JP3201601B2 - Semiconductor substrate cleaning method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates, in the manufacturing process of semiconductor device, it can in effectively removing material from the substrate surface without causing surface roughness of the substrate, and strictly the substrate surface condition after cleaning The present invention relates to a controllable method for cleaning a semiconductor substrate.

[0002]

2. Description of the Related Art In a manufacturing process of a semiconductor device or the like,
A function required for substrate cleaning is to efficiently remove contaminants such as particles, metal contamination, adsorbed molecules, ions, and the like and a native oxide film from the substrate surface without deteriorating the flatness of the substrate surface.

With the increase in the degree of integration of LSIs, the types of contaminants to be managed are increasing, the management level is becoming stricter, and higher controllability of the surface state is required. Therefore, in order to avoid cross contamination between processing lots and obtain reproducible cleaning performance and controllability of the substrate surface, it is desirable to use a new chemical for each cleaning.

[0004] On the other hand, due to the growing interest in environmental issues in recent years, production activities require consideration for the environment, such as energy saving and waste reduction. Among the semiconductor production processes, the wet cleaning process using a large amount of chemicals is a process with a high environmental load, and reducing the amount of chemicals is one of the important issues in the future.

[0005] Recycling of the same cleaning solution is
It is a desirable method from the viewpoint of reducing the amount of chemical solution used and reducing the cost and waste of chemicals.However, by recycling, the concentration of chemical components in the chemical solution, volatilization of the chemical solution components, and fluctuations in the chemical concentration due to decomposition can be reduced. Inevitable.

[0006] Currently, 30 semiconductor manufacturers have 30 wafers.
A process for reducing the thickness to 0 mm is being studied. However, even when the pitch between wafers is equal to 200 mm, a cleaning tank having a capacity 2.25 times larger than that of 200 mm is required due to an increase in the diameter of the wafer. The increase in the amount of cleaning liquid per batch due to the increase in the diameter of the wafer, as well as the control level of contamination and controllability of the substrate surface and the extension of the life of the chemical liquid are limited, so that it is inevitable to increase the amount of cleaning liquid.

[0007] Further, most of the wet cleaning processes are performed by heating in order to increase the cleaning efficiency, and lowering the temperature of the processing is also an issue from the viewpoint of energy saving. When the temperature is lowered, concentration fluctuations due to evaporation can be reduced, so that not only energy saving but also reduction of the replenishing amount of the chemical solution for maintaining the concentration and extension of the life of the chemical solution can be achieved.

In the current wet cleaning, a cleaning liquid that is responsible for the most important cleaning of removing particles from the wafer surface is an ammonia-hydrogen peroxide mixture (APM or SC-1), and has a volume ratio of NH ₃ : H _2. O ₂ : H
₂ O = 1: 1: to use those 5 at 75-85 ° C. is a standard condition.

In view of the present and future situations as described above, the demand for wet cleaning requires a high cleaning power for contaminants, low damage to the substrate, low concentration processing, low temperature processing, and a reduction in processing time, depending on the process immediately before and after the wet cleaning. In recent years, regarding this APM cleaning,
Various improvements according to the purpose have been made.

For example, in the technique described in Japanese Patent Application Laid-Open No. 3-254125, in order to reduce metal contamination from a chemical solution,
What used the volume ratio of pure water to 90-99.7% with respect to the whole cleaning liquid is used.

Further, in order to reduce the etching amount and the cost of the chemical solution, the technology described in Japanese Patent Application Laid-Open No. 4-107922 discloses that the volume ratio of the hydrogen peroxide solution in the cleaning solution is made higher than that of ammonia water and the ratio of pure water is reduced. High.

Further, in the technique described in Japanese Patent Application Laid-Open No. 6-112179, the volume of pure water is set to 20 times the total volume of ammonia water and hydrogen peroxide solution in order to control micro roughness (micro surface roughness). What was increased to 100 times is used as a cleaning liquid.

Further, there is a problem that it takes about 20 minutes to remove foreign matter with these conventional cleaning liquids.
With emphasis on shortening the processing time, see JP-A-10-18318.
In the technology described in Japanese Patent Application Laid-Open Publication No. H05-205, the following [Equation 5 ] and [Equation 6 ]
A technique for cleaning under the conditions specified in the above paragraph is disclosed.

(Equation 5)

(Equation 6) Here, x is NH ₃ concentration (mol / l) and y is H ₂ O ₂
The concentration (mol / l), T is the temperature of the processing solution (° C.), and t is the processing time (minute). Z is the concentration (mol / l) of undissociated hydrogen peroxide. When the conventional technique is used, the processing time required for removing foreign substances can be reduced, and the throughput can be improved.

As a technique related to this field, Japanese Patent Laid-Open Publication No. Hei 3-8336 discloses a method of forming a smooth BPSG film on a wafer in a method of manufacturing a semiconductor device. Before forming
A method of cleaning the wafer with an alkaline aqueous solution to which an oxidizing agent has been added is disclosed.

Further, Japanese Patent Application Laid-Open No. Hei 7-263384 discloses a cleaning liquid used for cleaning a semiconductor substrate after chemical mechanical polishing, in order to prevent heavy metal contamination and generation of particles on a wafer, by a capacity ratio of NH ₃ : H ₂ O. ₂ : H ₂ O =
0.25: 1: 5 or 1/70 ammonia composition
The cleaning liquid having the above is used. In cleaning the semiconductor substrate with this cleaning liquid, the processing temperature is 50 to 9
0 ° C., treatment time is 5 to 20 minutes.

In addition, JP-A-7-283182 discloses that
In a cleaning method after polishing a semiconductor substrate, first, HF-H
The metal contaminants are removed by washing with a Cl washing solution, then the attached particles are removed by washing in a previous stage by washing with a washing solution containing NH ₄ OH and H ₂ O ₂ , and finally the washing is performed by washing with dilute HCl. A method of cleaning by removing contaminant metals by stepwise cleaning is disclosed.

