DD221298A1 - PROCESS FOR PREPARING CR-SI DUENNIL FILM RESISTIVES - Google Patents

Abstract

The invention relates to a method for the production of Cr-Si Duennfilmwiderstaenden, preferably for integrated converter circuits. The goal is to increase the quality, and the task is to make the process compatible with the technological process of semiconductor manufacturing. According to the invention, by Hochratezerstaeuben a Cr-Si target and an Si target, the resistance layer is applied so that after a layer thickness of 30 to 100 A, but at least 3 times, interrupted and Si is applied; on average 10 A thick. During Si Aufstaeubens the pressure of the reactive gas is maintained at 2 10 5 mbar.

Description

-2-254 371 3

Embodiment. _v

The application of the Cr-Si resistor layer to 3 "silicon wafers with integrated D / A converter circuitry is described

described. -,, -. '.'

The required Hochratezerstaubungsanlage is equipped with 2 5-kW Plasmatronquellen, one of which is equipped with a Cr-Si target of the composition CrSi ₂ and the other a §i target. The residual gas pressure in the system is 5 10 ^"e mbar. It is oxygen up to a total pressure of 1.5 x 10 ^-5 mbar inserted and then with Ar inlet, a working pressure

set from 3.10 ~ ³ mbar. ^:

The silicon wafers are coated according to the invention as follows:

With a power of 600W, the Si wafers are each coated with CrSi for 30 seconds, which corresponds on the turntable to a respective layer thickness of 6 nm. This coating is interrupted 10 times, during which time 20s of Si becomes at power

dusted by 500W. This corresponds to an average layer thickness of 10 Å. Overall, this results after the end of this process a layer thickness of 70nm. "".

After structuring the resistive layer in a lift-off process, the Al interconnect layer is dusted and patterned. Subsequently, a SiCy layer is applied by CVD at 410T and a Formiergastemperung at 45O ⁰ C. After completion of the cycle I, the resistors have a TK of -50 ± 5ppm / K at a sheet resistance of 1.0 ± O, 2kOhm / Q). Layers of a Cr-Si target of composition 73.6at% Si in the same working gas in

conventionally prepared, show at the end of cycle I a TK> + 2POpPmZK after the same treatment.

Claims (1)

::. ·: './ · ₍ ·. ..' -1- 254371 3 Invention claim: A method for producing Cr-Si thin-film resistors by sputtering the resistive layer by high rate sputtering of a Cr-Si target having a Si content of 50 to 75at% and a Si target, characterized in that the coating with CrSi after reaching a film thickness of each 30 to 100A, but at least 3 times, is interrupted during each interruption in a thickness on average of '<10A on the coating surface Si dusting to disrupt the layer structure and that during the application of the Si layer, the partial pressure of the reactive gas to < 2-10 ~ ⁶ mbar at a deposition rate of 20Ä / min is maintained. : .. ''. '; Field of application of the invention The invention relates to a method for producing highly stable thin film resistors made of Cr-Si base material, which are preferably used in integrated Wandlerschaltun'gen. Characteristic of the known technical solutions. ', Cr-Si thin-film resistors used in semiconductor integrated circuits must be compatible in manufacturing and their characteristics with the manufacturing technology of the circuit, in particular, the temperature necessary to adjust the temperature coefficient TKR of the resistive layer must be such that subsequent heat treatments in cycle I the properties of the resistive layer are no longer adversely affected. Such heat treatments are z. B. Formiergastempern or CVD deposition of a SiO ₂ protective layer. A typical temperature value for this is 450 ^° C. '. , Cr-Si thin-film resistors, which are technically produced by high-rate sputtering, recrystallize at 300 ° C, 400 ° C and then show high positive TK values that are unsuitable for use. Therefore, various methods for increasing the so-called TK-O temperature are proposed. The delay in recrystallization in very thin layers <150 Å is known. However, such layers are extremely sensitive to contamination and layer thickness fluctuations and accordingly show no good long-term stability. The properties of these thin layers are essentially determined by the interfaces. Another possibility is to add heavy metals such as W, Mo to the target material, which are also used as diffusion barriers. The heavy metal content should, however, not exceed 2at%, otherwise the long-term stability deteriorates significantly. The TK temperature shift is max. 5OK and is often not enough. A comparable effect has the partial oxidation of the Cr-Si layer z. B. by adding oxygen to the working gas {partially reactive deposition). Oxygen, however, also influences the specific resistance ς of the layer, ς increases steeply with increasing oxygen content, the resistance layer "tilts" into an insulator layer Since the individual methods are not sufficient in themselves, one usually works in such a way that the atomization of the heavy metal target in the At 2 at% W addition and barely controllable maximum oxygen partial pressure, a TC between 0 and 50ppm / K can be achieved for Cr - ^ base material after 30min of annealing at 450 ° C, ie:, when exhausted of the technically possible and reasonable, a further shift is not possible. Object of the invention The shortcomings of the prior art should be largely avoided and the quality increase over the known methods. , .Development of the essence of the invention The invention has for its object to provide a method for producing Cr-Si thin-film resistors, dös, with the technological process steps of the circuit production (cycle I) is fully compatible. It is a Widarstandsschicht fcvx a TK-O setting temperature of 450 ... 50O ⁰ C with surface resistances in kOhm range at layer thicknesses of> 50nm, generated by not or only weakly reactive Plasmatronzerstäuben. In particular, it should be made possible that the TK adjustment and the CVD deposition of the passivation layer can be connected. According to the invention the object is achieved by sputtering of the resistive layer by Höchratezerstäuben a Cr-Si target having a Si content of 50 to 75at% and a Si target in that the coating with CrSi after a layer thickness of 30 to 100Ä, but at least 3 times, in order to disturb the lateral layer structure each time by sputtering of Si. The sputtered amount of Si over the coating surface should give on average <10 A thickness. During Si sputtering, the partial pressure of the reactive gas on S 2 · 10 ^-6 mbar is maintained at a deposition rate of 20 Å / min ~. This inventive, intermittent way of applying the layer allows the production of relatively thick (> 50nm) resistive layers at surface resistances> 1 kOhm / O- When comparing resistive layers according to this method and those in a known manner by sputtering a Cr-Si target were applied, wherein the Si content of the target corresponds to the total content in the layers according to the invention, there are significant differences. Despite equal Si content after tempering at 450 ° C, the TKR in the inventively produced layers by 150 ... 250ppm / K smaller than in layers that were prepared in a known manner. Apparently, the introduced impingement of the lateral layer structure impedes the recrystallization of the Cr-Si layer and thus causes an effective increase in the TK-O temperature. This process is very well controlled by the choice of Cr-Si single layer thicknesses or the number of interruptions. The position of the TK-O temperature is thus fixed so that it corresponds to the temperature that occurs in the subsequent further wafer processing as a maximum temperature: This eliminates an additional annealing step. The reproducibility of the setting of the critical parameters "sheet resistance", "layer thickness" (stability!) And "TKR" improves considerably compared with the reactive sputtering in the Ar-O ₂ mixture, since there an exponential-like dependence of the sheet resistance and the temperature jump Δ R / R _o is observed by the oxygen partial pressure In contrast, in the process according to the invention, the corresponding relationship to the additional amount of Si in the region of interest is approximately linear.