the processing chamber
³ / sec), the residence time τ _p of the processing gas in the processing chamber, which is defined as τ _p = V / S _p , is kept below twice the time constant τ _d of dissociation of the processing gas. A method of depositing a substance characterized by the above. 18. The method for depositing a substance according to claim 17, wherein the τ _p is maintained at 0.1 times or more of a time constant τ _d of dissociation of the processing gas. 19. The processing gas is discharged using ECR discharge, TCP discharge, ICP discharge, helicon discharge, or magnetron, and the value of τ _p is 10 msec or more 20
18. The method according to claim 17, characterized in that it is maintained at 0 msec or less.
Alternatively, the method of depositing the substance according to item 18. 20. The electron density n _e in the processing chamber is 1.
0 ¹¹ / cm ² or more, and the value of τ _p is 10 ms
The method for depositing a substance according to claim 17 or 18, characterized in that the deposition rate is maintained at ec or more and 200 msec or less. 21. The method for depositing a substance according to claim 19, wherein the value of τ _p is 100 msec or less. 22. The method of depositing a substance according to claim 17, wherein the substance is amorphous silicon.