[0017]

In the above prior art, since it is difficult to satisfy all the requirements under one cleaning condition, a cleaning condition that satisfies the most important requirements and satisfies other requirements to some extent is found. However, the time required to individually find the cleaning conditions is enormous.

Accordingly, the present invention has a performance that can meet the standard required for micro-roughness among the requirements required for APM cleaning, and has a high cleaning power for contaminants, low damage to substrates, Low concentration processing,
Cold treatment, shorter treatment time, meets at least one requirement of the high controllability of the substrate surface state after treatment, also properly offer cleaning method of a semiconductor substrate to add a function to meet further one or more of the above requirements The purpose is to do.

[0019]

According to the present invention, a cleaning liquid used for cleaning a semiconductor substrate comprises ammonia, hydrogen peroxide, and ultrapure water. Processing temperature (T (unit: K))
And the processing time (t (unit: minute)) and the molar concentration ratio (R) between ammonia and hydrogen peroxide are

(Equation 7) Is satisfied, the molar concentration of ammonia is 10 mol / l or less, and the molar concentration of hydrogen peroxide C (H ₂
O ₂ )

(Equation 8) Using a cleaning solution that satisfies the concentration condition
The board is washed .

In the above cleaning liquid, the processing temperature (T (unit: K)) of the semiconductor substrate and the processing time (t (unit:
Min)) and the molar ratio of ammonia to hydrogen peroxide (R)
And

(Equation 9) Can be satisfied.

In the above-mentioned cleaning solution, the molar concentration of hydrogen peroxide may be 0.16 mol / l or more.

In addition, in a method for cleaning a semiconductor substrate using a cleaning liquid comprising ammonia, hydrogen peroxide and ultrapure water,
The semiconductor substrate has a control value E corresponding to the cleaning power for surface contaminants and damage to the surface, wherein the control value E is substantially the square of the substrate etching amount (unit: Å);

(Equation 10) ((Σ (a _i × T ⁱ ) is a polynomial including at least terms of 1 / T, T ⁰ , T, a _i is a constant determined from the result of actual measurement of the substrate etching rate, n is a constant number, and T is a semiconductor substrate. , The processing time (unit: minute) for the semiconductor substrate, R is the molar concentration ratio of ammonia and hydrogen peroxide in the cleaning liquid, and the control value E is 10 or more and 10,000 or less. The processing temperature, the processing time, and the molar concentration ratio are determined in accordance with the predetermined value, and the molar concentration of ammonia is 10 mol / l or less, and the molar concentration of hydrogen peroxide C (H ₂ O ₂ ) is:

[Equation 11] And a method for cleaning a semiconductor substrate that satisfies the concentration condition represented by the following formula:

In the above method for cleaning a semiconductor substrate, the processing temperature, the processing time and the molar concentration ratio are determined corresponding to the control value E of not less than 100 and not more than 10000, and the molar ratio of ammonia is determined. When the concentration is 10 mol / l or less and the molar concentration C (H ₂ O ₂ ) of hydrogen peroxide is

(Equation 12) Can be satisfied.

In the above method for cleaning a semiconductor substrate, the molar concentration of hydrogen peroxide may be 0.16 mol / l or more.

Further, in the above method for cleaning a semiconductor substrate, the control value E is

(Equation 13) It can be characterized by the following.

Still further, in the above method for cleaning a semiconductor substrate, the control value E is

[Equation 14] It can be characterized by the following.

In the above-described method for cleaning a semiconductor substrate, the cleaning liquid may be prepared according to a predetermined molar concentration ratio.
It can be characterized in that the molar concentration of ammonia and the molar concentration of hydrogen peroxide are set.

Further, in the above-described method for cleaning a semiconductor substrate, the cleaning liquid may be set so that the molar concentration of ammonia and the molar concentration of hydrogen peroxide are reduced.

In addition, in the above method for cleaning a semiconductor substrate, the molar concentration ratio and the processing time are set based on a predetermined control value and a predetermined processing temperature. It is possible.

Further, in the above-described method for cleaning a semiconductor substrate, the processing temperature may be set to 35 degrees Celsius or more and 80 degrees Celsius or less.

Further, in the above-described method for cleaning a semiconductor substrate, the processing temperature is 35 ° C. or more and 40 ° C.
It can be characterized in that it is set to less than or equal to the degree.

In addition, in the above-described method for cleaning a semiconductor substrate, the molar concentration ratio and the processing temperature are set based on a predetermined control value and a predetermined processing time. Is possible.

Further, in the above-described method for cleaning a semiconductor substrate, the processing time may be set to 10 minutes or less.

[0034]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor to remove ammonia, hydrogen peroxide, a foreign matter of a semiconductor substrate made of ultra-pure water
I found a washing method .

The processing temperature (T (unit:
K)), the treatment time (t (unit: minute)), and the molar concentration ratio (R) between ammonia and hydrogen peroxide satisfy the relational expression expressed by the formula [Equation 7 ], and the molar concentration of ammonia in the cleaning solution ( C (NH ₃ )) is 10 mol / l or less, and the molar concentration of hydrogen peroxide (C (H ₂ O ₂ ))
8 ].

In the method of cleaning a semiconductor substrate according to the present invention, the control value (E) calculated by the formula [Equation 10 ] is used as an index of detergency for substrate surface contaminants and damage to the substrate surface by using the above cleaning liquid. It is characterized by doing.

In particular, for the control value (E), the equation [Equation 1]
4 ].

