Insulator material for use in RRAM

Abstract

The present disclosure relates generally to Hf-comprising materials for use in, for example, the insulator of a RRAM device, and to methods for making such materials. In one aspect, the disclosure provides a method for the manufacture of a layer of material over a substrate, said method including a) providing a substrate, and b) depositing a layer of material on said substrate via ALD at a temperature of from 250 to 500 C., said depositing step comprising: at least one HfX.sub.4 pulse, and at least one trimethyl-aluminum (TMA) pulse, wherein X is a halogen selected from Cl, Br, I and F and is preferably Cl.

Claims

1. A material comprising elements Hf, Al and O, wherein Hf represents from 17 to 23 at % of elements Hf, Al, C, O and X as measured by x-ray photoelectron spectroscopy (XPS); Al represents from 16 to 23 at % of elements Hf, Al, C, O and X as measured by XPS; C represents from 0 to 3 at % of elements Hf, Al, C, O and X as measured by XPS; O represents from 57 to 62 at % of elements Hf, Al, C, O and X as measured by XPS; and X represents from 0 to 1 at % of elements Hf, Al, C, O and X as measured by XPS, wherein X is a halogen selected from Cl, Br, I and F; wherein elements Hf, Al, C, O and X make up at least 90% of the at % composition of the material exclusive of hydrogen content as determined by XPS.

2. A device comprising a metal-insulator-metal stack comprising: a first metal layer, a layer of material according to claim 1, a HfO.sub.2 layer, and a second metal layer.

3. A memory device comprising a metal-insulator-metal stack of layers, wherein an insulator of the metal-insulator-metal stack comprises a layer of material according to claim 1.

4. A memory device according to claim 3, wherein the memory device is a resistive random-access memory.

5. The material according to claim 1, wherein elements Hf, Al, C, O and X make up at least 96% of the at % composition of the material exclusive of hydrogen content as determined by XPS.

6. The material according to claim 1, wherein elements Hf, Al, C, O and X make up at least 99% of the at % composition of the material exclusive of hydrogen content as determined by XPS.

7. The material according to claim 1, having a band gap up to about 6.5 eV.

8. The material according to claim 1, further comprising up to 5 at % hydrogen as determined by Time-of-Flight Elastic Recoil detection analysis.

9. A material comprising elements Hf, Al and C, wherein Hf represents from 34 to 40 at % of elements Hf, Al, C, O and X as measured by x-ray photoelectron spectroscopy (XPS), Al represents from 9 to 14 at % of elements Hf, Al, C, O and X as measured by XPS; C represents from 36 to 45 at % of elements Hf, Al, C, O and X as measured by XPS; O represents from 0 to 6 at % of elements Hf, Al, C, O and X as measured by XPS; and X represents from 2 to 6 at % of elements Hf, Al, C, O and X as measured by XPS, wherein X is a halogen selected from Cl, Br, I and F, wherein elements Hf, Al, C, O and X make up at least 90% of the at % composition of the material exclusive of hydrogen content as determined by XPS.

10. The material according to claim 9, wherein X is Cl.

11. The material according to claim 9, having a band gap up to about 6.5 eV.

12. A memory device comprising a metal-insulator-metal stack of layers, wherein an insulator of the metal-insulator-metal stack comprises a layer of material according to claim 9.

13. A memory device according to claim 11, wherein the memory device is a resistive random-access memory.

14. A device comprising a metal-insulator-metal stack comprising: a first metal layer, a layer of material according to claim 9, a HfO.sub.2 layer, and a second metal layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The disclosure will be further elucidated by means of the following description and the appended figures.

(2) FIG. 1 is a graph showing the mass gain of the substrate (a 300 mm wafer) after 100 full HfCl.sub.4/TMA cycles for a 4 s TMA pulse in function of the HfCl.sub.4 pulse length according to an embodiment of the present disclosure.

(3) FIG. 2 is a graph showing the mass gain of the substrate (a 300 mm wafer) after 100 full HfCl.sub.4/TMA cycles for a 3 s HfCl4 pulse in function of the TMA pulse length according to an embodiment of the present disclosure.

(4) FIG. 3 is a graph showing the evolution of the sheet resistance after 100 full HfCl.sub.4/TMA cycles for a 3 sec TMA pulse length in function of the HfCl.sub.4 pulse length according to an embodiment of the present disclosure.

(5) FIG. 4 is a graph showing the evolution of the sheet resistance uniformity after 100 full HfCl.sub.4/TMA cycles for a 3 sec TMA pulse length in function of the HfCl.sub.4 pulse length according to an embodiment of the present disclosure.

(6) FIG. 5 shows the temperature dependency of the growth per cycle HfCl.sub.4 (4 s)-purge-TMA (3 s)-purge according to an embodiment of the present disclosure.

(7) FIG. 6 shows the temperature dependency of the film density according to an embodiment of the present disclosure wherein a pulse sequence HfCl.sub.4 (4 s)-purge-TMA (3 s)-purge is repeated until saturation.

