JP3428056B2 - Semiconductor doping method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of doping a semiconductor, and more particularly to a method of manufacturing a semiconductor suitable for manufacturing a semiconductor element having a large surface to be doped, such as a thin film semiconductor element (device). Doping method. 2. Description of the Related Art A display element (apparatus) using a liquid crystal is, for example, two pieces each subjected to alignment processing by rubbing, for the purpose of large capacity and high density for television display and graphic display. Substrates are aligned with each other
A so-called twisted nematic (TN) type active matrix type liquid crystal display in which a nematic type liquid crystal composition is sandwiched between substrates arranged in parallel and facing each other so as to form 90 ° and placed in parallel with each other. The device is attracting attention. In this active matrix type liquid crystal display device, a method in which each pixel is driven and controlled by a semiconductor switch so that high contrast display without crosstalk can be performed is adopted. The amorphous silicon (a-Si) based semiconductor switch formed and arranged on the surface of the transparent insulating substrate is used because the semiconductor switch is capable of displaying a transmissive display and is easy to increase in area. Thin film transistors (TFT) are used. Meanwhile, the a-Si thin film transistor (TFT) has an inverted staggered structure in which a gate electrode is arranged in a lower layer and a source electrode and a drain electrode are arranged in an upper layer with an a-Si layer (film) as an active layer interposed therebetween. In many cases, the inverted staggered structure is roughly divided into those having a channel protective film between an a-Si active layer and a source electrode and a drain electrode, and those having no channel protective film. Is done. And in this type of a-Si based thin film transistor,
Normally, hole current is blocked by forming n-type low-resistance a-Si by plasma CVD between the a-Si layer and the metal layer separately constituting the source electrode and the drain electrode. To obtain an ohmic junction. On the other hand, plasma C
Since a problem unique to VD can be avoided, in a thin film transistor provided with a channel protective film, instead of forming the n-type low-resistance a-Si by film formation, a high-resistance a-
It is also known that Si is doped with a doping element such as P later by, for example, an ion implantation method to form an n-type low-resistance a-Si. However, in the method of doping a required one conductivity type doping element by the above-described ion implantation method, disadvantages such as low production yield of thin film transistors and poor mass productivity are recognized. Can be That is, in a doping method known as an ion implantation process for crystalline silicon, since a surface to be doped is generally small, an ion species (doping element) to be doped by mass separation using a magnetic field.
Is selected, but the surface to be doped has a large area.
In the case of a Si-based thin film transistor, as described above, a doping element cannot be selected by mass separation using a magnetic field and ion implantation cannot be performed. Therefore, doping must be performed by directly accelerating generated ions by an electric field without performing mass separation, so that undesired ions are simultaneously doped (implanted), and as a result, doping efficiency is reduced. Such adverse effects occur. [0005] For example, when an ionic element generated by plasma decomposition of PH ₃ is doped into an a-Si film by electric field acceleration, the PH ₃ is diluted with a diluent gas (eg, H ₂ ), and the mixture is plasma-treated. When the ions are decomposed and the resulting ionic elements are accelerated by an electric field and ion-implanted, a large amount of H ions present as plasma decomposition products are also implanted in the a-Si film, and there is a problem that the quality of the a-Si film is deteriorated. Further, even when an inert gas such as He is used as a diluent gas, ions of the inert gas are implanted into the a-Si film, and as a result, the Si-
There is a problem in that the quality of the a-Si film is degraded by causing the breaking of the Si bond or remaining between the lattices to disturb the a-Si network. That is, not only is the implantation efficiency of the required conductivity type ion element low, but also the quality of the a-Si film functioning as a thin film transistor is deteriorated, so that a thin film transistor having the desired performance cannot be manufactured with a high yield. There's a problem. SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances. Undesired element ions are selectively removed even when doping with an ionic element without mass separation by a magnetic field. It is an object of the present invention to provide a semiconductor doping method capable of selecting and doping a conductive doping element. [0007] The semiconductor doping method according to the present invention SUMMARY OF THE INVENTION includes the steps of forming a doped protective film on the semiconductor film, from the formed doped protective film,
Compound containing doping element
Plasma decomposition of a diluent gas containing an element with a large
Te, a step of implanting ions accelerated by an electric field, before
The doping protective film, wherein the doping protective film is
The doping element is implanted through
