JP2007274002A - Method of forming thin film using atomic-layer vacuum deposition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin film formation method using atomic-layer vacuum deposition which is applied to the formation of a gate insulating layer, having a high dielectric constant, less likely to be crystallized due to its being thermally stable, and proper film properties. <P>SOLUTION: A method of forming a thin film on a substrate 11, that uses atomic-layer vacuum deposition, comprises a pre-treatment step for terminating the surface of the substrate with a hydroxyl group (S102); a first step of forming a metal atom layer on the treated surface of the substrate 11 (S104) and forming an oxygen atom layer on the metal atom layer (S106); a second step of forming a layer of silicon atoms on the treated surface of the substrate (S108) and forming a layer of oxygen atoms on the silicon atom layer (S110), wherein either the first step or the second step is performed first. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a thin film forming method using an atomic layer deposition (ALD) method, and is particularly suitable for a method for forming a gate insulating film.

  The MOS transistor has a gate length of about 0.1 μm, and this miniaturization has led to an increase in device speed, a reduction in power consumption, and a reduction in the area occupied by the device. Recently, since many elements can be mounted on the same chip area, the multifunction of LSI has been realized. However, the pursuit of miniaturization of MOS transistors is expected to hit a large wall with a gate length of 0.1 μm as a boundary. One of the walls is the limit of thinning the gate insulating film.

Conventionally, the gate insulating film of a MOS transistor does not contain a fixed charge and can satisfy two characteristics indispensable for the operation of an element, that is, an interface state is hardly formed at the boundary with silicon (Si) in a channel region. Silicon oxide (SiO ₂ ) has been used. Since SiO ₂ can be easily formed with good controllability, it is effective for miniaturization of devices.

However, since the relative dielectric constant of SiO ₂ is as low as about 3.9, the generation of a gate length of 0.1 μm or later requires a film thickness of 3 nm or less in order to satisfy the transistor performance. However, with this film thickness, it was predicted that carriers would directly tunnel through the gate insulating film, increasing the leakage current between the gate and the substrate.

Therefore, in order to prevent the tunneling phenomenon, it has been studied to form a thick gate insulating film using a material having a relative dielectric constant larger than that of SiO ₂ , and the materials include aluminum oxide (Al ₂ O ₃ ), zirconium oxide ( Metal oxide films such as ZrO ₂ ) and hafnium oxide (HfO ₂ ) have been studied. Since these metal oxide films have a high relative dielectric constant, the same gate capacitance can be obtained as when the gate insulating film is made of SiO ₂ even if the film thickness is increased several times, thereby suppressing the tunneling phenomenon. Can do. In order to form these metal oxide films, a chemical vapor deposition (Metal-Organics Chemical Mechanical Deposition (MOCVD)) method using an organic metal gas is generally used.

  In recent years, there has also been reported a method of forming a metal oxide film by an ALD method in which reactants are periodically supplied to the substrate surface and film formation is performed in units of atomic layers (see Patent Document 1 below). Since the ALD method always performs adsorption in the surface motion region, it has a very excellent step coverage, and because the reactant is adsorbed by chemical replacement by periodic supply of each reactant, the film density is high, A film having a stoichiometric composition can be obtained.

JP 2001-152339 A

However, metal oxide films such as Al ₂ O ₃ , ZrO ₂ , and HfO ₂ have a high relative dielectric constant, but crystallize by heat treatment after film formation, and pass through crystal grain boundaries when used as a gate insulating film. As a result, a problem of leakage current has occurred. In addition, when such a metal oxide film is formed by the MOCVD method, there has been a problem that impurities such as carbon resulting from the reaction gas remain in the film and the film characteristics deteriorate. Therefore, there has been a demand for a thin film formation method capable of forming a gate insulating film having a higher relative dielectric constant than SiO ₂ , being thermally stable and less likely to be crystallized than a metal oxide film, and having good film characteristics.

