JP4869495B2 - Manufacturing method of semiconductor device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique related to a manufacturing technique of a semiconductor device having an integrated circuit using a thin film transistor (hereinafter referred to as TFT) on a substrate. In particular, the present invention relates to a technique for manufacturing a semiconductor device using an amorphous silicon layer.
[0002]
[Prior art]
Silicon is classified into single crystal silicon, polycrystalline silicon, and amorphous silicon (amorphous silicon) in its form. All forms have characteristics as semiconductors and are used in all semiconductor industry fields. Semiconductor devices are usually manufactured in a clean room.
[0003]
As the thin film semiconductor used for the TFT, it is easy to use amorphous silicon. Therefore, in order to improve the TFT characteristics, silicon having crystallinity may be used. In order to obtain silicon having such crystallinity, amorphous silicon is first formed and then crystallized by heating.
[0004]
In general, as shown in FIG. 9, (1) a base film is formed on a substrate such as glass or quartz by a CVD method or the like. Next, (2) an amorphous semiconductor layer is formed. In this specification, amorphous silicon is used as the amorphous semiconductor layer. At that time, a natural oxide film is formed on the surface of the amorphous semiconductor layer. (3) Cleaning including a natural oxide film removal step is performed. Next, (4) crystallization step (5) washing is performed.
[0005]
Therefore, amorphous silicon has a bare surface in the process before crystallization, and contamination of amorphous silicon becomes a problem. Contaminants in the clean room are dopant impurities for semiconductors such as B and P, alkali (earth) metals such as Na, K and Ca, and materials constituting equipment such as Fe, Ni, Cr, Cu and Al. Some elements are known.
[Problems to be solved by the invention]
For example, when boron B, phosphorus P, etc. are activated in the heat treatment process after (5), the threshold characteristics of the transistor characteristics fluctuate. Activation is the incorporation of carriers into the silicon crystal lattice. Regarding the contamination of boron, it is known that an air conditioning filter in a clean room is a source of contamination. (Chemical contamination in semiconductor process environment and countermeasures, 1997, Realize)
[0006]
In order to solve the above-described problems, the present invention provides a technique for reducing the adhesion amount of impurities such as boron to a silicon layer with respect to a technique for manufacturing a semiconductor device having an integrated circuit using a thin film transistor on a substrate. Is an issue.
[0007]
[Means for Solving the Problems]
In order to overcome such a problem, the concentration of boron between the film formation chamber for forming the amorphous silicon layer, the chamber for forming the oxide film, the film formation chamber, and the chamber for forming the oxide film the 2.0 × 10 ¹⁶ / cm ³ and a means for conveying the substrate held below, the semiconductor manufacturing device unit supplies provided with means and oxygen is irradiated with ultraviolet rays in the chamber to form the oxide film It is. A clean oxide film can be formed in a chamber for forming an oxide film without forming a natural oxide film on the surface after the amorphous silicon film is formed. Therefore, since the boron concentration is kept at 2.0 × 10 ¹⁶ / cm ³ or less and a clean oxide film is formed on the surface of the amorphous silicon layer, it is amorphous compared to the case where a natural oxide film is formed. Impurities such as boron on the surface of the porous silicon layer are reduced. Further, in the present invention, since the transfer can be performed in the semiconductor manufacturing apparatus, (2) formation of the amorphous semiconductor layer and (3) oxide film in FIG. 1 are not exposed to the atmosphere in the clean room. Formation can be performed continuously.