Characterized by comprising the step of at least removing the one located on a region of the semiconductor film. According to the present invention, a semiconductor element such as Si or Ge is plasma-decomposed into a doping element imparting a conductivity type such as B or P, and this plasma is accelerated by an electric field to perform ion implantation. The main point is to use a diluent gas having a higher atomic weight than the doping element for imparting a mold, while providing a doping protective film on the semiconductor surface, and having the doping protective film have a function of selecting an ion element to be implanted. That is, an ion element is implanted through the doping protection film to suppress the passage (transmission) of elemental ions having a large atomic weight, which function as a diluent gas, and selectively ion-implant a required conductivity-type doping element. Effectively avoiding or preventing the breaking of Si-Si bonds and the inter-lattice network due to the collective ion implantation, and at least capturing (carrying) undesired ion elements such as the diluent gas ions. The key point is that the protective film is removed by etching or the like. Here, the doping protection film capturing (carrying) the undesired ion element must be removed because it easily affects the characteristics of the manufactured semiconductor device (device). It does not necessarily have to be removed. According to the method of doping a semiconductor according to the present invention, the ion element which is ion-implanted without being selected by the doping protective film provided on the semiconductor surface can be provided with a diluting ion element and a required conductivity type. While being separated into functional doping ion elements, the diluted ion elements are selectively and efficiently captured (supported) by the doping protective film, and their passage to the semiconductor surface side is suppressed or prevented. Therefore, the breaking of the Si-Si bond and the disorder of the interstitial network due to the implantation of the diluting ion element can be completely avoided or prevented, and the doping protective film that selectively captures the diluting ion element can also be used after the ion implantation. Since it is removed, a semiconductor element (device) having good performance can be manufactured with high yield. An embodiment of the present invention will be described below with reference to FIGS. 1, 2 and 3. Embodiment 1 FIG. 1 is a cross-sectional view showing a part of a thin film transistor for an active matrix type liquid crystal device formed by applying a semiconductor doping method according to the present invention. You. First, a transparent insulating substrate 1, for example, a glass plate (7059, manufactured by Corning Incorporated) is prepared, and a gate electrode 2 made of, for example, Mo-Ta is formed and arranged on a predetermined area surface of the insulating substrate 1. Next, for example, the insulating substrate 1 is placed on the surface of the insulating substrate 1 on which the gate electrode 2 is formed and arranged.
A silicon oxide film 3a having a thickness of 0.3 μm is formed at a temperature of 00 ° C. by a normal pressure thermal CVD method, and then a silicon nitride film 3b having a thickness of 0.05 μm is formed by a plasma CVD method at a temperature of 350 ° C. Thus, a required Cade insulating film 3 is formed. Continued
As in the case of the silicon nitride film 3b, an a-
A semiconductor film 4 made of Si and a silicon nitride film serving as a channel protection film 5 are formed on the semiconductor film 4. afterwards,
A resist pattern is formed on the surface of the silicon nitride film, and the silicon nitride film is selectively etched to be processed into a predetermined shape as a channel protective film 5. At this point, the channel portion is protected by the channel protective film 5, and the a-Si4 surfaces forming the source and drain portions are exposed. Next, a doping protection film made of, for example, a polyimide resin is formed on the entire surface of the insulating substrate 1 on which the channel protection film 5 has been processed and formed, and then the source is formed according to a doping method (means) described in detail below. A doping element, for example, P is ion-implanted through the doping protective film into the a-Si4 surface forming the
The low resistance semiconductor region 6 is formed by molding. The doping here is performed as follows. For example, a reaction chamber containing a mesh-shaped circular high-frequency electrode having a diameter of 30 cm, a ground electrode facing the circular high-frequency electrode, and a mesh-shaped acceleration electrode disposed between the two electrodes, and a doping element in the reaction chamber. A compound-containing diluent gas supply port,
First, a doping apparatus including a turbo-molecular pump for exhausting the reaction chamber and an exhaust system connected to a rotary pump is prepared. Then, the insulating substrate 1 on which the doping protective film is formed is clamped on the ground electrode surface of the doping apparatus, and for example, PH ₃ and Kr (diluent) are supplied from the supply port to PH ₃₁ sccm, Kr 20. sc
While supplying (introducing) into the reaction chamber at a rate of cm, the turbo molecular pump and the rotary pump are driven to exhaust air from the exhaust system. At this time, by adjusting (adjusting) the valve opening of the exhaust system to control the pressure in the reaction chamber to about 10 ^-4 Torr and applying a high frequency of 13.56 MHz and 300 W to the high frequency electrode, discharge occurs. , PH ₃ and is the supply
Kr causes plasma decomposition. Here, the potential of the accelerating electrode is set to + with respect to the ground electrode to which the insulating substrate 1 is clamped.