In order to solve the above problems, a thin film forming method using the ALD method of the present invention is a method of forming a thin film on a substrate using an atomic layer deposition method, and the surface of the substrate is terminated with a hydroxyl group. After the pretreatment step, a first step of forming a layer of metal atoms on the treatment surface of the substrate and forming a layer of oxygen atoms on the metal atom layer, and a layer of silicon atoms on the treatment surface of the substrate And a second step of forming an oxygen atom layer on the silicon atom layer, and either the first step or the second step is performed first.

According to such a thin film formation method using the ALD method, a metal silicate film containing metal atoms, oxygen atoms, and silicon atoms is formed. As a result, since the metal silicate film to be formed contains a metal oxide, the dielectric constant is higher than that of a film of SiO ₂ alone, and since silicon oxide is contained, the crystal of the metal silicate film is higher than that of a film of metal oxide alone. The conversion temperature increases. Furthermore, by forming a metal silicate film using the ALD method, each layer can be stacked in units of atomic layers, and a metal silicate film having a stoichiometric composition can be formed, so that the composition ratio of the metal silicate film can be controlled. The relative dielectric constant and crystallization temperature can be adjusted. In addition, when a thin film is formed on a substrate using the ALD method, the gas atmosphere on the processing surface of the substrate is replaced with an inert gas after each atomic layer is formed, so that the reactive gas is compared with the MOCVD method. Impurities such as carbon can be prevented from being mixed into the film, and deterioration of film characteristics can be suppressed.

  Therefore, when forming a gate insulating film made of a metal silicate film by such a thin film formation method, it is possible to increase the relative dielectric constant and increase the film thickness by controlling the composition ratio of the metal silicate film. Therefore, the carrier tunneling phenomenon can be suppressed. Further, by increasing the crystallization temperature, the gate insulating film can be made thermally stable and difficult to crystallize, so that an increase in leakage current between the gate and the substrate can be suppressed.

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

(First embodiment)
An example of an embodiment related to a thin film forming method using the ALD method of the present invention will be described. First, in describing the thin film forming method, an ALD apparatus used in this method will be described with reference to a schematic sectional view of FIG.

  As shown in FIG. 4, the ALD apparatus used for the thin film formation method using the ALD method in this embodiment includes a reaction chamber 20 heated by an external heater (not shown). A gas switching valve 21 is installed in the upper part of the reaction chamber 20, and a plurality of pipes 22 provided for each gas are connected to the gas switching valve 21. The gas switching valve 21 is connected to a gas introduction port 23 provided in the reaction chamber 20. A shower head 24 for supplying the gas introduced from the gas inlet 23 to the surface of the substrate to be processed (substrate 11) is installed in the reaction chamber 20, and the substrate 11 is located at a position facing the shower head 24. A susceptor 25 is placed. Further, an exhaust port 26 for exhausting gas is formed at the bottom of the reaction chamber 20.

  When forming a thin film on the surface of the substrate 11 using the ALD apparatus as described above, the substrate 11 is first placed on the susceptor 25 in the reaction chamber 20. The gas switching valve 21 connects one of the plurality of pipes to the gas inlet 23, introduces a predetermined gas into the reaction chamber 20 from the gas inlet 23, and introduces the introduced gas into the shower head 23. To the processing surface of the substrate 11 for processing.

  Next, the embodiment of the thin film formation method using the ALD method of the present invention is described with reference to the formation method of the metal silicate film applied to the gate insulating film of the MOS transistor as an example. Based on the flowchart of FIG. 1 showing the above, description will be made with reference to the schematic diagrams of FIGS. In the present embodiment, an example in which an aluminum silicate film (Al silicate film) is formed as a metal silicate film will be described.

  First, although not shown in FIG. 1, the substrate 11 made of, for example, a silicon (Si) substrate is cleaned with a mixed solution of ammonia, hydrogen peroxide solution, or pure water to remove contamination of the surface of the substrate 11 due to organic matter or the like. . Then, the cleaned substrate 11 is immersed in, for example, a hydrofluoric acid aqueous solution (1% aq.) For 60 seconds to remove the natural oxide film on the surface of the substrate 11 (S101). As a result, as shown in FIG. 2A, hydrogen (H) atoms are bonded to silicon (Si) atoms on the surface of the substrate 11.

