The manifestation of the channeling effect in the manufacture of integrated circuits for bifet technology

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The manifestation of the channeling effect in the manufacture of integrated circuits for bifet technology

Verbitskiy Volodimir Grygorovych Doctor of Technical Sciences, Professor of Microelectronics Department, National Technical University of Ukraine «Igor Sikorsky Kyiv Polytechnic Institute», Kyiv

Verbitskiy Dmytro Olegovych postgraduate, Microelectronics Department, National Technical University of Ukraine «Igor Sikorsky Kyiv Polytechnic Institute», Kyiv

Abstract

transistor ion doping

The paper investigated the effect of channeling in the formation of JFET transistors by the method of ion doping for BiFET technology. Interest of the method in question consists in precise control of the introduction of impurities and achieving high concentrations. At the heart of the article. There is a review of the ion implantation device and a description of the stages of formation of the ion beam. Considered physical phenomena that arise during this alloying, as well as the advantages and disadvantages of this method. The universality of ion implantation (both in terms of the type of alloying substance and the type of material being doped) in the initial period of “low doses” allowed us not to limit ourselves by either physical or economic considerations and try to apply it wherever there is a solid body and the need to somehow change the properties its surface layer. Against the backdrop of a colossal expansion of the scope of work, for the time being it was possible not to notice individual failures in the application of ion implantation to certain systems and immediately move on to other tasks. Later, when the boom “Implantation can do everything!” gave way to a more in-depth and serious analysis, and some physical limitations of the implantation method began to become clear. This process began when, on the one hand, they began to try other, alternative methods to obtain the same results, and on the other hand, the “hybridization” of implantation techniques with traditional technologies began. In the production of

ICs, when using thin diffusion layers obtained by the method of ion implantation, it is necessary to take into account the effect of channeling. For this purpose, it is necessary to use modern implanters, which allows for accurate positioning of the samples by the angle between the axis of the ion beam and the crystallographic orientation of the target. The increasing complexity of the equipment and the associated price increase are inevitable, because there are no other ways to solve this problem. Reducing the cost of the implanter can be achieved by modifying one of the previous models in accordance with the requirements described above.

Keywords: ion implantation, implanter, channeling.

Вербицький Володимир Григорович доктор технічних наук, професор кафедри мікроелектроніки, Національний технічний університет України «Київський політехнічний інститут імені Ігоря Сікорського», м. Київ,

Вербіцький Дмитро Олегович аспірант кафедра мікроелектроніки Національний технічний університет України «Київський політехнічний інститут імені Ігоря Сікорського», м. Київ

ПРОЯВ ЕФЕКТУ КАНАЛЮВАННЯ У ВИГОТОВЛЕНІ ІНТЕГРАЛЬНИХ СХЕМ ЗА ТЕХНОЛОГІЄЮ BiFET

Анотація

У статті досліджено вплив каналування на формування JFET транзисторів методом іонного легування для технології BiFET. Інтерес розглянутого методу полягає в точному контролі введення домішок і досягненні високих концентрацій. Основа статті. Наведено огляд пристрою іонної імплантації та описано етапи формування іонного пучка. Розглянуто фізичні явища, які відбуваються при такому легуванні, а також переваги та недоліки цього методу. Універсальність іонної імплантації (як за типом легуючої домішки, так і за типом матеріалу, що легується) у початковий період «малих доз» дозволяла не обмежуватися ні фізичними, ні економічними міркуваннями і спробувати застосувати це скрізь, де з'являється тверде тіло і необхідно якось змінити властивості його поверхневого шару. На тлі колосального розширення обсягів робіт вдалося не помітити окремих невдач у застосуванні іонної імплантації до окремих систем і відразу перейти до інших завдань. Пізніше, коли бум "Імплантація може все!" поступилися місцем глибшому та серйознішому аналізу, і деякі фізичні обмеження методу імплантації почали ставати очевидними. Цей процес почався з того, що, з одного боку, почали пробувати інші, альтернативні методи отримання тих самих результатів, а з іншого -- почалася «гібридизація» методів імплантації з традиційними технологіями. При виготовленні ІС при використанні тонких дифузійних шарів, отриманих методом іонної імплантації, необхідно враховувати ефект каналування. Для цього необхідно використовувати сучасні імплантатори, які дозволяють точно позиціонувати зразки за кутом між віссю іонного пучка та кристалографічною орієнтацією мішені. Збільшення складності обладнання і пов'язане з цим подорожчання неминучі, оскільки інших шляхів вирішення цієї проблеми немає. Зниження вартості імплантера можна досягти шляхом модифікації однієї з попередніх моделей відповідно до описаних вище вимог.

