Patent Application
20060022228
This Application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2004-221490, filed on Jul. 29, 2004; the entire contents of which are incorporated herein by reference.
The invention relates to a method of manufacturing a silicon nitride film and a method of manufacturing a semiconductor device, and more particularly, to a method of manufacturing a silicon nitride film by LP-CVD (Low Pressure-Chemical Vapor Deposition) method, a method of manufacturing a semiconductor device comprising this method, and a semiconductor device.
Silicon nitride film is formed by LP-CVD method for the purpose of forming a sidewall or liner film of a gate electrode of a semiconductor device. However, when silicon raw material such as SiH2Cl2, SiCl4 and Si2Cl6, and NH3 are used for raw material in this case, chlorine contained in the silicon raw material and hydrogen contained in NH3 remain in the formed film as impurities. This phenomenon is particularly significant in film formation at low temperatures (e.g., 600° C. or less), which causes problems such as the decrease of density and wet etch resistance of the nitride film.
In this respect, a technique for forming a silicon nitride film by atomic layer deposition (ALD) using Si2Cl6 and NH3 has been proposed for the purpose of reducing impurity content while maintaining the Si/N ratio to be constant.
More specifically, in the case of this method, in a first step 110, silicon raw material gas containing chlorine such as SiH2Cl2 and Si2Cl6 is introduced onto a silicon wafer in a reaction chamber.
Next, in a second step 120, nitrogen gas is introduced to replace unreacted gas in the reaction chamber. Then, in a third step 130, activated nitrogen raw material gas is introduced into the reaction chamber.
Next, in a fourth step 140, nitrogen gas is introduced to replace unreacted gas in the reaction chamber.
By this technique, it is possible to form a film containing a smaller amount of chlorine impurities as compared to silicon nitride film formed by conventional LPCVD (see, e.g., Japanese Laid-Open Patent Application 2002-343793).
However, a nitride film used for a sidewall or liner film of a gate electrode of a semiconductor device requires a method of forming a nitride film of high film quality and with high coverage at a film formation temperature of 500° C. or less (e.g., film formation temperature of 450° C.) in order to achieve low thermal budget. On the contrary, according to conventional film formation methods, the amount of impurities in the film increases as the film formation temperature decreases, which causes a problem of the degradation of film quality in terms of wet etch resistance and the like.
For example, fabrication of a semiconductor device having metal gate electrodes by the damascene gate process requires a step of cleaning with HF solution after a liner film is formed with silicon nitride film. In the nitride film formed by the conventional technology at a film formation temperature of 500° C. or less, the amount of etching by HF solution is large, which makes it difficult to form an intended structure.
According to an aspect of the invention, there is provided a method of manufacturing a silicon nitride film that forms a silicon nitride film on a surface of a substrate comprising sequentially repeating: a first step of feeding a first gas containing silicon and nitrogen to the surface of the substrate; a second step of feeding a second gas containing nitrogen to the surface of the substrate; and a third step of feeding a third gas containing hydrogen to the surface of the substrate
According to other aspect of the invention, there is provided a method of manufacturing a semiconductor device comprising a step of forming a first silicon nitride film on a substrate including a semiconductor layer, the step of forming the first silicon nitride including sequentially repeating: a first step of feeding a first gas containing silicon and nitrogen to the surface of the substrate; a second step of feeding a second gas containing nitrogen to the surface of the substrate; and a third step of feeding a third gas containing hydrogen to the surface of the substrate.
According to other aspect of the invention, there is provided a semiconductor device comprising: a semiconductor layer; a gate insulation film provided on the semiconductor layer; a gate electrode provided on the gate insulation film; and a gate sidewall made of silicon nitride provided on a side surface of the gate electrode and the gate insulation film, a percentage of chlorine content in a portion adjacent to the gate electrode and the gate insulation film being smaller than the percentage of chlorine content in other portions.
According to other aspect of the invention, there is provided a semiconductor device comprising: a semiconductor layer; a gate insulation film provided on the semiconductor layer; a gate electrode provided on the gate insulation film; and a gate sidewall made of silicon nitride provided on a side surface of the gate electrode and the gate insulation film, an etching rate for hydrofluoric acid in a portion adjacent to the gate electrode and the gate insulation film being smaller than the etching rate for hydrofluoric acid in other portions.