Further, in the method of cleaning a semiconductor device using the cleaning liquid, the semiconductor device is cleaned at a processing temperature, that is, a cleaning liquid temperature of 35 to 80 degrees.

The above-mentioned cleaning liquid was obtained as a result of an experimental evaluation and a physicochemical analysis of the experimental results by the present inventors based on a known technique relating to APM cleaning.

Here, a known technique relating to APM cleaning will be described below. First, in June 1996, Silicon Science, U.
Known technologies disclosed on page 323 of the CS Semiconductor Technology Research Group are shown below.

The removal of foreign matter from the substrate surface by APM cleaning includes (1) lift-off of foreign matter due to the etching action of the substrate surface, and (2) static electricity due to both the lifted-off foreign matter and the surface charge of the substrate surface becoming negative. Rebound,
It arises from the two actions of

When the substrate surface is SiO ₂ ,
The higher the PM etching rate, the higher the pH, and the higher the pH, the greater the negative charges on the surface of the foreign matter and the surface of the substrate. That is, when the substrate surface is SiO _2, the amount of etching can be an index of the detergency of APM.

Even if the surface of the substrate is Si, if the concentration of hydrogen peroxide in the APM is higher than a predetermined value (the lower limit of hydrogen peroxide in APM cleaning), a predetermined thickness is immediately formed on the surface when the substrate comes into contact with the APM. is SiO ₂ film is formed of. S
formation rate of iO ₂ film faster than the etching rate of the SiO ₂ film, etching of the substrate surface progresses while always maintaining a predetermined thickness SiO ₂ film. Therefore, the substrate surface is Si
Also in the case of (1), the etching amount can be an index of the detergency of the APM.

Based on the above-mentioned known technology, as a result of the present inventors' experimental evaluation and physicochemical analysis of the experimental results, the value of the molar concentration of hydrogen peroxide in the APM cleaning was [
8 ], the molar concentration of hydrogen peroxide is equal to or greater than the lower limit of the value represented by [Equation 8 ], and the molar concentration of ammonia is 10 mol / l or less.
It has become clear that the etching amount of the Si substrate can be approximated by the square root of the E value shown by [Equation 10 ]. In particular, when the etching rate was 20 ° / min or less, the difference between the actually measured value and the calculated value of the etching amount was within ± 20%.

Next, embodiments of the present invention will be described in detail with reference to the drawings.

(First Embodiment) The composition relating to the cleaning liquid in the present invention is shown below.

FIGS. 1 (a) and 1 (a) show the composition represented by the ammonia concentration and the hydrogen peroxide concentration in the cleaning solution according to the present invention.
(B). In the shaded area of the area 2 shown in FIG. 1A, the molar concentration of hydrogen peroxide is 0.154 mol /
l or more, the molar concentration of ammonia is 10 mol / l or less,
In addition, the region satisfies the condition represented by [Equation 9] and indicates the concentration composition of the cleaning liquid in the present invention. In the hatched area of the area 1 shown in FIG. 1A, the molar concentration of hydrogen peroxide is 0.078 mol / l or more and 0.154 mol / l.
Hereinafter, the condition where the molar concentration of ammonia is 10 mol / l or less and the condition represented by [Equation 8 ] is satisfied. Included in this area 1,
In addition, when the relationship between the molar concentration of hydrogen peroxide and the temperature of the cleaning solution, which is shown in a region 3 corresponding to the hatched portion in FIG. 1B, is satisfied, the cleaning solution has the concentration composition of the present invention.

FIG. 2 shows the results of evaluating the etching amount of the substrate and the cleaning properties of the cleaning solutions having various compositions in the hatched portions in FIG. Foreign matter adhering to the substrate surface has an etching amount of 20Å
About 95% at the time of etching, and almost 1 when the etching amount is 30 °.
00% could be removed. It should be noted that almost no increase in the micro roughness was observed in the cleaning liquids of any composition.

When the molar concentration of ammonia is higher than the hatched portions in regions 1 and 2 in FIG. 1, the etching amount increases and the micro roughness slightly increases. However, within the range of the condition shown in [Equation 7], the micro roughness was 2 ° or less.

The etching amount in the composition having the largest etching amount in the composition represented by [Equation 7 ] is 100 °, and the use of the cleaning liquid of this composition makes it possible to remove even the foreign matter strongly adhered to the back surface of the substrate. 100% removal was possible. For the purpose of removing foreign matter, a cleaning solution having an etching amount of about 30 ° was suitable. However, for the purpose of forming a thin SiO ₂ film on the surface of the Si substrate, it was sufficient to perform the treatment under the conditions corresponding to the lower limit of the range represented by [Equation 8 ].

(Second Embodiment) The cleaning effect of the method for cleaning a semiconductor substrate according to the present invention will be described below.

In the cleaning of the semiconductor substrate, the cleaning is performed using a cleaning solution in which the molar concentration of hydrogen peroxide satisfies [Equation 8 ], the molar concentration of ammonia is 10 mol / l or less, and satisfies the condition shown in [Equation 8 ]. The amount of etching was measured on the surface of a Si substrate having a different crystal orientation and on the surface of a substrate on which polysilicon was formed.

When the result was analyzed physicochemically,
The etching amount can be expressed by the square root of the E value shown in [Equation 14 ], and within a limited temperature range, the E value is approximated by a mathematical expression including at least a 1 / T term and a real term (0th order term of T). did it. Furthermore, adding the first-order term of T proved to be effective in approximating the E value from room temperature, which is usually used for cleaning, to 85 degrees Celsius.

Using the results of the Si substrate surface having a predetermined crystal orientation, the coefficient of each term is optimized so that the actual measurement of the etching amount and the value of the square root of the E value show a good correlation.
14 ] was obtained.

FIG. 3 shows the correlation between the actually measured etching rate and the etching rate calculated by [Equation 14 ] (the square root of the E value divided by the processing time t).