Next, the substrate 11 processed as described above is introduced into the reaction chamber 20 of the ALD apparatus shown in FIG. 4 and placed on the susceptor 25. Subsequently, water vapor (H ₂ O), H ₂ O ₂ vapor or ozone (O ₃ ), which is a reaction product containing oxygen, is supplied to the processing surface of the substrate 11 (S 1 O ₂ ). As a result, as shown in FIG. 2B, hydrogen (H) bonded to Si on the surface of the substrate 11 is replaced with a hydroxyl group (OH group).

Thereafter, the inside of the reaction chamber 20 (see FIG. 4) is sufficiently purged with an inert gas made of, for example, nitrogen (N ₂ ) gas to replace the gas atmosphere on the processing surface of the substrate 11 (S103). Thereby, unreacted H ₂ O, H ₂ O ₂ , O ₃ and unnecessary reaction products are removed. Here, N ₂ gas is used as the inert gas, but the present invention is not limited to this, and Ar or the like may be used.

これにより、基板１１の処理表面にＯ原子の層を介してＡｌ原子の層が形成される。 Next, for example, trimethylammonium [Al (CH ₃ ) ₃ ] is supplied to the processing surface of the substrate 11 as the first reactant containing metal (here, the first reactant containing Al) (S104). As a result, a reaction represented by the following formula (1) occurs on the treated surface of the substrate 11 terminated with a hydroxyl group (OH group), and Al (CH ₃ ) ₃ is treated with the treated surface as shown in FIG. Is chemisorbed. Specifically, an aluminum (Al) atom of Al (CH ₃ ) ₃ is bonded to an oxygen (O) atom of the OH group.

As a result, an Al atom layer is formed on the processing surface of the substrate 11 via the O atom layer.

Here, Al (CH ₃ ) ₃ which is a metal organic gas is used as the first reactant containing Al. However, the present invention is not limited to this, and halogen such as trichloroaluminum (AlCl ₃ ) is used. System gases may also be used.

Thereafter, the reaction chamber 20 (see FIG. 4) is sufficiently purged with N2 gas to replace the gas atmosphere on the processing surface of the substrate 11 (S105). This removes unreacted Al (CH ₃ ) ₃ and methane (CH ₄ ) produced by this reaction.

これによりＡｌ原子の層上に、Ａｌ原子にＯ原子を結合させてＯ原子の層が積層された状態となる。 Next, for example, H ₂ O is supplied to the processing surface of the substrate 11 as a second reactant containing oxygen (S106). As a result, the reaction shown in the following formula (2) occurs, and the methyl group (CH ₃ group) on the surface of the substrate 11 on which Al (CH ₃ ) ₃ is adsorbed is replaced with an OH group as shown in FIG. 2 (d). Is done.

As a result, an O atom layer is bonded to the Al atom and an O atom layer is laminated on the Al atom layer.

Here, H ₂ O is used as the second reactant. However, the present invention is not limited to this, and any compound containing oxygen may be used, and H ₂ O ₂ or O ₃ may be used. When O ₃ is used as the second reactant, the terminal methyl group (CH ₃ group) on the surface of the substrate 11 on which Al (CH ₃ ) ₃ is adsorbed is replaced with oxygen (O).

Then, after replacing the CH ₃ group with the OH group, the reaction chamber 20 (see FIG. 4) is purged with N ₂ gas to replace the gas atmosphere on the processing surface of the substrate 11 (S107). This removes unreacted H ₂ O and CH ₄ generated by the above reaction.

これにより、Ｏ原子の層の上に、Ｏ原子にＳｉ原子を結合させてＳｉ原子の層が積層された状態となる。 Next, for example, tetrakisdimethylaminosilane [Si [N (CH ₃ ) ₂ ] ₄ ] is supplied to the treated surface of the substrate 11 as a third reactant containing silicon (Si) (S108). As a result, the reaction shown in the following formula (3) occurs, and as shown in FIG. 3E, Si [N (CH ₃ ) ₂ is bonded to the O atom of the terminal OH group bonded to Al on the surface of the substrate 11. ] ₄ ] Si atoms are bonded.

