JP3329902B2 - Surface treatment method and surface treatment device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment method and a surface treatment apparatus, and more particularly, to a surface treatment method and a surface treatment apparatus for a semiconductor substrate using an aqueous solution.

[0002]

2. Description of the Related Art In recent years, with the increasing integration of electronic circuits formed in semiconductor devices, there is an increasing need to keep the defect density on the surface or junction surface of the semiconductor device low. The defect is generally an interface state that causes trapping of electrons and holes existing on the semiconductor surface, and a lattice defect of a crystal. For example, the interface state density of a conventional MOS transistor is on the order of 10 ⁹ to 10 ¹¹ / cm ² , but in order to realize a highly integrated storage element or a high-performance device such as a quantum device, the interface state density is required. It is said that it is necessary to suppress the level density to 10 ⁹ / cm ² or less.

One of the causes of the generation of these interface states and lattice defects of crystals is that hydroxylation and surface roughening occurring on the surface of the semiconductor substrate in the step of applying a surface treatment such as cleaning to the semiconductor substrate, and the resulting aqueous solution It is considered to be the adsorption of metal ions therein.

That is, when a surface treatment of a Si semiconductor substrate or the like is performed in an aqueous solution, an aqueous solution having a wide pH range, which is acidic, alkaline, or neutral, is generally used as the treatment liquid. However, when surface treatment is performed using, for example, an alkaline aqueous solution, surface roughness occurs even on a relatively stable hydrogen-terminated Si surface. It is also known that even when a neutral aqueous solution is used as the treatment liquid, the Si surface is always hydroxylated due to the presence of OH ^- ions in the aqueous solution.

[0005] Such hydroxylation and surface roughening induce the adsorption of metal ions that are always present in an aqueous solution, and particularly when the surface is treated in an alkaline pH range, metal adsorption is likely to occur. In addition, these surface roughness, hydroxylation, and metal adsorption cause defects on the semiconductor surface, and at the same time, the adsorbed metal enters the inside of the semiconductor crystal and generates lattice defects inside the crystal. That is, when a bonding surface such as a pn junction is formed inside a semiconductor substrate, a defect always occurs in the bonding surface.

[0006]

As described above, conventionally, when surface treatment of a semiconductor substrate is performed using an aqueous solution as a treatment liquid, generation of defects on the surface of the semiconductor substrate and inside the crystal has been inevitable. . In order to minimize the generation of these defects, it is preferable to perform treatment in pure water at pH = 7. However, in the manufacturing process of a semiconductor element, a process of treating in an alkaline and acidic pH region is necessarily included. ing. Therefore, for example, when an alkaline aqueous solution is used, surface roughening of the semiconductor substrate, hydroxylation and metal adsorption necessarily occur, and a strong alkaline aqueous solution causes a remarkable etching phenomenon. Even when an aqueous solution having a concentration of contained metal ions lower than the detection limit is used, considerable metal adsorption occurs to induce defects.

Therefore, when a semiconductor substrate is subjected to surface treatment with an aqueous solution in a wide pH range, there is no effective means for suppressing hydroxylation, surface roughness, metal adsorption and the like to an extremely low level. This has been a major obstacle in developing a high-performance device that requires a very low defect density of a semiconductor element.

The present invention has been made in view of the above problems, and reduces the occurrence of hydroxylation, surface roughness, and metal adsorption when a surface treatment of a semiconductor substrate or the like is performed using an aqueous solution.
An object of the present invention is to provide a surface treatment method and a surface treatment apparatus capable of suppressing the defect density on the surface and inside of a semiconductor element to a very low level.

[0009]

Means for Solving the Problems The first invention of the present application made to achieve the above object is a surface treatment method for performing surface treatment of a member to be treated using an aqueous solution. The gist is to give a negative potential to the member to be processed with respect to the potential of the aqueous solution.

[0010] The second invention of the present application is a surface treatment apparatus for performing surface treatment of an object to be treated in an aqueous solution, wherein a container for accommodating the aqueous solution, and the object to be treated in the aqueous solution. The gist of the present invention is to provide a supporting means for supporting, and a potential applying means for applying a negative potential to the object to be processed in the aqueous solution when performing the surface treatment with respect to the potential of the aqueous solution.