(8) FIG. 7 shows the temperature dependency of the growth per cycle HfCl.sub.4 (5 s)-purge-TMA (4 s)-purge-H.sub.2O (1 s) according to an embodiment of the present disclosure.

(9) FIG. 8 shows the temperature dependency of the film density according to an embodiment of the present disclosure wherein a pulse sequence HfCl.sub.4 (5 s)-purge-TMA (4 s)-purge-H.sub.2O (1 s) is followed.

(10) FIG. 9a shows the optical properties of a film produced according to an embodiment of the present disclosure wherein a pulse sequence HfCl.sub.4 (5 s)-purge-TMA (4 s)-purge-H.sub.2O (1 s) is followed.

(11) FIG. 9b shows the optical properties of a film produced according to an embodiment of the present disclosure wherein a pulse sequence HfCl.sub.4 (5 s)-purge-TMA (4 s)-purge-HfCl.sub.4 (5 s)-purge-H.sub.2O (1 s) is followed.

(12) FIG. 10 shows the composition as determined by XPS for a material according to the first embodiment of the second aspect of the present disclosure for a deposition temperature of 370 C.

(13) FIG. 11 shows the composition as determined by XPS for a material according to the second embodiment of the second aspect of the present disclosure for a deposition temperature of 370 C.

(14) FIG. 12 shows the composition as determined by XPS for a material according to the first embodiment of the second aspect of the present disclosure for a deposition temperature of 340 C.

(15) FIG. 13 shows the composition as determined by XPS for a material according to the first embodiment of the second aspect of the present disclosure for a deposition temperature of 370 C.

(16) FIG. 14 is a schematic representation of a device according to an embodiment of the present disclosure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(17) The present disclosure will be described with respect to particular embodiments and with reference to certain drawings but the disclosure is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not necessarily correspond to actual reductions to practice of the disclosure.

(18) Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. The terms are interchangeable under appropriate circumstances and the embodiments of the disclosure can operate in other sequences than described or illustrated herein.

(19) Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. The terms so used are interchangeable under appropriate circumstances and the embodiments of the disclosure described herein can operate in other orientations than described or illustrated herein.

(20) Furthermore, the various embodiments, although referred to as preferred are to be construed as exemplary manners in which the disclosure may be implemented rather than as limiting the scope of the disclosure.

(21) The term comprising, used in the claims, should not be interpreted as being restricted to the elements or steps listed thereafter; it does not exclude other elements or steps. It needs to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression a device comprising A and B should not be limited to devices consisting only of components A and B, rather with respect to the present disclosure, the only enumerated components of the device are A and B, and further the claim should be interpreted as including equivalents of those components.

EXAMPLES

(22) All depositing steps have been performed in an ASM Pulsar 3000 connected to a Polygon 8300.

(23) The substrates were 300 mm Si (100) wafers having a 10 nm SiO2 top layer grown by rapid thermal oxidation.

(24) The precursor HfCl.sub.3 was purchased from ATMI and used as such.

Example 1: HfC Process

(25) Adequate pulse length will vary in function of the used experimental set up, the optimal pulse length for the present experimental set up was therefore determined experimentally.

(26) First, mass gain (mg) on the substrate at 370 C. was measured in function of HfCl.sub.4 pulse length (ms) (FIG. 1). It was observed that mass gain saturates at 11 mg for pulse lengths of 3 s or above.

(27) Second, mass gain (mg) on the substrate at 370 C. was measured in function of TMA pulse length (ms) (FIG. 2). It was observed that mass gain increases slowly with TMA pulse length. This was indicative of a small CVD component. Such CVD components get more dominant at higher temperature and are not favourable for ALD. This indicates that it is less advantageous to operate with a substrate above 370 C.

(28) It is advantageous for the HFC material to be a bad dielectric or a metal. Sheet resistance and sheet resistance uniformity has therefore been measured for various HfCl.sub.4 pulse lengths while keeping the TMA pulse at 3 seconds. The following pulse sequence was therefore performed on a substrate at 370 C.: HfCl.sub.4 (2-5 s)/N.sub.2 purge/TMA (3 s)/N.sub.2 purge. A shorthand description of this same sequence is HfCl.sub.4(2-5s)/TMA (3 s).

(29) The corresponding graphs are shown in FIGS. 3 and 4 where RS stands for sheet resistance, RS U. stands for sheet resistance uniformity, and p.l. stands for pulse length. From these graphs it was observed that the lowest sheet resistance and the best uniformity was obtained for the following pulse sequence: HfCl.sub.4 (4 s)/TMA (3 s). The resistivity of the obtained layer was about 20 mOhm.cm.

(30) The sequence HfCl.sub.4 (4 s)/TMA (3 s) was repeated until saturation at different temperatures in order to determine the temperature dependence of the growth per cycle (G. p. c.) (see FIG. 5).

(31) The thickness was measured by x-ray reflectivity. From FIG. 5, it is clear that the growth per cycle strongly increases above 300 C. and is best around 370 C. This indicates a usable temperature window of from 250 C. to 500 C. However, we know from FIG. 2 that it is less advantageous to operate with a substrate above 370 C., due to TMA decomposition (CVD component). No reaction and therefore no material layer deposition were observed below 250 C.