Ключові слова: іонна імплантація, імплантер, каналування.

The use of ion implantation in the manufacture of IC.

One of the directions of the use of ion doping in silicon microelectronics is theformation of high-resistance layers. Most often, relatively small doses of boron, phosphorus or arsenic (1012 ^ 1014 cm-2) in the energy range 10-400KeV are used for this. Impurities are introduced with high accuracy and reproducibility, do not cause amorphization of silicon. However, when using ion implantation one has to take into account some of its features.

Channeling effect

One of the main effects affecting the parameters of implantation is ion channeling - the oriented movement of particles along axial and planar channels. Despite the fact that channeling has been studied since the early 60s, [1], [2], [3], [4], [5], an adequate analytical model of ion channeling in the low-energy region is still not built and continues to be the subject theoretical and experimental work.

Axial and planar channeling occurs with low energy losses of the channeling ions. The chains of atoms located in the lattice sites, elastically perceive the impulse of a collision as a single whole, transferring it to the neighboring atoms of the chain [6]. The displacement of the chain atom in inelastic collisions with an ion causes a loss of energy and contributes to the dechanneling of the ion. Channeling is possible in a narrow range of angles of entry of the beam into the target. The critical channeling angle is usually greater at low ion beam energies [7]. Experimental studies for phosphorus give a critical de-channeling angle of -1 ° for the family of directions <100> and <111>, and -2 ° for <110> (Fig.1). The geometric model of the projection of the critical angles of channeling onto the silicon lattice, built in Jmol, taking into account the known diameters of singly charged boron ions (nB) and phosphorus (31P) and quadruple silicon ions at the lattice sites, gives the same values for the penetration depth. On the presented projection, the critical angles fit within the five unit cells of the silicon crystal lattice (Fig. 2). Further, the ion is captured with the involvement of a unit cell in motion along a channel at a distance of several thousand periods. For example, for phosphorus at 300 KeV, the penetration depth is ~ 1.2 pm, which is four timesthe depth of the distribution peak with non-canalizing doping.

Fig. 1. Channeling boron and phosphorus in the direction of [110]

Fig.2. The projection of the critical angles of channeling 11B and 31P on the crystal lattice of silicon

The method of ion implantation in different technologies

The experience of using ion implantation using the example of OA 140UD6 (analog MC1456) for the formation of a high-resistance base of the input pair of super-в transistors showed that with doses of doping impurity (11B) 0.5^1 pC^cm"2 in the energy range 50-100 KeV and subsequent deep distillation at4^5 pm with a specific resistance of the layer 5000Q/^ a high reproducibilityis achieved, both in the specific resistance of the layer and in the depth of thep-n junction. The punch- through breakdown Upt super-в transistors, which strongly depends on the total amount of impurities in the base, has a high uniformity over the surface of the plate. The punch-through breakdown is described by the expression:

Where:

q is the electron charge,

є - dielectric constant of silicon^ - vacuum dielectric constant.

Nc - impurity concentration in the reservoirWB is the metallurgical width of the base.

Qb is the total amount of impurity in the base under the emitter per unit area, associated with the resistance of the layer of uniformly alloyed base under theemitter by the ratio:

where:

g is the mobility of the main carriers,

Psbe is the layer resistance of a uniformly alloyed base under the emitter.

The expression is valid for a uniformly doped base; taking into account the real distribution profile gives insignificant differences from this model [8].

However, the transition to BiFET technology (KR140UD18, analogue LF355) revealed the presence of a significant variation in the cut-off voltage (Uco) of JFET transistors both on the plate surface and within the same technological batch loaded into the ion-doping process. The cross section of the structure of super-в and JFET transistors is shown in Fig. 3

In this case, the order of the dose of ion doping for the formation of the upper semiconductor gate (phosphorus) and the JFET channel (boron) is the same as for the high-resistance base of super-в transistors (boron). The total amount of impurity (boron) per unit area for a high-resistance base of a super-в transistor at U punch- through breakdown 1 V is 2^10n^cm"2, and for a JFET channel at Uco 1F3 V is 0.8-1>1012^cm'2

Fig.3. Cross section structure of super в and JFET transistors

The difference is that the shallow layers of the channel and the upper shutter of JFET are not subjected to long-term high-temperature distillation, therefore, the impurity distribution obtained in the process of ion implantation is preserved. The cut-off voltage of JFET transistors in BiFET technology is usually within 1 V, the breakdown voltage Ugd >50 V. This imposes a limit on the thickness of the channel, which should be, respectively, within 1 pm, and on the impurity concentration in the upper gate, which should not exceed 1016cm"3.