When the etching rate was 20 ° / min or less, the difference between the measured value and the calculated value was within ± 20%.
If the surface is Si, a coefficient for correcting the difference between the surfaces is experimentally determined, and the correction coefficient is multiplied by the etching amount obtained by the square root of [Equation 14 ] to obtain an APM having various compositions for various surfaces. The amount of etching was estimated.

Since there is a correlation between the etching amount of the substrate surface and the damage to the substrate surface, the control value E calculated by [Equation 14 ] is effective as an index of detergency against substrate surface contaminants and damage to the substrate surface.

The hydrogen peroxide concentration satisfies [Equation 8], the molar concentration of ammonia is 10 mol / l or less, and [Equation 8 ]
When a cleaning liquid satisfying the condition shown in ( 1 ) is used, the detergency evaluated using [Equation 14 ] as an index is the same if the R value, that is, the molar concentration ratio between ammonia and hydrogen peroxide is the same.

Therefore, under the same R value, the upper limit of the molar concentration of ammonia (10 mol / l) and the lower limit of the molar concentration of hydrogen peroxide (the lower limit expressed by [Equation 8 ] corresponding to the temperature of the cleaning solution) are set as follows. Among them, the molar concentrations of ammonia and hydrogen peroxide are set so that the molar concentrations of ammonia and hydrogen peroxide are the lowest.

By setting the molar concentrations of ammonia and hydrogen peroxide in this manner, the amount of ammonia and hydrogen peroxide used can be reduced, and the cost of chemicals and waste chemicals can be reduced, as well as the environmental burden.

Here, FIG. 4 shows the temperature dependence of the etching rate estimated by [Equation 14 ] with R values of 1, 10, and 100.

The etching rate at the processing temperature of 40 degrees Celsius is about 1/10 of the etching rate at the processing temperature of 80 degrees Celsius, and the etching rate when the R value is 1 and the processing temperature is 80 degrees Celsius is calculated as follows. To obtain at 40 degrees, the R value must be 1
It turned out that it had to be set to 00. Current APM cleaning is usually performed at 60-85 degrees Celsius,
This is performed at a temperature of 40 degrees Celsius or less in order to suppress damage to the substrate.

When the temperature is reduced from 80 degrees Celsius to 40 degrees Celsius while keeping the composition of the cleaning liquid as it is, the damage to the substrate is reduced, but the cleaning power is also reduced. Judging from the calculation result of the etching rate shown in FIG. 4, in order to lower the temperature from 80 degrees Celsius to 40 degrees Celsius and maintain the cleaning power, the processing time is set to about 10 times without changing the cleaning liquid composition. Must be done, which is a big negative in terms of productivity.

If the R value is selected so that the E value becomes constant even when the processing temperature is lowered by using [Equation 14 ], the effect of suppressing damage cannot be expected, but the energy for heating the cleaning liquid is reduced. it can.

Since the increase in the R value is larger than the degree of the temperature drop, the molar concentration of ammonia must be increased. However, if the molar concentration of hydrogen peroxide is set near the lower limit, the hydrogen peroxide can be reduced. Can suppress self-decomposition by lowering the temperature and reduce the amount of hydrogen peroxide used while maintaining the cleaning power. Therefore, it is possible to reduce power cost, chemical solution cost, waste chemical solution treatment cost, and environmental load.

Further, by performing the trial calculation shown in FIG. 4 using [Equation 14 ], the effect on the cleaning power when the processing temperature is lowered, and the composition of the cleaning liquid for maintaining the cleaning power by lowering the processing temperature. Can be estimated in advance, so that the process conditions can be changed efficiently.

Further, from the calculation result of the temperature dependency of the etching rate shown in FIG. 4, when the temperature is set to be higher by about 10 degrees, the etching rate is about doubled, and the processing time can be halved.

From Eq. ( 14 ), the E value is proportional to the square of the processing time t, and the E value and the R value are in a proportional relationship. Therefore,
If you want to reduce the processing time by 1 / x times at the same processing temperature,
That is, when you want to the etching amount x times may be set to R values ^doubled x.

By using the [Equation 14 ] and setting the R value and the processing temperature T so that the processing time t becomes a desired value under the same condition of the E value, the number of semiconductor processes can be increased. As a result, an increase in processing time required for APM cleaning can be suppressed.

Further, if the processing time t is set in accordance with the waiting time in the next step, the processing of the substrate does not wait for the next processing, so that contamination due to exposure to the atmosphere during the processing can be reduced. .

By performing the trial calculation shown in FIG. 4 or FIG. 5 using [Equation 14 ], the effect on the cleaning power when the processing temperature is lowered, and the cleaning liquid for maintaining the cleaning power by lowering the processing temperature. Can be estimated in advance, so that the process conditions can be changed efficiently.

Here, physicochemical considerations regarding the molar concentration of hydrogen peroxide used in the first or second embodiment and the mathematical expression represented by [Equation 10 ] or [Equation 14 ] in the control value E will be described below. Shown in

First, the molar concentration of hydrogen peroxide will be described below. Regarding surface cleaning of semiconductor devices, AP
The prior art relating to the M composition and the etching rate is shown below. (Edited by the Society of Silicon Technology, Japan Society of Applied Physics,
23-27, December 1998).

A in conventional APM cleaning
PM composition (for example, volume ratio NH ₃ : H ₂ O ₂ : H ₂ O =
It has been reported that the etching rate increases when the Si wafer is cleaned under a condition where the concentration of hydrogen peroxide is lower than that of (1: 1: 5 cleaning solution). (T.Futatsuki, K.Ohmi, KN
akamura, and T. Ohmi Proc. of Intern. Confer. onAdv
anced Microelectronics Device and Processing, pp.
425-430 (1994). Or HF Schmitt, M. Meuris, P.
W. Mertens, ALPRotondoro, MHHeyns, TQHurd, a
nd Z.Hatcher, Jpn.J.Appl.Phys., Vol.34, pp.727-73
1 (1995))

Regarding this phenomenon, the etching in the APM cleaning is as follows.

