The method of neutron transmutation doping of silicon

 

(57) Abstract:

Usage: in the technology of semiconductor materials for electronic devices and electrical industry. The invention is: to increase the utilization of neutrons in the way neutron transmutation doping of silicon, comprising the reciprocating movement of the containers with ingots of silicon through the exposure zone of the reactor channel and control averaged over the length of the bars of neutron fluence to set the desired fluence, simultaneously moving at least two containers. When changing direction in the exposure zone should be at least one container. When multiple moving in the exposure zone at the point of change of direction there is only one extreme of the container, and the irradiation process interrupt when set at the container half-fluence correct and change containers in places, keeping each of them the same orientation in the channel. In a single move the desired result is reached due to the fact that the container is exposed in this cycle, move with different velocities Vpis the speed with which protray the containers are moved between the overload range and area exposure, moreover, V/Vp2/, where the maximum allowable variation in the concentration transmutation impurity phosphorus in relative units. 2 C. p. F. - ly, 1 Il.

The invention relates to a manufacturing technology of semiconductor materials for devices of electronic and electrical industries.

Technology neutron transmutation doping (NTD) of silicon-based nuclear reaction

30Si(n )31Si31P (1) as a result of which eventually formed the core dopant is phosphorus. The distribution of these nuclei follows the distribution of the fluence of thermal neutrons by volume of silicon ingots. Usually in technology NTL silicon demands to uneven alloying - 3-5% or less. If the container with silicon under irradiation stationary relative to the radiation field (static mode), then its length, which is achieved by the non-uniform doping, several times or even ten times) less than the linear size of the active zone. Therefore, industrial reactors with large sizes of the active zone (a few meters), in static mode to irradiate containers with silicon length of 0.5 m or more. At regime cannot be irradiated, since the linear dimensions of the active area is less than one meter. In regard to research reactors in the process of irradiation of long containers or otherwise move relative to the irradiation zone to achieve acceptable uniformity of doping.

The known method NTL silicon [1] , including moving through the channel of a nuclear reactor at a constant speed continuously successive containers large extent with ingots of silicon. In this way the containers are loaded in the reactor channel from one side and unloaded from the other.

The most important and serious the advantage of this method is almost the full amount of the irradiation zone in the channel doping of silicon. If we ignore the gap between the silicon in the neighboring containers, it turns out that the entire volume of the channel and its radiation areas occupied by silicon. However, this method can be implemented only on a channel of the reactor, which can be accessed from both ends.

Known Tacke way NTL silicon [2] , selected as a prototype, including the reciprocating movement of the channel of the reactor through the exposure zone of the container with ingots of silicon, the control averaged over the length of the useful new and replacement containers. In this way the container is moved in both forward and reverse napravleniya until its useful volume is not completely beyond the area of exposure. Therefore, at each intersection of the irradiation zone all the elementary volumes of the bars are exposed to neutrons with the same fluence

Fi= (x)dx (2) where fi- neutron fluence accumulated in the i-th intersection of the irradiation zone; X1, X2- coordinates at the beginning and end of the irradiation zone; (x) - raspredelenie flux density of thermal neutrons; Vi- the speed of the container when the i-th intersection of the irradiation zone. The coordinates of the irradiation zone X1and X2chosen so that outside these coordinates irradiation ingots neutrons is negligible. In this way, at each intersection of the irradiation zone, the speed of travel of the container must be a constant, but its value can be changed when you change the direction of motion. When the reciprocating movement of the container through the exposure zone monitor neutron fluence, dialed useful volume of the container. As soon as it becomes equal to the desired, irradiation ceased. For this purpose, the container is removed from the irradiation zone and move to the place of transshipment of containers. In this way Proc. of the container technically rational to make use of one mechanism overload.

However, in this method, the utilization factor of the neutron radiation field is much smaller than in the method according to the similar.