When set to (plus), the cations generated by the discharge / plasma decomposition are selectively extracted, accelerated by an electric field, and driven into the doping protection film surface of the insulating substrate 1. In the implantation of cations by the electric field / acceleration, ion species having a lighter mass (atomic weight) are implanted deeper and faster, and implantation of a heavier (larger) ion species is stopped at a relatively shallow position. In other words, depending on the combination of the material and the thickness of the doping protective film and the acceleration voltage, the mass number 84
Most of the Kr ions are captured by the doping protective film, and the penetration (implantation) into the a-Si film 4 is prevented and suppressed. On the other hand, P ions having a mass number of 31 selectively penetrate the doping protective film and enter (inject) into the a-Si film 4. Therefore, a-
The deterioration of the Si film 4 is completely avoided. In this embodiment, when the thickness of the doping protective film made of a polyimide resin is 100 nm, P ions are formed in the a-Si regions forming the source and drain portions by setting the acceleration voltage to 60 KeV. It was selectively doped to make it n-type, and the low-resistance semiconductor region 6 was easily formed. Thereafter, when the doping protective film is selectively removed by, for example, etching, a clean low-resistance semiconductor region 6 is exposed. In the selective doping of P ions into the a-Si film 4, the H ions generated by the plasma decomposition of PH ₃ penetrate through the doping protective film, and
, The amount was small compared to the amount of ions generated from the diluent gas, so that there was almost no effect on the quality of the a-Si film. FIG. 2 shows the results of calculation by simulation of the concentration file when 10 ¹⁵ ions / cm ² of P ions and Kr ions are implanted into the above-mentioned doping protective film (polyimide resin film) at an acceleration voltage of 60 KeV. It is a curve figure. As can be seen from FIG. 2, the P ion has a depth of 96 nm.
Has a concentration peak of 2 × 10 ²² / cm ^{3 at the position} of, but the concentration peak of Kr ion is at a depth of 52 nm, and at a depth of 96 nm, it is only about 10 ¹⁵ / cm ³ . In other words, if the thickness of the polyimide resin film (doping protection film) is set to 100 nm, P penetrates the polyimide resin film and enters the a-Si film 4 to contribute to the n-type. The film is captured by the film and is prevented from entering the a-Si film 4. Next, a including the low-resistance semiconductor region 6
Processing the Si film 4 to set a channel region, a source region, and a drain region, and
(Indium Tin Oxide) is formed. Thereafter, a source electrode 8 connected to the pixel electrode 7 is formed on the source region, and a drain electrode 9 is formed on the drain region. Thus, an active element substrate having a thin film transistor (TFT) element 10 including the gate electrode 2, the gate insulating film 3, the semiconductor film 4 made of a-Si, the source electrode 8 and the drain electrode 9 was obtained. . Embodiment 2 In the case of Embodiment 1, the channel protective film 5 is processed and
After a doping protection film made of a polyimide resin was formed on the entire surface of the formed insulating substrate 1, doping was performed by changing some of the conditions such as doping elements. That is,
A reaction chamber containing a mesh-shaped circular high-frequency electrode having a diameter of 30 cm, a ground electrode facing the circular high-frequency electrode, and a mesh-shaped acceleration electrode disposed between the two electrodes, and a doping element is contained in the reaction chamber. First, a doping apparatus including a compound-dilution gas supply port and an exhaust system connected to a turbo molecular pump and a rotary pump for exhausting the reaction chamber is prepared. Then, the insulating substrate 1 having the doping protective film formed thereon is clamped on the ground electrode surface of the doping apparatus, and PBr ₃ is bubbled from the supply port with a carrier gas (diluent gas) Kr 20 sccm to enter the reaction chamber. While supplying (introducing), the turbo molecular pump and the rotary pump are driven to exhaust air from the exhaust system. At this time, by adjusting (adjusting) the valve opening of the exhaust system to control the pressure in the reaction chamber to about 10 ^-4 Torr and applying a high frequency of 13.56 MHz and 300 W to the high frequency electrode, discharge occurs. Then, the supplied PBr ₃ and Kr cause plasma decomposition. Here, the potential of the accelerating electrode is set to + with respect to the ground electrode to which the insulating substrate 1 is clamped.
When set to (plus), the cations generated by the discharge / plasma decomposition are selectively extracted, accelerated by an electric field, and driven into the doping protection film surface of the insulating substrate 1. In the implantation of cations by the electric field / acceleration, most of the Br ions having a mass number of 80 and the Kr ions having a mass number of 84 are captured by the doping protective film and penetrate (inject) into the a-Si film 4. P ions having a mass number of 31 selectively penetrate through the doping protective film, and the a-Si film 4
Enter (inject) inside. Therefore, degradation of the a-Si film 4 caused by undesired implantation of Kr ions is completely avoided. FIG. 3 shows the results of calculation by simulation of the concentration files when 10 ¹⁵ ions / cm ² of P ions and Kr ions are implanted into the above-mentioned doping protective film (polyimide resin film) at an acceleration voltage of 60 KeV. It is a curve figure. As can be seen from FIG. 3, the P ion has a depth of 96 nm.
