DD160382A3 - METHOD FOR PRODUCING SEMICONDUCTOR COMPONENTS - Google Patents

Abstract

The invention relates to the field of semiconductor technology. The aim of the invention is the improvement of device properties that can be achieved by increasing the Minoritaetstraeger life or improving the properties of the Si / SiO 2 deep interface. The object of the invention is thus the improvement of Gettereffektivitaet. The essence of the invention is the removal of an already by gettering pollution profile from the semiconductor body of a renewed getter process. The application of the invention is useful in the manufacture of all semiconductor devices, for the function of a high Minoritaetstraeger life and / or a very perfect semiconductor-isolator interface is required. These include e.g. Si diode targets, CCD devices, phototransistors and analog circuits.

Description

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Title of the invention

Process for the production of semiconductor devices

Field of application of the invention

The invention relates to silicon semiconductor technology and is expediently used in the production of all Si semiconductor components whose puncture requires a high minority carrier lifetime in the substrate or a very perfect interface. Such components include 2. B. Si diode targets. CCD devices, phototransistors, high-quality photodiodes, analog circuits and / uW circuits.

Characteristic of the known technical solutions

The minority carrier lifetime in a semiconductor substrate is substantially determined by the consensus of such impurities that form recombination centers near the center of the forbidden zone. Typical of such impurities are iron, copper, gold and zinc. Some of these contaminants are known to be due to phosphorus gettering or ion implantation of the wafer back or polysilicon coating

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the rear of the disc rendered ineffective v / earth. T. Ξ reports about these methods. Seidel, R.L.Muk and A.G, Cullis in J. Appl _e Physics, YoI. 46, NS 2, (1975) and Shih Ming Hu in US Pat . No. 4,035,335, among many other authors. "Apart from the usually lower gettering effect of ion implantation, this is less advantageous compared to gettering by phosphorous diffusion because, in contrast to ion implantation no gettering of alkali ions and other impurities in the planar layer is possible for phosphorus diffusion. The frequently used phosphorus diffusion termination usually takes place at temperatures between 800 and 1200 C with the addition of a suitable phosphorus compound to the carrier gas (POCl ,, PE *), such as, for example, J. , I. Lambert in Wiss. Beri ABG-Telefunken 46 (1973) 1 described «

In this case, the discs are arranged generally standing, so that both on the planar side and on the reasonably oxide-free back of the Scneibung can be made an occupancy with phosphorus glass. Thus, in addition to the heavy metal-denoting n ⁺ layer on the back of the disc, the selective generation of n ⁺ regions on the planar side allows, as z. B. for emitter regions of npn transistors' are needed. The planar-sided phosphorus glass layer can very effectively be used to get the alkali metal ions of the passivating silicon dioxide layer, as JM Eldridge et al. P. BaIk as early as 1968 in "Formation of phosphorsilicate glass films on silicon dioxide" Transactions of the Metallurgical Soc ₀ of AISE, Vol. 242, March 1968 have found »

α * W * λ h 9. rl 2

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Sin disadvantage of the known getter processes, however, is that after a gettering still remaining proportion of impurities always depends on the impurity concentration before getteri This concentration depends essentially on the effectiveness of the window cleaning before the high temperature processes and the cleanliness of all materials used during the high temperature processes from »Since the commonly used quartz material and the heating systems of the high-temperature installations are unavoidable impurity dispensers, one always strives for a maximum gettering effect. The effectiveness of a gettering increases with increasing Getterzeit "However, this is in the context of device fabrication is not of any length can be selected," so ll & oh pieces is in the previously known technical solutions that the theoretical possibilities of the gettering can be used only imperfectly "

Object of the invention

  The aim of the invention is the achievement of a greater Gettereffektivität within a given temperature-time load of the semiconductor wafers over the previously known technologies, especially if within the component manufacturing two or more phosphorus diffusion steps or other thawing processes are required or possible *