[0008]
In order to overcome the above problems, a method for manufacturing a semiconductor device of the present invention includes a first step of forming an amorphous silicon layer, and a boron concentration on the surface of the amorphous silicon layer of 2.0 × 10 ¹⁶ / a second step of forming an oxide film by oxidizing the surface of the amorphous silicon layer in a state maintained at cm ³ or less, a third step of removing the oxide film, and the amorphous silicon layer A fourth step of forming a crystalline silicon layer by crystallizing the amorphous silicon layer while maintaining a boron concentration of 2.0 × 10 ¹⁶ / cm ³ or less on the surface of A method for manufacturing a semiconductor device is provided. As shown in FIG. 1, the method of manufacturing a semiconductor device according to the present invention includes (1) formation of a first base film, (2) formation of an amorphous semiconductor layer, and (3) formation of an oxide film (with ozone water). And (4) cleaning (removal of the oxide film), (5) crystallization step, and (6) cleaning. In the (5) crystallization step, laser crystallization or thermal crystallization is performed. A natural oxide film is not formed on the surface after the amorphous silicon film is formed, and a clean oxide film is formed in (3). In the present invention, a clean oxide film is formed on the surface of the amorphous silicon layer, the boron concentration on the surface of the amorphous silicon layer is maintained at 2.0 × 10 ¹⁶ / cm ³ or less, and a crystallization step I do. By forming the oxide film, boron can be prevented from adhering to the amorphous silicon layer. Further, since boron on the oxide film can be easily removed with dilute hydrofluoric acid, crystallized silicon can be formed without attaching boron to the amorphous silicon layer. Here, the boron concentration is regulated to 2.0 × 10 ¹⁶ / cm ³ or less because the shift of the V _th of the TFT from FIG. 5 (the relationship between the channel dose in the active layer and the V _th of the TFT). Is to keep the voltage at 1.0V. When the volume density of 2.0 × 10 ¹⁶ / cm ³ is converted into the surface density, it is 1.1 × 10 ¹¹ / cm ² .
[0009]
Another method for manufacturing a semiconductor device according to the present invention is a method for manufacturing a semiconductor device in which ozone water is used to oxidize the surface of the amorphous silicon layer to form an oxide film. When this manufacturing method is used, the thickness of the oxide film can be formed uniformly.
[0010]
Another method for manufacturing a semiconductor device of the present invention is a method for manufacturing a semiconductor device in which oxygen is introduced and the surface of the amorphous silicon layer is oxidized by ultraviolet irradiation to form an oxide film.
[0011]
In another method of manufacturing a semiconductor device according to the present invention, the step of forming an amorphous silicon layer ((2) formation of an amorphous semiconductor layer) and the concentration of boron on the surface of the amorphous silicon layer are set to 2. The step of forming an oxide film by oxidizing the surface of the amorphous silicon layer ((3) formation of an oxide film) and the step of removing the oxide film while maintaining the surface at 0 × 10 ¹⁶ / cm ³ or less The step of removing the oxide film ((4) cleaning (removing the oxide film)) and the surface of the amorphous silicon layer are performed in a semiconductor manufacturing apparatus (CVD apparatus) that forms a sealed space. A step of forming a crystalline silicon layer by crystallization of the amorphous silicon layer while maintaining the boron concentration at 2.0 × 10 ¹⁶ / cm ³ or less ((5) crystallization step) Is a method of manufacturing a semiconductor device performed in an apparatus that forms a sealed space. Since the surface of the amorphous silicon layer is oxidized to form an oxide film, there is no problem of adhesion of impurities to the amorphous silicon layer even if the substrate being processed is exposed to an atmosphere in a clean room.
[0012]
The method of manufacturing a semiconductor device of the present invention includes a first step of forming an amorphous semiconductor layer on a substrate, a second step of transporting the substrate on which the amorphous semiconductor layer is formed, In the method for manufacturing a semiconductor device having a third step of forming an oxide film on the crystalline semiconductor layer, the second step and the third step are performed continuously without being exposed to the atmosphere in the clean room. This is a method for manufacturing a semiconductor device. In the present invention, since it can be transported in a semiconductor manufacturing apparatus, (2) formation of an amorphous semiconductor layer and (3) formation of an oxide film are continuous without being exposed to the atmosphere in a clean room. Can be performed.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
In this embodiment mode, after the amorphous semiconductor layer 103a is formed as shown in FIG. 2B, clean oxygen is introduced into a chamber 409 (FIG. 4) for forming an oxide film of the CVD apparatus, and UV irradiation is performed. The oxide film 104 is formed while being formed.
[0014]
In FIG. 2A, the substrate 101 includes polyethylene terephthalate (PET), polyethylene, in addition to glass substrates such as barium borosilicate glass and aluminoborosilicate glass represented by Corning # 7059 glass and # 1737 glass. A plastic substrate having no optical anisotropy such as naphthalate (PEN) or polyethersulfone (PES) can be used. When a glass substrate is used, heat treatment may be performed in advance at a temperature lower by about 10 to 20 ° C. than the glass strain point. First, the substrate is cleaned.