The present invention provides a surface treatment of an object to be treated using an aqueous solution such as a surface cleaning treatment with an aqueous solution and a cleaning treatment with pure water, or a general chemical surface treatment, and the treatment of an object to be treated in an aqueous solution. It can be applied to all surface treatments. Further, the object to be processed is not particularly limited.
A semiconductor substrate such as i, Ge, or a Si—Ge mixed crystal is exemplified. Further, in the present invention, the aqueous solution includes pure water, an optional processing solution for cleaning, and the like.

[0012]

According to the present invention, as described above,
It is possible to reduce hydroxylation, surface roughness, metal adsorption, and the like on the surface of the object which induces defects on the surface of the object or inside the crystal.

[0013]

Embodiments of the present invention will be described below. First, the principle of the present invention will be described.

Generally, in the surface treatment of a semiconductor substrate, those having a wide pH range from an acidic treatment solution to an alkaline treatment solution are appropriately used. When the surface treatment of a semiconductor substrate is performed using such an aqueous solution, a chemical change occurs on the surface of the semiconductor substrate, and the chemical change is a major cause of inducing surface defects and deteriorating the characteristics of the semiconductor element. .

As a result of the research conducted by the present inventors, it has been found that a certain kind of negatively charged anions, such as OH ⁻ , Cl ⁻ , F ^−, etc., existing in an aqueous solution have a great influence on this chemical change. Was revealed. This kind of anion is
It always exists in an aqueous solution in an ionized state. On the other hand, it is considered that a reaction intermediate of this anion and pentacoordination easily forms particularly on the surface of a semiconductor such as Si or Ge, and the reaction intermediate promotes a chemical reaction on the surface of the semiconductor substrate. An aqueous solution containing the least amount of ionic species containing anions is pure water having a pH of 7, and OH ^- ions also exist in this pure water. Therefore, for example, even in the hydrogen-terminated Si surface which is considered to be the most stable on the Si semiconductor surface, the hydroxylation proceeds in pure water. In yet alkaline aqueous solution of pH range, OH ^-
Since the number of ions is greatly increased, the speed of the chemical change is sharply increased, and the surface roughness of the semiconductor substrate becomes remarkable. These hydroxylation and surface roughening are considered to be the adsorption points of the metal ions present in the aqueous solution and cause metal adsorption.

That is, when a semiconductor substrate is subjected to surface treatment with an aqueous solution, an effective means for suppressing a chemical reaction on the surface of the semiconductor substrate is to keep anions present in the aqueous solution from approaching the surface of the semiconductor substrate. Therefore, in the present invention, a cathode bias (negative bias) is applied to make the semiconductor substrate a negative potential with respect to the potential of the aqueous solution, so that Coulomb repulsion prevents negatively charged anions from approaching the semiconductor substrate surface. I made it.

FIG. 1 is a schematic diagram showing the principle of the surface treatment method of the present invention. As shown in the figure, in the surface treatment method of the present invention, the semiconductor substrate 1 and the standard electrode 3 to be processed are immersed in an aqueous solution 11 filled in a liquid tank 9. The semiconductor substrate 1 is accommodated and supported in a cassette 5, and further connected to a negative electrode of a power supply 7, and a positive electrode of the power supply 7 is connected to the standard electrode 3. The standard electrode 3 is one electrode for applying a cathode bias to the semiconductor substrate 1. The standard electrode 3 corrects an electromotive force generated by a difference in ionization tendency of the semiconductor substrate 1 or the like immersed in the aqueous solution 11 to set a standard of potential. It is for keeping. Therefore, the value of the potential of the cathode bias is determined based on the open potential (OCP). The depth of immersion of the semiconductor substrate 1 in the aqueous solution 11 is preferably a depth that does not allow the connection portion of the wiring for connecting the semiconductor substrate 1 to the power supply 7 to enter the aqueous solution 11. This is to prevent metal ions of the wiring connected to the semiconductor substrate 1 from being dissolved in the aqueous solution 11.

By applying a cathode bias to the semiconductor substrate 1 in the above-described configuration, the negatively charged anions in the aqueous solution 11 repel the negatively biased semiconductor substrate 1 and approach the surface of the semiconductor substrate 1. The probability is significantly reduced. Therefore, a reaction intermediate serving as a medium for the chemical reaction on the surface of the semiconductor substrate 1 is less likely to be formed between the anion and the anion, and the occurrence of hydroxylation, surface roughening and metal adsorption is suppressed, and the defect density on the semiconductor substrate surface and inside is reduced. It is thought that it can be made smaller.