99 MOUIP 7 M * K V.IS 9. h

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Essence of the invention

In the course of the getter process is through. Incorporation of Phosphor Impacts in the Semiconductor Crystal Generates an n ⁺ Profile with erfc Distribution Since phosphorus atoms in the silicon lattice are energetically favored sites for the attachment of heavy metal atoms and other impurities, much of the undesired impurities in the n ⁺ layer are likely to accumulate in shape of compounds like Au ₂ Po »

Cu ₀ P, FeP on. The heavy metals bound in this way are no longer able to act as recombination centers. Their concentration in the getter layer depends on the impurity level of the semiconductor volume, the getter system and the process control

Getterung (temperature, time, doping offer) · Is the getter time sufficiently long, so that

»D

where d is the disk thickness, D "is the diffusion coefficient of the impurity to be removed and t is the getter time, then the impurity profile approximates the phosphor profile assuming that the probability of pairing with a heavy metal atom is the same for all phosphorus atoms. The total number Q of phosphorus atoms per

cm is given by the relationship:

² r-1 '

Q Ct). Y = T in c _a

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It can be seen that with increasing getter time fewer getter sites per unit time can be created, the heavy metal concentration in the semiconductor volume can decrease only as T due to the assumed equal distribution on all phosphorus atoms.

The same applies to the gettering of the planar side, With the gettering of contamination of the SiO 2 planar layer by a phosphorus glass high Ausgangskon concentrations within a given getter time can not always be lowered sufficiently, because a balance between the impurity concentrations in, during gettering liquid, phosphorus glass Moreover, the binding of the impurities in the phosphorous glass does not in all cases ensure their complete ineffectiveness in the operation of the components. "

Feature of the invention is a process control that allows for the same Getterzeit and temperature better getter effect characterized in that the getter process takes place in two or more steps and the impurities containing layers are removed after each gettering. Thus, before each subsequent gettering, there is a planar layer or a semiconductor body without the previously formed impurity profile, so that the renewal gettering can reduce the impurity concentration by the same factor as in the first gettering. The following example may prove this:

A 200 to thick p-doped silicon wafer (Έ = 5 χ 10 at / cur) contains a copper concentration of 1 χ 10 ¹⁴ At / cm ² , during the indiffusion of 10 ¹⁵

21 3 Z 5 O-

Phosphorus atoms per cm in the back of the disk at the first gettering, the copper concentration is reduced by two orders of magnitude to 2 χ 10 At / cnr, assuming the uniform distribution of copper atoms on all phosphorus atoms. A simple repetition of the gettering

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acts a drop of U _Cu to 1.4% 10 At / cur. If, however, before the second gettering, one removes the n ⁺ -layer with its heavy metal profile from the rear side of the disk, then U _Cu decreases

from 2 χ 10 ¹² to 2 χ 10 ¹⁰ 'At / cnP _# Thus, the result is almost two orders of magnitude better than that achievable by merely doubling the gettering time. In the example, copper was selected because, due to the high diffusion coefficient, the assumed equality * distribution of the impurities on all phosphorus already at getter times of 10 to 15 minutes at 90O ⁰ C sets. Other heavy metals, eg. B .. Gold, this requires much longer times, so that for a similar significant effect getter times of a few hours may be required. However, in practice, getter times of one to two hours at 900 ^° C. have proven to be good.

A similar improvement can be achieved for the gettering of the silicon dioxide layer if, before the second phosphorous gettering, the first phosphorus glass layer with the impurities gelled in it is completely removed. Prerequisite for the effectiveness of the intermediate etchings according to the invention are in addition to the mentioned sufficiently long getter also the avoidance of too large impurities from the getter system itself, what u. a · can be achieved with the avoidance of too high working temperatures.