According to other aspect of the invention, there is provided a semiconductor device comprising: a semiconductor layer; a first interlayer insulation film provided on the semiconductor layer and comprising a first silicon nitride film, a second silicon nitride film provided on the first silicon nitride film, and a third silicon nitride film provided on the second silicon nitride film, chlorine content in the first and third silicon nitride-films being smaller than chlorine content in the second silicon nitride film; a second interlayer insulation film provided on the first interlayer insulation film and having smaller dielectric constant than silicon nitride; and an electrode penetrating through the second interlayer insulation film and the first interlayer insulation film to the semiconductor layer.
According to other aspect of the invention, there is provided a semiconductor device comprising: a semiconductor layer; a first interlayer insulation film provided on the semiconductor layer and comprising a first silicon nitride film, a second silicon nitride film provided on the first silicon nitride film, and a third silicon nitride film provided on the second silicon nitride film, an etching rate for hydrofluoric acid in the first and third silicon nitride films being smaller than the etching rate for hydrofluoric acid in the second silicon nitride film; a second interlayer insulation film provided on the first interlayer insulation film and having smaller dielectric constant than silicon nitride; and an electrode penetrating through the second interlayer insulation film and the first interlayer insulation film to the-semiconductor layer.
The present invention will be understood more fully from the detailed description given herebelow and from the accompanying drawings of the embodiments of the invention. However, the drawings are not intended to imply limitation of the invention to a specific embodiment, but are for explanation and understanding only.
In the drawings:
Embodiments of the invention will now be described with reference to the drawings.
First, in a first step 11, raw material gas containing silicon and chlorine is introduced onto a substrate such as a silicon wafer placed in a reaction chamber. Such raw material gas may include, for example, SiH2Cl2 and Si2Cl6. This raw material gas is hereinafter referred to as “first gas”.
Next, in a second step 12, nitrogen gas is introduced to replace unreacted gas in the reaction chamber.
Next, in a third step 13, raw material gas containing nitrogen is introduced into the reaction chamber. The raw material gas containing nitrogen is hereinafter referred to as “second gas”.
Next, in a fourth step 14, nitrogen gas is introduced to replace unreacted gas in the reaction chamber.
Next, in a fifth step 15, raw material gas containing activated hydrogen is introduced into the reaction chamber. The raw material gas containing activated hydrogen is hereinafter referred to as “third gas”.
Finally, in a sixth step 16, nitrogen gas is introduced to replace unreacted gas in the reaction chamber.
The first to sixth steps described above is grouped into one cycle. A silicon nitride film with low chlorine concentration is formed by repeating this cycle until a desired film thickness is reached. The single cycle may have a duration of about 30 seconds, for example.
It should be noted that, for convenience of description,
Furthermore, for convenience of description,
In the reaction chamber 31, a silicon wafer 35 can be mounted on a wafer stage 36. On the sidewall of the reaction chamber 31, it is provided with an injector 32 for introducing the first gas (raw material gas containing silicon and nitrogen such as SiH2Cl2 and Si2Cl6), an injector 33 for introducing the second gas (raw material gas containing nitrogen such as NH3), an injector 34 for introducing the third gas (raw material gas of activated hydrogen), and an exhaust port 37 connected to a vacuum pump.
Activated hydrogen can be generated, for example, by application of a radio frequency wave of 13.56 MHz (megahertz) at 800 W (watt) by a RF generator in a remote plasma generator (not shown). Alternatively, hydrogen can be activated by contacting it with catalyst, or exposing it to ultraviolet radiation. The catalyst may include, for example, tungsten, platinum, palladium, molybdenum, tantalum, titanium, titanium oxide, vanadium, silicon, alumina, silicon carbide, and metallized ceramic. In addition, hydrogen may be activated by utilizing the principle of photocatalysis.
When hydrogen is activated by ultraviolet radiation, it is efficient that the wavelength of ultraviolet radiation is generally 400 nanometers or less.
The hydrogen thus activated is then introduced into the reaction chamber 31.
The second gas containing nitrogen may include, for example, NH3. Alternatively, gas containing activated nitrogen may be introduced. Also in this case, plasma can be used to activate nitrogen.
Film formation can be carried out in a condition of, for example, a temperature of 450° C., pressure of 130 Pa (pascal), Si2Cl6 flow rate of 10 cc, NH3 flow rate of 1000 cc, and H2 flow rate of 1000 cc. The duration of flowing these gases may be, for example, about 5, 10, and 20 seconds in this order.