As a result, the Si atom layer is laminated on the O atom layer by bonding the Si atom to the O atom.

Thereafter, the reaction chamber 20 (see FIG. 4) is purged with N ₂ gas to replace the gas atmosphere on the surface of the substrate 11 (S109). This removes unreacted Si [N (CH ₃ ) ₂ ] ₄ ] and dimethylamine (HN (CH ₃ ) ₂ ) produced by the above reaction.

Here, Si [N (CH ₃ ) ₂ ] ₄ ] is used as the third reactant containing Si. However, the present invention is not limited to this, and can be introduced as a gas. Any material may be used as long as it contains Si that can be bonded to the O atom of the terminal OH group bonded to. Examples of the third reactant containing Si include trisdimethylaminosilane [HSi [N (CH ₃ ) ₂ ] ₃ ], trisdiethylaminosilane [HSi [N (C ₂ H ₅ ) ₂ ] ₃ ], tetrakisdiethylaminosilane. _{[Si [n (C 2 H 5} ) 2] 4 ], tetraisopropoxysilane _{[Si (i-OC 3 H 7} ) 4 ], n- tetrabutoxysilane _{[Si (n-OC 4 H 9} ) 4 ], Organic systems containing Si such as t-tetrabutoxysilane [Si (t-OC ₄ H ₉ ) ₄ ], tetramethoxysilane [Si (OCH ₃ ) ₄ ], tetraethoxysilane [Si (OC ₂ H ₅ ) ₄ ] Gas.

これによりＳｉ原子の層上に、Ｓｉ原子にＯ原子を結合させてＯ原子の層が積層された状態となることから、基板１１の処理表面にはＯ原子の層を介して、Ａｌ原子の層、Ｏ原子の層、Ｓｉ原子の層、Ｏ原子の層が順次積層形成された状態となる。 Next, for example, water vapor (H ₂ O) is supplied to the processing surface of the substrate 11 as a second reactant containing oxygen (S110). As a result, a reaction represented by the following formula (4) occurs, and the terminal dimethylamino group on the treated surface of the substrate 11 on which Si [N (CH ₃ ) ₂ ] ₄ is chemisorbed as shown in FIG. [N (CH _{3) 2} group] is replaced with an OH group.

As a result, the O atom is bonded to the Si atom and the O atom layer is laminated on the Si atom layer, so that the Al atom is formed on the processing surface of the substrate 11 via the O atom layer. A layer, an O atom layer, an Si atom layer, and an O atom layer are sequentially stacked.

Thereafter, the reaction chamber 20 (see FIG. 4) is purged with N ₂ gas to replace the gas atmosphere on the processing surface of the substrate 11 (S111). This removes unreacted H ₂ O and NH (CH ₃ ) ₂ produced by this reaction.

  Next, it is determined whether the Al silicate film formed as described above has a desired film thickness (S112). If the Al silicate film has reached the desired film thickness, that is, if “Yes”, the film forming process is terminated.

On the other hand, when the desired film thickness has not been reached, that is, in the case of “No”, the process returns to S104 to perform the process from the step of forming the Al atom layer again until the Al silicate film has the desired film thickness. Repeat the process. In the case where the film thickness is confirmed after the process is repeated and the process is terminated, the second reactant is supplied to the process surface and purged with an inert gas, that is, after the process of S107 or S111. finish. When H ₂ O or H ₂ O ₂ is used as the second reactant, the end of the Al silicate film formed on the processing surface of the substrate 11 becomes an OH group. When this Al silicate film is used as a gate insulating film, The H is removed by a process such as film formation in a subsequent process.

According to such a thin film formation method using the ALD method, an Al silicate film is formed on the processing surface of the substrate 11. Since this Al silicate film contains Al oxide, the relative dielectric constant can be made higher than that of a film made of SiO ₂ alone, and since silicon oxide is contained, the film is made more than that of a film made of Al oxide alone. The crystallization temperature can be increased. Further, by forming such an Al silicate film by the ALD method, it is possible to form an Al silicate film having a stoichiometric composition by laminating each layer in an atomic layer unit, so that the composition ratio of the Al silicate film Can be easily controlled, and the relative dielectric constant and crystallization temperature can be adjusted.