In the method NTL silicon, comprising the reciprocating movement of the container with ingots of silicon on the reactor channel through the exposure zone and the control averaged over the length of the ingot container fluence of neutrons to set the desired fluence, through the exposure zone move at least two containers, when you change the direction of movement of the containers in the area of irradiation is at least one of the containers, and after one or more cycles of moving the irradiation process is interrupted and are replaced containers seats or replacement of at least one of them.

When multiple moving at the time of changing the direction of movement in the zone of irradiation is placed only at one extreme, the container, after the set of extreme containers half-fluence correct the irradiation process interrupt, change extreme containers in places, keeping each of them reorientation in the channel, after which the irradiation process continue.

In a single move in each cycle the containers to move with velocity vpthrough the exposure zone to the first container, for the remaining containers new place, following the movement of containers lead with velocity v to align the second container with its location in the previous cycle of irradiation at the time of the change of direction, after which the cycle of repeat exposure, and

V/Vp2/, (3) where the maximum allowable variation in the concentration transmutation impurity phosphorus in relative units.

The drawing schematically shows the channel reactor radiation zone, and the location of containers (conventionally shown is not the actual containers, and their useful - ingots - volumes) in the extreme positions when multiple (a - d) and a single (d - C) reciprocating movements.

When the process is irradiated with at least two containers with bullion (in the drawing, three containers), moving them back and forth through the exposure zone. Moreover, the amplitude of the move set so that the area of exposure when changing direction (positions a, b, C, g, with the repeated movements, the position e or C - in a single move) is present at least one container. In this method, the irradiation process is optionally interrupted before it is dialed to the desired neutron fluence on aout from one extreme position containers (position a) to another (position b) and back. After the extreme containers I and III will be called half-fluence correct, the additional irradiation is interrupted, i.e., all containers return to their place of overload. At the place of loading at the containers I and III of changing places, keeping each of them orientation in the channel. Then the containers are returned to the extreme (reciprocating movement) position (position) and continue to irradiation by moving the containers between the extreme positions (positions C and d). After extreme containers rest half fluence, they are replaced by new ones and continue the exposure.

When each radiation between containers pose such a gap that the distance from the center of the useful volume of each extreme of the container I and III to the useful volume of the adjacent container II was not less than half the length of the irradiation zone. If the extreme length of the container is not less than the length of the irradiation zone, the gap between it and the adjacent container may be missing.

Containers reciprocating move from one extreme position to the other and back to align the center of the useful volume of the outer container with the center of the irradiation zone, i.e. in positions a and g with the center of Vratna-directional movement of containers at they end up evenly along the length will be irradiated with the required fluence of neutrons.

Extreme containers can have the same or different length of useful volumes that are greater than or less than the length of the irradiation zone. For example, the length of the useful volume of the container I is less than the length of the irradiation zone, and the container III is greater than the length of the irradiation zone. Scroll in the container I point MIsuch that it is separated from the center of the useful volume of the container at a distance of X. Then in the position of a point MIhas the coordinate X such that X1X X2where X1and X2the coordinates of the boundaries of the zone of irradiation. When moving from a and b or from point MIpasses through the exposure zone of the path from X to X2. When moving from the position in the city or back point MIpasses through the exposure zone of the path from X1to X. If the containers reciprocating move with the same speed n times when typing the first half of the fluence and n times in the set of the second half, the point MI2n completely cross the whole area of the irradiation. Since all other points in position and located between the X1and X2they also 2n completely cross the whole area of the irradiation and will be irradiated by neutrons with the same fluence. Exactly the same fluence as the container I will be irradiated all points containeryou point M2the coordinate of the position b is less than X1. For the first n cycles of reciprocating motion, she never falls into the zone of irradiation. But for the next n cycles (from the position in g and Vice versa) she 2n completely crosses the radiation zone, i.e., is irradiated by neutrons with the same fluence. Exactly the same fluence in the end is any point of M3the coordinate of the position b is greater than X2: for the first n cycles she 2n completely crosses the radiation zone, and for the next n cycles it will not enter the radiation zone.