2132 50th

To remove the back silicon layer, the chemical etching has proven in an acid mixture consisting of nitric acid, hydrofluoric acid and acetic acid with an etching rate of about 3 / Um per minute. In total about 10 μm are removed after the planar side has been protected with beeswax, picein or in another suitable manner. To remove the planar-sided phosphorus glass layer, a weak overetching with buffered hydrofluoric acid is sufficient. If the phosphorous diffusion is carried out only for the purpose of gettering, the active regions of the later component must be protected by a passivation layer such as SiO ₂ or Si ₂ IT ₃ . In general, the use of phosphorus oxychloride or other phosphorus-halogen compound as a source of phosphorus and a process temperature between 800 and 100O ⁰ C recommended. Lower temperatures do not allow sufficient Getterwirkung, at higher temperatures increases the mentioned risk of additional contamination from the annealing system.

embodiment

Among other things, the invention can be used profitably in the production of CCD structures. The first phosphorous diffusion takes place exclusively for the purpose of gettering after the oxidation of the gate region and the removal of the resulting backside oxide. The gettering is useful at this point, since subsequently no high-temperature treatment at or above 1000 ⁰ C is used more, which would have a significant new contamination of the semiconductor result. Getterung is carried out at 900 ⁰ C over 45 minutes with POCl ₃ as a diffusion source. An η profile with an input

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penetration depth of the impurities of 0.7 / um generated. The planar-side phosphor glass layer and the transition layer between the phosphor glass layer and the pure silicon dioxide are removed by etching in dilute hydrofluoric acid, whereupon the gettering can be repeated if necessary. Following the removal of a layer of polysilicon on the planar side, its oxidation and the photolithographic production of planar windows, phosphorus diffusion for doping of the polysilicon regions can take place after repeated removal of the phosphorus glass layer or now only parts thereof. According to the invention, however, after covering the planar side with beeswax, a 10 μm thick layer of the already phosphorus-doped rear side is removed beforehand. It uses an acid mixture of EE ¹ , HUOo and CH, COOH with an etching rate of 3 / um per minute for silicon * The onset of gettering is effective on a disc that has already undergone heavy metal cleaning and yet no enriched surface layer more , The same sequence of gettering with subsequent backside etching is associated with each additional phosphorus diffusion. In the course of the fabrication of CCD structures, this process was repeated four times, with the result that an effective minority carrier lifetime To of 800 / Usec. at initial values of 10 / Usec. could be achieved. Furthermore, surface recombination velocities S_ below 1 cm / sec. and interface state densities IL. The average residual charge Q _sa / q was less than 1 χ 10 ¹ / cm ² .

transfer losses below 10 "^ % per transfer in buried channel CCD structures"

Claims (9)

213250 claim for invention 1, method for the production of semiconductor devices, characterized in that in the course of the component manufacturing two or more processes are used, forming the turfing layers, and that at least one of these layers is removed before a subsequent processing with the effect of removing 2. A process for the production of semiconductor devices according to item 1, characterized in that the getter processes are phosphorus diffusions which are carried out to produce n ⁺ -profiles in the semiconductor structure or only for the purpose of gettering, 3 · Method for the production of semiconductor devices according to item 1, characterized in that between two getter processes, the backside, the impurity containing, semiconductor layer is removed. 4 · Method for the production of semiconductor devices according to item 1 ,. characterized in that with repeated gettering of the planar layer containing the impurities. Part of it is removed completely at least once before a subsequent gettering · 5 · Method for the production of semiconductor devices according to item 1, characterized in that two or more different methods of gettering are used in the course of component manufacturing. 213250 6. A process for the production of semiconductor devices, characterized in that according to point 1 and 2, the phosphorus diffusions are preferably carried out between SOO and 1000 ⁰ C, 7. A process for the preparation of semiconductor devices according to item 1 and 2, characterized in that the getter times are between 45 and 200 minutes. 8. A process for the production of semiconductor devices according to item 1, 3 and 4, characterized in that the removal of the getter preferably takes place by nafichemische etching. 9. A process for the production of semiconductor devices according to item 1 and 4, characterized in that after the Phosphorgetterung a Siliziuindioxidschicht the resulting phosphorus layer including the lying below the phosphorus glass transition layer to pure silicon dioxide is completely removed before a subsequent further Phosphorgetterung or a coating with silicon nitride. contemplated documents: SU-PS 322 244 B 23 K, 19/00
SU-PS 659 319 B 23 K, 19/02
SU-PS 659 337 B 23 K, 37/04 For this 2 pages drawings