Embedded image And a chemical reaction formula represented by

Embedded image It has been confirmed that it can be calculated with high accuracy by a relational expression derived from a reaction model which is represented by a chemical reaction formula represented by the following two reaction formulas.

Since the etching rate is represented by the sum of the etching amounts by the reaction paths represented by the above two reaction equations, the etching rate is set to Er, and the contribution of the reaction of [Chemical Formula 1] in both reactions. Is α, and the contribution of the reaction of [Chemical Formula 2] in both reactions is β.

(Equation 15)

(Equation 16)

[Equation 17]

(Equation 18)

[Equation 19]

(Equation 20) The formula represented by the following holds.

Based on the above prior art, the inventor has set forth 35 degrees Celsius, 45 degrees Celsius, 55 degrees Celsius and 6 degrees Celsius.
The measured values of the unknowns k ₁ , k ₂ , and k ₃ at 5 degrees are shown in Table 1 below. The unit of the etching rate is Å / min.

[Table 1]

Referring to the above [Table 1], the inventor obtained an approximate expression relating to the temperature dependence of the unknowns k ₁ , k ₂ and k ₃ , and obtained the following [Equation 21 ] to [Equation 23 ].
Is obtained.

(Equation 21)

(Equation 22)

(Equation 23)

Further, according to the experimental results described in the above prior art, there is a correlation between the [OH ⁻ ] concentration in the cleaning solution, the contribution ratio α and the micro roughness, and as the contribution ratio α increases,
There is a tendency that the surface micro-roughness with respect to the [OH ⁻ ] concentration in the cleaning solution is reduced. The contribution rate α is 0.99
When it was 9 or more, the surface microroughness amount was constant regardless of the [OH ⁻ ] concentration in the cleaning solution.

The ion dissociation reaction formula for ammonia, hydrogen peroxide and water is as follows:

Embedded image

Embedded image

Embedded image Here, Ka (H ₂ O ₂ ), Kb (NH ₃ ) and Kw are
The dissociation constants of hydrogen peroxide, ammonia, and water are shown.

As prior art relating to the above dissociation constant,
S.Verhaverbeke, JWParker, CSMcConnell, Syn. Pr
oc. of Mat. Res. Soc., Vol. 477, pp. 47-56 (1997). According to this prior art, the above dissociation constants are measured every 25 degrees from 25 degrees Celsius to 80 degrees Celsius. The results are shown in Table 2 below.

[Table 2]

Based on [Table 2], A
An approximate expression for obtaining the dissociation constants of hydrogen peroxide, ammonia, and water in the range of 35 degrees Celsius to 80 degrees Celsius in the PM cleaning solution is shown. The approximate expression is shown below.

(Equation 24)

(Equation 25)

(Equation 26)

Here, the prior art shown above (Silicon Technology, Japan Society of Applied Physics, edited by 23-2,
7, p. 7, December 1998), it is assumed that the reaction contribution ratio indicates the ratio of the progress of the reaction pathway to all the reactions represented by [Chemical Formula 1] and [Chemical Formula 2]. By using the reaction contribution ratio, it is possible to calculate the etching rate and control the cleaning properties (surface microroughness, particle removal properties). Also, normal APM
In order to perform the processing, the value of α (reaction contribution rate corresponding to [Formula 1]) represented by [Equation 16 ] needs to be 0.999 or more.

According to the present invention, the etching rate is calculated and the cleaning properties (surface microroughness, particle removal properties) are controlled by directly comparing the dissolution rates of the Si wafers in [Chemical Formula 1] and [Chemical Formula 2]. Is made possible.

For the same substance, two chemical reactions A and B
If the relative ratio B / A of the reaction rates of both reactions is 1/100 or less in a reaction system in which It is possible. The relative ratio B / A is 1/1.
In the case of 000 or less, it is empirically possible that it is assumed that the reaction of only A is progressing in this reaction system, and that the progress of the reaction of B can be neglected.

Accordingly, when (reaction rate of [formula 1]) / (reaction rate of [formula 2]) ≧ 100, the reaction of [formula 2] can be approximately ignored.

Now, referring to [Equation 16], [Formula 1]
Is represented by αv ₁ , and the reaction rate of Si in [Chemical Formula 2] by βv ₂ ,

[Equation 27] In this case, the reaction of [Chemical Formula 2] can be ignored.

The etching rate Er at this time is as follows:
Is represented by v ₂ by corresponding to the reaction on the right side of

[Equation 28] It is represented by

[Equation 27 ] is replaced by [Equation 18 ], [Equation 19 ],
When transformed based on [Equation 20 ], [Formula 4] and [Formula 5],

(Equation 29) Is obtained.

A common logarithm is calculated for both sides of [Equation 29 ], and [Equation 21 ], [Equation 22 ], [Equation 23 ], [Equation 2 ]
4 ] and [Equation 25 ],

[Equation 30] Is obtained.

Now, in the range from 35 degrees Celsius to 80 degrees Celsius, the right side of [Equation 30 ] is −1.11 to −0.8.
1

(Equation 31) When the above condition is satisfied, the condition that the reaction of [Chemical Formula 2] can be approximately ignored in the entire range within the above temperature conditions is satisfied.

In the APM solution (pH <11), [H
_{Since 2} O ₂ ] (non-dissociated hydrogen peroxide concentration) can be approximated to the hydrogen peroxide concentration in the entire APM solution, the hydrogen peroxide concentration condition in the present invention is represented by [Equation 3].
0 ], and preferably the value represented by [Equation 31 ].