Where:

Uco - cutoff voltage,

Io is the saturation current at zero voltage at the gate.ga - the mobility of the main carriers,

Na is the impurity concentration in the channel,W - channel width,

L is the channel length,

a is the channel thickness.

The cause of the scatter of Uots JFET transistors can be the effect of channeling, since the path of ions in channeling is comparable with the thicknesses of the upper gate and the channel. Ion doping was carried out in a Vesuvius-5 implant, the design of which is shown in Fig.4.

Fig.4. The scheme of angles of alloying in the Vesuvius-5 implanter

Placing target plates on a rotating three-tier octahedral drum with vertical scanning by deflecting the ion beam along the axis of rotation of the drum gives a whole range of doping angles along both axes.

The projection of the ion beam in the doping zone has a diameter of about 2 cm (which corresponds to theoretical data [6] on the initial divergence of thebeam 0.5°). The angle a between the axis of the ion beam and the normal tothe surface of the plate changes as the 8-sided drum rotates from + 22.5° at the "advancing" edge of the plate, passing through 0° in the middle of the plate and then the edge of the plate leaves the doping zone under angle of

-22.5°. At the same time, different parts of the plate have different conditions for channeling. Simulation in Jmol shows that as the drum turns and the ion beam axis approaches the perpendicular, several new axial channels openfor a short time. The upper and lower parts of the plate also differ from the central part by an additional inclination of 3 °. On the upper and lower tiers of the drum, the corners of 3 ° and 9 ° are added to the lower and upper edges of the plate, respectively. The expected response surface of the Io JFET transistor (saturation current at zero voltage Ugd) is shown in Fig.5.

Fig.5. Expected response surface by lo value

The real response surface has significant asymmetry due to the fact that the boundaries of the channeling areas for boron (JFET channel) and phosphorus (upper JFET gate) can be misaligned due to the different arrangement of the plates on the drum in the processes of boron and phosphorus doping, the asymmetry of the drum, and also the scatter of the orientation of the initial target plates (Fig.6.).

Fig.6. Real lo Response Surface

There are four main cases of boron and phosphorus distribution in the channel and the upper gate of the JFET transistor, which can occur at different points on the plate surface (Fig.7.). The impurity distributions obtained as a result of modeling in the Suprem-3 program are taken as a basis.

Fig.7. Combinations of boron and phosphorus channeling options in the JFET transistor structure

For a differential input pair JFET in the OA scheme, a non-planar response surface according to Io and Ucm will lead to an increase in the asymmetry of the inputs, which will be reflected by an increase in the offset voltage values. To achieve 100% yield of ICs by the Io parameter, it is necessary to control the doping angle a with high accuracy, to have a high dose setting accuracy.Hence the requirements for implanters. The goniometric heads for each sample with adjustable tilt angles in three planes will help to solve this problem. A two-channel ion guide, which allows a testing beam of protons or electrons to be sent to a target, will allow to set targets with a guaranteed choice of either channeling or its absence, and over the entire surface of the plate.

New generation of implanters

Equipment used for ion doping, the so-called. Ion implanters can be presented in the form of a table (models with “intermediate” parameters are omitted).

Table 1 - Equipment used for ion doping

1, 2 - the ability to work with ions of a limited set of elements, stepwise control of the result with the adjustment of modes from process to process, limited means of current control of the process.

K2MV RBS (HVEE)

Beam energy up to 2 MeV,

Two ion lines (i.i. + structure analysis according to the RBS method),

Goniometric sample head (three degrees of freedom) with thepossibility of recording RBS spectra in channeling mode.

The stability of the beam energy is not worse than 0.2%.

Dose irregularities on the plate less than 1%,

The spread from sample to sample is not worse than 2%

Target scanning.

* Cost Singletron and Tandetron - tens of millions of dollars.

Conclusion

In the manufacture of ICs using thin diffusion layers obtained by ion implantation, it is necessary to take into account the effect of channeling. To do this, it is necessary to use modern implanters, which allows to ensure accurate positioning of samples by the angle between the axis of the ionbeam and the crystallographic orientation of the target. A mismatch of 1 already creates an unacceptable departure for the parameters of the elements, for example, the cut-off voltage of JFET transistors. The increasing complexity of equipment and its associated rise in price is inevitable, since there are no other ways to solve this problem. Reducing the cost of an implanter can be achieved by refining one of the previous models accordingto the requirements described above.

References

Lindhard, J., Kongel. D. & Vidensk S. (1965) Influence of Crystal Lattice on Motion of Energetic Charged Particles. Mat.-Fys. Medd, 34. Retrieved from https://www.osti.gov/biblio/4536390.