Has a concentration peak of 2 × 10 ²⁰ ions / cm ³ at the location, but the Kr ion concentration peak is at a depth of 52 nm, and at a depth of 96 nm, it is only about 10 ¹⁵ ions / cm ³ , and Br is almost the same. That is, if the thickness of the polyimide resin film (doping protection film) is set to 100 nm, P penetrates the polyimide resin film and enters the a-Si film 4 to contribute to the n-type. It is captured by the polyimide resin film and is prevented from entering the a-Si film 4. Also in this embodiment, when the thickness of the doping protective film made of polyimide resin is 100 nm, by setting the acceleration voltage to 60 KeV, the P-ion is formed in the a-Si region forming the source and drain portions. Was selectively doped to be n-type, and the low-resistance semiconductor region 6 was easily formed. Thereafter, when the doping protective film is selectively removed by, for example, etching, a clean low-resistance semiconductor region 6 is exposed. Next, the a-Si film 4 including the low-resistance semiconductor region 6 is processed to set a channel region, a source region, and a drain region, and a pixel electrode made of ITO (Indium Tin Oxide) is formed on the surface of the gate insulating film 3. 7 is formed. Thereafter, the pixel electrode 7 is formed on the source region.
And a drain electrode 9 on the drain region. Thus, the gate electrode 2, the gate insulating film 3, the semiconductor film 4 made of a-Si,
An active element substrate having a thin film transistor (TFT) element 10 having a source electrode 8 and a drain electrode 9 was obtained. It should be noted that the present invention is not limited to the embodiment described above, and various modifications can be made within the scope of the invention. For example, the combination of the doping element and the diluent gas is PI ₃ -Kr, PI ₃ -Xe, AsI ₃
In the case of p-type such as -Xe, BCl ₃ -Ar, BBr ₃ -Ar and the like are exemplified. In particular, when BBr ₃ is used instead of B ₂ H ₆ , since the mass of Br ₂ is larger than that of H ₂ , the selection by the doping protective film and the doping efficiency of B are improved. Further, as the semiconductor to be doped, a
−Si, for example, polysilicon, SiGe, SiC,
Examples include diamond. Further, examples of the doping protective film include an inorganic insulating film such as a silicon oxide film and a silicon nitride film, a metal thin film such as Mo and Cr, a photoresist film, and the like. The present invention is not limited to the manufacture of a switching element for an active matrix type liquid crystal display element, but may be applied to, for example, the manufacture of an a-Si contact sensor. Furthermore, the doping protective film after the doping is a region doped with ions of a dopant-dilution gas system, that is, a-
Although it is necessary to remove the low resistance semiconductor region 6 surface of the Si film 4, it is not always necessary to remove the other region surfaces. As described above, according to the method of doping a semiconductor according to the present invention, of the ion elements which are ion-implanted without being sorted by the toping protective film provided on the semiconductor surface, The diluted ionic element having a large mass number is selectively captured by the doping protective film, and the ionic element functioning to impart a required conductivity type enters the semiconductor through the doping protective film. In other words, the diluting ion element which has an adverse effect on the semiconductor film is selectively and efficiently captured (supported) by the doping protective film, while the required ion element passing through the doping protective film selectively enters the semiconductor surface. I do. Therefore, for example, disconnection of the Si—Si bond and disturbance of the interstitial network due to the implantation of the diluted ion element can be completely avoided or prevented, and it is possible to always perform good doping. In addition, in this doping method, mass separation by a magnetic field is not required for the ion species in the ion implantation step, so that a doping process on a large-area plate can be easily achieved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a principal part of a thin film transistor for an active matrix type liquid crystal display element, showing an application example of a semiconductor doping method according to the present invention. FIG. 2 is a curve diagram showing a profile simulation result of an implanted ion concentration in the semiconductor doping method according to the present invention. FIG. 3 is a curve diagram showing another profile simulation result of an implanted ion concentration in the semiconductor doping method according to the present invention. [Description of Signs] 1 ... Insulating substrate 2 ... Gate electrode 3 ... Kate insulating film
3a: Silicon oxide film 3b: Silicon nitride film 4: Semiconductor film 5: Channel protective film 6: Low resistance semiconductor region 7: Pixel electrode 8
... Source electrode 9 ... Drain electrode

Claims (1)

(57) [Claim 1] A step of forming a doping protection film on a semiconductor film, and a doping source from the formed doping protection film.
Compound containing nitrogen and having an atomic weight greater than that of the doping element
And a diluent gas including the element by plasma decomposition, a step of implanting ions accelerated by an electric field, a said doping protective film, the doped protective film
Through which the doping element is ion-implanted.
Semiconductor doping method characterized by comprising the step of at least removing <br/> removed by the one located on a region of the semiconductor film.