When the concentration of hydrogen peroxide with respect to the temperature of the APM solution is calculated based on [Equation 30 ], when the temperature of the APM solution is 80 degrees Celsius, [H ₂ O ₂ ] ≧ 0.155 m
ol / l, when the temperature of the APM solution is 35 degrees Celsius, [H ₂
O ₂ ] ≧ 0.078 mol / l, and has a correlation between the temperature of the APM solution and the hydrogen peroxide concentration as shown in FIG.

Next, the control value E will be described below. First, an amount represented by the square of the etching amount is set as the control value E. That is, the etching time is t (unit: minute)
Then, E = (Er × t) ² .

Hereinafter, the etching rate (Er) will be determined.
In the hydrogen peroxide concentration calculation process shown above, Si
The equation [Equation 28 ] for the wafer etching rate is obtained. By transforming [Equation 28 ] based on [Equation 22 ],

(Equation 32) Is obtained.

It determined according to derivation process shown below ^- {OH} where [0096] included in the number of 32. The equilibrium of the ion concentration in the APM solution is based on [Chem. 3], [Chem. 4], and [Chem. 5].

[Equation 33] It is expressed as Here, [] included in the chemical formula or the formula indicates the concentration of the ion or molecule shown in [] in the solution.

Under the following assumption, the ion concentration for each ion is obtained by approximation. (Assumption 1) The activity coefficient of the APM solution is set to 1 (assumed to be an ideal solution). Therefore ｛O
H ⁻ ｝ is equal to [OH ⁻ ]. (Assumption 2) The APM solution is an alkaline chemical, and the pH of the ammonia water is 1
The pH of the APM solution is 8 to 12
Between. Also, according to the prior art, the p
The value of H depends on the composition of the solution, but is between 10 and 10.
5 is disclosed. From this, [H ⁺ ] is 10 ⁻⁸ or less, and [OH ⁻ ] ≫ [H ⁺ ] holds.

By transforming [Equation 33 ] using these assumptions,

(Equation 34) Is obtained.

Since Ka is 10 ⁻¹² , the APM
Assuming that the pH of the solution is less than or equal to 11 (based on the prior art that the value of the pH of the APM solution is disclosed to be from 10 to 10.5), [H ⁺ ]> 10
⁻¹¹ , which can be approximated as [H ⁺ ] ≫Ka,
[Equation 34 ] is

(Equation 35) And can be transformed.

Further, based on [Formula 3] and [Formula 5],

Embedded image Is obtained, and [Equation 35 ] is

[Equation 36] And can be transformed.

Ammonia is a weak base and is mostly AP
M can be assumed to be dissolved in a molecular state in the M solution, and C (N
H ₃ ) ≫ [NH ₄ ⁺ ], so that [Equation 36 ]
Is

(37) And can be transformed.

Further, Ka (H ₂ O ₂ ) and Kw obtained by the formulas [Formula 24 ] and [Formula 25 ] and the minimum concentration of C (H ₂ O ₂ ) obtained by the formula [Formula 32 ] are obtained. From the correspondence, C
_{(H 2 O 2) × Ka} (H 2 O 2) »Kw approximation are possible, Equation 37] is

(38) And can be transformed.

Next, a formula expressing [OH ⁻ ] using [NH ₄ ⁺ ] is shown below.

[Equation 39]

Also, it can be assumed that ammonia is a weak base and most of it is dissolved in the APM solution in a molecular state.
Since C (NH ₃ ) ≫ [NH ₄ ⁺ ], [number
39 ]

(Equation 40) And can be transformed.

From this, under the conditions shown below, AP
[OH ⁻ ] in the M solution is determined using the ammonia concentration, the hydrogen peroxide concentration, the equilibrium constant of ammonia, hydrogen peroxide, and water. (Condition 1) The activity constant is set to 1. (Condition 2) The pH is between 8 and 11. (Condition 3) Ammonia is a weak base, and C (NH ₃ ) ≫ [NH ₄ ⁺ ] in the APM solution.

Further, Ka (H ₂ O ₂ ) and Ka (N
H ₄ ⁺ ) and Kw are constants determined by temperature. Therefore, under the conditions where the assumption made when obtaining [Equation 40 ] holds, it is shown that [OH ⁻ ] depends on the concentration ratio between ammonia and hydrogen peroxide. At APM,
Mixing ratio NH ₃ : H ₂ O ₂ : H ₂ O Among mixing ratio NH ₃ :
It is reported that when H ₂ O ₂ is the same, the etching rate of the Si substrate is the same, which is [OH ⁻ ].
Indicates that it greatly affects the etching rate.

[OH ⁻ ] used in [Equation 40 ] is replaced by [Equation 40 ].
32 ]

[Equation 41] Is obtained. The unit of the etching rate is Å / min.

When the control value E is obtained based on [Equation 41 ],

(Equation 42) Is obtained.

Here, based on Table 2, Ka (NH
₃ ) When an approximate expression of × Kw / Ka (H ₂ O ₂ ) is obtained,

[Equation 43] Or

[Equation 44] It is expressed as

The molar concentration ratio of ammonia and hydrogen peroxide R =
By transforming [Equation 42 ] using C (NH ₃ ) / C (H ₂ O ₂ ) and [Equation 43 ],

[Equation 45] Is obtained.

Further, when the molar concentration ratio R = C (NH ₃ ) / C (H ₂ O ₂ ) of ammonia and hydrogen peroxide and [Equation 44 ] are used to transform [Equation 42 ],

[Equation 46] Is obtained.

Therefore, the control value E is obtained from [Equation 45 ] and [Equation 46 ]. The control value represented by [Equation 14 ] is obtained from [Equation 46 ] obtained here.