Brandt W., Khan J., Potter D. & Horolo P (1965) Effect of Channeling of Low-Energy Protons on the X-Ray Production in Single Crystals. Physcal Review Letters Lett. Vol. 14. pp. 42-46. Retrieved from https://journals.aps.org/prl/issues/14/2.

Appleton B., Erginsoy C. & Gibson W. (1967) Channeling Effects in the Energy Loss of 3-11-MeV Protons in Silicon and Germanium Single Crystals. Physical Review Journal Archive. Vol.161. pp. 330-349. Retrieved from https://journals.aps.org/pr/abstract/10.1103/PhysRev.161.330.

Davies J. A., Eriksson L., Johansson N. & Mitchel I. (1969) Channeling of MeV He+ Ions in Tungsten and Other Crystals: An Intercomparison of Rutherford Scattering and of Characteristic L and M X-Ray Yields. Physical Review Journal Archive. Vol. 181. pp. 548-554. Retrieved from https://journals.aps.org/pr/issues/181/2.

Davis J. A. (1983) The Channeling Phenomenon- and Some of Its Applications. Physica Scripta. Vol. 28. pp. 294- 328. Retrieved from DOI 10.1088/0031-8949/28/3/006.

Soroka V., Ostashko V. & ect.(2015) Vymiriuvannia tovshchyny zariadnoi misheni modyfikovanym yadernym analitychnym metodom [Measurement of the thickness of the recharge target by a modified nuclear analytical method]. Tekhnika ta metody eksperementu [Experiment technique and methods]. Vol. 16. № 1. pp. 90-97. Retrieved from DOI: 10.15407/jnpae2015.01.090

Bragchenko M., Diuldia S. & Bakay A. (2006) Teoriia ta modeliuvannia implantatsii ioniv v monokrytalakh kremniia [Theory and modeling of ion implantation in silicon monocrystals]. Pytannia atomnoi nauky i tekhniky [Issues of atomic science and technology]. Vol. 1. pp. 539-621. Retrieved from DOI: 10.15407/jnpae2015.01.090 [in Ukraine].

Winifred M., Jack l. Raymond M (1976) Ion-implanted Super-Gain Transistors. JOURNAL OF SOLID-STATE CIRCUITS. Vol. SC-11. pp. 478.485.

Література

Lindhard, J., Kongel. D. & Vidensk S. (1965) Influence of Crystal Lattice on Motion of Energetic Charged Particles. Mat.-Fys. Medd, 34. Retrieved from https://www.osti.gov/biblio/4536390.

Brandt W., Khan J., Potter D. & Horolo P (1965) Effect of Channeling of Low-Energy Protons on the X-Ray Production in Single Crystals. Physcal Review Letters Lett. Vol. 14. pp. 4246. Retrieved from https://journals.aps.org/prl/issues/14/2.

Appleton B., Erginsoy C. & Gibson W. (1967) Channeling Effects in the Energy Loss of 3-11-MeV Protons in Silicon and Germanium Single Crystals. Physical Review Journal Archive. Vol.161. pp. 330-349. Retrieved from https://journals.aps.org/pr/abstract/10.1103/PhysRev.161.330.

Davies J. A., Eriksson L., Johansson N. & Mitchel I. (1969) Channeling of MeV He+ Ions in Tungsten and Other Crystals: An Intercomparison of Rutherford Scattering and of Characteristic L and M X-Ray Yields. Physical Review Journal Archive. Vol. 181. pp. 548-554. Retrieved from https://journals.aps.org/pr/issues/181/2.

Davis J. A. (1983) The Channeling Phenomenon- and Some of Its Applications. Physica Scripta. Vol. 28. pp. 294- 328. Retrieved from DOI 10.1088/0031-8949/28/3/006.

Soroka V., Ostashko V. & ect.(2015) Vymiriuvannia tovshchyny zariadnoi misheni modyfikovanym yadernym analitychnym metodom [Measurement of the thickness of the recharge target by a modified nuclear analytical method]. Tekhnika ta metody eksperementu [Experiment technique and methods]. Vol. 16. № 1. pp. 90-97. Retrieved from DOI: 10.15407/jnpae2015.01.090

Bragchenko M., Diuldia S. & Bakay A. (2006) Teoriia ta modeliuvannia implantatsii ioniv v monokrytalakh kremniia [Theory and modeling of ion implantation in silicon monocrystals]. Pytannia atomnoi nauky i tekhniky [Issues of atomic science and technology]. Vol. 1. pp. 539-621. Retrieved from DOI: 10.15407/jnpae2015.01.090 [in Ukraine].

Winifred M., Jack l. Raymond M (1976) Ion-implanted Super-Gain Transistors. JOURNAL OF SOLID-STATE CIRCUITS. Vol. SC-11. pp. 478.485.

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