[0015]
Then, in order to prevent impurity diffusion from the substrate 101, a base film 102 made of an insulating film such as a silicon oxide film, a silicon nitride film, or a silicon oxynitride film is formed on the surface of the substrate 101 where the TFT is formed. For example, a silicon oxynitride film 102a made from SiH ₄ , NH ₃ , and N ₂ O by plasma CVD is 10 to 200 nm (preferably 50 to 100 nm). Similarly, oxynitridation is made from SiH ₄ and N ₂ O. A silicon hydride film 102b is formed to a thickness of 50 to 200 nm (preferably 100 to 150 nm) ((A) formation of base film). Although the base film 102 is shown here as a two-layer structure, it may be formed by laminating a single layer film or two or more layers of the insulating film. In the semiconductor manufacturing apparatus (CVD apparatus) of FIG. 4, first, a substrate to be processed (not shown; hereinafter the same) is placed in a loader / unloader chamber 401, and a cleaning chamber 403 is transferred by a transfer robot 402a which is a means for transferring the substrate. The substrate to be processed is transported and cleaned with pure water. Next, the substrate being processed (not shown; the same applies hereinafter) is transferred to the loader / unloader chamber 404 by the transfer robot 402a. Next, the substrate being processed is heated in advance in the heating chamber 405, a silicon oxynitride film is formed in the first deposition chamber 406, and then a silicon oxynitride film is formed in the second deposition chamber 407. Film.
[0016]
The silicon oxynitride film 102a is formed by using a conventional parallel plate type plasma CVD method. The silicon oxynitride film 102a is introduced into the first deposition chamber with SiH ₄ as 10 SCCM, NH ₃ as 100 SCCM, and N ₂ O as 20 SCCM. The substrate temperature is 325 ° C., the reaction pressure is 40 Pa, and the discharge power density is 0.41 W / cm. ^{2. The} discharge frequency was 60 MHz.
[0017]
On the other hand, the silicon oxynitride silicon film 102b is introduced into the second deposition chamber with SiH ₄ as 5 SCCM, N ₂ O as 120 SCCM, and H ₂ as 125 SCCM. The substrate temperature is 400 ° C., the reaction pressure is 20 Pa, and the discharge power density is 0. 41 W / cm ² and a discharge frequency of 60 MHz. These films can be formed continuously only by changing the substrate temperature and switching the reaction gas.
[0018]
For example, as described above, after the silicon oxynitride film 102a and the silicon oxynitride silicon film 102b are continuously formed by the plasma CVD method, the reaction gas is changed from SiH ₄ , N ₂ O, H ₂ to SiH ₄ and H ₂ or By switching to only SiH _{4, the} film can be continuously formed without being exposed to the atmosphere in the clean room. As a result, contamination of the surface of the silicon oxynitride silicon film 102b can be prevented, and variation in characteristics and threshold voltage of the manufactured TFT can be reduced.
[0019]
Next, as shown in FIG. 2B, a semiconductor layer 103a having an amorphous structure with a thickness of 25 to 80 nm (preferably 30 to 60 nm) is formed by a known method such as a plasma CVD method or a sputtering method. . For example, an amorphous silicon film is formed to a thickness of 55 nm by plasma CVD. The semiconductor film having an amorphous structure includes an amorphous semiconductor layer and a microcrystalline semiconductor film, and a compound semiconductor film having an amorphous structure such as an amorphous silicon germanium film may be applied. In addition, the base film 102 and the amorphous semiconductor layer 103a can be formed continuously. As shown in FIG. 4, an amorphous semiconductor layer is formed on a substrate (not shown) being processed in the third film formation chamber 408.