Further, as compared with the MOCVD method, after the surface of the substrate 11 is treated with each reactant, the gas atmosphere on the treated surface of the substrate 11 is replaced with an inert gas. Can be prevented from being mixed into the film, and deterioration of the film characteristics of the Al silicate film can be suppressed. Further, in the step of S101, a natural oxide film on the surface of the substrate 11 is removed with a hydrofluoric acid aqueous solution (1% aq.), And H is bonded to Si on the surface of the substrate 11, thereby forming an Al silicate film and Since an intermediate layer made of SiO ₂ is not formed between the substrate 11 and the substrate 11, deterioration of film characteristics can be suppressed.

  Therefore, when a gate oxide film made of an Al silicate film is formed by such a method, the relative dielectric constant is increased to increase the thickness of the gate oxide film by controlling the composition ratio of the Al silicate film. Therefore, the carrier tunneling phenomenon can be suppressed. Further, by increasing the crystallization temperature, the gate oxide film can be made thermally stable and difficult to crystallize, so that an increase in leakage current between the gate and the substrate can be suppressed.

  In this embodiment, the example in which the aluminum silicate film is formed as the metal silicate film applied to the gate insulating film has been described. However, the present invention is not limited to this, and the metal that is combined with oxygen and has a high relative dielectric constant. It only has to be configured. Accordingly, the metal contained in the first reactant used to form the metal atom layer includes titanium (Ti), tantalum (Ta), zirconium (Zr), hafnium (Hf), indium (In), antimony ( Sb), lead (Pb), barium (Ba), praseodymium (Pr). Among these, in particular, the first reactant containing Al, Zr, and Hf is preferable because of its high versatility.

In this embodiment, in order to facilitate chemical adsorption of Al (CH ₃ ) ₃ used as the first reactant containing metal on the processing surface of the substrate 11, H is replaced with an OH group in the step of S 102. However, if the bond energy between the metal contained in the first reactant and Si on the surface of the substrate 11 is larger than the bond energy between Si and H, H is bonded to Si on the surface of the substrate 11. Thus, the first reactant may be supplied to the surface of the substrate 11 and the first reactant may be chemically adsorbed on the surface of the substrate 11. In this case, the metal atoms of the first reactant are directly bonded to Si on the substrate surface, and the steps S102 and S103 can be omitted.

  Further, in the present embodiment, as shown in FIG. 1, steps S104 to S107 (hereinafter referred to as step A), that is, a step of forming a layer of Al atoms and a layer of O atoms on the processing surface of the substrate 11 are formed. Then, the example of performing the steps S108 to S111 (hereinafter referred to as step B), that is, the step of stacking the Si atom layer and the O atom layer on the O atom layer has been described.

  However, this invention is not limited to this, You may perform the process A after performing the process B. FIG. In this case, a Si atom layer is formed on Si on the surface of the substrate 11 via an O atom layer. Furthermore, in this embodiment, when the desired film thickness has not been reached at the stage of S112, the process returns to S104 and the process from Step A is repeated. However, the process returns to S108 and the process from Step B is repeated. I do not care.

  That is, in the present invention, step A and step B need only be included once or more throughout the entire step, and the composition ratio of the Al silicate film to be formed is determined by the number of repetitions of step A and step B. Therefore, when the composition ratio of the Al silicate film is controlled to increase the relative dielectric constant of the Al silicate film, the content of the Al oxide and the layer of the O atom can be increased because the content of the Al oxide is increased. What is necessary is just to increase the frequency | count of the process A to form. On the other hand, when the crystallization temperature of the Al silicate film is increased, the silicon oxide content is increased, so that the number of times of the process B for forming the Si atom layer and the O atom layer is increased.