The raw material gas of activated hydrogen may include gas containing hydrogen radicals and atomic hydrogen. For example, when a hydrogen molecule is decomposed by plasma, catalyst or exposure to ultraviolet radiation, a hydrogen atom having an unpaired electron is obtained. This hydrogen atom has high reactivity, and is active.
The second gas containing nitrogen may also include amine-based gas such as hydrazine, except for NH3.
According to the present embodiment, a silicon nitride film with low chlorine content can be formed at low temperatures by following the steps described above. The film quality of the nitride film is improved by forming the film at low temperatures without applying extra heat to the semiconductor device under the manufacturing process, which results in an effect of improving the reliability of the semiconductor device.
More specifically, comparison was made among three kinds of films: a silicon nitride film 41 of a first comparative example formed by simultaneously introducing two kinds of gas, Si2Cl6 and NH3; a silicon nitride film 42 of a second comparative example formed by alternately introducing the first gas (Si2Cl6) and the second gas (activated NH3) and repeating it; and a silicon nitride film 43 according to the invention formed by introducing the first gas (Si2Cl6), the second gas (activated NH3), and then the third gas (activated hydrogen) and repeating it.
The chlorine concentration measured by the total-reflection X-ray fluorescence method was 1.40×1014 (cm2) for the silicon nitride film 41 of the first comparative example and 8.60×1013 (cm−2) for the silicon nitride film 42 of the second comparative example formed by conventional LPCVD, whereas it was 4.7×1013 (cm−2) for the silicon nitride film 43 formed by the method of the invention. That is, it was found that the invention can reduce the residual amount of chlorine by 65% relative to the silicon nitride film 41 of the first comparative example, and 45% relative to the silicon nitride film 42 of the second comparative example.
As described above, the invention can reduce the amount of chlorine impurities in the silicon nitride film, and improve the wet etch resistance. That is, the invention achieves a silicon nitride film with low thermal budget, constant Si/N ratio, and small amount of impurities, and can improve the film quality such as wet etch resistance by further reducing the amount of chlorine impurities relative to the conventional art.
For example, fabrication of a semiconductor device having metal gate electrodes by the damascene gate process requires a step of cleaning with HF solution after a liner film is formed with nitride film. In the nitride film formed by the conventional technology at a film formation temperature of 500° C. or less, the amount of etching by HF solution is large, which makes it difficult to form an intended structure. On the contrary, according to the invention, a nitride film with good quality having a small amount of etching by HF solution can be formed. As a result, problems associated with the manufacturing process can be avoided, and the electric properties can be improved.
In other words, the invention can achieve reduction of the amount of chlorine impurities in the silicon nitride film, and improve the wet etch resistance, thus providing significant industrial advantages.
Next, a method of manufacturing a semiconductor device comprising the method of manufacturing a silicon nitride film according to the invention will be described.
First, as shown in
Next, as shown in
Next, as shown in
As compared to the sidewall 71 according to the invention, the sidewall 81 of the comparative example has a higher concentration of chlorine 82 in the film. For example, diffusion of chlorine into the gate isolation film 83 or gate electrode 84 may decrease the reliability of the semiconductor device. On the contrary, in the sidewall 71 according to the invention, the amount of residual chlorine content is reduced. As a result, the amount of impurities diffusing into the gate isolation film 62 or gate electrode 73 can be held down, which achieves an effect of improving the reliability of the semiconductor device.
The invention achieves another advantageous effect in that a film of good quality with reduced concentration of chlorine content can be formed at low temperatures also in forming a gate insulation film and liner film (etching stopper film) made of silicon nitride film.
The surface portion of a silicon substrate is isolated and separated by component separation regions 101, and a MOSFET is formed in each of the separated wells 102. Each MOSFET comprises a source region 107, a drain region 108, and a channel 103 provided between them. A gate electrode 106 is provided on the channel 103 via a gate isolation film 104. LDD (lightly doped drain) regions 103D are provided between the source/drain region 107, 108 and the channel 103 for the purpose of preventing the so-called “short channel effect”. A gate sidewall 105 is provided adjacent to the gate electrode 106 on the LDD region 103D. The gate sidewall 105 is provided in order to form the LDD region 103D in a self-aligned manner.
Silicide layers 119 are provided on the source/drain region 107, 108 and the gate electrode 106 for improving contact with the electrodes. The upper side of this structure is covered with a first interlayer isolation film 110, a second interlayer isolation film 111 and a third interlayer isolation film 112, through which contact holes penetrate. Source contact 113S, gate contact 113G, and drain contact 113D are formed through the contact holes. Here, the first interlayer isolation film 110 and the third interlayer isolation film 112 can be formed, for example, from silicon nitride. The second interlayer isolation film 111 can be formed, for example, from silicon oxide.