[0020]
Next, as shown in FIG. 4, after the amorphous semiconductor layer is formed, clean oxygen is introduced into the chamber 409 in which the oxide film is formed by the gas introducing means 409g and irradiated with ultraviolet rays. As shown, the surface of the amorphous semiconductor layer 103a is oxidized to form an oxide film 104. The thickness of the oxide film 104 is 2 to 20 mm. Once an oxide film having such a thickness is formed, the formation of a natural oxide film hardly proceeds at room temperature (25 ° C.) even if the atmosphere is in a clean room. As described above, it is desirable that the amorphous semiconductor layer 103a and the oxide film 104 be continuously formed in the same CVD apparatus without being exposed to the atmosphere in the clean room ((B) amorphous Semiconductor layer formation / oxide film formation). Since the surface of the amorphous silicon layer is oxidized to form an oxide film, there is no problem of adhesion of impurities to the amorphous silicon layer even if the substrate being processed is exposed to an atmosphere in a clean room.
[0021]
Next, as shown in FIG. 4, the substrate being processed is transferred to the cleaning chamber 403 by the transfer robot 402a, and the gate valve 411a is closed. 404 to 409 are provided with gas introduction means 404p to 409p and exhaust means 404g to 409g, respectively. When the gate robot 411a is closed and the transfer robot 402b, which is a means for transferring a substrate, is to be operated, the substrate being processed may be placed in the loader / unloader chamber 412. The transport robot 402b is provided with exhaust means 402p.
[0022]
Next, as shown in FIG. 3A, cleaning with diluted hydrofluoric acid (HF: 0.5%, H ₂ O ₂ : 1.0% aqueous solution) is performed, and the oxide film 104 is removed. In addition, with respect to particles and contaminants attached to the surface of the oxide film 104, cleaning using ozone, ultrasonic cleaning that generates an intimate wave in pure water or a chemical solution by ultrasonic waves, and is cleaned by the impact, It can be removed by a megasonic cleaning technique which is an ultrasonic wave whose frequency is increased to about 1 MHz. A cycle cleaning in which cleaning with dilute hydrofluoric acid and cleaning using ozone or megasonic cleaning are repeated may be used ((A) cleaning). As shown in FIG. 4, the substrates being processed returned to the loader / unloader chamber 404 by the transfer robot 402b are subjected to spin cleaning processing one by one in the cleaning chamber 403. The spin rotation speed and time conditions may be determined as appropriate depending on the substrate area, coating material, and the like. The substrate after the cleaning process is collected in the loader / unloader chamber 401.
[0023]
The cleaning chamber 403 is purged with N ₂ to prevent contamination in the atmosphere. In the cleaning chamber 403, drainage and exhaust are also performed.
[0024]
Next, a crystallization step is performed to manufacture a crystalline semiconductor layer 103b from the amorphous semiconductor layer 103a as shown in FIG. As the method, a thermal annealing method (solid phase growth method) can be applied. In addition, the crystalline semiconductor layer 103b can be formed by a crystallization method using a catalytic element in accordance with the technique disclosed in Japanese Patent Application Laid-Open No. 7-130652. Next, cleaning is performed. ((B) Crystallization process / Washing)
[0025]
Thereafter, the semiconductor device can be completed through a known semiconductor manufacturing process. For example, crystallized silicon is subjected to the steps shown in FIG. 7 (etching of crystallized silicon, resist removal, oxide film formation (cleaning with ozone water), oxide film removal), and the gate insulating film is formed. Be filmed.
[0026]
As in this embodiment, it is preferable that a chamber for forming an oxide film is provided in the CVD apparatus. If this CVD apparatus is used, it can process in a vacuum including conveyance except for the chamber for forming the oxide film and the cleaning chamber.
[0027]
In this embodiment, (2) formation of an amorphous semiconductor layer, (3) formation of an oxide film, and (4) cleaning (removal of the oxide film) in FIG. 1 are performed in a semiconductor manufacturing apparatus (CVD apparatus). Is called.