  In addition, when repeating the process A and the process B, each process may be repeated alternately and each process may be performed continuously, respectively. In addition, the composition ratio of the Al silicate film may be different depending on the order in which the process A and the process B are repeated. In this case, it is necessary to set the number of times the process A and the process B are repeated in consideration of the order. is there.

It is a flowchart which shows 1st Embodiment which concerns on the thin film formation method using the ALD method of this invention. It is a schematic diagram which shows the lamination | stacking state of the atomic layer in 1st Embodiment (the 1). It is a schematic diagram which shows the lamination | stacking state of the atomic layer in 1st Embodiment (the 2). 1 is a schematic sectional view showing an example of an ALD apparatus used in a thin film forming method using an ALD method of the present invention.

Explanation of symbols

11 ... Board

Claims (9)

A method of forming a thin film on a substrate using an atomic layer deposition method, after a pretreatment step of terminating the surface of the substrate with a hydroxyl group,
Forming a layer of metal atoms on the treated surface of the substrate and forming a layer of oxygen atoms on the metal atom layer;
Forming a layer of silicon atoms on the processing surface of the substrate and forming a layer of oxygen atoms on the silicon atom layer;
Either of said 1st process and said 2nd process is performed previously. The thin film formation method using the atomic layer vapor deposition method characterized by the above-mentioned. The first step includes
After supplying a first reactant containing a metal to the processing surface of the substrate, and chemically adsorbing the first reactant on the processing surface to form the metal atom layer,
Replacing the gas atmosphere on the treated surface with an inert gas;
Next, after supplying a second reactant containing oxygen to the treated surface and reacting with the first reactant to form the oxygen atom layer,
Replacing the gas atmosphere on the treated surface with an inert gas;
The second step includes
After supplying a third reactant containing silicon to the processing surface of the substrate and chemically adsorbing the third reactant to the processing surface to form the silicon atom layer,
Replacing the gas atmosphere on the treated surface with an inert gas;
Next, after supplying a second reactant containing oxygen to the treated surface and reacting with the third reactant to form the oxygen atom layer,
The method of forming a thin film using an atomic layer deposition method according to claim 1, wherein the gas atmosphere on the treatment surface is replaced with an inert gas. The third reactant includes tetrakisdimethylaminosilane [Si [N (CH ₃ ) ₂ ] ₄ ], trisdimethylaminosilane [HSi [N (CH ₃ ) ₂ ] ₃ ], trisdiethylaminosilane [HSi [N (C ₂ H _{5) 2] 3],} tetrakis diethylaminosilane _{[Si [N (C 2 H 5} ) 2] 4 ], tetraisopropoxysilane _{[Si (i-OC 3 H 7} ) 4 ], n- tetrabutoxysilane [Si ( n-OC ₄ H ₉ ) ₄ ], t-tetrabutoxysilane [Si (t-OC ₄ H ₉ ) ₄ ], tetramethoxysilane [Si (OCH ₃ ) ₄ ], tetraethoxysilane [Si (OC ₂ H ₅ ) _4] thin film forming method using the atomic layer deposition method according to claim 2, wherein at least is one of the group consisting of. As the pretreatment step,
The method for forming a thin film using an atomic layer deposition method according to claim 1, wherein after the natural oxide film on the surface of the substrate is removed, a reactant containing oxygen is supplied to the surface of the substrate. The thin film forming method using an atomic layer deposition method according to claim 4, wherein the reactant containing oxygen is water vapor (H ₂ O) or hydrogen peroxide (H ₂ O ₂ ). A thin film with a controlled composition ratio is formed by repeating the first step and the second step and adjusting the number of repetitions of the first step and the second step. A thin film forming method using the atomic layer deposition method according to claim 1. The thin film formation method using the atomic layer deposition method according to claim 6, wherein the number of repetitions is adjusted so that the number of repetitions of the first step is larger than the number of repetitions of the second step. The thin film formation method using the atomic layer deposition method according to claim 6, wherein the number of repetitions is adjusted so that the number of repetitions of the second step is larger than the number of repetitions of the first step. The thin film forming method using an atomic layer deposition method according to claim 1, wherein the thin film is a gate insulating film.

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