March 8, 1966 F. H. DIL, JR 3,239,393 METHOD FOR PRODUCING SEMICONDUCTOR ARTICLES Filed Dec. 31, 1962 2. Sheets-Sheet FG. MATER ALS STEPS SEMCONDUCTOR COMPOUND CRYSTAL POLISH CHEMICAL POLISH ACCEPTOR DFFUSANT SOURCE INTRODUCE COMPOUND MEASURED CHARGE HAVING AN ON OF DFFUSANT FROM SAME PERODC COMPOUND GROUP AS CRYSTAL ANION EVACUATE HEAT TO VAPOR DIFFUSE FOR MEASURED TIME ATTACH ELECTRODES INVENTOR. FREDERICK H. DLL JR ATTORNEY March 8, 1966 F., H., DL, JR 3,239,393 METHOD FOR PRODUCING SEMCONDUCTOR ARTICLES Filed Dec. 31, 962 2. Sheets-Sheet 2 Šes is series NNNNN r N NNNNNNNN 3,239,393 United States Patent Office Patented Mar. 8, 1966 2. to produce precisely the desired results. For instance, 3,239,393 when metallic zinc is used as the diffusant material for METHOD FOR PRODUCING SEMCONDUCTOR a gallium arsenide substrate, it is very difficult to obtain ARTICLES the pure zinc metal with no zinc oxide film upon the metal. Frederick H. Dii, Jr., Patnam Waley, N.Y., assigor to 5 Furthermore, the metal is so tough that it is difficult to International Business Machines Corporation, New divide a pure metal sample into smaller pieces in order York, N.Y., a corporation of New York to obtain exactly the correct quantity for the diffusion Filed Dec. 31, 1962, Ser. No. 248,679 process. The zinc oxide on the surface of the metallic Zinc 7 Claims. (C. 48-189) diffusant material is very undesirable for a number of This invention relates to an improved diffusion process IO reasons. The oxygen is not wanted in the diffusion Vapor, for the production of Semiconductor devices, and more and the zinc oxide tends to form a protective coating particularly to an improved vapor diffusion process in over the zinc which inhibits the formation of the desired which the introduction of unwanted impurities is very zinc metal vapor which is required for the diffusion proc effectively and simply avoided, and which possesses other CSS. advantages contributing to the simple and trouble-free 5 Accordingly, it is another important object of this in production of articles composed of Semiconductor com vention to provide an improved vapor diffusion process pounds. for the production of semiconductor devices employing In the past, semiconductor devices have been produced semiconductor compound Substrates in which the prob almost exclusively from monatomic semiconductor ma eras related to the use of a pure metallic diffusant are terials. Such materials include, for instance, germanium 20 OWCO. and silicon as outstanding examples. However, it has Stated very concisely, therefore, it is an object of the recently become apparent that semiconductor compounds present invention to provide an improved vapor diffusion possess certain advantages in the production of Semi process for producing electrical Semiconductor devices conductor devices and some of these compounds are formed from semiconductor compound substrates and capable of producing devices having special properties 25 for assuring a clean and uncontaminated Source of dif which have not been observed with the monatomic Semi fusant material and a very effective protective atmosphere conductor materials. For instance, certain Group III for the vapor diffusion process. Group V compounds Such as gallium arsenide have been In carrying out the objects of this invention in one shown to display rather marked “laser' properties when preferred form of the method, a substrate crystal com properly fabricated in a semiconductor device. The 30 posed of an electrical semiconductor device compound term "laser,' as used here, means a device which is is heated in the presence of a vapor consisting essentially capable of operation as an optical maser for converting of the decomposition products of a compound of an ac electrical energy which it receives into a coherent optical ceptor cation element and an anion element from the light energy output, the output having a very limited wave same group in the periodic table as the anion of the Sub length spectrum, the conversion being carried out with a 35 strate compound. high degree of efficiency. The devices disclosed in a co The concentration of the acceptor cation element dif pending application Serial No. 234,150, filed on October fusant in the vapor is maintained at a low value Such that 30, 1962 by F. H. Dill et al. entitled “Lasers' and as no substantial alloying or plating will occur. signed to the same assignee as the present application il Further objects and advantages of this invention will lustrates this utility of semiconductor compounds. The 40 be apparent from the following description and the ac Semiconductor compounds, including gallium arsenide, companying drawings which are briefly described as fol as well as other Group III-Group V semiconductor com lows: pounds, and some of the Group II-Group VI semicon FIG. 1 is a flow diagram indicating the materials and ductor compounds are also known to be useful semicon steps which are employed in carrying out one form of the ductor materials for other more conventional purposes. 