[0028]
In this embodiment, clean oxygen after the formation of the amorphous semiconductor layer 103a is introduced into the chamber 409 for forming the oxide film of the CVD apparatus, and the oxide film 104 is formed by UV irradiation. A gas containing clean oxygen may be introduced into 409 after the semiconductor layer is formed and then released into the atmosphere to form an oxide film, or a method using ozone water that can form the oxide film uniformly, or heating An oxide film may be formed using a method using the hydrogen peroxide solution. Any method can be used as long as the thickness of the oxide film can be formed uniformly. Further, when the method using ozone water is adopted, it is preferable to use a CVD apparatus provided with a cleaning chamber. Advantages of using cleaning with ozone water include (1) to (3). (1) An oxide film is formed on the surface of the amorphous semiconductor layer by ozone, and contaminants adsorbed on the amorphous semiconductor layer are removed together with the oxide film using an acidic solution containing fluorine. Can be removed. (2) When the amorphous semiconductor layer is hydrophobic, the surface of the amorphous semiconductor layer becomes hydrophilic by oxidizing the surface with ozone, thereby increasing the cleaning effect. (3) If it is a trace amount carbon compound which exists in the clean room air atmosphere, it can be removed by oxidative decomposition with ozone.
[0029]
In this embodiment, since a clean oxide film is formed on the surface of the amorphous silicon layer, impurities such as boron adhering to the amorphous silicon layer are reduced as compared with the process of forming the natural oxide film.
[0030]
(Experiment 1) An experiment for examining whether or not the amount of contamination of an amorphous silicon layer by a natural oxide film is an amount that causes a device characteristic defect will be described. In this embodiment, boron contamination was examined.
[0031]
In the case of staying in (1), (2) and (3) between the steps of FIG. 7, the contamination density of boron adhering to the surface and existing at the interface between the gate insulating film and the crystalline silicon as it was was measured. The boron contamination density during the steps (1), (2), and (3) in FIG.
[0032]
In this embodiment, an experiment was performed using a 2-inch Si wafer that had been subjected to a cleaning process. In order to measure the contamination density of boron in the steps (1), (2), and (3) in FIG. 7, experiments were performed in the order of step C, step A, and step B in FIG. The boron contamination density during the steps (1), (2), and (3) in FIG. 6 can be regarded as the same as the boron contamination density during the steps (1), (2), and (3) in FIG. As shown in FIG. 6, Step C ((2) formation of an amorphous semiconductor layer, (3) formation of an oxide film (cleaning with ozone water), (4) cleaning with dilute hydrofluoric acid (described above) Removal of oxide film), (3) exposure to a clean room atmosphere for 3 hours, (2) formation of amorphous semiconductor layer), and then step A ((2) formation of amorphous semiconductor layer, (1) ▼ Exposure to clean room atmosphere for 3 hours, (3) Formation of oxide film (cleaning with ozone water (6-15 μg / cm ³ )), (4) Cleaning with dilute hydrofluoric acid (removal of the oxide film), (2 ) Formation of amorphous semiconductor layer), followed by Step B ((2) Formation of amorphous semiconductor layer, (3) Formation of oxide film (cleaning with ozone water), (2) In a clean room atmosphere After 3 hours exposure, (4) cleaning with dilute hydrofluoric acid (removal of the oxide film), (2) formation of amorphous semiconductor layer), SIMS (Secondary Ion Mass Spectroscopy) measurement was performed. In cleaning with ozone water, the substrate being processed was immersed in ozone water for 5 minutes and then washed with water for 10 minutes. In (1), (2) and (3) between the steps in FIG. 6, the substrate being processed is exposed to the clean room air atmosphere for 3 hours. FIG. 8 shows the result of the concentration of B by SIMS measurement in steps (1) to (3). The contamination density of boron was 4.2 × 10 ¹² / cm ² , 1.2 × 10 ¹² / cm ² , and 1.2 × 10 ¹³ / cm ² , respectively. When these are converted into volume concentrations in the active layer having a film thickness of 55 nm, they are 2.2 × 10 ¹⁷ / cm ² , 7.6 × 10 ¹⁷ / cm ² , and 2.2 × 10 ¹⁸ / cm ² .
[0033]
The boron contamination density during the process (1), (2), (3) in FIG. 6 can be regarded as the same as the boron contamination density during the process (1), (2), (3) in FIG. The amount of contamination between processes (1) is 3.5 times the amount of contamination between processes (2). (2) Immediately after the formation of the amorphous semiconductor layer, an oxide film is formed with ozone water. This state may be maintained until (4) cleaning (removal of the oxide film). (2) Between the formation of the amorphous semiconductor layer and the formation of the gate insulating film in FIG. 7, it is preferable to form an oxide film on the surface of the silicon layer to prevent boron from entering the silicon layer.