The cathode bias is not necessarily required to keep the bias voltage constant with time, but is preferably a constant voltage in order to continuously keep the anions in the aqueous solution 11 away from the surface of the semiconductor substrate 1. Although the voltage value depends on the pH value of the aqueous solution 11, the absolute value of the cathode bias with respect to the open potential is preferably 0.3 V or more, and usually about 1.0 V. However, it is not preferable to set the absolute value of the cathode bias to 10 V or more, since the possibility of lattice defects due to dielectric breakdown on the surface of the semiconductor substrate 1 increases. When a high potential cannot be applied to the semiconductor substrate 1 due to the purpose of the surface treatment, the open potential is about -100 mV (at least -20 mV).
A considerable effect can be observed even at a cathode bias of (.about.-30 mV).

The aqueous solution 11 includes pure water having a pH of 7 (including ultrapure water) as well as a wide range of p from acidic to alkaline.
The treatment liquid in the H region is used. Here, as the alkaline component contained in the aqueous solution 11, for example, NH ₄ O
Organic cholines and organic amines such as H, KOH and C ₅ H ₁₅ NO ₂ , and acidic components such as HF, HCl, HN
O ₃ and H ₂ SO ₄ are used. In some cases,
Mixtures of acidic and alkaline components are also used. Further, when the surface treatment is intended to remove the organic materials and particulate impurities, the aqueous solution containing the components, further H ₂ 0 ₂ is added.

Examples of these aqueous systems include NH ₄ O
_{H / H 2 O, NH 4} 0H / H 2 O 2 / H 2 O, HCl /
H ₂ O, HCl / H ₂ O ₂ / H ₂ O, HF / H ₂ O, H
F / H ₂ O ₂ / H ₂ O, H ₂ SO ₄ / H ₂ O, H ₂ SO
₄ / H ₂ O ₂ / H ₂ O, HCl / HNO ₃ / H ₂ O, H
F / NH ₄ OH / H ₂ O, HF / NH ₄ OH / H ₂ O ₂
/ H ₂ O, KOH / HF / H ₂ O, choline / H ₂ O, choline / H ₂ O ₂ / H ₂ O, choline / NH ₄ OH / H
₂ O, HF / HNO ₃ / H ₂ O, KOH / H ₂ O and the like.

Further, the following additives containing an organic chelating agent may be added to these aqueous solutions. That is,
Citric acid, tartaric acid, zincon, catechol, resorcinol, pyrogallol, tiron, 2oxycitropone, acetylacetone, triethanolamine, methylenephosphinic acid, diethylenetriaminepentaphosphinic acid, triethylenetetrahexaphosphinic acid, ethylenediaminetetraacetate chloranil, cyanuric acid And the like.

As the semiconductor substrate 1, a single crystal, polycrystal or amorphous of Si or Ge can be used, or a semiconductor made of a mixed crystal of Si-Ge may be used. Further, a compound semiconductor such as GaAs or GaAlAs can be used.

The liquid tank 9 is preferably made of a material other than metal, such as a synthetic resin, in order to minimize mixing of metal ions into the aqueous solution 11.

Next, the surface treatment apparatus of the present invention will be described with reference to the drawings. FIG. 2 is a configuration diagram of the surface treatment apparatus of the present invention. Here, the entirety of the semiconductor substrate 21 to be processed is
A voltage control system 30 as a potential applying means for controlling the potential of a semiconductor substrate 21 while controlling the temperature of the aqueous solution 31 is broadly divided into a temperature control system 40 for performing a surface treatment of the semiconductor substrate 21 while controlling the temperature of the aqueous solution 31.

The voltage control system 30 is connected to a semiconductor substrate 21 immersed in an aqueous solution 31, a standard calomel electrode 23, and a control electrode 27 to control a cathode bias applied to the semiconductor substrate 21 and a power supply. 35 and a voltage-current display device 37 and the like. Semiconductor substrate 21
Are accommodated in a cassette 25 as a supporting means, and are immersed in an aqueous solution 31 and supported. The standard calomel electrode 23 and the control electrode 27 are also immersed in the aqueous solution 31. The control electrode 27 is for applying a base voltage as a reference when the potential of the cathode bias applied to the semiconductor substrate 21 is controlled by the potentiostat 33. As a material of the control electrode 27, high-purity carbon that does not generate metal ions can be used, but platinum is more preferable. The standard calomel electrode 23 is one of the standard electrodes.
Is used to convert the cathode bias potential of the semiconductor substrate 21 to the potential of the standard hydrogen electrode into a standard value of the standard hydrogen electrode.