Further thereon, a fourth interlayer isolation film 114 and a fifth interlayer isolation film 115 are formed. In trenches penetrating through them, source wiring 116S, gate wiring 116G, and drain wiring 116D are each embedded. Here, the fourth interlayer isolation film 114 can be formed from silicon oxide. The fifth interlayer isolation film 115 can be formed from silicon nitride.
In manufacturing a semiconductor device as described above, according to the invention, not only the gate sidewall 105, but also the silicon nitride film constituting the gate insulation film 104, the first interlayer isolation film 110, the third interlayer isolation film 112, and the fifth interlayer isolation film 115 can be formed by the invention described above with reference to FIGS. 1 to 3.
First, as shown in
Here, in the step of forming the gate isolation film 104, the silicon nitride film can be formed by the method described above with reference to
In addition, also in the step of forming the gate sidewall 105, as described above with reference to
Next, as shown in
After the silicon nitride film is thus formed as the first interlayer isolation film 110, a silicon oxide film with a thickness of 600 nm is formed as the second interlayer isolation film 111 by plasma CVD using TEOS (tetraethoxysilane) gas at 600° C.
Alternatively, the second interlayer isolation film 111 may be made of material with lower dielectric constant. Such material may include silicon oxides having methyl group(s), silicon oxides having hydrogen group(s), and organic polymers. More specifically, the material may include, for example, various silsesquioxane compounds such as porous methyl silsesquioxane (MSQ), polyimide, fluorocarbon, parylene, and benzocyclobutene. The method of forming such materials may include the spin on glass (SOG) method in which a thin film is formed by spin coating and heat treating the solution.
After the second interlayer isolation film 111 is thus formed, as described in
Subsequently, resist is applied and patterned to form a resist pattern 120. The resist pattern 120 is formed, for example, by exposure at 120 nm diameter using an ArF exposure apparatus.
Next, as shown in
Next, as shown in
Subsequently, as shown in
At this time, etching can be stably carried out by using the third interlayer isolation film 112 made of silicon nitride film as an etching mask. More specifically, a large etching selection ratio can be easily obtained by causing etching rates to differ between the silicon oxide film constituting the second interlayer isolation film 111 and the silicon nitride film constituting the third interlayer isolation film 112. Consequently, the second interlayer isolation film 111 can be etched in a condition where it is firmly masked by the third interlayer isolation film 112. That is, a desired opening can be stably formed by eliminating problems such as variation of etching opening size due to mask degradation.
On the other hand, since the first interlayer isolation film 110 is formed from the same silicon nitride film as that of the third interlayer isolation film 112, the first interlayer isolation film 110 functions reliably as an etching stopper. That is, problems due to overetching and underetching can also be eliminated.
Next, as shown in
Next, as shown in
The surface is then polished by chemical mechanical polishing (CMP) for planarization. In this way, a structure in which contact metal is embedded as shown in
Next, as shown in
Next, as shown in
Then, as shown in
Subsequently, metal for wiring is deposited, and then smoothing is carried out by CMP polishing. In this way, as shown in
As described above, according to the present embodiment, the silicon nitride film constituting interlayer insulation films 110, 112, and 115 acting as an etching stopper and hard mask can be formed at low temperatures, thereby preventing deterioration of the silicide layer 119. In addition, the silicon nitride film constituting these interlayer insulation films has low concentration of residual chlorine, and thus is superior in terms of the reliability of the semiconductor device.
In this specific example, the gate insulation film comprises a first gate insulation film 62A and a second gate insulation film 62B. The first gate insulation film is made of silicon nitride with a thickness of about one nanometer, and is deposited by the method described above with reference to FIGS. 1 to 3. On the other hand, the second gate insulation film is made of high-k (high dielectric constant) material with a thickness of about five nanometers, and is formed by the conventional ALD method.
According to this specific example, the first gate insulation film 62A can prevent impurities such as boron from diffusing out of the gate electrode 73. More specifically, the gate electrode 73 is made of polysilicon and the like doped with impurities such as boron to increase its electric conductivity. On the other hand, in the silicon layer underlying the gate insulation film 62, the impurity concentration must be kept low for forming a channel. However, when the gate insulation film 62 has a smaller thickness, impurities may diffuse from the gate electrode 73 into the channel region of the silicon substrate 61.