The approximation formula used in the process of deriving the control value E is a constant term such as [Equation 44 ] and a first-order term of T, or a constant term such as [Equation 43 ] and 1
/ T. However, if the approximation formula used is changed to one containing a higher-order term, this control value E can be represented by the following general formula.

[Equation 47] (However, Σ (a _i × T ⁱ ) is at least 1 / T,
Ai is a polynomial including terms of T ⁰ and T, a _i is a constant determined from the actual measurement result of the substrate etching rate, n is a constant number, T is the processing temperature (unit: K) for the semiconductor substrate, and t is the processing time for the semiconductor substrate. (in minutes), R is the molar concentration ratio of ammonia and hydrogen peroxide cleaning liquid) this general formula [expression 47]
, A control value represented by [Equation 10 ] is obtained.

Next, specific experimental results are shown below. First, the conventionally used capacity ratio NH ₃ : H ₂ O ₂ : H ₂
The cleaning solution of O = 1: 1: 5 has an ammonia concentration of 2 mol.
/ L and a concentration of hydrogen peroxide of 2 mol / l are generally used.

(Experimental Example 1) Based on the results of FIG. 2, the etching amount was 30 ° and the processing time was 10
The semiconductor substrate was cleaned at a processing temperature of 65 degrees Celsius for a minute.

Since the square root of the E value can be approximated to the etching amount, an R value satisfying the condition was set as a value of 0.8331 when the E value was set to 900. Here, the hydrogen peroxide concentration condition is CT (H ₂ O ₂ ) ≧ 1.21-714 /
Assuming that the temperature margin is ± 3 degrees, the lower limit of the hydrogen peroxide concentration is 0.131 mol at 68 degrees Celsius.
/ L. Further, by securing a concentration variation margin of 10%, the concentration of hydrogen peroxide can be reduced to 0.145 mol / l.
And The ammonia concentration at this time was 0.120 mol /
1 and converted into a capacity ratio, NH ₃ : H ₂ O ₂ : H
₂ O = 8/15/1000.

The cleaning liquid was evaluated for foreign matter removal from the Si substrate, micro roughness, and etching rate.
Foreign matter can be removed by 99%, micro roughness is 1.6mm,
The etching amount of the substrate was 32 °.

Here, the conventionally used capacity ratio N
Compared with the case where H ₃ : H ₂ O ₂ : H ₂ O = 1: 1: 5 was used for cleaning, the concentration of ammonia was reduced to 1/18 and the concentration of hydrogen peroxide was reduced to 1/10.

(Experimental Example 2) An R value that can reduce the processing temperature to 40 ° C. while maintaining the same cleaning performance as the cleaning liquid of Example 1 (fixing the E value) and the processing time of 10 minutes was obtained. , 19.8.

For the cleaning liquid having an R value of 19.8, the hydrogen peroxide concentration condition is such that CT (H ₂ O ₂ ) ≧ 1.2.
1-714 / T, but assuming that the temperature margin is ± 3 degrees, the lower limit of the hydrogen peroxide concentration is 0.degree.
089 mol / l. Further, the density fluctuation margin is 1
By ensuring 0%, the concentration of hydrogen peroxide can be reduced to 0.1 m
ol / l. The ammonia concentration at this time was 2 mol /
1 and the ammonia concentration is equivalent to that of a conventionally used cleaning liquid having a volume ratio of NH ₃ : H ₂ O ₂ : H ₂ O = 1: 1: 5.

Here, when the processing time was extended to 15 minutes and the R value for ensuring the same cleaning performance as the cleaning solution of Example 1 was calculated, it was 8.8. In the cleaning solution having an R value of 8.8, when the concentration of hydrogen peroxide is 0.1 mol / l, the concentration of ammonia is 0.88 mol / l, and when converted into a volume ratio, NH ₃ : H ₂ O ₂ : H ₂ O = 11:
2: 180.

The cleaning liquid was evaluated for foreign matter removal from the Si substrate, micro roughness, and etching rate. The foreign matter could be removed by 99.5%, the micro roughness was 1.8 °, and the etching amount of the substrate was 35 °.

Compared with the first embodiment, the processing time is 1.5
However, the processing temperature can be reduced by 25 ° C., and the capacity ratio NH
_{3: H 2 O 2: H} 2 O = 1: 1: Compared to the use in washing ones 5, ammonia 1 / 2.5, to reduce the hydrogen peroxide concentration of 1/14 Was completed.

(Experimental Example 3) The cleaning performance equivalent to that of the cleaning solution of Example 1 was secured (the E value was fixed), and the R value capable of reducing the processing time to 8 minutes at the processing temperature of 65 ° C. was estimated. Was 1.30.

For the cleaning solution having an R value of 1.30, the condition of the concentration of hydrogen peroxide is as follows: CT (H ₂ O ₂ ) ≧ 1.2
1-714 / T, but assuming that the temperature margin is ± 3 degrees, the lower limit value of the hydrogen peroxide concentration is 0.1 at 68 degrees Celsius.
131 mol / l. Further, the density fluctuation margin is 1
By securing 0%, the concentration of hydrogen peroxide is reduced to 0.14.
5 mol / l. The ammonia concentration at this time was 0.1
9 mol / l, and when converted to a volume ratio, NH ₃ : H
₂ O ₂ : H ₂ O = 5/6/400.

The cleaning liquid was evaluated for foreign matter removal from the Si substrate, micro roughness, and etching rate. The foreign matter could be removed by 99.5%, the micro roughness was 1.7 °, and the etching amount of the substrate was 33 °.