The semiconductor substrate 21 and the standard calomel electrode 2
3 and the control electrode 27 are connected to a potentiostat 33. The potentiostat 33 converts the voltage of the power supply 35 to a set potential of the cathode bias, applies a constant voltage to the semiconductor substrate 21 and the standard calomel electrode 23 during the surface treatment, and stabilizes the cathode bias potential. The values of the cathode bias current and voltage are confirmed by the voltage-current display device 37.

The temperature control system 40 controls the temperature of the water 41 and the temperature of the water 41 as a container for storing the aqueous solution 31 via a water 41 as a temperature control medium. It comprises a temperature control medium circulation device 45. Here, by circulating the water 41 having a constant temperature into the constant temperature bath 43 by the temperature control medium circulating device 45,
The temperature of the water 41 is transmitted to the aqueous solution 31 via the liquid tank 29,
The temperature of the aqueous solution 31 is kept at a set constant temperature.
The temperature of the aqueous solution 31 affects the progress speed of the surface treatment and the like. In order to cope with various surface treatments, this aqueous solution 31
Is preferably controlled with an accuracy of the order of 0.1 ° C.

The configuration of the surface treatment apparatus of the present invention can be appropriately changed according to the purpose and the situation of using the apparatus. For example, if the surface treatment is performed in an environment where the ambient temperature is kept constant, such as in a clean room, or if the chemical change during the surface treatment is not significantly affected by the temperature, etc. There is no need to provide a control system.

Next, a first embodiment according to the present invention will be described. First, the (100) surface of an n-type Si semiconductor substrate having a resistivity of 4 Ωcm was exposed to a 48% aqueous HF solution for 1 minute and a pH = 5.5 aqueous HF / NH ₄ F solution for 1 minute.
Surface treatment was performed sequentially with pure water at H = 7.0 for 2 minutes. Next, this Si semiconductor substrate is immersed in pure water having a pH of 7.0 at a temperature of 25 ° C. in a surface treatment apparatus shown in FIG. 2, and a constant cathode bias of −0.5 V with respect to an open potential (OCP) is applied. The surface was cleaned while applying a voltage to the Si semiconductor substrate (Sample A).

As a comparative example, an n-type Si semiconductor substrate having a similar resistivity of 4 Ωcm, which was previously subjected to the same surface treatment, was placed at 25 ° C. in a surface treatment apparatus shown in FIG.
The surface was washed by leaving it in pure water of H = 7.0 (sample B). Here, FIG. 4 is a configuration diagram of a conventional surface treatment apparatus, in which a semiconductor substrate 1 to be processed is accommodated in a cassette 5 and immersed in pure water as an aqueous solution 11 filled with a liquid phase 9. . Further, the liquid tank 9 is accommodated in a constant temperature tank 53 filled with water 51 as a temperature control medium, and is temperature-controlled.

In the course of the above surface treatment with pure water, both samples A and B were taken out every unit time, and the temporal change of hydroxylation on the surface of the Si semiconductor substrate was examined. In particular,
The stretching vibration of the Si-OH bond generated on the sample surface (37
A 4.0 cm ^-1 ) intensity change was measured by high resolution electron loss spectroscopy. FIG. 3 shows the measurement results.

In FIG. 3, the horizontal axis represents the surface treatment time in pure water,
The vertical axis is the absorption spectrum intensity ratio of the stretching vibration of the Si—OH bond. As is clear from FIG. 3, in sample B, which had been subjected to surface treatment using a conventional surface treatment apparatus to which no cathode bias was applied, hydroxylation of the surface of the object to be treated rapidly progressed in the first few minutes, and then more slowly. Hydroxidation is progressing. On the other hand, the sample A in which the surface treatment was performed by applying a cathode bias to the semiconductor substrate, although the absorption spectrum intensity of the Si-OH bond on the surface was gradually increased, was close to the detection limit, and was 1 compared with the sample B. It turns out that it is lower than an order of magnitude. That is, the progress of hydroxylation on the surface of the Si semiconductor substrate is much lower in sample A than in sample B, and by applying a cathode bias to the object to be processed, the stable hydrogen-terminated Si surface is relatively well maintained. It was confirmed that the surface treatment was performed as it was.