(32) The temperature dependency of the material layer density was measured by x-ray reflectivity (see FIG. 6) on the same samples used for establishing FIG. 5. It can be seen in FIG. 6 that a higher density is obtained at higher temperatures. The density remains however relatively low (4-5 g/cm.sup.3 when compared to the bulk density (12.2 g/cm.sup.3) of full crystalline HfC according to the literature.

(33) The composition of the HfC material layer at various depths was determined by alternating etching (via Ar sputtering) and XPS analysis. This has been performed at a deposition temperature of 300 (FIG. 13), 340 (FIG. 12), and 370 C. (FIG. 10). Peaks characteristics of Hf, C, Al, Cl and O were found. At the deposition temperature of 370 C., the bulk concentration of C was from 41 to 44 at % as measured by XPS. The bulk concentration of Hf was from 35 to 38 at % as measured by XPS. The bulk concentration of Al was from 10 to 13 at % as measured by XPS. The bulk concentration of 0 was from 4 to 5 at % as measured by XPS. The bulk concentration of Cl was from 3 to 4 at % as measured by XPS. At the deposition temperature of 340 C., the bulk concentration of C was from 40 to 43 at % as measured by XPS. The bulk concentration of Hf was from 33 to 37 at % as measured by XPS. The bulk concentration of Al was from 9 to 12 at % as measured by XPS. The bulk concentration of 0 was from 6 to 9 at % as measured by XPS. The bulk concentration of Cl was from 5 to 7 at % as measured by XPS. At the deposition temperature of 300 C., the bulk concentration of C was from 32 to 38 at % as measured by XPS. The bulk concentration of Hf was from 30 to 37 at % as measured by XPS. The bulk concentration of Al was from 6 to 10 at % as measured by XPS. The bulk concentration of 0 was from 7 to 14 at % as measured by XPS. The bulk concentration of Cl was from 3 to 9 at % as measured by XPS.

(34) At each of these temperatures, the presence of the oxygen is believed to be due to the time the sample spent in the presence of air (30 min) before the XPS measurements. It can therefore in principle be reduced to zero.

Example 2: HfCO Process

(35) The following pulse sequence was performed on a substrate at 370 C.: HfCl.sub.4 (5 s)-N.sub.2 purge-TMA (5 s)-N.sub.2 purge-H.sub.2O (1 s)-N.sub.2 purge.

(36) The sequence HfCl.sub.4 (5 s)/TMA (5 s)/H.sub.2O (1 s)/was repeated at different temperatures in order to determine the temperature dependence of the growth per cycle (G. p. c.) (see FIG. 7).

(37) The thickness was measured by x-ray reflectivity. From FIG. 7, it is clear that the growth per cycle is best around 370 C. This suggests a usable temperature window of from 250 C. to 500 C. However, we know from FIG. 2 that it is less advantageous to operate with a substrate above 370 C., due to TMA decomposition (CVD component). No reaction and therefore no material layer deposition were observed below 250 C.

(38) The temperature dependency of the material layer density was measured by x-ray reflectivity (see FIG. 8). It can be seen in this figure that a the density decreases slowly between 300 and 370 C. The density remains however close to the expected bulk density. The expected bulk density is determined by an interpolation between bulk Al.sub.2O.sub.3 and HfO.sub.2.

(39) The composition of the HfCO material layer at various depths was determined by alternating etching (via Ar sputtering) and XPS analysis. Peaks characteristics of Hf, C, Al, and O were found. The bulk concentration of C was not determined because it was too close to the detection limit. The bulk concentration of Hf was from 18 to 23 at %. The bulk concentration of Al was from 16 to 21 at %. The bulk concentration of O was from 57 to 61 at %.

(40) FIG. 9a shows the optical properties ((absorption*photon energy).sup.2 vs. photon energy) of the material obtained via a pulse sequence HfCl.sub.4 (5 s)-purge-TMA (4 s)-purge-H.sub.2O (1 s)-purge.

(41) The band gap can be calculated from the optical properties by a linear interpolation of the square of the absorption coefficient to zero. These properties show that the obtained material is a dielectric material having a band gap of 6.3 eV.

(42) FIG. 9b shows the optical properties (absorption*photon energy).sup.2 vs. photon energy) of a material obtained via a pulse sequence HfCl.sub.4 (5 s)-purge-TMA (4 s)-purge-HfCl.sub.4 (5 s)-purge-H.sub.2O (1 s)-purge.

(43) The band gap can be calculated from the optical properties by a linear interpolation of the square of the absorption coefficient to zero. These properties show that the obtained material is a dielectric material having a band gap similar of 6.1 eV.

(44) FIG. 14 shows a device according to the fourth aspect of the present disclosure. It shows a substrate (1) on which a metal-insulator-metal stack is deposited, said stack comprising: A first metal layer (2), A layer of material according to any embodiment of the second or third aspect (3), A HfO.sub.2 layer (4), and A second metal layer (5).