As to the middle of the container II, each moving in the forward or reverse direction all his points are fully exposed. In one such move, he gathers evenly along its length fluence, defined by the expression (2). Its length can be any. Moreover, such (medium) containers may be few and they will be for the i-th move uniformly irradiated by neutrons with fluence in the expression (2). After secondary containers will dial the desired neutron fluence, the containers are moved to the loading site, replace the secondary containers for new and continuing the irradiation. The breaks in the irradiated medium containers mobitelom the movement of their containers move through the zone of irradiation (from position d to position e) as long while one of them (container I) is not completely beyond the area of exposure. When the containers are moved from position d in e such estimated velocity vpto each container after complete intersection zone radiation was irradiated by neutrons with the required fluence fopt. Therefore, after the first move the useful volume of the container I is uniformly irradiated by neutrons with the required fluence

Fopt= (x)dx. (4) Then the containers with velocity v is larger than vpreturn to the loading site. The containers I and II trying to enter additional neutron fluence. The container I completely crosses with velocity v the exposure zone. So it evenly along the length of gaining additional fluence

Fd= (x)dx, (5) which take into account when getting in the nominal doping. The container II is not completely crosses the radiation zone, so additional fluence along its length is distributed unevenly. The maximum possible irregularity occurs when one end of the container II is fully crosses the area of exposure and gaining additional fluence (5), and the second end is additionally not irradiated by neutrons. Therefore, the difference between the additional fluences will be no more, escaut for the remaining. When the second reciprocating cycle of irradiation containers move with velocity v to match the first (container II) its location in the previous cycle of irradiation at the time of changing the direction of motion (item W). The dierence additional fluences at the ends of the container II doubles

Fd(x)dx. (6) From the position W of the containers moving with velocity vpup until the useful volume of the first (container II) is not completely beyond the area of exposure (position C). Then the containers return with velocity v to the loading site, and recruit additional fluence on the container II also take into account how and when the irradiation container I to hit the nominal doping. Thus, the container II with an estimated speed v only once completely crosses the zone of irradiation. The dispersion concentration of the transmutation of an impurity of phosphorus is determined by the range of additional fluence of neutrons = (7) subject to (2) and (6)

2 . (8)

All other cycles of exposure do not differ from the second.

The irradiation of both the proposed method and the prototype of the number of fully irradiated containers is equal to the total number of breaks in the irradiation. At the same time, the second exposure is constantly present in the irradiation process at least one container with ingots of silicon. (56) 1. Smirnov, L. S. Solov'ev, S. P. , Stas C. D. and other Doping of semiconductors by means of nuclear reactions. Novosibirsk: Nauka, 1981, S. 138.

2. Neutron transmutation doping of semiconductors. Edited by j. Meese. M. : Mir, 1982, S. 104-122.

1. The METHOD of NEUTRON TRANSMUTATION DOPING of SILICON, comprising the reciprocating movement of the container with ingots of silicon on the reactor channel through the exposure zone and the control averaged over the length of the ingot container fluence of neutrons to set the desired fluence, characterized in that through the exposure zone move at least two containers, when you change the direction of movement of the containers in the area of irradiation is at least one of the containers, and after one or more cycles of moving the irradiation process is interrupted and are replaced containers seats or replacement of at least one of them.

2. The method according to p. 1, characterized in that the point of change of direction in the exposure zone only one place, at the container, after the set of extreme containers half-fluence correct the irradiation process interrupt, change extreme containers in places, keeping each of them remains the orientation the containers first move with velocity vpthrough the exposure zone to the outside of the first one, then return the containers with velocity v to the place of their replacement, remove the first container, the remaining containers are placed the following new and moving containers are to pause v to align the second container with its location in the previous cycle of irradiation at the time of the change of direction, after which the cycle of repeat exposure, and v/vpwhere vp- the speed at which moving the container through the exposure zone of the container is irradiated by neutrons with the required fluence, > maximum allowable variation of the concentration of transmutation impurities of phosphorus, Rel. unit

 

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