Next, a second embodiment according to the present invention will be described. First, on the surface of the n-type Si semiconductor substrate (100) in exactly the same manner as in the first embodiment, p was applied for 1 minute with a 48% aqueous HF solution and 1 minute with an aqueous HF / NH ₄ F solution having a pH of 5.5.
Surface treatment was sequentially performed with pure water of H = 7.0 for 2 minutes. After that, the surface of the Si semiconductor substrate was reduced to 70 using a cleaning solution in which an aqueous solution of NH ₄ OH (30%), an aqueous solution of H ₂ O ₂ (35%) and H ₂ O were mixed at a volume ratio of 1: 1: 5.
Washed at 10 ° C. for 10 minutes. In addition, this cleaning liquid contains Al and F
e and Ze were forcibly contaminated at a concentration of 1 ppb by each metal ion.

Next, in the surface treatment apparatus shown in FIG. 2, pure water having a pH of 7.0 was used as an aqueous solution, and the surface of the Si semiconductor substrate was washed for 10 minutes. At this time, the cathode bias was applied at a constant voltage of -0.5 V with respect to the open potential (sample A). Further, for comparison, in the conventional surface treatment apparatus shown in FIG.
The semiconductor substrate was washed with pure water having a pH of 7.0 for 10 minutes (sample B).

After the above surface treatment with pure water, samples A,
B is taken out, a hydrofluoric acid solution is dropped on the mirror-finished surface of each Si semiconductor substrate, and Al adsorbed on the surface is removed.
And the contaminating metals of Fe and Ze were dissolved in the droplets. The droplets were analyzed by a flameless atomic absorption method to measure the concentration of the contaminant metal adsorbed on the surface of the Si semiconductor substrate after the surface treatment with pure water. Table 1 shows the measurement results.

[0037]

[Table 1] As shown in Table 1, the surface treatment was performed by applying a cathode bias to the semiconductor substrate using the surface treatment apparatus of the present invention, as compared with the sample B subjected to the surface treatment by the conventional surface treatment apparatus to which no cathode bias was applied. In Sample A, it was confirmed that the concentration of each contaminant metal on the surface of the semiconductor substrate was suppressed to about 1/5.

[0038]

As described above, according to the present invention,
Hydroxylation, surface roughness, metal adsorption, etc. of the surface of the object when performing the surface treatment of the object using an aqueous solution are greatly reduced, and the defect density on the surface and inside of the object is extremely low. Can be suppressed to the level.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing the principle of a surface treatment method of the present invention.

FIG. 2 is a configuration diagram showing a surface treatment apparatus of the present invention.

FIG. 3 is a characteristic diagram showing a temporal change of hydroxylation on the surface of a Si semiconductor substrate during a surface treatment.

FIG. 4 is a configuration diagram showing a conventional surface treatment apparatus.

[Explanation of symbols]

 1,21 semiconductor substrate 3 standard electrode 5,25 cassette 7,35 power supply 9,29 liquid tank 11,31 aqueous solution 23 standard calomel electrode 27 control electrode 30 voltage control system 33 potentiostat 37 voltage-current display device 40 temperature control System 41 water 43 constant temperature bath 45 temperature control medium circulation device

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-4-342131 (JP, A) JP-A-5-190521 (JP, A) JP-A-5-138142 (JP, A) JP-A-6-138 97144 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 21/304

Claims (2)

(57) [Claims] 1. A surface processing method for performing surface treatment of the object to be processed with an aqueous solution, when performing the surface treatment, have a negative potential to the object to be processed with respect to the potential of the aqueous solution, Positive ions on the object
A surface treatment method characterized by inducing repulsion with anions that are coordinated with the surface. 2. A surface treatment apparatus for performing a surface treatment of the object to be processed in an aqueous solution, a container for accommodating the aqueous solution, and support means for supporting the object to be processed in said aqueous solution, said when performing the surface treatment, have a negative potential relative to the potential of the aqueous solution to be treated in the aqueous solution, the object to be processed
Surface treatment apparatus according to claim Rukoto a <br/> potential applying means for inducing a repulsive force between the coordinated anions cations.