[0034]
When a chamber for forming an oxide film is not provided in the CVD apparatus for forming an amorphous semiconductor layer, the time for exposing the substrate being processed to the atmosphere in the clean room within 60 minutes, preferably within 10 minutes. To. FIG. 5 shows the relationship between the channel dose in the active layer of the semiconductor device manufactured through the process of FIG. 9 and the _Vth of the TFT. Channel-doped boron also causes a shift in V _th if the crystallized silicon layer is activated from the atmosphere in the clean room while adhering to the amorphous silicon layer. Therefore, from FIG. 5, when 3.6 × 10 ¹⁷ / cm ³ of boron is deposited in 3 hours, V _th of 3.5 V is shifted, but within 60 minutes, the concentration is 1/3 of that Since the amount of adhesion can be suppressed to (1.2 × 10 ¹⁷ / cm ³ ), it can be suppressed to a V _th shift of 1.8 V. Further, if it is within 10 minutes, the adhesion amount can be suppressed to a concentration of 1/18 (2.0 × 10 ¹⁶ / cm ³ ), so that a V _th shift of 1.0 V can be suppressed. Further, the variation in the amount of boron contamination between the substrates and between the substrates shifts _Vth of 1.0 to 7.0 V.
[0035]
【The invention's effect】
In the present invention, since a clean oxide film is formed on the surface of the amorphous silicon layer, impurities such as boron adhering to the amorphous silicon layer are reduced as compared with the process of forming the natural oxide film.
[0036]
In addition, since it can be transported in the semiconductor manufacturing apparatus, (2) the formation of the amorphous semiconductor layer and (3) the formation of the oxide film are continuously performed without being exposed to the atmosphere in the clean room. It is possible to be
[0037]
Furthermore, the V _th shift of the TFT manufactured by the manufacturing process of the present invention can be suppressed to 1.0V.
[Brief description of the drawings]
FIG. 1 is a flowchart showing the present invention. FIG. 2 is a cross-sectional view showing a method for manufacturing a crystalline semiconductor layer according to a first embodiment.
3 is a cross-sectional view showing a method for manufacturing a crystalline semiconductor layer in Embodiment 1. FIG.
FIG. 4 is a semiconductor manufacturing apparatus according to the present invention. FIG. 5 is a relationship between a channel dose in an active layer and _Vth of a TFT. FIG. 6 is a flowchart showing an experimental process. 8 is a B concentration in steps (1) to (3). FIG. 9 is a flowchart showing a conventional method for manufacturing a crystalline semiconductor layer.

Claims (3)

A first step of forming a semiconductor film having an amorphous structure;
A second step of oxidizing the surface of the semiconductor film to form an oxide film;
A third step of removing the oxide film;
A fourth step of crystallizing the semiconductor film in a state where the boron concentration on the surface of the semiconductor film from which the oxide film has been removed is maintained at 2.0 × 10 ¹⁶ / cm ³ or less ;
Have
The first step and the second step are continuously performed in the first apparatus having a sealed space without being exposed to the atmosphere in the clean room ,
The method of manufacturing a semiconductor device, wherein the second step is performed by using ozone or by introducing oxygen and irradiating ultraviolet rays. A first step of forming a semiconductor film having an amorphous structure;
A second step of oxidizing the surface of the semiconductor film to form an oxide film;
A third step of removing the oxide film;
A fourth step of crystallizing the semiconductor film in a state where the boron concentration on the surface of the semiconductor film from which the oxide film has been removed is maintained at 2.0 × 10 ¹⁶ / cm ³ or less ;
Have
The first step and the second step are continuously performed in the first apparatus having a sealed space without being exposed to the atmosphere in the clean room ,
The third step and the fourth step are continuously performed in the second apparatus having a sealed space without being exposed to the atmosphere in the clean room ,
The method of manufacturing a semiconductor device, wherein the second step is performed by using ozone or by introducing oxygen and irradiating ultraviolet rays. ^{3. The} semiconductor device according to claim 1, wherein the second step is performed in a state where a boron concentration on a surface of the semiconductor film is maintained at 2.0 × 10 ¹⁶ / cm ³ or less. Production method.

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