45 method of this invention. As used in this specification the term "Group III-Group FIG. 2 illustrates the apparatus employed in carrying V compound' means a compound composed of elements at the preliminary steps in practicing a preferred form selected from Groups III and V of the periodic table. of the process of this invention. Some of the most popular methods for producing And FIG. 3 illustrates apparatus employed in the dif semiconductor devices employ vapor diffusion for the fusion step in practicing a preferred form of the process. purpose of introducing junction-forming impurities. Referring in more detail to FIG. 1, the semiconductor However, when using vapor diffusion for the production compound crystal which serves as the substrate is pref of semiconductor devices composed of semiconductor erably lapped, polished, and chemically polished. An compounds, the diffusion must be carried out at an ele acceptor diffusant source compound having an anion vated temperature which is likely to cause decomposition which is the same as the crystal anion or at least from of the semiconductor substrate compound. At these the same periodic group is then introduced into the pres temperatures, not only is there likely to be decomposition ence of the semiconductor compound crystal in a care due to disassociation, but also the substrate constituent fully measured charge. The two materials are placed in elements are likely to combine with impurity elements an enclosure which is evacuated and then heated for a 60 measured time to accomplish the desired vapor diffusion. which may be found in minute quantities within the Vapor The diffused crystal is then preferably diced to divide it deposition enclosure. into a number of separate devices and suitable electrodes Accordingly, one of the objects of the present inven are attached to each device. The electrodes may be pro tion is to provide an improved vapor diffusion process vided by alloying at the surfaces of the device, or by for the production of semiconductor devices having com 65 other known methods. It will be understood that this pound semiconductor substrates in which the problem exemplification of the process may be modified substan of degradation of the surface of the substrate during the tially without departing from the spirit of the invention. diffusion step is overcome. Thus, certain steps may be combined with others or elim Another important problem in the process of vapor inated as will appear more clearly from the remainder diffusion of semiconductor compound Substrates is that 70 of the specification and the claims. For instance, for a it is very difficult to obtain a perfectly clean and high deep diffusion penetration of a depth which substantially purity diffusant material in a carefully measured quantity exceeds the depth of individual Surface imperfections of 3,239,393 3 4. - a lapped surface, the polishing steps may be omitted, be is always chosen to be from the same group in the peri - cause the lapped surface is sufficiently smooth. odic table as the anion of the substrate compound. Fur The following illustrates in more detail a preferred ex thermore, the cation of the diffusant compound is always ample of the procedures followed to carry out the method chosen from a lower group in the periodic table so as to of the present invention. A slice from an 'N' type gal act as an acceptor. For instance, with a substrate of gal lium arsenide crystal is lapped, polished, and then chem lium arsenide, zinc arsenide or cadmium arsenide have ically polished to produce a very smooth flat surface for been found to be very effective diffusant sources. The the diffusion. The crystal wafer may be in a disc shape arsenic component of the diffusant serves to form a pro having a diameter of about 10 millimeters and a thickness tective arsenic vapor atmosphere during the diffusion of about 0.5 millimeter. As indicated in FIG. 2, the O process, and the zinc or the cadmium serve as an acceptor substrate 10 is placed in a quartz tube 12 having an inside material in the actual diffusion of the semiconductor Sur diameter of approximately 11 millimeters together with face. With a Group II-Group VI substrate compound, a charge 4 of zinc arsenide (ZnAs2). A typical charge, such as zinc selenide, a copper selenide diffusant material . of zinc arsenide is approximately 0.6 milligram. How is appropriate, with the copper serving as the acceptor. ever, the charge quantity may be in a wide range from 5 material. ... 0.01 milligram to 10 milligrams depending upon the The use of a compound as a diffusant source has a . amount of doping which is desired. The quartz tube 12, number of advantages.