In this respect, according to this specific example, the first gate insulation film 62A formed by the method described above with reference to FIGS. 1 to 3 can prevent impurities from diffusing out of the gate electrode 73. More specifically, as described above with reference to
Also in this specific example, the first gate insulation film 62A made of silicon nitride film formed by the method described above with reference to FIGS. 1 to 3 can prevent impurities from diffusing out of the gate electrode 73 into the silicon substrate 61, and thus maintain the performance of the transistor.
Also in this specific example, in a manner similar to that described above with reference to
Next, as shown in
Next, as shown in
On the contrary, the underlying first silicon nitride film 64A, which has low chlorine content and is compact, can prevent diffusion of chlorine into the substrate 61 and gate insulation film 62, and diffusion of other impurities. In addition, the manufacturing time can be reduced by forming the second silicon nitride film 64B by the method of the first or second comparative example. That is, when the method of the first comparative example is used, silicon nitride film can be deposited at a rate 10 or more times faster than in the method of the invention. The deposition rate of silicon nitride film in the method of the invention is about 0.9 angstrom per minute, for example, while the deposition rate of silicon nitride film in the method of the second comparative example as illustrated in
In other words, according to the structure shown in
In this specific example, the third interlayer insulation film 112 and the fifth interlayer insulation film 115 have three-layer stacked structure, respectively. More specifically, the third interlayer insulation film 112 comprises a first silicon nitride film 112A, a second silicon nitride film 112B, and a third silicon nitride film 112C. Similarly, the fifth interlayer insulation film 115 comprises a first silicon nitride film 115A, a second silicon nitride film 115B, and a third silicon nitride film 115C. In these stacked structures, the first and third silicon nitride films 112A, 112C, 115A, and 115C are formed by the method of the invention described above with reference to FIGS. 1 to 3. On the other hand, the second silicon nitride films 112B and 115B are formed by the method of the first or second comparative example described above with reference to
According to this specific example, the first and third silicon nitride films 112A, 112C, 115A, and 115C located on the upper and lower sides of the interlayer insulation films 112 and 115 have low residual chlorine, and the etching rate for them can be reduced. That is, they can be used as an etching stopper, and at the same time, they can prevent diffusion of chlorine or other impurities to the surroundings.
Furthermore, the second silicon nitride films 112B and 115B can be formed by the method of the first or second comparative example to reduce the manufacturing time as described above with reference to
In addition, such a three-layer structure can also be used for the first interlayer insulation film 110, for example. More specifically, the first interlayer insulation film 110 may have a three-layer structure, in which the upper and lower layer may be a silicon nitride film formed by the method of the invention, and the middle layer may be a silicon nitride film formed by the method of the comparative example. This can significantly reduce the manufacturing time while maintaining the effect of etching stopper and chlorine diffusion prevention.
More specifically, this variation begins with step 11 in which the first gas is introduced. In step 12, purge with nitrogen gas is carried out. Subsequently, in step 17, activated hydrogen is introduced as the third gas. Then chlorine contained in the silicon layer formed on the substrate reacts with activated hydrogen and is removed from the silicon layer.
Subsequently, in step 18, purge with nitrogen gas is carried out. Then in step 13, raw material gas containing nitrogen such as ammonia is introduced as the second gas. The subsequent steps are carried out in a similar manner to those shown in
According to this variation, after the first gas is introduced to form a silicon layer, activated hydrogen is introduced as the third gas (step 17) to abstract chlorine contained in the silicon layer. Furthermore, after the second gas is introduced to form a silicon nitride film, activated hydrogen is introduced (step 15) to abstract chlorine contained in the silicon nitride layer. In this way, residual chlorine is abstracted by activated hydrogen in each state of being a silicon layer and silicon nitride layer. As a result, the concentration of chlorine in the film can be further reduced.
The embodiments of the invention have been described with reference to specific examples.
However, the invention is not limited to these specific examples. For example, any element constituting the semiconductor device manufactured using the manufacturing method of the invention, even if the element is appropriately modified by those skilled in the art, is encompassed within the scope of the invention, as long as it comprises the feature of the invention.
While the present invention has been disclosed in terms of the embodiment in order to facilitate better understanding thereof, it should be appreciated that the invention can be embodied in various ways without departing from the principle of the invention. Therefore, the invention should be understood to include all possible embodiments and modification to the shown embodiments which can be embodied without departing from the principle of the invention as set forth in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-221490 | Jul 2004 | JP | national |