Compared with Example 1, the processing time can be reduced by 2 minutes, and the volume ratio NH ₃ : H ₂ O ₂ : H ₂ O = 1: 1: 5.
Compared to the case where the above was used for cleaning, the concentration of ammonia was reduced to 1/12 and the concentration of hydrogen peroxide was reduced to 1/10.

Further, in the above, an experimental example is shown in which cleaning by physical action such as ultrasonic waves is not used. Generally, the amount of etching on the substrate for obtaining the same cleaning effect is reduced to 1/2 to 1/3 by using cleaning by physical action in combination. Therefore, damage to the substrate can be further reduced.

[0129]

As described above, according to the present invention,
Of the requirements for APM cleaning, micro-roughness can meet the normally required level, high cleaning power against contaminants, low damage to substrates, low concentration processing, low-temperature processing, reduction in processing time, processing Cleaning that satisfies at least one requirement of high controllability of the subsequent substrate surface state can be performed.

Further, it is possible to reduce the power cost, the chemical solution cost, the waste chemical solution treatment cost, and the environmental load. in addition,
Since it is possible to predict the cleaning conditions for obtaining these effects, the efficiency of setting the cleaning conditions can be improved.

[Brief description of the drawings]

FIG. 1 is a graph showing an example of processing conditions of the present invention;
(A) shows the correlation between the molar concentration of hydrogen peroxide and the molar concentration of ammonia, and (b) shows the correlation between the molar concentration of hydrogen peroxide and the temperature of the cleaning solution.

FIG. 2 is a graph showing a relationship between a foreign substance removal rate and a substrate etching amount in foreign substance cleaning of a Si substrate surface.

FIG. 3 shows a measured value of an etching rate of a Si substrate and [Equation 1].
7 is a graph showing the correlation between the etching rate values (the square root of the E value represented by [Equation 1] divided by the processing time t) calculated by the following equation.

FIG. 4 is a graph showing the results of a trial calculation of the effect of the molar concentration ratio of ammonia and hydrogen peroxide and the processing temperature on the etching rate of a Si substrate by the method of the present invention.

FIG. 5 is a graph showing results of trial calculation of a molar concentration ratio of ammonia and hydrogen peroxide and a processing temperature by the method of the present invention, which are equivalent in cleaning power to a Si substrate.

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-10-183185 (JP, A) JP-A-2000-208475 (JP, A) JP-A-11-54468 (JP, A) JP-A-10-172940 (JP, A) JP-A-8-17775 (JP, A) JP-A-5-259141 (JP, A) JP-A-6-89888 (JP, A) JP-A-4-107922 (JP, A) ( 58) Surveyed field (Int.Cl. ⁷ , DB name) H01L 21/304 647 C11D 7/04, 7/18

Claims (10)

(57) [Claims] Claims: 1. An aqueous solution comprising ammonia, hydrogen peroxide, and ultrapure water.
In the method of cleaning a semiconductor substrate using a cleaning liquid, the cleaning power for the surface contaminants of the semiconductor substrate and the surface
Has a control value E corresponding to the damage to be performed.
The control value E is substantially equal to the substrate etching amount (unit: Å).
It is a square, and(Σ (ai × Ti) is at least 1 / T, T⁰, T term
Is a polynomial including_iIs the actual measurement of the substrate etching rate
A constant determined from the results, n is a constant number, and T is
Processing temperature (unit: K), and t is the processing temperature for the semiconductor substrate.
Processing time (unit: minute), R is ammonia / peroxidation of cleaning solution
Molar ratio of hydrogen)In particular, the control value E is (Equation 2)  Indicated by  Where the control value E is not less than 10 and not more than 10,000
The processing temperature, the processing time, and the
And the ammonia concentration is determined.
Degree is 10 mol / l or less, the molar concentration C of the hydrogen peroxide.
(H₂O₂) IsA method for cleaning a semiconductor substrate that satisfies the concentration condition represented by: 2. The control value E is 100 or more and 100
The processing temperature, the processing time, and the molar concentration ratio are determined corresponding to a predetermined value of not more than 00, the molar concentration of the ammonia is 10 mol / l or less, and the molar concentration of the hydrogen peroxide C ( H ₂ O ₂ ) 2. The method for cleaning a semiconductor substrate according to claim 1, wherein a processing condition expression represented by the following formula is satisfied. 3. The hydrogen peroxide has a molar concentration of 0.16 m.
The method for cleaning a semiconductor substrate according to claim 1, wherein the cleaning rate is at least ol / l. Wherein said cleaning solution, corresponding to molar ratios predetermined one of claims 1 to 3, characterized in that the molar concentration of the molar concentration of the hydrogen peroxide of said ammonia is set The method for cleaning a semiconductor substrate according to claim 1. Wherein said cleaning liquid, the washing of the semiconductor substrate according to claim 4, characterized in that the molar concentration to the molar concentration of the hydrogen peroxide of said ammonia is set to be lower
Purification method . Wherein said molar concentration ratio and the processing time, the control value set in advance, any one of claims 1 to 5, characterized in that it is set on the basis of a predetermined process temperature 3. The method for cleaning a semiconductor substrate according to item 1 . 7. The method according to claim 1, wherein the processing temperature is set to 35 degrees Celsius or more and 80 degrees Celsius or less.
7. The method for cleaning a semiconductor substrate according to any one of items 1 to 6 . 8. The method according to claim 1, wherein the processing temperature is set to 35 degrees Celsius or more and 40 degrees Celsius or less.
7. The method for cleaning a semiconductor substrate according to any one of items 1 to 6. The processing temperature and wherein said molar ratio is a control value set in advance, any one of claims 1 to 8, characterized in that it is set on the basis of a processing time predetermined 3. The method for cleaning a semiconductor substrate according to item 1 . 10. A semiconductor substrate cleaning method according to any one of claims 1 9, characterized in that the processing time is set to less than 10 minutes.